Abstract: Metal objects are treated by anodising the metal object in contact with an aqueous electrolyte, and then subjecting the anodised metal object to a reversed voltage. The anodising is performed in two stages, firstly to passivate with the formation of an oxide layer, and secondly to form regions in the oxide layer having a higher oxygen to metal atom ratio, for example pits or caps, in this oxide layer. The second stage of anodising is performed by applying a multiplicity of voltage cycles, each voltage cycle involving ramping the voltage between a lower threshold voltage and an upper threshold voltage, and then returning to the lower threshold voltage. The reversed voltage step forms a hydrous metal oxide in the regions of higher oxygen to metal atom ratio, and the oxide layer and hydrous metal oxide together constitute a surface layer which is integral with the metal object, and has ion exchange capacity.

Abstract: A method of etching silicon of a material comprising silicon, the method comprising the steps of partially covering a silicon surface of the material comprising silicon with an elemental metal and then carrying out a metal-assisted chemical etching of the silicon by exposing the partially covered silicon surface to an etching composition, wherein at least some of the elemental metal for the metal-assisted chemical etching is formed by either: (a) exposing the silicon surface to a composition comprising metal ions, wherein the elemental metal forms by reduction of the metal ions and wherein the composition comprising metal ions is substantially free of HF, or (b) depositing the elemental metal directly onto the silicon surface.