Investigating Selectorless Property within Niobium Devices for Storage Applications

Resistive random-access memory (RRAM) crossbar arrays have shown significant promise as drivers of neuromorphic computing, in-memory computing, and high-density storage-class memory applications. However, leakage current through parasitic sneak paths is one of the dominant obstacles for large-scale commercial deployment of RRAM arrays. To overcome this issue without compromising on the structural simplicity, the use of inherent selectors native to switching is one of the most promising ways to reduce sneak path currents without sacrificing density associated with the simple two-electrode structure. In this study, niobium oxide (NbO_x) was chosen as the resistive switching layer since it co-exhibits non-volatile memory and metal-insulator-transition selector behavior. Experimental results demonstrate abnormal phenomena in the reset process: a rapid decrease in current, followed by an increase when reset from the on state. The current conduction mechanism was examined through statistical analysis, and a conduction filament physical model was developed to explain the abnormal phenomenon. Under optimized operation conditions, non-linearity of ∼500 and fast switching speeds of 30 ns set and 50 ns reset were obtained. The switching behaviors with the intrinsic selector property make the NbO_x device an attractive candidate for future memory and in-memory computing applications.

Temperature tunable flexible photo absorbers based on near-infrared 1D photonic crystal hybridized W-doped VO2nanostructures

Vanadium dioxide is a potential candidate for energy efficient smart windows and have crystalline phase transition temperature (T_c) at 68 °C. So far, literatures mainly emphasis on different synthetic strategies of tungsten doped VO₂which is a most effective dopant to reduceT_cof VO₂to near room temperatures. Until now, there is no report shows the incorporation of flexible 1D photonic crystals as spectrally selective, temperature tunable device to control the changes in optical transmission modulations of W-VO₂nanostrtcures, especially in the near IR region for smart window application. W-doped VO₂with various tungsten contents were synthesized with a facile hydrothermal route. We found that, with 1.1 at% of tungsten doping in intrinsic VO₂, the metal to insulator transition temperature is brought down to 37 °C from 68 °C. IR transmission of VO₂thin film can be reduced from 70% to 40% around room temperature, after doping. Significant absorption enhancement has been observed for both VO₂and W-doped VO₂films, deposited over tunable SiO₂/Ta₂O₅based distributed Bragg reflector (DBR) fabricated over flexible PET (poly-ethylene terephthalate) substrates. On depositing VO₂over ∼70% reflecting DBR, optical transmission is reduced to ∼15% from 35% while the temperature varies to 380 K from 300 K in IR regime. Number of stacks plays a crucial role for effective IR extinctions. A high quality DBR is fabricated by increasing no. of stacks from 4 to 7, with optical transmission of DBR reduced to nearly 5% in stop band. However, with 1.1 at% of W-VO₂over such 95% reflecting flexible DBR, optical transmission vanishes nearly, around room temperature itself in the stop bands of that DBR, which clearly indicates the significant absorption enhancement. W-VO₂/DBR hybrid can substantially modulate the solar heat flux and also imbuing DBR over flexible PET substrates offers retrofitting of the existing windows for energy economy. Thus these structures have promising potential applications for optical devices and practical design for smart windows.

Construction of Schottky contact by modification with Pt particles to enhance the performance of ultra-long V2O5 nanobelt photodetectors

Schottky-contacted nanosensors have attracted extensive attention due to their high sensitivity and fast response time. In this article, we proved that the construction of Schottky contact by Pt nanoparticles (NPs) decoration can effectively improve the performance of V₂O₅ nanobelts photodetectors. After modified by Pt NPs, the photocurrent of V₂O₅ nanobelts is increased by more than two orders of magnitude, and the photoresponse speed is improved by at least three orders of magnitude. Detailed studies have shown that the performance enhancement is attributed to the formation of the Schottky contact at the electrode-semiconductor interface due to the decrease of surface gas adsorption and the increase of V₂O₅ work function after Pt NPs modification. The strong built-in field in the Schottky barrier region will quickly separate photogenerated carriers, thereby reducing the electron-hole recombination rate, resulting in the fast response time and an increase in the free carrier density. Moreover, it is found that this enhancement effect can be regulated by controlling the pressure to modulating the Schottky barrier height at the interface. Overall, the Pt NPs-modified V₂O₅ nanobelts photodetector exhibits a broad response spectrum (visible to near infrared), fast rise/fall response time (less than 6.12/6.15 ms), high responsivity (5.6 A/W), and high specific detectivity (6.9 × 10⁸ Jones). This study demonstrates the feasibility of building a Schottky barrier to enhance the photodetection performance, which provides a general and effective strategy towards the construction and its practical application of supersensitive and fast-response nanosensors.

Thermochromic VO2-SiO2composite coating from ammonium citrato-oxovanadate(IV)

Vanadium dioxide (VO₂) coating plays an important role in energy saving and environmental protection due to its unique reversible phase transition. To solve the daylighting issue of VO₂coating, a VO₂(M)-silicon dioxide (SiO₂) composite coating is fabricated from ammonium citrato-oxovanadate(IV) by a SiO₂-assisted coating method. The VO₂(M)-SiO₂composite coating possesses excellent thermochromic properties that have produced varying results, i.e. 49.2% of visible transmittance, 52.3% of transmittance reduction at 2000 nm wavelength, 12% of solar energy modulation (ΔT_sol) and a phase transition temperature of 56.0 °C. Our findings may pave the way to extending the large-scale application of smart windows based on thermochromic VO₂.

VO2 Nanostructures for Batteries and Supercapacitors: A Review

Vanadium dioxide (VO₂ ) received tremendous interest lately due to its unique structural, electronic, and optoelectronic properties. VO₂ has been extensively used in electrochromic displays and memristors and its VO₂ (B) polymorph is extensively utilized as electrode material in energy storage applications. More studies are focused on VO₂ (B) nanostructures which displayed different energy storage behavior than the bulk VO₂ . The present review provides a systematic overview of the progress in VO₂ nanostructures syntheses and its application in energy storage devices. Herein, a general introduction, discussion about crystal structure, and syntheses of a variety of nanostructures such as nanowires, nanorods, nanobelts, nanotubes, carambola shaped, etc. are summarized. The energy storage application of VO₂ nanostructure and its composites are also described in detail and categorically, e.g. Li-ion battery, Na-ion battery, and supercapacitors. The current status and challenges associated with VO₂ nanostructures are reported. Finally, light has been shed for the overall performance improvement of VO₂ nanostructure as potential electrode material for future application.

Research progress on the preparation methods for VO2 nanoparticles and their application in smart windows

Accompanied with drastic changes in photoelectric properties, vanadium dioxide (VO₂) exhibits a first order metal–insulator phase transition (MIT) at the temperature of about 68 °C.