Electro-optically triggered VO2 thin film memristor for neuronal logic circuit

Study of rectifying properties and true Ohmic contact on Sn doped V2O5 thin films deposited by spray pyrolysis method

V2O5 thin films were prepared by pulsed laser deposition (PLD). We studied the response of the phosphorescence energy of the double bond between vanadium and oxygen (V=O) on basicity. The results show that the insertion of Li+ leads to a blue shift of the wavelength for the V=O peak with increasing electric charge. The V2O5 thin films, soaked in dimethylsulfone (DMSO2), acetone, and dilute HNO3 solutions, also lead to a blue shift of the wavelength for the V=O peak. In addition, the electrical properties of the V2O5 thin films were studied by atomic force microscopy (AFM). The current–voltage (I–V) characterization of V2O5 thin films (Ts = room temperature, PO2 = vacuum) shows erasing, metastable reproducing and recording states. The reversibility of phase transitions for V2O5 thin films depends on the conditions for fabrication by PLD.

Enhanced visible and IR light-sensing performance of photoconductive VO2 (M1) nanorods thin film

The effect of oxygen flow rate on metal–insulator transition (MIT) characteristics of vanadium dioxide (VO2) thin films by pulsed laser deposition (PLD)

For growing high quality epitaxial VO2 thin films, the substrate with suitable lattice parameters is very important if considering the lattice matching. In addition, the thermal conductivity between the substrate and epitaxial film should be also considered. Interestingly, the c-plane of hexagonal 6H-SiC with high thermal conductivity has a similar lattice structure to the VO2 (010), which enables epitaxial growth of high quality VO2 films on 6H-SiC substrates. In the current study, we deposited VO2 thin films directly on 6H-SiC (0001) single-crystal substrates by pulsed laser deposition (PLD) and systematically investigated the crystal structures and surface morphologies of the films as the function of growth temperature and film thickness. With optimized conditions, the obtained epitaxial VO2 film showed pure monoclinic phase structure and excellent phase transition properties. Across the phase transition from monoclinic structure (M1) to tetragonal rutile structure (R), the VO2/6H-SiC (0001) film demonstrated a sharp resistance change up to five orders of magnitude and a narrow hysteresis width of only 3.3 °C.

Tailoring thermochromic and optical properties of VO2 thin films by pulsed laser deposition using different starting routes

Fabrication of pulsed-laser deposited V2O5 thin films for electrochromic devices

VO2 thin films deposited on fused quartz substrates were successfully fabricated by the pulsed-laser-deposition (PLD) technique. The obtained samples were examined by microscopy and x-ray diffraction (XRD). The films show a fast, passive thermochromic effect of semiconductor-to-metal phase transition (PT) with a characteristic hysterisis at ∼68°C. The thermochromic effect was measured as resistivity, optical transmission, and reflection versus temperature. Under pulsed laser excitation, an optically induced ultrafast PT of VO2 thin film was observed. Using the degenerate-four-wave-mixing (DFWM) technique, it was found that excited state dynamics is responsible for the induced lattice reorientation polarization, which results in the ultrafast PT.

Electronic and structural degrees of freedom are often intimately coupled in strongly correlated systems, which result in intriguing macroscopic and microscopic phenomena. Using the well-studied material VO2 as a prototype, here we explore the domain distribution across the metal–insulator transition (MIT). We use macroscopic as well as microscopic techniques, such as first-order reversal curve (FORC) and infrared imaging, to probe the domain distributions across the MIT. This study compares MIT in thin films of VO2 with different grain sizes grown by pulsed laser deposition and dc sputtering. We explore the relation between the nature of the FORC distribution and the corresponding thermal hysteresis due to interactions between the supercooled metallic domains and surrounding insulating matrix. Our multi-probe study with quantitative analysis provides a correlation between the growth, domain interaction, and domain nucleation process in MIT.

Transformation of crystalline structure and photoelectric properties in VO2/glass thin films by inserting TiO2 buffer layers

Structural, electrical and optical properties of pulsed laser deposited VO2 thin films on R- and C-sapphire planes

This work investigates and reports on the radio-frequency (rf) behavior in the frequency range of 5–35 GHz of germanium-doped vanadium dioxide (Ge-doped VO2) thin films deposited on silicon substrates via sputtering and pulsed laser deposition (PLD) with estimated Ge concentrations of 5 and 5.5%. Both films exhibit critical transition temperatures (Tc) of 76.2 and 72 °C, respectively, which are higher compared to that of the undoped VO2 which undergoes reversible insulator-to-metal phase transition at 68 °C. Both types of Ge-doped films show low hysteresis (<5 °C) in their conductivity versus temperature characteristics and preserve high off-state dc-conductivities (corresponding to the insulating state of the phase change material) of 13 S/m for the sputtered and 55 S/m for the PLD-deposited film, respectively. The dc on-state (corresponding to the conductive state of the phase change material) conductivity reaches 145,000 S/m in the case of the PLD film, which represents a significant increase compared to the state-of-the art values measured for undoped VO2 thin films deposited on identical substrates. In order to further understand the off-state dissimilarities and rf behavior of the deposited Ge-doped VO2 films, we propose an original methodology for the experimental extraction of the dielectric constant (εr) in the GHz range of the films below 60 °C. This is achieved by exploiting the frequency shift of resonant filters. For this purpose, we have fabricated coplanar waveguide structures incorporating ultracompact Peano space-filling curves, each resonating at a different frequency between 5 and 35 GHz on two types of substrates, one with the Ge-doped VO2 thin films and another one using only SiO2 to serve as the reference. The reported results and analysis contribute to the advancement of the field of metal–insulator–transition-material technology with high Tc for rf industrial applications.

We explore the possibility of tuning the metal-to-insulator transition (MIT) of crystalline VO2 thin films by strain engineering. We deposit high-quality VO2 epitaxial films of different thicknesses on TiO2 (110) substrates by pulsed laser deposition. The strain state of the deposited film varies with its thickness. This allows us to correlate the MIT characteristics with the strain state of the VO2 film by a careful characterization of the structural and electrical properties. Thin VO2 films on TiO2 (110) substrates are almost fully strained up to thicknesses of about 20 nm and exhibit tensile strain along the c axis of the (high-temperature) metallic rutile phase leading to an increase in the MIT temperature by as much as 30 °C in comparison to the almost fully relaxed 300 nm-thick VO2 film. The strain gradient within the thicker samples leads to a continuous serial switching of layered regions of the VO2 film from the insulating to the metallic state with increasing temperature.

ABSTRACTHighly oriented VO2 (M1) thin films are difficult to produce using non-crystalline substrates. For example, to produce such films on glass has required post-annealing or the use of a ZnO transparent layer. Here, we overcome this challenge and report highly oriented VO2 (M1) in the (100) plane directly on the glass substrate by pulsed laser deposition (PLD). We study the influence of the laser wavelengths (1064, 532, 355 and 266 nm) on the orientation of VO2 (M1) deposited on Corning glass. We find that the laser wavelength of 532 nm leads the most highly a-axis textured VO2 (M1) demonstrating the highest reversible metal-to-insulator at about 62 °C with a lowest hysteresis width of approximately 9 °C. One of the conditions is to select the green 532 nm wavelength laser in PLD as this particular laser wavelength also produces films with highest roughness value (of more than 60 nm) when compared to other wavelengths which produce films of roughness values less than 40 nm.

The influence of structural defects on the electrical and infrared emission properties of VO2 thin films