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The effects of current-path patterns on magnetotransport in spatially-confined structures by Monte Carlo simulation

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Chinese Physics B 2009年第11期18卷 5061-5065页

作者：伍建春孙华李振亚 Department of Physics and Jiangsu Key laboratory of thin films Soochow University

Simulations are performed on clusters of finite size to study the effects of size and current-path structure on magnetotransport in spatially-confined samples. Magnetotransport networks are established and calculated based on fractal structures including Koch curves and percolation backbones extracted from regular lattices. The structure pattern of clusters is shown to play an important role in the magnetotransport behaviours by affecting the magnetore- sistance fluctuations due to spin disorder in the systems of small size, which suggests the possibility of controlling the magnetotransport by the design of current-path configurations.

关键词： magnetoresistance percolation magnetotransport network

Spiral-wave dynamics in excitable medium with excitability modulated by rectangle wave

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Chinese Physics B 2011年第4期20卷 109-116页

作者：袁国勇 Department of Physics Hebei Normal University Hebei Advanced thin films laboratory

We numerically study the dynamics of spiral waves in the excitable system with the excitability modulated by a rectangle wave. The tip trajectories and their variations with the modulation period T are explained by the corre- sponding spectrum analysis. For a large T, the external modulation leads to the occurrence of more frequency peaks and these frequencies change with the modulation period according to their specific rules, respectively. Some of the frequencies and a primary frequency fl determine the corresponding curvature periods, which are locked into rational multiplies of the modulation period. These frequency-locking behaviours and the limited life-span of the frequencies in their variations with the modulation period constitute many resonant entrainment bands in the T axis. In the main bands, which follow the relation T/T12 = m/n, the size variable Rx of the tip trajectory is a monotonic increasing function of T. The rest of the frequencies are linear combinations of the two ones. Due to the complex dynamics, many unique tip trajectories appear at some certain T. We find also that spiral waves are eliminated when T is chosen from the end of the main resonant bands. This offers a useful method of controling the spiral wave.

关键词： spiral wave FitzHugh-Nagumo model frequency-locking

Diagnosis of a low pressure capacitively coupled argon plasma by using a simple collisional-radiative model

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Chinese Physics B 2011年第1期20卷 486-492页

作者：虞一青辛煜宁兆元 Key laboratory of thin films School of Physical Science and TechnologySoochow University

This paper proposes a simple collisional-radiative model to characterise capacitively coupled argon plasmas driven by conventional radio frequency in combination with optical emission spectroscopy and Langmuir probe measurements. Two major processes are considered in this model, electron-impact excitation and the spontaneous radiative decay. The diffusion loss term, which is found to be important for the two metastable states （4s[3/2]2, 4s＇[1/2]0）, is also taken into account. Behaviours of representative metastable and radiative states are discussed. Two emission lines （located at 696.5 nm and 750.4 nm） are selected and intensities are measured to obtain populated densities of the corresponding radiative states in the argon plasma. The calculated results agree well with that measured by Langmuir probe, indicating that the current model combined with optical emission spectroscopy is a candidate tool for electron density and temperature measurement in radio frequency capacitively coupled discharges.

关键词： capacitively coupled plasma collisional-radiative model optical emission spectroscopy Langmuir probe

Effect of Discharge Parameters on Properties of Diamond-Like Carbon films Prepared by Dual-Frequency Capacitively Coupled Plasma Source

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Plasma Science and Technology 2010年第1期12卷 53-58页

作者：杨磊辛煜徐海鹏虞一青宁兆元 Jiangsu Key laboratory of thin films School of Physical Science and TechnologySoochow University

Diamond-like carbon （DLC） films were prepared with CH4-Ar using a capacitively coupled plasma enhanced chemical vapor deposition （CCP-CVD） method driven by dual-frequency of 41 MHz and 13.56 MHz in combination. Due to a coupling via bulk plasma, the self-bias voltage depended not only on the radiofrequency （RF） power of the corresponding electrode but also on another RF power of the counter electrode. The influence of the discharge parameters on the deposition rate, optical and Raman properties of the deposited films was investigated. The optical band decreased basically with the increase in the input power of both the low frequency and high frequency. Raman measurements show that the deposited films have a maximal sp3 content with an applied negative self-bias voltage of -150 V, while high frequency power causes a continuous increase in the sp3 content. The measurement of atomic force microscope （AFM） shows that the surface of the deposited films under ion-bombardment becomes smoother than those with non-intended self-bias voltage.

关键词： dual-frequency capacitively coupled discharge DLC Raman spectroscopy

C_2F_6 /O_2 /Ar Plasma Chemistry of 60 MHz/2 MHz Dual-Frequency Discharge and Its Effect on Etching of SiCOH Low-k Film

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Plasma Science and Technology 2012年第1期14卷 48-53页

作者：袁颖叶超陈天葛水兵刘卉敏崔进徐轶君邓艳红宁兆元 School of Physics Science and Technology Jiangsu Key Laboratory of Thin FilmsSoochow University

This work investigated C2F6/O2/Ar plasma chemistry and its effect on the etching characteristics of SiCOH low-k dielectrics in 60 MHz/2 MHz dual-frequency capacitively coupled discharge. For the C2F6/Ar plasma, the increase in the low-frequency （LF） power led to an increased ion impact, prompting the dissociation of C2F6 with higher reaction energy. As a result, fluorocarbon radicals with a high F/C ratio decreased. The increase in the discharge pressure led to a decrease in the electron temperature, resulting in the decrease of C2F6 dissociation. For the C2F6/O2/Ar plasma, the increase in the LF power prompted the reaction between 02 and C2F6, resulting in the elimination of CF3 and CF2 radicals, and the production of an F-rich plasma environment. The F-rich plasma improved the etching characteristics of SiCOH low-k films, leading to a high etching rate and a smooth etched surface.

关键词： fluorocarbon plasma dual-frequency discharge low-k films etching

Room Temperature Ferromagnetism and Structure of Zn_(1-x)Cu_xO films Synthesized by Radio Frequency Magnetron Sputtering

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Plasma Science and Technology 2009年第5期11卷 582-586页

作者：陈学梅诸葛兰剑吴雪梅吴兆丰 School of Physical Science and Technology Soochow University Jiangsu Key laboratory of thin films Soochow University Jiangsu Key laboratory of thin films Soocbow University Analysis and Testing Center Sooehow University

Zn1-xCuxO thin films were synthesized by the radio frequency （RF） magnetron sputtering technique using a ZnO target containing different pieces of small Cu-chips. X-ray diffraction （XRD） and scanning electron microscopy （SEM） were employed to analyze the crystalline and microstructure of the film, and X-ray photoelectron spectroscopy （XPS） was used to establish the bonding characteristics and oxidation states of copper inside the ZnO host. Room temperature （RT） ferromagnetism was observed in the Znl-xCuxO films by a Quantum Design superconducting quantum interference device （SQUID） and the saturation magnetic moment of the films was found to decrease with the increase in Cu content.

关键词： RF magnetron sputtering Zn1-xCuxO film ferromagnetism

Effect of Low-frequency Power on F, CF_2 Relative Density and F/CF_2 Ratio in Fluorocarbon Dual-Frequency Plasmas

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Plasma Science and Technology 2010年第5期12卷 566-570页

作者：黄宏伟叶超徐轶君袁圆施国峰宁兆元 School of Physics Science and Technology Jiangsu Key Laboratory of Thin FilmsSoochow University

Effect of low-frequency power on F, CF2 relative density and F/CF2 ratio, in C2F6, C4F8 and CHF3 dual-frequency capacitively couple discharge driven by the power of 13.56 MHz/2 MHz, was investigated by using optical emission spectroscopy. High F, CF2 relative density and high F/CF2 ratio were obtained in a CHF3 plasma. But for C2F6 and C4Fs plasmas, the F, CF2 relative density and F/CF2 ratio all decreased significantly due to the difference in both reactive paths and reactive energy. The increase of LF power caused simultaneous increase of F and CF2 radical relative densities in C4Fs and CHF3 plasmas, but led to increase of F with the decrease in CF2 relative densities in C2F6 plasma due to the increase of lower energy electrons and the decrease of higher energy electrons in electron energy distribution function （EEDF）.

关键词： fluorocarbon plasma dual-frequency discharge low-k films etching

Trench gate IGBT structure with floating P region

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Journal of Semiconductors 2010年第2期31卷 11-13页

作者：钱梦亮李泽宏张波李肇基 State Key laboratory of Electronic thin films and lntegrated Devices University of Electronic Science and Technology of China State Key laboratory of Electronic thin films and Integrated Devices University of Electronic Science and Technology of China

A new trench gate IGBT structure with a floating P region is proposed,which introduces a floating P region into the trench accumulation layer controlled IGBT（TAC-IGBT）.The new structure maintains a low on-state voltage drop and large forward biased safe operating area（FBSOA） of the TAC-IGBT structure while reduces the leakage current and improves the breakdown *** addition,it enlarges the short circuit safe operating area（SCSOA） of the TAC-IGBT,and is simple in fabrication and *** results indicate that,for IGBT structures with a breakdown voltage of 1200 V,the leakage current of the new trench gate IGBT structure is one order of magnitude lower than the TAC-IGBT structure and the breakdown voltage is 150 V higher than the TAC-IGBT.

关键词： TAC-IGBT CT-IGBT accumulation channel floating P region SCSOA

Dynamics of Meandering Spiral Waves Driven by Two-Point Feedback

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Communications in Theoretical Physics 2011年第9期56卷 467-475页

作者：袁国勇 Department of Physics Hebei Normal University Hebei Advanced thin films laboratory

We numerically study the dynamics of meandering spiral waves in the excitable system subjected to a feedback signal coming from two measuring points located on a straight line together with the initial spiral core. The core location and size radius of the final attractors are computed, and they change with the position of the moving measuring point in a unique way. By the Fourier Spectral analysis, we find the frequency-locked behaviors different from the driving scheme of the external periodic force. It when the moving measuring point approaches closely is also found that the meandering spiral wave can be eliminated the boundary and its feedback gain is large enough. This offers an effective and convenient method for eliminating meandering spiral waves.

关键词： spiral wave frequency-locking feedback