Chemical Vapor Deposition of Three Aminosilancs on Silicon Dioxide: Surface Characterization, Stability, Effects of Silane Concentration, and Cyanine Dye Adsorption

Covalently bonded monolayers of two monofunctional aminosilanes (3-aminopropyldimethylethoxysilane. APDMES, and 3-aminopropyldiisopropylethoxysilane, APDIPES) and one trifunctional aminosilane (3-aminopropyltriethoxysilane, APTES) have been deposited on dehydrated silicon subsumes by chemical vapor deposition (CVD) at 150 C and low pressure (a few Torr) using reproducible equipment Standard surface analytical techniques such as x-ray photoelectron spectroscopy (XPS). contact angle gontometry, spectroscopic ellipsometry. atomic force microscopy, and time-of-flight secondary ion mass spectroscopy (ToF-SIMS) have been employed to characterize the resulting Films These methods indicate that essentially constant surface coverages arc obtained over a wide range of gas phase concentrations of the aminosilanes XPS data further indicate that the NIs/Si2p ratio is Iliac! after CVD with the trifunctional Wane (APTES) compared to the monofunctional ones, with a higher NIs/Si2p ratio lot APDMES compared to that for APDIPES A FM images show an average surface roughness of 0 12 - 0 15 inn among all three aminosilane films Stability tests indicate that APDIPES films retain most of their integrity at pH 10 for several hours and are more stable than APTEs or APDMES layers The films also showed good stability against storage in the laboratory ToF-SIMS of these samples showed expected peaks, such as CN-, as well as CNO-, which may arise from an interaction between monolayer amine groups and silanols. Optical absorption measurements on adsorbed cyanine dye at the surface of the aminosilane films show the formation of dimer aggregates on the surface This is further supported by ellipsometry measurements. The concentration of dye on each surface appeals lobe consistent with the density of the amines