Structural, transport, and ultrafast dynamic properties of V1-x N bx O2 thin films

We report the coherent study of structural, transport, and ultrafast dynamic properties of V1-xNbxO2 thin films. Films of a solid solution of V1-xNbxO2(0≤x≤1) are prepared on (0001) sapphire substrates using reactive target bias ion beam deposition. We found that, at room temperature, the low-temperature lattice symmetry of pure VO2 (monoclinic, P21/c) and NbO2 (tetragonal, I41/a) is only maintained at low substituting levels (x<0.1 and x>0.9) and regular rutile lattices are adopted by films with higher substituting levels (0.1<x<0.9). We characterized the dc transport properties and the photoinduced ultrafast dynamics at the terahertz frequency range, both of which demonstrate strong dependence on the film composition. At x∼0.5, both the dc conductivity and ultrafast response diminish, which corresponds to a strong localization of free charge carriers in the system. The strong composition dependence of film transport, ultrafast dynamic, and insulator-metal transition properties promises approaches to improve the performance of devices based on transition metal oxides.