Showing papers by "Yang-Tse Cheng published in 1991"

Epitaxial growth of aluminum nitride on Si(111) by reactive sputtering

Abstract: We have studied growth of aluminum nitride (AlN) on Si(111) by ultra‐high vacuum (UHV) reactive dc‐magnetron sputtering under a mixture of Ar and N2 gases. As‐grown films have been examined by x‐ray diffraction, Auger electron spectroscopy (AES), and transmission electron microscopy (TEM). Results of x‐ray diffraction show texturing with AlN [0001]//Si[111]. Complementary TEM examinations observe epitaxy of AlN on Si(111), with AlN[1120]//Si[220]. The AlN/Si interface is sharp and flat. The lowest substrate temperature required to achieve epitaxy Tepi has been determined to be ∼600 °C. A dislocation density in AlN film grown at 700 °C has been estimated to be ∼3×1011/cm2.

Epitaxial growth of α‐Fe films on Si(111) substrates

Abstract: Epitaxial α‐Fe films have been grown on HF cleaned Si(111) substrates at 30 °C by electron beam evaporation in an ultrahigh vacuum environment to a thickness of several thousands of Angstroms. Conventional θ−2θ x‐ray diffraction shows that only the Fe(222) peak is present, indicating that the films are oriented with the Fe(111) plane parallel to the Si(111) plane. Transmission electron microscopy shows that the Fe[110] direction is parallel to the Si[110] direction in the plane of the substrate.

Transition from lateral to transverse phase separation during film co‐deposition

Abstract: We report observations of two distinct types of phase‐separated microstructures in co‐deposited Al‐Ge films. In the initial stages of growth, lateral phase separation is observed, with a temperature dependence consistent with surface diffusion. As the film grows thicker, the Ge‐rich phase becomes increasingly buried, and a transverse phase‐separated microstructure results, consisting of an Al‐rich layer covering a Ge‐rich layer. This observation is explained in terms of the competition between surface and interfacial free energies. We discuss the kinetic aspects of the phase separation process, and the resulting behavior in the thick‐film limit.

Mass and geometry effects on the anisotropic transport in ion mixing

Abstract: Experimental investigations of the effect of target species atomic mass and system geometry on the anisotropic transport in the ion mixing of metallic systems are reported. Bilayer samples with zero heats of mixing and similar cohesive energies, but different atomic mass and geometry, such as Ta on top of Nb(Ta/Nb), Nb on top of Ta(Nb/Ta), Hf on top of Zr (Hf/Zr), and Zr on top of Hf(Zr/Hf) were irradiated by 300 keV Kr2+ at a dose of 2 × 1016 Kr2+/cm2 at 77 K. The samples were investigated using embedded markers and Rutherford backscattering spectrometry. The experimental results indicate that the anisotropic transport is dominated by a preferential displacement of the top layer species into the bottom layer. This is probably due to an anisotropy in the momentum distribution within the collision cascade. In addition, there is an enhancement of the inward displacement when the lighter species is on top indicating a small preferential recoil displacement of the lighter species over the heavier one.

The effects of elevated temperature on sputter depth profiles of silver/nickel bilayers

Abstract: The effect of elevated temperature on the sputtering behavior of silver/nickel bilayers was studied using Auger electron spectroscopy and argon ion sputtering while specimens were held at elevated temperatures (25, 135, 235, 335, and 435 °C). We find that the silver overlayer tranforms from a layer to islands during ion sputtering at temperatures above 100 °C. The transformation to islands is thought to relieve film stresses caused by film‐growth and/or lattice mismatch. Surface diffusion of silver is also observed at elevated temperature (>100 °C). This causes the lower surface energy metal (Ag) to cover the higher surface energy metal (Ni) in regions between the islands. These experiments show that properties of the system such as the heat of mixing, and the surface and interface energies need to be considered when the sputter depth profiling technique is used to study thin film structures, particularly when sputtering is performed at elevated temperatures.

Cohesive energy effects on anisotropic transport in ion mixing

Abstract: Experimental investigations of the effect of target species cohesive energy on anisotropic transport in ion mixing of metallic systems are reported. Bilayer samples with nearly zero heats of mixing, but different cohesive energy and geometry, such as W on top of Pd (W/Pd), Pd on top of W (Pd/W), Nb/Cu, Cu/Nb, Ag/V, and V/Ag, were irradiated with 300 keV Kr2+ at doses of 1 × 1016 Kr2+/cm2 and 2 × 1016 Kr2+/cm2 at 77 K. The samples were investigated using embedded markers and Rutherford backscattering spectrometry. The experimental results indicate a preferential transport of higher cohesive energy material into lower cohesive energy material — in some cases contrary to ballistic arguments. This phenomenon is explained in terms of thermally activated diffusion within thermal spikes.

Epitaxial Growth of α-Fe(111) ON Si(111) Studied by X-RAY Diffraction and Transmission Electron Microscopy

Abstract: Epitaxial α-Fe films have been grown on Si(111) substrates at 30 and 320°C by electron beam evaporation in an ultra high vacuum environment to a thickness between a few hundred and several thousand Angstroms. Conventional θ-2θ x-ray diffraction and transmission electron microscopy show that the α-Fe films are oriented with the Fe(111) plane parallel to the Si(111) plane and with the Fe[110] direction parallel to the Si[110] direction in the plane of the substrate.

On Concentration-Dependent Solid State Diffusion

Abstract: Using a master equation approach, we derive a general expression for the diffusion coefficient as a function of concentration-dependent jump rates. When this approach is applied to diffusion in a binary solid, Darken's equation for intrinsic diffusion coefficients is derived together with an expression for self diffusion coefficients which satisfies the semi-empirical Ugaste relationship. This analysis suggests that the Darken term and the self diffusion coefficients are in general related.