Figure 4 .

Development of the organic contents in the etching baths for meso- and macroporous silicon. Evaporation causes a decrease of the ethanol concentration in the mesoporous silicon etching bath of about 17 %; the step after 48 days is due to replenishment of the etching solution. The concentration of the acetic acid in the macroporous silicon etching bath is constant during the observation period due to a closed ‘bleed and feed’ reactor.