D. Schmeißer; K. Henkel; M. Bergholz; M. Tallarida

Abstract In ultrathin high- k oxide layers knowledge of the band line up and band gap is essential for modeling the transport properties and to learn about a device’s long term stability and reliability. However, such data are hard to determine in such ultrathin layers and usually ... [view more]

Abstract

In ultrathin high- k () oxide layers knowledge of the band line up and band gap is essential for modeling the transport properties and to learn about a device’s long term stability and reliability. However, such data are hard to determine in such ultrathin layers and usually are extrapolated from values for bulk samples or are taken from the literature. In our in situ approach we use electron energy loss spectroscopy, valence band photoelectron spectroscopy, X-ray absorption spectroscopy, and resonant inelastic X-ray scattering to obtain the loss function and the valence and conduction band densities of states. From such data we derive the values of the band offsets and of the band gap. We discuss the ability of this combination of different techniques for the analysis of such complex ultrathin dielectric systems and discuss in detail the properties of the native oxide in SiO₂/Si(001) and SiO₂/3C−SiC(001).

D. De; A. Kumar; S.M. Adhikari; S. Pahari; N. Islam; P. Banerjee; S.K. Biswas; S. Bhattacharya; K.P. Ghatak

Abstract We study the photoemission from quantum wire and quantum dot superlattices with graded interfaces of optoelectronic materials on the basis of newly formulated electron dispersion relations in the presence of external photo-excitation. Besides, the influence of a magnetic field on the photoemission from the aforementioned superlattices together... [view more]

Abstract

We study the photoemission from quantum wire and quantum dot superlattices with graded interfaces of optoelectronic materials on the basis of newly formulated electron dispersion relations in the presence of external photo-excitation. Besides, the influence of a magnetic field on the photoemission from the aforementioned superlattices together with quantum well superlattices in the presence of a quantizing magnetic field has also been studied in this context. It has been observed taking into account HgTe/Hg_1−x Cd _x Te and In _x Ga_1−x As/InP that the photoemission from these nanostructures increases with increasing photon energy in quantized steps and exhibits oscillatory dependences with the increase in carrier concentration. Besides, the photoemission decreases with increasing light intensity and wavelength, together with the fact that said emission decreases with increasing thickness exhibiting oscillatory spikes. The strong dependences of the photoemission on the light intensity reflects the direct signature of light waves on the carrier energy spectra. The content of this paper finds six applications in the fields of low dimensional systems in general.

Sh. Sohrabnezhad; A. Pourahmad; R. Rakhshaee; A. Radaee; S. Heidarian

Abstract This article reports the reduction of methylene blue (MB) by sulfide ions (S2−) in aqueous solution by a nanoAlMCM-41 catalyst. The results obtained showed that, under acidic conditions (pH=2) MB was reduced to the Leuco methylene blue (LMB) form by sulfide ... [view more]

Abstract

This article reports the reduction of methylene blue (MB) by sulfide ions (S²⁻) in aqueous solution by a nanoAlMCM-41 catalyst. The results obtained showed that, under acidic conditions (pH=2) MB was reduced to the Leuco methylene blue (LMB) form by sulfide ions and by changing the pH between 2.0 and 7.0 a reduction of the MB dye to the MBH₂ ⁺ form was observed. In alkaline media (pH=8), a reduction of methylene blue by sulfide ions to the MBH₂ ⁺ form and demethylation of the dye was observed simultaneously. The demethylation of MB leads to a thionine dye product. Using nanoAlMCM-41 but with encapsulated CoS nanoparticles only causes demethylation of MB in aqueous solution.

R. Khordad

Abstract The influence of temperature and pressure, simultaneously, on the binding energy of a hydrogenic donor impurity in a ridge GaAs/Ga1−x Al x As quantum wire is studied using a variational procedure within the effective mass approximation. The subband energy and the binding energy of the ... [view more]

Abstract

The influence of temperature and pressure, simultaneously, on the binding energy of a hydrogenic donor impurity in a ridge GaAs/Ga_1−x Al _x As quantum wire is studied using a variational procedure within the effective mass approximation. The subband energy and the binding energy of the donor impurity in its ground state as a function of the wire bend width and impurity location at different temperatures and pressures are calculated. The results show that, when the temperature increases, the donor binding energy decreases for a constant applied pressure for all wire bend widths. Also, the binding energy increases by increasing the pressure for a constant temperature for all wire bend widths. In addition, when the temperature and pressure are applied simultaneously the binding energy decreases as the quantum wire bend width increases. On the whole, it is deduced that the temperature and pressure have important effects on the donor binding energy in a V-groove quantum wire.

Qian Zhao; Yanhui Li; Xuping Zhou; Tingshun Jiang; Changsheng Li; Hengbo Yin

Abstract Ordered hexagonal arrangement MCM-41 mesoporous molecular sieves were synthesized by the traditional hydrothermal method, and Fe-loaded MCM-41 mesoporous molecular sieves (Fe/MCM-41) were prepared by the wet impregnation method. Their mesoporous structures were testified by X-ray diffraction (XRD) and the N2... [view more]

Abstract

Ordered hexagonal arrangement MCM-41 mesoporous molecular sieves were synthesized by the traditional hydrothermal method, and Fe-loaded MCM-41 mesoporous molecular sieves (Fe/MCM-41) were prepared by the wet impregnation method. Their mesoporous structures were testified by X-ray diffraction (XRD) and the N₂ physical adsorption technique. Carbon nanotubes (CNTs) were synthesized by the chemical vapor deposition (CVD) method via the pyrolysis of ethanol at atmospheric pressure using Fe/MCM-41 as a catalytic template. The effect of different reaction temperatures ranging from 600 to 800 ^∘C on the formation of CNTs was investigated. The resulting carbon materials were characterized by various physicochemical techniques such as transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and Raman spectroscopy. The results show that multi-wall carbon nanotubes (MWCNTs) with an internal diameter of ca. 7.7 nm and an external diameter of ca. 16.9 nm were successfully obtained by the pyrolysis of ethanol at 800 ^∘C utilizing Fe/MCM-41 as a catalytic template.

A. John Peter

Abstract The binding energy of laser dressed donor impurity is calculated under the influence of a magnetic field in a quantum well. The binding energy of the ground state of a donor is investigated, within the single band effective mass approximation, variationally for different concentrations at the well ... [view more]

Abstract

The binding energy of laser dressed donor impurity is calculated under the influence of a magnetic field in a quantum well. The binding energy of the ground state of a donor is investigated, within the single band effective mass approximation, variationally for different concentrations at the well centre. The effect of laser and magnetic fields on diamagnetic susceptibility of the hydrogenic donor is reported. The Landau energy levels of electrons in the quantum well as a function of magnetic field are reported. The results show that the diamagnetic susceptibility (i) decreases drastically as intensity of the laser field increases (ii) increases with the magnetic field strength (iii) decreases as the Al-concentration decreases and (iv) a variation of increase in binding energy is observed when non-parabolicity is included and this effect is predominant for narrow wells. Our results are in good agreement with previous investigations for other heterostructures in the presence of laser intensity.

Feng Chi; Huailing Zhao

Abstract We study the splitting of the Fano resonance in a Aharonov–Bohm interferometer with a quantum dot in each of its arms. Both intra- and inter-dot Coulomb repulsions are taken into account by employing the Keldysh nonequilibrium Green’s function technique. The single narrow Fano resonance ... [view more]

Abstract

We study the splitting of the Fano resonance in a Aharonov–Bohm interferometer with a quantum dot in each of its arms. Both intra- and inter-dot Coulomb repulsions are taken into account by employing the Keldysh nonequilibrium Green’s function technique. The single narrow Fano resonance in the noninteracting case is split into two in the presence of either intra- or inter-dot Coulomb interaction. We find that four Fano peaks emerge in the conductance or local density of states spectra when the two kinds of interactions exist simultaneously. Such behavior holds true for the accompanying broad Breit–Wigner type resonance. We also show that the positions of the Fano peaks can be tuned with the aid of the magnetic flux penetrating through the ring, which might have practical applications in device design or quantum computation.

M.A. Grado-Caffaro; M. Grado-Caffaro

Abstract A new theory for determining the quantized electron conductance through multi-atom nanowires is presented by introducing a transmission-probability function from the Fermi–Dirac distribution. By virtue of this formulation and by using an approximate relationship between the conductance and the electronic density of states, an expression... [view more]

Abstract

A new theory for determining the quantized electron conductance through multi-atom nanowires is presented by introducing a transmission-probability function from the Fermi–Dirac distribution. By virtue of this formulation and by using an approximate relationship between the conductance and the electronic density of states, an expression for the number of off-resonant conduction states is derived. In addition, some aspects related to atom–lead coupling are discussed. Our results agree well with experimental data.

Alexander Khitun; Mingqiang Bao; Kang L. Wang

Abstract We describe and analyze a cellular nonlinear network based on magnetic nanostructures for image processing. The network consists of magneto-electric cells integrated onto a common ferromagnetic film–spin wave bus. The magneto-electric cell is an artificial two-phase multiferroic structure comprising piezoelectric and ferromagnetic materials. ... [view more]

Abstract

We describe and analyze a cellular nonlinear network based on magnetic nanostructures for image processing. The network consists of magneto-electric cells integrated onto a common ferromagnetic film–spin wave bus. The magneto-electric cell is an artificial two-phase multiferroic structure comprising piezoelectric and ferromagnetic materials. A bit of information is assigned to the cell’s magnetic polarization, which can be controlled by the applied voltage. The information exchange among the cells is via the spin waves propagating in the spin wave bus. Each cell changes its state as a combined effect: magneto-electric coupling and the interaction with the spin waves. The distinct feature of a network with a spin wave bus is the ability to control the inter-cell communication by an external global parameter — magnetic field. The latter makes it possible to realize different image processing functions on the same template without rewiring or reconfiguration. We present the results of numerical simulations illustrating image filtering, erosion, dilation, horizontal and vertical line detection, inversion and edge detection accomplished on one template by the proper choice of the strength and direction of the external magnetic field. We also present numerical assets on the major network parameters such as cell density, power dissipation and functional throughput, and compare them with the parameters projected for other nano-architectures such as CMOL-CrossNet, Quantum-Dot Cellular Automata, and Quantum Dot-Image Processor. Potentially, the utilization of spin wave phenomena at the nanometer scale may provide a route to low-power consumption and functional logic circuits for special task data processing.

G. Polupan; A. Vivas Hernandez; Ye.S. Shcherbyna

Abstract The photoluminescence (PL) inhomogeneity has been studied in InAs quantum dots (QDs) embedded in the symmetric In0.15Ga0.85As/GaAs quantum wells (QWs) with QDs grown at different temperatures. It was shown that three reasons are responsible for the emission inhomogeneity in studied QD structures:... [view more]

Abstract

The photoluminescence (PL) inhomogeneity has been studied in InAs quantum dots (QDs) embedded in the symmetric In_0.15Ga_0.85As/GaAs quantum wells (QWs) with QDs grown at different temperatures. It was shown that three reasons are responsible for the emission inhomogeneity in studied QD structures: (i) the high concentration of nonradiative recombination centers in the capping In_0.15Ga_0.85As layer at low QD growth temperatures, (ii) the QD density and size distributions for the structure with QD grown at 510 ^∘C, (iii) the high concentration of nonradiative recombination centers in the GaAs barrier at higher QD growth temperatures.

Congxin Xia; Harold N. Spector

Abstract Within the framework of the effective mass approximation, the confined Franz–Keldysh effect is investigated theoretically in a cylindrical ZnO quantum dot (QD). Numerical results show that the application of an electric field can decrease the strength and the threshold energy of the optical absorption coefficient in... [view more]

Abstract

Within the framework of the effective mass approximation, the confined Franz–Keldysh effect is investigated theoretically in a cylindrical ZnO quantum dot (QD). Numerical results show that the application of an electric field can decrease the strength and the threshold energy of the optical absorption coefficient in ZnO QD. There are additional oscillations in the absorption above the effective band gap, which are due to the Franz–Keldysh effect which occurs in the presence of the electric field. Our results also show that the electric field has a more obviously influence on the optical absorption in cylindrical ZnO QD with larger dot height.