P.T., P.T. Araujo; P.B.C., P.B.C. Pesce; M.S., M.S. Dresselhaus; K. Sato; R. Saito; A. Jorio

Abstract In the last decade, many theoretical and experimental achievements have been made in the photophysics of single wall carbon nanotubes (SWNTs). Such accomplishments allowed us to gain a deep understanding of the photophysics behind the transition energy (E ii ) and the radial breathing mode frequency ... [view more]

Abstract

In the last decade, many theoretical and experimental achievements have been made in the photophysics of single wall carbon nanotubes (SWNTs). Such accomplishments allowed us to gain a deep understanding of the photophysics behind the transition energy (E _ii ) and the radial breathing mode frequency ( ω RBM ) () dependence on nanotube chirality (n, m). This work is devoted to assemble and discuss what has been done on the research of the SWNT electronic and vibrational properties, based on the radial breathing mode (RBM) resonance Raman spectroscopy. Attention is directed to the understanding of how a change in the environment changes the correlation between ( E ii , ω RBM ) () and (n, m). From the analysis of several data in the literature, we derive a simple routine for the ( E ii , ω RBM ) → ( n , m ) () assignment.

A.-S.F., A.-S.F. Obada; H.A., H.A. Hessian; A.-B.A., A.-B.A. Mohamed

Abstract Motivated by recent experiments wherein the Cooper box can be used to probe the decay of the resonator superposition state due to environmental decoherence. We theoretically investigate the dynamics of entanglement and mixedness of a superconducting qubit strongly coupled to a cavity field induced by a phase-damping ... [view more]

Abstract

Motivated by recent experiments wherein the Cooper box can be used to probe the decay of the resonator superposition state due to environmental decoherence. We theoretically investigate the dynamics of entanglement and mixedness of a superconducting qubit strongly coupled to a cavity field induced by a phase-damping reservoir governed by a master equation. With a phase-damping, the amount of the entanglement and the mixedness of the global system and of the resonator states have invariant dynamics while phase damping has no effect on the dynamic of the degree of the mixedness of the Cooper-pair state.

Chuxin Wu; Guofa Dong; Lunhui Guan

Abstract By a simple helium arc-discharged method, we explored the suitable conditions for producing graphene sheets by regulating gas pressures and currents. Graphene sheets containing monolayer, bilayer and few layers were obtained. The as-obtained graphene sheets were verified by transmission electron microscopy (TEM), electron ... [view more]

Abstract

By a simple helium arc-discharged method, we explored the suitable conditions for producing graphene sheets by regulating gas pressures and currents. Graphene sheets containing monolayer, bilayer and few layers were obtained. The as-obtained graphene sheets were verified by transmission electron microscopy (TEM), electron diffraction and scanning electron microscopy (SEM).

Ali Shakeri-Zadeh; Mahdi Ghasemifard; G. Ali Mansoori

Abstract Gold nanoparticles (AuNPs) represent a novel nanomaterials applied in various nanotechnology fields because of their special optical properties. On the other hand, folic acid and folate can be used for selective targeting of nanoparticles towards cancer cells. Folate conjugated AuNPs can be considered as an effective ... [view more]

Abstract

Gold nanoparticles (AuNPs) represent a novel nanomaterials applied in various nanotechnology fields because of their special optical properties. On the other hand, folic acid and folate can be used for selective targeting of nanoparticles towards cancer cells. Folate conjugated AuNPs can be considered as an effective nanoconjugate in the field of nanotargeted photothermal therapy of cancer. In the present work, we report our synthesis of a new nanoconjugate composed of folate, AuNP and 4-aminothiophenol (4Atp) as the linker and named Folate-4Atp-AuNP. The results of our investigations on properties of this new nanoconjugate are presented here including the effects of addition of folate and 4Atp to AuNP on its structural and optical properties. We studied the structural characteristics of Folate-4Atp-AuNP using X-ray diffraction. In addition, we determined its optical band gap energy (1.365eV), its optical constants using Kramers–Kronig analysis and we identified its metallic face-centered cubic (fcc) lattice structure and particular crystal planes. Our findings indicate that the presence of 4Atp and folate in Folate-4Atp-AuNP had no significant effect on its optical band gap energy. However, some appreciable changes in its optical constants were observed due to the presence of 4Atp and folate in nanoconjugate. The significant changes in optical constants values are apparently as a result of the presence of some special bonds and a few particular functional groups in the nanoconjugate.

Fanrong Ai; Aihua Yao; Wenhai Huang; Deping Wang; Xing Zhang

Abstract Aqueously dispersed NiPd nanoparticle alloys with various Ni/Pd molar ratios were synthesized by polyol process in the present work. Measurements such as XRD, ICP and TEM were performed to characterize the as-synthesized nanoparticles. The results confirmed the formation of NiPd nanoalloys and not simply mixtures ... [view more]

Abstract

Aqueously dispersed NiPd nanoparticle alloys with various Ni/Pd molar ratios were synthesized by polyol process in the present work. Measurements such as XRD, ICP and TEM were performed to characterize the as-synthesized nanoparticles. The results confirmed the formation of NiPd nanoalloys and not simply mixtures of the two metal nanoparticles. The PVP, which was used as capping agent to stabilize the nanoparticles and prevent them from oxidation or agglomeration, accounted for approximately 30% of the total mass fraction of the nanoparticles. The magnetic measurement revealed the as-synthesized NiPd nanoalloys exhibited ferromagnetic behaviors, and the saturation magnetization as well as heat-generation ability was enhanced with increasing Ni concentration. Upon exposure to an external alternation magnetic field of 60kHz and 7.5kA/m, specific power absorption rate (SAR) of the nanoalloy with the composition of Ni_63.8Pd_36.2 reached 40w/g, indicating high heat-generation ability.

Watchara Liewrian; Rassmidara Hoonsawat; I-Ming Tang

Abstract The effects of the bias voltage placed on a second gate which is positioned to the left of the ferromagnetic graphene (FG) layer on the switching of the charge and spin transports in a ferromagnetic graphene junction are studied. We show that the change in the bias ... [view more]

Abstract

The effects of the bias voltage placed on a second gate which is positioned to the left of the ferromagnetic graphene (FG) layer on the switching of the charge and spin transports in a ferromagnetic graphene junction are studied. We show that the change in the bias voltage from positive to negative (while maintaining the positive voltage on the first gate above the FG layer) can induce a switching from high to low conductance states in the junction. The voltage on the first gate is used to shift the Fermi level in the FG layer. Enhancement of the on/off conductance ratio on the switching is shown to be inversely proportional to the thickness of the second gate barrier. We show that by biasing the nanostructures with the voltage U ₂, the spin polarization can be increased and that as a consequence, the thickness of the FG barrier layer needed for spin-polarized transport can be reduced.

S.C. Pradhan; T. Murmu

Abstract Nonlocal elasticity theory is implemented to investigate the buckling behavior of single-layered graphene sheet (SLGS) embedded in an elastic medium. Nonlocal elasticity theory accounts for the small-size effects when dealing with nanostructures such as graphene sheets. Both Winkler-type and Pasternak-type foundation models are... [view more]

Abstract

Nonlocal elasticity theory is implemented to investigate the buckling behavior of single-layered graphene sheet (SLGS) embedded in an elastic medium. Nonlocal elasticity theory accounts for the small-size effects when dealing with nanostructures such as graphene sheets. Both Winkler-type and Pasternak-type foundation models are employed to simulate the interaction between the graphene sheet and the surrounding elastic medium. Based on principle of virtual work, governing differential equations for the aforementioned problem are derived. Differential quadrature method is being employed and numerical solutions for the buckling loads of SLGS are obtained. Numerical results show that the buckling loads of SLGS are strongly dependent on the small scale coefficients and the stiffness of the surrounding elastic medium. With elastic medium modeled as Winkler-type foundation, the nonlocal effects are found to have decrease–increase–decrease pattern with increase in stiffness of elastic medium.

Y. Park; H. Ko; I.-B. Shim; C.S. Kim; T. Kouh

Abstract Anodic aluminium oxide has been gaining much attention due to the formation of a highly ordered porous structure, and this self-ordered structure is very appealing as an alternate method for fabricating various nanostructures and devices. On top of this porous aluminium oxide substrate prepared by two-step... [view more]

Abstract

Anodic aluminium oxide has been gaining much attention due to the formation of a highly ordered porous structure, and this self-ordered structure is very appealing as an alternate method for fabricating various nanostructures and devices. On top of this porous aluminium oxide substrate prepared by two-step anodization technique, we have RF-sputtered Cu-Al-O thin films from a single-phase CuAlO₂ target at room temperature. These films show the formation of a highly ordered array of clusters on the nucleation sites provided by the porous substrate with their sizes increasing with film thickness, following the hexagonal pattern underneath. The corresponding surface coverage of the film on the substrate is proportional to the square of film thickness, which can be understood with a simple two-dimensional disk model. Our study suggests that the underlying structure of the anodic aluminium oxide substrate plays a crucial role on the growth of nanostructured thin films and affects the detailed growth mechanism.

M.S. Rabia

Abstract Using the spring-mass model and a matching method formalism, we investigate the scattering of acoustic phonons by a geometric defect (step) in a planar quantum waveguide. The mono-atomic step is treated as the perturbed interface between two single semi-infinite atomic layers occupying the half... [view more]

Abstract

Using the spring-mass model and a matching method formalism, we investigate the scattering of acoustic phonons by a geometric defect (step) in a planar quantum waveguide. The mono-atomic step is treated as the perturbed interface between two single semi-infinite atomic layers occupying the half spaces on either side of the step. In fact the planar waveguide is an isolated step in the direction perpendicular to the plan. As in the electronic case, the transmission coefficients are characterized by strong asymmetrical resonances, identified as Fano-like resonances, due to the degeneration of the localized states induced by the step and those of the propagation continuum. Whereas the interferences between diffused and reflected waves in the perturbed step region generate Fabry–Pérot oscillations. The resulted transmission and conductance spectra can thus be regarded as identifying features and may therefore be used for their characterization. The results could also be useful for controlling thermal conductance artificially and the design of phonon devices. To illustrate the method, a detailed discussion of the transmission spectra is presented for different geometries in the null and oblique incidence cases.

S. Nag; D.P. Bhattacharya

Abstract The theory of energy loss rate of the non-equilibrium electrons in a degenerate quantum surface due to piezoelectric interaction has been developed under the condition of low temperature when the well-known approximations of the traditional theory are hardly valid. Compared to the traditional results for non-... [view more]

Abstract

The theory of energy loss rate of the non-equilibrium electrons in a degenerate quantum surface due to piezoelectric interaction has been developed under the condition of low temperature when the well-known approximations of the traditional theory are hardly valid. Compared to the traditional results for non-degenerate surface layers the theory here reveals a complex and altogether different dependence of the loss rate upon the carrier energy and the lattice temperature. The numerical results for GaAs and ZnO show how significantly does the degeneracy level or the true phonon distribution or the inelasticity of the interaction affect the loss characteristics at low temperatures. The possible applications of the theory have been discussed.

Jun Wu; Jun Xia; Yu-ning Zhang; Wei Lei; Bao-ping Wang

Abstract Superhydrophobic surface is obtained by combining micro- and nano-scale ZnO nanowires and hydrophobic Teflon material in our recent experiment. We adopt an alkaline hydrothermal method to fabricate a series of ZnO nanowires surfaces with different roughness, which is realized by carefully controlling Zn-AD concentration. The... [view more]

Abstract

Superhydrophobic surface is obtained by combining micro- and nano-scale ZnO nanowires and hydrophobic Teflon material in our recent experiment. We adopt an alkaline hydrothermal method to fabricate a series of ZnO nanowires surfaces with different roughness, which is realized by carefully controlling Zn-AD concentration. The resulted surfaces all exhibit superhydrophilic traits, where a contact angle below 10° for a 3μL water droplet sits on these surfaces. The obtained superhydrophilicity comes from the combination of high surface energy of ZnO film and high surface roughness, which is in line with Wenzel’s model. Superhydrophobic surface is achieved after spin-coating Teflon. The excellent superhydrophobicity is attributed to the synergistic effect of high roughness and the low surface energy, which is explained by the Cassie model. The Zn-AD concentration of 0.1M is essential to fabricate the superhydrophobic surfaces.

M.A. Hidalgo; R. Cangas

Abstract In this paper we analyze the influence of the Rashba spin–orbit coupling on the quantum Hall magnetoresistivity in a two-dimensional electron system (2DES). The study is based on an analytical model for the integer quantum Hall effect (IQHE) and the Shubnikov-de Haas (SdH... [view more]

Abstract

In this paper we analyze the influence of the Rashba spin–orbit coupling on the quantum Hall magnetoresistivity in a two-dimensional electron system (2DES). The study is based on an analytical model for the integer quantum Hall effect (IQHE) and the Shubnikov-de Haas (SdH) phenomena. This model shows the behaviour of the Hall magnetoresistivity when the Rashba parameter is varied, and reproduces Hall plateaux of a 2DES confined in a III–V heterostructure. We also discuss the Rashba and Zeeman competition and its effect on the width of the Hall magnetoresistivity plateaux.

L.Z. Pei; H.S. Zhao; W. Tan; H.Y. Yu; Y.W. Chen; C.G. Fan; Qian-Feng Zhang

Abstract ZnO nanorods were prepared via a simple hydrothermal oxidization process on zinc substrate. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrum (EDS), transmission electron microscopy (TEM) and photoluminescence (PL) spectrum were used to characterize the nanorods. ... [view more]

Abstract

ZnO nanorods were prepared via a simple hydrothermal oxidization process on zinc substrate. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrum (EDS), transmission electron microscopy (TEM) and photoluminescence (PL) spectrum were used to characterize the nanorods. The nanorods are single crystalline wurtzite structure with a length longer than 10μm. The effects of the hydrothermal temperature, pressure and time on the morphology, diameter and length of the ZnO nanorods have been also analyzed. It is considered that time keeping the temperature and pressure is the main factor that influences the length of the ZnO nanorods. The PL spectrum shows a strong blue light emission at 439nm, which is considered to be caused by radiative recombination of photo-generated holes with singularly ionized oxygen vacancies. The growth process of the ZnO nanorods is proposed based on the solid–liquid–solid (SLS) mechanism.

Yi L. Chiew; Kuan Y. Cheong

Abstract Large amount of SiO x nanowires and Si/SiO x core-shell nanowires on silicon wafer had been synthesized through carbon-assisted growth. Carbon-assisted growth was employed in this study due to the lack of contamination from metallic catalysts and cheaper raw materials. The nanowires produced had... [view more]

Abstract

Large amount of SiO _x nanowires and Si/SiO _x core-shell nanowires on silicon wafer had been synthesized through carbon-assisted growth. Carbon-assisted growth was employed in this study due to the lack of contamination from metallic catalysts and cheaper raw materials. The nanowires produced had length up to 100μm and diameter ranging from 20 to 40nm. In this study, increasing the growth temperature (1100, 1200 and 1300°C) caused a change in the morphology of the nanowires from SiO _x to Si/SiO _x core-shell structures while increasing the soaking time of the heating profile (1, 2 and 4h) increased the length of nanowires.

C. Li; P.X. Yan; X.C. Li; E.M. Chong

Abstract Diamond-like carbon (DLC) nanodot arrays were prepared by filtered cathodic arc plasma (FCAP) technique at room temperature with the aid of anodic aluminum oxide (AAO) template at a bias of −50V. The average diameter of highly ordered and vertical DLC nanodots was ∼90nm,... [view more]

Abstract

Diamond-like carbon (DLC) nanodot arrays were prepared by filtered cathodic arc plasma (FCAP) technique at room temperature with the aid of anodic aluminum oxide (AAO) template at a bias of −50V. The average diameter of highly ordered and vertical DLC nanodots was ∼90nm, and the nanodot density was estimated to be ∼10¹⁰cm⁻². A broad asymmetric band attributed to characteristic band of DLC ranging from 1000 to 2000cm⁻¹ was detected by Raman spectrum. A sp³/(sp³+sp²) ratio of 68.2% was measured by X-ray photoelectron spectrum (XPS). A low threshold field of 4V/μm at 10mA/cm² and a high current density of 43.2mA/cm² at 5V/μm were achieved. And based on Fowler–Nordheim plot, the value of work function for the DLC nanodot arrays was estimated in the range 0.4–1.84 from a linear plot. The results show that the DLC nanodot arrays can be a promising candidate as a field emission emitter.

Jing-Min, J.-M. Hou

Abstract We study the spectrum of an electron gas subjected to a two-dimensional non-Bravais lattice potential and a perpendicular magnetic field simultaneously. We derive the difference equations, which are not periodic in the x direction for any value of the gauge potential in Landau gauge ( 0... [view more]

Abstract

We study the spectrum of an electron gas subjected to a two-dimensional non-Bravais lattice potential and a perpendicular magnetic field simultaneously. We derive the difference equations, which are not periodic in the x direction for any value of the gauge potential in Landau gauge ( 0 , Hx , 0 ) (). The spectrum has a fractal structure and is incommensurate along the magnitude of the magnetic field.

H.D. Karki; S. Elagoz; R. Amca; P. Baser; K. Atasever

Abstract The ground state binding energy dependency of hydrogenic impurities on dielectric constant mismatch is investigated in cylindrical quantum wires as a function of wire radius and alloy concentration. The calculations are done for a cylindrical GaAs/Ga1−x Al x As system with a uniform external magnetic field ... [view more]

Abstract

The ground state binding energy dependency of hydrogenic impurities on dielectric constant mismatch is investigated in cylindrical quantum wires as a function of wire radius and alloy concentration. The calculations are done for a cylindrical GaAs/Ga_1−x Al _x As system with a uniform external magnetic field applied parallel to the wire axis using the effective mass approximation and variational methods for finite confinement potentials. According to the obtained results, one can ascertain that in calculating binding energies omitting the dielectric mismatch of the system is justified for large wire radii. However, there is a sign change in contribution for the binding energy for smaller wire radii. Furthermore, the magnitude of the contribution is more pronounced for smaller wire radii and larger alloy concentrations.

Yi-Ze Wang; Feng-Ming Li; Kikuo Kishimoto

Abstract In this paper, the propagation characteristics of the longitudinal wave in nanoplates with small scale effects are studied. The equation of the longitudinal wave is obtained using the nonlocal elastic theory. The phase velocity and the group velocity are derived, respectively. The dispersion relation is analyzed ... [view more]

Abstract

In this paper, the propagation characteristics of the longitudinal wave in nanoplates with small scale effects are studied. The equation of the longitudinal wave is obtained using the nonlocal elastic theory. The phase velocity and the group velocity are derived, respectively. The dispersion relation is analyzed with different wave numbers and scale coefficients. It can be observed from the results that the dispersion properties of the longitudinal wave are induced by the small scale effects, which will disappear in local continuous models. The dispersion degree can be strengthened by increasing the scale coefficient and the wave number. Furthermore, the characteristics for the group velocity of the longitudinal wave in nanoplates can also be tuned by these factors.

D. Camacho; Y.M. Niquet

Abstract

We discuss the application of Keating's valence force field model to non-ideal wurtzite materials such as GaN, InN and AlN.

P.H. Dhuvad; A.C. Sharma

Abstract An ab-initio calculation of photoabsorption, and absorption threshold has been performed for (CdS) n , n=1–8, atomic clusters using time-dependent density functional formalism. We used both time-propagation method as well as the Casida's linear theory formalism to compute photoabsorption spectrum ... [view more]

Abstract

An ab-initio calculation of photoabsorption, and absorption threshold has been performed for (CdS) _n , n=1–8, atomic clusters using time-dependent density functional formalism. We used both time-propagation method as well as the Casida's linear theory formalism to compute photoabsorption spectrum for energies up to 15eV. The photoabsorption exhibits prominent peaks for energies between 0 and 15eV, and validity too of our methodology is not under any kind of question mark, in this energy range. The computed results from both time-propagation method as well as the Casida's formalism are found in good agreement with each other as well as with recently reported photoabsorption experimental data on (CdS) _n , atomic clusters, for UV frequency range. Our results show that the absorption thresholds lie in between 2.08 and 6.29eV, and first ionization energies of clusters varies from 3.14 to 8.92eV for all (CdS) _n clusters.

L.C. Low; A.H. You; L.L.Y. Andy; P.L. Cheang

Abstract The mean multiplication gain and excess noise factor of thin GaAs/Al0.6Ga0.4As heterojunction avalanche photodiodes (HAPDs) are simulated. The ionization coefficients of electron and hole in bulk GaAs and Al0.6Ga0.4As are used in this model to study the role of heterojunction in reducing ... [view more]

Abstract

The mean multiplication gain and excess noise factor of thin GaAs/Al_0.6Ga_0.4As heterojunction avalanche photodiodes (HAPDs) are simulated. The ionization coefficients of electron and hole in bulk GaAs and Al_0.6Ga_0.4As are used in this model to study the role of heterojunction in reducing excess noise. The band-edge discontinuities at the conduction and valence bands are included in our model which may influence the number of carrier crossing the heterojunction and hence modifies the dead space in the HAPDs. The mean multiplication gain and excess noise factor with electron- and hole-initiated multiplication for 0.1 and 0.2μm multiplication lengths in GaAs/Al_0.6Ga_0.4As HAPDs are shown. By considering the dead space effect, our model demonstrated a small noise mainly due to the localization of carrier ionization and the limited carrier feedback ionization at heterointerface. In our model, most of the ionizations occur in the first-initiated multiplication layer which reduces the randomness of carrier ionization and noise.

N.S. Das; B. Saha; R. Thapa; G.C. Das; K.K. Chattopadhyay

Abstract Phosphorus doped nanocrystalline NiO thin films were synthesized using radio frequency magnetron sputtering of a prefabricated target on glass and silicon substrates in argon atmosphere. X-ray diffraction studies confirmed the good crystallinity and proper phase formation. Phosphorus doping in NiO films was confirmed from the binding energy... [view more]

Abstract

Phosphorus doped nanocrystalline NiO thin films were synthesized using radio frequency magnetron sputtering of a prefabricated target on glass and silicon substrates in argon atmosphere. X-ray diffraction studies confirmed the good crystallinity and proper phase formation. Phosphorus doping in NiO films was confirmed from the binding energy determination by X-ray photoelectron spectroscopic studies. Morphological information was obtained from the atomic force microscopic measurement. Determination of band gaps from the UV–vis–NIR spectrophotometric measurement showed that it increased from 3.66 to 3.81eV corresponding to undoped and 10% P doped NiO thin films.

Agile Mathew; Malay Kumar Nandy

Abstract We present detailed results of the calculation for single electron states in a cylindrical quantum dot in the presence of a constant magnetic field in the axial direction. The quantum dot structure considered is with a finite barrier potential in the radial direction and infinite barrier potential in ... [view more]

Abstract

We present detailed results of the calculation for single electron states in a cylindrical quantum dot in the presence of a constant magnetic field in the axial direction. The quantum dot structure considered is with a finite barrier potential in the radial direction and infinite barrier potential in the z-direction. We show how the states and energy levels depend on the strength of the magnetic field for different quantum numbers. It is observed that energy levels with different quantum numbers group together at high magnetic fields.

Yukihito Matsuura

Abstract The electronic structures of infinite linear metallic chains have been examined by tight-binding band calculations. We have analyzed the band structures of these linear metallic chains, density of states, and Mulliken overlap populations. The band structure of the linear Rh and Ru chain possesses diffuse d... [view more]

Abstract

The electronic structures of infinite linear metallic chains have been examined by tight-binding band calculations. We have analyzed the band structures of these linear metallic chains, density of states, and Mulliken overlap populations. The band structure of the linear Rh and Ru chain possesses diffuse d bands that traverse the Fermi level, similar to that of the linear Cr and Co chain. On the other hand, the linear Cu chain possesses some narrow 4s bands in energy levels near the Fermi level. Changing the metal atoms of the central metallic chain can provide various electronic states.

Huixin Wang; Ming Li; Lide Zhang; Zhenshen Liu; Xiaoxia Zhao; Xiyan Dong

Abstract Highly ordered (FePt)1−x Cu x nanowire arrays have been fabricated successfully by double-pulse electro-deposition into the pores of a porous anodic aluminum oxide template. We have found that the addition of Cu to FePt nanowires is an effective approach for reducing the ordering temperature... [view more]

Abstract

Highly ordered (FePt)_1−x Cu _x nanowire arrays have been fabricated successfully by double-pulse electro-deposition into the pores of a porous anodic aluminum oxide template. We have found that the addition of Cu to FePt nanowires is an effective approach for reducing the ordering temperature of FePt. The coercivity of the (FePt)₈₈Cu₁₂ nanowire arrays is around 2kOe after annealing at 300°C for 1h, whereas that of FePt nanowire arrays shows several hundred Oe. X-ray diffraction characterization showed that only one set of L1₀ diffraction peaks appeared and no elemental Cu diffraction peaks were visible. This result, along with a varying c/a-lattice parameter ratio, suggests that Cu substitutes Fe or Pt in the ternary FePtCu alloy nanowires.

S. Ghatak; M. Sinha; A.K. Meikap; S.K. Pradhan

Abstract Nanocrystalline Mg–Zn ferrite is prepared by ball milling the stoichiometric powder mixture of MgO, ZnO and α-Fe2O3. The ternary Mg–Zn ferrite phase may not be obtained by heat treatment of the stoichiometric powder mixture of the oxides. The particle size of ferrite phase in ... [view more]

Abstract

Nanocrystalline Mg–Zn ferrite is prepared by ball milling the stoichiometric powder mixture of MgO, ZnO and α-Fe₂O₃. The ternary Mg–Zn ferrite phase may not be obtained by heat treatment of the stoichiometric powder mixture of the oxides. The particle size of ferrite phase in the ball milled samples remains almost unaltered (∼3nm) and that of in annealed samples increases up to ∼330nm. Alternate current conductivity and dielectric properties of nanocrystalline Mg–Zn ferrite in the temperature range 77≤T≤300K, applying magnetic field up to 1T in the frequency range 20Hz–1MHz, are being reported. The frequency dependence of conductivity has been described by power law σ′(f,T)∝f ^s and the frequency exponent ‘s’ is found to be anomalous temperature dependent. A detailed analysis of the temperature dependence of the universal dielectric response parameter ‘s’ revealed that the correlated barrier hopping is the dominating charge transport mechanism. The real part of the dielectric permittivity at a fixed frequency was found to follow the power law ε′(f,T)∝T ⁿ and the magnitude of the temperature exponent ‘n’ strongly decreases with increasing frequency. The dielectric permittivity shows a large degree of dispersion at low frequency, but rapid polarization at high frequencies, which can be interpreted by the Maxwell-Wagner capacitor model. The temperature dependence of resistance due to grain and grain boundary contribution exhibits two activation regions. The observed positive ac conductivity may be due to the change of grain and grain boundary resistances caused by the magnetic field.

Wen-Ming Ju; Ka-Di Zhu

Abstract The dynamics of a coherently driven localized exciton in a semiconducting single-wall carbon nanotube (SWNT) is investigated theoretically in terms of the perturbation treatment based on a unitary transformation. The decoherence rate of the exciton is obtained analytically and is compared with the one obtained with ... [view more]

Abstract

The dynamics of a coherently driven localized exciton in a semiconducting single-wall carbon nanotube (SWNT) is investigated theoretically in terms of the perturbation treatment based on a unitary transformation. The decoherence rate of the exciton is obtained analytically and is compared with the one obtained with Born–Markov approximation. The results indicate that the decoherence strongly depends on the exciton–phonon coupling constant and the Rabi frequency of the coherently driving field. Furthermore, since the exciton–phonon coupling for SWNT is relatively strong and Born–Markov approximation becomes increasingly unreliable, we do need the numerically precise approach to treat the dynamics of the exciton in SWNT.

Ö., O. Güllü; S. Asubay; Ş., S. Aydoğan; A. Türüt

Abstract The current–voltage (I–V) and the capacitance–voltage (C–V) characteristics of the Al/new fuchsin (NF)/n-Si device have been investigated at room temperature. The I–V characteristic of the device shows a good rectification. The ideality factor and the barrier height... [view more]

Abstract

The current–voltage (I–V) and the capacitance–voltage (C–V) characteristics of the Al/new fuchsin (NF)/n-Si device have been investigated at room temperature. The I–V characteristic of the device shows a good rectification. The ideality factor and the barrier height from the I–V characteristics have been determined as 3.14 and 0.80eV, respectively. A modified Norde's function combined with the conventional I–V method has been used to extract the parameters including the barrier height and the series resistance. The barrier height and the series resistance obtained from Norde's function have been compared with those from Cheung functions, and it has been seen that there was a good agreement between those from both method. It has also been seen that the values of diode capacitance increased up to the constant values for the forward bias.

Daizy Philip

Abstract Biological synthesis of gold and silver nanoparticles of various shapes using the leaf extract of Hibiscus rosa sinensis is reported. This is a simple, cost-effective, stable for long time and reproducible aqueous room temperature synthesis method to obtain a self-assembly of Au and Ag nanoparticles.... [view more]

Abstract

Biological synthesis of gold and silver nanoparticles of various shapes using the leaf extract of Hibiscus rosa sinensis is reported. This is a simple, cost-effective, stable for long time and reproducible aqueous room temperature synthesis method to obtain a self-assembly of Au and Ag nanoparticles. The size and shape of Au nanoparticles are modulated by varying the ratio of metal salt and extract in the reaction medium. Variation of pH of the reaction medium gives silver nanoparticles of different shapes. The nanoparticles obtained are characterized by UV–vis, transmission electron microscopy (TEM), X-ray diffraction (XRD) and FTIR spectroscopy. Crystalline nature of the nanoparticles in the fcc structure are confirmed by the peaks in the XRD pattern corresponding to (111), (200), (220) and (311) planes, bright circular spots in the selected area electron diffraction (SAED) and clear lattice fringes in the high-resolution TEM image. From FTIR spectra it is found that the Au nanoparticles are bound to amine groups and the Ag nanoparticles to carboxylate ion groups.

Yi Zhao; Suqing Duan; Wei Zhang

Abstract We study the metal–insulator transition in a tight-binding one-dimensional (1D) model with long-range correlated disorder. In the case of diagonal disorder with site energy within [ − W / 2 , W / 2 ] and having a power-law spectral density S ... [view more]

Abstract

We study the metal–insulator transition in a tight-binding one-dimensional (1D) model with long-range correlated disorder. In the case of diagonal disorder with site energy within [ − W / 2 , W / 2 ] () and having a power-law spectral density S ( k ) ∝ k − α (), we investigate the competition between the disorder and correlation. Using the transfer-matrix method and finite-size scaling analysis, we find out that there is a finite range of extended eigenstates for α > 2 (), and the mobility edges are at ± E c = ± | 2 − W / 2 | (). Furthermore, we find the critical exponent ν () of localization length ( ξ ∼ | E − E c | − ν ()) to be ν = 1 + 1.4 e 2 − α (). Thus our results indicate that the disorder strength W determines the mobility edges and the degree of correlation α () determines the critical exponents.

Chunxu Bai; Yanling Yang; Xiangdong Zhang

Abstract In this paper, an analytical form of the real-space non-interacting Green function of graphene material is developed. The transport properties of the relativistic electron through graphene-based double barrier structures have been investigated based on the real-space non-interacting Green function. It is shown ... [view more]

Abstract

In this paper, an analytical form of the real-space non-interacting Green function of graphene material is developed. The transport properties of the relativistic electron through graphene-based double barrier structures have been investigated based on the real-space non-interacting Green function. It is shown that the results computed by the real-space non-interacting Green function are in perfect agreement with those results, which is based on the transfer matrix method.

Jun Shen; Binghui Ge; Haibo Dong; Ning Zhang; Shudong Luo; Wenjun Ma; Xiaofeng Duan; Sishen Xie; Weiya Zhou

Abstract Heterostructures of side-to-side biaxial ZnS/Zn2SnO4 (ZTO) nanowires have been fabricated via a simple one-step thermal evaporation process. Structural characterization by high-resolution transmission electron microscopy and electron diffraction indicates that both the face-centered cubic spinel ZTO subsection and the wurtzite ZnS subsection ... [view more]

Abstract

Heterostructures of side-to-side biaxial ZnS/Zn₂SnO₄ (ZTO) nanowires have been fabricated via a simple one-step thermal evaporation process. Structural characterization by high-resolution transmission electron microscopy and electron diffraction indicates that both the face-centered cubic spinel ZTO subsection and the wurtzite ZnS subsection of the heterostructure are well crystallized with a distinct interface along the heterostructure axial direction. Based on detailed analysis of the growth process of biaxial ZnS/ZTO nanowire heterostructures, there are two dominating stages: a vapor–liquid–solid (VLS) controlled growth of ZTO sub-nanowire and a self-assembly growth of ZnS sub-nanowire onto the preformed ZTO base nanowire. A growth model of the heterostructures is proposed. The presented method would be flexible and feasible for the synthesis of other nano-heterostructures with non-oxide/oxide interface to meet the growing demands of nanoscale science and technology.

Cui-Di Feng; Hong-Xing He; R. Shen; Baigeng Wang; D.Y., D.Y. Xing

Abstract We numerically investigate an isolated hybrid ring consisting of two segments, one is an s-wave superconductor and the other is two dimensional electron gas with Rashba spin–orbit interaction. Considering an Aharonov–Bohm flux through the hole of the ring, we calculate the elementary excitation spectrum ... [view more]

Abstract

We numerically investigate an isolated hybrid ring consisting of two segments, one is an s-wave superconductor and the other is two dimensional electron gas with Rashba spin–orbit interaction. Considering an Aharonov–Bohm flux through the hole of the ring, we calculate the elementary excitation spectrum and the persistent current at zero temperature and finite temperature. It is found that there is a competition between superconducting pair potential and Rashba spin–orbit interaction. At zero temperature the competition is mainly determined by the length of the superconducting segment d S (). When the superconducting segment is short, quasi-particles is easy to tunnel through the superconducting segment and Rashba spin–orbit interaction effect is dominant which results in the elementary excitation spectrum splits and the persistent current obtains an additional peak. On the contrary, when the superconducting segment is long enough, the quasi-particles are difficult to tunnel through the superconducting segment and they enter the superconducting segment via Andreev reflection process. In this case Rashba spin–orbit interaction does not cause the split of the elementary excitation spectrum inside the energy gap, and thus the persistent current has no additional peak. At finite temperature, when the superconducting segment is short, although the spin split effect still exists, the peak of the persistent current resulting from Rashba spin–orbit interaction gradually disappears as the temperature rises.

J.A. Peters; B.W. Wessels

Abstract We report on the magnetotransport properties of an InMnAs magnetic semiconductor thin film over the temperature range of 19–61K. A small negative magnetoresistance is observed that becomes positive with increasing field. We find that the magnetoresistance of these films is well described by a semi-empirical model... [view more]

Abstract

We report on the magnetotransport properties of an InMnAs magnetic semiconductor thin film over the temperature range of 19–61K. A small negative magnetoresistance is observed that becomes positive with increasing field. We find that the magnetoresistance of these films is well described by a semi-empirical model that takes into account the third order p–d exchange Hamiltonian describing the negative contribution and a two-band model for the positive contribution. The negative magnetoresistance of the film originates from spin-dependent scattering of carriers by localized magnetic moments while the positive magnetoresistance is attributed to conduction via spin-split hybridized p–d sub-bands with different conductivities and mobilities.

Jianwen Xu; Ke Yu; Ziqiang Zhu

Abstract Cu dendritic nanostructures were synthesized on ITO glass substructure by electrochemical deposition. SEM images showed that these Cu dendritic nanostuctures revealed a clear and well-defined dendritic fractal structure with a pronounced trunk and highly ordered branches distributed on both sides of the trunk. The diffusion-limited aggregation... [view more]

Abstract

Cu dendritic nanostructures were synthesized on ITO glass substructure by electrochemical deposition. SEM images showed that these Cu dendritic nanostuctures revealed a clear and well-defined dendritic fractal structure with a pronounced trunk and highly ordered branches distributed on both sides of the trunk. The diffusion-limited aggregation (DLA) model was used to explain the fractal growth of Cu dendritic nanostructures. Field emission properties of these Cu dendritic nanostructures were measured, which have possessed good performance with the turn-on field of 7.5V/μm (defined as the electric field required to be detected at a current density of 0.1mA/cm²) and the field enhancement factor β of 1094.

Ali A. Orouji; S.A. Ahmadmiri

Abstract Source and drain regions are inseparable sections of carbon nanotube field effect transistor (CNTFET) whose parameters are effective for CNTFET performance. For the first time in this paper, design considerations of source and drain regions are presented by developing a two-dimensional (2-D) full quantum... [view more]

Abstract

Source and drain regions are inseparable sections of carbon nanotube field effect transistor (CNTFET) whose parameters are effective for CNTFET performance. For the first time in this paper, design considerations of source and drain regions are presented by developing a two-dimensional (2-D) full quantum simulation. The simulations have been done by the self-consistent solution of 2-D Poisson–Schrödinger equations, within the nonequilibrium Green’s function (NEGF) formalism. The effects of varying the source and drain parameters are investigated in terms of on–off current ratio, transconductance characteristics, drain conductance, and subthreshold swing. Simulation results demonstrate that we could improve the CNTFET performance with proper selection of the source and drain parameters.

Wei-Li Chen; Yan-Hsin Wang; Ming-Fei Chen; Man-Fang Huang; Jenn-Chyuan Fan

Abstract The structural and morphological properties of InN epilayers grown on Si(111) substrates by plasma-assisted molecular beam epitaxy were studied. The mosaic characteristics such as grain size, twist and tilt angles were extracted by performing symmetric and asymmetric rocking curves and reciprocal space mapping. According to... [view more]

Abstract

The structural and morphological properties of InN epilayers grown on Si(111) substrates by plasma-assisted molecular beam epitaxy were studied. The mosaic characteristics such as grain size, twist and tilt angles were extracted by performing symmetric and asymmetric rocking curves and reciprocal space mapping. According to X-ray diffraction analysis, the dislocation densities reduced from 1×10¹¹ to 2.27×10¹⁰cm⁻², when the substrate temperature was increased from 440 to 525°C. Edge-type dislocation densities estimated both by fitting the FWHM of ω-scans of various lattice planes based on cosine theorem of spherical trigonometry and by grazing incidence (112¯0) diffraction agree with plan-view transmission electron microscopy (TEM) results. Surface morphology revealed grains with flat or terrace-like features separated by deep trenches. Faceted pits associated with screw-type threading dislocations are observed and their densities are in good consistence with the results obtained from X-ray diffraction. Improved film quality is achieved by applying highest growth temperature within InN dissociation limit.

R. Angelucci; I. Boscolo; A. Ciorba; M. Cuffiani; L. Malferrari; A. Montanari; F. Odorici; S. Orlanducci; R. Rizzoli; M. Rossi; V. Sessa; M.L. Terranova; G.P. Veronese

Abstract Field Emission (FE) properties of vertically aligned Carbon Nanotubes (CNTs) grown in a nanoporous anodic aluminium oxide (AAO) template have been investigated. A 50-μm-thick AAO template was fabricated by electrochemical techniques. The nanotubes were synthesized in a CVD quartz hot wall furnace ... [view more]

Abstract

Field Emission (FE) properties of vertically aligned Carbon Nanotubes (CNTs) grown in a nanoporous anodic aluminium oxide (AAO) template have been investigated. A 50-μm-thick AAO template was fabricated by electrochemical techniques. The nanotubes were synthesized in a CVD quartz hot wall furnace using C₂H₂/N₂ mixtures as feeding gas. I–V measurements have been performed on samples after the nanotubes growth (type I samples) and after a partial Al₂O₃ removal (type II samples) in order to obtain segments of nanotubes protruding from the nanopores. The effects of the conditioning process and adsorbates release have been investigated. The emission curves have been analysed in the framework of the Fowler–Nordheim model. For the β factor enhancement, a different dependence on time has been evidenced for two types of investigated samples and has been tentatively correlated with materials modifications occurring under the HV polarisation (in case of type I samples) and with the damage induced by chemical etching (in case of type II samples). The values of emitted current density (up to 40mA/cm²) and the emission properties indicate that the proposed preparation methodology is suitable for the realization of robust and efficient CNT-based field emission devices and electron sources.

G. Rezaei; Z. Mousazadeh; B. Vaseghi

Abstract The linear and third order nonlinear optical absorption coefficient and refractive index changes of an elliptic quantum dot have been investigated, using the compact-density matrix formalism and an iterative method. In this regard, the effect of optical intensity, size and geometry of the dot on the... [view more]

Abstract

The linear and third order nonlinear optical absorption coefficient and refractive index changes of an elliptic quantum dot have been investigated, using the compact-density matrix formalism and an iterative method. In this regard, the effect of optical intensity, size and geometry of the dot on the optical absorption coefficient and refractive index changes are investigated. It is found that, not only the light intensity but also the size and the geometry of the dot have a great influence on the optical absorption coefficient and refractive index changes of the system.

Vladimir P., V.P. Zhdanov; Bengt Kasemo

Abstract Hydriding and dehydriding kinetics of nanoparticles depend on the particle size. Our calculations illustrate that the apparent (averaged over size) kinetics of an ensemble of particles can be dramatically different compared to those of single particles. Specifically, we analyze the hydriding kinetics, limited by diffusion of... [view more]

Abstract

Hydriding and dehydriding kinetics of nanoparticles depend on the particle size. Our calculations illustrate that the apparent (averaged over size) kinetics of an ensemble of particles can be dramatically different compared to those of single particles. Specifically, we analyze the hydriding kinetics, limited by diffusion of hydrogen atoms from the surface layer via the hydride shell to the metallic core, and the dehydriding kinetics limited by associative desorption of hydrogen from the surface layer. In both cases, the apparent kinetics are relatively slow in the later stage, their time scale for the given average size is much larger than that for a single particle of the same size, and some of the special features of the single-particle kinetics (e.g., the initial slowdown of dehydriding) can be partly or completely washed out. The scaling of the time scale of the kinetics with respect to the particle size, however, remains valid.

Haixia Chen; Jijun Ding; Shuyi Ma

Abstract Pure and Mg-doped zinc oxide (ZnO:Mg) films were deposited using RF reactive magnetron sputtering at different oxygen partial pressures. The microstructures and optical properties in doped ZnO films were systematically investigated by X-ray diffraction (XRD), scanning electronic microscopy (SEM) and fluorescence spectrophotometer... [view more]

Abstract

Pure and Mg-doped zinc oxide (ZnO:Mg) films were deposited using RF reactive magnetron sputtering at different oxygen partial pressures. The microstructures and optical properties in doped ZnO films were systematically investigated by X-ray diffraction (XRD), scanning electronic microscopy (SEM) and fluorescence spectrophotometer. The results indicated that ZnO grain orientation behavior was significantly affected by Mg-doping. And the ZnO:Mg film prepared at 15:10 had the best crystal quality among all ZnO:Mg films. The photoluminescence (PL) measurements at room temperature revealed a violet, two blue and a green emission. The origin of these emissions was discussed. It was also demonstrated that the optical band edge shifted to a shorter wavelength first as Mg was incorporated, and then to a longer wavelength with the increasing of oxygen partial pressures.

Zhi-Qiang, Z.-Q. Fan; Ke-Qiu, K.-Q. Chen

Abstract By applying first-principles quantum transport calculations, we investigate the transport properties of the oligo(p-phenylenevinylene)s molecular devices modulated with different side groups. The calculated results show that for the system modulated with – NH 2 , the highest occupied molecular orbital is localized, while ... [view more]

Abstract

By applying first-principles quantum transport calculations, we investigate the transport properties of the oligo(p-phenylenevinylene)s molecular devices modulated with different side groups. The calculated results show that for the system modulated with – NH 2 (), the highest occupied molecular orbital is localized, while for the system modulated with – NO 2 (), the lowest unoccupied molecular orbital is localized. The electron transport will be enhanced when modulated only with – NH 2 () or – NO 2 (), but will be weakened when modulated with both – NH 2 () and – NO 2 (). Negative differential resistance is observed in the system modulated with two – NH 2 (). A mechanism for the negative differential resistance behavior is suggested.

B. Vaseghi; F. Yazdani; G. Rezaei

Abstract We present the full quantum mechanical model to study the dynamics of an electron in an isotropic 2D quantum dot, interacting with an external quantized electromagnetic field. To this end a Hamiltonian which includes the confining (gate) effects as a two-dimensional isotropic harmonic oscillator and the... [view more]

Abstract

We present the full quantum mechanical model to study the dynamics of an electron in an isotropic 2D quantum dot, interacting with an external quantized electromagnetic field. To this end a Hamiltonian which includes the confining (gate) effects as a two-dimensional isotropic harmonic oscillator and the proper interacting terms is used to establish the time-evolution operator, and calculate the field population and time varying electron dynamical variables. We demonstrate that the expectation values of physical quantities such as photon mean number, electron position from the dot center, and the population of energy subbands oscillate uniformly or collapse and revive periodically, depending on the initial state of the field and its intensity.

R. Khordad

Abstract In the present work, We calculate the donor binding energy for a V-groove GaAs / Al x Ga 1 − x As quantum wire using a variational procedure within the effective mass approximation. We present a relation for the position-dependent effective mass in V-groove quantum... [view more]

Abstract

In the present work, We calculate the donor binding energy for a V-groove GaAs / Al x Ga 1 − x As () quantum wire using a variational procedure within the effective mass approximation. We present a relation for the position-dependent effective mass in V-groove quantum wire which is a function of wire parameters. Calculations are presented with both constant effective mass and position-dependent effective masses for different dimensions of ridge quantum wire. We find that the position-dependent effective mass plays an important effect in the binding energy of the donor impurity in a ridge quantum wire. Also, we observe that the position-dependent effective mass in x-direction depends on all wire parameters, but in y-direction it depends on only one wire parameter.

R.K. Gupta; K. Ghosh; P.K. Kahol

Abstract Gold–strontium titanate (Au–STO) Schottky diode is fabricated using pulsed laser deposition technique. The current–voltage characteristics of the device show non-linear behavior. The junction parameters such as ideality factor, barrier height, and series resistance are calculated using Cheung and Norde's methods. ... [view more]

Abstract

Gold–strontium titanate (Au–STO) Schottky diode is fabricated using pulsed laser deposition technique. The current–voltage characteristics of the device show non-linear behavior. The junction parameters such as ideality factor, barrier height, and series resistance are calculated using Cheung and Norde's methods. The effect of temperature on diode parameters is studied in details. It is observed that the barrier height varies almost linearly with temperature and the values increase from 0.39 to 0.72eV in temperature range 150–300K. The ideality factor decreases from 18 to 3 with increase in temperature from 150 to 300K. High ideality factor suggests formation of non-ideal Schottky junction between gold and STO.

Ruigang Zhang; Heqing Yang; Hua Zhao; Danxiao Zhang; Ruini Liu; Li Li; Hongxing Dong

Abstract Straight and zigzag-shaped nanowires of GaN have been grown in situ on the surface of the gallium grains and alumina ceramic substrates by heating metallic gallium grains on alumina ceramic wafers in the presence of NH3 at 1000 and 1050°C for 0.5h, and their controllable ... [view more]

Abstract

Straight and zigzag-shaped nanowires of GaN have been grown in situ on the surface of the gallium grains and alumina ceramic substrates by heating metallic gallium grains on alumina ceramic wafers in the presence of NH₃ at 1000 and 1050°C for 0.5h, and their controllable synthesis was achieved by changing the reaction temperature. The growth of straight and zigzag-shaped GaN nanowires is governed by a vapor–solid (V–S) process, and the evolution of straight GaN nanowires to zigzag-shaped nanowires may arise from the change of Ga/N ratio and GaN vapor concentration in the reaction system. A strong UV emission band centered at 372(362)nm and a weak blue emission peak at 460nm were observed from the straight and zigzag-shaped GaN nanowires.

W. Liu; J. Wan; M. Cahay; V. Gasparian; S. Bandyopadhyay

Abstract Recently, we used an effective spin concept to expound the analogy between spin-based quantum information processing and phase coherent charge transport through an array of elastic scatterers. Here, we extend that analogy by calculating an effective Shannon entropy for such an array and examining its various ... [view more]

Abstract

Recently, we used an effective spin concept to expound the analogy between spin-based quantum information processing and phase coherent charge transport through an array of elastic scatterers. Here, we extend that analogy by calculating an effective Shannon entropy for such an array and examining its various properties. For single-moded transport, the Shannon entropy is given by H bin ( | t | 2 ) = − | t | 2 log 2 | t | 2 − | r | 2 log 2 | r | 2 (), where | t | 2 () and | r | 2 () are the transmission and reflection probabilities through the array of scatterers. A lower bound for H bin ( | t | 2 ) () is found starting with the entropic quantum uncertainty principle. An important result is that although evanescent channels (modes) have | t | 2 = 1 − | r | 2 → 0 (), so that their own contribution to H bin ( | t | 2 ) → 0 (), they nevertheless have a profound influence on the total H bin ( | t | 2 ) () of the array and its associated signal-to-noise ratio (SNR) since they renormalize the transmission probabilities of the propagating modes. This is reminiscent of the well-known fact that evanescent modes influence the conductance of a structure by renormalizing the transmission probabilities of the propagating modes.

The numerical values of H bin ( | t | 2 ) () and its SNR are strongly sensitive to the nature of the elastic scatterers, i.e., whether they are attractive (negative potential), repulsive (positive potential), or a combination of both. In samples with repulsive scatterers, the SNR can be tuned over a wide range by applying a potential through a gate to change the scattering potentials from repulsive to attractive by moving their energy levels with respect to the quasi-Fermi level in the sample. We also found that the mean free path of an electron traversing a random array of elastic scatterers is the length scale at which the sum of the cross-correlation coefficients of the effective spin components reaches a minimum. At that point, the sum of the effective Heisenberg and Zeeman Hamiltonians associated with effective spins describing the propagating channels, reaches a minimum. Hence the mean free path can be viewed as an order parameter for a phase transition.

E. Kilicarslan; S. Sakiroglu; M. Koksal; H. Sari; I. Sokmen

Abstract The diamagnetic susceptibility and the binding energy of a hydrogenic donor in a quantum well with different mass anisotropy parameters γ=m ⊥/m || are investigated in the presence of a magnetic field using a trial wave function with two parameters in the framework of the effective ... [view more]

Abstract

The diamagnetic susceptibility and the binding energy of a hydrogenic donor in a quantum well with different mass anisotropy parameters γ=m _⊥/m _|| are investigated in the presence of a magnetic field using a trial wave function with two parameters in the framework of the effective mass approximation. It is observed that the effects of magnetic field on diamagnetic susceptibility of the donor in two-dimensional semiconductors with various effective mass anisotropy parameters are quite different. Also it has been found that for Si there is an obvious increase in the binding energy for spatially dependent screening compared with that for constant screening in the range of considered well widths, whereas the spatially dependent screening effect is small for Ge and GaAs materials.

S.P. Ryu; N.K. Cho; J.Y. Lim; W.J. Choi; J.D. Song; J.I. Lee; Y.T. Lee; C.G. Park

Abstract We investigated the effect of InGaAs and AlGaAs combination strain reducing layers on InAs quantum dots (QDs) grown by migration enhanced epitaxy. The samples were examined by cross-sectional transmission electron microscopy, low-temperature and power dependent photoluminescence (PL). We observed three different size distributions ... [view more]

Abstract

We investigated the effect of InGaAs and AlGaAs combination strain reducing layers on InAs quantum dots (QDs) grown by migration enhanced epitaxy. The samples were examined by cross-sectional transmission electron microscopy, low-temperature and power dependent photoluminescence (PL). We observed three different size distributions of QDs in the atomic force microscopy image. We found that PL peak 1, 2, and 3 came from three different size distributions, and the energy level of QDs could be modified by changing strain reducing layers irrelevantly to controlling QD height in our samples. Furthermore, we elucidated the role of InGaAs and AlGaAs layer on the energy level modification and related cross-sectional morphology of the QDs.

Shuzhen Yu; Guoqing Miao; Yixin Jin; Ligong Zhang; Hang Song; Hong Jiang; Zhiming Li; Dabing Li; Xiaojuan Sun

Abstract Catalyst-free InP nanowires were grown on Si (100) substrates by metal-organic chemical vapor deposition. Morphology, crystal structure, photoluminescence, and Raman scattering properties of the nanowires were investigated. Most nanowires are long and straight; the angles between the nanowires and the Si substrate are... [view more]

Abstract

Catalyst-free InP nanowires were grown on Si (100) substrates by metal-organic chemical vapor deposition. Morphology, crystal structure, photoluminescence, and Raman scattering properties of the nanowires were investigated. Most nanowires are long and straight; the angles between the nanowires and the Si substrate are diverse. The photoluminescence peak shows blue-shift from the band gap energy of bulk InP. Both the blue-shift of photoluminescence peak and the full width at half-maximum of photoluminescence spectrum increase with decreasing nanowires growth temperature. Due to laser-induced heating, the TO and LO phonon peaks of the nanowires reveal downshift and asymmetric broadening compared with those of bulk InP at room temperature.

W.W., W.W. Cheng; C.J., C.J. Shan; Y.X., Y.X. Huang; T.K., T.K. Liu; H. Li

Abstract We investigate the temporal evolution of entanglement of three spin qubits coupled to an XY spin-chain with Dzyaloshinsky–Moriya (DM) interaction environment. For an initial state with W, we find that the DM interaction can enhance slightly the decay of entanglement both in the weak coupling... [view more]

Abstract

We investigate the temporal evolution of entanglement of three spin qubits coupled to an XY spin-chain with Dzyaloshinsky–Moriya (DM) interaction environment. For an initial state with W, we find that the DM interaction can enhance slightly the decay of entanglement both in the weak coupling region and strong coupling one. However, for an initial state with GHZ, the decay of entanglement is very sensitive to the DM interaction in the strong coupling region.

N.V. Bondar; M.S. Brodyn

Abstract In two-phase disordered media composed of borosilicate glass with ZnSe or CdS quantum dots, the formation of a phase percolation transition of carriers for near-threshold concentrations that are manifested in optical spectra has been observed. Microscopic fluctuations of the quantum-dot density near the percolation threshold... [view more]

Abstract

In two-phase disordered media composed of borosilicate glass with ZnSe or CdS quantum dots, the formation of a phase percolation transition of carriers for near-threshold concentrations that are manifested in optical spectra has been observed. Microscopic fluctuations of the quantum-dot density near the percolation threshold were found that resembled the phenomenon of critical opalescence, where similar fluctuations of the density of a pure substance appear near to a phase transition. It is proposed that the dielectric mismatch between a matrix and ZnSe or CdS quantum dots plays a significant role in the carrier (exciton) delocalization, resulting in the appearance of a “dielectric Coulomb trap” beyond the QD border and the formation of surface states of excitons. The spatial overlapping of excitonic states at the critical density of quantum dots results in a tunneling of carriers and the formation of a phase percolation transition in such media.

R.A., R.A. Gherghescu; D.N., D.N. Poenaru; A. Solovyov; W. Greiner

Abstract The surface influence on deposited atomic clusters is accounted for as a change in the geometry of the free cluster from spheroidal to semispheroidal (oblate and prolate) shapes. The energy levels for the electrons are calculated using a deformed oscillator quantum well plus squared angular momentum half-... [view more]

Abstract

The surface influence on deposited atomic clusters is accounted for as a change in the geometry of the free cluster from spheroidal to semispheroidal (oblate and prolate) shapes. The energy levels for the electrons are calculated using a deformed oscillator quantum well plus squared angular momentum half-cut by an infinite wall located at the surface. The level scheme is used to compute the shell corrections, to which a macroscopic liquid drop energy is added. Clear minima of the total deformation energy are obtained for semispheroids at the same deformation, within a range of atom number from 2 to 100. These minima are interpreted as stable structures of various magic numbers for deposited atomic clusters.

Sergio S., S.S. Gomez; Rodolfo H., R.H. Romero

Abstract The binding energy of a negatively charged hydrogenic impurity with on- and off-center positions in a spherical Gaussian quantum dot was calculated with the configuration interaction method. Our calculations show that E b is always positive for on-center impurities with a maximum near to the radius... [view more]

Abstract

The binding energy of a negatively charged hydrogenic impurity with on- and off-center positions in a spherical Gaussian quantum dot was calculated with the configuration interaction method. Our calculations show that E b () is always positive for on-center impurities with a maximum near to the radius for one-electron stability of the potential well R c (). For off-center positions the binding energy can assume negative values within a range of the quantum dot radius, thus indicating the instability of the system.

V.L. Aziz Aghchegala; V.N. Mughnetsyan; A.A. Kirakosyan

Abstract The effect of interdiffusion of Al and Ga atoms on the binding energy of the hydrogen-like shallow donor impurity in spherically symmetric GaAs/Ga1−x Al x As quantum dot is investigated. The dependence of the binding energy on the diffusion length, as well as on dot... [view more]

Abstract

The effect of interdiffusion of Al and Ga atoms on the binding energy of the hydrogen-like shallow donor impurity in spherically symmetric GaAs/Ga_1−x Al _x As quantum dot is investigated. The dependence of the binding energy on the diffusion length, as well as on dot radius and impurity position are obtained. It is shown that the dependence of the binding energy on the diffusion length has non-monotonic behavior in both the cases of on- and off-center impurity and can be significantly different for varied values of the dot radius and the distance of impurity from the dot center.

S. Bellucci; P. Onorato

Abstract We employ a path integral semiclassical approach to compute the properties for electrons transported across quantum nanojunctions and with Rashba spin–orbit interaction (SOI). We use a piecewise semiclassical approximation for the particle orbital motion and solve the spin dynamics exactly by formulating a semiclassical theory for ... [view more]

Abstract

We employ a path integral semiclassical approach to compute the properties for electrons transported across quantum nanojunctions and with Rashba spin–orbit interaction (SOI). We use a piecewise semiclassical approximation for the particle orbital motion and solve the spin dynamics exactly by formulating a semiclassical theory for low dimensional systems with SOI. We obtain analytical results that can be compared with the calculations made by using the quantum waveguide approach.

The proposed devices, with Π () and T geometry, can be analyzed within the scope both of spin filtering and spin rotation. In fact some devices action results in a transformation of the qubit state carried by the spin, i.e. act as one-qubit spintronic quantum gates whose properties can be varied by tuning the strength of the SOI or by changing the geometrical and physical parameters in the experimentally feasible range.

Y.L., Y.L. Xie; J.J., J.J. Ying; G. Wu; R.H., R.H. Liu; X.H., X.H. Chen

Abstract We have systematically measured susceptibility, angle dependent magnetization and specific heat on LiCu 2 O 2 single crystal. When magnetic field (H) is rotated within ab plane, a twofold symmetry in magnetization is observed at 50 and 100K under H = 5 T , while a ... [view more]

Abstract

We have systematically measured susceptibility, angle dependent magnetization and specific heat on LiCu 2 O 2 () single crystal. When magnetic field (H) is rotated within ab plane, a twofold symmetry in magnetization is observed at 50 and 100K under H = 5 T (), while a jump in magnetization is observed at certain angle with the twofold symmetry at 10K. Specific heat shows two successive transitions at T c 1 = 24.7 K () and T c 2 = 23 K (), respectively. The first one at T c 1 () shows antiferromagnetic (AFM) nature, while the second one at T c 2 () shows ferromagnetic (FM) behavior. These behaviors can be interpreted by the recently reported magnetic structure, and confirm the magnetic structure through another way.

DeXing Li; Linhan Lin; Jiayou Feng

Abstract The poor light emission efficiency in silicon prevents its wide application in the field of optoelectronics. Tailoring silicon into direct band-gap semiconductor, will not only vigorously promote the development of silicon-based optoelectronic integrated circuits, but also make significant achievements in the field of solid-state ... [view more]

Abstract

The poor light emission efficiency in silicon prevents its wide application in the field of optoelectronics. Tailoring silicon into direct band-gap semiconductor, will not only vigorously promote the development of silicon-based optoelectronic integrated circuits, but also make significant achievements in the field of solid-state light sources and solar cells. This article explores the nature of the electronic states of the direct band-gap H-passivated silicon nanonets and discusses the mechanism of the band-edge momentum matrix enhancement by means of first-principles calculation. A well corresponding relationship between the band-edge levels of bulk-like silicon and silicon nanonet is established. The first several conduction bands of silicon nanonets have the characteristic of folding energy levels, but the quantum confinement effect induces larger enhancement in momentum matrix elements than those of traditional silicon nanostructures. Two nano-fabrication techniques are proposed to produce the nanonet structure, as is expected to be widely applied in optoelectronic integrated circuits.

Jianning Ding; Biao Kan; Ningyi Yuan; Junxiong Wang; Zhigang Chen; Xiaoshuang Chen

Abstract The electronic structure of (5,5)/(10,0) single wall carbon nanotube intramolecule junction under electric field is investigated based on the density functional calculation. The variations in the density of states (DOS) as well as in the local DOS of the junction are direction ... [view more]

Abstract

The electronic structure of (5,5)/(10,0) single wall carbon nanotube intramolecule junction under electric field is investigated based on the density functional calculation. The variations in the density of states (DOS) as well as in the local DOS of the junction are direction depended on the longitudinal electric field. The delocalization of electrons can be enhanced by transverse electric field, for example a peak is resulted at the Fermi level in the DOS. The Mulliken charges redistribute under the external electric field. Their population indicates that the charges concentrate at the interface. Furthermore, some discussions are made on the structure deformation, the highest occupied molecular orbital and the lowest unoccupied molecular orbital.

T. Li; X.H. Zhang; Y.G. Zhu; X. Huang; L.F. Han; X.J. Shang; H.Q. Ni; Z.C. Niu

Abstract The temperature dependence of hole spin relaxation time in both neutral and n-doped ultrathin InAs monolayers has been investigated. It has been suggested that D'yakonov–Perel (DP) mechanism dominates the spin relaxation process at both low and high temperature regimes. The appearance of a peak... [view more]

Abstract

The temperature dependence of hole spin relaxation time in both neutral and n-doped ultrathin InAs monolayers has been investigated. It has been suggested that D'yakonov–Perel (DP) mechanism dominates the spin relaxation process at both low and high temperature regimes. The appearance of a peak in temperature dependent spin relaxation time reveals the important contribution of Coulomb scatterings between carriers to the spin kinetics at low temperature, though electron–phonon scattering becomes dominant at higher temperatures. Increased electron screening effect in the n-doped sample has been suggested to account for the shortened spin relaxation time compared with the undoped one. The results suggest that hole spins are also promising for building solid-state qubits.

S. Narendar; S. Gopalakrishnan

Abstract In this paper, the nonlocal elasticity theory has been incorporated into classical Euler–Bernoulli rod model to capture unique features of the nanorods under the umbrella of continuum mechanics theory. The strong effect of the nonlocal scale has been obtained which leads to substantially different wave behaviors of... [view more]

Abstract

In this paper, the nonlocal elasticity theory has been incorporated into classical Euler–Bernoulli rod model to capture unique features of the nanorods under the umbrella of continuum mechanics theory. The strong effect of the nonlocal scale has been obtained which leads to substantially different wave behaviors of nanorods from those of macroscopic rods. Nonlocal Euler–Bernoulli bar model is developed for nanorods. Explicit expressions are derived for wavenumbers and wave speeds of nanorods. The analysis shows that the wave characteristics are highly over estimated by the classical rod model, which ignores the effect of small-length scale. The studies also shows that the nonlocal scale parameter introduces certain band gap region in axial wave mode where no wave propagation occurs. This is manifested in the spectrum cures as the region where the wavenumber tends to infinite (or wave speed tends to zero). The results can provide useful guidance for the study and design of the next generation of nanodevices that make use of the wave propagation properties of single-walled carbon nanotubes.

J. Doak; R.K. Gupta; K. Manivannan; K. Ghosh; P.K. Kahol

Abstract In this paper, a method is developed to calculate the absorbance spectra of nanoparticles solution containing a size distribution of particles using the Mie theory. The standard gold nanoparticles solutions were purchased and characterized with the UV–visible absorption spectroscopy and dynamic light scattering size measurements techniques. ... [view more]

Abstract

In this paper, a method is developed to calculate the absorbance spectra of nanoparticles solution containing a size distribution of particles using the Mie theory. The standard gold nanoparticles solutions were purchased and characterized with the UV–visible absorption spectroscopy and dynamic light scattering size measurements techniques. Model size distributions were fit to the experimental absorbance spectra using the method described herein. Good semi-quantitative fits were found, which elucidate qualitative differences between “small” and “large” gold nanoparticles.

A.L., A.L. Parakhonsky; M.V., M.V. Lebedev; A.A., A.A. Dremin

Abstract The effect of He–Ne illumination on giant optical fluctuations in the system of double GaAs/AlGaAs quantum wells under quantum Hall effect conditions was found. Typical behavior was revealed for such objects in total filling factor ν tot = 4 in dependence on He–Ne pumping power.... [view more]

Abstract

The effect of He–Ne illumination on giant optical fluctuations in the system of double GaAs/AlGaAs quantum wells under quantum Hall effect conditions was found. Typical behavior was revealed for such objects in total filling factor ν tot = 4 () in dependence on He–Ne pumping power. As initial stage the giant fluctuation intensity increased dramatically and then it steadily decreased. The increasing of giant fluctuation intensity at small power of the illumination is resulted presumably from the minimizing of a random potential effect on the Landau level shape. Subsequent decreasing of the noise level is connected with the decreasing of quasi-equilibrium electron concentration in two-dimensional system when He–Ne illumination power increasing.

G.A., G.A. Nemnes; L. Ion; S. Antohe

Abstract Thermo-electrical properties of ballistic cylindrical nanowires are investigated with respect to their internal nanostructuring. The large scale three-dimensional scattering problem associated with the open quantum system is solved efficiently in the R-matrix formalism, which is here coupled with the Implicitly Restarted Arnoldi Method. In ... [view more]

Abstract

Thermo-electrical properties of ballistic cylindrical nanowires are investigated with respect to their internal nanostructuring. The large scale three-dimensional scattering problem associated with the open quantum system is solved efficiently in the R-matrix formalism, which is here coupled with the Implicitly Restarted Arnoldi Method. In this approach, the first few propagating modes are accurately described, while the numerical performance is greatly enhanced. The thermopower indicates different qualitative behaviors when inducing opposite deformations on the potential energy surface of the unperturbed nanowire. The results are discussed in the context of nanowire arrays, which are potential candidates in a wide range of electronic and optoelectronic devices.

M.G., M.G. Barseghyan; Alireza Hakimyfard; S.Y., S.Y. López; C.A., C.A. Duque; A.A., A.A. Kirakosyan

Abstract We consider the effects of hydrostatic pressure and temperature on the binding energy and photoionization cross section of hydrogen-like impurity in Pöschl–Teller quantum well. The ground state energy and the impurity wave function are calculated using the variational method. The binding energy dependencies on the width... [view more]

Abstract

We consider the effects of hydrostatic pressure and temperature on the binding energy and photoionization cross section of hydrogen-like impurity in Pöschl–Teller quantum well. The ground state energy and the impurity wave function are calculated using the variational method. The binding energy dependencies on the width of the quantum well, the hydrostatic pressure, the impurity position and the temperature are reported. The dependencies of the photoionization cross section on incident photon energy for two different polarizations of the light, different values of hydrostatic pressure and temperature have been also considered. The results show that the binding energy is an increasing (decreasing) function of the hydrostatic pressure (temperature) and that the binding energy can increase or decrease depending not only on the values of the confining potential parameters, but also on the impurity position. In the case of the photoionization cross section, the results show that by changing the polarization of the light, the behavior of the photoionization cross section dependence on photon energy changes dramatically. Associated with the increasing (decreasing) of the binding energy with the hydrostatic pressure (temperature) there is a redshift (blueshift) of the photoionization cross section as a function of the energy of the incident photon.

E. Kasapoglu; F. Ungan; H. Sari; I. Sökmen

Abstract The combined effects of hydrostatic pressure and temperature on donor impurity binding energy in cylindrical GaAs/Ga0.7Al0.3As quantum wire in the presence of the magnetic field have been studied by using a variational technique within the effective-mass approximation. The results show that an increment in ... [view more]

Abstract

The combined effects of hydrostatic pressure and temperature on donor impurity binding energy in cylindrical GaAs/Ga_0.7Al_0.3As quantum wire in the presence of the magnetic field have been studied by using a variational technique within the effective-mass approximation. The results show that an increment in temperature results in a decrement in donor impurity binding energy while an increment in the pressure for the same temperature enhances the binding energy and the pressure effects on donor binding energy are lower than those due to the magnetic field.

Analahba Roy; L.E. Reichl

Abstract We study the avoided crossings in the dynamics of quantum controlled excitations for an interacting many-boson system in an optical lattice. Specifically, we perform numerical simulations of learning control in this system where the driving pulses connect the undriven stationary states in a manner characteristic of Stimulated... [view more]

Abstract

We study the avoided crossings in the dynamics of quantum controlled excitations for an interacting many-boson system in an optical lattice. Specifically, we perform numerical simulations of learning control in this system where the driving pulses connect the undriven stationary states in a manner characteristic of Stimulated Raman Adiabatic Passage (STIRAP). We demonstrate that the dynamics of such a transition is affected by chaos assisted passages, resulting in a loss in coherence of the final outcome in the adiabatic limit.

Nenad S. Simonović

Abstract It is shown that the effective carrier interaction in semiconductor thin films, which is essentially of a non-Coulomb type, depends on the layer thickness but it is not sensitive to the form of quantum well. As a consequence the analytical expression for the effective 2D interaction ... [view more]

Abstract

It is shown that the effective carrier interaction in semiconductor thin films, which is essentially of a non-Coulomb type, depends on the layer thickness but it is not sensitive to the form of quantum well. As a consequence the analytical expression for the effective 2D interaction potential, obtained using the parabolic quantum well model, can be used as a general (model-independent) formula. As an example, we have considered the electrons localized in a quantum dot. It is demonstrated that, when the quantum well confinement is much stronger than the lateral one, the results obtained using the 2D approach with the effective potential are in a good agreement with the full 3D calculations.

M.L. Ladrón de Guevara; G.A. Lara; P.A. Orellana

Abstract We study equilibrium and non-equilibrium transport of non-interacting electrons through two quantum dot molecules embedded in an Aharonov–Bohm interferometer, and focus in several quantum interference effects occurring in both regimes. We obtain analytical expressions for the transmission and the density of states, and we ... [view more]

Abstract

We study equilibrium and non-equilibrium transport of non-interacting electrons through two quantum dot molecules embedded in an Aharonov–Bohm interferometer, and focus in several quantum interference effects occurring in both regimes. We obtain analytical expressions for the transmission and the density of states, and we calculate numerically the current at zero temperature. We show that the system exhibits Fano resonances, total suppression of transmission, and bound states in the continuum. In equilibrium we find a magnetic flux-dependent effective level attraction and lines of perfect transmission when the intramolecular coupling is weak. This feature has strong consequences in the non-equilibrium regime, where the I–V characteristics displays a region of negative differential conductance induced by the magnetic flux. The current suffers an abrupt rise for small bias voltages as consequence of an effective level attraction of the hybridized levels produced by the flux. The decrease of current is result of the destruction of this effect when the bias is increased.

M. Santhi; A. John Peter

Abstract We study the effects of laser field intensity over the ground state binding energy of light and heavy hole excitons confined in GaAs/Ga1−x Al x As cylindrical quantum wire. We have applied the variational method using 1s-hydrogenic wavefunctions, in the framework of the single band... [view more]

Abstract

We study the effects of laser field intensity over the ground state binding energy of light and heavy hole excitons confined in GaAs/Ga_1−x Al _x As cylindrical quantum wire. We have applied the variational method using 1s-hydrogenic wavefunctions, in the framework of the single band effective mass approximation and computed the exciton binding energy as a function of the wire radius for different field of laser intensities. The valence-band anisotropy is included in our theoretical model by using different hole masses in different spatial directions. The results show that (i) the binding energy is found to increase with decrease in the wire radius, and decrease with increase in the value of laser field amplitude, (ii) the heavy-hole exciton in a cylindrical quantum wire is more strongly bound than the light-hole exciton and (iii) the binding energy of the impurity for the narrow wire is more sensitive to the laser field amplitude.

Saakshi Dhanekar; S.S. Islam; T. Islam; A.K. Shukla; Harsh

Abstract Porous silicon (PS) samples were prepared under different anodization conditions and correspondingly the sensor parameters were studied for organic vapours like methanol, ethanol, propanol, acetone and benzene at low ppm level using capacitive measurements. The surface morphology of the samples was characterized by scanning electron microscopy... [view more]

Abstract

Porous silicon (PS) samples were prepared under different anodization conditions and correspondingly the sensor parameters were studied for organic vapours like methanol, ethanol, propanol, acetone and benzene at low ppm level using capacitive measurements. The surface morphology of the samples was characterized by scanning electron microscopy (SEM), whereas Raman spectroscopic studies were made to identify the surface species formed due to surface passivation. Selective response was observed for either methanol or ethanol depending on the combined effect of the pore morphology of PS, its surface passivation and the concentration dependent molecular kinetics in vapour phase. A probabilistic approach of the concentration dependent vapour molecular kinetics is demonstrated to explain the sensor performance and selectivity studies.

Weijing Liu; Junyu Zhu; Zhi Wang; Xiaodong Tang

Abstract Dielectrophoresis is a potential technique which can be employed to manipulate micro-/nano-particles, fabricate micro/nano-devices and test the properties of materials in fluid. Among the influences on dielectrophoretic manipulation, the electrode configuration that dictates the radiation pattern of electric field is a point out... [view more]

Abstract

Dielectrophoresis is a potential technique which can be employed to manipulate micro-/nano-particles, fabricate micro/nano-devices and test the properties of materials in fluid. Among the influences on dielectrophoretic manipulation, the electrode configuration that dictates the radiation pattern of electric field is a point out one. In this paper, a novel wafer-level planar micro-electrode system was designed and fabricated by rapid, low-cost micro-fabrication technologies. This low-cost platform can meet the primary needs of DEP manipulation, is ideal for mass production and can augment the accessibility of DEP devices to end-users lacking fabrication facilities or knowledge.

Kanchan Sarkar; Nirmal Kumar Datta; Manas Ghosh

Abstract We explore the pattern of frequency-dependent linear and non-linear optical (NLO) response of electron impurity doped quantum dots harmonically confined in two dimensions. For some fixed values of transverse magnetic field strength ( ω c ), and harmonic confinement potential ( ω 0 ), ... [view more]

Abstract

We explore the pattern of frequency-dependent linear and non-linear optical (NLO) response of electron impurity doped quantum dots harmonically confined in two dimensions. For some fixed values of transverse magnetic field strength ( ω c ()), and harmonic confinement potential ( ω 0 ()), the influence of impurity location ( x 0 , y 0 ()) on the diagonal components of frequency dependent linear ( α xx () and α yy ()), and the first ( β xxx () and β yyy ()) NLO responses of the dot is computed through linear variational route. The non-linear polarizabilities undergo maximization at some typical oscillation frequency of the external field depending upon the impurity location.

Mahmoud Mirzaei; Masoud Giahi

Abstract We have performed density functional theory (DFT) calculations employing BLYP exchange functional and 6–31G* standard basis set by GAUSSIAN 98 package of program. The electronic structure properties of representative zigzag and armchair models of boron nitride nanotube (BNNT) and boron phosphide nanotube (BPNT) have... [view more]

Abstract

We have performed density functional theory (DFT) calculations employing BLYP exchange functional and 6–31G^* standard basis set by GAUSSIAN 98 package of program. The electronic structure properties of representative zigzag and armchair models of boron nitride nanotube (BNNT) and boron phosphide nanotube (BPNT) have been studied. The (6,0) and (4,4) structures have been optimized and the electric field gradient (EFG) tensors have been calculated at the sites of various boron-11 nuclei. The calculated EFG tensors have been converted to the equivalent experimental nuclear quadrupole resonance (NQR) parameters, quadrupole coupling constant and asymmetry parameter. The results revealed that the boron atoms at the edges of nanotubes play dominant roles in determining the electronic behaviors of BNNT and BPNT. The average of the calculated values of quadrupole coupling constants at the sites of boron-11 nuclei is in good agreement with experiments.

S.N. Sarangi; S. Rath; K. Goswami; S. Nozaki; S.N. Sahu

Abstract CdSe nanocrystals (NCs) with good crystallinity were successfully grown by an electrochemical deposition technique using two different single stranded (ss) DNA molecules, poly G (30) and poly C (30) as templates. A model describing the structural ordering in CdSe NCs using ssDNA and its... [view more]

Abstract

CdSe nanocrystals (NCs) with good crystallinity were successfully grown by an electrochemical deposition technique using two different single stranded (ss) DNA molecules, poly G (30) and poly C (30) as templates. A model describing the structural ordering in CdSe NCs using ssDNA and its conjugate is being proposed. TEM and GXRD measurements confirm the structural ordering in NC CdSe–DNA systems. FTIR measurements confirm the tagging of DNA to CdSe NC. Micro Raman scattering of structurally ordered CdSe NCs show strong phonon confinement.

Navendu Goswami; Dhirendra Kumar Sharma

Abstract In this paper we report the structural, electronic and optical properties of ZnO nanocrystals synthesized by a facile chemical method. ZnO nanoparticles prepared by this method were investigated employing X-ray diffraction (XRD), Transmission electron microscope (TEM), Atomic force microscope (AFM), Fourier transform ... [view more]

Abstract

In this paper we report the structural, electronic and optical properties of ZnO nanocrystals synthesized by a facile chemical method. ZnO nanoparticles prepared by this method were investigated employing X-ray diffraction (XRD), Transmission electron microscope (TEM), Atomic force microscope (AFM), Fourier transform infrared (FTIR), UV–Visible and Fluorescence (FL) spectroscopy. In order to study the effect of annealing on ZnO nanoparticles, we have analyzed pre- and post-annealed nanoparticles. It was observed that annealing treatment removes the impurities and consequently enhances the purity of ZnO nanoparticles without influencing their wurtzite phase. The absorption and excitation transitions occurring in annealed ZnO nanoparticles are similar to those in unannealed ZnO; however, some fluorescence emissions are altered. On the one hand, annealing assists in obtaining the pure ZnO nanoparticles without affecting their size and crystal structure; on the other hand channels of radiative combination are affected by the annealing process.

M. Eskandari; V. Ahmadi; S.H. Ahmadi

Abstract Aluminum-doped zinc oxide nanorod arrays are deposited on glass by a solution method at low temperature (80°C). The as-grown samples are characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), UV–vis spectroscopy and Raman spectroscopy. We observe that Raman... [view more]

Abstract

Aluminum-doped zinc oxide nanorod arrays are deposited on glass by a solution method at low temperature (80°C). The as-grown samples are characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), UV–vis spectroscopy and Raman spectroscopy. We observe that Raman spectroscopy of aluminum-doped zinc oxide nanorods is different from undoped zinc oxide nanorods. The intensity of Raman peak at 437cm⁻¹ decreases for aluminum-doped zinc oxide nanorods sample while a peak at 750cm⁻¹ appears. X-ray diffraction (XRD) shows aluminum-doped zinc oxide nanorods grown in (002) orientation.

C.L. Yuan; W. Lei

Abstract This manuscript presents a study on the growth stress of Al2O3 nanocrystals in Lu2O3 matrix and its resultant effect on the optical properties of Al2O3 nanocrystals. The high-resolution transmission electron microscopy study reveals the complete isolation of Al2O3 nanocrystals embedded in Lu2O3 matrix. Two dimensional finite element... [view more]

Abstract

This manuscript presents a study on the growth stress of Al₂O₃ nanocrystals in Lu₂O₃ matrix and its resultant effect on the optical properties of Al₂O₃ nanocrystals. The high-resolution transmission electron microscopy study reveals the complete isolation of Al₂O₃ nanocrystals embedded in Lu₂O₃ matrix. Two dimensional finite element calculations clearly demonstrate that Al₂O₃ nanocrystals certainly experience great compressive stress in Lu₂O₃ matrix. This may lead to a great deal of defects formed around or inside Al₂O₃ nanocrystals to relax the compressive stress incurred by Al₂O₃ nanocrystals, leading to the photoluminescence emission observed.

César O., C.O. Stoico; C. Manuel Carlevaro; Danilo G., D.G. Renzi; Fernando Vericat

Abstract In this comprehensible article we develop, following Fantoni and Rosati formalism, a hypernetted chain approximation for one-dimensional systems of fermions. Our scheme differs from previous treatments in the form that the whole set of diagrams is grouped: we do it in terms of non-nodal, ... [view more]

Abstract

In this comprehensible article we develop, following Fantoni and Rosati formalism, a hypernetted chain approximation for one-dimensional systems of fermions. Our scheme differs from previous treatments in the form that the whole set of diagrams is grouped: we do it in terms of non-nodal, non-composite and elementary graphs. This choice makes the deduction of equations more transparent. Equations for the pair distribution functions of one component systems as well as binary mixtures are obtained. We apply they to experimentally realizable quasi-one-dimensional systems, the so-called quantum wires which we model, within Sommerfeld–Pauli spirit, as a one-dimensional electron gas or as an electron–hole mixture. In order to use our one-dimensional equations we consider pair potentials that depend on the wires width.

S. Narendar; S. Gopalakrishnan

Abstract This paper presents the effect of nonlocal scaling parameter on the terahertz wave propagation in fluid filled single walled carbon nanotubes (SWCNTs). The SWCNT is modeled as a Timoshenko beam, including rotary inertia and transverse shear deformation by considering the nonlocal scale effects. A uniform fluid ... [view more]

Abstract

This paper presents the effect of nonlocal scaling parameter on the terahertz wave propagation in fluid filled single walled carbon nanotubes (SWCNTs). The SWCNT is modeled as a Timoshenko beam, including rotary inertia and transverse shear deformation by considering the nonlocal scale effects. A uniform fluid velocity of 1000m/s is assumed. The analysis shows that, for a fluid filled SWCNT, the wavenumbers of flexural and shear waves will increase and the corresponding wave speeds will decrease as compared to an empty SWCNT. The nonlocal scale parameter introduces certain band gap region in both flexural and shear wave mode where no wave propagation occurs. This is manifested in the wavenumber plots as the region where the wavenumber tends to infinite (or wave speed tends to zero). The frequency at which this phenomenon occurs is called the “escape frequency”. The effect of fluid density on the terahertz wave propagation in SWCNT is also studied and the analysis shows that as the fluid becomes denser, the wave speeds will decrease. The escape frequency decreases with increase in nonlocal scaling parameter, for both wave modes. We also show that the effect of fluid density and velocity are negligible on the escape frequencies of flexural and shear wave modes.

Y. Chen; X.L. Xu; G.H. Zhang; H. Xue; S.Y. Ma

Abstract Er-doped ZnO films were deposited by direct current co-reactive magnetron sputtering technique and the microstructure and the optical properties of the ZnO films were investigated. XRD analysis reveals that the substrate temperatures have an evident effect on the (002) preferential orientation and the Er-doped ... [view more]

Abstract

Er-doped ZnO films were deposited by direct current co-reactive magnetron sputtering technique and the microstructure and the optical properties of the ZnO films were investigated. XRD analysis reveals that the substrate temperatures have an evident effect on the (002) preferential orientation and the Er-doped ZnO film deposited at room temperature consists of an amorphous phase. The blue shift of the optical band gap was observed in the ZnO:Er films compared with undoped ZnO film, and the Er-doped ZnO film deposited at room temperature has the largest band gap (about 3.99eV). The main reason for the broadening of the band gap is attributed to the amorphous phase in the Er-doped ZnO film. Meanwhile, the red shift of the band gap in the ZnO:Er films deposited at high temperature was observed as the crystallinity of the fim became better.

Qin Zhou; Ye Yang; Jie Ni; Zhengcao Li; Zhengjun Zhang

Abstract Fast detection of persistent organic pollutants in environment at the trace amount is important but difficult. We demonstrate here a simple method to detect 2, 3, 3′, 4, 4′- pentachlorinated biphenyl by the surface-enhanced Raman scattering technique, using aligned Ag nanorods as substrates.... [view more]

Abstract

Fast detection of persistent organic pollutants in environment at the trace amount is important but difficult. We demonstrate here a simple method to detect 2, 3, 3′, 4, 4′- pentachlorinated biphenyl by the surface-enhanced Raman scattering technique, using aligned Ag nanorods as substrates. By this way 2, 3, 3′, 4, 4′- pentachlorinated biphenyl dissolved in acetone can be detected to a concentration of 10⁻⁸mol/L, in tens of seconds. This study provides possibly a fast, simple and sensitive technique for the detection of those organic hazardous not soluble in water.

S. Patibandla; G.M., G.M. Atkinson; S. Bandyopadhyay; G.C., G.C. Tepper

Abstract In most technologically important semiconductors, the two main spin relaxation mechanisms are the D’yakonov–Perel’ (DP) and the Elliott–Yafet (EY) modes. In the former, the spin relaxation rate increases, while in the latter it decreases, with increasing carrier mobility. Accordingly, the... [view more]

Abstract

In most technologically important semiconductors, the two main spin relaxation mechanisms are the D’yakonov–Perel’ (DP) and the Elliott–Yafet (EY) modes. In the former, the spin relaxation rate increases, while in the latter it decreases, with increasing carrier mobility. Accordingly, the DP mode should dominate in high-mobility samples and the EY mode in low-mobility ones. We have carried out experiments in high-mobility bulk and low-mobility nanowire samples of germanium and found that indeed the DP mode dominates in the high-mobility samples and the EY mode in the low-mobility ones. The DP relaxation time was found to be three orders of magnitude shorter than the EY relaxation time. This suggests that low-mobility samples may be preferable for some spintronic applications.

J. Yang; L.L. Ke; S. Kitipornchai

Abstract Nonlinear free vibration of single-walled carbon nanotubes (SWCNTs) is studied in this paper based on von Kármán geometric nonlinearity and Eringen's nonlocal elasticity theory. The SWCNTs are modeled as nanobeams where the effects of transverse shear deformation and rotary inertia are considered within the framework ... [view more]

Abstract

Nonlinear free vibration of single-walled carbon nanotubes (SWCNTs) is studied in this paper based on von Kármán geometric nonlinearity and Eringen's nonlocal elasticity theory. The SWCNTs are modeled as nanobeams where the effects of transverse shear deformation and rotary inertia are considered within the framework of Timoshenko beam theory. The governing equations and boundary conditions are derived by using the Hamilton's principle. The differential quadrature (DQ) method is employed to discretize the nonlinear governing equations which are then solved by a direct iterative method to obtain the nonlinear vibration frequencies of SWCNTs with different boundary conditions. Zigzag (5, 0), (8, 0), (9, 0) and (11, 0) SWCNTs are considered in numerical calculations and the elastic modulus is obtained through molecular mechanics (MM) simulation. A detailed parametric study is conducted to study the influences of nonlocal parameter, length and radius of the SWCNTs and end supports on the nonlinear free vibration characteristics of SWCNTs.

P. Agnihotri; S. Bandyopadhyay

Abstract An analytical expression is derived for the conductance modulation of a ballistic two-dimensional Datta–das spin field effect transistor (SPINFET) as a function of gate voltage. Using this expression, we show that the recently observed conductance modulation in a two-dimensional SPINFET structure does not match... [view more]

Abstract

An analytical expression is derived for the conductance modulation of a ballistic two-dimensional Datta–das spin field effect transistor (SPINFET) as a function of gate voltage. Using this expression, we show that the recently observed conductance modulation in a two-dimensional SPINFET structure does not match the theoretically expected result very well. This calls into question the claimed demonstration of the SPINFET and underscores the need for further careful investigation.

Yiming Fu; Jin Zhang

Abstract Based on a modified couple stress theory, a new Timoshenko beam model is established to address the size effect of microtubules (MTs) in this paper. The bending equation and the buckling equation are derived from the minimum total potential energy principle. Results obtained from the present ... [view more]

Abstract

Based on a modified couple stress theory, a new Timoshenko beam model is established to address the size effect of microtubules (MTs) in this paper. The bending equation and the buckling equation are derived from the minimum total potential energy principle. Results obtained from the present model show that length dependence of MTs is related not only to shear effect but also to size effect, and the size effect is coupled in the shear effect, which means that the phenomenon of length dependence will disappear when the shear effect is neglected. Moreover, when very long MTs are considered, the persistence lengths are related to the internal material length scale parameter, which is different from the conclusions obtained from the classical and previous nonlocal beam models. The effect of the internal material length scale parameter on the buckling wavelength, the buckling growth rate and the buckling amplitude of the MTs is also discussed in this paper, and a comparison between present and previous results is presented.

Yong-An Lv; Yan-Hong Cui; Xiao-Nian Li; Xiang-Zhi Song; Jian-Guo Wang; Mingdong Dong

Abstract The understanding of the interaction between Au and carbon nanotubes (CNTs) is very important since Au/CNTs composites have wide applications in many fields. In this study, we investigated the dispersion of Au nanoparticles on the CNTs by transmission electron microscopy and the bonding mechanism between Au... [view more]

Abstract

The understanding of the interaction between Au and carbon nanotubes (CNTs) is very important since Au/CNTs composites have wide applications in many fields. In this study, we investigated the dispersion of Au nanoparticles on the CNTs by transmission electron microscopy and the bonding mechanism between Au clusters and CNTs by means of density functional theory calculations. Both experimental and theoretical studies show that point defects are the anchoring sites of Au nanoparticles. The mechanisms of enhanced bond between Au and CNTs via the point defects are explained by the analysis of density of states, charge transfer and frontier molecular orbitals.

Guo-Ping Guo; Rui Yang; Xi-Feng Ren; Lu-Lu Wang; Hong-Yan Shi; Bo Hu; Shu-Hong Yu; Guang-Can Guo

Abstract Excitation of surface plasmons in a single silver nanowire using higher-order-mode light shows that nanowire waveguide has no request on the spatial mode of the input light, which is determined by its orbital angular momentums (OAM) in the experiment. The excitation efficiency can be controlled... [view more]

Abstract

Excitation of surface plasmons in a single silver nanowire using higher-order-mode light shows that nanowire waveguide has no request on the spatial mode of the input light, which is determined by its orbital angular momentums (OAM) in the experiment. The excitation efficiency can be controlled by adjusting the light polarization. Experimental result also indicates that the propagating modes of surface plasmons in nanowire are not the OAM eignenstates.

Zhao Guo; Bin Lu; Xue Jiang; Jijun Zhao; Rui-Hua Xie

Abstract The lowest-energy structures of medium-sized Li n (n=20, 30, 40, 50) clusters are determined from simulated annealing technique followed by geometry optimization within the framework of density functional theory. The shapes of magic-number Li20 and Li40 clusters are nearly spherical while those... [view more]

Abstract

The lowest-energy structures of medium-sized Li _n (n=20, 30, 40, 50) clusters are determined from simulated annealing technique followed by geometry optimization within the framework of density functional theory. The shapes of magic-number Li₂₀ and Li₄₀ clusters are nearly spherical while those of the other clusters are ellipsoid. The growth of Li _n clusters is based on core of multi-layered pentagonal bipyramids with other atoms capped on the surface. The binding energies of the Li _n clusters were computed and compared with experiments. At magic-number sizes (n=20, 40), Li _n clusters possess relatively larger HOMO–LUMO gaps and higher ionization potentials, corresponding to the closure of electron shell. The molecular orbitals of the lithium clusters can be grouped into electron shells and their spatial distributions resemble the atomic orbitals. The average polarizability of the Li clusters reduces rapidly with cluster size and can be approximately described by a classical metallic sphere model. The optical absorption spectra of Li _n clusters from time-dependent density functional theory calculations show giant resonance phenomenon, and resonance peak blueshifts with increasing cluster size.

Cai-Juan Xia; De-Sheng Liu; Chang-Feng Fang; Peng Zhao

Abstract By applying nonequilibrium Green’s function formalism combined first-principles density functional theory, we investigate the electronic transport properties of the butadienimine-based optical molecular switch with and without substituents. The influence of HOMO–LUMO gaps and the spatial distributions of molecular orbitals on the electronic transport through... [view more]

Abstract

By applying nonequilibrium Green’s function formalism combined first-principles density functional theory, we investigate the electronic transport properties of the butadienimine-based optical molecular switch with and without substituents. The influence of HOMO–LUMO gaps and the spatial distributions of molecular orbitals on the electronic transport through the molecular device are discussed in detail. Theoretical results show that the donor/acceptor substituent plays an important role in the electronic transport of molecular devices. The switching performance can be improved to some extent through suitable donor and acceptor substituents.

A.H. Reshak; J. Ebothe; A. Wojciechowski; W. Kuznik; A. Popeda

Abstract Inorganic nano-crystallites (NC) (CdO, ZnO, ZnS, ZnSe) incorporated into photopolymer matrices (7.5% by weight) were optically treated by coherent bicolor nano-second laser pulses at Er3+ glass laser lines at 1.54 and 0.77μm. We have achieved a sufficiently... [view more]

Abstract

Inorganic nano-crystallites (NC) (CdO, ZnO, ZnS, ZnSe) incorporated into photopolymer matrices (7.5% by weight) were optically treated by coherent bicolor nano-second laser pulses at Er3+ glass laser lines at 1.54 and 0.77μm. We have achieved a sufficiently good effective second-order susceptibility coefficients (up to 2.8pm/V) at wavelengths 1.54μm. The maximal second-order optical susceptibility was achieved for NC sizes equal to about 30nm. Relaxation processes are studied.

H. Dutta; S.K. Pradhan

Abstract High-energy ball-milling of monoclinic (m) ZrO2–anatase (a)TiO2 mixture (3:2 molar ratio) at room temperature results in partial formation of nanocrystalline orthorhombic ZrTiO4 phase after 8h of milling. ZrTiO4 phase is formed from the high pressure srilankite (s)-TiO2 based TiO2... [view more]

Abstract

High-energy ball-milling of monoclinic (m) ZrO₂–anatase (a)TiO₂ mixture (3:2 molar ratio) at room temperature results in partial formation of nanocrystalline orthorhombic ZrTiO₄ phase after 8h of milling. ZrTiO₄ phase is formed from the high pressure srilankite (s)-TiO₂ based TiO₂–ZrO₂ solid-solution. In-situ high temperature annealing of ZrTiO₄, m-ZrO₂ and a-TiO₂ powder mixture results in complete transformation of ZrTiO₄ at 1073K. Microstructure characterization of the ball-milled and in-situ annealed samples in terms of several lattice imperfections is made employing the Rietveld’s method of structure refinement using X-ray powder diffraction data. Phase transformation kinetics and in addition to microstructure parameters, relative phase abundances of different phases are revealed from the Rietveld analysis. The analysis reveals that the ZrTiO₄ is formed from the isostructure s-TiO₂ based TiO₂–ZrO₂ solid-solution with ∼11nm particle size after annealing at 1073K.

D. Sakellari; N. Frangis; E.K. Polychroniadis

Abstract Transmission electron microscopy investigation revealed a phase separation in the NiCuZn ferrites. In a cubic (Ni,Zn)Fe2O4 matrix precipitates of the cubic Fe0.64Ni0.36 were found constructing an almost periodic array of nanowires. The nanowires were grown endotaxially in the matrix, i.e. the ... [view more]

Abstract

Transmission electron microscopy investigation revealed a phase separation in the NiCuZn ferrites. In a cubic (Ni,Zn)Fe₂O₄ matrix precipitates of the cubic Fe_0.64Ni_0.36 were found constructing an almost periodic array of nanowires. The nanowires were grown endotaxially in the matrix, i.e. the corresponding cubic axes of the two structures are almost perfectly parallel one to the other, with deviations smaller than 1°. Moreover the interfaces between the matrix and the precipitates are very well defined crystallographic planes, mainly parallel to {111}. These features of the nanowires allow them to be considered as a self-organized nanostructure.

R. Biswas; S. Mukhopadhyay; C. Sinha

Abstract The effects of the external homogeneous electric field on the transmission coefficient and the ballistic conductance are studied theoretically for an electron across a graphene double barrier structure. The Klein transmission is noted for the normal to near normal incidence only. The electrons are found to be confined... [view more]

Abstract

The effects of the external homogeneous electric field on the transmission coefficient and the ballistic conductance are studied theoretically for an electron across a graphene double barrier structure. The Klein transmission is noted for the normal to near normal incidence only. The electrons are found to be confined by the external static electric field for the glancing incidence and not for the normal incidence. Although the conductance profile for the lower barrier widths is almost sinusoidal in nature, some interesting features occur for the higher barrier width of the structure. The oscillations in the below barrier conductance are greatly suppressed by the external field. Some negative differential conducting regions are also noted, being quite sensitive to the Fermi energy of the system.

Majid Vaezzadeh;