Functional organic single crystals for solid‐state laser applications

Because of long‐range order and high chemical purity, organic crystals have exhibit unique properties and attracted a lot of interest for application in solid‐state lasers. As optical gain materials, they exhibit high stimulated emission cross section and broad tunable wavelength emission as similar to their amorphous counterpart; moreover, high purity and high order give them superior properties such as low scattering trap densities, high thermal stability, as well as highly polarized emission. As electronic materials, they are potentially able to support high current densities, thus making it possible to realize current driven lasers. This paper mainly describes recent research progress in organic semiconductor laser crystals. The building molecules, crystal growth methods, as well as their stimulated emission characteristics related with crystal structures are introduced; in addition, the current state‐of‐the‐art in the field of crystal laser devices is reviewed. Furthermore, recent advances of crystal lasers at the nanoscale and single crystal light‐emitting transistors (LETs) are presented. Finally, an outlook and personal view is provided on the further developments of laser crystals and their applications.     

基于微扫描镜的激光投影

利用微机械加工技术制造出一种新型微扫描镜,结合半导体激光器,可用于投影显示.激光器发出的光束被两个分别沿着X轴、Y轴扭转的镜面相继反射,扫描出二维图形.实验测得扫描镜在15 V电压,频率为扫描镜谐振频率2倍的方波信号驱动下,镜子的光学扫描角度达±12°.由于每个镜子都沿各自轴以简谐规律扭转,扫描所得投影为李萨如图形.通过分析图形的形成原理并用Matlab仿真,选出了适用用于任意图案显示的扫描镜谐振频率组合(X轴2 400 Hz, Y轴2 425 Hz).该组合可以形成194×192个像素点,刷新频率为25 Hz.在此基础上提出了一种通过调制激光开关来进行投影显示的方法.     

石英晶体振荡法监控膜厚研究

给出了石英晶体振荡法监控膜厚的基本原理,在相同的工艺条件下分别用光电极值法和石英晶体振荡法监控膜厚,对制备的增透膜的反射光谱曲线进行了比较,并对石英晶体振荡法的监控结果做了误差分析.结果表明:石英晶体振荡法不仅膜厚监控精度高,而且能监控沉积速率,获得稳定的膜层折射率,从而有效地控制薄膜的光学性能.     

An STM study of the localized atomic reaction of 1,2- and 1,4-dibromobenzene at Si(1 1 1)-7 × 7

A comparative study is reported of the thermal reaction of 1,2- and 1,4-dibromobenzene (1,2- and 1,4-diBrPh) on Si(1 1 1)-7 × 7, investigated by STM. Some results are given for the intermediate case of 1,3-diBrPh. The STM images gave evidence of a different pattern of reaction to yield pairs of Br-Si for 1,2-, 1,3- and 1,4-diBrPh. The ratio of pairs of Br-Si to single bromination events was 1:2 for 1,2-diBrPh and 1:3 for 1,4-diBrPh. In many cases organic residue from the bromination reaction, R-Si, was evident in the STM image. The products R-Si and Br-Si were found to be bound to adjacent Si, for both 1,2- and 1,4-diBrPh. The mean Br?Br pair separation at the surface depended on the parent molecule, being 7.6 Å for 1,2-diBrPh, 10.3 Å for 1,3-diBrPh, and 11.3 Å for 1,4-diBrPh. These separations are, in each case, about 4 Å greater than the separation of the Br-atoms in the intact parent molecule, which increases systematically down the series. There was a marked decrease in the percentage of R-Si accompanying the Br-Si in going down the series, decreasing from 70% for 1,2- to 20% for 1,4-diBrPh; this was interpreted as being due to a decrease in the percentage of `benzene-mediated' reaction dynamics, in which the benzene ring was bound to the surface. At moderately increased surface temperature (45 °C) the reaction of 1,2- and also 1,4-diBrPh no longer resulted in R-Si formation, suggesting that the dynamics had altered from benzene-mediated to `bromine-mediated'.     

Effect of annealing on the nanoscratch behavior of multilayer Si0.8Ge0.2/Si films

In this study, we examined the nanoscratch behavior of annealed multilayered silicon-germanium (SiGe) films comprising alternating sublayers (Si) deposited using an ultrahigh-vacuum chemical vapor deposition (UHV/CVD) system. Annealing consisted of ex situ thermal treatment in a furnace system. We used a nanoscratch technique to investigate the nanotribological behavior of the SiGe films and atomic force microscopy (AFM) to observe deformation phenomena. Our AFM morphological studies of the SiGe films revealed that pile-up phenomena occurred on both sides of each scratch. The scratched surfaces of the SiGe films that had been subjected to various annealing conditions exhibited significantly different features, it is conjectured that cracking dominates in the case of SiGe films while ploughing dominates during the scratching process. We obtained higher coefficients of friction (μ) when the ramped force was set at 6000 μN, rather than 2000 μN, suggesting that annealing of SiGe films leads to higher shear resistance; annealing treatment not only produced misfit dislocations in the form of a significantly wavy sliding surface but also promoted scratching resistance.     

盐酸氯丙嗪1H NMR、 13C NMR谱的归属及结构表征

通过运用¹H-¹H COSY(¹H-¹H COrrelation SpectroscopY)、TOCSY(TOtal Correlation SpectroscopY)、HSQC(Heteronuclear Single Quantum Correlation)、HMBC (Heteronuclear Multiple Bond Correlation)、NOESY(Nuclear Overhauser Enhancement SpectroscopY)等多种二维核磁技术,对盐酸氯丙嗪（Chlorpromazine hydrochloride CPZ· HCl）在CDCl₃、CD₃COCD₃和D₂O三种溶剂中的¹H、¹³C NMR谱进行了准确归属（重点集中于谱峰重叠程度较高的芳香族区域）．实验表明：杂环上N与苯环存在部分共轭;在CDCl₃、CD₃COCD₃中,侧链卷曲至芳环上方处于屏蔽区,且侧链上N为较稳定的四面体构型;比较了CPZ· HCl在不同溶剂与浓度下的¹H NMR谱的变化,对文献中其核磁共振谱（特别是芳香区的谱峰）归属的争议作了解释．量子化学计算结果与实验结果相吻合．     

Assignment of surface IR absorption spectra observed in the oxidation reactions: 2H + H2O/Si(1 0 0) and H2O + H/Si(1 0 0)

Infrared reflection absorption spectroscopy that used buried metal layer substrates (BML-IRRAS) and density functional cluster calculations were employed to investigate the water related oxidation reactions of 2H + H₂O/Si(1 0 0)-(2 × 1), 2D + H₂O/Si(1 0 0)-(2 × 1), and H₂O + H/Si(1 0 0)-(2 × 1). In addition to the oxygen inserted coupled monohydrides, which were previously reported in the former reaction system, we report several other oxidized Si hydride species in our BML-IRRAS experiments. Three new pairs of vibrational bands are identified between 900 and 1000 cm⁻¹. These vibrational frequencies were calculated using Si9 and Si10 cluster models that included all possible structures from zero to five oxygen insertions into the top layer silicon atoms using a B3LYP gradient corrected density functional method with a polarized 6-31G** basis set for all atoms. The three pairs of vibrational modes are assigned to the scissoring modes of adjacent and isolated SiH₂ with zero, one, and two oxygen atoms inserted into the Si back bonds. All the other newly observed vibrational peaks related to Si oxidation are also assigned in this study. The Si-O stretching bands observed in the reaction 2D + H₂O/Si(1 0 0)-(2 × 1) show an isotope effect, which suggests that in the system 2H + H₂O/Si(1 0 0)-(2 × 1) also, hydrogen atom tunneling plays an important role for the insertion of oxygen atoms into Si back bonds that form oxidized adjacent dihydrides.     

Investigation of a mutual interaction force at different pressure amplitudes in sulfuric acid

This paper investigates the secondary Bjerknes force for two oscillating bubbles in various pressure amplitudes in a concentration of 95% sulfuric acid.The equilibrium radii of the bubbles are assumed to be smaller than 10 μm at a frequency of 37 kHz in various strong driving acoustical fields around 2.0 bars (1 bar=10 5 Pa).The secondary Bjerknes force is investigated in uncoupled and coupled states between the bubbles,with regard to the quasi-adiabatic model for the bubble interior.It finds that the value of the secondary Bjerknes force depends on the driven pressure of sulfuric acid and its amount would be increased by liquid pressure amplitude enhancement.The results show that the repulsion area of the interaction force would be increased by increasing the driven pressure because of nonlinear oscillation of bubbles.     

不同气体环境下532nm激光诱导硅表面形貌的研究

研究了在不同气体环境下,利用532 nm Nd∶YAG纳秒脉冲激光累积辐照单晶硅表面形成的微结构,结果表明,在其他条件相同,背景气体不同的情况下,背景气体对硅表面形貌的形成起着重要的作用。具体分析了真空、N2和SF6 3种环境气氛下形成的微结构,结果显示,在SF6中形成的锥形微结构的数密度比在N2和真空中的大,并且锥形具有更大的纵横比;在N2、真空和SF6中形成的微结构尺寸依次减小。SF6气氛下,激光辅助化学刻蚀的效率比在真空和N2气氛中的高。另外,辐照区域边缘有波纹微结构形成,分析认为,该微结构的形成是由表面张力波的冷却导致的。     

Photoemission intensity oscillations in the valence bands of C70 film

We have measured and analyzed the photoemission spectra (PES) of a C₇₀ film in the photon energy region from 13.4 eV to 98.4 eV. The photoelectron intensities of two C 2p π-derived features (denoted by A and B) oscillate regularly in the whole energy region with some fine structures below ∼30 eV. To obtain the detailed information of the oscillations, we have developed a sophisticated but practical procedure for intensity calculation. The procedure consists of two core concepts. The first is ascribing the PES features to their corresponding molecular orbitals with the help of density functional calculations. The second is a background subtraction algorithm. With this procedure, we obtained the oscillating behavior for individual features (A and B), which is by and large consistent with the predictions based on the spherical symmetric approximation although C₇₀ has the ellipsoidal shape. Owing to the solid state effect, the oscillating amplitudes of the A/B intensity ratios are smaller than those of gas phase C₇₀, but an orbital shift reported recently was not observed on our sample. The oscillating curve of a deeper feature, which consists of both σ and π states, are also reported.