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

• Published in: Nano letters Vol. 14; no. 5; pp. 2394 - 2400
• Main Authors: Favaloro, Tela, Suh, Joonki, Vermeersch, Bjorn, Liu, Kai, Gu, Yijia, Chen, Long-Qing, Wang, Kevin X, Wu, Junqiao, Shakouri, Ali
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 14.05.2014
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Domain walls; Electron states; Exact sciences and technology; Insulators; Joule heating; Low-dimensional structures (superlattices, quantum well structures, multilayers): structure, and nonelectronic properties; Materials science; Metal-insulator transitions and other electronic transitions; Microscopy; Nanocrystalline materials; Nanoscale materials and structures: fabrication and characterization; Nanostructure; Phase boundaries; Physics; Quantum wires; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Vanadium dioxide; Vanadium oxides; thermoreflectance microscopy; Vanadium dioxide; Peltier effect; Joule heating; metal−insulator domain wall; Temperature distribution; Metal-insulator transition; Domain walls; Nanostructures; Monoclinic lattices; Heat treatments; Interfaces; Nanometer scale; Monocrystals; Stress effects; Polarity; Band offset; Nanowires; Nanostructured materials; Crystal structure
• ISSN: 1530-6984; 1530-6992; 1530-6992
• DOI: 10.1021/nl500042x

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.