The method comprises (a) connecting a source of constant current in a series circuit with the plasma and the semiconductor body, (b) periodically illuminating the metal being anodized with light to produce photocurrents when the metal approaches the completion of anodization, (c) monitoring the voltage across the source of constant current, and (d) terminating the plasma anodization when the monitored voltage ceases to fluctuate as a result of the aforementioned periodic illumination.
A method is described for thinning an epitaxial layer (16) of a wafer (12) that is to be used in producing diodes having a specified breakdown voltage and which also facilitates the thinning process. Current is passed through the epitaxial layer, by connecting a current source between the substrate (14) of the wafer and an electrolyte (20) in which the wafer is immersed. When the wafer is initially immersed, the voltage across the wafer initially drops and then rises at a steep rate (from 56 to 58). When light is applied to the wafer the voltage drops (from 60 to 62), and when the light is interrupted the voltage rises again (from 66 to 68). These changes in voltage, each indicate the breakdown voltage of a Schottky diode that could be prepared from the wafer at that time. The epitaxial layer is thinned by continuing to apply current through the wafer while it is immersed and light is applied, to form an oxide film (24) and when the oxide film is thick the wafer can then be cleaned of oxide and the testing and thinning continued. Uninterrupted thinning can be achieved by first forming an oxide film, and then using an electrolyte that dissolves the oxide about as fast as it is being formed, to limit the thickness of the oxide layer.
Oxidation treatments by ionic bombardment or post-discharge result in the formation on the surface of passivatable metals and alloys of a layer of oxide having a thickness of a few micrometers which protects the substrates from subsequent corrosion. The gas activated by the electric discharge is put in contact with the surface of the part (2) to be oxidized, which is brought to a temperature of 350.degree. to 650.degree. C. The treatment may be employed in particular for forming a protective covering on an element or a complete framework composed of a zirconium alloy of a fuel assembly of a water-cooled nuclear reactor.
A method for determining the potential of zero charge of an unpowdered semiconductor material. The semiconductor material is used as the working electrode 12 of a standard three-electrode photoelectrochemical cell 11. The onset potential of the semiconductor material is measured at several different cell temperatures. The slope of the graph of onset potential versus temperature is used to compute the potential of zero charge.
A method of producing composite oxide ceramic fluorine polymer layers on articles of aluminum, magnesium, titanium or their alloys, particularly of light metal components, includes introducing particles of fluorine polymers into the capillary system of an oxide ceramic layer. The particles have a particle size which at least in one dimension is smaller than the diameter of the capillaries. The article is then subjected to alternating pressure conditions.
