Aqueous hydrogen peroxide and sodium hypochlorite in the pH range 7-9 are more effective chemomechanical polishing reagents for gallium arsenide than is dibromine in methanol. Sodium hypochlorite is an acceptable alternative to hydrogen peroxide for gallium arsenide: it also produces good-quality surface finishes on cadmium telluride over the same pH range. The results of dip-etch and polishing reactions, studied using [825r]-labelled dibromine, atomic absorption spectroscopy (AAS) and pH or concentration variation, are used to propose a model for chemomechanical polishing of these materials.

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The sparingly soluble material (the passivating layer) formed during chemomechanical polishing of silica wafers by [HF,J--cerium(~v) oxide-sucrose mixtures at low pH has been identified as K,SiF, coated with a thin silica layer.

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Hydrogen peroxide is an effective chemical polish for gallium arsenide in the pH range 6-8.5. The polished gallium arsenide surface has a surface roughness of <1 nm and is superior to that obtained from polishing with dibromine-methanol solutions.

Co-ordination compounds of iodine(i), including those with tetraazamacrocyclic ligands, have been prepared either by direct reaction with the [I(NCMe),]+ cation or by the previously reported ligandinduced disproportionation reaction of I,. The syntheses and the properties of the iodine complexes so prepared are compared with analogous work involving bromine, iron( 11) or copper(l1).

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