Li Fuming

Characterization of carbon nitride films modified by low energy ion-beam bombardment

Abstract Based on our previous synthesis of carbon nitride films containing beta-C 3 N 4 polycrystal grains, post-treatment of these deposited films using low-energy nitrogen ion-beam bombardment was carried out in order to improve the concentration of beta-C 3 N 4 structures in the films. Transmission electron microscopy (TEM) and electron diffraction (ED) measurements showed that the fraction of crystal carbon nitride structure in the films has been improved after such a treatment. X-ray photoelectron spectroscopy (XPS) and Raman analyses confirmed the improvement of the fraction of carbon nitride bonding structures in the modified films. The fractions of amorphous carbon and graphite-like carbon in the films were decreased after the bombardment.

CNx Films Deposited by Laser Ablation of Graphite Under Low Energy Nitrogen-Ion Beam Bombardment

Deposition of CNx thin films on Si(111) has been performed by laser ablation of graphite under a low-energy nitrogen ion beam bombardment. Films with a maximum N-concentration of 34% are obtained. The N species is found to be relatively constant along the depth of films. X-ray spectroscopy data confirm the existence of covalent C - N bonds. Nanocrystallites structure has been detected in the amorphous matrix of the films. Qualitative hardness tests indicate that the films are relatively hard and adhesive.

A Model for Light-Driven Proton Pump and Transfer in Bacteriorhodopsin

A theoretical model was assumed to describe the kinetic processes of light-driven proton pump and motion. The calculation shows that the photovoltage signals are greatly affected by experimental conditions including pulse width of excitation and impedance of measurement system. At the same excitation, only a negative photovoltage signal can be observed with small impedance and both the negative and positive signals can be observed with large impedance. With the same impedance, shorter response time of the pulsed photoelectric signals is responsible for shorter pulsed excitation. All these phenomena are in good agreement with the experimental results.

Optimization of Scatterer Concentration in High-Gain Scattering Media

We report the scatterer concentration-dependent behaviour of laser action in high-gain scattering media. A modified model of a random laser is proposed to explain the experimental results in good agreement. We may use this modified model to design and optimize the random laser system. A further detailed model is needed to quantitatively analyse the far-field distribution of random laser action.

Light-Induced Charge Separation and Transfer in Bacteriorhodopsin

The photo-voltage signals in bacteriorhodopsin(bR) excited by 1064 nm pulse laser are different from those by 532 or 355 nm. It shows that the positive and negative photoelectric signals are produced by the motion of the positive and negative charges, respectively, and more energy is needed for producing the positive charges than the negative. The mechanism of light-induced charge generation and charge transfer in bR was studied and analyzed by measuring the photoelectric signals with different impedance of measuring circuit and different pulse-width of 532 nm laser as pump light.

Formation of Carbon Nitride Films by Nitrogen Ion Bombardment on C60 Films

The synthesis of covalent carbon nitride films becomes an important subject in the materials research field. As a new synthetic method two low-energy (400 and 1000 eV) nitrogen ion beams are used to bombard on C60 thin films individually. The bombarded films are used for Raman and x-ray photoelectron spectroscopy (XPS) measurements. The results of the analyses show that under the bombardment of 400 eV nitrogen ion beam, the film still contains a large amount of undestructed C60 molecules. In the case of 1000 eV bombardment, only a little amount of C60 molecules is kept undestructed. The experimental results also show that the destructed carbon species will combine chemically with nitrogen ions to form stable covalent carbon nitride, confirmed by the Raman peaks of, e.g., 2240 cm-1. The XPS N1s and C1s lines also indicate the formation of covalent carbon nitride in the bombarded films.

Ion-Beam Bombarding Effects on Deposition of Carbon Nitride Films by Laser Ablation

In order to obtain high quality carbon nitride films, x-ray photoelectron spectroscopy and Raman spectrum were used to analyze several kinds of film: (a) laser-ablated amorphous carbon (a-C) films, (b) a-C films after a 1 keV nitrogen ion beam bombardment. (c) carbon nitride (CNx) films synthesized by ablation assisted with ion beam bombardment, (d) CNx films after a 50 eV nitrogen ion beam bombardment, and (e) CNx films after 1 keV nitrogen ion beam bombardment. The comparison among these films showed that the concurrent deposition of CNx films by ablation and a nitrogen ion beam should be better than the post-treatment of a-C films by nitrogen ion beam bombardment. In the case of concurrent deposited CNx films, a post-treatment by a nitrogen ion beam bombardment with an appropriate energy (possibly less than 1 keV) was proposed to improve the ratio of C-N binding structures in the deposited films.

A PVK-based high-performance photorefractive polymer composite under a low external electric field

We describe a PVK-based photorefractive polymer composite doped with disperse red 1, poly-butylacrylate and TNF. Using the two-beam coupling experiment, we investigate its photorefractive properties as well as the dynamic process of the index gratings in the sample. We observe the photorefractive effect in the absence of an applied external electric field. The two-beam coupling gain coefficient was measured to reach a value as high as 140 cm-1 in the absence of an external applied electric field and a value of 470 cm-1 at a poling dc electric field of 25V/µm.

Characterization of the high-voltage pulsed discharge plasma of ammonia by emission spectroscopy

We have used optical emission spectroscopy to characterize the high-voltage pulsed discharge of ammonia. Ammonia was highly dissociated in the discharge at low pressures. More atomic nitrogen was generated as compared to the discharge of nitrogen gas at the same pressure of 0.8kPa. We discuss the elimination of the oxygen impurity in the ammonia discharge and we estimate the time-dependent atomic excitation temperature and the electron density from the measured spectra.

EMISSION AND MASS SPECTRAL ANALYSES OF LASER ABLATED AlN PLUMES

The emission spectrum of the 3Πi-3Πi (0-0) AlN band and some N+ and N emission lines have been studied in the visible region for the laser ablated plumes. The Stark-shift and Stark broadening were observed. The component species in the ablated plumes were analyzed by time of flight mass spectroscopy. The electron density and the temperature were calculated from the Stark-shift and Stark broadening of N (2D) emission line. The densities of AlN+, Al+, N+, AlN, N and Al were estimated by the mass spectra and the Saha equation.