脉冲高能量密度等离子体材料表面改性及其应用

脉冲高能量密度等离子体（pulsed high energy density plasma, PHEDP）是一项新的材料表面改性技术.它集高电子温度、高能量密度、高定向速度于一身,在制备薄膜时具有沉积薄膜的温度低、沉积效率高、能量利用率高的优点,并兼具表面溅射、离子注入、冲击波和强淬火效应等综合效应;它可以制备纳米晶或非晶硬质薄膜,提高基底材料的表面硬度和耐磨、耐蚀性能;能够实现非金属材料表面金属化,所制备薄膜与基底之间存在很宽的混合过渡区,因此膜/基结合良好.文章主要介绍了作者近年来在该领域的部分研究成果,简要介绍了脉冲高能量密度等离子体的原理、特点及应用.分析了脉冲等离子体与材料相互作用的基本物理现象.     

Ag/TiN复合薄膜制备及其表面增强拉曼光谱研究

高灵敏基底材料是表面增强拉曼光谱(SERS)技术应用的关键。本研究采用电化学沉积法将氮化钛(TiN)薄膜与贵金属银复合,利用两者协同效应提高SERS灵敏度。借助XRD、SEM、UV-VIS和Raman等测试手段系统探究了电化学沉积参数对复合基底SERS性能的影响。研究发现,当沉积液浓度为5 mmol/L、沉积电压为5 V及沉积时间为5 min时,复合基底单质Ag和TiN两种物相共存,Ag纳米颗粒沿优势晶面生长,银颗粒在TiN薄膜上生长为棒状结构,分布均匀。与其他沉积参数下制备的基底相比,上述条件下合成的复合薄膜展现出较明显的等离子体共振吸收双峰,表明体系中Ag和TiN两相间产生等离子体共振叠加效应,电磁场耦合作用增强,局部表面等离子体共振耦合作用增加,薄膜表面形成更多的SERS“热点”,并有助于促进电荷转移,进而赋予基底较为优异的SERS性能。这证实了优化电化学沉积参数来调控复合薄膜形貌从而改善SERS基底性能的可行性,可为采用电化学沉积技术制备Ag/TiN复合薄膜作为SERS基底材料提供技术支持。     

脉冲高能量密度等离子体法制备TiN薄膜及其摩擦磨损性能研究

利用脉冲高能量密度等离子体技术在室温条件下在45号钢基材上制备出了超硬耐磨TiN薄膜.利用XRD，XPS，AES，SEM等手段分析了薄膜的成分及显微组织结构，并测试了薄膜的硬度分布及摩擦磨损性能.结果表明：薄膜主要组成相为TiN，薄膜组织致密、均匀，与基材之间存在较宽的混合界面；薄膜硬度高，在干滑动磨损实验条件下具有优异的耐磨性及较低的摩擦系数. 关键词： 脉冲高能量密度等离子体 TiN膜 显微组织 耐磨性     

脉冲高能量密度等离子体沉积(Ti,Al)N薄膜组织及其性能研究

利用脉冲高能量密度等离子体技术在室温条件下在45＃钢基材表面沉积了高硬度耐腐蚀(Ti, Al)N薄膜. 利用扫描电子显微镜、X射线衍射、X射线光电子能谱、俄歇电子能谱分析了薄膜的显微组织.利用纳米压痕仪测试了薄膜的纳米硬度.测试了薄膜在05mol/L H2SO4水溶液中的耐蚀性. 测试结果表明：薄膜主要组成相为(Ti, Al)N，同时含有少量的AlN,薄膜的纳米硬度高达26 GPa,薄膜具有良好的耐蚀性，与1Cr18Ni9Ti奥氏体不锈钢相比，耐蚀性提高了一个数量级. 关键词： 脉冲高能量密度等离子体 薄膜 纳米硬度 耐蚀性     

金银/氮化钛表面增强拉曼基底制备及对烟酸的定量检测

表面增强拉曼光谱技术对分子具有特异性识别以及快速无损检测的能力,使其在药物检测方面具有重大的潜力。通过贵金属和氮化钛之间协同作用,使复合基底具有较高的SERS性能,提供了一种基于SERS技术的药物检测方法。采用电化学沉积及自组装法,制备出贵金属/氮化钛复合薄膜。研究表明,在复合薄膜中存在面心立方晶型TiN、金属单质Au和Ag三种物相;电子显微镜显示平均粒径分别为90和50 nm的金属Au和Ag颗粒均匀分布在TiN薄膜表面;基底的紫外-可见吸收图谱中出现了贵金属金与银纳米颗粒及TiN薄膜三者的特征等离子体共振吸收峰。以该复合薄膜为SERS基底,对烟酸溶液进行拉曼检测。结果显示,贵金属/氮化钛复合薄膜对烟酸具有显著的SERS效应,最低检测浓度为10-5 mol·L-1,对1 033 cm-1处烟酸拉曼信号强度及浓度取对数,发现两者间呈一定线性关系,其R2为0.969,得益于TiN,Au和Ag之间可发生表面等离子体共振引起电磁场增强,以及电荷转移效应。研究还发现,烟酸通过COO-基团垂直吸附在贵金属/氮化钛基底表面;在酸性环境下,烟酸N原子质子化主要以阳离子N＋H（Ⅰ）形式存在;在碱性环境时,主要以阴离子COO-（Ⅲ）形式存在。绞股蓝总甙溶液中模拟烟酸非法添加,该复合基底对其最低的拉曼检测浓度是10-5 mol·L-1,为现场快速检测非法添加药物提供了新途径。     

等离子体化学气相沉积及其在沉积超硬膜方面的应用

本文简要介绍了等离子体化学气相沉积的基本原理和几种主要类型的工艺特点，着重介绍了等离子体化学气相沉积在沉积超硬膜方面的新进展，主要包括制备氮化钛类薄膜、立方氮化硼薄膜、类金刚石薄膜及金刚石薄膜。     

大气压电晕等离子体射流制备氧化钛薄膜

大气压等离子体因具有很多独特优势从而在材料制备和表面工艺领域备受关注.本文利用大气压针-板电晕放电等离子体射流制备氧化钛(TiO_2)薄膜,研究了电晕极性和放电参数对薄膜特性的影响.实验测试了正负电晕等离子体射流的电学性能、发展过程和发射光谱,并对不同条件下制备的TiO_2薄膜进行了表征和分析.结果表明:负电晕等离子体射流制备的TiO_2薄膜表面更均匀而且薄膜中钛(Ti)含量更高.正负电晕等离子体射流制备的薄膜的结合力均优于4.7 N/cm,表面电阻低于10~(10) Ω.此外,发现TiO_2薄膜在基底表面沉积和在气相中成核存在竞争机制,并进一步阐述了电晕放电等离子体制备薄膜的成膜机理和不同极性放电的差异.本文结果将为大气压等离子体制备均匀、致密的功能氧化物薄膜材料提供有益参考.     

等离子体增强脉冲激光沉积o-BN薄膜

利用等离子体增强脉冲激光沉积系统在Si（100）基底上沉积出了高质量的o-BN薄膜,利用红外光谱（FTIR）、X射线衍射谱（XRD）和原子力显微镜照片对o-BN薄膜进行了表征.通过红外光谱（FTIR）得到o-BN薄膜的红外峰特征峰值为1189cm^-1,1585cm^-1和1450cm^-1;由XRD谱得到o-BN薄膜的（111）,（020）,（021）,（310）和（243）各晶面的衍射峰, 特别是（310）和（243）晶面的衍射峰非常强;通过原子力显微镜照片清楚看到BN薄膜具有尖状突起的表面形貌. 关键词： 等离子体增强脉冲激光沉积 氮化硼薄膜 X射线衍射谱     

晶相β—C3N4薄膜的制备

晶相β－Ｃ３Ｎ４薄膜的制备是近年来材料物理学的一个重要课题，采用微波增强等离子体化学气相沉积的方法，成功地制备了基本上均匀、连续、致密的β－Ｃ３Ｎ４晶体薄膜，晶粒的氮碳含量比正好为４：３，并且其（１００）面平行于Ｓｉ（１００）的表面。拉曼谱中在２５０ｃｍ＾－１和３０２ｃｍ＾－１处出现二个特征峰 。     

室温下用脉冲激光沉积E-BN薄膜

 在利用等离子体增强脉冲激光沉积系统沉积立方氮化硼（cBN）薄膜时，发现了氮化硼（BN）材料的E-BN相，并利用扫描电镜和红外吸收光谱及X射线衍射技术对薄膜样品进行了分析，得到了制备较高质量E-BN薄膜的一些热力学参数及时间参数，验证了现有的E-BN结构的形成理论。     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Multi-pulse operation of a Kerr-lens mode-locked femtosecond laser

Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser.     

Propagation of Helmholtz-Gauss beams in weak turbulent atmosphere

Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored.     

An effective method for reducing speckle noise in digital holography

An effective method for reducing the speckle noise in digital holography is proposed in this paper.Different from the methods based on classical filtering technique,it utilizes the multiple holograms which are generated by rotating the illuminating light continuously.The intensity images reconstructed by a series of holograms generated by rotating the illuminating light possess different speckle patterns.Hence by properly averaging the reconstructed intensity fields,the speckle noises can be reduced greatly.Experimental results show that the proposed method is simple and effective to reduce speckle noise in digital holography.     

Influence of purity of HfO2 on reflectance of ultraviolet multilayer

The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO2 single laver films was much laxger than that of the other impurities such as Ti and Fe.which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2.With these two kinds of HfO2 and the same kind of SiO2.we deposited HfO2/SiO2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively,which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films.     

Speech enhancement by array crosstalk resistant ANC and spectrum subtraction

Microphone array-based speech enhancement has great importance for speech communications and speech recognition. To reduce the aperture of the microphone array and to increase the effect of the speech enhancement will greatly broaden the application areas of the microphone array. An array crosstalk resistant adaptive noise cancellation method is therefore presented. And then an improved spectral subtraction algorithm is further cascaded to obtain better enhancement results. Theoretic analysis and experiments indicate that the proposed scheme needs only a very small microphone array while it simultaneously achieves a higher SNR improvement. Besides, the proposed scheme can be used in many noisy environments and is easy for real-time implementation.