钛基底的纳米金刚石掺混纳米碳管的场发射特性

在纳米金刚石场发射的基础上, 研究了纳米金刚石掺混纳米碳管的场发射特性。采用电泳沉积法形成了纳米金刚石与纳米碳管的复合涂层, 经热处理后制备出阴极样品, 然后进行微观表征, 再进行场发射特性测试与发光测试。结果表明, 与未掺混的纳米金刚石阴极样品相比, 复合涂层阴极样品的场发射开启电场明显减小, 场发射电流提高, 在较低的电场下阳极表面荧光粉就可以发光, 但发光不均匀, 出现了"边沿发光"的现象。分析了纳米金刚石掺混纳米碳管场发射性能提高的机理, 是由于纳米碳管掺入之后, 涂层的电子输运能力得到增强, 涂层中有效发射体的数目增加。最后, 解释了"边沿发光"现象的成因。     

ZnO纳米棒的低温溶液法制备、光电特性研究及其在有机/无机复合电致发光中的应用

利用水热法制备了垂直于衬底的定向生长的ZnO纳米棒,利用扫描电子显微镜及光致发光的方法对其形貌及光学特性进行了表征,利用场发射性能测试装置对ZnO纳米棒的场发射性能进行了测试.结果表明:利用水热法在较低的温度(95 ℃) 下生长了具有较好形貌和结构的ZnO纳米棒,并表现出了较好的场发射特性,当电流密度为1 μA/cm²时,开启电场是2.8 V/μm,当电场为6.4 V/μm时,电流密度可以达到0.67 mA/cm²,场增强因子为3360.稳定性测试表明,在5 h内,4.5 V/μm的电场下,其波动不超过25%.将制备的ZnO纳米棒应用到有机/无机电致发光中,其中ZnO纳米棒为电子传输层,m-MTDATA(4,4',4″-tris{N,(3-methylphenyl)-N-phenylamino}-triphenylamine) 为空穴传输层,得到了ZnO的342 nm的紫外电致发光,此发光较ZnO纳米棒光致发光的紫外发射有约40 nm的蓝移. 关键词： ZnO纳米棒 场发射 水热法 有机/无机复合电致发光     

热处理对纳米金刚石涂层场发射性能的影响

用旋涂法在金属钛衬底上涂敷纳米金刚石,经过适当的热处理形成金刚石涂层与金属钛衬底的化学键合,即形成衬底与涂层之间的过渡层,从而为纳米金刚石颗粒提供电子,使其成为有效的发射体。用扫描电镜、原子力显微镜、X射线衍射和拉曼散射等手段分析了温度对键合效果以及场发射性能的影响,温度过高或过低都不利于提高纳米金刚石涂层的场发射性能,只有在700℃左右对样品进行热处理,才能得到较好的键合状态。改变涂膜时旋涂的次数以获得不同涂层厚度的样品,对其在700℃的相同温度下进行热处理,发现涂层过厚或过薄都不利于样品发射性能的提高。旋涂9次并于700℃热处理的样品具有较好的场发射性能,其发射阈值场强可达4.6V/μm,而15.3V/μm场强下的电流密度为59.7μA/cm2。     

后处理工艺对钛基纳米金刚石涂层场发射特性的影响

采用胶带粘贴、金相砂纸摩擦、射频氢等离子体工艺对钛基纳米金刚石涂层进行了处理,分析了它们对样品的微观表征、场发射性能、发光效果的影响。首先通过电泳法将金刚石粉末移植到金属钛片上,然后经过真空热处理、表面后处理工艺形成了场发射阴极涂层,最后对样品进行了微观表征、场发射特性与发光测试。结果表明,胶带处理在场强达到10 V/μm时,场发射电流密度从50μA/cm~2增j加到72μA/cm~2;金相砂纸处理在10 V/μm场强下的场发射电流由48μA/cm~2提高到82μA/cm~2;适当的氢等离子体处理有助于降低表面功函数,使得金刚石表面的悬键被氢原子饱和,在其表面形成C—H键,进一步降低了电子亲和势,从而提高了样品的场发射性能和发光均匀性。     

钛基纳米金刚石涂层场发射阴极

设计了一种新的金刚石场发射阴极工艺.用旋涂法在金属钛片上涂覆纳米金刚石涂层，经过适当条件的真空热处理，实现钛与金刚石之间的化学键合即欧姆接触，从而形成以金属钛为衬底，碳化钛键合层为过渡层，金刚石纳米颗粒为场发射体的场发射阴极.样品的阈值场强可达6.3V/μm，场发射电流密度在21 V/μm场强下可达到60.7 μA/cm2.提出了样品的结构模型,并分析了其电子输运方式.样品的Fowler-Nordheim曲线基本为一直线，根据经典场发射理论，可以证实其电子发射机制为场发射.观察到在获得稳定的场发射性能之前存在激发过程，并对其作了简单解释.     

基于图形化生长纳米氧化锌场致发射阴极阵列的研究

采用光刻技术在覆盖有氧化锌(ZnO)薄膜的ITO玻璃片衬底上实现图形化生长,结合水热法在衬底上制备出结构完整、排列一致的ZnO矩形和圆环型单元阵列。在图形化的基础上二次生长ZnO纳米锥阵列,锥长度最大可达到10μm,远大于一次生长的长度,并且发现锥顶有很多精细的类似针状的纳米量级微细结构。分析了非图形化、图形化一次以及图形化二次生长的ZnO纳米锥阵列的场致发射性能。使用图形化二次生长的ZnO纳米锥阴极阵列制作了12.7cm(5inch)的场发射显示器(FED),能实现全屏发光。实验结果表明,图形化二次生长的ZnO纳米锥阵列发射电流密度为最大,可达0.6mA/cm2,其开启场强为2.5V/μm。图形化生长ZnO纳米锥的方法是一种能较好改善材料场发射性能的好方法,为寻求良好场发射性能材料的制备提供了一条有效的实验途径。     

纳米金刚石的变温场发射

研究了温度变化对沉积在钛基底上的纳米金刚石的场发射特性的影响,发现纳米金刚石场发射电流随温度和电场的升高而增大,场发射特性偏离了传统的Fowler-Nordheim理论,场发射电流的稳定性基本没有变化.分析了场发射电流增大的机理,表明是由于纳米金刚石的尺度效应以及外电场下金刚石产生了大量的热载流子共同作用的结果.研究还表明基底钛在温度升高到一定程度后,在外加电场下会有较大的电流产生,对场发射造成较大的影响,表明基底钛具有一定的温度敏感性和电压敏感性. 关键词： 场发射 纳米金刚石 尺度效应 热载流子     

纳米金刚石的变温场发射

研究了温度变化对沉积在钛基底上的纳米金刚石的场发射特性的影响,发现纳米金刚石场发射电流随温度和电场的升高而增大,场发射特性偏离了传统的Fowler-Nordheim理论,场发射电流的稳定性基本没有变化.分析了场发射电流增大的机理,表明是由于纳米金刚石的尺度效应以及外电场下金刚石产生了大量的热载流子共同作用的结果.研究还表明基底钛在温度升高到一定程度后,在外加电场下会有较大的电流产生,对场发射造成较大的影响,表明基底钛具有一定的温度敏感性和电压敏感性.     

激光晶化形成纳米硅材料的场电子发射性质研究

利用KrF准分子激光退火超薄非晶硅膜,并结合热退火技术制备了单层纳米硅薄膜并研究了薄膜的场电子发射性质.在晶化形成的纳米硅薄膜中可以观测到稳定的场电子发射现象,其开启电场从原始淀积的非晶硅薄膜的17V/μm降低到8.5V/μm,而场发射电流密度可以达到0.1mA/cm².激光晶化后形成的纳米硅材料的场电子发射特性的改善可以从薄膜表面形貌的改变以及高密度纳米硅的形成所导致的内部电场增强作用来解释. 关键词： 纳米硅 场发射 激光晶化     

两步化学沉积法制备ZnO薄膜及其场发射特性

在低温常压条件下,以ITO玻璃为衬底,采用电化学法与湿化学法结合的两步化学沉积法制备了团簇状ZnO薄膜。利用XRD,SEM分析了薄膜结构和表面形貌,并采用二极管结构在高真空条件下对薄膜进行了场发射性能测试。稳定发射后,开启电场为3.0 V/μm。当电场为5.8 V/μm时,电流密度为583.3 μA/cm²。研究表明:两步化学沉积法低温制备ZnO薄膜是可行的,且该薄膜具有良好的场发射性能。     

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.