Modified With 3-mercaptopropyltrimethoxysilane Research Articles

Ultrathin Gold Island Films on Silanized Glass. Morphology and Optical Properties

Evaporated gold island films have been the subject of studies dealing with a variety of spectroscopic and sensing applications. Development of these and other applications requires film stability as well as tunability of the morphology and optical properties of the island films. In the present work, ultrathin, island-type gold films were prepared by evaporation of 1.0−15.0 nm (nominal thickness) gold at a rate of 0.005−0.012 nm s-1 onto glass substrates modified with 3-mercaptopropyl trimethoxysilane (MPTS), the latter used to improve the Au adhesion to the glass. The morphology of the films, either unannealed or annealed (20 h at 200 °C), was studied using atomic force microscopy (AFM) and high-resolution scanning electron microscopy (HR-SEM). The information provided by the two imaging techniques is complementary, giving a good estimate of the shape of the islands and its variation with film thickness and annealing. The optical properties of the films were examined using transmission UV−vis spectroscopy, showing a strong dependence of the localized Au surface plasmon (SP) band on the morphology of the island films. The imaging and spectroscopy indicate a gradual transition from isolated islands to a continuous film upon increasing the Au thickness.

Layer-by-layer accumulation of cadmium sulfide core—silica shell nanoparticles and size-selective photoetching to make adjustable void space between core and shell

Layer-by-layer accumulation of monolayers of silica-coated cadmium sulfide (CdS) was achieved through repeated monolayer deposition–hydrolysis cycles using CdS particles (average diameter: 5 nm) modified with 3-mercaptopropyltrimethoxysilane (MPTS) and glass substrates. Absorption spectroscopic analyses of the resulting yellow films revealed that each layer had almost the same thickness, the estimated density of which corresponded to ca. 66% of that for close hexagonal packing of nanoparticles. Monochromatic light irradiation at 488, 458, or 436 nm onto the film immersed in oxygen-saturated aqueous methylviologen solution caused a decrease in the size of the CdS core depending on the irradiation wavelength, while atomic force microscopic analyses suggested that the size of the silica shell of the immobilized nanoparticles was almost unchanged by irradiation, i.e., the immobilized silica-coated CdS nanoparticles had void spaces between the photoetched core and the silica shell, and their sizes could be regulated by choosing the wavelength of irradiation light. This size-selective photoetching was applied to nanoparticulate films that had been heat-treated at 473, 573 or 673 K to observe the blue-shift of the absorption edge of CdS to the irradiation wavelength. The amount of CdS remaining in the film after the photoetching process depended on the temperature of heat treatment. The largest amount among as-prepared and heat-treated samples was obtained at 473 K and decreased with an increase in temperature. The growth of particles, i.e., the diminution of particle number, and/or the diminution of number of separated independent shells may account for this dependence.