Figure 1

(a) Transition temperature (solid circles) as a function of $x$. Inset schematizes metallic rutile and insulating monoclinic structures. The former has a high-symmetry tetragonal structure with V ions staying at the body center, whereas the latter distorts in a monoclinic structure by forming V-V dimers with tilted bonding. Open circles represent the temperature where tiny resistivity upturn appears in the metallic ground-state samples with 0.07 ≤ $x$ ≤ 0.10 [see (d) for $x$ $=$ 0.08 as an example]. (b) A schematic of the sample. The film thickness is about 80 nm. (c) A top-view photograph of the patterned W:VO${}_2$ film (gray, 220 × 100 μm${}^2$) attached with Au/Al electrodes (yellow/light gray). The remaining part (brown/dark gray) is insulating TiO${}_2$ substrate exposed by etching. The red/gray-dashed square indicates the area of x-ray irradiated region (460 × 580 μm${}^2$). (d) Temperature dependence of resistivity for W:VO${}_2$ ($x$ $=$ 0.04, 0.065, and 0.08) films. The resistivity of the $x$ $=$ 0.065 sample is also measured under constant x-ray irradiation with a photon flux density of 5.4 × 10${}^{14}$ cm${}^{-2}$ s${}^{-1}$, which shows a metallic behavior below 50 K.Reuse & Permissions

Figure 2

(a) Electrical resistivity (upper) and out-of-plane lattice constant (lower) of the W:VO${}_2$ ($x$ $=$ 0.065) film as a function of temperature. The PIPT experiment with the x-ray irradiation (5.4 × 10${}^{14}$ cm${}^{-2}$ s${}^{-1}$ for 1 min) was performed at 9 K (dashed blue/dark gray arrows). Resistivity value can be tuned by the irradiation time as shown by the yellow/light gray middle line (8.4 × 10${}^{11}$ cm${}^{-2}$ s${}^{-1}$ for about 4 min) as an example in the upper panel. (b) Variation of XRD patterns for (002) reflection peak of the W:VO${}_2$ film at each stage denoted with (1)–(4) in the lower panel of (a).Reuse & Permissions

Figure 3

X-ray exposure-time dependence of the electrical conductivity (on the left ordinate) and of the intensity for (002) Bragg reflection peak in the insulating phase denoted with a black line in Fig. 2b on the right ordinate. The photon flux density was 8.4 × 10${}^{11}$ cm${}^{-2}$ s${}^{-1}$, and the x-ray irradiation was intermittently turned off as indicated by zero-diffraction intensity periods. The phase transition proliferation is only under the x-ray irradiation but with negligible relaxation during the x-ray turnoff period.Reuse & Permissions

Figure 4

(a) XRD patterns of the film during the PIPT at 9 K in the chorological order from bottom (0 s) to top (2,000 s) under x-ray irradiation with a photon flux density of 8.4 × 10${}^{11}$ cm${}^{-2}$ s${}^{-1}$. The initial (insulating) and final (metallic) states are highlighted in blue/dark gray and red/gray, respectively. (b) Typical XRD patterns with Gaussian fitting as composed of insulating (blue/dark gray, left), metallic (red/gray, right), and intermediate (gray/light gray, middle) components. The intermediate constituent (#) comes from nanometer-scale phase-separated fractions of the insulating and metallic states. (c) Time dependence of volume fraction (upper) and diffraction peak-top intensity (lower). The blue/dark gray and red/gray lines represent the insulating and metallic phases, respectively. (d) Metal volume fraction vs diffraction peak intensity for the insulating phase. The blue/dark gray line shows the result of fitting with an arbitrary function for the data mining procedure to deduce the metallic volume fraction from the diffraction intensity.Reuse & Permissions

Figure 5

Resistivity (upper) and peak intensity of (002) reflection for the insulating phase (lower) are plotted as a function of irradiation time at 9 K with different x-ray photon flux densities. The transition time scale obviously changes with the photon flux density.Reuse & Permissions

Figure 6

(a) Both the conductivity (left) and the metal volume fraction (right) are well scaled with the total x-ray dose or the time-integrated irradiation photon sheet density, independent of flux density. A linear plot of the metal volume fraction against total photon density is shown in the inset. The dashed line is a linear fit. (b) The relation of the conductivity vs the metal volume fraction for different photon flux densities. The solid line (black) is a fitted result with the relation that σ $=$ σ${}_0$($V$-$V_0$)${}^S$ the critical percolation volume ($V_{\mathrm{c}}$) is around 5% and the exponent $S$ $=$ 1.5. The inset shows the log-log plot for this.Reuse & Permissions