Fabrication of Chemical Gradient Using Space Limited Plasma Oxidation and its Application for Droplet Motion

A novel, simple, versatile, rapid, and inexpensive method, space limited oxygen plasma oxidation is developed to fabricate chemical gradient on both alkylsilane and alkanethiol self-assembled monolayers (SAMs) surface. XPS data confirm that the methyl groups of alkane SAMs are converted into oxidized carbon functional groups. The influences of RF power, O-2 flow rate, and the wedge shape on gradient formation are investigated in details. Gradient surfaces with various scales and depths are formed by simply changing the wedge shape or plasma generation parameters. The application of formed chemical gradient on droplet motion has been demonstrated as well.