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Articles 1 - 5 of 5
Full-Text Articles in Nanoscience and Nanotechnology
Rough Interfaces In Thz Quantum Cascade Lasers, Tillmann Kubis, Gerhard Klimeck
Rough Interfaces In Thz Quantum Cascade Lasers, Tillmann Kubis, Gerhard Klimeck
Gerhard Klimeck
The impact of interface roughness scattering on the device performance of state-of-the-art THz quantum cascade lasers is theoretically analyzed using the non-equilibrium Green’s function formalism. It is shown that for a particular direct transition QCL design style rough interfaces hardly change the electronic energy spectrum, but dramatically reduce the occupation inversion and the optical gain. A spatial separation leading to a diagonal transition laser, leads in contrast to a limited sensitivity to interface roughness. Diagonal transition QCL designs result in a better device performance and an improved reliability with respect to interface roughness induced by growth quality variations.
A Comprehensive Atomistic Analysis Of Bandstructure Velocities In Si Nanowires, Neophytos Neophytou, Hans Kosina, Gerhard Klimeck
A Comprehensive Atomistic Analysis Of Bandstructure Velocities In Si Nanowires, Neophytos Neophytou, Hans Kosina, Gerhard Klimeck
Gerhard Klimeck
A 20 band sp3d5s* spin-orbit-coupled, semi-empirical, atomistic tight-binding (TB) model is used with a semi-classical, ballistic transport model, to theoretically examine the bandstructure carrier velocity under non-degenerate conditions in silicon nanowire (NW) transistors. Infinitely long, uniform, cylindrical and rectangular NWs, of cross sectional diameters/sides ranging from 3nm to 12nm are considered. For a comprehensive analysis, n-type and p-type NWs in [100], [110] and [111] transport orientations are examined. The carrier velocities of p-type [110] and [111] NWs increase by a factor of ~2X as the NWs’ diameter scales from D=12nm down to D=3nm. The velocity of n-type [110] NWs also …
Bdf-Like Methods For Nonlinear Dynamic Analysis, S. Dong
Bdf-Like Methods For Nonlinear Dynamic Analysis, S. Dong
PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems
We present several time integration algorithms of second-order accuracy that are numerically simple and effective for nonlinear elastodynamic problems. These algorithms are based on a general four-step scheme that has a resemblance to the backward differentiation formulas. We also present an extension to the composite strategy of the Bathe method. Appropriate values for the algorithmic parameters are determined based on considerations of stability and dissipativity, and less dissipative members of each algorithm have been identified. We demonstrate the convergence characteristics of the proposed algorithms with a nonlinear dynamic problem having analytic solutions, and test these algorithms with several three-dimensional nonlinear …
Entropy Considerations In Numerical Simulations Of Non-Equilibrium Rarefied Flows, Sruti Chigullapalli, A. Venkattraman, M. S. Ivanov, Alina A. Alexeenko
Entropy Considerations In Numerical Simulations Of Non-Equilibrium Rarefied Flows, Sruti Chigullapalli, A. Venkattraman, M. S. Ivanov, Alina A. Alexeenko
PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems
Non-equilibrium rarefied flows are encountered frequently in supersonic flight at high altitudes, vacuum technology and in microscale devices. Prediction of the onset of non-equilibrium is important for accurate numerical simulation of such flows. We formulate and apply the discrete version of Boltzmann’s H-theorem for analysis of non-equilibrium onset and accuracy of numerical modeling of rarefied gas flows. The numerical modeling approach is based on the deterministic solution of kinetic model equations. The numerical solution approach comprises the discrete velocity method in the velocity space and the finite volume method in the physical space with different numerical flux schemes: the first-order, …
A Parallel Spectral Element Method For Dynamic Three-Dimensional Nonlinear Elasticity Problems, S. Dong, Z. Yosibash
A Parallel Spectral Element Method For Dynamic Three-Dimensional Nonlinear Elasticity Problems, S. Dong, Z. Yosibash
PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems
We present a high-order method employing Jacobi polynomial-based shape functions, as an alternative to the typical Legendre polynomial-based shape functions in solid mechanics, for solving dynamic three-dimensional geometrically nonlinear elasticity problems. We demonstrate that the method has an exponential convergence rate spatially and a second-order accuracy temporally for the four classes of problems of linear/geometrically nonlinear elastostatics/elastodynamics. The method is parallelized through domain decomposition and message passing interface (MPI), and is scaled to over 2000 processors with high parallel performance.