Peculiar photocurrent response due to Gamma-X coupling in a GaAs/AlAs heterostructure

Peculiar current jumps and hysteresis in current-voltage curves are reported in an illuminated heterostructure consisting basically of a thick AlAs layer and a narrow GaAs quantum well. These novel features come from the photon-assisted transfer of electron-hole pairs and the resultant charge polarization in the structure, mainly caused by the resonant Gamma-X coupling at the heterointerfaces. Using the transfer-matrix method, the simulated current density-voltage curve reproduces the main features of the experimental observations in the case where the influence of resonant Gamma-X coupling at the heterointerfaces is included, further confirming the physical mechanism involved. The structure presented here may be used as a new type of photonic memory cell and also as an optically controlled switch.

TUNNELING ESCAPE TIME OF ELECTRONS FROM A QUANTUM-WELL WITH GAMMA-X MIXING EFFECT

By using the envelope function method we calculated the tunneling escape time of electrons from a quantum well. We adopted a simplified interface matrix to describe the GAMMA-X mixing effect, and employed a wave packet method to determine the tunneling escape time. When the GAMMA state in the well was in resonance with the X state in the barrier, the escape time reduced remarkably. However, it was possible that the wave functions in two different channels, i.e., GAMMA-GAMMA-GAMMA and GAMMA-X-GAMMA, could interfere destructively, leading the escape time greater than that of pure GAMMA-GAMMA-GAMMA tunneling.

NEW FORMATION MECHANISM OF ELECTRIC-FIELD DOMAIN DUE TO GAMMA-X SEQUENTIAL TUNNELING IN GAAS/ALAS SUPERLATTICES

We have studied the sequential tunneling of doped weakly coupled GaAs/ALAs superlattices (SLs), whose ground state of the X valley in AlAS layers is designed to be located between the ground state (E(GAMMA1)) and the first excited state (E(GAMMA2)) of the GAMMA valley in GaAs wells. The experimental results demonstrate that the high electric field domain in these SLs is attributed to the GAMMA-X sequential tunneling instead of the usual sequential resonant tunneling between subbands in adjacent wells. Within this kind of high field domain, electrons from the ground state in the GaAs well tunnel to the ground state of the X valley in the nearest AlAs layer, then through very rapid real-space transfer relax from the X valley in the AlAs layer to the ground state of the GAMMA valley of the next GaAs well.

STATE MIXING IN INAS/GAAS QUANTUM DOTS AT THE PRESSURE-INDUCED GAMMA-X CROSSING

于2010-11-17批量导入

激波管壁AlO自由基B~2∑~+-X~2∑~+和C~2∏_r-X~2∑~+带系辐射光谱的研究

爆轰驱动过程中产生的高温高压气流对铝质膜片、激波管壁产生烧蚀和冲刷作用,以致激波管壁、端盖上附有氧化铝等杂质,而高温下AlO自由基在气体分子的高速碰撞下被激发并产生强烈的辐射,从而干扰了高温气体辐射光谱的分析。用爆轰驱动加热技术将空气加热到4 000~7 000 K,利用多通道光学分析仪对AlO自由基辐射光谱进行分析,实验发现在460~530 nm波长范围内有多支辐射非常强烈的AlO自由基B2Σ+-X2Σ+(T00=20 689 cm-1)带系辐射谱带,且每支谱带都由多个带头组成,带头间隔约为2 nm,带头处于高频位置并向低频方向伸延。通过实验与理论计算相结合,重点分析了AlO自由基B2Σ+-X2Σ+带系辐射光谱的结构特征。AlO自由基C2Πr-X2Σ+(T00=33 047 cm-1)带系辐射光谱处于270~335 nm波长范围内,其辐射强度相对于B2Σ+-X2Σ+带系较弱,并且与OH基A2Σ+-X2Π(T00=32 682 cm-1)带系辐射光谱互相干扰而难以分辨,对该波段高温空气的辐射光谱分析产生不利的影响。

Fabrication, thermal stability and mechanical properties of novel (W0.5Al0.5)C-0.8-Co composite prepared by mechanical alloying and hot-pressing sintering

A novel cemented carbides (W0.5Al0.5)C-0.8-Co with different cobalt contents were prepared by mechanical alloying and hot-pressing technique. Hot-pressing technique as a common technique was performed to fabricate the bulk bodies of the hard alloys. The novel cemented carbides have superior mechanical properties compared to WC-Co. The density, operating cost of the novel material were much lower than WC-Co. There is almost no eta-phase in the (W0.5Al0.5)C-0.8-Co cemented carbides system although the carbon deficient get the value of 20%, and successfully got the nanostructured rounded (W0.5Al0.5)C-0.8 particles.

(Ce_(0.9)Nd_(0.1))_(1-x)Mo_xO_(2-δ)(0.00≤x≤0.10)的合成、表征与电性能

采用溶胶-凝胶法合成(Ce0.9Nd0.1)1-xMoxO2-δ(x=0.00、0.02、0.05、0.10)氧化物,通过X射线衍射(XRD)、场发射扫描电镜(FESEM)等手段对氧化物进行结构表征,交流阻抗谱测试电性能.结果表明:所有样品均为单一萤石立方结构;少量MoO3的加入提高了材料的致密性,降低了材料的总电阻、晶界电阻和晶界电阻在总电阻中所占比例,提高了材料的电导率.1200℃烧结样品24h,测试温度700℃时,(Ce0.9Nd0.1)1-xMoxO2-δ(x=0.00)总电导率和晶界电导率分别为0.05和0.19S·m-1,掺Mo材料(Ce0.9Nd0.1)1-xMoxO2-δ(x=0.02)的总电导率和晶界电导率分别为2.42和3.96S·m-1.

High-pressure sintering study of a novel hard material (W0.5Al0.5)C-0.5 without binder metal

A novel hard material of (W0.5Al0.5)C-0.5 has been successfully sintered under high-pressure (4.5 GPa). The influence of sintering time and temperature on the microstructure, Vickers microhardness and density of the as-prepared specimens are well described. Interestingly, sintering temperature has an amazing influence on the hardness, density and microstructure of the specimen while the sintering time does not. It is found that the most suitable sintering condition from our work is 1600 degrees C and 10 min under pressure of 4.5 GPa. The hardness and relative density of the as-prepared sample can reach 2340 kg mm(-2) and 98.62%, respectively. The cell parameters of the sintered specimen is found to be little smaller than that of the powder, which we propose is related to the high pressure.

Convenient preparation and properties of C-60(OH)(x)

In this paper, we introduce a very convenient method to produce water soluble C-60 derivatives- fullerols by the reaction of C-60 with potassium in toluene solution, FT-IR, H-1 NMR and FABMS proved the multi-hydroxyl and C-60 cage structures of the products, The properties of unstability to light, heat, basicity of aqueous solution and the solubility in some common polar solvents were also described.

新的稀土锂钒酸盐[Y_(0.5-x)Li_(1.5)VO_4:(Dy~(3+),Eu~(3+))_x]多波段发光

本文首次报道了新的稀土锂钒酸盐Y_(0.5-x)Li_(1.5)VO_4:(Dy~(3+),Eu~(3+))_x多晶粉末的制备,多波段发光和结构. 样品的制备是采用稀土氧化物(Y_2O_3Dy_2O_3和Eu_2O_3)纯度为99.99％与光谱纯的V_2O_5和Li_2CO_3按化学计量比混匀,在

Estudio del vitrocerámico (1-x) Li2B4O7-xBi2WO6 (0 > x < 0.35) usando el método Rietveld

[Tesis] ( Maestría en Ciencias con Orientación en Ingeniería Cerámica) U.A.N.L.

Aplicación de los Diagramas de Gantt a la programación del B.U.P. y C.0.U.

Las fases necesarias para elaborar un diagrama de Gant son: determinación de las actividades principales; estimación de la duración efectiva de las mismas; enunciación en el diagrama de las actividades principales y de su relación entre si; representación gráfica de su duración; su utilización sus limitaciones, las actividades que se presentan tienen que ser limitadas perfectamente sin excederse en detalles. Tienen a su favor que son fácilmente realizables por personas no especializadas y que su representación sinóptica e intuitiva es muy útil. En definitiva, podemos decir que es un método útil para las programaciones de los docentes y puede contribuir a la mejora de la enseñanza, ya que proporciona un método sencillo de resumir las progresiones efectuadas y anotar la marcha de las actividades es de fácil seguimiento y una clara visión de conjunto lo que contribuirá a una clara coordinación.

C(0) and bi-Lipschitz K-equivalence of mappings

In this paper we investigate the classification of mappings up to K-equivalence. We give several results of this type. We study semialgebraic deformations up to semialgebraic C(0) K-equivalence and bi-Lipschitz K-equivalence. We give an algebraic criterion for bi-Lipschitz K-triviality in terms of semi-integral closure (Theorem 3.5). We also give a new proof of a result of Nishimura: we show that two germs of smooth mappings f, g : R(n) -> R(n), finitely determined with respect to K-equivalence are C(0)-K-equivalent if and only if they have the same degree in absolute value.