Temperature Dependence Of Transmission Research Articles

Alteration of the upper critical solution temperature (UCST) behavior of the nonionic polymer poly(N-acryloyl-nipecotamide) by its terminal group

Influences of the terminal group of non-ionic polymer with upper critical solution temperature on cloud points (CPs) has been one of curious research topics, however, detailed investigation has not been conducted so far. This study investigates the effect of the terminal group of poly(N-acryloyl-nipecotamide)s (PNANAms) on their CPs in aqueous solution. PNANAms with different molecular weights (Mn) ranging from 4,100 to 34,300 and different terminal end groups were successfully synthesized via reversible addition–fragmentation chain transfer (RAFT) polymerization. The temperature-dependent optical transmittance of aqueous solutions of the PNANAms revealed that their CP was influenced by their terminal group, in addition to their Mn and polymer concentration. PNANAms with low Mn (Mn ≥ 7,500) and a hydrophobic (dodecyl) terminal group exhibited poor solubility, whereas PNANAms with a moderate Mn (Mn ≤ 10,200) and hydrophilic (maleimide or carboxylic) terminal groups were readily soluble in aqueous solution. However, PNANAms with a high Mn (Mn = 34,300) were hardly soluble in aqueous solution. The poor solubility of such PNANAms suggests that strong inter- and intramolecular hydrogen bonds were formed among the polymer chains, increasing their CP. PNANAm with a low Mn (Mn = 4,100) and the hydrophobic terminal and that with a moderate Mn (13,200 ≤ Mn ≤ 18,200) and hydrophilic terminal groups exhibited CPs in aqueous solution. The CP of PNANAms with carboxylic terminal groups was also influenced by the solution pH owing to the deprotonation of these groups. The size of polymeric aggregates was directly observed using phase-contrast microscopy, and the temperature-dependent aggregation and dispersion of the polymers were described in terms of the inter- and intramolecular hydrogen bonds formed among PNANAm chains. Finally, a cell viability assay was conducted to explore the possibility of the applications of PNANAm in the fields of biomaterials and regenerative therapy.

In-situ characterization of the semiconductor-metal phase transition in vanadium dioxide thin films

Vanadium dioxide (VO2) exhibits a reversible first-order semiconductor-metal phase transition (SMT) near 68 °C at ambient pressure, consisting in a structural transformation from a low-temperature semiconducting monoclinic phase to a high-temperature metallic rutile phase. This phenomenon is investigated on thin films of VO2, with thickness ranging from 15 to 300 nm, which are deposited on a silica substrate by magnetron sputtering. The films are systematically characterized at the morphological, structural, and optical level by using Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), Grazing Incidence X-ray Di↵raction (GIXRD), Raman Spectroscopy, Spectrophotometry, and Spectroscopic Ellipsometry. The SMT is investigated in-situ by Optical Spectroscopy in the VIS-NIR spectral range and by Grazing Incidence X-ray Di↵raction (GIXRD). Compared to their bulk counterpart, thin films display broader phase transitions upon thermal excitation. This is evidenced by monitoring the temperature-dependent transmittance at specific wavelengths which reveals a hysteretic behaviour, whose thermal width and amplitude depends on the film thicknesses. Additionally, changes in peak positions and intensities in in-situ GIXRD di↵raction spectra further elucidate the phase transition dynamics.

Enhanced thermo-electro-optical and dielectric properties of carbon nanoparticle-doped polymer dispersed liquid crystal based switchable windows

The effect of temperature as well as voltage on switchable smart windows was studied. These smart windows are composites of a polymer and a liquid crystal (LC) and collectively known as polymer dispersed liquid crystal (PDLC) films. In order to enhance the efficiency of the smart windows/PDLC films, the LC material was doped with carbon nano particles (CNP) in various concentrations ranging from 0 to 0.1%. To examine the efficacy and the temperature dependent performance of the CNP doped PDLC (CPDLC) film, firstly morphological and thermo-morphological studies were performed using polarizing optical microscopy (POM). POM in combination with temperature changes allows to record texture changes and the nematic-isotropic transition of the composite films for applied voltage. The complete electro-optical (EO) study comprising of voltage and temperature dependent transmittance, threshold voltage (Vth), saturation voltage (Vsat), contrast ratio (CR) and response time measurement was performed through an assembled EO set-up. To infer intermolecular cooperative processes between polymer and the dipoles of the LC, the relaxation mechanism of the composite films for various temperatures was studied by employing Debye and Cole-Cole models in dielectric spectroscopy. Parameters like dielectric strength and dissipation factor were determined to allow optimization of the CPDLC films.

Thermochromic VO[formula omitted] thin film from electron beam evaporated V[formula omitted]O[formula omitted]/Ni/V[formula omitted]O[formula omitted] and V[formula omitted]O[formula omitted]/Co/V[formula omitted]O[formula omitted] multilayer stack system

The oxygen–vanadium system presents different equilibrium phases amongst which monoclinic and tetragonal forms of VO2 exist below and above the phase transition temperature of 68 °C. The structure can be explained by pure Mott phase transition with Peierls electron-lattice distortion giving ultrafast transformation of the semiconducting monoclinic VO2 to metallic rutile structure. Hence, practical applications in technology can be explored such as; switching devices, thermal relays and energy management, sensors and actuators, electrochromic and photochromic memories. In this study, VO2 thermochromic thin films were deposited on a quartz glass substrate by electron beam evaporation technique in ultrahigh vacuum at room temperature using sandwich structured V2O5/metal (Ni, Co)/V2O5 multilayer target followed by post-annealing at 500 °C under vacuum. The morphology and crystal structure were investigated by X-ray diffraction, Ultraviolet/Visible/Near Infrared spectrophotometry, and scanning electron microscopy analyses. The sandwich structure effectively regulates the stoichiometry and polymorphs of the material. It was observed that the polymorph of the films switch from VO2 (B) to VO2 (M) when the Ni and Co middle layer reached 7 nm and 10 nm respectively. For the aforementioned thicknesses of the Ni and Co layers, the V2O5/Ni/V2O5 and V2O5/Co/V2O5 multilayers showed thermochromic properties. For V2O5/Ni (7 nm)/V2O5 and V2O5/Co (10 nm)/V2O5 multilayer films, the temperature-dependent spectral transmission measurements show the change in optical range of ∼ 65% and ∼ 43% respectively after the phase transition at wavelength 2500 nm. Transmission measurements of VO2 thin films, were determined at temperatures below and above the phase transition temperature in both the visible and the near-infrared ranges of the electromagnetic spectrum. The temperature-dependent optical transmittance measurement for V2O5/Co (10 nm)/V2O5 multilayer films shows that the multilayer exhibits thermochromic properties and has higher phase transition temperature.

Steady-state and dynamic characteristics of deep UV luminescence in rock salt-structured MgxZn1−xO

Temperature-dependent cathodoluminescence spectra were measured for rock salt-structured MgxZn1−xO films with x = 0.95–0.61. The Mg0.95Zn0.05O film exhibited the shortest deep UV peak wavelength of 199 nm (6.24 eV) at 6 K. Relatively high equivalent internal quantum efficiencies of 0.9%–11% were obtained. The Tauc plots, which were obtained from temperature-dependent optical transmittance measurements, exhibited large Stokes-like shifts of 0.7–0.9 eV at 6–300 K. Time-resolved photoluminescence (PL) signals at 7 K exhibited fast and slow decay components. The fast decay component had PL lifetimes of 2.59–3.08 ns, and the slow decay component far exceeded the measurement time range of 12.5 ns. The fast decay constant reflected the transfer lifetime of the photoexcited carriers to certain trapping centers. These centers were tentatively ascribed to Zn-related isoelectronic trapped-hole centers and may be a cause of the large Stokes-like shifts. The signals at 300 K exhibited very short PL lifetimes of 120–180 ps. The PL lifetimes were mainly attributed to the nonradiative recombination lifetime. Simultaneous decreases in the Zn-related isoelectronic trapped-hole centers and the nonradiative recombination centers were found to be necessary to improve the DUV emission properties of RS-MgxZn1−xO films.

Tunable terahertz electromagnetically induced transparency based on a composite structure superconducting metamaterial.

We experimentally present a tunable electromagnetically induced transparency (EIT)-like response in bright-bright mode resonators. In contrast to previous studies, we used NbN film and a gold film composite structure metamaterial. A significant slow-light effect could be observed at the transmission window, and the maximum group index could reach 100. As a variation in temperature alters the intrinsic ohmic loss of superconducting NbN film, a temperature-dependent transmittance and slow-light effect were observed. To better illustrate the physical mechanism of the two modes, a hybrid coupling model was introduced to fit the experimental transmission spectra and extract the characteristic parameters of sub-resonators. We found excellent agreement with experimental results. Our results provide deeper insight into the metamaterial analogs of an EIT-like response and offer an alternative approach for engineering slow-light devices, bandpass filters, and switches/modulators at terahertz frequencies.

Temperature effects on optical characteristics of thermally evaporated CuSbSe2 thin films for solar cell applications

CuSbSe2 thin film was deposited by co-evaporation of binary CuSe and Sb2Se3 sources. The structural and morphological properties of the deposited thin film were investigated with X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray analysis measurements. XRD pattern indicated that deposited thin film has an orthorhombic crystalline structure with the preferential orientation of (013) direction. SEM image presented that the thin film surface is almost uniform. The optical characteristics of the deposited CuSbSe2 thin film were investigated in detail by performing room temperature Raman, temperature-dependent transmittance spectroscopy, and photoluminescence techniques. Raman spectrum exhibited one mode at around 210 cm−1 associated with Ag vibrational mode. The derivative spectroscopy technique was used to obtain the band gap energy of the films. Temperature dependence of band gap energy was investigated by considering the Varshni model. The rate of change of band gap energy, absolute zero value of gap energy, and Debye temperature were determined as −1.3 × 10−4 eV/K, 1.21 eV, and 297 ± 51 K, respectively. The photoluminescence spectrum indicated the room temperature direct band gap energy as 1.30 eV.

Infrared optical properties modulation of VO2 thin film fabricated by ultrafast pulsed laser deposition for thermochromic smart window applications

Over the years, vanadium dioxide, (VO2(M1)), has been extensively utilised to fabricate thermochromic thin films with the focus on using external stimuli, such as heat, to modulate the visible through near-infrared transmittance for energy efficiency of buildings and indoor comfort. It is thus valuable to extend the study of thermochromic materials into the mid-infrared (MIR) wavelengths for applications such as smart radiative devices. On top of this, there are numerous challenges with synthesising pure VO2 (M1) thin films, as most fabrication techniques require the post-annealing of a deposited thin film to convert amorphous VO2 into a crystalline phase. Here, we present a direct method to fabricate thicker VO2(M1) thin films onto hot silica substrates (at substrate temperatures of 400 °C and 700 °C) from vanadium pentoxide (V2O5) precursor material. A high repetition rate (10 kHz) femtosecond laser is used to deposit the V2O5 leading to the formation of VO2 (M1) without any post-annealing steps. Surface morphology, structural properties, and UV–visible optical properties, including optical band gap and complex refractive index, as a function of the substrate temperature, were studied and reported below. The transmission electron microscopic (TEM) and X-ray diffraction studies confirm that VO2 (M1) thin films deposited at 700 °C are dominated by a highly texturized polycrystalline monoclinic crystalline structure. The thermochromic characteristics in the mid-infrared (MIR) at a wavelength range of 2.5–5.0 μm are presented using temperature-dependent transmittance measurements. The first-order phase transition from metal-to-semiconductor and the hysteresis bandwidth of the transition were confirmed to be 64.4 °C and 12.6 °C respectively, for a sample fabricated at 700 °C. Thermo-optical emissivity properties indicate that these VO2 (M1) thin films fabricated with femtosecond laser deposition have strong potential for both radiative thermal management or control via active energy-saving windows for buildings, and satellites and spacecraft.

VO2 films on flexible thin polyimide films: Fabrication and characterization of electrical and optical properties in insulator-metal transition

We report on the realization of thin polyimide films on which phase transition vanadium dioxide (VO2) films grow. Biased reactive sputtering achieved b-axis-oriented growth of VO2 films on ZnO-buffered polyimide films with a thickness of 8.5 μm. By peeling off the polyimide films from a quartz substrate, stand-alone VO2/ZnO/polyimide layered films that exhibited insulator-metal transition (IMT) with nearly three orders of resistivity change were fabricated. Dependence of IMT on a mechanical curvature was investigated for demonstrating the high flexibility. Temperature-dependent optical transmittance at 1.45 μm showed a high switching ratio for infrared light in VO2/ZnO/polyimide layered films. The proposed structure can be utilized for active metasurfaces that control terahertz waves with quite low reflection loss due to its small thickness.

Control of Stimuli Sensitivity in pH-Switchable LCST/UCST-Type Thermosensitive Dendrimers by Changing the Dendrimer Structure

Stimuli-sensitive materials, such as pH- and temperature-responsive polymers, are useful as smart materials. Phenylalanine (Phe)-modified polyamidoamine (PAMAM) dendrimers with succinic acid termini, PAMAM-Phe-Suc, have been reported as unique pH-switchable lower critical solution temperature (LCST)-/upper critical solution temperature (UCST)-type thermosensitive polymers. Regulating the phase transition behavior of dendrimers is important for their applications. This study investigated the relationship between the dendrimer structure and stimuli sensitivity. Phe-modified PAMAM dendrimers with cyclohexanedicarboxylate termini (PAMAM-Phe-CHex) and sulfonate termini (PAMAM-Phe-SO3Na) were synthesized. The temperature-dependent transmittance of these aqueous dendrimer solutions was examined at various pH values. PAMAM-Phe-CHex with Phe at all termini (PAMAM-Phe64-CHex) demonstrated a broad UCST-like phase transition at pH 7.0 but lacked an LCST-type phase transition. PAMAM-Phe-CHex with ≤ 27 Phe residues showed both LCST- and UCST-like phase transitions at different pH values, but the phase transition was broad. PAMAM-Phe-SO3Na showed both LCST- and UCST-type phase transitions at different pH values, and the transition temperature increased as the bound Phe number decreased. Thus, the phase transition behavior of PAMAM-Phe-SO3Na dendrimers can be regulated by varying the Phe/PAMAM ratios.

Design and reactive magnetron sputtering of thermochromic coatings

Thermochromic coatings based on vanadium dioxide exhibit great potential in various fields, including smart energy-saving windows with temperature-dependent transmittance in the infrared at preserved transmittance in the visible. However, these promises come with challenges concerning the low-temperature preparation of high-quality crystalline VO2-based films by industry-friendly techniques and the simultaneous optimization of all coating characteristics, such as thermochromic transition temperature, luminous transmittance, and modulation of solar energy transmittance. This Perspective outlines these challenges, highlights the recent progress in the field of design and reactive magnetron sputtering of thermochromic coatings, explains the physics that allowed this progress, and provides ideas and recommendations for future research. A combination of the advantages of controlled high-power impulse magnetron sputtering with the not yet fully experimentally utilized multilayered designs constitutes the main reason why further progress is anticipated in the future.

Numerical derivation and validation of the angular, hemispherical and normal emissivity and reflectivity of common window glass

The thermal radiative properties of glazing materials are fundamental inputs for evaluating the energetic performance and thermal behaviour of buildings. These properties are required for many practical applications ranging from infrared thermography to building performance simulation and thermal comfort evaluations. Soda–lime–silica glass is the most widely used glass, worldwide, for glazing and the derivation of its thermal and optical properties are the subject of this work. Based on experimentally acquired spectral reference measurement data for soda-lime glass, the complex-valued Fresnel equations are solved and Monte-Carlo integration is carried out over the black-body spectrum, as well as over the hemisphere. These calculations are performed for various radiative temperatures to establish their temperature dependencies, and additionally the temperature-dependent transmittance of soda-lime glass was analysed. By applying a non-linear optimisation algorithm, computationally efficient practical fitting formulae for the angular reflectivity, emissivity and absorptivity are derived. All equations are numerically solved with a high degree of accuracy. The determination of the hemispherical total emissivity for this type of glass confirms the current accepted value (∼0.2%) originally derived by Rubin (1985). A simple yet robust experimental design, based on thermography, is used to validate the results of the numerical reflectivity model. Additionally, we provide angular functions, fitting functions and additional constants that were hitherto unavailable. The practical benefits of the fitting formulae provided are considerable in relation to modelling the reflection of thermal radiation on glazed surfaces, and are demonstrated in two case-study applications in the appendix.

Synthesis of Temperature-Responsive Polymers Containing Piperidine Carboxamide and N,N-diethylcarbamoly Piperidine Moiety via RAFT Polymerization.

In this study, poly(N-acryloyl-nipecotamide) (PNANAm), poly(N-acryloyl-isonipecotamide) (PNAiNAm), and poly(N-acryloyl-N,N-diethylnipecotamide) (PNADNAm) are synthesized as novel temperature-responsive polymers using reversible addition-fragmentation chain-transfer polymerization. Aqueous solutions of these three polymers are examined via temperature-dependent optical transmittance measurements. The PNANAm sample with a hydrophilic terminal group shows an upper critical solution temperature (UCST) in phosphate-buffered saline (PBS) when its molecular weight (Mn ) is 7600 or higher, whereas PNANAm (Mn < 7600) is soluble. The UCST is influenced by molecular weight and the polymer concentration. In contrast, PNANAm sample with nonionic terminal group shows UCST, when Mn is below 7600, suggesting that the terminal nonionic group possibly increases UCST of PNANAm. The urea addition experiment suggests that the driving force for expression of UCST of PNANAm is the formation of inter-and intramolecular hydrogen bonds among the polymer chains. PNAiNAm is soluble in PBS but exhibits an UCST in an appropriate concentration of ammonium sulfate. In contrast, PNADNAm exhibits a lower critical solution temperature. Comparing the chemical structure of these polymers and their phase transition behaviors suggests that the carboxamide group position in the piperidine ring could determine the UCST expression. These results could help design temperature-responsive polymers with a desired the cloud point temperature.

Acetylation of Cyclodextrin-Threaded Polyrotaxanes Yields Temperature-Responsive Phase Transition and Coacervate Formation Properties.

Stimuli-responsive materials have received considerable attention for their application in biomedical fields. Herein, the temperature-dependent phase transition behavior of acetylated polyrotaxanes (Ac-PRXs) consisting of acetylated cyclodextrins threaded onto a linear axle polymer in aqueous solution is investigated. The aqueous solutions of Ac-PRXs exhibit temperature-dependent transmittance changes when the degree of acetylation is 30-40%. Upon increasing the temperature, Ac-PRXs are dehydrated and acetyl groups are subsequently associated through hydrophobic interactions. Interestingly, the Ac-PRXs form coacervate droplets with a diameter of ≈2-3 µm above their cloud points. These temperature-responsivities of Ac-PRXs are observed for other PRXs with different axle polymer molecular weights and compositions. Consequently, the acetylation of PRXs is an attractive chemical modification for yielding temperature-responsivities, and Ac-PRXs can be applied as temperature-responsive supramolecular materials.

Structural and temperature-tuned optical characteristics of Bi12GeO20 sillenite crystals

Sillenite compounds exhibit unique photorefractive and electro-optic characteristics providing attractiveness to these materials in various optoelectronic applications. The present paper aims at investigating one of the members of this family. Structural and optical characteristics of Bi12GeO20 (BGO) were studied by means of x-ray diffraction, Raman spectroscopy and temperature-dependent transmittance measurements. Obtained transmission curves in the wavelength range of 350−1100 nm and at different applied temperatures between 10 and 300 K were employed to find out the absorption coefficient dependence on the photon energy. Tauc relation revealed the presence of an energy gap of 2.49 eV at room temperature. Extension of energy gap up to 2.57 eV due to decreased temperature down to 10 K was deduced by the analysis. In order to have reliable results, the energy gap value was corroborated by utilizing derivative spectral method and well consistency between both methods was indicated. Energy gap change with temperature was also discussed in the study using an empirical formula developed by Varshni. Energy gap at absolute zero and rate of band gap alteration with temperature were determined as 2.57 eV and −2.4 × 10−4 eV K − 1, respectively. Taking into account the previously reported studies on investigation of band gap characteristics of BGO, intrinsic BiGe3++VO+ defect could be responsible for the revealed energy value of 2.49 eV which is much lower than reported band gap energy of ~3.2 eV.

Investigation of phase transitions in vegetable oils through temperature-dependent optical measurements: supercooling effect

Measurements of the phase transitions in vegetable oils such as coconut, palm (fruit), palm kernel (from the seeds), macauba (Acrocomia aculeata) and its biodiesel have been taken through temperature-dependent optical transmittance. Room-temperature optical transmittance spectroscopy experiments in the UV–Vis–NIR region showed that oils begin to transmit at different wavelengths and present different wavelength rates of light transmission. A peak level of absorption at 930 nm is present for all samples and attributed to the third harmonic of vibrational mode of chemical groups with covalent C–H bonds. Viscosity and density measurements of the vegetable oils and biodiesel were also carried out in order to aid in the interpretation of their thermal behavior. The phase transition regions were determined, and the supercooling effect was detected in the oils due to their high viscosity. The effect was not observed in the macauba biodiesel due to its low viscosity.

Analysis of temperature-dependent transmittance spectra of Zn0.5In0.5Se (ZIS) thin films

Temperature-dependent transmission experiments of ZnInSe thin films deposited by thermal evaporation method were performed in the spectral range of 550–950 nm and in temperature range of 10–300 K. Transmission spectra shifted towards higher wavelengths (lower energies) with increasing temperature. Transmission data were analyzed using Tauc relation and derivative spectroscopy. Analysis with Tauc relation was resulted in three different energy levels for the room temperature band gap values of material as 1.594, 1.735 and 1.830 eV. The spectrum of first wavelength derivative of transmittance exhibited two maxima positions at 1.632 and 1.814 eV and one minima around 1.741 eV. The determined energies from both methods were in good agreement with each other. The presence of three band gap energy levels were associated to valence band splitting due to crystal-field and spin–orbit splitting. Temperature dependence of the band gap energies were also analyzed using Varshni relation and gap energy value at absolute zero and the rate of change of gap energy with temperature were determined.

Temperature-dependent transmittance nanocomposite hydrogel with high mechanical strength and controllable swelling memory behavior

In this work, physical cross-linking hydrogel with high mechanical strength, excellent transmittance, and controllable swelling performance has been successfully fabricated through in situ polymerization method. The obtained samples could dissipate a large amount energy in one cyclic tensile test through the crack of hydrogen bond formed between the carbonyl groups of polymer chains and hydroxyl group anchoring on the surface of clay platelets. The controllable swelling behaviors endowed the MD-NC gel with swelling induced shape recovery ability, and the potential directional swelling performance of the gels could propose a promising prospect in many actual applications, such as biomaterials, padding matters, and tissue engineering.

Aerogel-Directed Energy-Storage Films with Thermally Stimulant Multiresponsiveness.

Phase change materials offer enormous potential for thermal energy storage due to their high latent heat and chemical stability. Researchers have developed numerous innovative strategies to overcome the leakage of organic phase change materials and enhance thermal performance. However, the manufacture of form-stable, free-standing energy storage films based on phase change materials with high latent heat remains difficult. Therefore, the present study focused on the production of free-standing, form-stable energy storage films with high phase-change enthalpy and thermally stimulant multiresponsiveness from the simple composite of paraffin with a polytetrafluoroethylene/silica (PTFE/SiO2) aerogel framework, where paraffin was effectively confined in PTFE/SiO2. The resulting paraffin/PTFE/SiO2 films exhibited a large phase change enthalpy (128 J/g) at a paraffin content of 62.8 wt %. The temperature-dependent wettability, transmittance, and mechanical properties of this composite film have also been investigated.

Manipulating Behaviors from Heavy Tungsten Doping on Interband Electronic Transition and Orbital Structure Variation of Vanadium Dioxide Films.

Vanadium dioxide (VO2) with a metal-insulator transition (MIT) has been supposed as a candidate for optoelectronic devices. However, the MIT temperature ( TMIT) above room temperature limits its application scope. Here, high-quality V1- xW xO2 films have been prepared by pulsed laser deposition. On the basis of temperature-dependent transmittance and Raman spectra, it was found that TMIT increases from 241 to 279 K, when increasing the doping concentration in the range of 0.16 ≤ x ≤ 0.20. The interband electronic transitions and orbital structures of V1- xW xO2 films have been investigated via fitting transmittance spectra. Moreover, with the aid of first-principles calculations, an effective orbital theory has been proposed to explain the unique phenomenon. When the W doping concentration increases, the π* and dII orbitals shift toward the π orbital. Meanwhile, the energy gap between the π* and dII orbitals decreases at the insulator state. It indicates that the bandwidth is narrowed, which impedes MIT. In addition, the overlap of the π* and dII orbitals increases at the metal state, and more doping electrons occupy the π* orbital induced by increasing W doping concentration. It manifests that the Mott insulating state becomes more stable, which further improves TMIT. The present work provides a feasible approach to tune TMIT via orbital variation and can be helpful in developing the potential VO2-based optoelectronic devices.