Adam Stabile

Single-Nanowire Raman Microprobe Studies of Doping-, Temperature-, and Voltage-Induced Metal–Insulator Transitions of WxV1–xO2 Nanowires

Considerable recent research interest has focused on mapping the structural phase diagrams of anisotropic VO(2) nanobeams as model systems for elucidating single-domain behavior within strongly correlated electronic materials, to examine in particular the coupling of lattice and orbital degrees of freedom. Nevertheless, the role of substitutional doping in altering the phase stabilities of competing ground states of VO(2) remains underexplored. In this study, we use individual nanowire Raman microprobe mapping to examine the structural phase progressions underlying the metal-insulator transitions of solution-grown W(x)V(1-x)O(2) nanowires. The structural phase progressions have been monitored for three distinctive modes of inducing the electronic metal-insulator phase transition: as a function of (a) W doping at constant temperature, (b) varying temperature for specific W dopant concentrations, and (c) varying applied voltage for specific W dopant concentrations. Our results suggest the establishment of a coexistence regime within individual nanowires wherein M1 and R phases simultaneously exist before the percolation threshold is reached and the nanowire becomes entirely metallic. Such a coexistence regime has been found to exist during both temperature- and voltage-induced transitions. No evidence of an M2 phase is observed upon inducing the electronic phase transition by any of the three distinctive methods (temperature, doping, and applied voltage), suggesting that substitutional tungsten doping stabilizes the M1 phase over its M2 counterpart and further corroborating that the latter phase is not required to mediate M1→R transformations.

Separating electric field and thermal effects across the metal-insulator transition in vanadium oxide nanobeams

We present results from an experimental study of the equilibrium and non-equilibrium transport properties of vanadium oxide nanobeams near the metal-insulator transition (MIT). Application of a large electric field in the insulating phase across the nanobeams produces an abrupt MIT, and the individual roles of thermal and non-thermal effects in driving the transition are studied. Transport measurements at temperatures (T) far below the critical temperature (Tc) of MIT, in nanoscale vanadium oxide devices, show that both T and electric field play distinctly separate, but critical roles in inducing the MIT. Specifically, at T≪Tc, electric field dominates the MIT through an avalanche-type process, whereas thermal effects become progressively critical as T approaches Tc.

Electrically tunable resonant scattering in fluorinated bilayer graphene

We thank X. Hong for helpful discussions. A.S., J.L., and J.Z. are supported by ONR under Grant No. N00014-11-1-0730 and by NSF CAREER Grant No. DMR-0748604. A.F. and N.M.R.P. acknowledge EC under Graphene Flagship (Contract No. CNECT-ICT-604391). A.F. gratefully acknowledges the financial support of the Royal Society (U.K.) through a Royal Society University Research Fellowship. We acknowledge use of facilities at the PSU site of NSF NNIN.

Electrically driven metal-insulator switching in δ-KxV2O5 nanowires

Metal-insulator transition (MIT) in δ-KxV2O5 nanowires is studied via tuning temperature, voltage, and current. In the temperature-driven case, a massive drop in resistance over ∼4 orders of magnitude at ∼380 K is reported [C. J. Patridge et al., Nano Lett. 10, 2448 (2010)]. Our observation of electrically driven MIT results from a systematic study in any δ-MxV2O5 system (M is the intercalation ion). In the voltage-driven case, the threshold voltage follows an exponential relation with temperature. In the current-driven case, a negative differential resistance region is observed. These results suggest that δ-KxV2O5 is an interesting oxide system exhibiting strong electrically driven MIT and will hence be useful in several switching applications.