Microstructure Evolution of Amorphous Si1-xGex Thin Films

1997 ◽  
Vol 472 ◽  
Author(s):  
H. Y. Tong ◽  
Q. Jiang ◽  
D. Hsu ◽  
T. J. King ◽  
F. G. Shi
Keyword(s):  
Thin Film ◽  
Thin Films ◽  
Free Energy ◽  
Energy Barrier ◽  
Composition Dependence ◽  
Composition Range ◽  
Thin Film Transistor ◽  
Free Energy Barrier ◽  
Amorphous Si ◽  
Good Agreement

ABSTRACTThe composition dependence of the nucleation free energy barrier W* in amorphous Si1-xGex thin films is investigated. Within the composition range of x = 0.25 ∼ 0.52, the nucleation free energy barrier exhibits a maximum, which is in a good agreement with our theoretical analysis. The results are significant for processing polycrystalline SiGe thin films with desirable microstructures for thin film transistor applications. In addition, the incubation time of crystallization of amorphous Si1-xGex (x=0.5) thin films is investigated as a function of temperature.

Free-Energy Barrier to Crystallite Nucleation in Solid-Phase Crystallized Poly-Silicon Thin Films

1997 ◽  
Vol 472 ◽  
Author(s):  
Hideya Kumomi ◽  
Frank G. Shi
Keyword(s):  
Thin Films ◽  
Free Energy ◽  
Energy Barrier ◽  
Solid Phase ◽  
Free Energy Barrier ◽  
Solid Phase Crystallization ◽  
Silicon Thin Films ◽  
Nucleation Barrier ◽  
Amorphous Si ◽  
Amor Phization

ABSTRACTWe introduce a non-Arrhenius method for measuring free-energy barrier to nucleation, W*, directly from size distribution of crystallites. W* is determined independent of any model for the nucleation barrier and independent of energy barrier to growth. The method is applicable to three-dimensionally growing crystallites, planar crystallites in thin films, and both compact and fractal crystallites. We apply the method to dendritic crystallites obtained by solid-phase crystallization of amorphous Si thin films into which Si+ ions are implanted at various conditions prior to the isothermal annealing. The ion implantation suppresses the nucleation of the crystallites and enhances the crystallite size of the resulting polycrystalline films. The directly measured W* increases as the accelerating energy or the dose of the Si+ ions increases. This result suggests that the observed suppression of the nucleation could not be accounted for simply by the amor-phization of the preexisting crystallites by the ion bombardment.

THEORETICAL INVESTIGATIONS ON THE MECHANISM OF ACTIVATION OF AMMONIA BY A p-DIMETHYLAMINOPYRIDINE COORDINATED SI=O DOUBLE BOND

2012 ◽  
Vol 11 (02) ◽  
pp. 437-481 ◽  
Author(s):  
YUN-QING HE ◽  
ZE-QIN CHEN ◽  
YING XUE
Keyword(s):  
Hydrogen Bond ◽  
Free Energy ◽  
Energy Barrier ◽  
Intermolecular Hydrogen Bond ◽  
Free Energy Barrier ◽  
Theoretical Investigations ◽  
Unique Pair ◽  
First Time ◽  
Good Interpretation ◽  
Good Agreement

Recently, Xiong et al. reported an activation of ammonia by p-dimethylaminopyridine (DMAP) coordinated silanone (DMAP→Si(L)=O, DS) affording a unique pair of sila-hemiaminal (SH) and silanoic amide (SA) tautomers (Xiong Y, Yao S, Müller R, Kaupp M, Driess M, J Am Chem Soc132:6912, 2010). In this paper, the mechanisms of the activation of ammonia affording SH and SA, the successive generation of hydrogen bonded complex pair SH–SA and the tautomerization between SH and SA have been intensively investigated computationally for the first time at MP2/6-311+G(2d,p)//B3LYP/6-31+G(d,p) level in toluene. The concerted Paths C and D with ammonia assistance are determined by our calculations to be the dominant pathways corresponding to forming SH and SA from DS, respectively. The free energy barrier of Path C affording SH from DS is 14.45 kcal/mol, and that of Path D affording SA is 21.46 kcal/mol. So it is determined theoretically that Path C is dynamically dominant over Path D. And the pair SH–SA is formed then spontaneously by intermolecular hydrogen bond (O–H ⋯ O′) without any barrier. While the tautomerization between SH and SA is nonsignficant resulting from the corresponding relative high barriers (23.79 kcal/mol for process from SH to SA and 26.52 kcal/mol for process from SA to SH). Our results are in good agreement with and good interpretation of the experimental results by Xiong et al.

DFT study on the hydrolysis of metsulfuron-methyl: A sulfonylurea herbicide

2018 ◽  
Vol 17 (08) ◽  
pp. 1850050 ◽  
Author(s):  
Qiuhan Luo ◽  
Gang Li ◽  
Junping Xiao ◽  
Chunhui Yin ◽  
Yahui He ◽  
...  
Keyword(s):  
Free Energy ◽  
Water Molecule ◽  
Carbonyl Group ◽  
Energy Barrier ◽  
Density Functional ◽  
Free Energy Barrier ◽  
Functional Theory ◽  
Metsulfuron Methyl ◽  
Catalytic Role ◽  
Hydrolysis Of

Sulfonylureas are an important group of herbicides widely used for a range of weeds and grasses control particularly in cereals. However, some of them tend to persist for years in environments. Hydrolysis is the primary pathway for their degradation. To understand the hydrolysis behavior of sulfonylurea herbicides, the hydrolysis mechanism of metsulfuron-methyl, a typical sulfonylurea, was investigated using density functional theory (DFT) at the B3LYP/6-31[Formula: see text]G(d,p) level. The hydrolysis of metsulfuron-methyl resembles nucleophilic substitution by a water molecule attacking the carbonyl group from aryl side (pathway a) or from heterocycle side (pathway b). In the direct hydrolysis, the carbonyl group is directly attacked by one water molecule to form benzene sulfonamide or heterocyclic amine; the free energy barrier is about 52–58[Formula: see text]kcal[Formula: see text]mol[Formula: see text]. In the autocatalytic hydrolysis, with the second water molecule acting as a catalyst, the free energy barrier, which is about 43–45[Formula: see text]kcal[Formula: see text]mol[Formula: see text], is remarkably reduced by about 11[Formula: see text]kcal[Formula: see text]mol[Formula: see text]. It is obvious that water molecules play a significant catalytic role during the hydrolysis of sulfonylureas.

COMPARING FOLDING MECHANISMS OF DIFFERENT PRION PROTEINS BY Gō MODEL

2013 ◽  
Vol 12 (08) ◽  
pp. 1341004
Author(s):  
XUE WU ◽  
TING FU ◽  
ZHI-LONG XIU ◽  
LIU YIN ◽  
JIN-GUANG WANG ◽  
...  
Keyword(s):  
Free Energy ◽  
Prion Protein ◽  
Energy Barrier ◽  
Prion Proteins ◽  
Coarse Grained ◽  
Transmissible Spongiform Encephalopathies ◽  
Free Energy Barrier ◽  
Spongiform Encephalopathies ◽  
Go Model ◽  
Folding Free Energy

Prions are associated with neurodegenerative diseases induced by transmissible spongiform encephalopathies. The infectious scrapie form is referred to as PrP Sc , which has conformational change from normal prion with predominant α-helical conformation to the abnormal PrP Sc that is rich in β-sheet content. Neurodegenerative diseases have been found from both human and bovine sources, but there are no reports about infected by transmissible spongiform encephalopathies from rabbit, canine and horse sources. Here we used coarse-grained Gō model to compare the difference among human, bovine, rabbit, canine, and horse normal (cellular) prion proteins. The denatured state of normal prion has relation with the conversion from normal to abnormal prion protein, so we used all-atom Gō model to investigate the folding pathway and energy landscape for human prion protein. Through using coarse-grained Gō model, the cooperativity of the five prion proteins was characterized in terms of calorimetric criterion, sigmoidal transition, and free-energy profile. The rabbit and horse prion proteins have higher folding free-energy barrier and cooperativity, and canine prion protein has slightly higher folding free-energy barrier comparing with human and bovine prion proteins. The results from all-atom Gō model confirmed the validity of C α-Gō model. The correlations of our results with previous experimental and theoretical researches were discussed.

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