Abstract
A new method for the growth of nanoporous thin films is described. The process is targeted to the formation of titanium dioxide (TiO 2 ) through a low-temperature inorganic-filler chemical vapor deposition (CVD) process. The growth technique employs gas-phase reaction of an alkali metal (Na) and a metal halide (TiCl 4 ) and subsequent thin film growth within a low-pressure coflow diffusion reactor. Titanium and salt were codeposited from the gas phase on a heated graphite substrate placed within the reaction zone. After deposition, salt was removed from the surface through a water rinse, yielding a nanoporous structure. The remaining thin film was oxidized to yield titanium dioxide. Qualitative analysis of surface nanostructure and quantitative analysis of pore characteristics showed that the films contained TiO 2 in both anatase and rutile phases, with porosities ranging between 55 and 67%. The dependence of film thickness and pore characteristics on reactant velocity, substrate temperature, and reactant concentration are presented. The synthesis scheme should be generic to the formation of a wide variety of metal and metal oxide porous thin films.
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