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A comprehensive investigation of metal–alloy induced crystallization (MAIC) of amorphous silicon (a-Si) is presented. The crystallization processes in three microstructurally principally different, representative types of metal(-alloy)/a-Si systems, Alx(Ge1−x)/a-Si, AgxAl1−x/a-Si, and AlxZn1−x/a-Si, have been monitored by in situ heating x-ray diffraction (XRD) from 25 °C up to 475 °C, until crystallization of a-Si was completed. The obtained experimental results have been systematically compared to predictions obtained by applications of thermodynamic models based on calculations of interface and crystallization energies for the determination of so-called critical thicknesses and initial crystallization temperatures. From the investigation of the MAIC processes in the metal–alloy/a-Si systems, it has been demonstrated that the crystallization temperature and the crystallization kinetics can be well tailored and optimized by controlling the composition and microstructure of the metal alloys. This research, on the one hand, exposes the fundamental, principal role of interface thermodynamics on the crystallization processes and, on the other hand, opens new possibilities for the growth of technologically important, pure, crystalline semiconductor thin films at very low temperatures, as compared to the crystallization temperature of isolated, bulk semiconductor materials. [ABSTRACT FROM AUTHOR]

The high-temperature oxidation of ZrAl2 upon exposure to pure O2 at 800–950 °C was studied in terms of the oxidation kinetics and the formation mechanism of the oxide layer. The alloy followed parabolic oxidation kinetics, and the activation energy of oxidation was 239 ± 14 kJ/mol. During the early stages of oxidation below 850 °C, a single-layer oxide formed due to the crystallization of the initially formed amorphous oxide layer. A multilayer oxide structure developed at higher temperatures, due to the slightly higher affinity of oxygen for Zr than for Al and the oxidation-induced compositional changes. [ABSTRACT FROM AUTHOR]

The thermal crystallization of heavily hydrogenated, amorphous Ge ( a-Ge :H) and ultra-pure amorphous Ge ( a-Ge ) thin films was investigated, on a comparative basis, by X-ray diffraction and high-resolution transmission electron microscopy (HRTEM) performed during in situ heating. It was found that the crystallization process in a-Ge :H is pronouncedly retarded, due to the initial presence of hydrogen-induced nano voids . The crystallization of a-Ge :H initiates only after considerable reduction of the amount of nano voids in the amorphous matrix by thermally induced coarsening of the nano voids leading to nano pores in the a-Ge :H. Such retarded crystallization leads to the formation of nanocrystalline , porous Ge with nanocrystal sizes below 20 nm, in contrast with the fast formation of very large-grained (grain sizes of hundreds of nanometer) polycrystalline Ge upon thermal crystallization of pure a-Ge . [ABSTRACT FROM AUTHOR]

Abstract: Al-induced crystallization (AIC) of amorphous Si x Ge1−x (a-Si x Ge1−x ) solid solutions, with compositions over the entire range of the isomorphous Si–Ge system, was investigated. The crystallization progress was monitored in detail, at low temperatures from 150 to , by in situ X-ray diffraction while gradually increasing the annealing temperature until crystallization was completed, allowing for an evaluation of the crystallization kinetics. The formation of single-phase crystalline Si x Ge1−x solid solutions upon AIC of a-Si x Ge1−x (0 x 1) was observed at all annealing temperatures. Concentration–depth profiling by Auger electron spectroscopy provided a detailed insight into the diffusion processes occurring in the early stage of the low-temperature AIC process and the intriguing phenomenon of layer exchange of the Al and a-Si x Ge1−x sublayers. On the basis of evaluation of the Si and Ge diffusion coefficients, the results suggest that, upon AIC, both Si and Ge atoms diffuse at comparable rates into the Al layer in the low temperature range investigated. The degree of completeness of the layer-exchange process after full crystallization is a function of the a-Si x Ge1−x composition; complete layer exchange occurs for all Al/a-Si x Ge1−x specimens containing more than 27at.% Si. [Copyright &y& Elsevier]

Al-induced crystallization (AIC) of amorphous SixGe1–x (a-SixGe1–x) alloys with compositions over the entire range of the isomorphous Si–Ge system has been investigated. The crystallization progress was monitored by dedicated in situ x-ray diffraction analysis while gradually increasing the annealing temperature. Auger sputter-depth profiling was applied to investigate the occurrence of Al-induced layer exchange of the Al and a-SixGe1–x sublayers after complete crystallization. A-SixGe1–x alloys with x < 0.13 and x > 0.41 show largely different AIC behaviors with respect to crystallization rate and possible layer exchange of the Al and a-SixGe1–x sublayers upon crystallization. A thermodynamic model for AIC of a-SixGe1–x alloys is presented, which well explains these experimental observations and thereby demonstrates the dominant role of interface thermodynamics in the AIC process of amorphous semiconductors. The model can be used to predict the AIC behaviors of a-SixGe1–x alloys over the entire composition range at specified annealing temperatures. [ABSTRACT FROM PUBLISHER]

The oxidation of amorphous Al 0.44 Zr 0.56 alloys upon exposure to pure O 2 (g) at 500 and 560 °C (and p O2 = 1 × 10 5 Pa) was investigated by a combinatorial experimental approach using X-ray diffraction, spectroscopic ellipsometry, transmission electron microscopy and Auger electron spectroscopy. During the early stages of oxidation at 500 and 560 °C, an amorphous (Zr,Al)-oxide layer of homogeneous composition and uniform thickness is formed, which is enriched in Zr with respect to the alloy substrate. At 500 °C, both the alloy substrate and the oxide layer remain amorphous during continued oxidation, whereas at 560 °C, a crystalline tetragonal ZrO 2 ( t -ZrO 2 ) phase nucleates after prolonged oxidation, while the alloy remains amorphous. The nucleation and growth of t -ZrO 2 at 560 °C occurs exclusively close to the interface between the initially formed amorphous (Zr,Al)-oxide layer and the alloy, immediately underneath a region of Al enrichment in the substrate, as triggered by oxidation-induced compositional changes in the alloy below the reacting alloy/oxide interface and a favorable energy of the interface between t -ZrO 2 crystallites and the amorphous alloy matrix. The growing t -ZrO 2 oxide crystallites eventually laterally coalesce to form a continuous layer constituted of branches of dendrite-shaped t -ZrO 2 phase crystallites surrounded by an Al-rich amorphous Al–Zr alloy matrix. The underlying mechanism of the oxidation process is discussed. [ABSTRACT FROM AUTHOR]

The high-temperature oxidation of ZrAl2 upon exposure to pure O2 at 800–950 °C was studied in terms of the oxidation kinetics and the formation mechanism of the oxide layer. The alloy followed parabolic oxidation kinetics, and the activation energy of oxidation was 239 ± 14 kJ/mol. During the early stages of oxidation below 850 °C, a single-layer oxide formed due to the crystallization of the initially formed amorphous oxide layer. A multilayer oxide structure developed at higher temperatures, due to the slightly higher affinity of oxygen for Zr than for Al and the oxidation-induced compositional changes. [ABSTRACT FROM AUTHOR]

Graphene of thickness a few atomic layers has been grown in Ni/a-C bilayers at temperatures as low as 300 °C by Ni-induced crystallization of the amorphous carbon (a-C) in high vacuum. The mechanism of such very low-temperature growth of graphene has been investigated by a combinatorial experimental approach including x-ray diffraction, scanning electron microscopy, Auger electron spectroscopy, x-ray photoelectron spectroscopy and transmission electron microscopy. The growth of this few atomic layer thickness graphene has been found to be mediated by a coupled grain-boundary (GB) diffusion/surface diffusion mechanism. GBs in the top Ni sublayer provide fast diffusion paths for C atoms through the Ni layer, as a result of which graphene layers form above the Ni. The revealed low-temperature growth mechanism of graphene induced by contact with a metal can be applicable in advancing research fields as metal-matrix graphene composites and advanced energy storage devices. Image 1 [ABSTRACT FROM AUTHOR]

[Display omitted] • Graphene was formed by Cu-induced crystallization of amorphous carbon at 300 °C. • A combined experimental approach including AES, XPS, Raman spectroscopy and HRTEM was used. • Graphene formation occurs at the Cu top surface, Cu grain boundaries and the Cu/a-C interface. • The process may provide a promising support for synthesizing Cu/graphene composites at low temperatures. Graphene or graphene-like carbon-reinforced copper matrix composites have gained extensive application prospects in aerospace and electronic fields due to their high electrical, thermal conductivity and excellent machining performance. The preparation of Cu/graphene composites at a relatively low temperature is highly demanded for practical applications. Herein, we develop an approach for synthesizing few-layer graphene (FLG) by contacting amorphous carbon (a-C) with Cu at a low annealing temperature of 300 °C. The mechanism of such low-temperature growth of graphene was discussed by the combined experimental methods of scanning electron microscopy, Auger electron spectroscopy, cross-sectional transmission electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. It is found that the formation of FLG is mediated by the grain-boundary (GB) diffusion, interfacial diffusion and surface diffusion of carbon atoms simultaneously. The high density of Cu GBs can provide a fast diffusion path for "free" C atoms in the a-C sublayer, and the graphene layer was formed at the Cu GBs, at the Cu/a-C interface and on top of the Cu layer where carbon atoms are present. The Cu-induced growth of graphene at low temperatures may provide a promising support for synthesizing Cu/graphene composites in the future. [ABSTRACT FROM AUTHOR]