Local tuning of conductivity in amorphous titanium oxide films by selective electron beam irradiation

Amorphous TiO2 (a-TiO2) films electrodeposited on steel substrates have recently been found highly e-beam sensitive, allowing for reduction and crystallization with high lateral resolution. We here report on the strong correlation between the e-beam-induced changes in oxidation state and film structure, as observed by transmission electron microscopy and Micro-Raman spectroscopy, and the local film conductivity (sigma), measured by conductive atomic force microscopy (c-AFM). c-AFM at constant applied potentials reveals a low a of 1.9 x 10(-4) Omega(-1) cm(-1) for a-TiO2 and a further decrease of a by up to a factor 5.5 x 10(-3) at locally reduced spots, rather than an enhancement in conductivity consistently reported in literature upon reduction of crystalline TiO2. However, sigma significantly rises with the first appearance of anatase phase in micro-Raman spectra, and makes a second large jump coinciding with the formation of TiO, with a being 2 x 10(+4) times higher than in the surrounding a-TiO2, We further observe a rectifying effect due to the presence of micrometer-sized anatase/steel Schottky barrier diodes at locally crystallized spots. The absolute probe current rather than the current density is found responsible for e-beam-induced crystallization, underlining the thermal nature of crystallization at electron energies disqualifying atomic displacement. Structural changes are strictly limited to the irradiated area with anatase nanocrystals being extended nearly throughout the 60 nm thick film, not showing preferential orientation. The results demonstrate the possibility of e-beam-induced confined tuning of sigma in the amorphous oxide film in both directions. This observation is novel and will allow for high-resolution patterning of electrical properties in amorphous semiconducting oxides.