Self-oriented Growth of GaN Films on Molten Gallium

2004 ◽  
Vol 831 ◽  
Author(s):  
Hongwei Li ◽  
Hari Chandrasekaran ◽  
Mahendra K Sunkara ◽  
Ramon Collazo ◽  
Zlatko Sitar ◽  
...  
Keyword(s):  
Nitrogen Plasma ◽  
Free Standing ◽  
Oriented Growth ◽  
Cross Sectional ◽  
Electron Diffraction Technique ◽  
Columnar Grains ◽  
Hrtem Micrographs ◽  
Amorphous Quartz ◽  
Convergent Beam ◽  
Quartz Substrates

ABSTRACTThis paper presents a concept of growing near single crystal quality GaN films over large areas through self-oriented growth of GaN platelets on molten gallium. The experiments were performed by nitridation of Ga films on amorphous quartz substrates using nitrogen plasma at low pressures of few mTorr. XRD texture analysis of the free standing GaN flakes with areas over 25 mm2 exhibited an overall c-axis tilt of 2.2°, while showing primary reflections from (0002) and (0004) planes. Further more, the cross-sectional TEM micrographs showed that the resulting GaN films are free from dislocation crops inside the grains but showed diffraction contrast due to small misorientation between the grains. The twist and tilt angles between adjacent columnar grains were determined using convergent beam electron diffraction technique to be less than 8° and 1°, respectively. HRTEM micrographs of the grain boundaries showed sharp interfaces with both twisted and perfect attachments.

Computer-Aided Analysis of Oriented Crystallites by Diffraction Pattern Simulation and Tilt-Stage Control in a TEM

1997 ◽  
Vol 3 (S2) ◽  
pp. 1015-1016
Author(s):  
L.E. Thomas ◽  
L.A. Chariot ◽  
J.T. Stanley
Keyword(s):  
Small Sample ◽  
Hot Water ◽  
Metal Corrosion ◽  
Desktop Computer ◽  
Cross Sectional ◽  
Surface Corrosion ◽  
Computer Aided ◽  
Columnar Grains ◽  
Diffraction Patterns ◽  
Convergent Beam

Electron diffraction patterns taken in the transmission electron microscope (TEM) provide information about crystal structures and orientations in small sample areas. Extracting this information and manipulating local crystal orientations has become a great deal easier with the availability of desktop computer programs that allow simulation matching of experimental patterns and crystallographic control of sample tilting in the TEM. This presentation will illustrate an application of computer-aided crystallography for analyzing oriented crystallites in an experimentally complex material.The surface corrosion films that form on reactive metals such as hafnium or zirconium in hot water provided our example. Cross-sectional examinations of the corrosion films revealed a columnar microstructure of monoclinic HfO2/ZrO2 grains extending normal to the metal/corrosion-film interface.The columnar grains were only about 50 nm in width, and thus were too small to analyze individually by selected-area diffraction. Local strains in the films smeared the diffraction fine structure so there was little hope for analysis by convergent-beam diffraction methods.

Growth of Oriented Gallium Nitride Films on Amorphous Substrates by Self Assembly

2002 ◽  
Vol 743 ◽  
Author(s):  
Hongwei Li ◽  
Mahendra K. Sunkara
Keyword(s):  
Thin Films ◽  
Gallium Nitride ◽  
Self Assembly ◽  
Electron Cyclotron Resonance ◽  
Nitrogen Plasma ◽  
X Ray Diffraction ◽  
Sem Images ◽  
Amorphous Substrates ◽  
Amorphous Quartz ◽  
Quartz Substrates

ABSTRACTC-plane oriented thin films of gallium nitride (GaN) were grown on both amorphous quartz substrates and single crystalline c-sapphire substrates at sub-atmospheric pressures by exposing molten gallium thin films to electron cyclotron resonance (ECR) microwave generated nitrogen plasma. Gallium nitride crystals nucleated from molten gallium and self-aligned with respect to each other due to the mobility of nitrogenated gallium and formed textured film directly on amorphous substrates. Scanning electron microscopy (SEM) images and X-ray Diffraction (XRD) spectra confirmed the orientation among crystals. Micro-Raman spectra exhibited a FWHM of 3 cm−1. Self-assembled, nanocrystalline GaN thin films were obtained when spin-coated gallium thin films (< 1 μm) on quartz substrates were nitrided.

scholarly journals Sensitivity of quantitative symmetry measurement algorithms for convergent beam electron diffraction technique

2021 ◽  
Vol 51 (1) ◽  
Author(s):  
Hyeongsub So ◽  
Ro Woon Lee ◽  
Sung Taek Hong ◽  
Kyou-Hyun Kim
Keyword(s):  
Electron Diffraction ◽  
Cross Correlation ◽  
Structural Changes ◽  
Small Strain ◽  
Convergent Beam Electron Diffraction ◽  
Digital Microscopy ◽  
Beam Electron ◽  
R Factor ◽  
Electron Diffraction Technique ◽  
Convergent Beam

AbstractWe investigate the sensitivity of symmetry quantification algorithms based on the profile R-factor (Rp) and the normalized cross-correlation (NCC) coefficient (γ). A DM (Digital Micrograph©) script embedded in the Gatan digital microscopy software is used to develop the symmetry quantification program. Using the Bloch method, a variety of CBED patterns are simulated and used to investigate the sensitivity of symmetry quantification algorithms. The quantification results show that two symmetry quantification coefficients are significantly sensitive to structural changes even for small strain values of < 1%.

Pulsed laser deposition of oriented V2O5 thin films

2000 ◽  
Vol 15 (10) ◽  
pp. 2249-2265 ◽  
Author(s):  
Jeanne M. McGraw ◽  
John D. Perkins ◽  
Falah Hasoon ◽  
Philip A. Parilla ◽  
Chollada Warmsingh ◽  
...  
Keyword(s):  
Thin Films ◽  
Pulsed Laser Deposition ◽  
Oxygen Pressure ◽  
Pulsed Laser ◽  
Laser Deposition ◽  
Glass Substrates ◽  
Wide Range ◽  
Phase Pure ◽  
Amorphous Quartz ◽  
Quartz Substrates

We have found that by varying only the substrate temperature and oxygen pressure five different crystallographic orientations of V2O5 thin films can be grown, ranging from amorphous to highly textured crystalline. Dense, phase-pure V2O5 thin films were grown on SnO2/glass substrates and amorphous quartz substrates by pulsed laser deposition over a wide range of temperatures and oxygen pressures. The films' microstructure, crystallinity, and texturing were characterized by electron microscopy, x-ray diffraction, and Raman spectroscopy. Temperature and oxygen pressure appeared to play more significant roles in the resulting crystallographic texture than did the choice of substrate. A growth map summarizes the results and delineates the temperature and O2 pressure window for growing dense, uniform, phase-pure V2O5 films.

The acquisition of morphosyntax in Italian: A cross-sectional study

2009 ◽  
Vol 30 (1) ◽  
pp. 23-52 ◽  
Author(s):  
CLAUDIA CAPRIN ◽  
MARIA TERESA GUASTI
Keyword(s):  
Cross Sectional Study ◽  
Inflectional Morphology ◽  
Null Subjects ◽  
Sectional Study ◽  
Free Standing ◽  
Cross Sectional ◽  
Verb Inflections ◽  
New Evidence

ABSTRACTThis study provides new evidence concerning the pattern of acquisition of free and bound morphemes in Italian, based on the speech of 59 children recorded through a cross-sectional method. We found that inflectional morphology is mastered before free-standing morphology. Despite the great variety of verb inflections, the analyses showed that children partially master present indicative from early productions. Although free-standing morphemes are used correctly, they are optionally omitted. Here we have explored the use and omission of articles, clitics, the copula, and auxiliaries and have shown that omission is subject to certain constraints. Articles are mainly omitted from the root of the clause, much as null subjects, because from this position the requirement of clausal identification is voided. A higher omission of accusative clitics than dative clitics was observed that has also been explained in terms of the uniqueness checking constraint: accusative, but not dative clitics need to check the D feature twice, because the former, but not the latter, trigger past particle agreement. The uniqueness checking constraint has been adopted to explain the higher omission of auxiliaries with respect to the copula: the former, but not the latter, have to check the T feature twice. Together, these findings suggest that children omit, but in principled ways.

Free-standing cobalt hydroxide nanoplatelet array formed by growth of preferential-orientation on graphene nanosheets as anode material for lithium-ion batteries

2014 ◽  
Vol 2 (48) ◽  
pp. 20706-20713 ◽  
Author(s):  
Jisheng Zhou ◽  
Jingming Li ◽  
Kunhong Liu ◽  
Ling Lan ◽  
Huaihe Song ◽  
...  
Keyword(s):  
Lithium Ion Batteries ◽  
Anode Material ◽  
Anode Materials ◽  
High Performance ◽  
Graphene Nanosheets ◽  
Lithium Ion ◽  
Preferential Orientation ◽  
Cobalt Hydroxide ◽  
Free Standing ◽  
Oriented Growth

Co(OH)2 arrays/GNSs composites, which are constructed by preferentially oriented growth, exhibit a high-performance when used as anode materials for lithium-ion batteries.

Influence of Duty Cycle on Composition and Microstructure of Siliconized Layer Using Pulse Electrodeposition

2010 ◽  
Vol 139-141 ◽  
pp. 666-669 ◽  
Author(s):  
Hai Li Yang ◽  
Yan Li ◽  
Yun Gang Li ◽  
Guo Zhang Tang ◽  
Ning He ◽  
...  
Keyword(s):  
Duty Cycle ◽  
Molten Salts ◽  
Layer Structure ◽  
Silicon Steel ◽  
Average Current Density ◽  
Cross Sectional ◽  
Columnar Grains ◽  
Average Current ◽  
Si Content ◽  
Equiaxed Grains

The siliconized layer was pulse electrodeposited on grain oriented low-silicon steel sheet substrate in KCl-NaCl-NaF-SiO2 molten salts and the influence of duty cycle on the composition and microstructure of the siliconized layer was investigated. The results showed that when the duty cycle was in the range of 10% to 50% at average current density 30mA/cm2, Si content of siliconized layers was similar and the thickness of the layer was did not change much with different duty cycle. Cross sectional observation revealed that the siliconized layers had a two-layer structure. The top layer composed of columnar grains and a transition layer with equiaxed grains was close to the substrate. The layer was unsmooth when the duty cycle was 10%. While the surface appeared smooth and dense and the grains were fine when the duty cycle were 20% and 30%. The layer became more porous as the duty cycle increased to 40% and 50%.

scholarly journals Use of clinical data to augment healthcare worker contact tracing during the COVID-19 pandemic

2021 ◽  
Author(s):  
Peter Hong ◽  
Joshua C Herigon ◽  
Colby Uptegraft ◽  
Bassem Samuel ◽  
D Levin Brown ◽  
...  
Keyword(s):  
Healthcare Worker ◽  
Clinical Data ◽  
Cross Sectional Study ◽  
Contact Tracing ◽  
Clinical Event ◽  
Event Data ◽  
Free Standing ◽  
Cross Sectional ◽  
Secondary Use ◽  
Epidemiologic Surveillance

Abstract Objective This work examined the secondary use of clinical data from the electronic health record (EHR) for screening our healthcare worker (HCW) population for potential exposures to patients with coronavirus disease 2019. Materials and Methods We conducted a cross-sectional study at a free-standing, quaternary care pediatric hospital comparing first-degree, patient-HCW pairs identified by the hospital’s COVID-19 contact tracing team (CTT) to those identified using EHR clinical event data (EHR Report). The primary outcome was the number of patient-HCW pairs detected by each process. Results Among 233 patients with COVID-19, our EHR Report identified 4,116 patient-HCW pairs, including 2,365 (30.0%) of the 7,890 pairs detected by the CTT. The EHR Report also revealed 1,751 pairs not identified by the CTT. The highest number of patient-HCW pairs per patient was detected in the inpatient care venue. Nurses comprised the most frequently identified HCW role overall. Conclusion Automated methods to screen HCWs for potential exposure to patients with COVID-19 using clinical event data from the EHR are likely to improve epidemiologic surveillance by contact tracing programs and represent a viable and readily available strategy which should be considered by other institutions.

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