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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]

Structural disordering leads to outstanding mechanical properties of amorphous alloys. Many properties are strongly related to formation of surface oxide layers. An in-depth understanding of effect of structural disordering of amorphous alloys on oxide evolution is essential for applications. This paper presents a review of recent comparative oxidation studies of Zr-based amorphous and single-phase crystalline counterpart alloys. Three representative model alloy systems are selected: Zr–Cu and Zr–Al representing alloys with components of different and similar oxygen affinities, respectively, and Zr–Cu–Al representing multi-component alloys. In combination with molecular dynamic simulations, the fundamental role of the structural disordering of parent alloys in the oxidation processes is revealed. The oxidation of Zr–Cu–Al–Ni amorphous alloys at the supercooled liquid temperature region is further reviewed to clarify the relationship between oxidation and substrate crystallization. • A focused review of role of structural disordering of amorphous alloys on thermal oxidation. • Three representative alloys with simple compositions were selected as model alloy systems. • Structural disorder of parent alloys influences strikingly oxide evolution and oxidation kinetics. • The disputes on the oxidation kinetics of amorphous and crystalline states were clarified. [ABSTRACT FROM AUTHOR]

The natural oxidation of amorphous Cu x Zr 1- x ( x  = 0.33, 0.5, 0.67 and 0.75) alloys has been studied by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and cross-sectional transmission electron microscopy. It is revealed that passivation behavior occurs for amorphous Cu x Zr 1- x alloys where x  ≤ 0.67, which provides an effective composition range of amorphous CuZr alloys for long time service. A thin (2–5 nm) ZrO 2 film is formed on top of amorphous alloys, with a Cu-enriched amorphous alloy layer at below. Surprisingly, tetragonal ZrO 2 nucleates between the oxide film and the alloy at room temperature in the naturally oxidized am-Cu 0.33 Zr 0.67 alloy. Amorphous Cu 2 O layer forms on top of the oxide film and surface segregation forming metallic Cu occurs for amorphous Cu x Zr 1- x when x ≥ 0.75. [ABSTRACT FROM AUTHOR]

• The commonly disregarded role of noble constituents on the oxidation of metallic glasses is revealed. • Amorphous Cu-Zr-Al alloys are designed as a model system which contains one noble and two similarly ignoble constituents. • The oxidation for Cu-poor Cu-Zr-Al alloy involves synchronous oxidation of Zr and Al. • Chemical interaction of Cu with Al in the Cu-rich Cu-Zr-Al alloys induces preferential oxidation of Zr over Al. • The study offers a new perspective for rational design of surficial oxide structures. The competition between synchronous oxidation and preferential oxidation of Zr and Al in amorphous Cu-Zr-Al alloys has been investigated. Oxide-layer growth on Cu-poor Cu-Zr-Al alloys occurs by synchronous oxidation of Zr and Al. However, for relatively high Cu alloying contents, synchronous oxidation of Zr and Al becomes disturbed by the increased chemical interaction of Cu with Al, which immobilizes Cu and Al atoms from oxidation. Consequently, only Zr is preferentially oxidized. The findings provide fundamental insights on the role of nobler alloy constituents on the oxidation mechanism of multi-component alloys, which opens new avenues for rational design of surficial oxide structures. [ABSTRACT FROM AUTHOR]

• The fundamental role of atomic structure on thermal oxidation of alloys is revealed. • Al-Zr was selected as the model alloy system to circumvent preferential oxidation effect. • Structural order of parent alloys influences strikingly oxide compositions and oxidation kinetics. • Underlying mechanisms were disclosed by molecular dynamics simulations. • The study offers a new perspective in the field of surface engineering. To reveal the fundamental role of structural order of the parent alloy on the oxidation mechanism, thermal oxidation of amorphous and crystalline Al–Zr alloys with identical compositions were investigated in detail. An (Al 0.68 Zr 0.32)O 1.66 amorphous oxide emerged on crystalline Al 2 Zr, whereas an (Al 0.33 Zr 0.67)O 1.83 amorphous oxide formed on amorphous Al 68at.% Zr 32at.% under the same conditions. Oxidation kinetics was fast and linear for crystalline Al 2 Zr but slow and parabolic for amorphous Al 68at.% Zr 32at.%. The underlying mechanisms of such striking differences were disclosed by molecular dynamics simulations. The findings thus offer new prospects in the field of surface engineering. [ABSTRACT FROM AUTHOR]

• Thermal oxidation of amorphous Cu-Zr alloys with different Cu/Zr ratios has been studied. • High-resolution AES depth profiling and cross-sectional analytic HRTEM analyses were performed. • Cu-enriched nanoparticles emerge due to localized Cu-accumulation by selective oxidation of Zr. • Microstructures of Cu-enriched nanoparticles depend on stabilities of parent alloys. • The composition-dependent microstructure of oxidized Cu x Zr 1− x influences oxidation kinetics. The thermal oxidation of amorphous Cu–Zr alloys with different Cu:Zr ratios was studied by X-ray diffraction, Auger electron spectroscopy, and cross-sectional transmission electron microscopy. It was revealed that amorphous ZrO 2 /Cu-enriched bilayers are formed on the amorphous Cu–Zr alloys at 200–250 °C by the selective oxidation of Zr atoms in the alloys. Amorphous Cu-enriched particles (diameter: ~10 nm) are distributed randomly in the amorphous Cu-enriched sublayer of the am-Cu 33at.% Zr 67at.% alloy, due to the sluggish atomic diffusion in the amorphous Cu-enriched layer. In contrast, crystalline Cu-enriched particles (diameter: ~20 nm) are distributed densely in the amorphous Cu-enriched sublayer of the Cu 50at.% Zr 50at.% alloy. The different states of the Cu-enriched particles in the amorphous Cu-enriched sublayer of the am-Cu 33at.% Zr 67at.% and Cu 50at.% Zr 50at.% alloys are ascribed to thermodynamic reasons. The oxidation rate of amorphous Cu 50at.% Zr 50at.% alloy is faster than that of amorphous Cu 33at.% Zr 67at.% alloy, since the crystalline nanoparticles in the Cu-enriched sublayer provide fast migration pathways for ions, whereas the thick amorphous Cu-enriched sublayer presents as a diffusion barrier in the case of amorphous Cu 33at.% Zr 67at.% alloy. [ABSTRACT FROM AUTHOR]