Defect and structural imperfection effects on the electronic properties of BiTeI surfaces

The surface electronic structure of the narrow-gap seminconductor BiTeI exhibits a large Rashba-splitting which strongly depends on the surface termination. Here we report on a detailed investigation of the surface morphology and electronic properties of cleaved BiTeI single crystals by scanning tunneling microscopy, photoelectron spectroscopy (ARPES, XPS), electron diffraction (SPA-LEED) and density functional theory calculations. Our measurements confirm a previously reported coexistence of Te- and I-terminated surface areas

New generation of two-dimensional spintronic systems realized by coupling of Rashba and Dirac fermions

Intriguing phenomena and novel physics predicted for two-dimensional (2D) systems formed by electrons in Dirac or Rashba states motivate an active search for new materials or combinations of the already revealed ones. Being very promising ingredients in themselves, interplaying Dirac and Rashba systems can provide a base for next generation of spintronics devices, to a considerable extent, by mixing their striking properties or by improving technically significant characteristics of each other. Here, we demonstrate that in BiTeI@PbSb2Te4 composed of a BiTeI trilayer on top of the topological insulator (TI) PbSb2Te4 weakly- and strongly-coupled Dirac-Rashba hybrid systems are realized. The coupling strength depends on both interface hexagonal stacking and trilayer-stacking order. The weakly-coupled system can serve as a prototype to examine, e.g., plasmonic excitations, frictional drag, spin-polarized transport, and charge-spin separation effect in multilayer helical metals. In the strongly-coupled regime, within similar to 100 meV energy interval of the bulk TI projected bandgap a helical state substituting for the TI surface state appears. This new state is characterized by a larger momentum, similar velocity, and strong localization within BiTeI. We anticipate that our findings pave the way for designing a new type of spintronics devices based on Rashba-Dirac coupled systems.

Medição de espessura de filmes eletrodepositados em suporte metálico por EDXRF

Esse trabalho apresenta a técnica de fluorescência de raios X por dispersão de energia (EDXRF) para calcular a espessura de filmes metálicos finos por ser de custo relativamente baixo, não destrutiva e que permite também uma análise qualitativa e até quantitativa dos elementos do revestimento. As espessuras do Níquel, Zinco e Cromo sobre aço, foram calculadas utilizando cinco procedimentos diferentes e todas as relações matemáticas obtidas foram baseadas na lei de atenuação de Beer-Lambert, que relaciona as intensidades Kα e/ou Kβ e as relações específicas do material (coeficiente de atenuação, μm). Os resultados experimentais para as espessuras do Zinco e Níquel, utilizando somente a intensidade Kα, apresentaram valores próximos dos valores estimados. Quando foi considerada a razão Kα/Kβ, os resultados experimentais divergiram bastante do estimado. Para calcular a espessura do Cromo foi necessário utilizar um método em que as camadas são calculadas separadamente, pois o revestimento de Cromo é composto por múltiplas camadas (Cromo, Cobre e Níquel), Os resultados para a espessura do Cromo foram satisfatórios.

Effects of pot fishing on the physical condition of snow crab (Chionoecetes opilio) and southern Tanner crab (Chionoecetes bairdi)

The effects of commercial fishing with crab pots on the physical condition of the snow crab (Chionoecetes opilio) and southern Tanner crab (C. bairdi) were investigated in the Bering Sea and in Russian waters of the Sea of Okhotsk. In crabs that were subjected to pot hauling, the presence of gas embolism and the deformation of gill lamellae were found in histopathological investigations. Crab vitality, which was characterized subjectively through observation of behavioral responses, depended on not only the number of pot hauls but also the time between hauls. Immediately after repeated pot hauls at short time intervals (≤3 days), we observed a rapid decline in vitality of crabs. When hauling intervals were increased to >3 days, the condition of crabs did not significantly change. After repeated pot hauls, concentration of the respiratory pigment hemocyanin ([Hc]) was often lower in the hemolymph of crabs than in the hemolymph of freshly caught animals. Our research indicated that changes in [Hc] in crabs after repeated pot hauls were caused by the effects of decompression and not by starvation of crabs in pots or exposure of crabs to air. We suggest that the decrease in [Hc] in hemolymph of snow and southern Tanner crabs was a response to the adverse effects of decompression and air-bubble disease. The decrease in [Hc] in affected crabs may be a result of mechanisms that regulate internal pressure in damaged gills to optimize respiratory circulation.

On a classical problem of acoustic wave scattering by a free vortex: Numerical modelling

The scattering of sound from a point source by a Rankine vortex is investigated numerically by solving the Euler equations with the novel high-resolution CABARET method. For several Mach numbers of the vortex, the time-average amplitudes of the scattered field obtained from the numerical modeling are compared with the theoretical scaling laws' predictions. Copyright © 2009 by Sergey Karabasov.

Microphotoluminescence investigation of InAs quantum dot active region in 1.3 mu m vertical cavity surface emitting laser structure

Microphotoluminescence (mu-PL) investigation has been performed at room temperature on InAs quantum dot (QD) vertical cavity surface emitting laser (VCSEL) structure in order to characterize the QD epitaxial structure which was designed for 1.3 mu m wave band emission. Actual and precise QD emission spectra including distinct ground state (GS) and excited state (ES) transition peaks are obtained by an edge-excitation and edge-emission (EEEE) mu-PL configuration. Conventional photoluminescence methods for QD-VCSELs structure analysis are compared and discussed, which indicate the EEEE mu-PL is a useful tool to determine the optical features of the QD active region in an as-grown VCSEL structure. Some experimental results have been compared with simulation results obtained with the aid of the plane-wave admittance method. After adjustment of epitaxial growth according to EEEE mu-PL measurement results, QD-VCSEL structure wafer with QD GS transition wavelength of 1300 nm and lasing wavelength of 1301 nm was obtained.

~(19)F+~(27)Al耗散反应产物激发函数的长程关联

在中国原子能科学研究院的HI-13串列静电加速器上完成了19F+27Al耗散反应产物的激发函数测量。束流19F的入射能量从110.25MeV到118.75MeV,步长250keV,测量了实验室系+57°,+31°,-15°和-29°出射的类弹产物B,C,N,O,F和Ne的激发函数。观测到激发函数具有耗散反应的特征涨落结构,分析了激发函数之间的长程角度关联以及强烈的电荷数关联。

重离子弹性散射中的角分散研究

简要评述了重离子弹性散射角分散研究的内容、方法及物理意义。通过前角区重离子弹性散射产物微分截面的角分布测量,作出角分散图ln(dσ/dθ)-θ2。分析经典偏转函数,从而在实验上确定了反应系统的核虹角。在低能、重靶的重离子反应系统中,核虹角远小于擦边角。晕核及弱束缚核比稳定核具有更小的核虹角和更大的核相互作用范围。经典偏转函数的计算有助于提供一套光学势参数,以便于拟合弹性散射产物的微分截面。

小角度范围内弱束缚核~(17)F弹性散射微分截面的奇异行为(英文)

在兰州放射性束流线(RIBLL)上完成了17F／17O+208Pb的弹性散射微分截面角分布测量．分析了17F／17O弹性散射产物微分截面的对数(ln(dσ／dθ))随散射角平方(θ2)的依赖关系．结果表明,在所测量的角度范围内(6°-20°),17O的这一依赖关系可以用一条直线很好地拟合,而17F的这一依赖关系需要两条不同斜率的直线才能拟合．17F数据拟合中的这种斜率改变可能起因于17F的奇异结构．对其他实验组数据的分析支持以上的结论,即在一定的角度范围内,弱束缚核与稳定核相比,弹性散射产物微分截面的对数与散射角平方的依赖关系有明显的差异,这可以作为深入研究“晕核”和“皮核”的一个新探针．

~(19)F+~(27)Al耗散反应中双核系统的转动与形变

测量了19F+27Al耗散反应产物B,C,N,O,F和Ne的激发函数,入射束流的能量从110．25MeV 到118．75MeV,能量步长为250keV．从产物的能量自关联函数中提取了反应中所形成的中间双核系统的转动惯量,与相粘模型计算的刚体转动惯量相比较,结果表明形成的双核系统有大的形变．

~(19)F+~(27)Al耗散反应产物截面测量中的不重复性

在中国原子能科学研究院的HI-13串列静电加速器上完成了114MeV和118．75MeV的19F+27Al 耗散反应产物B,C,N,O,F,Ne,Na和Mg的微分截面测量．条形27Al同位素靶的大小尺寸为 10mm×50mm,平均厚度约67μg／cm2．固定入射束流19F的能量,通过移动靶位,先后轰击了靶上20个不同的位置．实验结果表明,在弹靶系统、入射能量以及探测系统都相同的多次独立的微分截面测量中,截面的涨落不呈现高斯型几率分布．截面测量的这种不重复现象难以用有限计数率的统计性质来解释．

(19)~F+(27)~Al耗散反应中双核系统的转动与衰变

测量了19F+27Al耗散反应产物B,C,N,O,F和Ne的激发函数,入射束流的能量从110.25MeV 到118.75MeV,能量步长为250keV.用能量自关联函数方法从激发函数中提取了各反应产物的平均衰变宽度,利用同时考虑反应中所形成的中间双核系统的转动特性和衰变特性而发展了的Ericson核反应统计理论,讨论了19F+27Al耗散反应中双核系统随时间的演化过程.

~(19)F+~(27)Al反应产物的角分布、角分散与耗散机制

完成了114MeV19F+27Al深部非弹性碰撞产物的角分布测量.分析了反应产物B,C,N,O,F,Ne,Na,Mg和Al的实验室系角分布,讨论了反应形成的中间双核系统随时间演化过程中角分布所表现出的耗散特点.从实验上提取了反应产物各元素的角分散参数并作了角分散参数的理论拟合,讨论了角分散参数的物理意义以及角分散参数与耗散反应产物的电荷数Z之间的依赖关系.

~(19)F+~(27)Al深部非弹性碰撞产物的角分布

完成了19F+27Al深部非弹性碰撞产物的角分布测量.初步分析了反应产物B,C,N,O,F,Ne,Na,Mg和Al的实验室系角分布,展现出深部非弹性反应机制的特点,显示了反应系统随时间的演化过程.