Chemical Vapor Deposition of Azidoalkylsilane Monolayer Films

Abstract

N₃-functionalized monolayers on silicon wafer substrates are prepared via the controlled vapor-phase deposition of 11-azidoundecyltrimethoxysilanes at reduced pressure and elevated temperature. The quality of the layer is assessed using contact angle, attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), and ellipsometry measurements. At 60 °C, longer deposition times are needed to achieve monolayers with similar N₃ density compared to depositions at 145 °C. The monolayers formed via the vapor phase are denser compared to those formed via a solvent-based deposition process. ATR-FTIR measurements confirm the incorporation of azido-alkyl chains in the monolayer and the formation of siloxane bridges with the underlying oxide at both deposition temperatures. X-ray photon spectroscopy shows that the N₃ group is oriented upward in the grafted layer. Finally, the density was determined using total reflection X-ray fluorescence after a click reaction with chlorohexyne and amounts to 2.5 × 10¹⁴ N₃ groups/cm². In summary, our results demonstrate the formation of a uniform and reproducible N₃-containing monolayer on silicon wafers, hereby providing a functional coating that enables click reactions at the substrate.