Search Results - (Author, Cooperation:Y. Xin)

2018-01-19

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Geosciences

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Medicine

Natural Sciences in General

Physics

Genetics, Microbiology

2015-11-19

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

*Biomedical Research ; Developing Countries ; *Health Resources ; Humans ; *Internationality ; *Mental Disorders/epidemiology/genetics ; *Nervous System Diseases/epidemiology/genetics ; Substance-Related Disorders/epidemiology

2016-01-29

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

1089-7550

AIP Digital Archive

Physics

Nominal ZnTlBaCuO4.5, CdTlBaCuO4.5, and HgTlBaCuO4.5 samples have been prepared under different conditions and have been studied by resistance and ac-susceptibility measurements compared to nominal TlBaCuO3.5 samples. In general, the ZnTlBaCuO4.5 samples required less strict heating conditions to reach zero resistance near liquid nitrogen temperature; the CdTlBaCuO4.5 samples had lower Tc; the HgTlBaCuO4.5 samples showed slightly improved Tc at certain conditions. In contrast to La2−xSrxCuO4, Zn-addition did not significantly depress Tc of TlBaCuO. This observation is worthy to be investigated further. Hardness of the ZnTlBaCuO4.5 and CdTlBaCuO4.5 samples was greatly increased, which could have importance in the practical applications of these materials.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

The nucleation and growth of Hg1−xCdxTe on CdTe(211)B/Si(211) substrates by molecular beam epitaxy are comprehensively studied by in situ reflection high energy electron diffraction and transmission electron microscopy. Microtwins are observed to be formed at the interface, but are overgrown later as the growth proceeds. It is shown that the three-dimensional growth at the nucleation stage of HgCdTe on CdTe(211)B/Si and CdZnTe(211)B is more likely due to the higher surface energy of Hg1−xCdxTe than that of CdTe(211)B and CdZnTe(211)B. © 2000 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Systematic studies of the postgrowth annealing of molecular beam epitaxial deposited SrS:Cu films are reported. In the as-grown SrS:Cu films, the grain size was small and the luminescence very weak. A step-annealing procedure in a H2S atmosphere was developed and found to be a very efficient way to improve the crystallinity and luminescent properties without damage to the low temperature glass substrate and insulator layer of the device. A model is presented in terms of the free energy of formation and the reaction kinetics of Cu with H2S. It was proposed that the weak luminescence in the as-grown films was attributed to Cu atoms segregated at the grain boundaries in the SrS film. The oxidation of atomic Cu by H2S and the diffusion of Cu+ into the SrS lattice during annealing were responsible for the grain growth and the improved luminescent properties. © 1999 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

A comprehensive view of the microstructure of (111)B CdTe films grown on miscut (001)Si substrates by molecular beam epitaxy has been obtained by transmission electron microscopy and scanning transmission electron microscopy. It is found that in the initial growth stage, CdTe nucleates with a dominance of one particular domain: a domain with (111)B polarity and orientation of [11−2]CdTe//[1−10]Si, although there are also some other domains of different polarity and orientation. The dominance of one type domain is due to the reduction of the surface symmetry by using the miscut substrate and by using optimum growth conditions. As the growth proceeds, a single-crystal film is produced by the dominating domain overgrowing the minority domains nucleated at the film–substrate interface. This results in the final film of single-crystal character having (111)B polarity with [11−2]CdTe along [1−10]Si. © 1998 American Institute of Physics.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

We have established a quick and easy, modified dc method to measure thermoelectric power for bulk high transition-temperature (Tc) superconductors. The temperature range investigated is from 300 to 50 K. The apparatus was developed on the basis of our already-existing commercial APD (APD CRYOGENICS INC, Allentown, Pennsylvania) superconductor characterization cryostat with a limited amount of extra instrumentation. The thermoelectric power is measured continuously within the temperature range by the control of a computer, a real time Seebeck coefficient S(T) versus temperature curve is plotted on the computer screen during the measurement, and the data can be saved to a disk. The entire processing period for each sample takes less than 2 h. This apparatus was calibrated with pure lead. By measuring on high Tc superconductors which are well known in thermoelectric power, the system has been shown to have high accuracy and reliability.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Superconducting Hg-based cuprate thin films have been fabricated on (100) SrTiO3 substrate using rf sputtering and post-Hg-vapor annealing. These films are dominated by c-axis-oriented Hg-1223 phase as indicated by x-ray diffraction and SQUID measurements. Using four-probe technique, the Tc,onset was found to be 130–132 K and Jc was up to 8.5×104 A/cm2 at 77 K and zero field. © 1995 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Annealing studies are reported on molecular-beam epitaxial grown SrS:Cu which has potential as a blue phosphor for full color electroluminescent (EL) displays. It was found that annealing under a sulfur flux at 650 °C greatly improved film quality and luminescent brightness. This was attributed to the reduction of sulfur vacancies, and a large enhancement in the grain size of these thin-film phosphors. Using this procedure, EL devices with a luminance of 26 cd/m2 at 40 V above the turn-on threshold voltage with chromaticity coordinates of x=0.17, y=0.29 were obtained. © 1999 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Double positioning boundaries on {12¯10} and {11¯00} planes in wurtzite GaN epilayer grown by molecular beam epitaxy on {1¯1¯1¯}B GaP are described. Transmission electron microscopy observations demonstrate that the {12¯10} boundary extending a short distance along the c axis is characterized by a displacement of 1/2〈101¯1〉 and is associated with single growth faults in the basal plane. This boundary forms as a consequence of island coalescence. Conversely, the {11¯00} boundary originates at the epilayer/substrate interface and runs through the whole epilayer, while g.R analysis combined with high resolution electron microscopy suggests a displacement of 1/3n〈112¯0〉 (n〉3) in the basal plane with an additional shift along 〈0001〉 of 1/n〈0001〉(n〉3). © 1997 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We demonstrate the growth of large-area, domain-free CdTe(111)B single crystals on As-passivated Si(111) substrates by molecular beam epitaxy using ZnTe buffer layers. The crystal quality of the CdTe(111)B/ZnTe(111)B/Si(111) films was examined by x-ray diffraction (56 arcs), etch-pit-density (2×105 cm−2) analysis, and transmission electron microscopy, and was found to be comparable to or better than the best CdTe(111)B films grown directly on vicinal Si(001). Surface reconstructions were observed by reflection high-energy electron diffraction at different stages. Diffraction intensity oscillations demonstrated the layer-by-layer growth mode of the CdTe surface. An interface model for these films is proposed. © 1999 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Here we present the first direct observation of the atomic structure of threading dislocation cores in hexagonal GaN. Using atomic-resolution Z-contrast imaging, dislocations with edge character are found to exhibit an eight-fold ring core. The central column in the core of a pure edge dislocation has the same configuration as one row of dimers on the {10-10} surface. Following recent theoretical work, it is proposed that edge dislocations do not have deep defect states in the band gap, and do not contribute to cathodoluminescence dislocation contrast. On the other hand, both mixed and pure screw dislocations are found to have a full core, and full screw dislocation cores were calculated to have states in the gap. © 1998 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

An Mn pinning effect which limits the grain size in SrS:Mn thin films is reported. The SrS:Mn films exhibit spectrally identical saturated electroluminescent (EL) and photoluminescent (PL) green emissions at 5400 Å with CIE coordinates of x=0.33 and y=0.64. However, although strong PL emission was obtained, the EL emission was very weak. It is proposed that the weak EL emission is attributed to the small grain size caused by a Mn pinning effect. The mechanisms of the grain growth and Mn pinning effect in SrS are proposed and discussed in this letter. © 1999 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

The dependence of magnetization on the applied magnetic field and temperature was measured carefully near their Curie temperatures for two perovskite manganite samples: La0.67Ca0.33MnOδ and La0.60Y0.07Ca0.33MnOδ. It is suggested by the results that these materials can be utilized as both the thermal storage (passive regeneration) and as the working material (active regeneration) in an active magnetic regenerative refrigerator with very large temperature span, for their significant entropy change upon the application of a magnetic field and the easily tuned Curie temperatures. © 1996 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

The magnetic and transport properties of a perovskite-type crystal sample with a nominal composition La0.67Ca 0.33MnOx have been investigated in the temperature range from 5 to 300 K with applied magnetic fields up to 5 T. Magnetization data obtained in the zero-field-cooled process exhibit the magnetic behavior with a Néel temperature, TN∼50 K and Curie temperature, TC∼300 K. The interesting feature in the temperature dependence of magnetoresistance is the appearance of a peak at T∼50 K, with value Δρ/ρ=[ρ(0)−ρ(5 T)]/ρ(5 T)=1300% at the Néel temperature, rather than at Curie temperature. © 1996 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

The effect of As passivation of Si(111) substrates on the subsequent molecular beam epitaxial growth of CdTe(111) is investigated through a detailed comparison of the microstructures of two types of films. The film grown on a substrate treated with a Te flux is found to exhibit a rough film-substrate interface and has very poor crystalline quality with a (111)A orientation. In contrast, a CdTe film grown under identical conditions except for the Si substrate treated with an As flux is observed to have an atomically abrupt film-substrate interface and a single-domain structure in the technologically more relevant (111)B orientation. A growth mechanism for the formation of these high-quality single-domain CdTe(111)B films is proposed. © 1999 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

A comprehensive study of grain growth in strontium sulfide (SrS) thin-film electroluminescent (TFEL) phosphors is reported. It is suggested that the grain growth during annealing is influenced by the migration of the dopant ion from the grain boundary into a lattice position. The difference in the free energy of formation between SrS and the sulfur compounds of the dopants changes the activation energy for the grain boundary movement and promotes the grain growth. This understanding has successfully been used to explain the grain growth phenomena observed in SrS TFEL phosphors with different dopants, such as Cu, Ag, Mn, and Ga. © 1999 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

The electronic structure of pure edge threading dislocations in metalorganic vapor phase epitaxy grown wurtzite GaN thin films has been studied directly by atomic resolution Z-contrast imaging and electron energy loss spectroscopy in a scanning transmission electron microscope. Dislocation cores in n-type samples grown in N-rich conditions show no evidence for the high concentration of Ga vacancies predicted by previous theoretical calculations. Nitrogen K-edge spectra collected from edge dislocation cores show a sudden and significant increase in the intensity of the first fine-structure peak immediately above the edge onset compared to the bulk spectra. The origin of this increase is discussed. © 2000 American Institute of Physics.

Electronic Resource

1460-9568

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Based on the observation that in adult mice the carbohydrate epitope L2/HNK-1 is detectable on Schwann cells in ventral spinal roots, but only scarcely in dorsal roots (Martini et al., Dev. Biol., 129, 330–338, 1988), the possibility was investigated that the carbohydrate is involved in the outgrowth of regenerating motor neuron axons on peripheral nerve substrates expressing the epitope. To monitor whether the L2 carbohydrate remains present during the time periods in which regenerating axons penetrate the denervated distal nerve stumps, the expression of L2 in motor and sensory branches of the femoral nerve was investigated in normal animals and after a crush lesion. During the first two postoperative weeks, L2 immunoreactivity remained high in the myelinating Schwann cells of the motor branch, whereas L2 immunoreactivity was virtually absent in the sensory branch. In a first experimental approach, cryosections of ventral and dorsal spinal roots and of motor and sensory nerves of adult rats and mice were used as substrates for neurite outgrowth. Neurites of motor neurons from chicken embryos were ∼35% longer after 30 h of maintenance on ventral roots than on dorsal roots. Neurites from sensory neurons had the same length on dorsal as on ventral motors and were as long as neurites from motor neurons grown on dorsal roots. L2 antibodies reduced neurite outgrowth of motor neurons on ventral roots but not on dorsal roots. Neurite outgrowth of sensory neurons on both roots was not altered by the antibodies. Neurite outgrowth of motor neurons on a mixture of the extracellular matrix glycoprotein laminin and the L2 carbohydrate-carrying glycolipid was significantly higher than on the laminin substrate mixture with GD1b ganglioside or sulphatide. L2 antibodies reduced neurite outgrowth of motor neurons by 50% on the L2 glycolipid, but not on GD1b or sulphatide. These observations indicate that the L2 carbohydrate promotes neurite outgrowth of motor neurons in vitro and may thus contribute to the preferential reinnervation of motor nerves by regenerating motor axons in vivo.

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