Holes doping effect on the phase transition of VO2 film via surface adsorption of F4TCNQ molecules

The holes doping effect on the metal-insulator transition (MIT) behavior of VO2 film is investigated via the tetrafluorotetracyanoquinodimethane (F(4)TCNQ) molecules adsorption induced surface charge transfer. Comparing with the MIT process of pristine VO2 film, a critical temperature decrease of about 4 degrees C for the F(4)TCNQ covered VO2 sample is observed. The MIT depression mechanism is deeply investigated based on detailed experiments including synchrotron radiation photon electronic spectroscopy (SRPES), X-ray absorption near-edge structure (XANES) spectroscopy and variable temperature Raman spectroscopy. Results indicate that the electronic structures of F(4)TCNQ covered VO2 sample are changed clearly due to the effective holes doping. In addition, the doped holes also change the V 3d orbital occupancy and weaken the electron-electron correlation as well, lowering the crystalline stability energy. Both of the above effects are in favor of triggering the earlier occurrence of MIT, resulting in the decrease of critical temperature. (C) 2018 Elsevier B.V. All rights reserved.