Han Chen Liu

Theory of the Rectifying Performance in Molecular Device: The Role of Anchoring Groups

The electronic transport of the single molecule via different anchoring groups is studied using density functional theory in conjunction with the nonequilibrium Green’s function. The results show that the electronic transport properties are strongly dependent on the anchoring groups. Asymmetric electrical response for opposite biases is observed resulting in significant rectification in current. The transmission coefficients and spatial distributions of molecular orbitals under various external biases voltage are analyzed, and it suggests that the asymmetry of the coupling between the molecule and the electrodes with external bias leads to rectifying performance.

The I-V Characteristics of the 3,3',5',5-Tetra-Tert-Butyl-Azobenzene Optical Molecular Switch: A First-Principles Study

By applying nonequilibrium Green’s function formalism combined first-principles density functional theory, we investigate the electronic transport properties of 3,3′,5,5′-Tetra-tert-butyl-azobenzene(meta-TBA) optical molecular switch. This molecular switch comprises a meta-TBA molecule with the trans and cis forms, which can be reversed from one structure to another one upon photoexcitation. The influence of HOMO-LUMO gaps and the spatial distributions of molecular orbitals on the electronic transport through the molecular device are discussed in detail. Theoretical results show that there is a large current ratio in bias window, which suggests that this system can be one of good candidates for optical switches due to this unique advantage, and have real applications in the molecular circuit.

The Study on the Periodic Left-Handed Materials of Convex-SRRs Structure

The split ring resonators is the basic structure unit ,it is important constituent part of periodic left-handed materials (LHMs).The convex split ring resonators (convex-SRRs) structure is the new SRRs, the new periodic LHMs are made of convex-SRRs structure unit.The convex-SRRs structure is arranged periodically 3 * 4 matrix along XOY plane and arranged periodically 3 * 2 * 1 matrix along the YOZ plane. These convex-SRRs structure units in space periodic aligned to the prism shape, the new artificial materials come into being.In order to prove that the convex-SRRs structure periodic materials are left-handed materials (LHMs), the microwave transmission and negative refractive are simulated using the materials of convex-SRRs structure prism. First the permeability and permittivity of convex-SRRs structure materials are negative value by simulation the microwave transmission, this is the symbol of the left hand material properties. Second by simulation, prism’s experiment of convex-SRRs structure materials has a negative refractive effect, These simulations demonstrate that the materials of convex-SRRs structure periodic arrangement are LHMs.

First-Principles Study of Triangle Terarylene as a Possible Optical Molecular Switch

Using non-equilibrium Green’s function formalism combined with first-principles density functional theory, we investigate the electronic transport properties of a triangle terarylene(open- and closed-ring forms) optical molecular switch. The influence of the HOMO-LUMO gaps and the spatial distributions of molecular orbitals on the quantum transport through the molecular device is discussed. Theoretical results show that the conductance of the closed-ring is 3-8 times larger than that of open-ring, which expect that this system can be one of good candidates for optical switches due to this unique advantage, and may have some potential applications in future molecular circuit.

Identification of ZnO Defect Structure by PL Spectroscopy

Defect structure of ZnO determines the optoelectronic characteristics of ZnO crystal and film. The identification and modulation of the defect structure is the foundation of the manufacture of optoelectronic devices. Although a good deal of research has been carried out about intrinsic defects and doping defects in ZnO, it is difficult to obtain a conclusive result accepted by all. In the paper, ZnO film is prepared by sol-gel method and the defect structure is expressed by photoluminescent (PL) spectroscopy. Based on some basic rules the intrinsic defect structure of ZnO is confirmed and the interaction of impurity Li and intrinsic defect is discussed. At the same time, some new electronic levels are proposed. It is surprising that although there are fourteen peaks in PL spectra of ZnO film, almost all the peaks can be identified by these basic rules.

Electronic Transport Properties of the Azobenzene-Based Optical Molecular Switch with Different Substituents

By applying nonequilibrium Green’s function formalism combined first-principles density functional theory, we investigate the electronic transport properties of the azobenzene -based optical molecular switch with different substituents. Theoretical results show that the donor/acceptor substituent plays an important role in the electronic transport of molecular devices. The switching performance can be improved to some extent through suitable donor and acceptor substituents.

Features and Technology of Piezoelectric Hydrophone

A piezoelectric hydrophone is design and made with Pb(Zr,Ti)O3 ceramic. The technology is presented and its impedance characteristics and directivity are researched. Experimental result manifests its usability of the hydrophone.

Structural and photoluminescent properties of Li-doped ZnO film prepared by sol-gel technique

The effect of an impurity as a donor or an acceptor in ZnO film is determined by its distribution in ZnO lattice. In this paper the distribution of Li is investigated by X-ray diffraction (XRD) and photoluminescence (PL). It is found that Li-doped ZnO films own different dependence on heat treatment temperature by contrast with pure ZnO films. For Li-doped ZnO films, although the crystallinity is promoted after heat treatment at 500oC, it is impeded effectively after heat treatment at 600oC. The abnormal phenomenon implies that Li preferential inhabits at Zn-sublattice to form a substitutional defect as an acceptor unless Li content exceeds its solubility in Zn-sublattice. The change of the PL spectra of pure ZnO films after heat treatment at different temperatures reveals that the PL peak at 650nm origins from interstitial defects. Moreover, with the increase of Li content, the intensity of the peak at 650nm decreases firstly and then increases again. This interesting changing trend further reveals that superfluous Li will enter into the octahedral interspaces as donors. As a conclusion it is proposed that it is difficult to obtain high conductive p-ZnO by monodoping of Li.

Measurement of Absorption Spectrum of Media by Grating Spectrometer

In order to measure quantum yield (quantum efficiency) of light in the research of fluorescence excitation, rapid prototyping of micro-structure and photochemical, the absorption spectrum must be precisely measured. Therefore, the reflection on optical media interface, absorption and transmission in the medium must also be considered. In this article, we exhibit a set of reasonable experimental method which is designed to measure absorption spectrum by grating spectrometer. The results show that the obtained absorption lines are properly reliable if we select an appropriate way to settle the sample. Furthermore, it can be well generalized and applied to the selection of fluorescence excitation spectrum, photochemical reaction spectrum, photoelectric device spectrum.

The Quantum Length Dependence of Conductance in Molecular Device: An Ab Initio Study

By Applying Nonequilibrium Green’s Function Formalism Combined First-Principles Density Functional Theory, we Investigate the Electronic Transport Properties of Thiophene and Furan Molecules with Different Quantum Length. the Influence of HOMO-LUMO Gaps and the Spatial Distributions of Molecular Orbitals on the Electronic Transport through the Molecular Device Are Discussed in Detail. the Results Show that the Transport Behaviors Are Determined by the Distinct Electronic Structures of the Molecular Compounds. the Length Dependence of Molecular Conductance Exhibits its Diversity for Different Molecules.