KARYOTYPE EVOLUTION OF SHREW MOLES (SORICOMORPHA: TALPIDAE)

The Chinese long-tailed mole (Scaptonyx fusicaudus) closely resembles American (Neurotrichus gibbsii) and Japanese (Dymecodon pilirostris and Urotrichus talpoides) shrew moles in size, appearance, and ecological habits, yet it has traditionally been classified either together with (viz subfamily Urotrichinae) or separately (tribe Scaptonychini) from the latter genera (tribe Urotrichini sensu lato). We explored the merit of these competing hypotheses by comparing the differentially stained karyotypes of S.fusicaudus and N. gibbsii with those previously reported for both Japanese taxa. With few exceptions, diploid chromosome number (2n = 34), fundamental autosomal number (FNa = 64), relative size, and G-banding pattern of S. fusicaudus were indistinguishable from those of D. pilirostris and U. talpoides. In fact, only chromosome 15 differed significantly between these species, being acrocentric in D. pilirostris, subtelocentric in U. talpoides, and metacentric in S. fusicaudus. This striking similarity is difficult to envisage except in light of a shared common ancestry, and is indicative of an exceptionally low rate of chromosomal evolution among these genera. Conversely, the karyotype of N. gibbsii deviates markedly in diploid chromosome and fundamental autosomal number (2n = 38 and FNa = 72, respectively), morphology, and G-banding pattern from those of Scaptonyx and the Japanese shrew moles. These differences cannot be explained by simple chromosomal rearrangements, and Suggest that rapid chromosomal reorganization Occurred ill the karyotype evolution of this species, possibly due to founder or bottleneck events.

基于从头算的缬氨酸两性离子和水分子的相互作用势

首先用从头算方法计算缬氨酸两性离子同处于160种不同位置的水分子的相互作用能, 计算 时采用最小基组并进行了基组重叠修正, 最后对计算得的相互作用能Slater-Kirkwood 公式作色散能修正; 然后进行势函数的拟合, 即舍弃12个相互作用能大于5Kcal/mole或原子间距离小于1.68A的布点, 对其余148个布点进行拟合。拟合结果的标准偏差为SD=0.48Kcal/mole。图1表3参13

Theoretical gain of strained GeSn0.02/Ge1-x-y ' SixSny ' quantum well laser

Using effective-mass Hamiltonian model of semiconductors quantum well structures, we investigate the electronic structures of the Gamma-conduction and L-conduction subbands of GeSn/GeSiSn strained quantum well structure with an arbitrary composition. Our theoretical model suggests that the band structure could be widely modified to be type I, negative-gap or indirect-gap type II quantum well by changing the mole fraction of alpha-Sn and Si in the well and barrier layers, respectively. The optical gain spectrum in the type I quantum well system is calculated, taking into account the electrons leakage from the Gamma-valley to L-valley of the conduction band. We found that by increasing the mole fraction of alpha-Sn in the barrier layer and not in the well layer, an increase in the tensile strain effect can significantly enhance the transition probability, and a decrease in Si composition in the barrier layer, which lowers the band edge of Gamma-conduction subbands, also comes to a larger optical gain.

Al composition variations in AlGaN films grown on low-temperature GaN buffer layer by metalorganic chemical vapor deposition

We have investigated the optical properties of AlGaN grown on sapphire. It is found that two main luminescence peaks occur in the cathodoluminescence (CL) spectra of AlGaN films, and their energy separation increases with the increase of Al source flux during the growth. Spatially resolved CL investigations have shown that the line splitting is a result of variation of AlN mole fraction within the layer. The Al composition varies in both lateral and vertical direction. It is suggested that the difference in the surface mobility of Al and Ga atoms, especially, its strong influence on the initial island coalescence process and the formation of island-like regions on the uneven film surface, is responsible for the Al composition inhomogeneity. (C) 2008 Elsevier B.V. All rights reserved.

Investigations on V-defects in quaternary AlInGaN epilayers

The characteristics of V-defects in quaternary AlInGaN epilayers and their correlation with fluctuations of the In distribution are investigated. The geometric size of the V-defects is found to depend on the In composition of the alloy. The V-defects are nucleated within the AlInGaN layer and associated with threading dislocations. Line scan cathodoluminescence (CL) shows a redshift of the emission peak and an increase of the half width of the CL spectra as the electron beam approaches the apex of the V-defect. The total redshift decreases with decreasing In mole fraction in the alloy samples. Although the strain reduction may partially contribute to the CL redshift, indium segregation is suggested to be responsible for the V-defect formation and has a main influence on the respective optical properties. (C) 2004 American Institute Of Physics.

Lateral phase separation in AlGaN grown on GaN with a high-temperature AIN interlayer

The influences of a high-temperature (HT) AlN interlayer (IL) on the phase separation in crack-free AlGaN grown on GaN have been studied. The depth-dependent cathodoluminescence (CL) spectra indicate a relatively uniform Al distribution in the growth direction, but the monochromatic CL images and the CL spectra obtained by line scan measurements reveal a lateral phase separation in AlGaN grown on relatively thick HT-AlN ILs. Moreover, when increasing the thickness of HT-AlN IL, the domain-like distribution of the AlN mole fraction in AlGaN layers is significantly enhanced through a great reduction of the domain size. The morphology of mesa-like small islands separated by V trenches in the HT-AlN IL, and the grain template formed by the coalescence of these islands during the subsequent AlGaN lateral overgrowth, are attributed to be responsible for the formation of domain-like structures in the AlGaN layer. (c) 2005 American Institute of Physics.

The effect of In content on high-density InxGa1-xAs quantum dots

We have successfully grown self-assembled InxGa1-xAs (x = 0.44, 0.47, 0.50) quantum dots (QDs) with high density (> 10(11)/cm(2)) by MBE. The effect of In content on the high-density QD is investigated by atomic force microscopy (AFM) and photoluminescence (PL) spectra. It is found that sample with In-mole-fraction of 0.5 shows small size fluctuation and high PL intensity. The influence of growth temperature on high-density QD is also investigated in our experiment. (c) 2005 Elsevier B.V. All rights reserved.

Theoretical analysis of gate voltage-controlled subband states in an AlxGa1-xN/GaN heterostructure

The subband structure and inter-subband transition as a function of gate voltage are determined by solving the Schrodinger and Poisson equations self-consistently in an AlxGa1-xN/GaN heterostructure. Different aluminum mole fraction and thickness of AlxGa1-xN barrier are considered. Calculation results show that energy difference between the first and second subband covers a wide range (from several tens to hundreds milli-electron volt) by applying different gate voltage, which corresponds to the midinfrared and long-wave infrared wavelength scope. Furthermore, such a modulation on the subband transition energy is much more pronounced for the structure with thin barrier. When the applied positive gate voltage is increased, the triangle well formed at the interface turns to be deeper and narrower, which enhances the confinement for electrons. As a result, the overlap between electron wave function at two subbands increases, and thus the optical intersubband transition also enhances its intensity. This tendency is in good agreement with the available data in the literature. (c) 2005 Elsevier B.V. All rights reserved.

Crack-free InAlGaN quaternary alloy films grown on Si(111) substrate by metalorganic chemical vapor deposition

Crack-free In0.08Al0.25Ga0.67N quaternary films, with and without thick (> 1.5 mum) high-temperature-GaN (HTGaN) interlayer, have been grown on Si(1 1 1) substrates by a low-pressure metalorganic chemical vapor deposition (MOCVD) system. Mole fractions of In and Al in quaternary alloy layers are determined by Energy dispersive spectroscopy (EDS) and Rutherford backscattering spectrometry (RBS), which are recorded as similar to8% and similar to25-27%, respectively. High-resolution X-ray diffraction (HRXRD) and room temperature photoluminescence (RT-PL) results evidence the film's single crystal structure and the existence of local In- and/or Al-rich regions. Compared with GaN film grwon on Si(1 1 1) substrate, no crack is observed in the quaternary ones. Two explanations are proposed. First, mismatch-induced strain is relaxed significantly due to gradual changes of In concentration. Second, the weak In-N bond is likely to break when the sample is cooled down to the room temperature, which is expected to favor the releasing of thermal stress. (C) 2004 Elsevier B.V. All rights reserved.

Enhanced Pockels effect in GaN/AlxGa1-xN superlattice measured by polarization-maintaining fiber Mach-Zehnder interferometer

Six-period 4 nm GaN/10 nm AlxGa1-xN superlattices with different Al mole fractions x were prepared on (0001) sapphire substrates by low-temperature metal-organic chemical vapor deposition. The linear electro-optic (Pockels) effect was studied by a polarization-maintaining fiber-optical Mach-Zehnder interferometer system with an incident light wavelength of 1.55 mu m. The measured electro-optic coefficients, gamma(13)=5.60 +/- 0.18 pm/V, gamma(33)=19.24 +/- 1.21 pm/V (for sample 1, x=0.3), and gamma(13)=3.09 +/- 0.48 pm/V, gamma(33)=8.94 +/- 0.36 pm/V (for sample 2, x=0.1), respectively, are about ten times larger than those of GaN bulk material. The enhancement effect in GaN/AlxGa1-xN superlattice can be attributed to the large built-in field at the interfaces, depending on the mole fraction of Al. (C) 2007 American Institute of Physics.

The influence of internal electric fields on the transition energy of InGaN/gaN quantum well

We present a new way to meet the amount of strain relaxation in an InGaN quantum well layer grown on relaxed GaN by calculating and measuring its internal field. With perturbation theory, we also calculate the transition energy of InGaN/GaN SQWs as affected by internal fields. The newly reported experimental data by Graham et al. fit our calculations well on the assumption that the InGaN well layer suffered a 20% strain relaxation, we discuss the differences between our calculated results and the experimental data. Our calculation suggests that with the increase of indium mole fraction in the InGaN/GaN quantum well, the effect of polarization fields on the luminescence of the quantum well will increase. Moreover, our calculation also suggests that an increase in the quantum well width by only one monolayer can result in a large reduction in the transition energy. (c) 2006 Elsevier B.V. All rights reserved.

Modification of emission wavelength of self-assembled In(Ga)As/GaAs quantum dots covered by InxGa1-xAs(0 <= x <= 0.3) layer

Red shifts of emission wavelength of self-organized In(Cla)As/GaAs quantum dots (QDs) covered by 3 nm thick InxGa1-xAs layer with three different In mole fractions (x = 0.1, 0.2 and 0.3, respectively) have been observed. Transmission electron microscopy images demonstrate that the stress along growth direction in the InAs dots was reduced due to introducing the InxGa1-xAs (x = 0.1, 0.2 and 0.3) covering layer instead of GaAs layer. Atomic force microscopy pictures show a smoother surface of InAs islands covered by an In0.2Ga0.8As layer. It is explained by the calculations that the redshifts of the photoluminescence (PL) spectra from the QDs covered by the InxGa1-xAs (x greater than or equal to 0.1) layers were mainly due to the reducing of the strain other than the InAs/GaAs intermixing in the InAs QDs. The temperature dependent PL spectra further confirm that the InGaAs covering layer can effectively suppress the temperature sensitivity of PL emissions. 1.3 mum emission wavelength with a very narrow linewidth of 19.2 mcV at room temperature has been obtained successfully from In,In0.5Ga0.5As/GaAs self-assembled QDs covered by a 3-nm In0.2Ga0.2As strain reducing layer. (C) 2001 Elsevier Science B.V. All rights reserved.

Effect of InxGa1-xAs (0 <= x <= 0.4) capping layer on self-assembled 1.3 mu m wavelength InAs/GaAs quantum islands

We report the effect of InchiGa1-chiAs (0 less than or equal to chi less than or equal to0.4) capping layer on photoluminescence (PL) properties of 1.3 mum wavelength self-assembled InAs quantum islands, which are formed via depositing 3.5 monolayers (ML) InAs on GaAs (1 0 0) substrate by molecular beam epitaxy (MBE). Compared with the InchiGa1-chiAs capping layer containing a larger In mole fraction chi greater than or equal to0.2 and the GaAs capping layer (chi = 0), the InAs islands covered by the In0.1Ga0.9As layer show PL with lower emission energy, narrower full-width at half-maximum (FWHM), and quite stronger intensity. The PL peak energy and FWHM become more temperature dependent with the increase of In content in the InchiGa1-chiAs capping layer (chi greater than or equal to0.2), while the InAs islands covered by the In0.1Ga0.9As layer is much less temperature sensitive. In addition, the InAs islands covered by the In0.1Ga0.9As capping layer show room temperature PL wavelength at about 1.3 mum. (C) 2001 Published by Elsevier Science B.V.

Effects of interdiffusion on the luminescence of InAs/GaAs quantum dots covered by InGaAs overgrowth layer

We have studied the effects of postgrowth rapid thermal annealing on the optical properties of 3-nm-height InAs/GaAs quantum dots covered by 3-nm-thick InxGa1-xAs (x = 0, 0.1, and 0.2) overgrowth layer. At higher annealing temperature (T greater than or equal to 750 degreesC), the photoluminescence peak of InGaAs layer has been observed at lower-energy side of the InAs quantum-dot peak. In addition, the blueshift in photoluminescence (PL) emission energy is found to he similar for all samples with increasing the annealing temperature from 650 to 850 degreesC. However, the trend of narrowing of photoluminescence linewidth is significantly different for InAs quantum dots with different In mole fractions in InGaAs overgrowth layer. These results suggest that the intermixing in the lateral direction plays an important role in helping to understand the modification of optical properties induced by rapid thermal annealing. (C) 2000 Elsevier Science B.V. All rights reserved.

Application of the compatibility relationship(1) in seeking a functional relationship among species' equilibrium quantities in complex systems

A new algorithm, representing an important advance in determination of the functional relationship, is first reported here. The algorithm is very useful and convenient for analyzing the incorporation of impurities. To show how the algorithm works, two early and well-known vapor phase epitaxy (VPE) experiments-Ashen's (Ashen, D. J.; Dean, P. J.; Hurle, D. T. J.; Mullin, J. B.; Royle, A.; White, A. M. Gallium Arsenide and Related Compounds, Institute of Physics Conference Series 24, 1974; Institute of Physics: London, 1975; p 229.), involving the doping of silicon and DiLorenzo's (DiLorenzo, J. V. J. Cryst. Growth 1972, 17, 189.), involving the mole fraction effect-are calculated to find the functional relationship between the Si contamination and the partial pressure of HCl. The calculated curves agree with the experimental results. A conclusion that the calculated values are greater than the true values has been drawn.