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Direct measurement of free-energy barrier to nucleation of crystallites in amorphous silicon thin films (1994)

Shi, Frank G.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 76 (1994), S. 5149-5153

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ISSN: 1089-7550

Source: AIP Digital Archive

Topics: Physics

Notes: A method is introduced to a measure the free-energy barrier W*, the activation energy, and activation entropy to nucleation of crystallites in amorphous solids, independent of the energy barrier to growth. The method allows one to determine the temperature dependence of W*, and the effect of the preparation conditions of the initial amorphous phase, the dopants, and the crystallization methods on W*. The method is applied to determine the free-energy barrier to nucleation of crystallites in amorphous silicon (a-Si) thin films. For thermally induced nucleation in a-Si thin films with annealing temperatures in the range of from 824 to 983 K, the free-energy barrier W* to nucleation of silicon crystals is about 2.0–2.1 eV regardless of the preparation conditions of the films. The observation supports the idea that a-Si transforms into an intermediate amorphous state through the structural relaxation prior to the onset of nucleation of crystallites in a-Si. The observation also indicates that the activation entropy may be an insignificant part of the free-energy barrier for the nucleation of crystallites in a-Si. Compared with the free-energy barrier to nucleation of crystallites in undoped a-Si films, a significant reduction is observed in the free-energy barrier to nucleation in Cu-doped a-Si films. For a-Si under irradiation of Xe2+ at 105 eV, the free-energy barrier to ion-induced nucleation of crystallites is shown to be about half of the value associated with thermal-induced nucleation of crystallites in a-Si under the otherwise same conditions, which is much more significant than previously expected. The present method has a general kinetic basis; it thus should be equally applicable to nucleation of crystallites in any amorphous elemental semiconductors and semiconductor alloys, metallic and polymeric glasses, and to nucleation of crystallites in melts and solutions.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.357229

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Dynamic scaling of the cluster-size distribul nucleation: Precoalescence stages (1994)

Shi, Frank G. ; Seinfeld, John H.

Hoboken, NJ : Wiley-Blackwell

AIChE Journal 40 (1994), S. 11-18

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ISSN: 0001-1541

Keywords: Chemistry ; Chemical Engineering

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology

Notes: The dynamic evolution of the cluster-size distribution (CSD) in the precoalescence stages of nucleation and growth for sizes within and beyond the nucleation barrier layer (NBL) has been obtained. The existence of several universal kinetic laws of nucleation is predicted. In the precoalescence stages of nucleation, the CSD for sizes within and beyond the NBL obeys dynamic scaling relations. In a range of sizes beyond the NBL, the CSD exhibits a universal power law behavior, the exponent of which depends only on the interphase monomer transfer mechanism. Based on the results for the CSD, a general foundation is developed for nucleation kinetic measurements including the determination of the nucleation barrier and the inter-facial monomer transport rate by measuring the CSD. A preliminary comparison with an experimental study confirms the predicted dynamic scaling and the power law behavior of the CSD in the early stages of nucleation and growth.

Additional Material: 4 Ill.