Investigations of the effect of curing conditions on the structure and stability of amino-functionalized organic films on silicon substrates by Fourier transform infrared spectroscopy, ellipsometry, and fluorescence microscopy

The effect of curing on the structure and stability of amino-functionalized organic films on silicon substrates was investigated using Fourier transform infrared spectroscopy (FTIR), ellipsometry, and fluorescence microscopy. Amino-terminated organic films were prepared on silicon wafers by self-assembling 3-aminopropyltriethoxysilane (APTES) in toluene, cured at different conditions, and washed by sonication in water. For APTES films without curing/or cured at 25 °C, the thickness of APTES films decreased by as much as 65% after sonication in water. FTIR spectra indicate that a substantial amount of physisorbed and/or partially condensed APTES was removed and surface amino groups were oxidized to imines. For APTES films cured at 100 °C, ellipsometric measurements and FTIR spectra showed that the thickness was decreased by ∼10% and that remaining loosely bound APTES had become condensed after curing. Further sonication in water caused no significant changes in the thickness and structure. Independent fluorescence measurements support ellipsometric results and FTIR studies. Our investigations suggest that freshly prepared APTES films are mechanically unstable in aqueous solutions and that proper curing process is required to form physically stable APTES films.