Membranes for micropumps from macroporous silicon

Macroporous silicon is prepared with strongly modulated pore diameter by ap plying a sawtooth-like illumination profile. Taking into account diffusion limited mass transport, 25 perfectly identical modulations have been achiev ed, corresponding to a total pore depth of 200 mum. Qualitatively the pore growth may be well characterized by the established model from the literatu re but fur this non-steady-state situation some extensions become necessary . The: obtained asymmetric pore profiles make this system an ideal candidat e as membranes in particle-size selective micropumps.