Wu Quan-De

Electrical Phenomena of C60-Tetracyanoquinodimethane Thin Films

The electrical properties of C60-tetracyanoquinodimethane (TCNQ) thin films fabricated by using an ionized-cluster-beam method in a high vacuum system were investigated. The films were characterized by transmission electron microscopy (TEM) and electronic spectroscopy. The spectroscopic results evidenced the formation of the charge-transfer complex system in C60-TCNQ thin films and the TEM results revealed the microstructure of the films. The film thickness is of about 100 nm. The electromotive intensity at the transition point is a few 107 V/m. The possible mechanism of the electrical phenomena of the films is discussed in the paper.

Response time of photoemission of ultrafine particle thin film

The response time of photoemissive materials is required for detecting ultrashort duration laser pulses. In this paper, the response time of photoemission in ultrafine particle thin film is studied, and the transit time spread (TTS) and response time of peak value (tM) are discussed. The photoelectrons response time will increase with increasing energy of photons. If the surface potential barrier of thin film declines, the photoemissive sensitivity or quantum yield will rise, however the response time will also increase, which means that response-time characteristic gets worse. As an example, the response time for Ag-O-Cs thin film is calculated for different cases when photoelectrons, excited in Ag ultrafine particles, travel through Cs2O semiconductor layer to the surface and escape into vacuum. The calculated response time is about 50 fs if this thin film is irradiated by infrared rays of wavelength 1.06 μm.

Nucleation and growth of ultrafine particles and conditions of epitaxy

The idea of free energy has been used in the discussion of physical conditions for nucleaton of clusters and or ultrafine particles on substrates. The physical picture of ultrafine particle growth are explained. Conditions of epitaxial growth are also discussed.

Multialkali Effects and Polycrystalline Properties of Multialkali Antimonide Photocathodes

Publisher Summary This chapter discusses the multialkali effects and polycrystalline properties of multialkali antimonide photocathodes. The concept of multialkali effects is aligned with the fact that photocathodes of high sensitivity may be obtained if antimony is combined with more than one alkali metal. Because of the background of its real applications, the characteristics of the multialkali photocathode, especially its integral sensitivity and spectral response in the red and near-infrared light regions, have been improved successively in the recent past. It is believed that this photocathode still has large potential. One of the significant problems in this regard is the influence of the polycrystalline grain sizes and grain boundaries on photoemission. Usually a semiconductor model was used for the multialkali photocathode, but it is really a monocrystal model. This model cannot be used to discuss its spectral response, quantum yield, or integral sensitivity. In addition to the influence of the composition and surface structure of the photocathode, the grain sizes and grain boundaries also have obvious influence on photoemissive properties. The physical basis for the multialkali effect and the influence of the grain sizes and grain boundaries on photoemission are discussed in this chapter.

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.