Effect of laser wavelength in PLD in the orientation and thermochromic properties of VO 2 (Ml) on a glass substrate
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MRS Advances © 2020 Materials Research Society DOI: 10.1557/adv.2020.161
Effect of laser wavelength in PLD in the orientation and thermochromic properties of VO2 (M1) on a glass substrate BN Masina1, 2*, AA Akande1,3, B Mwakikunga1 1
Council for Scientific and Industrial Research, National Laser Centre, PO BOX 395, Pretoria, 0001, South Africa 2
School of Physics, University of KwaZulu-Natal, Private Bag X54001, Durban, 4000, South Africa 3
CSIR NextGen Enterprises and Institutions, Advanced Internet of Things, PO BOX 395, Pretoria, 0001, South Africa
ABSTRACT
Highly oriented VO2 (M1) thin films are difficult to produce using non-crystalline substrates. For example, to produce such films on glass has required post-annealing or the use of a ZnO transparent layer. Here, we overcome this challenge and report highly oriented VO 2 (M1) in the (100) plane directly on the glass substrate by pulsed laser deposition (PLD). We study the influence of the laser wavelengths (1064, 532, 355 and 266 nm) on the orientation of VO2 (M1) deposited on Corning glass. We find that the laser wavelength of 532 nm leads the most highly a-axis textured VO2 (M1) demonstrating the highest reversible metal-to-insulator at about 62 °C with a lowest hysteresis width of approximately 9 °C. One of the conditions is to select the green 532 nm wavelength laser in PLD as this particular laser wavelength also produces films with highest roughness value (of more than 60 nm) when compared to other wavelengths which produce films of roughness values less than 40 nm.
INTRODUCTION: Vanadium dioxide (VO2) has been studied extensively because its transition is near room temperature [1-3]. For example, single crystal VO 2 (M1) exhibits a change in *
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electrical resistivity in the order of 105 over a temperature change of 0.1 qC at 68 qC [4]. Because of its dramatic changes in electrical resistivity and infrared transmission which occur across the phase transition, this material has potential as a switching device [5] and in thermal sensing [6]. The properties of VO 2 thin films, in contrast to single crystalline VO2, can be largely affected by several factors such as strain [7], defect density [8], and the existence of multivalent vanadium ions (V 2+, V3+, V4+, V5+) [9]. These discrepancies make it difficult to deposit high quality VO 2 thin films with sharp transition widths, narrow thermal hysteresis, and large electrical and optical property changes. Additionally, the magnitude of the resistivity change and the size of the hysteresis width are both very sensitive to the stoichiometry and the crystalline structure of the VO 2 thin film. There has been several research works performed in an attempt to reduce the transition temperature by
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