Dual metal–insulator and insulator–insulator switching in nanoscale and Al doped VO2

• Published in: Journal of physics. D, Applied physics Applied physics, 2008-01, Vol.41 (1), p.015402-015402 (5)
• Main Authors: Gentle, A, Smith, G B
• Format: Article
• Language: English
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Electron states and collective excitations in thin films, multilayers, quantum wells, mesoscopic and nanoscale systems; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Electronic transport in multilayers, nanoscale materials and structures; Exact sciences and technology; Physics; Thin films and multilayers
• ISSN: 0022-3727; 1361-6463
• DOI: 10.1088/0022-3727/41/1/015402

Thin films of VO2 doped with aluminium, or with nanoscale grain sizes, have been produced. They display semiconductor resistive behaviour above the transition temperature Tc, but a metallic and plasmonic optical response. All samples optically switch over almost identical large ranges at the transition, but have quite variable resistive switching. At fixed grain size a rigorous new quantitative correlation is found between semiconductor resistivity below Tc and the activation energy above Tc as Al doping level varies. Large crystals doped with Al also display this dual behaviour. A possible mechanism is discussed involving fast local fluctuations on neighbouring V4+ ions involving transient dimers with no net spin. Such fluctuations would then need to interact and correlate their motion over the scale of a nanograin within the lifetime of the dimer excitation.