(705a) Low Temperature Synthesis of High Surface Area Titanium Carbide with Tunable Pore Sizes

High surface area, porous titanium carbide films have been synthesized employing physical vapor deposition of titanium at glancing angles under high vacuum within an ethylene ambient. The composition and morphology of the TiC films were studied as a function of deposition conditions including ethylene pressure, titanium deposition angle, substrate temperature during growth and post-deposition annealing temperature. Scanning and transmission electron microscopy shows that at high or glancing deposition angles (~ 80º-85º) synthesis produces films composed of arrays of porous nanocolumns of TiC while deposition at more moderate angles, less than 70º, results in continuous, reticulated films. X-ray diffraction, electron diffraction, and x-ray photoelectron measurements reveal that polycrystalline TiC is formed even at deposition temperatures as low as 310 K. The surface area, porosity and pore size distribution have been investigated using a combination of in vacuu and ex situ techniques including; temperature programmed desorption, toluene adsorption-desorption isotherms, and spectroscopic ellipsometry. The maximum specific surface area (840 m²/gram) is obtained by growth with an incident titanium deposition angle of 65º, an ethylene pressure of 1.5 x 10^-7 Torr, and a substrate growth temperature of ~ 350 K. We show that this deposition method provides direct control of the films' morphology, porosity, and pore size distribution. Films can be synthesized with pore sizes ranging from the micro- to mesopore regime via control of the deposition angle. Titanium carbide films created in this study are thermally robust and resistant to sintering, retaining greater than 70% of their initial surface area after annealing to 1000 K. The ability to deposit TiC near room-temperature should allow these films to be deposited onto a wide variety of substrates.