Effect of Annealing Time on the Cyclic Characteristics of Ceramic Oxide Thin Film Thermocouples

Oxide thin film thermocouples (TFTCs) are widely used in high-temperature environment measurements and have the advantages of good stability and high thermoelectric voltage. However, different annealing processes affect the performance of TFTCs. This paper studied the impact of different annealing times on the cyclic characteristics of ceramic oxide thin film thermocouples. ITO/In₂O₃ TFTCs were prepared on alumina ceramics by a screen printing method, and the samples were annealed at different times. The microstructure of the ITO film was studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The results show that when the annealing temperature is fixed, the stability of the thermocouple is worst when it is annealed for 2 h. Extending the annealing time can improve the properties of the film, increase the density, slow down oxidation, and enhance the thermal stability of the thermocouple. The thermal cycle test results show that the sample can reach five temperature rise and fall cycles, more than 50 h, and can meet the needs of stable measurement in high temperature and harsh environments.

Sputtering Flexible VO2 Films for Effective Thermal Modulation

Flexible vanadium dioxide (VO₂) thermochromic films show great potential for large-scale fabrication and possess broader applications compared with VO₂ coatings on rigid substrates. However, the fabrication of flexible VO₂ films remains a challenge so far, leading to the scarcity of research on flexible VO₂ films for smart windows. With the aim to obtain a flexible VO₂-based films with excellent optical properties and a long service life, we designed and successfully fabricated a flexible ITO/VO₂/ITO (IVI) film on the colorless transparent polyimide substrate, which could be directly attached to glasses for indoor temperature modulation. This flexible IVI film effectively enhances the luminous transmittance (T_lum) and solar modulation ability (ΔT_sol) (15 and 68% increase relative to a VO₂ single layer), reduces the thermal emissivity (ε_T) (50.7% decrease relative to a VO₂ single layer), and exhibits better durability than previously reported structures. Such excellent comprehensive performance offers it great potential in practical applications on smart windows. This work is supposed to provide a new strategy for facile direct fabrication of flexible VO₂ films and broaden the applications of flexible VO₂ in more coatings and devices.

Controlled growth of porous oxygen-deficient NiCo2O4 nanobelts as high-efficiency electrocatalysts for oxygen evolution reaction

NiCo₂O₄ with a controlled oxygen vacancy concentration introduced by an Ar-annealing process greatly improved OER activity.

Understanding the Phase Transition Evolution Mechanism of Partially M2 Phased VO2 Film by Hydrogen Incorporation

Studies on the hydrogen incorporated M1 phase of VO₂ film have been widely reported. However, there are few works on an M2 phase of VO₂. Recently, the M2 phase in VO₂ has received considerable attention due to the possibility of realizing a Mott transition field-effect transistor. By varying the postannealing environment, systematic variations of the M2 phase in (020)-oriented VO₂ films grown on Al₂O₃(0001) were observed. The M2 phase converted to the metallic M1 phase at first and then to the metallic rutile phase after hydrogen annealing (i.e., for H₂/N₂ mixture and H₂ environments). From the diffraction and spectroscopy measurements, the transition is attributed to suppressed electron interactions, not structural modification caused by hydrogen incorporation. Our results suggest the understanding of the phase transition process of the M2 phase by hydrogen incorporation and the possibility of realization of the M2 phased-based Mott transition field-effect transistor.

Efficient MoWO3/VO2/MoS2/Si UV Schottky photodetectors; MoS2 optimization and monoclinic VO2 surface modifications

The distinctive properties of strongly correlated oxides provide a variety of possibilities for modulating the properties of 2D transition metal dichalcogenides semiconductors; which represent a new class of superior optical and optoelectronic interfacing semiconductors. We report a novel approach to scaling-up molybdenum disulfide (MoS2) by combining the techniques of chemical and physical vapor deposition (CVD and PVD) and interfacing with a thin layer of monoclinic VO2. MoWO3/VO2/MoS2 photodetectors were manufactured at different sputtering times by depositing molybdenum oxide layers using a PVD technique on p-type silicon substrates followed by a sulphurization process in the CVD chamber. The high quality and the excellent structural and absorption properties of MoWO3/VO2/MoS2/Si with MoS2 deposited for 60 s enables its use as an efficient UV photodetector. The electronically coupled monoclinic VO2 layer on MoS2/Si causes a redshift and intensive MoS2 Raman peaks. Interestingly, the incorporation of VO2 dramatically changes the ratio between A-exciton (ground state exciton) and trion photoluminescence intensities of VO2/(30 s)MoS2/Si from < 1 to > 1. By increasing the deposition time of MoS2 from 60 to 180 s, the relative intensity of the B-exciton/A-exciton increases, whereas the lowest ratio at deposition time of 60 s refers to the high quality and low defect densities of the VO2/(60 s)MoS2/Si structure. Both the VO2/(60 s)MoS2/Si trion and A-exciton peaks have higher intensities compared with (60 s) MoS2/Si structure. The MoWO3/VO2/(60 s)MoS2/Si photodetector displays the highest photocurrent gain of 1.6, 4.32 × 108 Jones detectivity, and ~ 1.0 × 1010 quantum efficiency at 365 nm. Moreover, the surface roughness and grains mapping are studied and a low semiconducting-metallic phase transition is observed at ~ 40 °C.

Impacts of Oxygen Vacancies on Zinc Ion Intercalation in VO2

The aqueous zinc ion battery has emerged as a promising alternative technology for large-scale energy storage due to its low cost, natural abundance, and high safety features. However, the sluggish kinetics stemming from the strong electrostatic interaction of divalent zinc ions in the host crystal structure is one of challenges for highly efficient energy storage. Oxygen vacancies (V_O^••), in the present work, lead to a larger tunnel structure along the b axis, which improves the reactive kinetics and enhances Zn-ion storage capability in VO₂ (B) cathode. DFT calculations further support that V_O^•• in VO₂ (B) result in a narrower bandgap and lower Zn ion diffusion energy barrier compared to those of pristine VO₂ (B). V_O^••-rich VO₂ (B) achieves a specific capacity of 375 mAh g^-1 at a current density of 100 mA g^-1 and long-term cyclic stability with retained specific capacity of 175 mAh g^-1 at 5 A g^-1 over 2000 cycles (85% capacity retention), higher than that of VO₂ (B) nanobelts (280 mAh g^-1 at 100 mA g^-1 and 120 mAh g^-1 at 5 A g^-1, 65% capacity retention).

Reversible and repeatable phase transition at a negative temperature regime for doped and co-doped spin coated mixed valence vanadium oxide thin films

Smooth, uniform mixed valance vanadium oxide (VO) thin films are grown on flexible, transparent Kapton and opaque Al6061 substrates by the spin coating technique at a constant rpm of 3000. Various elements e.g., F, Ti, Mo and W are utilized for doping and co-doping of VO. All the spin coated films are heat treated in a vacuum. Other than the doping elements the existence of only V⁴⁺ and V⁵⁺ species is noticed in the present films. Transmittance as a function of wavelength and the optical band gap are also investigated for doped and co-doped VO thin films grown on a Kapton substrate. The highest transparency (∼75%) is observed for the Ti, Mo and F (i.e., Ti–Mo–FVO) co-doped VO system while the lowest transparency (∼35%) is observed for the F (i.e., FVO) doped VO system. Thus, the highest optical band gap is estimated as 2.73 eV for Ti–Mo–FVO and the lowest optical band gap (i.e., 2.59 eV) is found for the FVO system. The temperature dependent phase transition characteristics of doped and co-doped VO films on both Kapton and Al6061 are studied by the differential scanning calorimetry (DSC) technique. Reversible and repeatable phase transition is noticed in the range of −24 to −26.3 °C.

Smooth, uniform mixed valance vanadium oxide (VO) thin films are grown on flexible, transparent Kapton and opaque Al6061 substrates by the spin coating technique at a constant rpm of 3000.

Natural and induced growth of VO2 (M) on VO2 (B) ultrathin films

This work examines the synthesis of single phase VO₂ (B) thin films on LaAlO₃ (100) substrates, and the naturally-occurring and induced subsequent growth of VO₂ (M) phase on VO₂ (B) films. First, the thickness (t) dependence of structural, morphological and electrical properties of VO₂ films is investigated, evidencing that the growth of VO₂ (B) phase is progressively replaced by that of VO₂ (M) when t > ~11 nm. This change originates from the relaxation of the substrate-induced strain in the VO₂ (B) films, as corroborated by the simultaneous increase of surface roughness and decrease of the c-axis lattice parameter towards that of bulk VO₂ (B) for such films, yielding a complex mixed-phase structure composed of VO₂ (B)/VO₂ (M) phases, accompanied by the emergence of the VO₂ (M) insulator-to-metal phase transition. Second, the possibility of inducing this phase conversion, through a proper surface modification of the VO₂ (B) films via plasma treatment, is demonstrated. These natural and induced VO₂ (M) growths not only provide substantial insights into the competing nature of phases in the complex VO₂ polymorphs system, but can also be further exploited to synthesize VO₂ (M)/VO₂ (B) heterostructures at the micro/nanoscale for advanced electronics and energy applications.

VO2 /TiN Plasmonic Thermochromic Smart Coatings for Room-Temperature Applications

Vanadium dioxide/titanium nitride (VO₂ /TiN) smart coatings are prepared by hybridizing thermochromic VO₂ with plasmonic TiN nanoparticles. The VO₂ /TiN coatings can control infrared (IR) radiation dynamically in accordance with the ambient temperature and illumination intensity. It blocks IR light under strong illumination at 28 °C but is IR transparent under weak irradiation conditions or at a low temperature of 20 °C. The VO₂ /TiN coatings exhibit a good integral visible transmittance of up to 51% and excellent IR switching efficiency of 48% at 2000 nm. These unique advantages make VO₂ /TiN promising as smart energy-saving windows.

Enhanced visible transmittance and reduced transition temperature for VO2 thin films modulated by index-tunable SiO2 anti-reflection coatings

Index-tunable anti-reflection SiO₂ coatings prepared on the surface of VO₂ films by sol–gel dip-coating technique to enhance the visible and infrared transmittance of SiO₂/VO₂ films.