Zhang Jinyu

Solution of the time-dependent Schrödinger equation with absorbing boundary conditions

The performances of absorbing boundary conditions (ABCs) in four widely used finite difference time domain (FDTD) methods, i.e. explicit, implicit, explicit staggered-time, and Chebyshev methods, for solving the time-dependent Schrodinger equation are assessed and compared. The computation efficiency for each approach is also evaluated. A typical evolution problem of a single Gaussian wave packet is chosen to demonstrate the performances of the four methods combined with ABCs. It is found that ABCs perfectly eliminate reflection in implicit and explicit staggered-time methods. However, small reflection still exists in explicit and Chebyshev methods even though ABCs are applied.

Schottky Barrier Formation at a Carbon Nanotube–Scandium Junction

Recent experiment shows that scandium (Sc) can make a good performance contact with carbon nanotubes (CNTs) to fabricate n-type field effect transistor (n-FET). We study the Schottky barrier (SB) of scandium (Sc) and palladium (Pd) with a (8,0) single-wall CNT (SWCNT) using first-principles calculation. It is found that the p-type SB height (SBH) of the Pd–CNT contact is about 0.34 eV, which is in good agreement with the experimental data. For the Sc-CNT contact, an n-type contact is formed and the SBH is about 0.08 eV in agreement with the experimental observations. Our calculation demonstrates that by contacting CNT with Pd and Sc, p-FET and n-FET can be fabricated, respectively. The dipole effect at the interface is used to explain our result.

THE F-SPIN FORMALISM OF THE NEUTRON-PROTON INTERACTING BOSON MODEL

The neutron-proton interacting boson model is presented in the F-spin formalism. Hamiltonian and transition operators are rewritten in the F-spin formalism based on group chain U(12) superset of U(6) x SUF(2). Matrix elements are given explicitly in terms of the cfps with F-spin. Different forms of Hamiltonian in IBM-2 are compared, and their relations are given.

Numerical Analysis of Alternating-Current Small-Signal Response in Graphene Nanoribbons

Alternating-current small-signal admittances of armchair graphene nanoribbons are investigated using the method of non-equilibrium Greens function. The calculated ac admittances show an oscillatory response between inductive and capacitive behaviors, which is a result of the finite length of the graphene nanoribbon. The effects of hydrogen-passivated edges on ac response are demonstrated. At low frequency, the edge effects transform the inductive behavior in a metallic graphene nanoribbon into a capacitive one. Finally, the effects of variations in the width and bandgap of a graphene nanoribbon on its dynamic response are investigated.

The Structure of the Neutron-Rich Nd Isotopes in the IBM*

The spectra and E2 transition properties of Nd146-156 isotopes are studied in the interacting boson model in the light of new experimental data. It is found that Nd146-150 are in the transition from the vibrational limit to the rotational limit. From Nd-152 onward, the isotopes are nearly perfect rotors. Possible deformation saturation is discussed in the interacting boson model.

Description of the Structure of 88-96Sr in the IBM*

The neutron-rich even-even Sr isotopes are studied in the interacting boson model. The semi-closed nucleus 88Sr is studied in the framework of the IBM1, and 90-96Sr are studied in the neutron-proton interacting boson model. The spectrum and E2, M1 transition properties are calculated and compared with experiment.

Simulation and Experimental Validation of the Effect of Surface Texture on Fluid Film Formation

A surface texturing process with the photolithography and wet etching methods was established. By optimizing the process parameters, surface textures with regular dimples on steel plates were obtained. The textured steel plates were tested on Falex friction test machine against lapped smooth brass plates under different loads. Test results of friction coefficient have shown that both of the dimple dimension and distribution patterns influence the friction characteristics remarkably, and some of the tested textures result in lower friction than the non-textured samples. In order to reveal the mechanism of surface texturing and to reduce the cost of experiments, a numerical simulation program which can deal with mixed lubrication analysis has been developed, based on the Patir & Cheng’s average flow model the Kogut & Etsion’s friction model. The tendency of the simulation results of friction coefficient is consistent with the experimental one for some typical load cases. Therefore, the design and optimazation of surface texture in tribological applications can be assisted by numerical simulation of mixed lubricantion.

Derivative of Electron Density in Non-Equilibrium Green's Function Technique and Its Application to Boost Performance of Convergence

The non-equilibrium Greens function (NEGF) technique provides a solid foundation for the development of quantum mechanical simulators. However, the convergence is always of great concern. We present a general analytical formalism to acquire the accurate derivative of electron density with respect to electrical potential in the framework of NEGF. This formalism not only provides physical insight on non-local quantum phenomena in device simulation, but also can be used to set up a new scheme in solving the Poisson equation to boost the performance of convergence when the NEGF and Poisson equations are solved self-consistently. This method is illustrated by a simple one-dimensional example of an N++ N+ N++ resistor. The total simulation time and iteration number are largely reduced.

Time-Dependent Transport in Nanoscale Devices

A method for simulating ballistic time-dependent device transport, which solves the time-dependent Schrodinger equation using the finite difference time domain (FDTD) method together with Poissons equation, is described in detail. The effective mass Schrodinger equation is solved. The continuous energy spectrum of the system is discretized using adaptive mesh, resulting in energy levels that sample the density-of-states. By calculating time evolution of wavefunctions at sampled energies, time-dependent transport characteristics such as current and charge density distributions are obtained. Simulation results in a nanowire and a coaxially gated carbon nanotube field-effect transistor (CNTFET) are presented. Transient effects, e.g., finite rising time, are investigated in these devices.

Mixing of Pseudo-Goldstone Bosons and Effects on HERA High-Q2 Events*

We study the mixing of pseudo-Goldstone bosons predicted by technicolor theory and the effects on HERA high-Q2 events. We find that: (a) there exist two scalar leptoquarks with and with for ; (b) the and can contribute the required cross section to account for the excesses of NC and CC high-Q2 events; (c) the coexistence of and may be responsible for the splitting of averaged mass of the H1 and ZEUS high-Q2 neutral current events.