Laser processing of titanium: Oxide formation for electronic applications

The formation of laser-induced oxide layers on titanium surfaces has been widely investigated for coloring and marking applications. Complex titanium-based oxides exhibiting multiple phases can be achieved through laser patterning. Laser processing offers several advantages in that discrete areas can be modified leading to patterns with differing optical and electronic properties. To date, most research has focused on the formation and thickness control of TiO2, a wide bandgap semiconductor (similar to 3.2 eV), as a means to control coloration. However, for many applications, including photodetectors and photocatalysts, a semiconductor oxide with a narrow bandgap (< 1 eV) is preferred to allow for strong absorption into the mid-IR. Other oxides and sub-oxides, such as Ti2O3, have been identified as a byproduct of laser surface processing. In addition to its narrow bandgap, bulk Ti2O3 offers the unique property of having a semiconductor-metal transition at around 150 - 200 degrees C where resistivity switches over an order of magnitude. Because of these properties, we investigate the optimization of laser processing conditions using picosecond and femtosecond laser irradiation to form Ti2O3. The effect of laser fluence, scan speed, pulse frequency, and sample chamber pressure will be discussed. Additionally, Ti2O3 thin films were grown via pulsed laser deposition to study structural phase purity, where the effect of growth temperature on optical and electrical properties is explored.