Selective scanning tunneling microscope light emission from rutile phase of VO₂

We observed scanning tunneling microscope light emission (STM-LE) induced by a tunneling current at the gap between an Ag tip and a VO₂ thin film, in parallel to scanning tunneling spectroscopy (STS) profiles. The 34 nm thick VO₂ film grown on a rutile TiO₂ (0 0 1) substrate consisted of both rutile (R)- and monoclinic (M)-structure phases of a few 10 nm-sized domains at room temperature. We found that STM-LE with a certain photon energy of 2.0 eV occurs selectively from R-phase domains of VO₂, while no STM-LE was observed from M-phase. The mechanism of STM-LE from R-phase VO₂ was determined to be an interband transition process rather than inverse photoemission or inelastic tunneling processes.