Formation of Thiolate and Phosphonate Adlayers on Indium−Tin Oxide:  Optical and Electronic Characterization

Variable angle reflectance Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were used to investigate adlayers on indium−tin oxide (ITO) and fluorine-doped tin oxide surfaces. A close-packed, ordered adlayer was observed to form on both surfaces by 1-hexadecanethiol through thiolate−indium or thiolate−tin bonding on the two surfaces, respectively. Additionally, a close-packed, ordered adlayer of 12-phosphonododecanoic acid was observed to form on ITO through a phosphonate−indium bonding interaction. The chain length dependence of adlayer formation was studied using alkane thiols of varying chain lengths, and the enthalpic factors affecting adlayer formation were modeled using density functional theory calculations along with periodic boundary conditions.