Single VO2 Research Articles

Three‐Dimensional Imaging of the Structural Phase Transition in a Single Vanadium Dioxide Nanocrystal

Vanadium dioxide (VO2) is a strongly correlated material that exhibits a number of structural phase transitions (SPT) near to room temperature of considerable utility for various technological applications. When reduced to the nanoscale, a foreknowledge of surface and interface properties of VO2 during the SPT can facilitate the development of devices based on VO2. Herein, it is shown that Bragg coherent X‐ray diffractive imaging (BCDI) combined with machine learning is an effective means to recover three‐dimensional images of a single VO2 nanocrystal during a temperature‐induced SPT from a room‐temperature monoclinic phase to a high‐temperature rutile phase. The findings reveal the coexistence of multiple phases within the nanocrystal throughout the transition, along with missing density which indicates the presence of a newly formed rutile phase.

A Flexible Artificial Spiking Photoreceptor Enabled by a Single VO2 Mott Memristor for the Spike-Based Electronic Retina.

The neuromorphic vision system that utilizes spikes as information carriers is crucial for the formation of spiking neural networks. Here, we present a bioinspired flexible artificial spiking photoreceptor (ASP), which is realized by using a single VO2 Mott memristor that can simultaneously sense and encode the stimulus light into spikes. The ASP has high spike-encoded photosensitivity and ultrawide photosensing range (405-808 nm) with good endurance (>7 × 107) and high flexibility (bending radius ∼5 mm). Then, we put forward an all-spike electronic retina architecture that comprises one layer of ASPs and one layer of artificial optical nerves (AONs) to process the spike information. Each AON consists of a single Mott memristor connected in series with a neuro-transistor that is a multiple-input floating-gate MOS transistor. Simulation results demonstrate that the all-spike electronic retina can successfully segment images with high Shannon entropy, thus laying the foundation for the development of a spike-based neuromorphic vision system.

Tunable ultra-broadband terahertz metamaterial absorber enabled by high-order resonances of single square VO2 patch

Tunable ultra-broadband terahertz metamaterial absorber enabled by high-order resonances of single square VO2 patch

Hot corrosion behaviours of the LaYbZr2O7 thermal barrier coatings in different corrosive salts

In this study, the LaYbZr2O7 (LYZ) thermal barrier coatings (TBCs) were deposited by air plasma spray (APS) and were subjected to hot corrosion in the single V2O5 salts and the mixture of V2O5+Na2SO4 with different Na2SO4 content at 1000 °C. The reaction mechanism and corrosion layer evolution of the LYZ coating in different corrosive molten were comparatively investigated. After hot corrosion in the single V2O5 salt, the surface of the LYZ coating develops a dense corrosion layer, which could keep structural integrity with the extension of exposure time, indicating the LYZ coating showed higher resistance to the V2O5 corrosion. However, the dense layer failed to form on the surface of the LYZ coating in the V2O5+Na2SO4 mixed salts. With the increase of Na2SO4 content, the corrosion products formed on the surface of the LYZ coating gradually decreased, and the corrosion layer disappeared. The dominant reason for the difference was that the addition of Na2SO4 resulted in the acidity reduction of the mixed salts, which eventually caused a decrease in the corrosion rate. Compared with the single V2O5, the V2O5+Na2SO4 mixed salts showed higher penetration ability in the LYZ coating and could be more damaging.

A V2O5/MWCNTs composite thin film gas sensor for the fast detection of ammonia

In the present study, we develop a new ammonia gas sensor by using sol-gel method and post annealing process. The structure, morphology, and composition of the gas sensor have been characterized by SEM, XRD, XPS, and Raman. The results prove that the V2O5/MWCNTs (multi-walled carbon nanotubes) composite thin film was successfully deposited on alumina substrate. By comparing the responses of the gas sensor to ammonia gas at different temperatures, we find out that the sensor shows good response and excellent response time to ammonia gas at 200 ℃. At this temperature, the sensor exhibits a response of 20% for 100 ppm of ammonia gas with a response time of only 8 s. We find its response time is better than that of ammonia sensors based on single V2O5 or MWCNTs materials. The outstanding sensitivity and unique response curve can be mainly attributed to the semiconductor properties of the two materials and the formation of P-N heterojunction at their interface.

Annealing-induced characterization of sputtered V2O5 thin films and Ag/V2O5/p-Si heterojunctions

V2O5 thin films were deposited on glass and p-type silicon substrates by radio frequency (RF) sputtering of a single V2O5 target. Half of the samples were annealed at 500 °C at room ambient for an hour. The morphological, structural, and optical properties of the thin films were analyzed by atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and UV–Vis data. The results showed that while the as-grown V2O5 thin films had smooth surfaces with an amorph phase, annealed films had rougher surfaces with grains in the polycrystalline phase. It is also reported that the band gap of V2O5 thin films decreased from 2.47 to 2.37 eV. Furthermore, the electrical properties of Ag/V2O5/p-Si junctions were analyzed by current-voltage (I–V) measurements. It was presented that both Ag/V2O5/p-Si structures with as-grown and annealed V2O5 thin films had exciting rectifying behaviors. It was observed that while the barrier heights of the rectifying junctions were nearly the same, the ideality factor and series resistance values of the Ag/V2O5/p-Si device fabricated by annealed V2O5 thin film were higher than the device with as grown V2O5 thin film. Finally, the photoelectrical properties of both samples were analyzed by I–V under various light intensities. It was seen that both Ag/V2O5/p-Si devices had exciting photosensing behavior. While the increase in reverse bias current values with the increase in light intensity was observed for both devices, it was seen that the device obtained by as-grown thin film had much more sensitivity to light.

Exercise pulmonary hypertension by the mPAP/CO slope in primary mitral regurgitation.

Exercise-induced pulmonary hypertension (PH), defined by a mean pulmonary arterial pressure over cardiac output (mPAP/CO) slope >3 mmHg/L/min, has important diagnostic and prognostic implications. The aim of this study is to investigate the value of the mPAP/CO slope in patients with more than moderate primary mitral regurgitation (MR) with preserved ejection fraction and no or discordant symptoms. A total of 128 consecutive patients were evaluated with exercise echocardiography and cardiopulmonary testing. Clinical outcome was defined as the composite of mitral valve intervention, new-onset atrial fibrillation, cardiovascular hospitalization, and all-cause mortality. The mean age was 63 years, 61% were male, and the mean LVEF was 66 ± 6%. The mPAP/CO slope correlated with peak VO2 (r = -0.52, P < 0.001), while the peak systolic pulmonary artery pressure (sPAP) did not (r = -0.06, P = 0.584). Forty-six per cent (n = 59) had peak exercise sPAP ≥60 mmHg, and 37% (n = 47) had mPAP/CO slope >3 mmHg/L/min. Event-free survival was 55% at 1 year and 46% at 2 years, with reduced survival in patients with mPAP/CO slope >3 mmHg/L/min (hazard ratio, 4.9; 95% confidence interval, 2.9-8.2; P < 0.001). In 53 cases (41%), mPAP/CO slope and peak sPAP were discordant: patients with slope >3 mmHg/L/mmHg and sPAP <60 mmHg (n = 21) had worse outcome vs. peak sPAP ≥60 mmHg and normal slope (n = 32, log-rank P = 0.003). The mPAP/CO slope improved predictive models for outcome, incremental to resting and exercise sPAP, and peak VO2. Exercise PH defined by the mPAP/CO slope >3 mmHg/L/min is associated with decreased exercise capacity and a higher risk of adverse events in significant primary MR and no or discordant symptoms. The slope provides a greater prognostic value than single sPAP measures and peak VO2.

Low- and high-volume blood-flow restriction treadmill walking both improve maximal aerobic capacity independently of blood volume.

Assess the effect of low- and high-volume blood flow restriction training (BFR) on maximal aerobic capacity (VO2 max) and determine if alteration in VO2 max is mediated through changes in hemoglobin mass (Hbmass) and blood volume. Participants' Hbmass (CO-rebreathe), single, and double-leg VO2 max and blood volume regulating hormonal responses (renin and copeptin) were measured before and after BFR training. Training consisted of treadmill walking either (1) twice-daily for 4week (CON and BFRHV ) or (2) twice-weekly for 6week (BFRLV ). Each session consisted of five intervals (3 min, 5% incline, 5 km/h, 100% of lowest occlusion pressure), with 1 min of standing rest between sets. VO2 max increased using both training exposures, in as quickly as 2-weeks (BFRLV baseline to 4week: +315 ± 241 mL (8.7%), p = 0.02; BFRHV baseline to 2week: +360 ± 261 mL (7.9%), p < 0.01), for the BFRLV and BFRHV groups, with no change in CON. Single- and double-leg VO2 max improved proportionately (single/double-leg VO2 max ratio: BFRLV 78 ± 4.9-78 ± 5.8%, BFRHV 79 ± 6.5-77 ± 6.5%), suggesting that the mechanism for increased VO2 max is not solely limited to central or peripheral adaptations. Hbmass remained unchanged across groups (CON: +10.2 ± 34 g, BFRLV : +6.6 ± 42 g, BFRHV : +3.2 ± 44 g; p = 0.9), despite a significant release of blood volume regulating hormones after initial BFR exposure (renin +20.8 ± 21.9 ng/L, p < 0.01; copeptin +22.0 ± 23.8 pmol/L, p < 0.01), which was blunted following BFRHV training (renin: +13.4 ± 12.4 ng/L, p = 0.09; copeptin: +1.9 ± 1.7 pmol/L, p = 0.98). BFR treadmill walking increases VO2 max irrespective of changes in Hbmass or blood volume despite a large release of blood volume regulating hormones in response to BFR treadmill walking.

Hot corrosion mechanism and thermal cycling performance of air-plasma-sprayed LaYbZr2O7 thermal barrier coatings in the vanadate-containing molten salts

LaYbZr2O7 has been regarded as a promising thermal barrier coatings (TBC) material due to its excellent mechanical and thermal properties. In this study, the LaYbZr2O7 coating was prepared by atmospheric plasma spraying (APS), and its hot corrosion mechanism and thermal cycling performance in vanadate-containing molten salts (V2O5 and Na2SO4 + V2O5) were investigated. Results indicated the hot corrosion reaction of LaYbZr2O7 coatings in molten V2O5 was temperature dependent, attributed to the thermal decomposition of ZrV2O7 above 800 °C. A continuous dense corrosion layer could form on the top surface of LaYbZr2O7 coatings after hot corrosion in molten V2O5 salt, effectively preventing the further penetration of molten salt. However, the dense corrosion layer could not form when exposed to Na2SO4 + V2O5 molten salts at 1000 °C, since the formation of NaVO3 could improve the mobility of molten salts and slow the precipitation reaction rate of corrosion products. Furthermore, thermal cycling tests indicated that the Na2SO4 + V2O5 mixture could be more detrimental to LaYbZr2O7 coatings than single V2O5 salt, and the dense corrosion layer could act as a sacrifice layer to protect the inner coating from corrosion degradation. The hot corrosion mechanism of LaYbZr2O7 was discussed in detail based on the Lewis acid-base and dissolution-precipitation rule.

Polarization-insensitive phase-modulated metasurface using single thermally stimulated vanadium dioxide chip.

Considering that typically more than two pin diodes or other tunable elements are required in the unit cell of polarization-insensitive reconfigurable metasurfaces (RMs), this paper proposes a new approach to design a polarization-insensitive RM unit using only one VO2 chip. A polarization-insensitive phase-modulated metasurface (PMM) using single VO2 chip is presented. The surface layer is composed of an outer ring and an inner cross, with a VO2 chip loaded at the connection of the cross. As the VO2 chip can be connected with the metal patch on all sides, only one VO2 chip is used in this polarization-insensitive design. By thermally controlling VO2 chips switch between low-resistance and high-resistance states, the PMM achieves a 1-bit phase shift within 180° ± 37° from 7.85 to 15 GHz. A prototype is fabricated and measured, and the measured results have verified the correction of the design and analysis of the designed PMM.

Thermochromic performance enhancement by geometric structure optimization of VO2 nanoarrays for smart window application

The localized surface plasmon resonance (LSPR) exhibited by vanadium dioxide (VO2) has expanded its utility in thermochromic smart windows. Here, guided by the absorption characteristics of a single VO2 nanoparticle (NP) with a radius between 10 to 60 nm on a glass substrate, we numerically conducted an extensive analysis of the optical properties of VO2 nano-cylinder arrays. We achieved a significant enhancement in the performance of thermochromic smart windows by optimizing the geometric structure of the VO2 arrays. Such a performance enhancement relies on the on-off switch properties of LSPR in VO2 nano-cylinder arrays. Smaller (r≤ 60) ones with high aspect ratios (> 0.75) shows a higher absorption contribution in their extinction effect and a more energetic LSPR peak located in the near-infrared spectra. Those characteristics significantly improve the thermochromic performance of smart windows via enhancing the transmission contrast between the high-temperature rutile state and the low-temperature monoclinic state of VO2. At a transmittance luminous (Tlum) efficacy of 60.03%, an excellent 20.03% in solar spectrum modulation ability (ΔTsol) can be attained. Compared to flat films with an identical Tlum, ΔTsol of the periodically cylindrical-structured film is raised by 234%.

Sandwich-like MXene bridged heterostructure electrode enables anti-aggregation and superior storage for aqueous zinc-ion batteries

Severe aggregation and sluggish reaction kinetics are the main research challenges that impair the storage performance of cathode materials for aqueous zinc-ion batteries. In this work, we report the concept of sandwich-like Ti3C2Tx MXene-bridged VO2 heterostructure (VO2/Ti3C2Tx) design to simultaneously relieve the self-aggregation and boost the interfacial storage kinetics. When acting as cathode material, such VO2/Ti3C2Tx electrode can deliver a high specific capacity 415 mAh g−1 at 0.1 A g−1 after 110 cycles, as well as 338 mAh g−1 at 1 A g−1 after 300 cycles, much higher than that of the pure VO2 case. Moreover, such electrode also exhibits remarkably rate capability and cyclic stability, which can retain a specific capacity of 170 mAh g−1 at the high current density of 5 A g−1 after 1500 cycles. The superior storage performance should be mainly benefited from the mixed-dimensional heterogeneous engineering. In addition, the evolution of crystal structure and valence state of electrode upon cycling were investigated, thus a storage mechanism can be revealed. That is, single VO2 phase would be transformed into the VO2 and ZnxV2O5·nH2O mixed phase, with a highly reversible H+/Zn2+ insertion/extraction behavior. Such strategy proposed in this work can be also applied for other kinds of cathode materials and promoting the development of aqueous zinc-ion batteries.

Tunable triple-broadband terahertz metamaterial absorber using a single VO2 circular ring

Vanadium dioxide (VO2) has been widely used in tunable terahertz (THz) metamaterial absorbers. So far, many kinds of tunable broadband or dual-broadband THz metamaterial absorbers based on VO2 have been proposed. However, tunable triple-broadband THz metamaterial absorbers have been rarely investigated. In this paper, we present a tunable triple-broadband THz metamaterial absorber using a single VO2 circular ring. The absorptivity of proposed absorber exceeds 90% in the three frequency bands of 0.73–3.08 THz, 4.83–7.13 THz and 8.72–11.12 THz, and the absorption bandwidths are 2.35 THz, 2.30 THz and 2.40 THz, respectively. We can continuously tune the absorptivity from 20% to over 90% by altering the conductivity of VO2. The physical mechanism of triple-broadband absorption is explained by the electric field distributions at absorption peaks. The influences of incident and polarization angles on the absorption performance are also investigated.

Liquid Precursor-Guided Phase Engineering of Single-Crystal VO2 Beams.

The study of VO2 flourishes due to its rich competing phases induced by slight stoichiometry variations. However, the vague mechanism of stoichiometry manipulation makes the precise phase engineering of VO2 still challenging. Here, stoichiometry manipulation of single-crystal VO2 beams in liquid-assisted growth is systematically studied. Contrary to previous experience, oxygen-rich VO2 phases are abnormally synthesized under a reduced oxygen concentration, revealing the important function of liquid V2 O5 precursor: It submerges VO2 crystals and stabilizes their stoichiometric phase (M1) by isolating them from the reactive atmosphere, while the uncovered crystals are oxidized by the growth atmosphere. By varying the thickness of liquid V2 O5 precursor and thus the exposure time of VO2 to the atmosphere, various VO2 phases (M1, T, and M2) can be selectively stabilized. Furthermore, this liquid precursor-guided growth can be used to spatially manages multiphase structures in single VO2 beams, enriching their deformation modes for actuation applications.

Liquid Precursor‐Guided Phase Engineering of Single‐Crystal VO2 Beams

AbstractThe study of VO2 flourishes due to its rich competing phases induced by slight stoichiometry variations. However, the vague mechanism of stoichiometry manipulation makes the precise phase engineering of VO2 still challenging. Here, stoichiometry manipulation of single‐crystal VO2 beams in liquid‐assisted growth is systematically studied. Contrary to previous experience, oxygen‐rich VO2 phases are abnormally synthesized under a reduced oxygen concentration, revealing the important function of liquid V2O5 precursor: It submerges VO2 crystals and stabilizes their stoichiometric phase (M1) by isolating them from the reactive atmosphere, while the uncovered crystals are oxidized by the growth atmosphere. By varying the thickness of liquid V2O5 precursor and thus the exposure time of VO2 to the atmosphere, various VO2 phases (M1, T, and M2) can be selectively stabilized. Furthermore, this liquid precursor‐guided growth can be used to spatially manages multiphase structures in single VO2 beams, enriching their deformation modes for actuation applications.

A simple two-step approach to the fabrication of VO2-based coatings with unique thermochromic features for energy-efficient smart glazing

Vanadium dioxide (VO2) is considered as one of the most promising materials for the next generation of energy-efficient smart glazing since it experiments a reversible metal-to-insulator transition at near room temperature. Nevertheless, the complexity and high cost associated to the fabrication of VO2-based nanostructures limit the transfer of this technology to the industrial scale. Aware of this opportunity, we present a simple and advantageous method for the fabrication of VO2 coatings on glass substrates which comprises the initial sputtering of vanadium thin films at glancing angles and the subsequent very fast oxidation of such systems in open air atmosphere. Relying on the accurate control of the thermal treatment parameters, as well as the enhanced reactivity of the high surface-to-volume porous deposited structures, thermochromic VO2 coatings were achieved and then characterized by means of scanning electron microscopy, grazing incidence X-ray diffraction, variable temperature UV-vis-NIR spectrophotometry, and resistivity measurements. These investigations allowed us to determine the key role that oxidation temperatures and times not only play in modulating the optical performance of the film, but also in the surprising and advantageous decrease in the transition temperature (up to 12 °C lower than the standard value for pure VO2), which is attained without incorporating doping agents. This fact, together with the remarkable values of luminous transmittance (∼50 %) and solar modulation ability (5–10 %) accomplished for our best samples, opens up an alternative and simpler pathway towards the large-scale manufacturing of VO2 coatings for smart window applications, reaching, on a preliminary basis, similar or even better performances than those obtained so far for single and undoped VO2 films.

Modulation of Switching Characteristics in a Single VO2 Nanobeam with Interfacial Strain via the Interconnection of Multiple Nanoscale Channels.

We demonstrate the modulation of electrical switching properties through the interconnection of multiple nanoscale channels (∼600 nm) in a single VO2 nanobeam with a coexisting metal-insulator (M-I) domain configuration during phase transition. The Raman scattering characteristics of the synthesized VO2 nanobeams provide evidence that substrate-induced interfacial strain can be inhomogeneously distributed along the length of the nanobeam. Interestingly, the nanoscale VO2 devices with the same channel length and width exhibit distinct differences in hysteric current-voltage characteristics, which are explained by theoretical calculations of resistance change combined with Joule heating simulations of the nanoscale VO2 channels. The observed results can be attributed to the difference in the spatial distribution and fraction ratios of M-I domains due to interfacial strain in the nanoscale VO2 channels during the metal-insulator transition process. Moreover, we demonstrate the electrically activated resistive switching characteristics based on the hysteresis behaviors of the interconnected nanoscale channels, implying the possibility of manipulating multiple resistive states. Our results may offer insights into the nanoscale engineering of correlated phases in VO2 as the key materials of neuromorphic computing for which nonlinear conductance is essential.

Downhole FT-MIR Spectrometer Using Perfect Metasurface Absorber

Realization of “Fourier transform infrared (FT-IR) on a chip” holds the potential of a disruptive technology for downhole chemical analysis within the oil and gas industry. One of the critical obstacles to downhole integration though has been the cooling requirements of conventional technologies. Here, we report the design and numerical analysis of an uncooled miniaturized Fourier transform mid-infrared (FT-MIR) spectrometer compatible with downhole thermal environments, enabled by a broadband mid-infrared metasurface detector/source combination derived from a geometric inversion of a set of conformal mapping contours. The metasurface is numerically found to exhibit a near-zero index metamaterial (NZIM) behavior with absorption characterized by surface plasmon resonances confined to the ultrathin ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda $ </tex-math></inline-formula> /300) metasurface plane, making the absorption properties of the microbolometer design much less sensitive to the remaining support structure than in typical designs. This feature allows the metasurface to be integrated on a single VO2 substrate operated at elevated downhole temperatures that coincide with the metal–insulator transition region. Within this transition region, the VO2 material exhibits enhanced thermometric properties, enabling an uncooled microbolometer design with predicted maximum detectivity <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${D}^{*} = 1.5\times {10}^{{10}}\,\,\text {cm} \sqrt {\text {Hz}}/\text {W}$ </tex-math></inline-formula> and noise equivalent difference temperature (NEDT) of 1 mK at a modulation frequency of 500 Hz. These parameters approach entry-level lab FT-MIR spectrometers and could represent a significant step in deploying mid-infrared spectroscopy into oilfield downhole logging applications.

Reconfigurable SAW Resonators and Tunable Filters Using Monolithically Integrated VO₂ Switches

This article presents novel reconfigurable surface acoustic wave (SAW) resonators using switching elements based on vanadium oxide (VO2) phase change material. The switching elements are integrated monolithically with the resonators on the same chip using an in-house fabrication process, which allows the compact implementation of the proposed reconfigurable resonators. The frequency of the resonator is tuned between two different states by changing the configuration of interdigitated electrodes within the SAW resonator and by using a set of tuning electrodes and VO2 switches. Experimental results are presented for the first reconfigurable resonator with six VO2 switching elements. The resonator is tuned from 700 to 720 MHz, while the quality factor is maintained above 350 over the tuning range. A second reconfigurable resonator with a modified structure is proposed to reduce the number of required VO2 switching elements for an even more compact implementation and reduction in the required dc power consumption. The second reconfigurable resonator based on a single VO2 switching element has a tuning range from 712 to 730 MHz and a quality factor better than 514. Design, implementation, and measurement results for tunable filters based on the proposed frequency tuning method are presented. A proof-of-concept six-pole tunable filter shows center frequency tuning from 944 to 971 MHz with a 36-MHz bandwidth and an insertion loss better than 3.6 dB over the tuning range. Another three-pole filter is implemented using the proposed reconfigurable resonators with monolithically integrated VO2 switches. The filter demonstrates a measured center frequency of 713 and 733 MHz for the low and high channels, respectively, while the insertion loss is better than 2.5 dB. High power and nonlinear test results are presented for both the reconfigurable resonators and filters. The monolithic integration of the VO2 switches with SAW resonators allows the practical implementation of higher order tunable SAW filters for wireless applications without any major performance degradation or increase in the size of the filter.

Phase Transition and Optical Properties of VO2 and Al: ZnO/VO2 Thin Films

Thermochromic Vanadium dioxide (VO2) has strong potential for smart window applications but its commercial scale usage is limited due to low visible light transmission. To address this issue, aluminum doped zinc oxide (AZO) anti-reflecting layer is integrated with VO2 layer in the present work. VO2 single layer and AZO/VO2 bilayer thin film samples were deposited by sputtering technique on quartz substrate. The single-phase growth of VO2 and AZO in single layer and bilayer thin film samples is confirmed by X-ray diffraction measurements. Monoclinic M1 phase of VO2 is detected in VO2 and AZO/VO2 thin film samples at room temperature. Monoclinic to rutile structural phase transition (SPT) in these samples is studied by performing temperature-dependent X-ray diffraction measurements. SPT in VO2 thin film samples is close to 68 °C and SPT temperature appears slightly lower in AZO/VO2 sample as compared to VO2 sample. Spectral transmittance measurement at room temperature showed significant improvement in the visible transmittance of AZO bilayer film than that of single layer VO2 thin film. These results demonstrate the possibility of integration of anti-reflecting layers such as AZO with VO2 layer for better visible transmittances suitable for large-scale smart window applications.