MeV Au ion induced modifications at Co/Si interface

We report on room temperature MeV Au ion induced modifications at the Co/Si interfaces. Nanometers size thin film of Co and Si were grown by ultra high vacuum (UHV) electron beam evaporation technique on Si(1 1 1) surface and were irradiated by 1.5 MeV Au²⁺ ions at a fluence of 5 × 10¹⁴ ions cm⁻². High-resolution transmission electron microscopy (HRTEM) along with energy filter imaging technique has been employed to study the formation of Co-Si alloy at the interface. Formation of such surface alloy has been discussed in the light of ion-matter interaction in nanometer scale regime.     

Influence of magnetic quantization on the Einstein relation in non-linear optical, optoelectronic and related materials: Simplified theory, relative comparison and suggestion for experimental determination

In this paper, we have investigated the Einstein relation for the diffusivity-to-mobility ratio (DMR) under magnetic quantization in non-linear optical materials on the basis of a newly formulated electron dispersion law by considering the crystal field constant, the anisotropies of the momentum-matrix element and the spin-orbit splitting constant, respectively, within the frame work of k·p formalism. The corresponding result for the three-band model of Kane (the conduction electrons of III-V, ternary and quaternary compounds obey this model) forms a special case of our generalized analysis. The DMR under magnetic quantization has also been investigated for II-VI (on the basis of Hopfield model), bismuth (using the models of McClure and Choi, Cohen, Lax and parabolic ellipsoidal, respectively), and stressed materials (on the basis of model of Seiler et al.) by formulating the respective electron statistics under magnetic quantization incorporating the respective energy band constants. It has been found, taking n-CdGeAs₂, n-Hg_1−xCd_xTe, p-CdS, and stressed n-InSb as examples of the aforementioned compounds, that the DMR exhibits oscillatory dependence with the inverse quantizing magnetic field due to Subhnikov de Haas (SdH) effect with different numerical values. The DMR also increases with increasing carrier degeneracy and the nature of oscillations are totally dependent on their respective band structures in various cases. The classical expression of the DMR has been obtained as a special case from the results of all the materials as considered here under certain limiting conditions, and this compatibility is the indirect test of our generalized formalism. In addition, we have suggested an experimental method of determining the DMR for degenerate materials under magnetic quantization having arbitrary dispersion laws. The three applications of our results in the presence of magneto-transport have further been suggested.     

Effect of size quantization on the effective mass in ultrathin films ofn-Cd3As2

An attempt is made to investigate the effects of size quantization on the effective mass in ultrathin films ofn-Cd₃As₂. It is found that the effective mass at the Fermi level depends on the size quantum number due to the effect of crystal-field splitting, resulting in different effective masses at the Fermi level corresponding to different electric subbands. It is also observed that the different effective masses closely approach each other, for a given film thickness, with increasing electron concentration and, for a given electron concentration, with increasing film thickness.     

Band Jahn-Teller type structural transition in La3−xS4 compounds

La-chalcogenides La₃S₄ in pure state or with small number of vacancies at La-sites undergo cubic to tetragonal structural transition which can be explained on the basis of a band Jahn-Teller model. Some characteristics of band Jahn-Teller transition associated with a two-fold degenerate band are discussed on the background of the recent experimental results on La_3?xS₄ compounds.     

Effect of size quantization on the Einstein relation in ultrathin films of non-parabolic semiconductors

An attempt is made to investigate the effect of size quantization on the diffusivity-mobility ratio of the carriers in ultrathin films of semiconductors having Kane-type nonparabolic energy bands. It is shown, takingn-type InSb as an example, that the ratio oscillates both with increasing film thickness and with increasing carrier concentration under degenerate conditions and remains unaffected otherwise. The corresponding results for parabolic semiconductors are also obtained from the expressions derived.     

Oscillatory effective mass in degenerate narrow-gap semiconductors in a quantizing magnetic field

An attempt is made to study the effect of a quantizing magnetic field on the effective electron mass in degeneraten-type narrow-gap semiconductors at low temperatures. It is found, takingn-Hg_1−x Cd _x Te as an example, that the effective electron mass shows an oscillatory magnetic-field dependence as is expected because of the dependence of the effective mass in degenerate non-parabolic bands on Fermi energy which oscillates with changing magnetic field. The amplitude of oscillations is, however, found to be significantly influenced by the alloy composition whereas the period is found to be independent of the band non-parabolicity, i.e. of the compositional parameter in ternary semiconductors.     

Perturbation theory of optical fibres with power-law core profile

The characteristics of graded-index optical fibres with power-law core profile and homogeneous cladding have been studied using perturbation theory. Analytical expressions are derived for the cut-off frequency, propagation constant and, in the case of leaky modes, the attenuation coefficient of an arbitrary mode on such a fibre. For the case of monomode fibres, excellent agreement is found with existing theoretical results for the propagation constant of the HE₁₁ mode and cut-off frequency of the TE₀₁ mode.On leave from Department of Physics, IIT, New Delhi, India.