Polytype Stability and Defect Reduction in 4H-SiC Crystals Grown via Sublimation Technique

1999 ◽  
Vol 572 ◽  
Author(s):  
R. Yakimova ◽  
T. Iakimov ◽  
M. Syvdijarvi ◽  
H. Jacobsson ◽  
P. Råback ◽  
...  
Keyword(s):  
Growth Rate ◽  
Experimental Evidence ◽  
Temperature Interval ◽  
Growth Front ◽  
Morphological Instability ◽  
Surface Kinetics ◽  
Defect Reduction ◽  
Initial Stage ◽  
Good Crystalline Quality ◽  
Sublimation Technique

ABSTRACTReproducible growth of 4H-SiC with good crystalline quality has been obtained in a temperature interval around 2350°C and on 4H-SiC C-face seeds. It has been observed that morphological instability may appear at the initial stage of growth, causing formation of defects. Experimental evidence has been found that supersaturation and surface kinetics are responsible for the polytype stability, while growth front and growth mode address defect reduction. An explanation of the findings has been suggested. It has been shown that starting the growth with a relatively low growth rate ( ≈ 100 μm/h ) can be beneficial for the crystal quality.

Effect of Additional HCl on the Surface Morphology of High Quality GaN on Sapphire by HVPE

2001 ◽  
Vol 693 ◽  
Author(s):  
X.Q. Xiu ◽  
R. Zhang ◽  
D.Q. Lu ◽  
L. Gu ◽  
B. Shen ◽  
...  
Keyword(s):  
Growth Rate ◽  
Surface Morphology ◽  
Smooth Surface ◽  
Growth Front ◽  
Hydride Vapor Phase Epitaxy ◽  
Nucleation Density ◽  
High Quality ◽  
Lower Growth ◽  
Initial Stage ◽  
Lower Growth Rate

AbstractThe effect of introduction of additional HCl on the surface morphology and structural properties of hydride vapor phase epitaxy grown GaN during growth is investigated, and high quality GaN with smooth surface on sapphire is obtained by adding the additional HCl into the HVPE reactor. The result is attributed to the control of polarity of GaN films during growth. The additional HCl altered the equilibrium at the GaN growth front, and the reversible reaction decreased the nucleation density or growth rate. Further, lower growth rate promote the surface diffusion and the coalescence over (0001) plane. Additional HCl may improve the surface morphology by suppressing the (000-1) polarity growth in the initial stage of the growth.

Prospects for Cooperation Between Russia and Syria in Various Scenarios of Military Conflict Development

2021 ◽  
pp. 50-55
Author(s):  
Alheder Haled
Keyword(s):  
Growth Rate ◽  
Inverse Correlation ◽  
Foreign Economic Policy ◽  
Military Conflict ◽  
Political Situation ◽  
Gdp Growth Rate ◽  
Initial Stage ◽  
Military Conflicts ◽  
The Military ◽  
The Relationship

The paper is devoted to determining the prospects for cooperation between Russia and the Syrian Arab Republic in various scenarios of military conflicts. In order to identify the relationship between the success of the country's foreign economic policy and the military conflicts waged on its territory, a study was conducted of such indicators of Syria as: the growth rate of the peace index and the GDP growth rate. A strong inverse correlation is revealed, which means that the level of political situation and peace in the state determines the efficiency of the economy. In view of this, various scenarios of the development of the military conflict in Syria have been studied: at the initial stage, at the stage of active hostilities, at the present stage of overcoming the crisis. The last stage involves four different scenarios for the development of a military conflict, including a local nature and a protracted nature with the involvement of other countries of the world. Options for developing cooperation between Russia and Syria have been identified for each scenario. Taking into account the assessment of the international political situation, the two most likely scenarios for further military events in Syria are identified, and the prospects for cooperation between Russia and Syria in these conditions are outlined.

MBE Growth of GaN Films in Presence of Surfactants: The Effect of Mg and Si

1999 ◽  
Vol 595 ◽  
Author(s):  
Guido Mula ◽  
Bruno Daudin ◽  
Christoph Adelmann ◽  
Philippe Peyla
Keyword(s):  
Growth Rate ◽  
Theoretical Model ◽  
Diffusion Barriers ◽  
Surface Kinetics ◽  
Growth Behaviour ◽  
Mbe Growth ◽  
Foreign Species

AbstractWe present here a description and an analysis of the modifications in the growth behaviour of GaN induced by the presence of foreign species. The particular cases of Mg and Si are analysed. Profound changes, both in microscopic and macroscopic scales, occur in presence of Mg, even for fluxes of about 1/1000th of the Ga flux. The growth rate can be increased by almost 50%, depending of the III/V ratio and on the amount of Mg. A theoretical model is proposed to describe the observed effect. It is found that Mg induces changes in the Ga and N diffusion barriers and acts as a surfactant. The effect is stronger on the a-GaN than on the α-GaN, where N is more tightly bonded. The effect of Si is by far less pronounced, probably because it is more easily incorporated than Mg, and its effect on the surface kinetics is then strongly reduced.

Observation of Growth Front on the Initial Stage of Goss Abnormally-Growing Grain in Fe-3%Si Steel

2013 ◽  
Vol 753 ◽  
pp. 307-310
Author(s):  
Kyung Jun Ko ◽  
Jong Tae Park ◽  
Chan Hee Han
Keyword(s):  
Solid State ◽  
Grain Boundary ◽  
Three Dimensional ◽  
Secondary Recrystallization ◽  
Growth Front ◽  
Very High Frequency ◽  
Grain Boundary Mobility ◽  
Initial Stage ◽  
The Matrix

During abnormal grain growth, a few Goss grains grow exclusively fast and consume the matrix grains. The Goss abnormally-growing grain (AGG) has peculiar features which are irregular grain boundaries and very high frequency of peninsular grains nearby the growth front of AGG and island grains trapped inside AGG. These features might provide a clue for clarifying the mechanism of Goss AGG. The experimentally-observed microstructural feature and grain boundary characterization of Goss were approached by the solid-state wetting mechanism. In this study, observing the three-dimensional wetting morphology in serial section images of Goss AGG by EBSD, we report some direct microstrucrual evidence supporting solid-state wetting mechanism for Goss AGG. The solid-state wetting mechanism for the evolution of the Goss AGG in Fe-3%Si steel explains the microstructural features evolved during secondary recrystallization, which cannot be approached by the conventional theories based on the grain boundary mobility.

Evaluation of Growth Front Velocity in Ultrastable Glasses of Indomethacin over a Wide Temperature Interval

2014 ◽  
Vol 118 (36) ◽  
pp. 10795-10801 ◽  
Author(s):  
Cristian Rodríguez-Tinoco ◽  
Marta Gonzalez-Silveira ◽  
Joan Ràfols-Ribé ◽  
Aitor F. Lopeandía ◽  
Maria Teresa Clavaguera-Mora ◽  
...  
Keyword(s):  
Temperature Interval ◽  
Growth Front ◽  
Front Velocity ◽  
Wide Temperature Interval

Effect of surface kinetics on the step coverage during chemical vapor deposition

1999 ◽  
Vol 14 (6) ◽  
pp. 2377-2380 ◽  
Author(s):  
Gyeong Soon Hwang ◽  
Sang Heup Moon ◽  
Suk Woo Nam ◽  
Chee Burm Shin
Keyword(s):  
Growth Rate ◽  
Chemical Vapor Deposition ◽  
Vapor Deposition ◽  
Numerical Study ◽  
Chemical Vapor ◽  
Surface Kinetics ◽  
Nonlinear Kinetics ◽  
High Tendency ◽  
Step Coverage ◽  
Limited Process

Profile evolution simulations during chemical vapor deposition based on a 2D continuum model reveal that the type of surface kinetics plays an important role in determining step coverage of films deposited in high aspect ratio trenches and vias. Linear surface kinetics, resulting from an adsorption rate limited process, is found to cause difficulty in bringing about conformal step coverage in deep narrow trenches without reducing the growth rate considerably. Under such condition, void-free filling cannot be achieved while maintaining a growth rate acceptable to integrated circuit (IC) manufacturing. The numerical study also suggests that the high tendency of the precursor for chemical equilibrium on a surface, resulting in nonlinear kinetics by a surface reaction limited process, is crucial to achieve a uniform step coverage as typically observed in SiO2 deposition from tetraethylorthosilicate (TEOS).

scholarly journals Bacterial Quorum Sensing Stabilizes Cooperation by Optimizing Growth Strategies

2016 ◽  
Vol 82 (22) ◽  
pp. 6498-6506 ◽  
Author(s):  
Eric L. Bruger ◽  
Christopher M. Waters
Keyword(s):  
Growth Rate ◽  
Quorum Sensing ◽  
Experimental Evidence ◽  
Fundamental Problem ◽  
Growth Yield ◽  
Cellular Growth ◽  
Growth Strategies ◽  
High Cell ◽  
Content Type ◽  
Cell Densities

ABSTRACTCommunication has been suggested as a mechanism to stabilize cooperation. In bacteria, chemical communication, termed quorum sensing (QS), has been hypothesized to fill this role, and extracellular public goods are often induced by QS at high cell densities. Here we show, with the bacteriumVibrio harveyi, that QS provides strong resistance against invasion of a QS defector strain by maximizing the cellular growth rate at low cell densities while achieving maximum productivity through protease upregulation at high cell densities. In contrast, QS mutants that act as defectors or unconditional cooperators maximize either the growth rate or the growth yield, respectively, and thus are less fit than the wild-type QS strain. Our findings provide experimental evidence that regulation mediated by microbial communication can optimize growth strategies and stabilize cooperative phenotypes by preventing defector invasion, even under well-mixed conditions. This effect is due to a combination of responsiveness to environmental conditions provided by QS, lowering of competitive costs when QS is not induced, and pleiotropic constraints imposed on defectors that do not perform QS.IMPORTANCECooperation is a fundamental problem for evolutionary biology to explain. Conditional participation through phenotypic plasticity driven by communication is a potential solution to this dilemma. Thus, among bacteria, QS has been proposed to be a proximate stabilizing mechanism for cooperative behaviors. Here, we empirically demonstrate that QS inV. harveyiprevents cheating and subsequent invasion by nonproducing defectors by maximizing the growth rate at low cell densities and the growth yield at high cell densities, whereas an unconditional cooperator is rapidly driven to extinction by defectors. Our findings provide experimental evidence that QS regulation prevents the invasion of cooperative populations by QS defectors even under unstructured conditions, and they strongly support the role of communication in bacteria as a mechanism that stabilizes cooperative traits.

Characteristics of the Initial Stage of CaCO3 Crystallization Fouling on Straight Oblique Fin Tube

2013 ◽  
Vol 671-674 ◽  
pp. 2535-2541
Author(s):  
Ping Zhao ◽  
Jian Sheng ◽  
Hua Zhang
Keyword(s):  
Growth Rate ◽  
Induction Period ◽  
Nucleation Rate ◽  
Homogeneous Nucleation ◽  
Particle Concentration ◽  
Concentration Increase ◽  
Fouling Resistance ◽  
Initial Stage ◽  
Fin Tube ◽  
Resistance Decrease

To investigate the effect of CaCO3 concentration and velocity on scaling fouling process on plain and SOFT, experiments have been done at different CaCO3 concentration and velocity on the two kind tubes. The results are that the homogeneous nucleation rate and the growth rate are both increase when CaCO3 concentration increases. This make the scaling particle concentration and foulant ions concentration increase, the former gets more scaling on tubes and the later enlarges the heterogeneous nucleation rate and growth rate. Higher velocity decreases the nucleation of scaling, scaling crystal and fouling resistance, but it can prolong the induction period. Higher velocity increases nucleation rate on SOFT first, but the induction period extends and the mass of scaling and fouling resistance decrease. SOFT has a bigger heat transfer coefficient than PT at both clean and fouling conditions and it has smaller fouling resistance even a little more scaling.

scholarly journals The Biology and Trematode Parasites of the GastropodLittorina Neritoides(L.) on the Plymouth Breakwater

1941 ◽  
Vol 25 (1) ◽  
pp. 41-67 ◽  
Author(s):  
Averil M. Lysaght
Keyword(s):  
Growth Rate ◽  
Life History ◽  
Experimental Evidence ◽  
Breeding Season ◽  
Water Discharge ◽  
Downward Migration ◽  
Size Groups ◽  
The Waves ◽  
Trematode Parasites

An account is given of the distribution, life history and trematode parasites ofLittorina neritoideson the Plymouth Breakwater; a few observations from other localities are included.The smaller snails are most abundant on the exposed southern slopes of the Breakwater. Many of the larger ones live more or less permanently in water in small cylindrical pits on the top of the Breakwater. This habitat is apparently very similar to that described by Fischer-Piette (1932) as occupied permanently by this species at Cap Martin; Lebour (1935) has sometimes found it in water in other places in the Plymouth area.The conditions necessary for metamorphosis of the larvae, the need of the adults for shelter from the force of the waves, and the requirements for spawning appear to be of more importance in determining the choice of habitat than the negatively geotactic and varying phototactic responses found in this species by Fränkel (1927).The breeding season lasts from September to April. The males are ripe about two months before most of the females. Experimental evidence is given which makes it most improbable that there is any downward migration for spawning. From the examination of plankton samples it appears that there is a fortnightly spawning rhythm coincident with high tides, and that even the snails living in water discharge their eggs only at these periods.The distribution of the size groups is discussed. The proportion of males decreases significantly in the larger size groups and it is probable that there is a difference in the growth-rate of the sexes.

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