Surface and buried interface layer studies on challenging structures as studied by ARXPS

Abstract

Previous extensive studies were performed at Surface Science Western on the treatment of III-V semiconductors to produce surfaces suitable for subsequent epitaxial growth. X-ray photoelectron spectroscopy (XPS) was used to study oxide formation and capping techniques, and to monitor changes that would occur upon thermal desorption. The effects of a remote plasma on these surfaces were studied as well as to apply thin dielectric films of Si 3 N 4 in order to study interfacial properties. Angleresolved XPS (ARXPS) was performed in many cases to ascertain oxide layer thickness, uniformity, and structure. For the types of surfaces studied-mirror finished semiconductors, ARXPS is straightforward, and the angular dependence is obtained by physically altering the surface orientation with respect to the analyser. While the sample can be repositioned with care to analyse the same spot, changing the angle will effectively change the sampling area, further, surface topography can preclude the use of ARXPS. Use of parallel PARXPS, now available on recent instrumentation, can alleviate these problems. In this case, photoelectrons are collected simultaneously from a large angle. A multichannel detector allows this to be split into smaller angles thereby giving the PARXPS spectra without physically tilting the sample. Further, because the sample is not tilted, topographical effects are minimised allowing meaningful data to be extracted from not so perfect samples. To illustrate this, a detailed PARXPS study on a gallium Indium eutectic (EGaIn) will be presented. Various methods of extracting the depth information from these spectra will be discussed. Finally, the application of using PARXPS to study buried interfaces will be briefly discussed.

Sonication-enabled rapid production of stable liquid metal nanoparticles grafted with poly(1-octadecene-alt-maleic anhydride) in aqueous solutions

“…Spontaneous formation of an oxide skin on the surface of the metal helps to stabilize the resulting LM NPs. The oxide skin of gallium-based is composed primarily of gallium oxide 19,20 and the growth of the oxide could be controlled either through thiolation 21 or thermal oxidation 22 . While the thiolation mitigates (but not eliminates) the growth of the oxide skin, in thermal oxidation, the oxide skin grows thicker with increasing temperature, as expected.…”

Chameleon Metals: Autonomous Nano‐Texturing and Composition Inversion on Liquid Metals Surfaces

“…Oxidation, however, depends on stoichiometry, oxidant diffusion, reduction potential ( E 0 ), microstructure, cohesive energy density, atomic size, temperature, and pressure . In metallic alloys, the complexity of this oxidation process necessitates a kinetics‐driven differentiation and in situ self‐assembly across a thin (7–30 Å) interface . Selectively engineering this thin, complex, tangential, component(s) of a material is challenging due to entropic domination by the bulk …”

“…This initial stoichiometric dictated oxidation, kinetically self‐sorts based on E 0 , cohesive energy density, atomic size (hence diffusivity), and oxygen partial pressure . At t >0, the lowest E 0 element eventually dominates the exterior surface of the metal . For a eutectic (or other stable) alloy mixture, continued oxidation may perturb the bulk equilibrium composition as one (or more) of the components is selectively removed.…”

“…For a eutectic (or other stable) alloy mixture, continued oxidation may perturb the bulk equilibrium composition as one (or more) of the components is selectively removed. This compositional change, albeit small, induces an interface accumulation of higher E 0 component(s) . Shift from statistical‐ (at t =0) to E 0 ‐driven oxidation, coupled with diminished oxidant flux, leads to formation of sub‐oxides beneath the oxidized low E 0 component, while the interface phase‐segregated components bridge the sub‐oxides to the bulk .…”

“…Shift from statistical‐ (at t =0) to E 0 ‐driven oxidation, coupled with diminished oxidant flux, leads to formation of sub‐oxides beneath the oxidized low E 0 component, while the interface phase‐segregated components bridge the sub‐oxides to the bulk . This self‐sorting process leads to a structured, layered interface with sharp composition gradients . Such sharp concentration gradients imply that the oxide‐bulk metal interface has a high chemical potential gradient, (Δ μ ).…”