Separating the insulator-to-metal transition (IMT) from the structural phase transition (SPT) in VO2 is central to controlling correlated-oxide transitions; such control may be useful for terahertz-switching applications. We investigate the relative evolution of electronic transport and structure in VO2/AlN/Si. Independent resistance–temperature (R–T) measurements give Tc,H = 347.5 K; paired R–T/X-ray diffraction (XRD) shows that the resistance decrease precedes the major evolution of the tracked out-of-plane diffraction peak, with an approximately 8.2 K difference between their operational midpoints. Separately paired Raman measurements reveal V–V mode softening and residual spectral weight during the resistance decrease, and ultraviolet photoelectron spectroscopy (UPS) shows an approximately 0.13 eV deeper occupied V 3d onset relative to the Al2O3-supported reference. Electrically driven oscillations demonstrate device operation under the stated circuit conditions. These observations are compatible with a Mott-assisted interpretation of electronic–lattice coupling. AlN-mediated strain remains a possible contributor motivated by prior characterization of this growth platform.
In VO2 thin-film devices, the two-probe resistance ratio can differ from the four-probe value because the measured resistance includes the top-metal/VO2 contacts. Au, Mo, Rh, Cr, Pt, V, Ti, and W electrodes were compared using two-probe and four-probe R–T measurements, crossing-wire contact measurements, and W/SiO2/VO2 control devices. All devices exhibited a pronounced four-probe resistance decrease between 25 °C and 85 °C, whereas RR2p/RR4p ranged from 42.0% for W to 185.4% for Au. V, Ti, and W had ratios below 100% and larger crossing-wire RcA values at 85 °C. A series-resistance model taking the four-probe ratio as the channel resistance ratio gave lower bounds on the combined contact contribution: 58.0% of the two-probe resistance at 85 °C for W, and 46.1% and 36.1% at 25 °C for Au and Mo, respectively. The analysis distinguishes a larger relative contact contribution at high temperature from a large resistance ratio associated with a greater relative contact contribution at low temperature. Inserting a SiO2 interlayer below 3 nm increased RR2p/RR4p for W from 42.0% to 87.3%, with comparable low-temperature resistance and lower high-temperature resistance. The comparison shows that contact formation affects how the VO2 channel transition is reflected in the two-probe response.
Electron density is a crucial plasma parameter, and the microwave cutoff method is widely used for its precision and low measurement uncertainty. To extend this method to high-density and corrosive plasmas, dielectric materials such as ceramics are frequently used for probe components. However, cutoff probes with dielectric bodies can exhibit periodic resonance peaks in their transmission spectra under both vacuum and plasma conditions, obscuring the cutoff minimum and hindering reliable determination of the cutoff frequency. Here, electromagnetic simulations and experiments reveal that these features originate from structural resonance supported by the dielectric probe body. To suppress this effect, an electrical connection was introduced between the coaxial cable shields near the antennas. This modification effectively suppressed structural resonance and enabled clearer identification of the cutoff frequency under plasma conditions, improving the reliability of electron density measurement in harsh plasma environments.
This work demonstrates weak-birefringence sensing using periodic nonlinearity (PNL) in a quadrature interferometer, where PNL is utilized as a sensing mechanism rather than treated solely as an error source. A weak birefringence-induced phase perturbation is converted into a measurable change in the PNL amplitude at a dedicated spatial frequency, enabling static retardance sensing without polarization modulation. Experimentally, the measured PNL response exhibited a highly linear region over the 5--60nm retardance range, with R2=0.9999. The observed amplitude fluctuations corresponded to an equivalent retardance standard deviation of approximately 36pm, or about 0.36mrad of phase retardation at 632.8nm. The measured response also revealed distinct effects of quadrature phase offset and gain imbalance, consistent with the predicted deformation of the PNL minimum. These results show that PNL-based phase-to-amplitude transduction provides a simple and sensitive approach for static weak-retardance measurements in quadrature interferometric systems.
