Structural and electronic recovery pathways of a photoexcited ultrathin VO${}_{2}$ film

Structural and electronic recovery pathways of a photoexcited ultrathin VO $_{2}$ film

Haidan Wen, Lu Guo, Eftihia Barnes, June Hyuk Lee, Donald A. Walko, Richard D. Schaller, Jarrett A. Moyer, Rajiv Misra, Yuelin Li, Eric M. Dufresne, Darrell G. Schlom, Venkatraman Gopalan, and John W. Freeland

Phys. Rev. B 88, 165424 – Published 25 October 2013

Abstract

The structural and electronic recovery pathways of a photoexcited ultrathin vanadium dioxide (VO $_{2}$ ) film at nanosecond time scales have been studied using time-resolved x-ray diffraction and transient optical absorption techniques. The recovery pathways from the tetragonal metallic phase to the monoclinic insulating phase are highly dependent on the optical pump fluence. At pump fluences higher than the saturation fluence of 14.7 mJ/cm $^{2}$ , we observed a transient structural state with lattice parameter larger than that of the tetragonal phase, which is decoupled from the metal-to-insulator phase transition. Subsequently, the photoexcited VO $_{2}$ film recovered to the ground state at characteristic times dependent upon the pump fluence as a result of heat transport from the film to the substrate. We present a procedure to measure the time-resolved film temperature by correlating photoexcited and temperature-dependent x-ray diffraction measurements. A thermal transport model that incorporates changes of the thermal parameters across the phase transition reproduces the observed recovery dynamics. The optical excitation and fast recovery of ultrathin VO $_{2}$ films provides a practical method to reversibly switch between the monoclinic insulating and tetragonal metallic state at nanosecond time scales.

Received 26 June 2013

DOI:https://doi.org/10.1103/PhysRevB.88.165424

Authors & Affiliations

Haidan Wen^1,*, Lu Guo², Eftihia Barnes², June Hyuk Lee¹, Donald A. Walko¹, Richard D. Schaller^3,4, Jarrett A. Moyer⁵, Rajiv Misra⁶, Yuelin Li¹, Eric M. Dufresne¹, Darrell G. Schlom^7,8, Venkatraman Gopalan^2,†, and John W. Freeland^1,‡

¹Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA
²Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania 16802, USA
³Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois 60439, USA
⁴Department of Chemistry, Northwestern University, Evanston, Illinois 60208, USA
⁵Department of Physics, University of Illinoi at Urbana-Champaign, Urbana, Illinois 61801, USA
⁶Department of Physics, Pennsylvania State University, University Park, Pennsylvania 16802, USA
⁷Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853, USA
⁸Kavli Institute at Cornell for Nanoscale Science, Ithaca, New York 14853, USA

^*Corresponding author: wen@aps.anl.gov
^†vxg8@psu.edu
^‡freeland@aps.anl.gov

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Vol. 88, Iss. 16 — 15 October 2013

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Images

Figure 1
The resistivity of the VO $_{2}$ film as a function of temperature. The inset shows the monoclinic and tetragonal lattice structures of VO $_{2}$ .Reuse & Permissions
Figure 2
(a) Representative 400 Bragg peaks at various temperatures. $M$ and $T$ mark the peak position of monoclinic and tetragonal lattice structures of VO $_{2}$ . (b) Representative 400 Bragg peaks at 100 ps after 800-nm optical excitation at various pump fluences. The counting statistics are worse than that in (a) because the data-collection rate is significantly reduced to match the repetition rate of the pump laser. (c) The change of 400 Bragg peak position (square) and intensity (circle) as a function of the film temperature (black) or pump fluence (red) at 100 ps after photoexcitation. The stars represent the initial states after photoexcitation at specific fluences, with corresponding arrows showing the recovery pathways of the Bragg peak (see text). The solid vertical lines indicate the threshold and saturation fluences of the structural phase transition with the corresponding temperature $T_{1}$ and $T_{2}$ , which divide the plot into three regions. The light blue region indicates the monoclinic structure phase. The white region indicates the fluence or temperature range where the phase transition occurs. The light yellow region indicates the fluence range where non-thermal effects are prominent upon photoexcitation. The dashed lines show the projected thermal recovery pathways.Reuse & Permissions
Figure 3
(a) The change of 400 Bragg peak position as a function of the pump-probe delay at various fluences. The dashed lines indicate the Bragg peak position of monoclinic and tetragonal VO $_{2}$ . (b) The change of 400 Bragg peak intensity as a function of the pump-probe delay at various fluences. (c) The change of 400 Bragg peak position as a function of the pump-probe delay at the base sample temperature below (313 K, triangles) and above (375 K, diamonds) the transition temperature.Reuse & Permissions
Figure 4
The change of lattice parameter (symbols/dashed lines) measured by ultrafast x-ray diffraction and the induced absorption [optical density (OD)] at 1450 nm (thick lines) measured by ultrafast transition absorption spectroscopy as a function of the delay.Reuse & Permissions
Figure 5
The change of 400 Bragg peak position and integrated intensity (circles) as a function of the pump-probe delay, compared with a thermal transport model (solid lines) at pump fluences of (a) 14.3 mJ/cm $^{2}$ and (b) 29 mJ/cm $^{2}$ . The insets show the calculated film temperature as a function of time. The dashed lines indicate the temperature range where the transition occurs.Reuse & Permissions

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