Silanization of the Wafer Substrates

Si wafers with 285 nm SiO₂ were cleaned by rinsing with 2-propanol and milli-Q water. After being blown dry, the substrates were immersed in a warm piranha (mixture of H₂SO₄ and H₂O₂) solution for at least 60 min, rinsed with deionized water, and dried at 150 °C for 1 h. Thus, cleaned, hydrophyllized, and dried the substrates were immersed in a 10% solution of trimethoxyoctadecylsilane (OTS, Sigma-Aldich, 90+%) in hexane and incubated at 60 °C overnight. For trimethylsilane (TMS) modification, TMSCl was used instead in combination with a few drops of ethyldiisopropylamine. The following day the substrates were rinsed sequentially using hexane, toluene, ethanol, and water before being heated at 110 °C for at least 1 h. The quality of the surface modifications was verified by sessile drop contact angle measurements which showed contact angles of ∼100° for the OTS-modified surfaces and ∼84° for TMS-modified surfaces.