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41.
分析了硬x射线同轴相衬成像过程,在菲涅耳衍射的基础上,提出了基于强度传播方程(Transport of Intensity equation)的相位恢复算法,并利用数值法模拟研究了相衬成像和相位恢复过程,从而验证了这一相位恢复算法。 相似文献
42.
J. Zhong G. Saraf H. Chen Y. Lu Hock M. Ng T. Siegrist A. Parekh D. Lee E. A. Armour 《Journal of Electronic Materials》2007,36(6):654-658
ZnO nanotips are grown on epitaxial GaN/c-sapphire templates by metalorganic chemical vapor deposition. X-ray diffraction
(XRD) studies indicate that the epitaxial relationship between ZnO nanotips and the GaN layer is (0002)ZnO||(0002)GaN and
(101̄0)ZnO||(101̄0)GaN. Temperature-dependent photoluminescence (PL) spectra have been measured. Sharp free exciton and donor-bound
exciton peaks are observed at 4.4 K with photon energies of 3.380 eV, 3.369 eV, and 3.364 eV, confirming high optical quality
of ZnO nanotips. Free exciton emission dominates at temperatures above 50 K. The thermal dissociation of these bound excitons
forms free excitons and neutral donors. The thermal activation energies of the bound excitons at 3.369 eV and 3.364 eV are
11 meV and 16 meV, respectively. Temperature-dependent free A exciton peak emission is fitted to the Varshni’s equation to
study the variation of energy bandgap versus temperature. 相似文献
43.
Govindhan Dhanaraj Yi Chen Hui Chen Dang Cai Hui Zhang Michael Dudley 《Journal of Electronic Materials》2007,36(4):332-339
A chemical vapor deposition (CVD) system was designed and fabricated in our laboratory and SiC homo-epitaxial layers were
grown in the CVD process using silicon tetrachloride and propane precursors with hydrogen as a carrier gas. The temperature
field was generated using numerical modeling. Gas flow rates, temperature field, and the gradients are found to influence
the growth rates of the epitaxial layers. Growth rates were found to increase as the temperature increased at high carrier
gas flow rate, while at lower carrier gas flow rate, growth rates were observed to decrease as the temperature increased.
Based on the equilibrium model, “thermodynamically controlled growth” accounts for the growth rate reduction. The grown epitaxial
layers were characterized using various techniques. Reduction in the threading screw dislocation (SD) density in the epilayers
was observed. Suitable models were developed for explaining the reduction in the SD density as well as the conversion of basal
plane dislocations (BPDs) into threading edge dislocations (TEDs). 相似文献
44.
Structural changes accompanying thermal transformation in a chrysotile asbestos sample of Indian origin upto a temperature
of 900°C have been investigated by x-ray method. The changes in lattice parameters have been systematically measured by applying
a least square refinement technique and the crystallite size and strain defects at different stages have been estimated by
line profile analysis of the diffraction peaks. The present study also confirms the earlier results on stepwise transformation
of chrysotile fibres. This sequence of transformation has been explained assuming two different types of crystallites as reported
in kaolinite. 相似文献
45.
W. Wong-Ng H. F. McMurdie C. R. Hubbard A. D. Mighell 《Journal of research of the National Institute of Standards and Technology》2001,106(6):1013-1028
The Research Associateship program of the Joint Committee on Powder Diffraction-International Centre for Diffraction Data (JCPDS-ICDD, now known as the ICDD) at NBS/NIST was a long standing (over 35 years) successful industry-government cooperation. The main mission of the Associateship was to publish high quality x-ray reference patterns to be included in the Powder Diffraction File (PDF). The PDF is a continuing compilation of patterns gathered from many sources, compiled and published by the ICDD. As a result of this collaboration, more than 1500 high quality powder diffraction patterns, which have had a significant impact on the scientific community, were reported. In addition, various research collaborations with NBS/NIST also led to the development of several standard reference materials (SRMs) for instrument calibration and quantitative analyses, and computer software for data collection, calibration, reduction, for the editorial process of powder pattern publication, analysis of powder data, and for quantitative analyses. This article summarizes information concerning the JCPDS-ICDD organization, the Powder Diffraction File (PDF), history and accomplishments of the JCPDS-ICDD Research Associateship. 相似文献
46.
Mark D. Vaudin 《Journal of research of the National Institute of Standards and Technology》2001,106(6):1063-1069
Preferred crystallographic orientation, or texture, occurs almost universally, both in natural and man-made systems. Many components and devices in electronic and magnetic systems are fabricated from materials that have crystallographic texture. With the rapidly increasing use of thin film technology, where sharp axisymmetric crystallographic texture normal to the film plane is frequently observed, the occurrence and impact of texture are rising. Thin film applications in which the texture of the material plays a key role in determining properties and performance are broad: complex oxides in random access memory devices, ZnO thin film resonators for cell phone applications, metallic alloys in magnetic recording media, and Al and Cu interconnects in integrated circuits are but a few examples. Texture is established during the synthesis or post-synthesis heat treatment of a material and thus has a strong dependence upon processing history. Accurate measurement of texture is not simple and a variety of tools and approaches are being actively employed in texture studies. X-ray, neutron and electron diffraction based techniques are practiced around the world at varying levels of complexity with regard to equipment and analysis methods. Despite the well-documented existence of these varied approaches, many reported texture measurements on electronic materials are based solely on the relative intensities of conventional θ-2θ x-ray diffraction peaks, which typically yield inaccurate results. NIST has developed quantitative texture measurement techniques that employ equipment commonly available in most industrial and academic settings. A number of examples of texture measurement in ceramic and metal systems will be presented, taken from the historical development and application of these techniques at NIST over the past 7 years. 相似文献
47.
The effect of thiourea, urea and guanidin on zinc deposits obtained from chloride baths under continuous current conditions
are described and discussed. The corrosion behaviour of the deposits was investigated in an aerated 3.5% NaCl solution; anodic
polarization curves, polarization resistance (R
p) measurements and weight-loss studies were performed. The corrosion resistance of zinc deposits improved in the presence
of urea. The deposit morphology was analyzed using Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) was used
to determine the preferred crystallographic orientations of the deposits. The preferred crystallographic orientations of zinc
deposits (112) do not change in the presence of urea and guanidin except for an increase in the peak intensity of the (112)
plane. In the presence of thiourea, zinc deposits crystallise in two textures; (100) and (110). The influence of each additive
and the difference between additives on the zinc deposits are also discussed. 相似文献
48.
利用X-射线衍射、电子探针、化学组成和夹杂物分析等方法系统分析了中国石油化工股份有限公司中原油田分公司某采油厂油气集输管道的失效机理,从而为集输系统腐蚀的有效防护提供了理论依据。 相似文献
49.
C. Yuan T. Salagaj W. Kroll R. A. Stall M. Schurman C. Y. Hwang Y. Li W. E. Mayo Y. Lu S. Krishnankutty R. M. Kolbas 《Journal of Electronic Materials》1996,25(5):749-753
High quality InGaN thin films and InGaN/GaN double heterojunction (DH) structures have been epitaxially grown on c-sapphire
substrates by MOCVD in a production scale multi-wafer-rotating-disc reactor between 770 to 840°C. We observed that shroud
flow (majority carrier gas in the reaction chamber) is the key to obtaining high quality InGaN thin films. High purity H2 as the shroud flow results in poor crystal quality and surface morphology but strong photolumines-cence (PL) at room temperature.
However, pure N2 as the shroud flow results in high crystal quality InGaN with an x-ray full width at half maximum (FWHM)InGaN(0002) of 7.5 min and a strong room temperature PL peaking at 400 nm. In addition, InGaN/GaN single heterojunction (SH) and DH structures
both have excellent surface morphology and sharp interfaces. The full width at half maximum of PL at 300K from an InGaN/GaN
DH structure is about 100 meV which is the best reported to date. A high indium mole fraction in InGaN of 60% and high quality
zinc doped InGaN depositions were also achieved. 相似文献
50.
Kurt F. J. Heinrich 《Journal of research of the National Institute of Standards and Technology》2002,107(6):483-485
Quantitative electron probe analysis is based on models based on the physics or x-ray generation, empirically adjusted to the analyses of specimens of known composition. Their accuracy can be estimated by applying them to a set of specimens of presumably well-known composition. 相似文献