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Barium Oxyfluoride plays an important role, as a precursor species, in the nucleation and growth of YBa2Cu3O7− δ (YBCO) via the low fluorine metal organic decomposition (MOD low-fluorine) route. In this contribution, we present a study on the thermodynamics of oxyfluoride by processing experimental data on YBCO growth on LaAlO3 (LAO) substrates. The analysis allows one to determine the standard enthalpy and the standard entropy changes for oxyfluoride formation from barium oxide and barium fluoride. To identify the thermodynamically more favorable route to oxyfluoride formation in the MOD low-fluorine process, the free energy change for the formation of the precursor, through reactions involving gas water, has been determined. The free energy of formation via fluoride and water indicates higher stability of oxygen rich oxyfluoride for P HF 2 P H 2 O < 10 − 6 . In the framework of nucleation theory, the present results are needed to study the effect of precursor composition on film orientation. [ABSTRACT FROM AUTHOR]

A model was used to investigate the role of coverage-time during island growth at a solid surface with application to diamond deposition from the gas phase. The results showed that pretreatment of the substrate surface had a significant effect on the nucleation rate of diamond deposition from the gas phase. Small particles left over the substrate surface enhanced the nucleation rate.

Focuses on a model kinetics that should represent a guideline for describing the nucleation process at solid substrate as it occurs in the chemical vapor deposition process. Processes comprising the kinetic scheme; Conditions of low surface coverage; Application to diamond deposition.

In this paper we investigate the connection between Voronoi tessellation and the KJMA approach of space filling. In particular, we study how nuclei, in their growth, cover a given Voronoi cell. This approach leads to an integral equation for the cell-size distribution function. Starting from the 1D case, that is solved exactly, we extend the results to the d D case. The analysis allows to find a rationale to the phenomenological parameter entering the Gamma distribution function and to improve the description of the transformation through the knowledge of the kinetics of grain formation. Moreover, the nucleus size distribution function has been calculated as a function of the transformed fraction. [ABSTRACT FROM AUTHOR]

We report on the characterization of electroformed copper. Different copper films have been deposited, on a brass rod, paying attention to modify only one parameter of the galvanic bath for each specimen (acidity, temperature, density of current, etc.). The samples obtained have been analyzed by residual resistivity ratio (RRR) to evaluated the electrical conductivity, with the nanoindenter to measure the hardness and the reduced modulus and with the X-ray diffraction to calculate the average dimensions of the grains. The comparative analysis of all the data gives us the set of parameters required to obtain a good electrical conductor, working at cryogenic temperatures and mechanically resistant. [ABSTRACT FROM AUTHOR]

The theory of Kolmogorov-Johnson-Mehl-Avrami for phase transition kinetics is subjected to severe limitations concerning the functional form of the growth law. This paper is devoted to sidestepping this drawback through the use of the correlation function approach. Moreover, we put forward an easy-to-handle formula, written in terms of the experimentally accessible actual extended volume fraction, which is found to match several types of growths. Computer simulations have been performed for corroborating the theoretical approach. [ABSTRACT FROM AUTHOR]

Among several aspects concerning the growth of thin films on solid surfaces, we focus our discussion on the physical observable known as the island size distribution function (SDF). Since this is a subject large enough to require a full review, even a whole book, we have limited our survey to the scaling properties of the distribution function and to some of its possible shapes. In particular, we discuss the fast and slow nucleation processes in diffusional growth and the KJMA (Kolmogorov-Johnson-Mehl-Avrami) distributions. Space has been given to the mathematical demonstration of the principal equations, in order to render the paper usable also to neophytes of thin film growth. Experimental particle (SDFs) are also reported and discussed. [ABSTRACT FROM AUTHOR]

The goal of this minireview is restricted to describe how the theoretical basis of Kolmogorov (1937)–Johnson-Mehl (1939) –Avrami (1939–41) model has evolved from its birth up to the present day. The model, which dates back to the late of 1930s, has the purpose of describing the kinetics of a phase transformation. Given the nature of this article, although there are hundreds (if not thousands) of experimental data concerning the most disparate topics, which are interpreted on the basis of the KJMA model, no arguments relating to these, will be touched upon. Starting from the ingenious concept of phantom nuclei, firstly introduced by Avrami to get the exact kinetics, we review theoretical approaches which overcome such concept. We will show how spatial correlation among nuclei plays a fundamental role in these modelings. • The concept of phantom nucleus in the KJMA theory is revisited. • Phantom can be avoided using correlation functions. • Overgrowth phenomena in parabolic growth cured through correlation functions. [ABSTRACT FROM AUTHOR]

Abstract: The evolution of the energy distribution function of the adatoms is described by means of the Chapman–Kolmogorov equation with the inclusion of an extra term which takes account of diatom formation. At steady state the integrodifferential equation is solved in closed form for a two band system, where “hot adatoms” are assumed to populate the high energy band. It is shown that, depending on the ratio of the density of states of the bands and on the transition probabilities for both energy dissipation and recombination, a kinetic transition takes place which is accompanied by enhanced reaction rates. The model is discussed also in connection to previous approaches based on the diffusion equation in energy space and on rate equations for a discrete set of adatom states. [Copyright &y& Elsevier]

It has been shown that the Kolmogorov–Johnson–Mehl–Avrami (KJMA) solution of phase transition kinetics can be set as a problem of correlated nucleation (Phys. Rev. B 65 (2002) 172301). In this paper the equivalence between the standard solution and the approach that makes use of the actual nucleation rate, i.e., that takes into account spatial correlation among nuclei and/or grains, is shown by a direct calculation in case of linear growth and constant nucleation rate. As a consequence, the intrinsic limit of KJMA theory due to the phenomenon of phantom overgrowth is, at last, overcome. Thanks to this new approach it is possible, for instance, to describe phase transition governed by diffusion. [Copyright &y& Elsevier]

The transformation of the 2223 ( n=3) phase in the 2201 ( n=1) phase by heating the sample in Ar atmosphere was studied. The subsequent cycling of the sample temperature and the oxygen enrichment of the gas phase convert the 2201 ( n=1) phase in the 2223 ( n=3) phase in the presence of the 2212 ( n=2) and CaPbO compound. The in situ resistivity measurements, T values and XRD carried out on the sample confirm these phase changes. The experiment indicates that this process is oxygen dependent at low oxygen partial pressure. [ABSTRACT FROM AUTHOR]

We propose a scheme of rate equations for stable dimers that permits the description quite satisfactorily of the evolution of the number of islands in the entire range of surface coverage. The characteristic time for coalescence and the capture number are computed through a stochastic approach for both random and nonrandom arrangements of nuclei. Rate equations are applied to describe kinetic Monte Carlo simulations previously published, in the whole range of surface coverages. It is found that to reproduce the simulation, the effect of the nonrandomicity of the nuclei distribution must be taken into account. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A recent paper by Fernando C. Pérez-Cárdenas [Journal of Non-Crystalline Solids: X 1 (2019) 100002], is rooted on the certainty according to which Avrami's kinetics is just a very good approximation of the exact solution because of the inclusion of phantoms in the model. In what follows we will prove that the thesis of ref. [1] is erroneous. • The role of phantom nuclei in Avrami model is highlighted. • The growth rate of actual nuclei as a function of transformed volume is commented. • The equivalence between Kolmogorov and Avrami approaches is reinforced. [ABSTRACT FROM AUTHOR]