Improving the electrical contact at a Pt/TiO2 nanowire interface by selective application of focused femtosecond laser irradiation

In this paper, we show that tightly focused femtosecond laser irradiation is effective in improving nanojoining of an oxide nanowire (NW) (TiO₂) to a metal electrode (Pt), and how this process can be used to modify contact states. Enhanced chemical bondings are created due to localized plasmonically enhanced optical absorption at the Pt/TiO₂ interface as confirmed by finite element simulations of the localized field distribution during irradiation. Nano Auger electron spectroscopy shows that the resulting heterojunction is depleted in oxygen, suggesting that a TiO_2-x layer is formed between the Pt electrode and the TiO₂ NW. The presence of this redox layer at the metal/oxide interface plays an important role in decreasing the Schottky barrier height and in facilitating chemical bonding. After laser irradiation at the cathode for 10 s at a fluence of 5.02 mJ cm^-2, the Pt/TiO₂ NW/Pt structure displays different electrical properties under forward and reverse bias voltage, respectively. The creation of this asymmetric electrical characteristic shows the way in which modification of the electronic interface by laser engineering can replace the electroforming process in resistive switching devices and how it can be used to control contact states in a metal/oxide interface.