Considerations on the kinetic correlation between SiC nitridation and etching at the 4H-SiC(0001)/SiO2 interface in N2 and N2/H2 ambient

2021 ◽  
Author(s):  
Tianlin Yang ◽  
Koji KITA
Keyword(s):  
High Temperature ◽  
Early Stage ◽  
Etching Rate ◽  
Surface Roughening ◽  
Activation Process ◽  
Rate Limiting Step ◽  
Nitridation Process ◽  
N Incorporation ◽  
Rate Limiting ◽  
Kinetics Of

Abstract Kinetics of SiC surface nitridation process of high-temperature N2 annealing was investigated with 4H-SiC(0001)/SiO2 structure based on the correlation between the rates of N incorporation and SiC consumption induced by SiC etching. During the early stage of the annealing process, the rate-limiting step for N incorporation would be the removal of the topmost C atoms in the slow-etching case, while it would be another reaction step, probably the activation process of nitrogen in the fast-etching case. The SiO2 layer thickness and the annealing ambient which serve as the parameters to affect the SiC etching rate, would determine the N incorporation rate according to the kinetic correlation between the N incorporation and SiC etching. The SiC consumption observed during high-temperature annealing in N2 or N2/H2 ambient would be induced by the active oxidation by residual O2 or H2O in the ambient, which would lead to the SiC surface roughening.

Kinetics of cyclization of S-ethoxycarbonylmethylisothiouronium chloride to 2-imino-4-thiazolidone

1979 ◽  
Vol 44 (3) ◽  
pp. 912-917 ◽  
Author(s):  
Vladimír Macháček ◽  
Said A. El-bahai ◽  
Vojeslav Štěrba
Keyword(s):  
Hydrochloric Acid ◽  
Dilute Hydrochloric Acid ◽  
Base Catalysis ◽  
General Base ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Kinetics Of Formation ◽  
Acid Catalyzed ◽  
Rate Limiting ◽  
Kinetics Of

Kinetics of formation of 2-imino-4-thiazolidone from S-ethoxycarbonylmethylisothiouronium chloride has been studied in aqueous buffers and dilute hydrochloric acid. The reaction is subject to general base catalysis, the β value being 0.65. Its rate limiting step consists in acid-catalyzed splitting off of ethoxide ion from dipolar tetrahedral intermediate. At pH < 2 formation of this intermediate becomes rate-limiting; rate constant of its formation is 2 . 104 s-1.

Kinetics and mechanism of cyclization of N-(2-methoxycarbonylphenyl)-N’-methylsulphonamide to 3-methyl-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide

1991 ◽  
Vol 56 (8) ◽  
pp. 1701-1710 ◽  
Author(s):  
Jaromír Kaválek ◽  
Vladimír Macháček ◽  
Miloš Sedlák ◽  
Vojeslav Štěrba
Keyword(s):  
Potassium Hydroxide ◽  
Acid Catalysis ◽  
Potassium Hydroxide Solution ◽  
Hydroxide Solution ◽  
General Base ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Cyclization Kinetics ◽  
Rate Limiting ◽  
Kinetics Of

The cyclization kinetics of N-(2-methylcarbonylphenyl)-N’-methylsulfonamide (IIb) into 3-methyl-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide (Ib) has been studied in ethanolamine, morpholine, and butylamine buffers and in potassium hydroxide solution. The cyclization is subject to general base and general acid catalysis. The value of the Bronsted coefficient β is about 0.1, which indicates that splitting off of the proton from negatively charged tetrahedral intermediate represents the rate-limiting and thermodynamically favourable step. In the solutions of potassium hydroxide the cyclization of dianion of the starting ester IIb probably becomes the rate-limiting step.

High field 1H NMR Studies of Sol-Gel Kinetics

1986 ◽  
Vol 73 ◽  
Author(s):  
Bruce D. Kay ◽  
Roger A. Assink
Keyword(s):  
Equilibrium Distribution ◽  
Sol Gel ◽  
Nmr Studies ◽  
H Nmr ◽  
Rate Limiting Step ◽  
Rate Of Hydrolysis ◽  
Acid Catalyzed ◽  
Product Species ◽  
Rate Limiting ◽  
Kinetics Of

ABSTRACTHigh resolution 1H NMR spectroscopy at high magnetic fields is employed to study the reaction kinetics of the Si(OCH3)4:CH3OH:H2O sol-gel system. Both the overall extent of reaction as a function of time and the equilibrium distribution of species are measured. In acid catalyzed solution, condensation is the rate limiting step while in base catalyzed solution, hydrolysis becomes rate limiting. A kinetic model in which the rate of hydrolysis is assumed to be independent of the adjacent functional groups is presented. This model correctly predicts the distribution of product species during the initial stages of the sol-gel reaction.

scholarly journals Exploitation of the IDO Pathway in the Therapy of Rheumatoid Arthritis

2013 ◽  
Vol 6s1 ◽  
pp. IJTR.S11737 ◽  
Author(s):  
Richard O. Williams
Keyword(s):  
Rheumatoid Arthritis ◽  
Anthranilic Acid ◽  
Kynurenine Pathway ◽  
Gene Encoding ◽  
Rate Limiting Step ◽  
Tryptophan Metabolites ◽  
Synthetic Derivative ◽  
Rate Limiting ◽  
Kinetics Of ◽  
Draining Lymph Nodes

Indoleamine 2,3-dioxygenase (IDO) is the first and rate-limiting step along the kynurenine pathway and is thought to play a key role in immune homeostasis through depletion of tryptophan and accumulation of kynurenines. In this review we summarize recent research into the possibility of harnessing the IDO pathway for the therapy of rheumatoid arthritis. Inhibition of IDO activity, or knockout of the gene encoding IDO, was shown to cause an increase in the severity of collagen-induced arthritis, an animal model of rheumatoid arthritis. The increased severity of disease was associated with elevated numbers of pathogenic Th1 and Th17 cells in the joints and draining lymph nodes. In another study, analysis of the kinetics of expression of downstream kynurenine pathway enzymes during the course of arthritis revealed a potential role for tryptophan metabolites in resolution of arthritis. Furthermore, the therapeutic administration of L-kynurenine or [3,4-dimethoxycinnamonyl]-anthranilic acid (a synthetic derivative of 3-hydroxy-anthranilic acid) significantly reduced both clinical and histological progression of experimental arthritis. These findings raise the possibility of exploiting the IDO pathway for the therapy of autoimmune disease.

Kinetic analysis of segmentation gene interactions in Drosophila embryos

Development ◽  
1999 ◽  
Vol 126 (7) ◽  
pp. 1515-1526 ◽  
Author(s):  
A. Nasiadka ◽  
H.M. Krause
Keyword(s):  
Target Genes ◽  
Vast Number ◽  
Rate Limiting Step ◽  
Degradation Rates ◽  
Time Required ◽  
Potential Interactions ◽  
Rate Limiting ◽  
Kinetics Of ◽  
Synthesis And Degradation ◽  
Drosophila Embryos

A major challenge for developmental biologists in coming years will be to place the vast number of newly identified genes into precisely ordered genetic and molecular pathways. This will require efficient methods to determine which genes interact directly and indirectly. One of the most comprehensive pathways currently under study is the genetic hierarchy that controls Drosophila segmentation. Yet, many of the potential interactions within this pathway remain untested or unverified. Here, we look at one of the best-characterized components of this pathway, the homeodomain-containing transcription factor Fushi tarazu (Ftz), and analyze the response kinetics of known and putative target genes. This is achieved by providing a brief pulse of Ftz expression and measuring the time required for genes to respond. The time required for Ftz to bind and regulate its own enhancer, a well-documented interaction, is used as a standard for other direct interactions. Surprisingly, we find that both positively and negatively regulated target genes respond to Ftz with the same kinetics as autoregulation. The rate-limiting step between successive interactions (&lt;10 minutes) is the time required for regulatory proteins to either enter or be cleared from the nucleus, indicating that protein synthesis and degradation rates are closely matched for all of the proteins studied. The matching of these two processes is likely important for the rapid and synchronous progression from one class of segmentation genes to the next. In total, 11 putative Ftz target genes are analyzed, and the data provide a substantially revised view of Ftz roles and activities within the segmentation hierarchy.

THE ALTERATION OF INTRACELLULAR ENZYMES: IV. KINETICS OF CATALASE ALTERATION INDUCED BY CHEMICAL AGENTS

1956 ◽  
Vol 34 (1) ◽  
pp. 25-38
Author(s):  
J. Gordin Kaplan ◽  
Woon-Ki Paik
Keyword(s):  
Molecular Level ◽  
Narrow Range ◽  
Intact Cell ◽  
Cellular Level ◽  
Causal Connection ◽  
Rate Limiting Step ◽  
Chemical Agents ◽  
The Difference ◽  
Rate Limiting ◽  
Kinetics Of

The rate with which n-butanol alters the properties of yeast catalase has been studied as a function of temperature and concentration of altering agent. Activation energies for catalase alteration lay within the rather narrow range of 20–23 kcal./mole, thus confirming a prediction made previously on the basis of the difference in energies of activation for heat destruction of altered and unaltered catalases. Alteration by optimal concentration of butanol was a reaction of zero order. Chloroform also altered yeast catalase with an activation energy within this range of μ values. The close agreement in μ values leads us to conclude that the action of these two altering agents, at all concentrations, is characterized by the same rate-limiting step, even though their action differs in other respects. It was concluded that catalase alteration is probably all-or-none on the molecular level, rather than on the cellular level. Alteration was invariably accompanied by a decrease in the size of the treated cells; alteration was sometimes accompanied by changes in the cytochrome spectrum, but there was no causal connection between these two events. These data are consistent with the interfacial hypothesis, which, in its present crude form, pictures alteration as consisting essentially in the desorption of catalase from some intracellular interface at which it is normally bound in the intact cell.

Effect of Medium on Acid-Catalyzed Decomposition of N-(Phenylazo)-Substituted Nitrogen Heterocycles

1999 ◽  
Vol 64 (10) ◽  
pp. 1654-1672 ◽  
Author(s):  
Miroslav Ludwig ◽  
Iva Bednářová ◽  
Patrik Pařík
Keyword(s):  
Rate Constant ◽  
Principal Component ◽  
Catalyst Particle ◽  
Pivalic Acid ◽  
Linear Regression Method ◽  
Catalytic Rate Constant ◽  
Rate Limiting Step ◽  
Acid Catalyzed ◽  
Rate Limiting ◽  
Kinetics Of

Four N-(phenylazo)-substituted saturated nitrogen heterocyclics were synthesized and their structure was confirmed by 1H and 13C NMR spectroscopy. The kinetics of their acid-catalyzed decomposition were studied at various concentrations of the catalyst (pivalic acid) in 40, 30, and 20% (v/v) aqueous ethanol at 25 °C. The values obtained for the observed rate constants were processed by the non-linear regression method according to the suggested kinetic models and by the method of principal component analysis (PCA). The interpretation of the results has shown that the acid-catalyzed decomposition of the heterocyclics under the conditions used proceeds by the mechanism of general acid catalysis, the proton being the dominant catalyst particle of the rate-limiting step. The decrease in the observed rate constant at higher concentrations of the catalyst was explained by the formation of a non-reactive complex composed of the undissociated acid and the respective N-(phenylazo)heterocycle. The effect of medium and steric effect of the heterocyclic moiety on the values of catalytic rate constant are discussed.

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