Impedance Analysis of Liquid Film Formed on Electrically Stressed Cr Thin Films

Electric field initiated chemical reactions result in surface modifications which have potential applications in the field of micro- and nano-scale patterning and the same is demonstrated through the electrolithography (ELG) technique. In ELG, electrochemical reaction backed modifications on chromium (Cr) thin films have resulted in patterns having a width in the nanometer range. The chemical reaction on the Cr surface results in the formation of a liquid compound. The reaction equation has a similar anatomy to that of a local anodic oxidation reaction. The liquid material formation process takes place under the influence of both unidirectional and alternating electric fields. However, the true nature of the formed liquid region, specifically its electronic characteristic, remains unknown. In this study, we explore the electrical properties of the said liquid domain by employing impedance spectroscopy. Frequency sweeps are carried out in a range spanning five orders of magnitude, from 10 Hz to 1 MHz, on the liquid region formed on electrical stressing of Cr films of thickness 100 nm. Based on the studies, a simple equivalent electrical circuit is proposed. The circuit model is justified with fundamental physics. The impedance spectroscopy results also help us to estimate a time constant for the liquid material formation process. The results of this study will help us better regulate the material formation process on Cr thin films and thereby control the ELG process better.