We have formed self-assembled monolayers (SAMs) of alkanethiolates on5-nmand l0-nm-thick films of gold supported on titanium-primed glass. These electrically-conductive films transmit visible light,s upport SAMs that have wetting properties superior to those of SAMs supported on opaque 200-nm-thick films commonly used in this area of surface chemistr),6 and have surfaces that are smoother than those of thicker films. We present two examples demonstrating the combination of flexibility in control of surface chemistry offered by SAMs of alkanethiols and optical transparency provided by these thin films: measurements of the adsorption of RNase A [EC 3.L27.51labeled with eosin-5-isothiocyanate (EITC) on methyland hexaethylene glycol-terminated SAMs using transmission spectroscopy, and observations of the differential attachment and growth of living MG63 osteosarcoma cells on patterned SAMs of hydroxyland methyl-terminated alkanethiolates using conventional phasecontrast microscopy. To prepare 5-nmand 10-nm-thick films of gold on titaniumprimed glass, we sequentially deposited I nm of titanium at 0.I nm/s and gold at 0.1 nm/s; thick fi lms of gold (200 nm) were deposited at 0.5 nm/s on glass primed with 5 nm of titanium at 0.2 nm/s.7'E For studies of protein adsorption,0.5 nm of t itanium and 5 nm of gold were deposited on each side of glass substrates. The continuity of these films of gold was verified using X-ray photoelectron spectroscopy (XPS).e They also were electrically conductive, with the resistivit ies (7.1 + 0.3) x lO{ O-cm (5nm-thick Au), (4.8 + 0.4) x l0-6 O-cm (10-nm-thick Au), and (3.7 + 1.5) x l0{O-cm (200-nm-thickAu).r0 SAMswere formed by chemisorption from I mM ethanolic solutions of co-functionalized alkanethiols for 2 h at room temperature. The transparency of SAMs on thin films of gold increased withdecreasing thicknessof gold (Figure l). Films became more blue and gray as the thickness of gold decreased (200-nm-thick gold had the same color as bulk gold). Formation of SAMs on these films did not affect their transparency or color.rr Transparency could be increased using a (3-mercaptopropyl)trimethoxysiloxy layer rather than titanium as an adhesion promoter between gold and glass, but evaporation of titanium was a more