Intraband absorption in the 8-12 mu m band from Si-doped vertically aligned InGaAs/GaAs quantum-dot superlattice

Normal-incident infrared absorption in the 8-12-mu m-atmospheric spectral window in the InGaAs/GaAs quantum-dot superlattice is observed. Using cross-sectional transmission electron microscopy, we find that the InGaAs quantum dots are perfectly vertically aligned in the growth direction (100). Under the normal incident radiation, a distinct absorption peaked at 9.9 mu m is observed. This work indicates the potential of this quantum-dot superlattice structure for use as normal-incident infrared imaging focal arrays application without fabricating grating structures. (C) 1998 American Institute of Physics. [S0003-6951(98)01151-6].

A 12-bit 300 MHz CMOS DAC for high-speed system applications

This paper describes a 12-bit 300 MHz CMOS DAC for high-speed system applications. The proposed DAC consists of a unit current-cell matrix for 8 MSBs and a binary-weighted array for 4 LSBs. In order to ensure the linearity of DAC, a double Centro symmetric current matrix is designed by using the Q(2) random walk strategy. To minimize the feedthrough and improve the dynamic performance, the drain of the switching transistors is isolated from the output lines by adding two cascoded transistors.

A direct digital frequency synthesizer with fourth-order phase domain Delta Sigma noise shaper and 12-bit current-steering DAC

This paper presents a direct digital frequency synthesizer (DDFS) with a 16-bit accumulator, a fourth-order phase domain single-stage Delta Sigma interpolator, and a 300-MS/s 12-bit current-steering DAC based on the Q(2) Random Walk switching scheme. The Delta Sigma interpolator is used to reduce the phase truncation error and the ROM size. The implemented fourth-order single-stage Delta Sigma noise shaper reduces the effective phase bits by four and reduces the ROM size by 16 times. The DDFS prototype is fabricated in a 0.35-mu m CMOS technology with active area of 1.11 mm(2) including a 12-bit DAC. The measured DDFS spurious-free dynamic range (SFDR) is greater than 78 dB using a reduced ROM with 8-bit phase, 12-bit amplitude resolution and a size of 0.09 mm(2). The total power consumption of the DDFS is 200)mW with a 3.3-V power supply.

12 W high efficiency single frequency ring laser

Single-frequency output power of 12 W at 1064 nm is demonstrated. Pumped by a fiber-coupled diode laser, the Nd:YVO4 produces 58.6% of the slope efficiency with respect to absorbed pump power, and 52.7% of the optical-optical efficiency and nearly diffraction-limited output with a beam quality parameter of M-2 approximate to 1.11. To the best of our knowledge, this is the highest slope efficiency and optical-optical efficiency in single-frequency Nd:YVO4 ring laser. The slope efficiency of the single frequency laser is close to the limit of the efficiency. [GRAPHICS] output spectrum of the single-frequency Nd:YVO4 ring laser

假单胞菌P_(12)对菲的降解

从武汉石油化工厂的活性污泥中，分离到一株可以以菲为唯一碳源和能源的假单胞菌P_(12)该菌经靛蓝产生法测定有双加氧酶，在菲无机盐培养基中生长时，有3-菲酚物质积累，经检测有一条质粒带。用丝裂霉素C消除质粒后的菌落，失去了降解菲的能力，说明P_(12)对菲的降解功能是由质粒控制的。

Pulse-front matched ultra-broadband optical parametric chirped pulse amplifier for sub-12 fs pulse generation

We propose a LBO-based ultra-broadband chirped pulse optical parametric amplifier employing pulse-front-matching to yield transform-limited sub-12-fs pulses. Measurement of the maximum possible gain bandwidth for the LBO-based OPCPA demonstrates more than 60nm gain bandwidth FWHM. For the generation of TL pulses by the use of this OPCPA, a suitable combination of OPCPA and PFM is first presented. The PFM pump geometry realizes tilt-free signal amplification, and permits this OPCPA to generate TL sub-12-fs pulses.

Cyanex302及CA-12萃取稀土动力学的研究

随着萃取技术的不断发展，人们日益要求更加深入的了解萃取过程的机制及其动力学特性。以便有效地控制和强化萃取过程，提高萃取效率，或者利用萃取动力学的差异来实现某些分离嘴过程。尽管许多萃取过程进行得很快，但是人们也发现不少的金属鳌合物萃取体系，其萃取过程相当缓慢。因而这类体系的萃取机制和萃取动力学问题已日益引人注目。除此而外，在设计，放大或改进萃取设备时，研究和掌握有关萃取过程的动力学规律也有十分重要意义。在本文中主要对稀土萃取动力学进行了研究，得到主要结果如下：1．研究了硫代有机磷酸Cyan.ex302萃取饵的动力学。通过测定各种萃取条件对萃取速率的影响，获得了萃取速率方程，并讨论了萃取的控制过程。实验发现萃取剂中的杂质对萃取具有较大的加速作用，这对工业生产具有一定的实际意义。2.用两相滴定法测定了两种新合成的J梭酸萃取剂CA-12和CA-100的某些重要的物理常数。这将有助于深入研究它们的萃取性质及机理。3．用层流恒界面池研究了CA-12萃取La, Gd,Er, Yb和Y的动力学。考察了各种因素对萃取速率的影响，获得了它们的萃取速率方程，实验发现了它们的萃取控速步骤并推测了其萃取机理。4．研究了HEHEHP对CA-12萃取Yb和Y的动力学的影响。实验发现在CA一12中加入少量的HEHEHP后，萃取活化能显著降低，萃取速率明显加快。由于加入HEHEHP后，萃取Yb的活化能的降低要比萃取Y的活化能降低的程度大'，所以使Yb和Y的萃取分离因素加大。5．用两相滴定法研究了HEHEHP萃取铭的机理，CA-12萃取稀土及其相关离子的机理。并计算了它们相应的平衡常数。

Co(salen)作为辅酶B_(12)模型物及化学修饰电极的电化学研究

本论文从合成Co(salen)开始，对Co(salen)在电化学现场合成辅酶B_(12)模型物的工作进行了尝试。进一步地，用Co(salen)制作了两种化学修饰电极，并对它们的性质进行了较为详细的考察。同时还将这两种修饰电极应用于电催化研究工作，得到了较为满意的结果。

Kinetics of dissociative water adsorption on stepped Si(001), on Si(115), Si(113), Si(5,5,12) and Si(112)

We present photoelectron spectroscopic and low energy electron diffraction measurements of water adsorption on flat Si samples of the orientations (001), (115), (113), (5,5,12) and (112) as well as on curved samples covering continuously the ranges (001)-(117) and (113)-(5,5,12)-(112). On all orientations, water adsorption is dissociative (OH and H) and non-destructive. On Si(001) the sticking coefficient S and the saturation coverage Theta(sat) are largest. On Si(001) and for small miscuts in the [110]-azimuth, S is constant nearly up to saturation which proves that the kinetics involves a weakly bound mobile precursor state. For (001)-vicinals with high miscut angles (9-13 degrees), the step structure breaks down, the precursor mobility is affected and the adsorption kinetics changed. On (115), (113), (5,5,12) and (112), the values of S and Theta(sat) are smaller which indicates that not all sites are able to dissociate and bind water. For (113) the shape of the adsorption curves Theta versus exposure shows the existence of two adsorption processes, one with mobile precursor kinetics and one with Langmuir-like kinetics. On (5,5,12), two processes with mobile precursor kinetics are observed which are ascribed to adsorption on different surface regions within the large surface unit cell. From the corresponding values of S and Theta(sat), data for structure models are deduced. (C) 1997 Elsevier Science B.V.

Electron diffraction and photoemission studies of clean and water-covered Si(5,5,12) and Si(112) surfaces

The structure of silicon surfaces in the orientation range (113)-(5,5,12)-(337)-(112) has been investigated using high resolution LEED and photoemission both on a spherical and on flat samples. We find that Si(5,5,12) [5.3 degrees from (113) and 0.7 degrees from (937)] is the only stable orientation between (113) and (111) and confirm the result of Baski et al. [Science 269, 1556 (1995)] that it has a 2 x 1 superstructure with a very large unit cell of 7.68 x 53.5 Angstrom(2). Adsorption measurements of water on Si(5,5,12) yield a mobile precursor kinetics with two kinds of regions saturating at 0.25 and 0.15 ML which are related to adsorption on different sites. Using these results, a modified structure model is proposed. Surfaces between (113) and (5,5,12) separate into facets of these two orientations; between (5,5,12) and (112), they separate into (5,5,12) and (111) facets. (337) facets in this range may be considered as defective (5,5,12) facets.

Long period two-dimensional gratings for 8-12 mu m quantum well infrared photodetectors

By considering all possible high order diffracted waves, the authors investigate the spectral response of two-dimensional gratings for quantum well infrared photodetectors (QWIPs). A new method is proposed that using long period gratings may improve grating quality and reduce the resulting cross talk in grating-coupled QWIPs. A sensitivity analysis indicates that the influence of variation of the grating constant on the coupling efficiency is less sensitive for the long period gratings than for the short ones. A large coupling efficiency has been demonstrated for long period gratings. The calculated wide grating response spectra are in good agreement with the experiment result. (C) 1996 American Institute of Physics.

Absorption and Raman spectra of Se-8-ring clusters in zeolite 5A

Samples with different weight ratio of Se to zeolite 5A (Se composition) have been prepared by loading Se into the cages of zeolite 5A and the measurements of the absorption and Raman spectra have been carried out for the prepared samples. The measured absorption edges of the samples close and blue shifted to the value for monoclinic Se containing Se-8-ring, suggesting the formation of Se-8-ring clusters dagger in the cages. The continuous and broadening features of the absorption spectra are interpreted by the strong electron-phonon coupling in Se-8-ring clusters. The sample with high Se composition has a red shift of the absorption band edge relative to the samples with less Se composition. It is tentatively attributed to the reason that with different Se composition, single Se-8-ring clusters and double Se-8-ring clusters are formed in the cages of zeolite 5A. A single broad band at about 262 cm(-1) is observed in the Raman spectra, that gives the further support of the formation of Se-8-ring clusters. Copyright (C) 1996 Elsevier Science Ltd