On the carrier contribution to the elastic constants in ultrathin films of bismuth under quantizing magnetic field

We present a simple analysis of the carrier contribution to the elastic constants in ultrathin films of Bi under magnetic quantization in accordance with McClure-Choi, Cohen, Abrikosov, Lax and parabolic ellipsoidal band models in the presence of spin, broadening and temperature respectively. It appears that the said contribution increases with increasing electron concentration and decreasing film thickness in various manners. The McClure and Choi model shows this more significantly than other models. We have also suggested an experimental method of determining the said contribution in degenerate materials having arbitrary dispersion laws.     

Theoretical analysis of the effective electron mass in ultrathin films of ternary chalcopyrite semiconductors in the presence of crossed electric and magnetic fields

An attempt is made to investigate theoretically the effective electron mass in ultrathin films of ternary chalcopyrate semiconductors in the presence of crossed electric and magnetic fields on the basis of a newly derivedE-k dispersion relation of the conduction electrons, which includes various types of anisotropies in the energy spectrum. It is found, takingn-CdGeAs₂ as an example, that the effective electron mass at the Fermi level depends on the Fermi energy and the magnetic and size quantum numbers, respectively, which is a characteristic feature of cross-fields. It is also observed that the crystal field parameter effectively enhances the numerical magnitude of the effective Fermi level mass. The corresponding results for isotropic parabolic energy bands are also obtained from the expressions derived.     

Epitaxial growth of thin films of V2VI3 semiconductors

Epitaxial growth conditions of V₂VI₃ semiconductors have been studied using the molecular beam epitaxy technique, which was applied to the growth of Sb₂Te₃ on Bi₂Te₃ substrates. These substrates were prepared by gradient freeze method in a Bridgman apparatus. Ingots were cleaved along the (0001) plane. The deposition conditions have been studied as a function of two parameters: substrate temperature and flux ratios of the two elements. The quality of these epilayers was controlled by SEM and X-ray diffraction. Epilayers of good quality have been obtained for the first time.     

Effect of level broadening on the photoelectric emission from a single quantum well in ultrathin film under the influence of a quantizing magnetic field

The photoelectric emission from a quasi-two-dimensional electron gas (Q2DEG) in a single quantum well (SQW) formed in wide-gap semiconductor films has been theoretically investigated, under magnetic quantization incorporating Landau level broadening arising due to electron impurity scattering. The photoelectric current density has been computed for a Q2DEG formed in n-type GaAs film and is found to be modified in the presence of level broadening. The photoemission from a quasi-zero-dimensional electron gas (QODEG) formed in the ultrathin film under the influence of a quantizing magnetic field applied normal to the film has also been compared with that for the QODEG formed in a quantum box.     

On the diffusivity-mobility ratio in ultrathin films of bismuth in the presence of crossed electric and magnetic fields

The Einstein relation is studied for the diffusivity-mobility ratio of the carriers in ultrathin films of bismuth in the presence of crossed electric and magnetic fields at very low temperatures, and the numerical results are presented for McClure and Choi, hybrid, Cohen, Lax, and ellipsoidal parabolic energy bands by formulating the respective modified carrier energy spectra. It is found that this ratio increases with decreasing film thickness, increasing electron concentration, and decreasing magnetic field. The quantum oscillations of the ratio show up much more significantly in the McClure than in the other models.     

A simple analysis of the Einstein relation in quantum confined non-parabolic semiconductors in the presence of a parallel magnetic field

An attempt is made to study the Einstein relation for the diffusivity-mobility ratio of the carriers in quantum confined non-parabolic semiconductors in the presence of a parallel magnetic field at low temperatures on the basis of new electron dispersion laws of quantum wells (QWs) and quantum wells wires (QWWs) of such materials. It is found, taking QW and QWWs of Hg_1–xCd_xTe and In_1–xGa_xAs_yP_1–y lattice-matched to InP as examples, that the diffusivity-mobility ratio increases with increasing electron concentration, decreasing alloy composition and decreasing film thickness in various oscillatory manners in both the cases. The magnetic field and the quantum wire structure enhance the numerical values of the same ratio. We have suggested an experimental method of determining the Einstein relation in degenerate materials having arbitrary dispersion laws. In addition, the corresponding well-known results of relatively wide-gap quantum confined materials in the absence of the magnetic field have been obtained as special cases of our generalized formulations, under certain limiting conditions.     

Influence of non-axial magnetic field in a 3D3V Particle-In-Cell plasma model

In this article we report on results obtained using a newly developed self-consistent fully 3D Particle-In-Cell code for modelling of plasma-solid interaction.The model presented here involves a hollow cylindrical chamber opened to the plasma, with a thin cylindrical guard at the inlet and a strong external magnetic field limiting access of charged particles to the cylindrical wall. This model layout might provide more insight into processes taking place during magnetron deposition of thin films onto porous media. It is also a basis for probe diagnostics in fusion plasma research.The magnetic field is either parallel or slightly inclined with respect to the cylindrical axis. The results presented are axial and azimuthal ion current densities and cumulative distribution functions of ions impinging on the cylindrical surface for several angles of magnetic field inclination. They confirm the importance of proper alignment with magnetic field in certain geometries.Efficiency and possibilities of further extensions to the 3D model are also briefly discussed.     

Liquid-gated ambipolar transport in ultrathin films of a topological insulator Bi2Te3

Using ionic-liquid (IL) gating in electric-double-layer transistors (EDLTs), we investigate field-effect electrical transport properties of ultrathin epitaxial films of a topological insulator (TI), Bi(2)Te(3). Because of their extreme thinness, the Bi(2)Te(3) films show a band gap opening and resulting semiconducting transport properties. Near room temperature, an obvious ambipolar transistor operation with an ON-OFF ratio close to 10(3) was observed in the transfer characteristics of liquid-gated EDLTs and further confirmed by a sign change of the Hall coefficients. Modulation of the electronic states and a phase transition from a semiconducting conduction (dR(xx)/dT < 0) to a metallic transport (dR(xx)/dT > 0) were observed in the temperature-dependent resistance of the ultrathin Bi(2)Te(3) channel, demonstrating that the liquid gating is an effective way to modulate the electronic states of TIs.     

Magnetoresistance effect of bismuth in a quantizing field

The magnetoresistance effect in bismuth has been studied at the very low temperature limit when the lattice scattering is dominant in solids. Results show that the magnetoresistance oscillates with the dc magnetic field and displays sharp, cusplike discontinuities due to the nonlinear and singular properties of the energy band structure of bismuth for the modified nonellipsoidal, nonparabolic (MNENP) model.     

Thermal convection in the presence of a vertical magnetic field

Summary The interaction between thermal convection and an external uniform magnetic field in the vertical is numerically simulated within a computational domain of a horizontally periodic convective box between upper and lower rigid plates. The numerical technique is based on a spectral element method developed earlier to simulate natural thermal convection. In this work, it is extended to a magnetoconvection problem. Its main features are the use of rescaled Legendre-Lagrangian polynomial interpolants in expanding the flow variables except the pressure for which a modal expansion in terms of lower order polynomials is used to avoid the complicated staggered grid approach. The technique is validated in the steady roll and oscillatory convective regimes where various experimental and numerical results are available in the literature. The effect of a vertical magnetic field in such a way to inhibit the convective motions has been demonstrated.     

Atomically smooth ultrathin films of topological insulator Sb2Te3

The growth and characterization of single-crystalline thin films of topological insulators (TIs) is an important step towards their possible applications. Using in situ scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES), we show that moderately thick Sb₂Te₃ films grown layer-by-layer by molecular beam epitaxy (MBE) on Si(111) are atomically smooth, single-crystalline, and intrinsically insulating. Furthermore, these films were found to exhibit a robust TI electronic structure with their Fermi energy lying within the energy gap of the bulk that intersects only the Dirac cone of the surface states. Depositing Cs in situ moves the Fermi energy of the Sb₂Te₃ films without changing the electronic band structure, as predicted by theory. We found that the TI behavior is preserved in Sb2Te3 films down to five quintuple layers (QLs).      

Gap parameters and collective modes for 3He-B in the presence of a strong magnetic field

First we determine the 4 × 4 matrix Green's function for a p-wave pairing superfluid in a magnetic field where the order parameter is given by a real 3 × 3 matrix. For the B phase we take an order parameter which is equal to ₁ times a 3 × 3 matrix, yielding a rotation of angle about the z-axis and a dilatation ₂/₁ along the z-axis. Then the self-consistency equation for the 4 × 4 matrix self-energy reduces to three equations for ₁, ₂, and cos , and a fourth equation for the renormalized Larmor frequency. We find that, for increasing field, ₁ increases and ₂ decreases with respect to the zero-field gap _00. Above a (temperature-dependent) critical field we find ₂ = 0 and ₂ = 90° corresponding to the planar state of lowest dipole energy. The correlation functions for the order parameter collective modes are calculated with the help of a previous theory. The results can be expressed in terms of six universal functions describing internal magnetization and virtual excitations of pairs of quasiparticles with all spin orientations. The complete set of eigenfrequencies as functions of the field is calculated for T = 0 and q = 0. The longitudinal NMR frequency is found to be almost independent of the field. We find a splitting of the pair-vibration frequencies (8/5) ^1/2₀₀ and (12/5)^1/2₀₀ which is linear in the field. This splitting is caused by fluctuations involving the spin-singlet component of the anomalous propagator. The splitting of the pair-vibration frequency (12/5)^1/2₀₀ (of the order 6H MHz, H in kG) should be observable by sound absorption experiments in strong magnetic fields.     

Polaritons in hollow cylinders in the presence of a dc magnetic field

We study the effects of a dc external magnetic field on the polaritons propagating in hollow dielectric cylinders, taking into account the retardation effects. In solving Maxwell's equations we show that only the TM modes can propagate in these systems, and we obtain the dispersion relation of the confined-surface-polariton modes. The effects of geometric parameters and the external magnetic field on the propagation of surface-polariton modes are also analyzed and show significant influence on the behavior of the modes. Numerical results are presented for the dispersion relation of surface polaritons with GaAs as the optically active medium.     

X-ray photoelectron spectroscopic studies of evaporated V2O2and co-evaporated V2O5/B2O3 films

X-ray photoelectron spectra of evaporated V₂O₅ and co-evaporated V₂O₅/B₂O₃ thin films have been investigated. The photoelectron spectrum of a simple V₂O₅ film shows the splitting of the V 2p level in accordance with the spins. The values of binding energies corresponding to V 2p and O1s are comparable with those reported previously. For co-evaporated V₂O₅/B₂O₃ films a chemical shift in the O 1s level has been observed which has been attributed to the changed chemical environment of oxygen as a result of the presence of boron and vanadium atoms. The values of binding energies for V 2p_3/2 and O 1s corresponding to simple evaporated V₂O₅ and co-evaporated V₂O₅/B₂O₃ show the presence of V₂O₄ species in the films.     

A magnetic field sensor based on the mechanoelectric effect in semiconductors

A highly sensitive magnetic field transducer based on the mechanoelectric effect in semiconductors is proposed.     

Catalysis on oriented ultrathin films of platinum on Al2O3

The selectivity of the hydrogenolysis of methylcyclopentane on model thin film catalysts was investigated and the morphology of the particles was checked in parallel by transmission electron microscopy and transmission electron diffraction. The catalysts were island-stage platinum films of defined orientation obtained by evaporating platinum onto (100)- and (111)-oriented NaCl substrates, backing with Al₂O₃ and dissolving the substrate.The catalysts were quite inactive as long as the single-crystal surface was unchanged, and any increase in activity was accompanied by a change in morphology. The results are compared with those obtained on non-oriented films as well as on bulk single-crystal surfaces.     

Optical absorption spectra of evaporated V2O5 and co-evaporated V2O5/B2O3 thin films

The optical absorption spectra of evaporated V₂O₅ and co-evaporated V₂O₅/B₂O₃ thin films have been studied. For higher photon energies, the absorption is found to be due to a direct forbidden electronic transition process from the oxygen 2p band to the vanadium 3d band in a similar way to that observed in crystalline V₂O₅. The exponential behaviour of absorption edge for lower photon energies is attributed to the electronic transitions between the tailed-off d-d states corresponding to V⁴⁺ ions. For co-evaporated V₂O₅/B₂O₃ films the optical energy gap is observed to increase with the increase in V₂O₅ content of the composite films.     

Infrared absorption spectra of evaporated V2O5 and co-evaporated V2O5/B2O3 thin films

The Fourier transform infrared spectra of different compositions of evaporated V₂O₅/B₂O₃ thin films have been investigated. Most of the absorption bands corresponding to V₂O₅ and B₂O₃ films coincide with those reported by other authors. The short-range order in amorphous V₂O₅ films is found to be conserved. The absorption spectra indicate a boroxol ring structure for B₂O₃ films. In co-evaporated V₂O₅/B₂O₃ films the boron is observed to substitute in the V₂O₅ network such that the coordination number of vanadium ion remains unchanged. The presence of a number of bands corresponding to -OH groups indicates the hygroscopic character of the films.