SiNx插入层的生长位置对GaN外延薄膜性质的影响

系统研究了纳米量级的多孔 SiNx插入层生长位置对高质量GaN外延薄膜性质的影响.高分辨X射线衍射测量结果表明:SiNx插入层生长在CaN粗糙层上能够得到最好的晶体质量.利用测量结果分别计算出了螺位错和刃位错的密度.此外,GaN薄膜的光学、电学性质分别用Raman散射能谱、低温光致发光能谱和霍尔测量的方法进行了表征.实...     

Si-SnO_2异质结的电学和光学性质

本文研究了Si—SnO_2 异质结(Heterojunction)的电学和光学性质。半导体SnO_2薄膜是通过将蒸发在Si单晶(111)面上的Si进行连续氧化的方法得到的。SnO_2 薄膜具有带隙为3.5ev的退化了的n型半导体的性质。n-n型Si-SnO_2 异质结的伏——安特性显示出很好的整流性质。光电压的测量表明,在室温下,n-n型Si-SnO_2 异质结的光响应是分布在400-1200mμ的广阔区间之内。n-n型Si-SnO_2 异质结的能带图根据这些电学和光学的测量结果来确定。     

InZnO薄膜透明导电的制备及其柔性的表征

利用激光脉冲沉积(PLD)技术在室温条件下将IZO薄膜生长在塑料衬底上,通过控制生长压强来调节薄膜的电学性质。然后对光电性质最优的薄膜进行了柔性测试,结果显示薄膜的内弯折半径小于9 mm后电阻会显著增加,对于弯折引起的电学性能的变化进行了初步的讨论。     

薄膜厚度对La1.85Sr0.15CuO4薄膜结构和超导电性的影响

使用直流同轴磁控溅射法,在SrTiO3(STO)衬底上成功制备出c取向的La1.85Sr0.15CuO4(LSCO)超导薄膜.通过电输运测量系统和X射线衍射仪研究了薄膜厚度对LSCO(x＝0.15)薄膜电学性质和晶体结构的影响.实验证明随着膜厚增加,(006)衍射峰的半高宽(Full Width at Half Maximum,FWHM)逐渐减小,薄膜的取向性增强,与此同时,薄膜的超导转变温度TC逐渐提高.     

沉积温度和快速退火对磁控溅射法制备的AZO薄膜性能的影响

探究了不同衬底温度下由磁控溅射法制备的氧化锌掺铝(AZO)薄膜的结构、光学和电学性能,以及快速退火处理对样品电学性能的改善作用.实验结果表明:随着衬底温度的升高,薄膜样品的载流子浓度、霍尔迁移率和电导率提高,并在400℃附近达到较好水平,但高温的衬底沉积出的样品薄膜的XRD图谱半高全宽相对于低温衬底并没有明显变小.测量退火处理后的样品薄膜的电学性质,发现短时间的真空退火能改善低温沉积的AZO薄膜的电导率,与提高衬底温度有类似的改善效果,700℃的退火温度能达到最好效果.     

氮等离子体辅助脉冲激光沉积生长p型ZnO:N薄膜的光学和电学性质

通过氮气等离子体辅助脉冲激光沉积(PLD)技术制备了氮掺杂氧化锌(ZnO:N)薄膜.经过低温快速热退火(RTA)处理后,ZnO:N薄膜呈现p型导电特性.利用X射线光电子能谱(XPS)、光致发光(PL)和霍尔测量对ZnO:N薄膜中N的化学状态及其光学和电学性质进行了系列的研究.结果表明:所制得的p型ZnO:N薄膜为高度补...     

磁控溅射法制备ZnO/YBCO异质结及电学特性

利用磁控溅射技术在YBCO上沉积ZnO薄膜,获得ZnO/YBCO异质结.测量其不同温度下的电学性质,样品显示良好的整流特性,并且随着温度的升高,ZnO/YBCO异质结电流逐渐增大.     

热处理方式对ZAO薄膜结构以及电学性质的影响

采用溶胶-凝胶旋转涂敷方法在普通玻璃衬底上生长ZAO薄膜.每涂敷1层薄膜,都要在一定的温度下对薄膜进行1次热处理,连续涂敷7层,最后再对部分薄膜在600℃的马弗炉中退火2h.采用X射线衍射和薄膜电阻率分别来表征涂敷薄膜的结构特征和电学特性.实验结果表明:每次涂敷薄膜后所设定温度的大小以及最后是否再对薄膜进行退火处理直接影响着制备薄膜的结构特征和电学性质.     

常压MOCVD生长ZnO薄膜及其性质

用常压MOCVD在蓝宝石 (0 0 0 1)面上生长了氧化锌 (ZnO)薄膜。用AFM、室温PL谱、Hall测量、X射线双晶衍射、卢瑟福背散射 /沟道技术等分析方法研究了样品的表面形貌、结构性能、发光性能和电学性能。AFM分析结果显示 ,薄膜呈六角柱状结晶 ,表面平整 ,粗糙度 (RMS)为 6 .2 5 7nm ,平均晶粒直径达 1.895 μm。室温PL测量该样品在 380nm处有很强的近带边发射 ,半峰全宽为 15nm。使用Hall测量检查了薄膜的电学性质。室温下该样品的载流子浓度为 2× 10 17cm-3 ,迁移率为 75cm2 ·V-1·s-1。用X射线双晶衍射和卢瑟福背散射 /沟道效应研究了薄膜的结晶质量 ,样品的双晶衍射ω扫描半峰全宽为 0 .0 4° ,沟道效应的最小产额比χmin为 3.1%。     

MgxZn1-xO/Au/MgxZn1-xO夹层透明导电薄膜的制备及光电性质研究

采用操作简单的溶胶-凝胶法和射频磁控溅射法在石英衬底上分别制备了MgxZn1-xO薄膜和MgxZn1-xO/Au/MgxZn1-xO夹层结构的透明导电薄膜并对样品进行退火处理。利用紫外-可见分光光度计、X射线衍射仪、光致发光、霍尔效应测试对在不同退火温度下薄膜的晶体结构、光学和电学性质进行表征分析,并研究退火温度对其影响。测试结果表明:所制备的薄膜样品均具有良好的c轴(c-axis)取向并呈现出六角纤锌矿结构。Mg组分的增加使得ZnO基薄膜的光学带隙逐渐增大,PL发光谱和吸收光谱的谱线出现了明显的蓝移现象,但薄膜的电学特性有所降低。而在MgxZn1-xO/Au/MgxZn1-xO夹层结构的薄膜样品中,Au夹层的存在使薄膜的光学性质变差,在紫外区域透光率约为60%。但薄膜的电学性质得到明显改善,相比MgxZn1-xO薄膜,其电阻率和迁移率显著提高。此外通过高温退火处理可以有效提高所制备薄膜的晶体质量,进一步提高样品电学特性,其中经过500℃退火后的薄膜迁移率达到了40.9cm2·Vs-1,电阻率为0.005 7Ω·cm。但随着退火温度的进一步升高,薄膜晶体尺寸从25.1nm增大到32.4nm,从而降低了该薄膜的迁移率。因此该夹层结构的MgxZn1-xO/Au/MgxZn1-xO薄膜对于促进ZnO基透明导电薄膜在深紫外光学器件中的应用有重要作用。     

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.