COLOR CHANGES IN THIN POROUS SILICON FILMS CAUSED BY VAPOR EXPOSURE

Thin films of porous silicon formed by electrochemically etching silic on wafers changed color when exposed to an ambient atmosphere saturate d in various organic solvent vapors. The degree of the color change wa s related to the refractive indices of the solvents. Analysis of the d ata using a four-layer optical model indicated that the film refractiv e index increased up to 15% when solvent molecules replaced air in the pores. Solvent condensing from the saturated atmosphere filled up to 45% of the total void volume. Thermally oxidizing the films to make th em hydrophilic resulted in surfaces which changed color upon exposure to water. (C) 1996 American Institute of Physics.