Growth and characterization of high surface area titanium carbide

High surface area, porous titanium carbide (TiC) films have been synthesized employing physical vapor deposition of titanium at glancing angles under high vacuum within an ethylene ambient. The composition, surface area, 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 postdeposition annealing temperature. At high or glancing deposition angles (∼80-85°) synthesis produces films composed of arrays of porous nanocolumns of TiC, while deposition at more moderate angles, less than 70°, results in continuous, reticulated films. The maximum specific surface area (840 m ²/g) is obtained by growth with an incident titanium deposition angle of 65°, an ethylene pressure of 1.5 × 10 ^-7 Torr, and a substrate growth temperature of ∼350 K. This result is in contrast to previous investigations using related physical vapor deposition techniques which have generally shown that films with the greatest porosity and surface area are grown by deposition at cryogenic temperatures (T ≤ 77 K). The fact that the surface area is maximized at this uncharacteristically high growth temperature implies that thermally induced decomposition of ethylene and the subsequent desorption of reaction byproducts are important steps for the synthesis of these materials. Not only does deposition of TiC at 350 K result in high specific surface areas, but electron diffraction measurements indicate that these films are polycrystalline. 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.