AFM induced formation of SiO2 structures in the electrochemical nanocell

Nanostructures of SiO2 are formed in the so-called nanocell by AFM tip-indu ced oxidation of Si. The highly resistive electrolyte is formed by a thin w ater film in wet gas atmosphere. AFM measurements prove that the water film thickness increases with both p(H2O) and electric field strength. Water co nsumption by Si oxidation and water electrolysis is compensated by field en hanced water condensation from the gas phase. Due to the absence of a refer ence electrode, current dependent potential drops at the tip and in the wat er film cannot be compensated. At constant cell voltage DeltaU, the potenti al drop within the formed oxide Delta phi (ox) depends not only on DeltaU, but on the polarisation time t and the lateral coordinate x as well. Measur ements of current transients in the nanocell and a macroscopic cell show th at the oxide growth kinetics are similar, but the quantitative result diffe rs due to the 3D structure of the oxide and the variation of Delta phi (ox) (t,x). Investigation of electron transfer reactions in the macro- and nanoc ell show that anodic oxygen evolution is possible at high electric fields w hich is explained by hole tunnelling. Direct tunnelling of electrons from t he tip to the Si substrate can only take place in the initial stages of oxi de formation through few oxide monolayers. Therefore, faradaic processes ca n be evaluated in the later stage of experiment. For electrochemical nanosy stem technology, the oxidation in a one-step process allows the formation o f positive Si-structures, while a multistep process followed by etching of the oxide allows the defined formation of pits. (C) 2001 Elsevier Science L td. All rights reserved.