Films and fibers of oriented single wall nanotubes

As-produced nanotubes form a light, fragile and isotropic soot. Different efforts are made to process nanotubes into macroscopic forms of more practical use and more controlled properties. We briefly review in this paper two methods recently proposed to make films of magnetically aligned nanotubes and fibers by using an electrophoretic method. Preferential orientation of the nanotubes in the plane of the films or along the fiber axis is an important feature of the obtained materials. Then we describe in details a different, spinning like, process for making fibers out of single wall carbon nanotubes. This process consists of dispersing the nanotubes in a surfactant solution, re-condensing the nanotubes in the flow of a polymer solution to form a nanotube mesh, and then collating this mesh to a nanotube fiber. The behaviors of the surfactant-stabilized dispersions, which are also presented, are critical for this process. The degree of nanotubes alignment in dried fibers has been characterized by X-ray scattering. It is found to be smaller than the alignment obtained in the previous materials. However, the processing is simpler and faster and potentially scalable for large-scale production.     

Effect of doping polyacrylic acid with some dopants as studied by different techniques

The molecular weight of polyacrylic acid (PAA) was determined by a viscometric method using NaNO₃ as solvent at 30°C. The specific electric conductivities (σ) of PAA as well as PAA doped with carbon black (CB), chromium oxide (Cr₂O₃), and cupferron with different concentrations (from 0.25 to 1 wt %) were measured at a temperature range 360–400 K. IR spectra of some polymers were determined and it was shown that when PAA was doped with 0.5 wt % CB, a C? O? C band appeared at 775–875 cm^?1. The positron annihilation lifetime (PAL) spectra in PAA doped with the above‐mentioned dopants were measured as a function of their concentrations. It was observed that the short lifetime intensity I₁ decreased, whereas the intermediate lifetime intensity I₂, which is related to the conductivity of the material, increased with increasing the wt % of Cr₂O₃ and cupferron as well as at low concentrations of CB. These results are discussed in terms of the conducting island model. It was found that there were distinct positive relationships between σ and I₂. © 2002 John Wiley & Sons, Inc. J Appl Polym Sci 84: 877–883, 2002; DOI 10.1002/app.10381     

Origin of visible photoluminescence from porous silicon as studied by Raman spectroscopy

In this paper we discuss the different models proposed to explain the visible luminescence in porous silicon (PS). We review our recent photoluminescence and Raman studies on PS as a function of different preparation conditions and isochronal thermal annealing. Our results can be explained by a hybrid model which incorporates both nanostructures for quantum confinement and silicon complexes (such as SiH _x and siloxene) and defects at Si/SiO₂ interfaces as luminescent centres.     

Nd：MgO：LiNbO3晶体的荧光光谱及其双晶体腔内互倍频实验

采用激光感生荧光技术测量了Ｎｄ：ＭｇＯ：ＬｉＮｂＯ３晶体的偏振荧光光谱，简要地说明了Ｎｄ：ＭｇＯ：ＬｉＮｂＯ３双晶体腔内互倍频的基本原理，并在实验中用染料激光作泵浦源实现了其双晶体腔内互倍频运转；得到５４３ｎｍ横模倍频绿光单端输出约ＹＭＷ，腔前泵浦阈值约３８ＭＷ，总转换效率约为１．３％。     

短波长相干光与原子团受激发射

多种原子团及其离子已具有在VUV/XUV波段产生受激发射的能力。本文介绍了产生短波长相干辐射的方法、研究现状、研究方法和原子团的结构与受激发射。     

用变角XPS定量分析研究GaAs光电阴极激活工艺

用变角X射线光电子能谱 (XPS)技术分析了GaAs光电阴极的激活工艺 ,定量计算了阴极表面激活层和界面氧化层的厚度和组成。界面氧化物是由于O原子穿过激活层 ,扩散到GaAs与 (Cs,O)激活层的界面上而形成的。导入过量O会增加O GaAs界面层的厚度 ,而对 (Cs,O)激活层厚度影响较小。在激活过程中 ,严格控制和减少每次导入的O量是减少界面氧化层厚度 ,提高灵敏度的重要途径。在第一步激活后的阴极样品 ,通过较低温度的加热和再激活 ,能获得比第一步高出 30 %的光电灵敏度的原因是较低温度加热减少了界面氧化层的厚度和界面势垒     

氨基磺酸系高性能减水剂的研制开发

本文主要讨论了氨基磺酸系高性能减水剂的合成过程及后期混凝土试验情况。通过对反应温度、反应时间、溶液浓度和酸碱度、投料顺序及速度、第四单体的选择等反应条件的控制,合成具有最佳分子结构的最终产物,并通过红外光谱图和核磁共振谱图对合成主产物的分子结构进行了验证。同时,大量的混凝土试验说明氨基磺酸高性能减水剂具有优良的保坍性能。     

Charge transfer resistance of spray deposited and compressed counter electrodes for dye-sensitized nanoparticle solar cells on plastic substrates

Electrochemical impedance spectroscopy was used to determine the effective charge transfer resistances of porous dye-sensitized solar cell counter electrodes prepared by low-temperature spray deposition and compression of conductive carbon and platinized Sb-doped SnO₂ powders on indium tin oxide-coated plastic substrates. The charge transfer resistances were 0.5–2 and 8–13 Ω cm², respectively, when using 3-methoxypropionitrile as the electrolyte solvent. The manufacturing method used lends itself to produce mechanically stable and even-quality electrodes in an easy and fast manner.     

Investigation of Ni/4H-SiC diodes as radiation detectors with low doped n-type 4H-SiC epilayers

The development of SiC minimum ionising particle (MIP) detectors imposes severe constrains in the electronic quality and the thickness of the material due to the relatively high value of the energy required to produce an electron–hole pair in this material by MIP against the value for Si. In this work, particle detectors were made using semiconductor epitaxial undoped n-type 4H-SiC as the detection medium. The thickness of the epilayer is on the order of 40 μm and the detectors are realised by the formation of a nickel silicide on the silicon surface of the epitaxial layer (Schottky contact) and of the ohmic contact on the back side of 4H-SiC substrate. The low doping concentration (6×10¹³ cm⁻³) of the epilayer allows the detector to be totally depleted at relatively low reverse voltages (100 V). We present experimental data on the charge collection properties by using 5.486 MeV -particles impinging on the Schottky contact. A 100% charge collection efficiency (CCE) is demonstrated for reverse voltages higher than the one needed to have a depletion region equal to the -particle extrapolated range in SiC. The diffusion contribution of the minority change carriers to CCE is pointed out. By comparing measured CCE values to the outcomes of drift–diffusion simulation, values are inferred for the hole lifetime within the neutral region of the charge carrier generation layer.