银纳米线的侧向生长及其抑制研究

采用多元醇法,在不同温度,不同PVP滴加速度和加入量的条件下合成了银纳米线。利用XRD, UV-Vis, SEM和TEM对银纳米线及其侧向生长过程进行了观察和分析。UV-Vis表明银纳米线在纵向生长的同时发生了侧向生长。而且表示银纳米线侧向生长的紫外吸收光谱峰在银纳米线合成后期发生了明显的红移,由384 nm红移至约388 nm处,表明银纳米线合成后期直径迅速增长,银纳米线发生了快速的侧向生长。SEM研究表明银纳米线直径在反应前期(15～23 min)只增加了20 nm,而在反应后期(23～30 min)银纳米线直径增加了近150 nm,SEM观察结果与UV-Vis分析结论一致。同时还发现银纳米线直径不仅与晶种大小有关而且与银线外覆盖的银层厚度有关,银源以吸附在银线侧面的小银颗粒为附着点沿其侧面多点沉积导致了银纳米线的侧向生长;降低反应液温度(165 ℃降至155 ℃),降低PVP滴加速度(67 mL·h-1减小到49 mL·h-1)以及减少银纳米线合成后期PVP加入量可抑制银纳米线的侧向生长,显著提高银纳米线长径比,银纳米线直径由200 nm减小至100 nm左右,长度仍保持在100 μm以上。     

Y掺杂Si纳米线的光致发光特性

以n型单晶Si(111)为衬底,利用Au作为催化剂,在温度、N₂流量和生长时间分别为1 100 ℃,1.5 L·min-1和60 min的条件下,基于固-液-固生长机制,生长了直径为60～80 nm、长度为数十微米的高密度Si纳米线。随后,以Y₂O₃粉末为掺杂源,采用高温扩散方法对Si纳米线进行了钇(Y)掺杂。利用扫描电子显微镜、X射线衍射仪和荧光分光光度计对不同掺杂温度(900～1 200 ℃)、掺杂时间(15～60 min)和N₂流量(0～400 sccm)等工艺条件下制备的Y掺杂Si纳米线的形貌、成分、结晶取向以及激发光谱和发射光谱特性进行了详细的测量和表征。结果表明,在掺杂温度为1 100 ℃,N₂流量为200 sccm、掺杂时间为30 min和激发波长为214 nm时,Y掺杂Si纳米线样品表现出较好的发光特性。样品分别在470～500和560～600 nm范围内出现了两条发光谱带。560～600 nm的发光带由两个发光峰组成,峰位分别为573.6和583.8 nm,通过结构分析可以推测,这两个发光峰是由Y3+在Si纳米线的带隙中引入的杂质能级引起的。而470～500 nm较宽的发光带同样来源于Y离子在Si纳米线带隙中引入的与非晶SiO_x壳层中氧空位能级十分接近的杂质能级。     

Ce掺杂Si纳米线的制备及其蓝光发射特性

以抛光和“金字塔”织构表面的单晶Si(100)为衬底,分别以Au和Au-Al为金属催化剂,在温度为1 100 ℃、N₂气流量为1 500 sccm、生长时间为15～60 min等工艺条件下,制备了直径约为50～200 nm、长度为数微米至数十微米和不同分布的Si纳米线。然后,利用CeO₂粉末为掺杂剂,在温度为1 100～1 200 ℃、N₂流量为1 000 sccm、掺杂时间为30～60 min等工艺条件下对Si纳米线进行Ce掺杂。实验研究了不同Si纳米线长度、密度和分布等对Ce3+蓝光发射的影响。室温下利用Hitachi F-4600型荧光分光光度计对样品的激发光谱和发射光谱进行了测试和分析,同时利用FLS920全功能型荧光光谱仪对样品的荧光量子效率进行了测试。结果表明,在Si纳米线生长时间为30 min、织构表面和密度相对较低时以及最佳激发光波长为328 nm时,样品发射光波长为405 nm(5d→2F_5/2)荧光强度较大,实现了强的蓝光发射,其荧光量子效率达到了65.57%。通过光谱功率分布和CIE-1931标准公式进行计算,Ce掺杂Si纳米线样品的色坐标为(0.16, 0.03);发光强度大,量子效率高使其在照明、显示等领域有着潜在的应用价值,同时对Si纳米线在发光领域的研究和应用具有一定的参考价值。     

锡催化剂助生长法制备孪晶ZnO纳米线及其结构表征

用SnO和Zn的均匀混合物在高温下共烧通过VLS机制制备出孪晶ZnO纳米线的均匀结构。SEM图像显示孪晶ZnO纳米线的直径在100~200nm之间,长度在几十微米到几百微米之间的范围内,有的甚至达到了毫米级,产率也非常的高。TEM图像中ZnO孪晶纳米线顶端的金属Sn颗粒表明了孪晶结构的Sn催化生长。高分辨电子图谱显示了氧化锌纳米线孪晶结构的特征。电子衍射分析发现孪晶氧化锌的晶带轴的方向是[0110],孪晶面为(1013),并且通过明场像和暗场像分析了孪晶纳米线的晶格关系,确定了孪晶纳米线的汽-液-固(VLS)生长机制。     

硅和锗纳米线的原子排布和电荷分布的密度泛函紧束缚方法研究

低维硅锗材料是制备纳米电子器件的重要候选材料，是研发高效率、低能耗和超高速新一代纳米电子器件的基础材料之一，有着潜在的应用价值。采用密度泛函紧束缚方法分别对厚度相同、宽度在0.272 nm~0.554 nm之间的硅纳米线和宽度在0.283 nm~0.567 nm之间的锗纳米线的原子排布和电荷分布进行了计算研究。硅、锗纳米线宽度的改变使原子排布，纳米线的原子间键长和键角发生明显改变。纳米线表层结构的改变对各层内的电荷分布产生重要影响。纳米线中各原子的电荷转移量与该原子在表层内的位置相关。纳米线的尺寸和表层内原子排列结构对体系的稳定性产生重要影响。     

Tb掺杂Si纳米线的光致发光特性

以金属Au-Al为催化剂,在温度为1 100 ℃,N₂气流量为1 500 sccm、生长时间为30 min,从Si(100)衬底上直接生长了直径约为50～120 nm、长度为数百纳米的高密度、大面积的Si纳米线。然后,利用Tb₂O₃在不同温度(1 000～1 200 ℃)、掺杂时间(30～90 min)和N₂气流量(0～1 000 sccm)等工艺条件下对Si纳米线进行了Tb掺杂。最后,对Si(100)衬底进行了Tb掺杂对比。室温下,利用荧光分光光度计(Hitachi F-4600) 测试了Tb掺杂Si纳米线的光致发光特性。实验研究了不同掺杂工艺参数(温度、时间和N₂气流量)对Tb3+绿光发射的影响。根据Tb3+能级结构和跃迁特性对样品的发射光谱进行了分析。结果表明,在温度为1 100 ℃,N₂气流量为1 500 sccm、时间为30 min等条件下制备的Si纳米线为掺杂基质,Tb掺杂温度为1 100 ℃,N₂气流量为1 000 sccm、光激发波长为243 nm时,获得了最强荧光发射,其波长为554 nm(5D₄→7F₅),同时还出现强度相对较弱的494 nm(5D₄→7F₆),593 nm(5D₄→7F₄)和628 nm(5D₄→7F₃)三条谱带。Tb掺杂的体Si衬底在波长554 nm处仅有极其微弱的光致发光峰。     

氧化锡纳米线的拉曼光谱和光致发光光谱研究

用表面限制剂对水热法生成的前驱物加以限制生长的方法成功制备了氧化锡纳米线结构,TEM和HRTEM的结果表明该纳米线由沿[001]方向生长的氧化锡单晶组成,纳米线直径在5-10纳米、长度100-500纳米。利用拉曼光谱和发光光谱对其生长过程和发光现象进行了详细的研究,结果表明,细长的氧化锡纳米线出现356、515、691 cm-1新的拉曼振动模以及600 nm较强的光致发光。     

衬底对化学气相沉积法制备氧化硅纳米线的影响

通过化学气相沉积法在不同衬底上制备了大量的氧化硅纳米线.选用衬底为Si片、带有约100nm厚SiO2氧化层Si片和石英片.利用场发射扫描电子显微镜(SEM)和透射电镜(TEM，配备有能谱仪)对样品的表面形貌、结构和成分进行研究.结果表明：这些纳米线都为非晶态，但在不同衬底上生长的纳米线形貌、尺寸和化学成分不同.讨论了各种衬底对不同特征氧化硅纳米线生长的影响. 关键词： 化学气相沉积 纳米线 纳米颗粒     

硫掺杂ZnO纳米线的电化学制备及发光特性

"采用电场辅助电化学沉积法,利用阳极氧化铝模板模板制备了高度择优取向的硫掺杂ZnO单晶纳米线．X射线衍射仪、隧道电子显微镜、选取电子衍射对所得样品的结构、形貌分析表明,所得纳米线是沿(101)择优取向的六方纤锌矿结构单晶纳米线,长约几十微米、平均直径约70 nm. X射线光电子能谱对化学组成的分析进一步证实掺杂硫原子的存在．用荧光光谱仪(PL)对S掺杂前后的ZnO纳米线进行光学特性测量发现,S掺杂较大地改变了ZnO纳米线的发光性质．在PL谱中,除了有典型的ZnO纳米线在378、392 nm处的强紫外发光峰     

Eu掺杂Si纳米线的光致发光特性

利用Si(111)衬底, 以Au-Al为金属催化剂, 基于固-液-固生长机理, 在温度为1100℃, N₂气流量为1.5 L/min、生长时间为30–90 min等工艺条件下, 制备了直径约为100 nm、长度为数微米的高密度、均匀分布、大面积的Si纳米线(～10¹⁰ cm^-2). 对Si纳米线进行了Eu掺杂, 实验研究了不同长度的Si纳米线以及不同掺杂温度、掺杂时间等工艺参数对Eu离子红光发射的影响, 利用扫描电子显微镜和X射线衍射仪对Si纳米线表面形貌和Eu掺杂后Si纳米线的结晶取向进行了测量和表征; 室温下利用Hitachi F-4600型荧光分光光度计对样品的激发光谱和发射光谱进行了测试和分析. 结果表明: 在Si纳米线生长时间为30 min、掺杂温度为1000℃、 最佳激发波长为395 nm时, 样品最强荧光波长为619 nm (⁵D₀→⁷F₂); 同时, 还出现了576 nm (⁵D₀→⁷F₀), 596 nm (⁵D₀→⁷F₁), 658 nm (⁵D₀→⁷F₃)和708 nm (⁵D₀→⁷F₄)四条谱带.     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

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.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

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.     

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.