| The fabrication and characterization of single crystalline titanium nitride (TiN) films. TiN films were grown by a pulsed laser deposition technique using a variety of deposition parameters such as substrate temperature, ambient gas pressure, target-substrate distance, substrate materials, etc. The characterization techniques included primarily x-ray diffraction, scanning electron microscopy, atomic force microscopy, nanoindentation, electrical transport and Hall measurements. The TiN thin films fabricated at temperatures in the range of 500-800 °C in vacuum ambient are found to be epitaxial with (111) orentation. TiN films were controllably oxidized in situ to TiNO phase by introducing nitrogen gas with trace amount of oxygen. AFM and SEM characterization of TiN thin films have shown that all the films are smooth with roughness less than 0.3 nm. TiN thin films deposited in vacuum show pure metallic behavior whereas the films deposited in nitrogen ambient at 50 and 200 mTorr pressure show semiconducting behavior. The Hall measurements and data analysis have shown that the charge carriers are electron in metallic TiN films while the charge carriers are holes in case of semiconducting TiNO films. The band gap of TiN films deposited in 200 mTorr of nitrogen was 0.13 eV whereas bandgap for TiN film deposited in 50 mTorr nitrogen ambient was 0.014 eV. The ability to convert metallic TiN films into semiconducting TiNO films and then further being able to tune TiNO bandgap can be regarded as one of the most important successes of this work. The bandgap engineering of TiNO might open up a new avenue in the photocatalytic splitting of water for fuel cell applications using solar light. |
