Abstract
In this study, we found electrochemical wetting on a surface of a silicon substrate by direct voltage. The surfaces of silicon substrates do not have good wettability in usual condition. We observed here that a wetting area between a silicon substrate and a ultrapure water drop on the silicon surface expanded and a contact angel became almost zero degrees when direct voltage was impressed. Voltages inducing wetting are various and are dependent on crystal directions of substrate surfaces, voltage directions, and so on. However, this phenomenon is irreversible for ultrapure water. Next, experiments using some solutions containing several kinds of ions instead of ultrapure water were conducted. In general, drops of the solutions spread by lower voltage than drops of ultrapure water. When a cathode is contacted to a substrate an anode is immersed in a drop of sodium sulfate solution, the spread of the drop occurs. Then, shrinkage is observed when the reverse voltage is applied. Surface tension is a dominant and important force to micro size structures. At last, we show some types of micro actuator using surface tension controlled electrically in order to apply these phenomena to MEMS.
