Diffusive Transport in Quasi-2D and Quasi-1D Electron Systems

Quantum-confined semiconductor structures are the cornerstone of modern-day electronics. Spatial confinement in these structures leads to formation of discrete low-dimensional subbands. At room temperature, carriers transfer among different states due to efficient scattering with phonons, charged impurities, surface roughness and other electrons, so transport is scattering-limited (diffusive) and well described by the Boltzmann transport equation. In this review, we present the theoretical framework used for the description and simulation of diffusive electron transport in quasi-two-dimensional and quasi-one-dimensional semiconductor structures. Transport in silicon MOSFETs and nanowires is presented in detail.Comment: Review article, to appear in Journal of Computational and Theoretical Nanoscienc

Electron mobility in silicon nanowires

The low-field electron mobility in rectangular silicon nanowire (SiNW) transistors was computed using a self-consistent Poisson-Schr\"{o}dinger-Monte Carlo solver. The behavior of the phonon-limited and surface-roughness-limited components of the mobility was investigated by decreasing the wire width from 30 nm to 8 nm, the width range capturing a crossover between two-dimensional (2D) and one-dimensional (1D) electron transport. The phonon-limited mobility, which characterizes transport at low and moderate transverse fields, is found to decrease with decreasing wire width due to an increase in the electron-phonon wavefunction overlap. In contrast, the mobility at very high transverse fields, which is limited by surface roughness scattering, increases with decreasing wire width due to volume inversion. The importance of acoustic phonon confinement is also discussed briefly

Shift of the 21+^+_1 state of 10^{10}Be in the ternary cold fission of 252^{252}Cf

Recent experimental data indicate that in the ternary cold fission of $^{252}$Cf the energy of the first excited state of the accompanying light cluster $^{10}$Be is decreased by an amount ranging between $\approx$ 6 and 26 keV. A model is proposed to calculate the shift of the vibrational 2$^+_1$ state in $^{10}$Be when its heavy companions are the even-even nuclei $^{146}$Ba and $^{96}$Sr. The stiffness parameters of the $\beta$-vibrations are calculated within the self-consistent Hartree-Fock method with BCS pairing correlations taken into account, and its change is determined by the interaction of the light cluster with the heavy fragments. The results are pointing to a dependence of the shift magnitude and signature on the relative distance between the three clusters and their mutual orientation. Eventually it is the anharmonic perturbation of the spherical vibrator which is responsible for obtaining a negative energy shift of the 2$^+_1$ state.Comment: 4 pages, 3 figure

Job Mix Formulation for Bituminous Concrete Grade II Using C# Programming

Bituminous Concrete mix design is a complex process and different methods are proposed by a number of researchers. Marshall’s method of mix design is one such process, which became very popular among the practitioners in India and elsewhere. SUPERPAVE method of mix design which takes into account climatic and traffic factors for aggregate and binder selection. It has gained its prominence and is observed to be superior to any other well-known mix design processes. Aggregate gradation adopted for the mix design plays a crucial role in the performance of the mix. Many researchers have developed mechanisms to work out Job Mix Formulations (JMF) so as to reach the appropriate aggregate mix in the field.The analytical phase of JMF deals with the method of blending of aggregates from the identified stockpiles in order to fulfill the requirements of gradation as specified by agencies for a given layer of flexible pavements. Methods proposed for aggregate blending includes the graphical methods, trial and error method and optimization techniques. The aim of these techniques is two-fold; the first is to optimize the cost involved in blending from the known unit cost of individual stockpiles; and the other is to fulfill the gradation recommendations of the local agencies and parameters suggested in other methods. In this research, an attempt has been made to develop C# (C-Sharp) application in .NET framework using the sequential search technique to work out the best blend of aggregate particles by ensuring the requirements mentioned in MoRTH’s (Ministry of Road Transport & Highways, India) recommended practice. Bailey’s method and the maximum density line have been recommended in 0.45 power chart and incorporating optimization criteria. Grade II bituminous concrete has been chosen for the research. It was clearly observed that the fine aggregate fraction in the stockpiles influences the final Job Mix Formulation. The devleloped tool can accommodate up to 5 stockpiles. It was also observed that the Bailey’s requirements are more stringent when compared with MoRTH requirements as far as JMF is considered. The developed tool is capable of generating the blends with Recycled Asphalt Pavement (RAP) aggregate blends

Ternary configuration in the framework of inverse mean-field method

A static scission configuration in cold ternary fission has been considered in the framework of mean field approach. The inverse scattering method is applied to solve single-particle Schroedinger equation, instead of constrained selfconsistent Hartree-Fock equations. It is shown, that it is possible to simulate one-dimensional three-center system via inverse scattering method in the approximation of reflectless single-particle potentials.Comment: 8 pages, 1 figure, iopart.cls, to be published in Int.J.Mod.Phys.

On Landauer vs. Boltzmann and Full Band vs. Effective Mass Evaluation of Thermoelectric Transport Coefficients

The Landauer approach to diffusive transport is mathematically related to the solution of the Boltzmann transport equation, and expressions for the thermoelectric parameters in both formalisms are presented. Quantum mechanical and semiclassical techniques to obtain from a full description of the bandstructure, E(k), the number of conducting channels in the Landauer approach or the transport distribution in the Boltzmann solution are developed and compared. Thermoelectric transport coefficients are evaluated from an atomistic level, full band description of a crystal. Several example calculations for representative bulk materials are presented, and the full band results are related to the more common effective mass formalism. Finally, given a full E(k) for a crystal, a procedure to extract an accurate, effective mass level description is presented.Comment: 33 pages, 8 figure

Kolektivne i jednočestične strukture u jezgrama bogatim neutronima

The neutron-rich nuclei of 104,106Mo, 139,141Ba, 139Xe, 115,117Ag and 133,135Te have been studied by using the spontaneous fission source of 252Cf with the Gammasphere array. In the present work, the collective and single particle structures in these neutron-rich nuclei have been reported. Gamma type vibrational bands in 104,106Mo, particle and hole states, including candidates for tilted rotor bands in 133,135Te and a 7/2[413] rotational band in both 115,117Ag have been observed. The N = 83 135Te and 139Ba show marked differences associated with differences in their particle and hole states. New levels in 141Ba and 139Xe extend evidence for two opposite parity doublets characteristic of stable octupole deformation.Proučavali smo neutronima bogate jezgre 104,106Mo, 139,141Ba, 139Xe, 115,117Ag i 133,135Te pomoću izvora spontane fisije 252Cf, primjenom uređaja Gammasphere. Prikazujemo njihove kolektivne i jednočestične strukture. Opazili smo γ-vibracijske vrpce u 104,106Mo, čestična i šupljinska stanja, uključivši kandidate za nagnutu rotorsku vrpcu u 133,135Te i rotacijsku vrpcu 7/2[413] u 115,117Ag. Jezgre 135Te i 139Ba s N = 83 su izrazito različite zbog razlika u njihovim čestičnim i šupljinskim stanjima. Novi nivoi jezgara 141Ba i 139Xe daju dodatni dokaz za postojanje dvaju dubleta suprotne parnosti koji su karakteristični za stabilnu oktupolnu deformaciju