The Influence of the Arsine Source on the Purity of InGaAs Grown by Hydride VPE

1988 ◽  
Vol 144 ◽  
Author(s):  
D. Noel Buckley ◽  
M. M. Matthiesen
Keyword(s):  
Electron Microscopy ◽  
Carrier Concentration ◽  
Molecular Sieves ◽  
Growth Conditions ◽  
Constant Growth Rate ◽  
High Background ◽  
Feed Line ◽  
Hall Effect Measurements ◽  
Constant Growth ◽  
Scanning Electron

ABSTRACTThe relatively high background carrier concentration obtained in unintentionally doped epitaxial layers of III-V materials imposes a limitation on applications of the hydride VPE process. It is usually attributed to impurities in the gas sources. Results are presented for InGaAs grown by hydride VPE using a range of growth conditions. Carrier concentrations and growth rates for the various samples were determined using, respectively, Polaron electrochemical profiler measurements and scanning electron microscopy. It is shown that the observed background carrier concentration increased with increasing input mole fraction of arsine under conditions of constant growth rate. This strongly implicates the arsine feed gas as a predominant source of impurity. Attempts to purify the arsine feed gas using sodium alumina-silicate molecular sieves are described. Polaron electrochemical profiler measurements and Hall effect measurements on samples grown both with and without molecular sieves in the arsine feed line are presented. From a comparison of the corresponding values of carrier concentration and mobility it is shown that Type 4A molecular sieves were not effective in removing dopant impurities from the 4% arsine-hydrogen mixture used.

scholarly journals Scanning electron microscopy and molecular dynamics of surfaces of growing and ablating hexagonal ice crystals

2009 ◽  
Vol 9 (5) ◽  
pp. 20739-20763 ◽  
Author(s):  
W. C. Pfalzgraff ◽  
R. M. Hulscher ◽  
S. P. Neshyba
Keyword(s):  
Electron Microscopy ◽  
Molecular Dynamics ◽  
Scanning Electron Microscopy ◽  
Climate Models ◽  
Growth Conditions ◽  
Ice Crystals ◽  
Variable Pressure ◽  
Radiative Balance ◽  
Hexagonal Ice ◽  
Scanning Electron

Abstract. Optical properties of cirrus ice clouds play an important role in regulating Earth's radiative balance. It has been hypothesized that the surfaces of cirrus ice crystals may be characterized by mesoscopic (micrometer-scale) texturing, or roughness, in order to explain discrepancies between theoretical and observed light-scattering properties. Here, we present the first clearly resolved observations of surfaces of hexagonal ice crystals, using variable-pressure scanning electron microscopy. During growth conditions, the ice surface develops trans-prismatic strands, separated from one another by distances of 5–10 μm. These strands become more pronounced during ablation, and exhibit a wider range of separations. Under re-growth conditions, faceting is re-established initially at prismatic edges. Molecular dynamics studies of a free-standing ice Ih nanocolumn showed no trans-prismatic strands at the atomistic level, suggesting that these strands originate at a spatial scale greater than 10 nm. The observed surface roughness could be used to construct more realistic representations of cirrus clouds in climate models, and constrain theories of ice crystal growth and ablation.

Investigation of growth conditions of fibrous deposits in carbon arc

1997 ◽  
Vol 12 (6) ◽  
pp. 1551-1557 ◽  
Author(s):  
P. Byszewski ◽  
K. Ukalski ◽  
E. Mizera ◽  
E. Kowalska
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Energy Flow ◽  
Growth Conditions ◽  
Electric Arc ◽  
Buffer Gas ◽  
Condensation Rate ◽  
Carbon Arc ◽  
Scanning Electron ◽  
Gas Pressures

Carbon fibrous deposits grown in carbon dc electric arc at various buffer gas pressures and arc currents were investigated by transmission and scanning electron microscopy. The fibers contained in the deposits consisted of bundles of carbon tubes. It was found that yield and morphology were very sensitive to both parameters; sintering of the tubes could be prevented by adjusting buffer gas pressure for a given current. It is argued that these parameters control expansion of carbon gas and condensation rate, and therefore energy flow to the cathode. To purify samples by oxidation and to observe differences in resistance against oxidation of samples obtained at various conditions, the thermogravimetry method was used.

MBE GROWTH OF GaAs NANOWHISKERS STIMULATED BY THE ADATOM DIFFUSION

2007 ◽  
Vol 06 (03n04) ◽  
pp. 225-231 ◽  
Author(s):  
V. G. DUBROVSKII ◽  
I. P. SOSHNIKOV ◽  
A. A. TONKIKH ◽  
V. M. USTINOV ◽  
G. E. CIRLIN ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Molecular Beam ◽  
Growth Conditions ◽  
Growth Mechanisms ◽  
Vapor Liquid Solid ◽  
Mbe Growth ◽  
Drop Radius ◽  
Adatom Diffusion ◽  
Vapor Liquid Solid Mechanism ◽  
Scanning Electron

The growth mechanisms of GaAs nanowhiskers (NWs) during molecular beam epitaxy (MBE) are studied theoretically and experimentally. A kinetic model of the diffusion-induced NW growth is presented that allows one to predict the dependence of NW length on the drop radius and on the technologically controlled MBE growth conditions. The results of scanning electron microscopy studies of GaAs NWs grown at different conditions on the GaAs (111) B surface activated by Au are presented and analyzed. It is shown that the length of NWs increases with decreasing the drop radius and with decreasing the deposition rate of GaAs , while its temperature dependence has a certain maximum. The aspect ratio of MBE-grown GaAs NWs is higher than 100. The maximum length of NWs is several times larger than the effective thickness of the deposited GaAs . The obtained results demonstrate that the NW growth is controlled by the adatom diffusion toward their tip rather than by the adsorption-induced vapor–liquid–solid mechanism. The growth conditions' influence on the NW morphology may be used for the controlled fabrication of NWs by MBE for different applications.

Formation of Biofilms by Listeria monocytogenes under Various Growth Conditions

2005 ◽  
Vol 68 (1) ◽  
pp. 92-97 ◽  
Author(s):  
ANDREW G. MOLTZ ◽  
SCOTT E. MARTIN
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Stainless Steel ◽  
Listeria Monocytogenes ◽  
Cell Density ◽  
Polyvinyl Chloride ◽  
Growth Medium ◽  
Biofilm Formation ◽  
Growth Conditions ◽  
Scanning Electron

Eight strains of Listeria monocytogenes (7644, 19112, 15313, Scott A, LCDC, 10403S, SLCC, and 1370) produce biofilms when grown on polyvinyl chloride microtiter well plates. The growth medium (tryptic soy broth [TSB] or modified Welshimer's broth [MWB] at 32°C) influenced the amount of biofilm formed; maximum biofilms were formed in MWB by six strains and in TSB by the remaining two strains. This result suggests that the growth medium is critical in development of L. monocytogenes biofilm. This organism also produced biofilms on stainless steel chips. Biofilm formation on these chips was observed following growth in TSB at 4, 20, and 37°C. After 20 h of incubation at 20 or 37°C, the cell density was approximately 106 CFU per chip, and after 4 days incubation at 4°C, the cell density was 105 CFU per chip. L. monocytogenes strain Scott A biofilm formation on stainless steel chips was visualized using scanning electron microscopy, which revealed dense aggregates of cells held together by meshlike webbing.

The Chemical Iodination of Silver

1986 ◽  
Vol 39 (6) ◽  
pp. 827 ◽  
Author(s):  
GD Campbell ◽  
FJ Lincoln ◽  
IM Ritchie
Keyword(s):  
Electron Microscopy ◽  
Growth Conditions ◽  
Average Thickness ◽  
Metal Oxidation ◽  
Ambient Conditions ◽  
X Ray Diffraction ◽  
X Ray ◽  
Structural Identity ◽  
Polycrystalline Silver ◽  
Scanning Electron

Kinetic experiments are reported on the chemical formation of AgI layers on polycrystalline silver substrates. The AgI layers, up to several micrometres in average thickness, were grown under ambient conditions by reacting a rotating silver disc with solutions of iodine dissolved in ethanol and with aqueous triiodide solutions. The morphology and structural identity of the AgI layers were determined by scanning electron microscopy and powder X-ray diffraction, respectively. Depending upon the growth conditions employed, either porous or compact AgI deposits could result, and thus the rate of formation of AgI could be limited by a diffusion step in solution, or by some slower transport step across the layers. The AgI layers were inhomogeneous, and often consisted of discrete crystallites. Thus, the metal oxidation theories developed for planar and isotropic product layers could not be applied to the formation of AgI layers under ambient conditions.

Scanning Electron Microscopy of Clostridium Botulinum Under Varying Growth Conditions

1972 ◽  
Vol 30 ◽  
pp. 324-325
Author(s):  
John B. Ewell ◽  
Philip P. McGrath ◽  
Lee J. Stevan ◽  
John M. Wehrung
Keyword(s):  
Electron Microscopy ◽  
Clostridium Botulinum ◽  
Morphological Changes ◽  
Type A ◽  
Toxin Production ◽  
Growth Conditions ◽  
Tetraacetic Acid ◽  
Carbohydrate Source ◽  
The Past ◽  
Scanning Electron

The toxin produced by Clostridium botulinum type A is a well-known and a well-studied neurotoxin but not many of these studies have correlated the morphological changes of the bacteria with toxin production. Toxin production in type A has been related to autolysis as well as carbohydrate source. Furthermore, toxin production can be inhibited or eliminated if growth occurs in the presence of ethylenediamine tetraacetic acid (EDTA). During the past year we have attempted to use the scanning electron microscope for this correlation of toxin production with morphology under varying conditions of cultivation.

Stoichiometry of Fe, Mn and Co in the marine diazotroph Crocosphaera subtropica ATCC51142 in Fe- and P-limited continuous cultures

2020 ◽  
Vol 656 ◽  
pp. 19-33
Author(s):  
A Marki ◽  
R Fischer ◽  
TJ Browning ◽  
E Louropoulou ◽  
R Ptacnik ◽  
...  
Keyword(s):  
Steady State ◽  
Growth Conditions ◽  
Marine Phytoplankton ◽  
Constant Growth Rate ◽  
Batch Cultures ◽  
Marine Systems ◽  
Elemental Stoichiometry ◽  
State Growth ◽  
Constant Growth

We investigated trace element stoichiometries of the nitrogen-fixing marine cyanobacterium Crocosphaera subtropica ATCC51142 under steady-state growth conditions. We utilized exponentially fed batch cultures and varied iron (Fe) concentrations to establish nutrient limitation in C. subtropica growing at a constant growth rate (0.11 d-1). No statistical difference in cell density, chlorophyll a, particulate organic carbon (C), nitrogen (N) and phosphorus (P) were observed between consecutive days after Day 14, and cultures were assumed to be at steady state with respect to growth for the remaining 11 d of the experiment. Cultures were limited by P in the highest Fe treatment (41 nmol l-1) and by Fe in the 2 lower-concentration Fe treatments (1 and 5 nmol l-1). Cell size and in vivo fluorescence changed throughout the experiment in the 1 nmol l-1 Fe treatment, suggesting ongoing acclimation of C. subtropica to our lowest Fe supply. Nevertheless, Fe:C ratios were not significantly different between the Fe treatments, and we calculated an average (±SD) Fe:C ratio of 32 ± 14 µmol mol-1 for growth at 0.11 d-1. Steady-state P-limited cells had lower P quotas, whilst Fe-limited cells had higher manganese (Mn) and cobalt (Co) quotas. We attribute the increase in Mn and Co quotas at low Fe to a competitive effect resulting from changes in the supply ratio of trace elements. Such an effect has implications for variability in elemental stoichiometry in marine phytoplankton, and potential consequences for trace metal uptake and cycling in marine systems.

Pathogenesis of Human Hair Defects

1974 ◽  
Vol 32 ◽  
pp. 12-13
Author(s):  
P.S. Porter ◽  
T. Aoyagi ◽  
R. Matta
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Human Hair ◽  
Standard Techniques ◽  
Scanning Electron

Using standard techniques of scanning electron microscopy (SEM), over 1000 human hair defects have been studied. In several of the defects, the pathogenesis of the abnormality has been clarified using these techniques. It is the purpose of this paper to present several distinct morphologic abnormalities of hair and to discuss their pathogenesis as elucidated through techniques of scanning electron microscopy.

The Critical Point Drying Method Applied to Scanning Electron Microscopy of L-929 Cells

1970 ◽  
Vol 28 ◽  
pp. 278-279
Author(s):  
Charles TurnbiLL ◽  
Delbert E. Philpott
Keyword(s):  
Electron Microscopy ◽  
Carbon Dioxide ◽  
Surface Tension ◽  
Critical Point ◽  
Freeze Drying ◽  
Attractive Alternative ◽  
Crystal Formation ◽  
Critical Point Drying ◽  
Time Required ◽  
Scanning Electron

The advent of the scanning electron microscope (SCEM) has renewed interest in preparing specimens by avoiding the forces of surface tension. The present method of freeze drying by Boyde and Barger (1969) and Small and Marszalek (1969) does prevent surface tension but ice crystal formation and time required for pumping out the specimen to dryness has discouraged us. We believe an attractive alternative to freeze drying is the critical point method originated by Anderson (1951; for electron microscopy. He avoided surface tension effects during drying by first exchanging the specimen water with alcohol, amy L acetate and then with carbon dioxide. He then selected a specific temperature (36.5°C) and pressure (72 Atm.) at which carbon dioxide would pass from the liquid to the gaseous phase without the effect of surface tension This combination of temperature and, pressure is known as the "critical point" of the Liquid.

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