The Polarity of GaN: a Critical Review

1998 ◽  
Vol 3 ◽  
Author(s):  
E. S. Hellman
Keyword(s):  
Critical Review ◽  
Polar Axis ◽  
Epitaxial Films ◽  
Wurtzite Structure ◽  
Bulk Crystals ◽  
Standard Framework

GaN, AlN and InGaN have a polar wurtzite structure and epitaxial films of these materials typically grow along the polar axis. Although the polarity of these nitrides has been studied by quite a number of techniques, many results in the literature are in conflict. In this paper an attempt is made to lay out a set of polarity assignments to provide a context for discussion of these results. A “standard framework” is proposed to correlate the disparate results, and the framework is used to draw general conclusions about the polarity of bulk crystals, VPE and MBE epitaxial films, and devices.

Weak‐field magnetoresistance symmetry in epitaxial films and bulk crystals ofp‐type SnTe

1978 ◽  
Vol 49 (8) ◽  
pp. 4442-4445 ◽  
Author(s):  
R. S. Allgaier ◽  
Bland Houston ◽  
J. B. Restorff
Keyword(s):  
Weak Field ◽  
Epitaxial Films ◽  
Bulk Crystals

Structural and Magnetic Characterization of Rare Earth and Transition Metal Films Grown on Epitaxial Buffer Films on Semiconductor

1989 ◽  
Vol 151 ◽  
Author(s):  
R. F. C. Farrow ◽  
S. S. P. Parkin ◽  
V. S. Speriosu ◽  
A. Bezinge ◽  
A. P. Segmuller
Keyword(s):  
Rare Earth ◽  
Structural Characteristics ◽  
Metal Films ◽  
Epitaxial Films ◽  
Coherency Strain ◽  
Magnetic Data ◽  
Bulk Crystals ◽  
Structural Effects ◽  
X Ray

ABSTRACTStructural and magnetic data are presented and discussed for epitaxial films of rare earth metals ( Dy, Ho, Er) on LaF3 films on the GaAs(TTT) surface and Fe on Ag films on the GaAs(001) surface. Both systems exhibit unusual structural characteristics which influence the magnetic properties of the metal films. In the case of rare earth epitaxy on LaF3 we present evidence for epitaxy across an incommensurate or discommensurate interface. Coherency strain is not transmitted into the metal which behaves much like bulk crystals of the rare earths. In the case of Fe films , tilted epitaxy and long-range coherency strain are confirmed by X-ray diffractometry. Methods of controlling some of these structural effects by modifying the epitaxial structures are presented.

Gkowth of YBa2Cu3O7-δ Single Crystals and Films by a Flux and a Sputtering Methods

1987 ◽  
Vol 99 ◽  
Author(s):  
K. Takagi ◽  
M. Hirao ◽  
M. Hiratani ◽  
H. Kakibayashi ◽  
T. Aida ◽  
...  
Keyword(s):  
Single Crystals ◽  
High Resolution Electron Microscopy ◽  
Growth Conditions ◽  
Epitaxial Films ◽  
Electric Resistivity ◽  
Periodic Lattice ◽  
Flux Growth ◽  
Bulk Crystals ◽  
Resolution Electron ◽  
Diffusion Of Impurities

ABSTRACTYBa2Cu3O7-δ single crystals and epitaxial films are grown and characterized. In flux growth for bulk crystals, effects of growth conditions on yield and electric resistivity of crystals are examined. The yield of flaky crystals depends on the formation of cavities. The transition temperature is 86 K after annealing in an oxygen atmosphere. Films are prepared on SrTiO3 by sputtering and epitaxial growth is confirmed by high resolution electron microscopy. Periodic lattice defects are observed near the interface between the substrate and the film. It seems that these defects result from the diffusion of impurities from the substrate.

Epitaxial IV-VI Semiconductor Films

1986 ◽  
Vol 90 ◽  
Author(s):  
T. K. Chu ◽  
A. Martinez
Keyword(s):  
Optical Transition ◽  
Infrared Detector ◽  
Optical Devices ◽  
Epitaxial Films ◽  
Small Scale ◽  
Persistent Photoconductivity ◽  
Semiconductor Films ◽  
Bulk Crystals ◽  
Detector Arrays ◽  
Growth Method

ABSTRACTEpitaxial films of IV-VI semiconductors and their alloys form the basis of an infrared detector technology that offers advantages in material stability as well as spectral versatility. These films are prepared by epitaxial hot-wall techniques and their material properties are essentially the same as those of bulk crystals. Because of their stability, multilayer growths of the materials can be achieved in a straight-forward manner. To date, multi-color detectors and small scale two-color detector arrays have been demonstrated successfully. A brief review of the growth method and the growth characteristics is given. Recent advances in superlattice research, especially those of interest to electro-optical devices, will be discussed. These include persistent photoconductivity and sub-bandgap optical transition.

scholarly journals Оптические и структурные свойства эпитаксиальных слоев Hg-=SUB=-0.7-=/SUB=-Cd-=SUB=-0.3-=/SUB=-Te

2021 ◽  
Vol 55 (11) ◽  
pp. 1040
Author(s):  
Д.А. Андрющенко ◽  
М.С. Ружевич ◽  
А.М. Смирнов ◽  
Н.Л. Баженов ◽  
К.Д. Мынбаев ◽  
...  
Keyword(s):  
Solid Solution ◽  
Optical Properties ◽  
Diffraction Data ◽  
Epitaxial Films ◽  
Structural Quality ◽  
Bulk Crystals ◽  
X Ray Diffraction ◽  
X Ray ◽  
Photoluminescence Studies

The results of comparative studies of the optical and structural properties of Hg0.7Cd0.3Te bulk crystals and epitaxial films grown by various methods are presented. The data of photoluminescence studies performed in the temperature range 4.2−300K showed the similarity of the optical properties of different samples and indicated a significant disordering of the solid solution. According to X-ray diffraction data, however, the scale of the disordering was not directly related to the structural quality of the material. The prospects for using the material grown by various methods in optoelectronics applications are discussed.

Properties Of Homoepitaxially Mbe-Grown Gan

1996 ◽  
Vol 423 ◽  
Author(s):  
T. Suski ◽  
J. Krueger ◽  
C. Kisielowski ◽  
P. Phatak ◽  
M. S. H. Leung ◽  
...  
Keyword(s):  
Metalorganic Chemical Vapor Deposition ◽  
Molecular Beam ◽  
Chemical Vapor ◽  
Epitaxial Films ◽  
Chemical Vapor Deposition Method ◽  
Bulk Crystals ◽  
Acceptor Pair ◽  
Dominant Band ◽  
Bulk Single Crystals ◽  
Donor Acceptor

AbstractBulk single crystals of GaN were used for epitaxial growth of GaN films by molecular beam epitaxy. Low temperature photoluminescence yields much higher intensity emission in the near bandedge region for epitaxial films with respect to the situation in bulk crystals. Character of this luminescence changes also. Dominant band-to-band transitions in the bulk crystals are exchanged by bound exciton and/or donor-acceptor pair transitions observed in the epitaxial layers. We will compare the obtained results with the available data on the homoepitaxial samples grown by metalorganic chemical vapor deposition method and discuss the importance of establishing the basic information on energetic positions of excitonic transitions in stress free samples.

Lattice imaging and pore structure of β ferric oxyhydroxide

1978 ◽  
Vol 36 (1) ◽  
pp. 264-265
Author(s):  
T. Baird ◽  
J.R. Fryer ◽  
S.T. Galbraith
Keyword(s):  
Electron Microscopy ◽  
Room Temperature ◽  
Bulk Material ◽  
Model Structure ◽  
Bulk Crystals ◽  
Lattice Imaging ◽  
Thin Sections ◽  
Ferric Oxyhydroxide ◽  
Resolution Electron ◽  
Hydrolysis Of

Introduction Previously we had suggested (l) that the striations observed in the pod shaped crystals of β FeOOH were an artefact of imaging in the electron microscope. Contrary to this adsorption measurements on bulk material had indicated the presence of some porosity and Gallagher (2) had proposed a model structure - based on the hollandite structure - showing the hollandite rods forming the sides of 30Å pores running the length of the crystal. Low resolution electron microscopy by Watson (3) on sectioned crystals embedded in methylmethacrylate had tended to support the existence of such pores.We have applied modern high resolution techniques to the bulk crystals and thin sections of them without confirming these earlier postulatesExperimental β FeOOH was prepared by room temperature hydrolysis of 0.01M solutions of FeCl3.6H2O, The precipitate was washed, dried in air, and embedded in Scandiplast resin. The sections were out on an LKB III Ultramicrotome to a thickness of about 500Å.

Precipitation in Al + 4% Cu Epitaxial Films

1968 ◽  
Vol 26 ◽  
pp. 384-385
Author(s):  
S. Herd ◽  
S. M. Mader
Keyword(s):  
Solid Solution ◽  
Bulk Material ◽  
Epitaxial Films ◽  
Detectable Change ◽  
Cu Films ◽  
Solution Treated ◽  
Single Crystal Films ◽  
Crystal Films ◽  
Diffraction Patterns ◽  
Deposited Films

Single crystal films in (001) orientation, about 1500 Å thick, were produced by R-F sputtering of Al + 4 wt % Cu onto cleaved KCl at 150°C substrate temperature. The as-deposited films contained numerous θ-CuAl2 particles (C16 structure) about 0.1μ in size. They were transferred onto Mo screens, solution treated and rapidly cooled (within about ½ min) so as to retain a homogeneous solid solution. Subsequently, the films were aged in vacuum at various temperatures in order to induce precipitation and to compare structures and morphologies of precipitate particles in Al-Cu films with those found in age hardened bulk material.Aging for 3 weeks at 60°C or 48 hrs at 100°C did not produce any detectable change in high resolution micrographs or diffraction patterns. In this range Guinier-Preston zones (GP) form in quenched bulk material. The absence of GP in the present experiments in this aging range is perhaps due to the cooling rate employed, which might be more equivalent to an aged and reverted bulk material than to a quenched one.

Epitaxial growth manner and structure of superconducting oxide films

1990 ◽  
Vol 48 (4) ◽  
pp. 2-3
Author(s):  
Yoshichika Bando ◽  
Takahito Terashima ◽  
Kenji Iijima ◽  
Kazunuki Yamamoto ◽  
Kazuto Hirata ◽  
...  
Keyword(s):  
Ultrathin Films ◽  
Film Surface ◽  
High Energy ◽  
Epitaxial Films ◽  
Layer By Layer ◽  
Initial Growth ◽  
In Situ Growth ◽  
High Quality ◽  
Activated Reactive Evaporation

The high quality thin films of high-Tc superconducting oxide are necessary for elucidating the superconducting mechanism and for device application. The recent trend in the preparation of high-Tc films has been toward “in-situ” growth of the superconducting phase at relatively low temperatures. The purpose of “in-situ” growth is to attain surface smoothness suitable for fabricating film devices but also to obtain high quality film. We present the investigation on the initial growth manner of YBCO by in-situ reflective high energy electron diffraction (RHEED) technique and on the structural and superconducting properties of the resulting ultrathin films below 100Å. The epitaxial films have been grown on (100) plane of MgO and SrTiO, heated below 650°C by activated reactive evaporation. The in-situ RHEED observation and the intensity measurement was carried out during deposition of YBCO on the substrate at 650°C. The deposition rate was 0.8Å/s. Fig. 1 shows the RHEED patterns at every stage of deposition of YBCO on MgO(100). All the patterns exhibit the sharp streaks, indicating that the film surface is atomically smooth and the growth manner is layer-by-layer.

Semi-synthesis as a tool for broadening the health applications of bioactive olive secoiridoids: a critical review

2021 ◽  
Author(s):  
Manuela Oliverio ◽  
Monica Nardi ◽  
Maria Luisa Di Gioia ◽  
Paola Costanzo ◽  
Sonia Bonacci ◽  
...  
Keyword(s):  
Critical Review ◽  
Natural Compounds ◽  
Effective Strategy ◽  
Synthetic Analogues ◽  
Health Applications ◽  
Natural And Synthetic

Semi-synthesis is an effective strategy to obtain both natural and synthetic analogues of the olive secoiridoids, starting from easy accessible natural compounds.

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