Si Sn Alloys Research Articles

Thin Films of Semiconducting SnSi Alloys Grown by Pulsed Laser Deposition

ABSTRACTSemiconducting SnxSi1−x (0≤x≤0.6) thin-film alloys have been grown by pulsed laser deposition (PLD). These new materials are amorphous to X-rays and display small positive optical band gaps, suggesting potential applications in solar cells. The tin silicide films were grown by depositing very thin (1–30 Å) alternating atomic layers from individual Sn and Si targets utilizing an automated multi-target holder coupled to a conventional PLD system. The value of x was selected by controlling the thickness of the atomic layers. The films were characterized by X-ray diffraction, optical absorption, Rutherford backscattering spectroscopy, temperature-dependent resistivity, and X-ray photoelectron spectroscopy. Tin segregation is prevented by keeping the Sn layer thickness below a critical value. Compositions beyond x > 0.6 led to semimetallic SnxSi1−x films with tin crystallites.

EXAFS Study of Metal-Coated Particles Produced by Ball Milling

EXAFS measurements have been carried out on mixtures of Sn with Ge and Si, and Pt with SiO2 which have been ball milled for extended periods. In these systems the brittle component (Ge, Si, or SiO2) is ground to nanocrystalline dimensions while the ductile metal is found to coat the outer surface of the particles. Analysis shows that in the Sn-Ge and Sn-Si systems, mixing at the interface is found to form apparently cubic SnGe and SnSi alloys respectively. In the Pt-SiO2 system while no mixing is observed, the Pt is found to be highly dispersed on the surface of SiO2 particles.

Effect of nonequilibrium interface kinetics on cellular breakdown of planar interfaces during rapid solidification of Si-Sn

During rapid solidification, nonequilibrium interface kinetics alter the predictions of the Mullins-Sekerka theory for the stability of a planar interface against cellular breakdown. The velocity-dependence of the partition coefficient and of the Sn concentration at the onset of cellular breakdown have been measured during pulsed laser melting of Si-Sn alloys. The Mullins-Sekerka theory is modified by inserting a velocity-dependent partition coefficient and a velocity-dependent slope of the “kinetic liquids”, both of which are extracted from the continuous growth model for interface kinetics. These nonequilibrium interface kinetic effects increase the predicted critical concentration for cellular breakdown by two orders of magnitude for Sn in Si, and account fairly well for the experimental results.

Post-forming tensile properties of superplastically bulge formed high strength α/β Ti–Al–Mo–Sn–Si alloy (IMI 550)

The effect of biaxial superplastic deformation at 900°C on ambient temperature tensile properties and texture of high strength α/β titanium alloy sheet of nominal composition Ti–4Al–4Mo–2Sn–0·5Si (IMI 550) has been examined. Superplastic straining led to significant decreases in both proof stress and tensile strength values. Heat cycling studies on as received sheet material showed that the decreases in strength were in part due to the influence of temperature, but this had little effect on elongation. The further losses in strength after superplastic forming were attributable to grain growth. The decreases in elongation after superplastic deformation were believed to be due mainly to changes of tensile specimen geometry, while the more isotropic tensile behaviour which was observed was due to the gradual removal of the relatively low level of texture in the as received material. Application of the standard heat treatment to the as received IMI 550 sheet material led to increases in proof stress and tensile strength values of ~70 and ~170 MN m−2, respectively, and to a slight decrease in elongation. Heat treatment of heat cycled and superplastically bulge formed specimens increased the proof stress and tensile strength values almost to the levels attained in the as received material.MST/684

Post-forming tensile properties of superplastically bulge formed high strength α/β Ti–Al–Mo–Sn–Si alloy (IMI 550)

The effect of biaxial superplastic deformation at 900°C on ambient temperature tensile properties and texture of high strength α/β titanium alloy sheet of nominal composition Ti–4Al–4Mo–2Sn–0·5Si (IMI 550) has been examined. Superplastic straining led to significant decreases in both proof stress and tensile strength values. Heat cycling studies on as received sheet material showed that the decreases in strength were in part due to the influence of temperature, but this had little effect on elongation. The further losses in strength after superplastic forming were attributable to grain growth. The decreases in elongation after superplastic deformation were believed to be due mainly to changes of tensile specimen geometry, while the more isotropic tensile behaviour which was observed was due to the gradual removal of the relatively low level of texture in the as received material. Application of the standard heat treatment to the as received IMI 550 sheet material led to increases in proof stress and tensile strength values of ~70 and ~170 MN m−2, respectively, and to a slight decrease in elongation. Heat treatment of heat cycled and superplastically bulge formed specimens increased the proof stress and tensile strength values almost to the levels attained in the as received material.MST/684

8Li spin-lattice relaxation in liquid LiSn and LiSi alloys

The spin-lattice relaxation time, T 1, of 8Li has been measured in a number of liquid LiSn and LiSi alloys, both as a function of temperature and of applied magnetic field. The relaxation rate, 1/T 1, in liquid LiSn plotted as a function of concentration exhibits a minimum at about 28 at.% Sn. This is qualitatively explained in terms of electron charge transfer from Li to the less electropositive Sn. Varying the concentration and the temperature, deviations were observed from the relation ση≌ constant (σ denotes the electrical conductivity and η the Korringa enhancement). In liquid LiSi, the spin lattice relaxation rate is a decreasing function of the Si concentration up to approximately 43 at.% Si.

Silicon-stabilized grey tin

Melt-spun Sn–Si alloy tapes were transformed to the grey modification at −30 °C to give compact specimens. On subsequent heating, the grey tin phase was seen to be stable to elevated temperatures, e.g., 90 °C for the Sn–0.6 wt % S alloy.

Growth of epitaxial layers of silicon by sublimation through thin alloy zones

The vapour-liquid-solid mechanism of crystal growth is used to obtain epitaxial silicon layers at low temperatures. The layers are grown by a sublimation technique, the silicon being deposited on to a single crystal silicon substrate via a thin liquid alloy zone of Au-Si. Epitaxial silicon layers, up to 15 μm thick and free from stacking faults, are grown at temperatures as low as 500 ± 25°C. Epitaxial growth is also obtained under Cu-Si, In-Si or Sn-Si alloy zones and has stacking fault densities in the range 5 × 103 cm-2 to 107 cm-2. The minimum temperature at which epitaxial growth is observed is at 300°C using an In-Si alloy. The advantages and disadvantages of applying the vapour-liquid-solid mechanism to the growth of epitaxial layers are discussed, particularly the problem of incorporation of the alloy in the growing layer.