Gary S. Silverman

Tuning the optical properties of mesoporous TiO2 films by nanoscale engineering.

The optical properties of spin-coated titanium dioxide films have been tuned by introducing mesoscale pores into the inorganic matrix. Differently sized pores were templated using Pluronic triblock copolymers as surfactants in the sol-gel precursor solutions and adjusted by varying the process parameters, such as the polymer concentration, annealing temperature, and time. The change in refractive index observed for different mesoporous anatase films annealed at 350, 400, or 450 °C directly correlates with changes in the pore size. Additionally, the index of refraction is influenced by the film thickness and the density of pores within the films. The band gap of these films is blue-shifted, presumably due to stress the introduction of pores exerts on the inorganic matrix. This study focused on elucidating the effect different templating materials (Pluronic F127 and P123) have on the pore size of the final mesoporous titania film and on understanding the relation of varying the polymer concentration (taking P123 as an example) in the sol-gel solution to the pore density and size in the resultant titania film. Titania thin film samples or corresponding titanium dioxide powders were characterized by X-ray diffraction, cross-section transmission electron microscopy, nitrogen adsorption, ellipsometery, UV/vis spectrometry, and other techniques to understand the interplay between mesoporosity and optical properties.

Properties of TCO anodes deposited by APCVD and their applications to OLEDs

Doped ZnO is one of the materials currently being considered in industrial applications as a possible replacement for ITO as a transparent conducting oxide. The properties of doped ZnO anodes prepared at Arkema Inc. are analyzed in 3D using high-throughput mapping tools. The 2D resistivities of the coatings measured by 4-point probe compare well with the resistivity values calculated from the spectroscopic ellipsometer measurements. It was found that the dependence of effective mass of doped ZnO on Hall-electron concentration influences optically-calculated mobilities and electron concentrations. To study the variation of the film properties along z-axis, the films are polished using mechanical planarization technique. The electrical and crystallographic depth profiles for these films are studied by differential Hall-effect and grazing-angle x-ray spectroscopy. The electron mobility increases continuously from the glass-film interface (12 cm2/Vs) to the ZnO film surface (19 cm2/Vs). The electron concentration depth profile has bell-like dependence with a maximum at 1.55 x 1021 cm-3. In addition to the increasing grain size, the texture coefficients for the (002) reflection decrease and (103) reflection increase towards the air-film interface. Examples of the applications of the doped ZnO anodes in the OLED structures suggest improvement of external quantum efficiency with introduction of an Al2O3 undercoat.