Recent developments in instrumentation in ellipsometry

Reactively sputtered nickel oxide (NiOx) films provide transparent, antireflective, electrically conductive, chemically stable coatings that also are highly active electrocatalysts for the oxidation of water to O2(g). These NiOx coatings provide protective layers on a variety of technologically important semiconducting photoanodes, including textured crystalline Si passivated by amorphous silicon, crystalline n-type cadmium telluride, and hydrogenated amorphous silicon. Under anodic operation in 1.0 M aqueous potassium hydroxide (pH 14) in the presence of simulated sunlight, the NiOx films stabilized all of these self-passivating, high-efficiency semiconducting photoelectrodes for >100 h of sustained, quantitative solar-driven oxidation of water to O2(g).

https://nanoenergy.kaust.edu.sa/Documents/2015-18.pdf

Stable solar-driven oxidation of water by semiconducting photoanodes protected by transparent catalytic nickel oxide films

Semiconductors with small band gaps (<2 eV) must be stabilized against corrosion or passivation in aqueous electrolytes before such materials can be used as photoelectrodes to directly produce fuels from sunlight. In addition, incorporation of electrocatalysts on the surface of photoelectrodes is required for efficient oxidation of H2O to O2(g) and reduction of H2O or H2O and CO2 to fuels. We report herein the stabilization of np+-Si(100) and n-Si(111) photoanodes for over 1200 h of continuous light-driven evolution of O2(g) in 1.0 M KOH(aq) by an earth-abundant, optically transparent, electrocatalytic, stable, conducting nickel oxide layer. Under simulated solar illumination and with optimized index-matching for proper antireflection, NiOx-coated np+-Si(100) photoanodes produced photocurrent-onset potentials of −180 ± 20 mV referenced to the equilibrium potential for evolution of O2(g), photocurrent densities of 29 ± 1.8 mA cm–2 at the equilibrium potential for evolution of O2(g), and a solar-to-O2(g) co...

Stable Solar-Driven Water Oxidation to O2(g) by Ni-Oxide-Coated Silicon Photoanodes.

https://pure.tue.nl/ws/files/2095230/619987.pdf

Investigation of thin-film α- and β-Ni(OH)2 electrodes in alkaline solutions

2 – Optical Physics of Materials

An ellipsometer for following film growth

An optical study of the deposition and conversion of nickel hydroxide films

Measurements in deaerated neutral borate electrolyte which is free of ferrous ions support the duplex film model in which the outer layer gives the electrode its passive properties, and the current is limited by the field in the inner layer across which the overpotential appears Different results are obtained in neutral electroytes which contain ferrous ions or are saturated with air, but there is no sign in neutral electrolyte of the layer-conversion reactions which take place in strong basic electrolytes

An ellipsometric study of the passivity of iron in neutral borate electrolyte

The design and performance of a stepping-motor driven self-nulling ellipsometer are described in detail. Three levels of instrumentation are discussed: (i) the basic instrument which has been in use in our laboratory for over ten years, (ii) the addition of a ministepping drive to provide increased resolution, and (iii) the addition of quadrature Faraday modulators to provide increased speed. It is concluded that developments in technology have made this type of instrument an inexpensive alternative to the conventional manual ellipsometer.© (1977) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Jack L. Ord

Papers

An ellipsometer for following film growth

An optical study of the deposition and conversion of nickel hydroxide films

An ellipsometric study of the passivity of iron in neutral borate electrolyte

Self-Nulling Ellipsometer Design