We investigated the control of two important parameters of vanadium dioxide (VO2) microcrystals, the phase transition temperature and speed, by varying microcrystal width. By using the reflectivity change between insulating and metallic phases, phase transition temperature is measured by optical microscopy. As the width of square cylinder-shaped microcrystals decreases from ∼70 to ∼1 μm, the phase transition temperature (67 °C for bulk) varied as much as 26.1 °C (19.7 °C) during heating (cooling). In addition, the propagation speed of phase boundary in the microcrystal, i.e., phase transition speed, is monitored at the onset of phase transition by using the high-speed resistance measurement. The phase transition speed increases from 4.6 × 102 to 1.7 × 104 μm/s as the width decreases from ∼50 to ∼2 μm. While the statistical description for a heterogeneous nucleation process explains the size dependence on phase transition temperature of VO2, the increase of effective thermal exchange process is responsible for the enhancement of phase transition speed of small VO2 microcrystals. Our findings not only enhance the understanding of VO2 intrinsic properties but also contribute to the development of innovative electronic devices.
Bibliographical noteFunding Information:
H.J. thanks the Basic Science Research Program for support through grants from the National Research Foundation of Korea (NRF) funded by the Korean Government (MOE), NRF-2012R1A1A2006948. B.S.M. acknowledges support from NRF-2015R1A5A1009962(C-AXS, SRC) , NRF-2015R1A2A2A01004084 and GIST College''s 2015 TBP Research Fund. H.J. thanks Yonsei University for financial support during sabbatical leave in 2015. The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, Materials Science Division, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 at Lawrence Berkeley National Laboratory.
© 2015 American Chemical Society.
All Science Journal Classification (ASJC) codes
- Materials Science(all)