The substrate consists of regions of patterned Au on Si. This was cleaned with piranha solution, rinsed in DI water, then blow dried with N2.
The solvent was 200 proof (anhydrous) ethanol, and the concentration of the silane was 3 mM. The immersion time was 20 min. After that, the sample was sonicated in ethanol, then rinsed in DI water.
I was expecting the Si regions to bond to the silane and become hydrophobic (this was what I observed in other solvents like DCM and toluene). However, the opposite happened - the silicon became hydrophilic, the gold became hydrophobic. Why did this occur?
In the case of DCM and toluene, the solutions became slightly cloudy after a few minutes; however, the ethanolic solution remained clear.
Unless carefully handled ethanol solutions of chlorosilanes are difficult to deposit reproducibly. You probably have inverted deposition in which the fluoroalky end is against the substrate and the chloroformed end converted to silanols and faces out. Try toluene as a solvent @ 2% concentration of the silane. After immersion, allow exposure to atmospheric moisture/humidity for a few hours then heat to ~110°C for ~ 5 minutes.
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