Fracture properties of silicon carbide thin films by bulge test of long rectangular membrane

This paper reports the mechanical properties and fracture behavior of silicon carbide (3C-SiC) thin films grown on silicon substrates. Using bulge testing combined with a refined load-deflection model of long rectangular membranes, which takes into account the bending stiffness and prestress of the membrane material, the Young's modulus, prestress, and fracture strength for the 3C-SiC thin films with thicknesses of 0.40 and 1.42 mu m were extracted. The stress distribution in the membranes under a load was calculated analytically. The prestresses for the two films were 322 +/- 47 and 201 +/- 34 MPa, respectively. The thinner 3C-SiC film with a strong (111) orientation has a plane-gstrain moduli of 415 +/- 61 GPa, whereas the thicker film with a mixture of both (111) and (110) orientations exhibited a plane-strain moduli of 329 +/- 49 GPa. The corresponding fracture strengths for the two kinds of SiC films were 6.49 +/- 0.88 and 3.16 +/- 0.38 GPa, respectively. The reference stresses were computed by integrating the local stress of the membrane at the fracture over edge, surface, and volume of the specimens and were fitted with Weibull distribution function. For the 0.40-mu m-thick membranes, the surface integration has a better agreement between the data and the model, implying that the surface flaws are the dominant fracture origin. For the 1.42-mu m-thick membranes, the surface integration presented only a slightly better fitting quality than the other two, and therefore, it is difficult to rule out unambiguously the effects of the volume and edge flaws.

High responsivity resonant-cavity-enhanced InGaAs/GaAs quantum-dot photodetector for wavelength of similar to 1 mu m at room temperature

The characteristics of a resonant cavity-enhanced InGaAs/GaAs quantum-dot n-i-n photodiode with only a bottom distributed Bragg reflector used as the cavity mirror, are reported. To suppress the dark current, an AlAs layer is inserted into the device structure as the blocking layer. It turns out that the structure still possesses the resonant coupling nature, and makes Rabi splitting discernible in the photoluminescence spectra. The measured responsivity spectrum of the photocurrent shows a peak at lambda = 1030 nm, and increases rapidly as the bias voltage increases. A peak responsivity of 0.75 A/W, or equivalently an external quantum efficiency of 90.3%, is obtained at V-bias = -1.4 V.

Magneto - Transport of electron symmetric and antisymmrtric states in highly doped InGaAs/InAlAs single quantum well

Beating patterns in longitudinal resistance caused by the symmetric and antisymmetric states were observed in a heavily doped InGaAs/InAlAs quantum well by using variable temperature Hall measurement. The energy gap of symmetric and antisymmetric states is estimated to be 4meV from the analysis of beating node positions. In addition, the temperature dependences of the subband electron mobility and concentration were also studied from the mobility spectrum and multicarrier fitting procedure.

Growth of Ge quantum dot mediated by boron on Ge wetting layer

We, report on the influence of boron on the formation of Ge quantum dots. The investigated structure consists of a Ge wetting layer, on which a sub-monolayer boron is deposited and subsequently a Ge top layer. For sufficiently thin Ge top layers, the strain field induced by boron on Ge wetting layer destabilizes the Ge top layer and causes the formation of small Ge quantum dots. However, for thicker Ge top layers, boron on the Ge wetting layer diffuses into Ge layers, compensates partly the strain and delays the evolution of Ge quantum dots. By this method, small Ge quantum dots with high density as well as size uniformity can be formed by optimizing the growth condition. (c) 2005 Elsevier B.V. All rights reserved.

Effects of phase-breaking on long-range charge transfer in DNA: Partially-coherent-tunneling model study

The mechanism of hole charge transfer in DNA of various lengths and sequences is investigated based on a partially coherent tunneling theory (Zhang et al., J Chem Phys 117:4578, 2002), where the effects of phase-breaking in adenine-thymine and guanine-cytosine base pairs are treated on equal foot. This work aims at providing a self-consistent microscopic interpretation for rate experiments on various DNA systems. We will also clarify the condition under which the simple superexchange-mediated-hopping picture is valid, and make some comments on the further development of present theory.

Cathodoluminescence on GaN hexagonal pyramids on submicron dot-patterns via selective MOVPE

Three-dimensional GaN pyramids have been successfully obtained on submicron dot-patterned (0001) sapphire substrates by using the selective metalorganic vapor phase epitaxy (MOVPE) technique. The dot-pattern is a hexagon arranged with a 0.5-mu m width and 1.0-mu m spacing. The GaN structure comprises a hexagonal pyramid covered with six {1 (1) over bar 01} pyramidal facets on the side of a hexagonal pyramid having a (0001) facet on the top. Cathodoluminescence (CL) measurement was carried our. on the hexagonal pyramid at low temperature. Two distinct spectra were observed to occur at about 359 and 329 nm. The higher energy is thought to be related to GaN dot, and the lower one is due to GaN dot band edge emission. The intensities of the two spectra were investigated as a function of temperature in the range of 135-150 K. (C) 2000 Published by Elsevier Science B.V.

“中介逻辑”与Woodruff三值逻辑系统

在《“中介逻辑”的特征问题》一文里,我们对近来朱梧梗、肖奚安等同志发表的称为“中介逻辑”的命题系统MP的三个联接词(对立否定),～(模糊否定)与→(蕴含)建立了如下的三值真值表:

多线程程序数据竞争的静态检测

多线程并发程序的广泛使用带来了更多的数据竞争错误．传统的数据竞争静态检测由于对并发语义和别名信息的保守分析会导致很多假错误．因此，提出了一个精确有效的静态检测框架：分析应用了精确的别名分析并静态模拟了访问事件发生序；为提高分析效率，检测算法提出了一个以对象为中心，结合Escape分析缩小检测范围的检测算法并配合设计了压缩的别名等价类表示．检测框架在一个静态Java编译器JTool上做了实现，对于测试程序取得了很好的分析结果．

本氏针茅与柳枝稷光合生理生态特征比较研究

采用美国LI—COR公司生产的Li-6400便携式光合测定系统,选择在干旱季节里,在田间自然条件下,测定并比较研究了引种牧草柳枝稷和天然牧草本氏针茅两种禾本科植物的光合生理生态特征的日变化。结果表明,柳枝稷属于高光合、低蒸腾和高水分利用效率的植物,具有较强的气孔调节能力。柳枝稷之所以具有较高的光合速率,主要是因为它具有较强的叶肉细胞羧化能力,较低的气孔导度降低了蒸腾速率,从而提高了水分利用效率;本氏针茅属于较低光合,较高蒸腾和低水分利用效率的植物,但二者均能在黄土高原保持良好的生长。