Jicheng Zhou

Electrode metal dependence of the rectifying performance for molecular devices: A density functional study

Carrying out theoretical calculations using the nonequilibrium Green’s function method combined with the density functional theory, the transport properties of the terphenyl molecule connected to the two Y (Y=Li, Al, or Au) metal electrodes are investigated. The results show that the electrode metals have a distinct influence on rectifying performance of such devices. For the Au electrode system, we can observe a best rectifying performance, next for the Al electrode system, and the rectifying effect can be nearly neglected for the Li electrode system. Our findings suggest that the rectifying characteristics are intimately related to electrode materials.

Study on the hot deformation behaviors of Al-Zn-Mg-Cu-Cr aluminum alloy

The hot deformation behaviors and microstructures of Al-Zn-Mg-Cu-Cr aluminum alloy have been studied using thermal simulation test, optical microscopy and transmission electron microscopy. As a result, the true stress versus true strain curves and the microstructures under various deformation conditions are obtained. The microstructures gradually incline to dynamic-recrystallization with the deformation temperature rising and the recrystallization grains refine with the decrease of deformation temperature or with raising the strain rates. The quantitative relationship between the Zener-Hollomon parameter (Z) and average recrystallization grain size in the subsequent heat treatment is set up.

Electrode conformation-induced negative differential resistance and rectifying performance in a molecular device

Carrying out theoretical calculations using the nonequilibrium Green’s function method combined with the density functional theory, the transport properties of a carbon wire connected to two Au electrodes are investigated. The results show that the negative differential resistance and rectifying performance can be observed apparently when a pure carbon chain is connected to two asymmetric Au electrodes. The main origin of the negative differential resistance behavior is a suppression of the highest occupied molecular orbital resonance at certain bias voltage. Also shown is that it is possible to make the negative differential resistance disappear and rectifying performance be weakened only by adding side groups to a wire.

Effect of sputtering pressure and rapid thermal annealing on optical properties of Ta2O5 thin films

Abstract Ta 2 O 5 thin films were deposited by DC reactive magnetron sputtering followed by rapid thermal annealing(RTA). Influence of sputtering pressure and annealing temperature on surface characteristics, microstructure and optical property of Ta 2 O 5 thin films were investigated. As-deposited Ta 2 O 5 thin films are amorphous. It takes hexagonal structure ( δ -Ta 2 O 5 ) after being annealed at 800 °C. A transition from δ -Ta 2 O 5 to orthorhombic structure ( L -Ta 2 O 5 ) occurs at 900–1 000 °C. Surface roughness is decreased after annealing at low temperature. Refractive index and extinction coefficient are decreased when annealing temperature is increased.

Length and end group dependence of the electronic transport properties in carbon atomic molecular wires

Carrying out theoretical calculations using the nonequilibrium Greens function method combined with the density functional theory, the transport properties of functionalized atomic chains of carbon atoms with different lengths are investigated. The results show that the I-V evolution and rectifying performance can be affected by the length of wire when both ends of it is capped with the benzene-thiol attached with an amino group and the pyridine attached with nitro group. But when capped with the benzene-thiol attached with an amino group and the nitro group, we can observe a surprised result that different systems show similar I-V characteristics and their transport properties are almost independent of molecular length, which suggests that this is a favorable way to design more ideal molecular interconnecting wires with a high length-independent conductance behavior.

Particle swarm optimization computer simulation of Ni clusters

Abstract The stable structures and energies of Ni clusters were investigated using particle swarm optimization(PSO) combined with simulated annealing(SA). Sutton-Chen many-body potential was used in describing the interatomic interactions. The simulation results indicate that the structures of Ni clusters are icosahedral-like and binding energy per atom tends to approach that of bulk materials when the atoms number increases. The stability of Ni clusters depends not only on size but also on symmetrical characterization. The structure stability of Ni n clusters increases with the increase of total atom number n . It is also found that there exists direct correlation between stability and geometrical structures of the clusters, and relatively higher symmetry clusters are more stable. From the results of the second difference in the binding energy, the clusters at n =3 is more stable than others, and the magic numbers effect is also found.

Microstructure and optical properties of TiO2 thin films deposited at different oxygen flow rates

To research the influence of oxygen flow rate on the structural and optical properties of TiO2 thin film, TiO2 films on glass were deposited by reactive magnetron sputtering. The microstructure and optical properties were measured by X-ray diffractometry, AFM and UV-VIS transmittance spectroscopy, respectively. The results show that the films deposited at oxygen flow rate of 10 mL/min has the lowest roughness and the highest transmittance. The absorption angle shifts to longer wavelengths as oxygen flow rates increase from 5 to 10 mL/min, then to shorter ones as the oxygen flow rate increase from 10 to 30 mL/min. The band gap is 3.38 eV, which is nearly constant in the experiment. For the TiO2 thin films deposited at 10 mL/min of oxyge flow rate, there are nano-crystalline structures, which are suitable for anti-reflection (AR) coating in the solar cells structure system.

Electronic transport of the silane chain doped with phosphorus and boron atoms

Based on the nonequilibrium Green’s function method combined with the density functional theory, the properties of a silane chain doped with phosphorus and boron atoms connected to two Au electrodes are investigated. It has been found that a barrier similar to the p-n junction is formed in the molecule because of the different electronegativities of phosphorus and boron atoms. The electronic transport properties of two parallel silanes are also investigated when they are positioned between two identical electrodes. The results show that direct interactions between chains may strengthen the rectifying effect when their separation is set suitably. The rectifying effect may disappear when their separation is altered to other values due to the splitting of the frontier molecular orbitals, which contributes to the formation of new transport channels.

Total-dose-induced edge effect in SOI NMOS transistors with different layouts

The total-dose-induced edge effect in SOI NMOS transistors with different layouts is presented. Experimental results show that the edge effect is very sensitive to their layouts. Among the transistors hardened by design, the H-gate and ringed-source transistors do not behave as expected. At high radiation doses, the edge leakage currents appear for both transistors. Compared to the unhardened two-edged transistor, their total-dose-induced edge leakage paths and the role of layouts on edge effect are discussed.

Diffusion barrier performance of nanoscale TaNx thin-film

Abstract TaN x nanoscale thin-films and Cu/TaN x multilayer structures were deposited on P-type Si(100) substrates by DC reactive magnetron sputtering. The characteristics of TaN x films and thermal stabilities of Cu/TaN x /Si systems annealed at various temperatures were studied by four-point probe(FPP) sheet resistance measurement, atomic force microscopy(AFM), scanning electron microscope-energy dispersive spectrum (SEM-EDS). Alpha-Step IQ Profilers and X-ray diffraction(XRD), respectively. The results show that the surfaces of deposited TaN x thin-films are smooth. With the increasing of N 2 partial pressure, the deposition rate and root-mean-square(RMS) decrease, while the content of N and sheet resistance of the TaN x thin-films increase, and the diffusion barrier properties of TaN x thin-films is improved. TaN 1.09 can prevent interdiffusion between Cu and Si effectively after annealing up to 650 °C for 60 s. The failure of TaN x is mainly attributed to the formation of Cu 3 Si on TaN/Si interface, which results from Cu diffusion along the grain boundaries of polycrystalline TaN.