Direct Observation of Nanoscale Peltier and Joule Effects at Metal-Insulator Domain Walls in Vanadium Dioxide Nanobeams

Tela Favaloro, Purdue University, Birck Nanotechnology Center
Joonki Suh, University of California - Berkeley
Bjorn Vermeersch, Purdue University, Birck Nanotechnology Center
Kai Liu, University of California - Berkeley
Yijia Gu, Penn State University
Long-Qing Chen, Penn State University
Kevin X. Wang, University of California - Berkeley
Junqiao Wu, University of California - Berkeley, Penn State University
Ali Shakouri, University of California - Santa Cruz; Birck Nanotechnology Center, Purdue University

Abstract

The metal to insulator transition (MIT) of strongly correlated materials is subject to strong lattice coupling, which brings about the unique one-dimensional alignment of metal insulator (M-I) domains along nanowires or nanobeams. Many studies have investigated the effects of stress on the MIT and hence the phase boundary, but few have directly examined the temperature profile across the metal insulating interface. Here, we use thermoreflectance microscopy to create two-dimensional temperature maps of single-crystalline VO2 nanobeams under external bias in the phase coexisting regime. We directly observe highly localized alternating Peltier heating and cooling as well as Joule heating concentrated at the M I domain boundaries, indicating the significance of the domain walls and band offsets. Utilizing the thermoreflectance technique, we are able to elucidate strain accumulation along the nanobeam and distinguish between two insulating phases of VO2 through detection of the opposite polarity of their respective thermoreflectance coefficients. Microelasticity theory was employed to predict favorable domain wall configurations, confirming the monoclinic phase identification.

Discipline(s)

Nanoscience and Nanotechnology