17 resultados para 331.87

em Chinese Academy of Sciences Institutional Repositories Grid Portal


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We report an experiment of trapping of neutral Rb-87 atoms on a, self-made atomchip. The H-shaped atomchip is made by magnetron sputtering technology, which is different from the atomchip technology of other teams. We collect 3 x 10(6) Rb-87 atoms in the mirror magneto-optical trap (MOT) using the external MOT coils, and 1 X 10(5) Rb-87 atoms are transferred to U-MOT using U-shaped wire in chip and a pair of bias coils.

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This paper has observed linewidth narrowing of dark states in rubidium cell by using the Hanle configuration. The reduction of the coherent resonance width under the transition of Rb-87 F-g = 1 -> F-e = 0 is observed and the qualitative explanation about its mechanism is presented. Multiple subnatural width dips are obtained with a linearly polarized laser beam for the transition of Rb-87 F-g = 0, 1, 2. The feature of negative and positive slope, namely dispersionlike feature, is observed in the transmitted light.

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We have experimentally studied the parametric excitation of Rb-87 atoms in a quadrupole-Ioffe-configuration trap. The temperature of an atomic cloud and number of trapped atoms versus time and modulation frequency of the parametric excitation field have been measured. We also noticed that the contribution of atomic collisions to the energy distributions can not be ignored in the case of weak excitation, which results in a lower temperature of the atomic cloud than by Gehm [Phys. Rev. A 58, 3914 (1998)] predicted.

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We report a room temperature study of the direct band gap photoluminescence of tensile-strained Ge/Si0.13Ge0.87 multiple quantum wells grown on Si-based germanium virtual substrates by ultrahigh vacuum chemical vapor deposition. Blueshifts of the luminescence peak energy from the Ge quantum wells in comparison with the Ge virtual substrate are in good agreement with the theoretical prediction when we attribute the luminescence from the quantum well to the c Gamma 1-HH1 direct band transition. The reduction in direct band gap in the tensile strained Ge epilayer and the quantum confinement effect in the Ge/Si0.13Ge0.87 quantum wells are directly demonstrated by room temperature photoluminescence.

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Self-aligned InAs quantum wires (QWRs) or three-dimensional (3D) islands are fabricated on GaAs(331)A substrates by molecular beam epitaxy (MBE). InAs QWRs are selectively grown on the step edges formed by GaAs layers. The surface morphology of InAs nanostructures is carefully investigated by atomic force microscopy (AFM) measurements. Different growth conditions, such as substrate temperature, growth approaches, and InAs coverage, exert a great effect on the morphology of InAs islands. Low substrate temperatures favour the formation of wirelike nanostructures, while high substrate temperatures favour 3D islands. The shape transition is attributed to the trade-off between surface energy and strain energy. A qualitative agreement of our experimental data with the theoretical results derived from the model proposed by Tersoff and Tromp is achieved.

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We have studied the effect of molecular beam epitaxy growth conditions on the surface morphology of strained InAs/GaAs(331)A films. Our results reveal that InAs nanowires aligned along the [1 (1) over bar0] direction are formed under As-rich conditions, which is explained by the effect of anisotropic buffer layer surface roughing. Under In-rich conditions, however, the surface morphology of the InAs layers is characterized by a feature of island-pit pairs. In this case, cooperative nucleation of islands and pits can lower the activation barrier for domain growth. These results suggest that the surface morphology of strained InAs layers is highly controllable. (C) 2005 American Institute of Physics.

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Morphology evolution of high-index GaAs(331)A surfaces during molecular beam epitaxy (MBE) growth has been investigated in order to achieve regularly distributed step-array templates and fabricate spatially ordered low-dimensional nano-structures. Atomic force microscope (AFM) measurements have shown that the step height and terrace width of GaAs layers increase monotonically with increasing substrate temperature. By using the step arrays formed on GaAs(331)A surfaces as the templates, we have fabricated highly ordered InGaAs nanowires. The improved homogeneity and the increased density of the InGaAs nanowires are attributed to the modulated strain field caused by vertical multi-stacking, as well as the effect of corrugated surface of the template. Photoluminescence (PL) tests confirmed remarkable polarization anisotropy.

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Self-organized InAs quantum wires (QWRs) were fabricated on the step edges of the GaAs (331)A surface by molecular beam epitaxy. The lateral size of InAs QWRs was saturated by the terrace width (i.e., 90 nm) while the size along the step lines increased with the increasing thicknesses of the InAs layers, up to 1100 nm. The height of InAs QWRs varied from 7.9 nm to 13 nm. The evolution of the morphology of InAs QWRs was attributed to the diffusion anisotropy of In adatoms.

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Morphology evolution of high-index (331)A surfaces during molecular beam epitaxy (MBE) growth have been investigated in order to uncover their unique physic properties and fabricate spatially ordered low dimensional nanostructures. Atomic Force Microscope (AFM) measurements have shown that the step height and terrace width of GaAs layers increase monotonically with increasing substrate temperature in conventional MBE. However, this situation is reversed in atomic hydrogen-assisted MBE, indicating that step bunching is partly suppressed. We attribute this to the reduced surface migration length of Ga adatoms with atomic hydrogen. By using the step arrays formed on GaAs (331)A surfaces as the templates, we fabricated laterally ordered InGaAs self-aligned nanowires.

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Surface morphology evolution of strained InAs/GaAs(331)A films was systematically investigated in this paper. Under As-rich conditions, InAs elongated islands aligned along [1 (1) over bar0] are formed at a substrate temperature of 510 degrees C. We explained it as a result of the anisotropic diffusion of adatoms. Under In-rich conditions, striking change has occurred with respect to the surface morphology of the InAs layers. Instead of anisotropic InAs elongated islands, unique island-pit pairs randomly distributed on the whole surface were observed. Using cooperative nucleation mechanisms proposed by Jesson et al. [Phys. Rev. Lett. 77, 1330 (1996)], we interpret the resulting surface morphology evolution.

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Step like morphology of (331)A high-index surfaces during atomic hydrogen assisted molecular beam epitaxy (MBE) growth has been investigated. Atomic Force Microscope (AFM) measurements show that in conventional MBE, the step heights and terrace widths of GaAs layers increase monotonically with increasing substrate temperatures. The terrace widths and step densities increase with increasing the GaAs layer thickness and then saturates. And, in atomic hydrogen assisted MBE, the terrace width reduces and density increases when depositing the same amount of GaAs. It attributes this to the reduced surface migration length of Ga adatoms with atomic hydrogen. Laterally ordered InAs self-aligned nano-wires were grown on GaAs (331)A surfaces and its optical polarization properties were revealed by photoluminescence measurements.

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采用分子束外延方法在CaAs(331)A高指数衬底上制备自对齐InAs纳米线(QWRs)或者三维(3D)岛状结构.InAs纳米线(QWRs)选择性生长在CaAs层的台阶边缘.通过原子力显微镜(AfM)仔细研究了InAs纳米微结构的表面形貌,发现不同的生长条件,包括:衬底温度、生长速率、和InAs层厚度等,对InAa表面形貌有很大的影响.如,低温更容易导致线状纳米微结构的形成,而高温更利于3D岛状结构形成.表面形貌的转变归结于表面能同应变能之间的竞争.