The electrical characterization of materials, particularly superconductors, semiconductors, and those undergoing metal-insulator transitions (MITs), relies significantly on resistivity and Hall measurements as a function of temperature. The van der Pauw four-point probe method is commonly used for such measurements, which involves resistance measurements for different circuit configurations connected to sample contacts. However, repeating these measurements at different temperatures is challenging and time consuming. This study introduces a novel approach utilizing a switching circuit controlled by an Arduino device and a LabVIEW program to automate resistance measurements for different electrical configurations. The effectiveness of this setup was demonstrated by testing V2O3 thin film samples deposited on Al2O3 (001) substrates using DC magnetron sputtering. The MIT temperature of the sample was 115 K during heating and 100 K during cooling. The sample exhibited p-type charge carriers with a Hall coefficient of 1.3 +/- 0.1 x 10-4 cm3/C and Hall mobility of 1.7 x 10-1 cm2/V center dot s, which is consistent with findings from other studies employing commercial equipment.

Ferroelectret nanogenerators were recently introduced as a promising alternative technology for harvesting kinetic energy. Here we report the device's intrinsic properties that allow for the bidirectional conversion of energy between electrical and mechanical domains; thus extending its potential use in wearable electronics beyond the power generation realm. This electromechanical coupling, combined with their flexibility and thin film-like form, bestows dual-functional transducing capabilities to the device that are used in this work to demonstrate its use as a thin, wearable and self-powered loudspeaker or microphone patch. To determine the device's performance and applicability, sound pressure level is characterized in both space and frequency domains for three different configurations. The confirmed device's high performance is further validated through its integration in three different systems: a music-playing flag, a sound recording film and a flexible microphone for security applications.

The compound V3O5, a member of the vanadium oxide Magnéli series, exhibits a metal-insulator transition near 430 K, the highest known temperature value among all vanadium oxides. It has been studied before mainly in single-crystal form, and for the very few cases in which thin films have been fabricated before, the procedure has required extensive post-deposition annealing of other oxides or vanadium metal at high temperatures in tightly controlled atmospheres. For the present work, V3O5 films were deposited directly on SiO2 glass substrates, without subsequent annealing, by DC magnetron sputtering. X-ray diffraction study of the samples evidenced oxygen deficiency, accommodated by oxygen vacancies. Resistivity measurements from 300 to 500 K revealed the metal-insulator transition by Tc ∼ 430 K, with an associated resistivity change by a factor of 20, and no detectable hysteresis in heating-cooling cycles, in agreement with most single-crystal studies. Resistivity values obtained were, however, lower than published results for bulk crystal values, particularly at temperatures below Tc. This was attributed to conduction electrons generated by the oxygen vacancies. Gradual resistivity increase in a very thin sample, through heating in air at temperatures up to 500 K, lends support to this argument. Using a pump-probe scattering technique, the V3O5 films were also probed for ultrafast nonlinear optical response. A reduction in the transient relative scattered light signal was recorded, which reached –10% within ∼800 fs. This observed response, likely related to the photoinduced insulator-to-metal phase transition, should stimulate additional interest in this material.

Using ultrafast angle-resolved light scattering technique, we were able to trigger photoinduced phase transition processes in V_2O_3 film grown on a glass substrate. The phase transition is caused by photoacoustic wave in the film and appears as coherent oscillations of scattering signal at various time scales. These processes strongly depend on the size of microstructures constituting the V_2O_3 film. One of the key findings of our study is the presence of a size dependent phase transition threshold for V_2O_3 microstructures, where small size structures (<0.5µm) have lowest contribution to the phase transition. The presence of this threshold can be well described by considering uneven internal strain in the films which is one of the key parameters controlling phase transition dynamics in various vanadium oxides.

Thin films of B-phase VO2 were grown by pulsed-laser deposition on glass and (100)-cut MgO substrates in a temperature range from 375 to 425 °C and at higher gas pressures than usual for this technique. The films were strongly oriented, with ab-planes parallel to the substrate surface. Detailed study of surface morphology through Atomic Force Microscopy images suggest significant differences in evolution as a function of growth temperature for films on the two types of substrates. Measurements of electrical conductivities through cooling-heating cycles from room temperature to 120 K showed changes of five orders of magnitude, with steeper changes between room temperature and ∼150 K, which corresponds with the extended and reversible phase transition known to occur for this material. At lower temperatures conductivities exhibited Arrhenius behavior, indicating that no further structural change was occurring and that conduction is thermally activated. In this lower temperature range, conductivity of the samples can be described by the near-neighbor hopping model. No hysteresis was found between the cooling and heating braches of the cycles, which is at variance with previous results published for VO2 (B). This apparent lack of hysteresis for thin films grown in the manner described and the large conductivity variation as a function of temperature observed for the samples suggests this material could be of interest for infrared sensing applications.