Zhao Xing-Yu

Field-ion microscopy observation of single-walled carbon nanotubes

Field-ion microscopy (FIM), a tool for surface analysis with atomic resolution, has been employed to observe the end structure of single-walled carbon nanotubes (SWCNTs). FIM images revealed the existence of open SWCNT ends. Amorphous carbon atoms were also observed to occur around SWCNTs and traditional field evaporation failed to remove them. Heat treatment was found to be efficacious in altering the end structures of SWCNT bundles. Carbon and oxygen atoms released from heated tungsten filament are believed to be responsible for the decoration imposed on the SWCNT ends.

Simulations of the flipping images and microparameters of molecular orientations in liquids according to the molecule string model

The relaxation dynamics of liquids is one of the fundamental problems in liquid physics, and it is also one of the key issues to understand the glass transition mechanism. It will undoubtedly provide enlightenment on understanding and calculating the relaxation dynamics if the molecular orientation flipping images and relevant microparameters of liquids are studied. In this paper, we first give five microparameters to describe the individual molecular string (MS) relaxation based on the dynamical Hamiltonian of the MS model, and then simulate the images of individual MS ensemble, and at the same time calculate the parameters of the equilibrium state. The results show that the main molecular orientation flipping image in liquids (including supercooled liquid) is similar to the random walk. In addition, two pairs of the parameters are equal, and one can be ignored compared with the other. This conclusion will effectively reduce the difficulties in calculating the individual MS relaxation based on the single-molecule orientation flipping rate of the general Glauber type, and the computer simulation time of interaction MS relaxation. Moreover, the conclusion is of reference significance for solving and simulating the multi-state MS model.

An extended chain Ising model and its Glauber dynamics

It was first proposed that an extended chain Ising (ECI) model contains the Ising chain model, single spin double-well potentials and a pure phonon heat bath of a specific energy exchange with the spins. The extension method is easy to apply to high dimensional cases. Then the single spin-flip probability (rate) of the ECI model is deduced based on the Boltzmann principle and general statistical principles of independent events and the model is simplified to an extended chain Glauber—Ising (ECGI) model. Moreover, the relaxation dynamics of the ECGI model were simulated by the Monte Carlo method and a comparison with the predictions of the special chain Glauber—Ising (SCGI) model was presented. It was found that the results of the two models are consistent with each other when the Ising chain length is large enough and temperature is relative low, which is the most valuable case of the model applications. These show that the ECI model will provide a firm physical base for the widely used single spin-flip rate proposed by Glauber and a possible route to obtain the single spin-flip rate of other form and even the multi-spin-flip rate.

Monte Carlo simulations of the relaxation dynamics of the spatial relaxation modes in the molecule-string model

According to the molecule-string model for glass transition, a more exact Monte Carlo protocol to simulate all the spatial relaxation modes (SRMs) of the string are proposed. The variations of the simulated relaxation times of the SRMs with temperature and string length are consistent with the predictions of the string relaxation equation of the model, i.e. the theretical predictions and the simulation results verify each other. It should be pointed out that the necessary condition of molecule string used as a collective unit in liquid is that the qualitative characteristics of the SRMs cannot be changed when the inter-string interactions are taken into account. This needs to study the coupling between the SRMs, but till now, the corresponding exact solutions have not been achieved, and only the self-consistent relaxation mean-field method is vailable. Therefore, the present simulation protocol will provide a necessary basis to study the coupling between the SRMs of neighboring strings, including the feasibility of the mean-field method.

Coherent field emission from a multi-walled carbon nanotube with two open-ended branches

Interference fringes are obtained in a field-emission microscopy (FEM) study of a multi-walled carbon nanotube (MWCNT) with two open-ended branches. The FEM pattern, which is composed of three parallel streaks, can be interpreted by using classical Youngs double-slit interference with the ends of the two MWCNT branches treated as two secondary sources of the electron wave. The origin of the coherency of the electron beams from the two branches is discussed on the basis of the quantitative analysis of the FEM pattern. The result suggests a new approach to obtaining a coherent electron source.

First-principles Calculation of the Conductance of the Al-C 60 -Al Junction

The conductance of an Al-C60-Al molecule junction is calculated using a density functional theory combined with Greens function method. When the molecule is connected to the electrodes and allowed to relax, resonant conductance is the main feature of the transport properties of the Al-C60-Al molecule junction. The conductance around the Fermi level is determined to be about 1.14G0 (G0=2e^2/h). Analysis of the density of states projected onto the frontier molecular orbitals of the C60 molecule shows that electron transport occurs primarily through the lowest unoccupied molecular orbital (LUMO) and the second lowest unoccupied molecular orbital (LUMO+1) of C60. The dependence of the junction conductance on the distance between the C60 molecule and the electrodes is also discussed.