A substrate is placed on a charging surface, to which a first voltage is applied. Etch-resistant dry particles are placed in a cup in a nozzle to which a second voltage, less than the first voltage, is applied. A carrier gas is directed through the nozzle, which projects the dry particles out of the...http://www.google.es/patents/US6780491?utm_source=gb-gplus-sharePatente US6780491 - Microstructures including hydrophilic particles
