Epitaxial Growth and Electrical Properties of VO2 on LSAT (111) substrate

We report the epitaxial growth and the electrical properties, especially the metal-to-insulator transition (MIT), of vanadium dioxide (VO2) thin films synthesized on LSAT (111) ([LaAlO3]0.3[Sr2AlTaO6]0.7) substrates by pulsed laser deposition. X-ray diffraction studies show that the epitaxial relationship between the VO2 thin films and LSAT substrate is given as VO2(020)||LSAT(111) and VO2[001]||LSAT[11-2]. We observed a sharp four orders of magnitude change in the longitudinal resistance for the VO2 thin films around the transition temperature. We also measured distinct Raman spectra below and above the transition point indicating a concomitant structural transition between the insulator and metallic phases, in agreement with past investigations.Comment: 14 pages, 4 figures, 1 tabl

Correlation Assisted Phonon Softenings and the Mott-Peierls Transition in VO2_{2}

To explore the driving mechanisms of the metal-insulator transition (MIT) and the structural transition in VO2, we have investigated phonon dispersions of rutile VO2 (R-VO2) in the DFT and the DFT+U (U : Coulomb correlation) band calculations. We have found that the phonon softening instabilities occur in both cases, but the softened phonon mode only in the DFT+U describes properly both the MIT and the structural transition from R-VO2 to monoclinic VO2 (M1-VO2). This feature demonstrates that the Coulomb correlation effect plays an essential role of assisting the Peierls transition in R-VO2. We have also found from the phonon dispersion of M1-VO2 that M1 structure becomes unstable under high pressure. We have predicted a new phase of VO2 at high pressure that has a monoclinic CaCl2-type structure with metallic nature

Electrodynamics of the vanadium oxides VO2 and V2O3

The optical/infrared properties of films of vanadium dioxide (VO2) and vanadium sesquioxide (V2O3) have been investigated via ellipsometry and near-normal incidence reflectance measurements from far infrared to ultraviolet frequencies. Significant changes occur in the optical conductivity of both VO2 and V2O3 across the metal-insulator transitions at least up to (and possibly beyond) 6 eV. We argue that such changes in optical conductivity and electronic spectral weight over a broad frequency range is evidence of the important role of electronic correlations to the metal-insulator transitions in both of these vanadium oxides. We observe a sharp optical transition with possible final state (exciton) effects in the insulating phase of VO2. This sharp optical transition occurs between narrow a1g bands that arise from the quasi-one-dimensional chains of vanadium dimers. Electronic correlations in the metallic phases of both VO2 and V2O3 lead to reduction of the kinetic energy of the charge carriers compared to band theory values, with paramagnetic metallic V2O3 showing evidence of stronger correlations compared to rutile metallic VO2.Comment: 11 pages, 7 figure

Metal-insulator Transition (MIT) Materials for Biomedical Applications

Transitional metal oxides get considerable interest in electronics and other engineering applications over few decades. These materials show several orders of magnitude metal-insulator transition (MIT) triggered by external stimuli. Bio-sensing using Vanadium dioxide (VO2), a MIT material is largely unexplored. In this short article, we investigate the VO2 based thermal sensor performance for measuring the biomolecule concentration. Active sensing layer is chromium and niobium co-doped VO2 as it shows 11.9%/°C temperature coefficient of resistance (TCR) with practically no thermal hysteresis. Our study demonstrated that VO2 based microsensors can be used to measure the biomolecule concentrations, which produce temperature changes in the mK range. For 1mK change in temperature, the maximum detection voltage is near 0.4V

Changes in Pain Perception in Women During and Following an Exhaustive Incremental Cycling Exercise

Exercise has been found to alter pain sensitivity with a hypoalgesic response (i.e., diminished sensitivity to pain) typically reported during and/or following high intensity exercise. Most of this research, however, has involved the testing of men. Thus, the purpose of the following investigation was to examine changes in pain perception in women during and following exercise. Seventeen healthy female subjects (age 20.47±.87; VO2 peak 36.77± 4.95) volunteered to undergo pain assessment prior to, during, and after a graded exhaustive VO2 peak cycling challenge. Heart Rate (HR) and Oxygen Uptake (VO2) were monitored along with electro-diagnostic assessments of Pain Threshold (PT) and Pain Tolerance (PTOL) at: 1) baseline (B), 2) during exercise (i.e., 120 Watts), 3) at exhaustive intensity (VO2 peak), and 4) 10 minutes into recovery (R). Data were analyzed using repeated measures ANOVA to determine differences across trials. Significant differences in PT and PTOL were found across trials (PT, p = 0.0043; PTOL p = 0.0001). Post hoc analyses revealed that PT were significantly elevated at VO2 peak in comparison to B (p = 0.007), 120 Watts (p = 0.0178) and R (p = 0.0072). PTOL were found to be significantly elevated at 120 Watts (p = 0.0247), VO2 peak (p \u3c 0.001), and R (p = 0.0001) in comparison to B. In addition, PTOL were found to be significantly elevated at VO2 peak in comparison to 120 Watts (p = 0.0045). It is concluded that exercise-induced hypoalgesia occurs in women during and following exercise, with the hypoalgesic response being most pronounced following exhaustive exercise

Phase-Change Control of Interlayer Exchange Coupling

Changing the interlayer exchange coupling between magnetic layers in-situ is a key issue of spintronics, as it allows for the optimization of properties that are desirable for applications, including magnetic sensing and memory. In this paper, we utilize the phase change material VO2 as a spacer layer to regulate the interlayer exchange coupling between ferromagnetic layers with perpendicular magnetic anisotropy. The successful growth of ultra-thin (several nanometres) VO2 films is realized by sputtering at room temperature, which further enables the fabrication of [Pt/Co]2/VO2/[Co/Pt]2 multilayers with distinct interfaces. Such a magnetic multilayer exhibits an evolution from antiferromagnetic coupling to ferromagnetic coupling as the VO2 undergoes a phase change. The underlying mechanism originates from the change in the electronic structure of the spacer layer from an insulating to a metallic state. As a demonstration of phase change spintronics, this work may reveal the great potential of material innovations for next-generation spintronics