Hydrogen stabilization of metallic vanadium dioxide in single-crystal nanobeams

Hydrogen Diffusion and Stabilization in Single-Crystal VO2 Micro/Nanobeams by Direct Atomic Hydrogenation

“…Raman spectra from the dark colored regions of the hydrogenated VO 2 nanobeams (blue curve in Figure 1e) are dominated by weak and broad bands, resembling spectra of VO 2 in the rutile phase (R) 24,32 . Baking a previously fully hydrogenated VO 2 nanobeam in air at 250 8 o C for 20 min restores its Raman spectrum to be nearly identical to that of the as-grown monoclinic state, indicating excellent reversibility of the atomic hydrogenation.…”

“…Before hydrogenation, the conductance of the VO 2 devices changes by a factor of over 10 3 at the metal-insulator transition temperature of ~ 395 K and shows the hysteresis during the cooling and heating cycles. This increased transition temperature compared with bulk material at 341 K is due to the built-in compressive strain in VO 2 nanobeams embedded on substrates 14,15,24 . After being hydrogenated above the MIT temperature for 15 min, the phase transition vanishes and the devices show comparatively high conductivity down to 5 K, indicating relatively metallic character of hydrogenated VO 2 .…”

“…[9][10][11][12][13] Therefore, much effort has been made to modulate the MIT by various approaches such as strain engineering, 14,15 ionic liquid gating, [16][17][18] electric field-induced oxygen vacancy, 19 and chemical doping. [20][21][22][23][24][25] In terms of chemical doping, using metal elements such as tungsten during growth can dramatically change the transition properties 20,26 , but it is an irreversible process. Recently, we have demonstrated that reversible doping with atomic hydrogen alters the electronic phase transition.…”

“…This partial conversion of the beams to a hydrogen-stabilized metallic state agrees well with the results seen when catalytic spillover is used to introduce hydrogen at the ends of similarly prepared nanobeams. 24 In contrast to the spillover situation, in this case atomic hydrogen had access to all exposed faces of the beam. Based on optical signatures of the beam state, hydrogen diffusion in directions transverse to the beam growth direction (i.e., normal to the beam sidewalls) is clearly far slower than diffusion along the beam growth direction from the exposed ends of the beam.…”

Research Update: Nanoscale electrochemical transistors in correlated oxides

“…[10][11][12][13][14][15][16] Conventionally, the amount of hydrogen ions (H + )/oxygen ions (O 2 ) in an oxide has been controlled by annealing the sample under redox gas atmosphere, 11,12,17,18 in aqueous solution 13,14 or with a hydrogen spillover method. 10,15 All of these methods require a high temperature of at least 150 • C. Recently, electric fields have been used for both hydrogenation and oxidation of oxides at room temperature. 16,[19][20][21] For example, a strong electric field in an ionic liquid (IL) gate induces oxygen vacancy formation 042303-2 T. Kanki and H. Tanaka APL Mater.…”