Search Results - (Author, Cooperation:W. Qian)

2018-01-23

American Chemical Society (ACS)

0887-0624

1520-5029

Chemistry and Pharmacology

Energy, Environment Protection, Nuclear Power Engineering

Process Engineering, Biotechnology, Nutrition Technology

2018-02-03

American Chemical Society (ACS)

0887-0624

1520-5029

Chemistry and Pharmacology

Energy, Environment Protection, Nuclear Power Engineering

Process Engineering, Biotechnology, Nutrition Technology

2018-06-14

Institute of Physics Publishing (IOP)

1748-0221

Physics

2012-06-16

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Acetylation ; Arabidopsis/*genetics/*metabolism ; Arabidopsis Proteins/chemistry/genetics/*metabolism ; Chromatin/metabolism ; DNA Glycosylases/metabolism ; *DNA Methylation ; DNA, Plant/*metabolism ; Gene Silencing ; Genes, Plant ; Histone Acetyltransferases/chemistry/genetics/*metabolism ; Histones/metabolism ; Methylation ; Mutation ; Nuclear Proteins/genetics/metabolism ; Protein Structure, Tertiary ; Transgenes

2016-04-16

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

2018-03-06

The American Association for Cancer Research (AACR)

1078-0432

1557-3265

Medicine

2018-05-27

BMJ Publishing

2044-6055

Medicine

Open access, Smoking and tobacco

2018-11-16

The American Association for Cancer Research (AACR)

1078-0432

1557-3265

Medicine

1089-7550

AIP Digital Archive

Physics

The electron optical properties of nanometer sized field-emission cathodes are examined for suitability as electron sources for low-voltage scanning electron microscopy, low-voltage transmission point projection microscopy, and low-voltage transmission and reflection electron holography. First-order electron optical properties, aperture and chromatic aberrations, and source coherence are computed using an all-orders numerical method, and compared with analytically computed properties where possible. The electron optical properties of planar emitters, conventional field-emission tips, and new nanotip structures are compared in the absence of space-charge effects. It is found that the spherical and chromatic aberrations of nanotips are dominated by their base structures and that beams produced by nanotips can be considered as totally coherent.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

The brightness of nanometer-sized field-emission-electron sources have been measured experimentally. Ultrasharp tungsten (111) single-crystal tips were fabricated in situ using Ne sputtering and field evaporation, and monitored using field ion microscopy. The average brightness of single-atom-terminated nanotips was found to be 3.3×108 A cm−2 sr−1 at 470 V, or 7.7×1010 A cm−2 sr−1 when extrapolated to 100 kV. These results show an improvement of about two orders of magnitude in source brightness over existing cold field-emission-electron sources, and produce a beam with greater particle flux per unit energy than those obtainable using current synchrotron/wiggler/undulator devices.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

0.15 THz coherent acoustic phonons have been observed in gold nanoparticles embedded in TiO2 thin films by virtue of femtosecond time-resolved transmissivity measurements at room temperature. The generation of these phonons is attributed to the resonant excitation of localized surface plasmon in gold nanoparticles. Their damping time is 55 ps which is acquired by fitting the oscillatory part of time-resolved transmissivity to single exponentially damped cosine function. © 2000 American Institute of Physics.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

We describe some details of the production of 57Fe and C60 ions by the Nielsen source. Some application results are also given.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

The initial stages of molecular beam epitaxy of GaSb on highly mismatched GaAs(001) substrates were investigated. Transmission electron microscopy was used to analyze the defect structure in GaSb islands and at their interfaces with GaAs(001) at different stages of growth. Based on experimental observations, we propose that the semiperiodic net of 90° misfit dislocations at the GaSb/GaAs(001) interface nucleate homogeneously at the leading edges of advancing {111} planes. After nucleation, they glide inwards along the interface plane to reach their equilibrium position. Threading dislocations in GaSb layers were directly correlated with the misfit dislocation net. We demonstrate that there are no threading defects in GaSb islands when their interfaces consist solely of 90° misfit dislocations, and that threading dislocations in the GaSb epilayer are all associated with minority 60° misfit dislocations nucleated in growing islands. The number of threading dislocations per unit area of the GaSb film is found to be independent of GaSb coverage, indicating that island coalescence does not substantially increase the number of 60° dislocations. © 1997 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We report large-scale synthesis of silica nanowires (SiONWs) using an excimer laser ablation method. Silica was produced in the form of amorphous nanowires at a diameter of ∼15 nm and a length up to hundreds micrometers. The SiONWs emit stable and high brightness blue light at energies of 2.65 and 3.0 eV. The intensity of the emission is two orders of magnitude higher than that of porous silicon. The SiONWs may have potential applications in high-resolution optical heads of scanning near-field optical microscope or nanointerconnections in future integrated optical devices. © 1998 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Microstructure of α-GaN films grown by organometallic vapor phase epitaxy on sapphire substrates using low temperature AlN (or GaN) buffer layers has been studied by transmission electron microscopy. The defects which penetrate the GaN films are predominantly perfect edge dislocations with Burgers vectors of the 1/3〈112¯0〉 type, lying along the [0001] growth direction. The main sources of threading dislocations are the low angle grain boundaries, formed during coalescence of islands at the initial stages of GaN growth. The grain sizes range from 50 to 500 nm, with in-plane misorientations of less than 3°. The nature of these threading dislocations suggests that the defect density would not likely decrease appreciably at increasing film thickness, and the suppression of these dislocations could be more difficult. © 1995 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Electron optical properties of nanometer diameter field emission electron sources have been calculated using ray tracing methods. The spherical and chromatic aberration coefficients referred to the object plane were found to be on the order of angstroms. The effective source size was estimated to be much smaller than that in a conventional field emission source. The ultimate resolution of a lensless point projection electron microscope, which depends on both the source aberrations and the effective source size, were also in the order of angstroms. The beam angular half-width on the anode was 7.4° relative to the virtual image position on the optic axis, and the corresponding coherence width was 9.6°, suggesting that the source is totally coherent.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Structural investigations of organometallic vapor phase epitaxy grown α-GaN films using high-resolution transmission electron microscopy and scanning force microscopy have revealed the presence of tunnel-like defects with 35–500 A(ring) radii that are aligned along the growth direction of the crystal and penetrate the entire epilayer. These defects, which are termed "nanopipes,'' terminate on the free surface of the film at the centers of hexagonal growth hillocks and form craters with 600–1000 A(ring) radii. Either one or two pairs of monolayer-height spiral steps were observed to emerge from the surface craters which allowed us to conclude that nanopipes are the open cores of screw dislocations. The measured dimensions of the defects are compared to Frank's theory for the open-core dislocation. © 1995 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Three kinds of coherent phonons (0.30, 1.90, and 3.75 THz) have been observed in silver nanoparticles embedded in BaO thin films by means of the femtosecond time-resolved pump-probe technique. The generation of 0.3 THz coherent phonons is attributed to the resonant excitation of localized surface plasmon of silver nanopaticles, and the resonant impulsive stimulated Raman scattering in silver aggregates is responsible for the generation of 1.90 and 3.75 THz coherent phonons. © 1999 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We report the large-scale synthesis of silicon nanowires (SiNWs) using a simple but effective approach. High purity SiNWs of uniform diameters around 15 nm were obtained by sublimating a hot-pressed silicon powder target at 1200 °C in a flowing carrier gas environment. The SiNWs emit stable blue light which seems unrelated to quantum confinement, but related to an amorphous overcoating layer of silicon oxide. Our approach can be used, in principle, as a general method for synthesis of other one-dimensional semiconducting, or conducting nanowires. © 1998 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Layers of AlBN were grown on sapphire by organometallic vapor-phase epitaxy at 1050 °C using triethylboron, trimethylaluminum, and ammonia as precursors. It is shown that boron is readily incorporated into the layers and its concentration in the solid phase can be as high as 40%. However, single phase Al1−xBxN films can only be grown for compositions not exceeding x=0.01. For higher boron concentrations in the solid the second B-rich phase is formed. This phase was identified as wurtzite BN based on the results of transmission electron microscopy and x-ray diffraction. The growth of this thermodynamically unfavorable phase becomes possible, most probably, because it occurs within the framework provided by wurtzite AlN islands first formed on the surface and setting up the sites for lateral growth of wurtzite BN. That leads to formation of columnar structure of AlN and BN crystallites oriented in the basal plane and existing side by side. © 1997 American Institute of Physics.

Electronic Resource