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Active and widely controllable phase transition optical materials have got rapid applications in energy-efficient electronic devices, field of meta-devices and so on. Here, we report the optical properties of the vanadium dioxide (VO2)/aluminum-doped zinc oxide (Al:ZnO) hybrid n-n type heterojunctions and the corresponding electro-optic performances of the devices. Various structures are fabricated to compare the discrepancy of the optical and electrical characteristics. It was found that the reflectance spectra presents the wheel phenomenon rather than increases monotonically with temperature at near-infrared region range. The strong interference effects was found in the hybrid multilayer heterojunction. In addition, the phase transition temperature decreases with increasing the number of the Al:ZnO layer, which can be ascribed to the electron injection to the VO2 film from the Al:ZnO interface. Affected by the double layer Al:ZnO, the abnormal Raman vibration mode was presented in the insulator region. By adding the external voltage on the Al2O3/Al:ZnO/VO2/Al:ZnO, Al2O3/Al:ZnO/VO2 and Al2O3/VO2/Al:ZnO thin-film devices, the infrared optical spectra of the devices can be real-time manipulated by an external voltage. The main effect of joule heating and assistant effect of electric field are illustrated in this work. It is believed that the results will add a more thorough understanding in the application of the VO2/transparent conductive film device.

InN superconductivity is very special among III–V semiconductors, as other III–V semiconductors (such as GaAs, GaN, InP, InAs, etc.) usually lack strong covalent bonding and thus seldom show superconductivity at low temperatures. Here, we probe the different superconducting phase transitions in InN highlighted by its microstructure. Those chemical-unstable phase-separated inclusions, such as metallic indium or In2O3, are intentionally removed by HCl acid etching. The quasi-two-dimensional vortex liquid-glass transition is observed in the sample with a large InN grain size. In contrast, the superconducting properties of InN with a small grain size are sensitive to acid etching, showing a transition into a nonzero resistance state when the temperature approaches zero. Since the value of ξ0 (the zero-temperature-limit superconducting coherence length) is close to the grain size, it is suggested that individual InN grains and intergrain coupling should be responsible for the sample-dependent InN superconducting phase transition. Our work establishes a guideline for engineering superconductivity in III-nitride.

Despite the extensive study of two-dimensional layered KNb3O8 (KN), there still remains some vital problems need to be clarified for future applications in environmental purification. Here we demonstrated the successful preparation of interlayer-controlled KN nanoflakes using alkaline hydrothermal conditions by adjusting the amount of thiourea in the reaction. This process resulted in KN nanoflakes with a larger specific surface area than previously reported. Moreover, the initial pH of dye solution and discrepant preferential orientation of interlayer peak have been proved to significantly influence the adsorption and photocatalysis performances of KN. In addition, relevant photocatalysis mechanisms have been expounded, by combined the first-principles calculation. The present work could be helpful in revealing the intrinsic adsorption-photocatalysis features of KN and other similar niobates.

Copper ferrites are emerging transition metal oxides that have potential applications in energy storage devices. However, it still lacks in-depth designing of copper ferrites based anode architectures with enhanced electroactivity for lithium-ion batteries. Here, we report a facile synthesis technology of copper ferrites anchored on reduced graphene oxide (CuFeO2@rGO and Cu/CuFe2O4@rGO) as the high-performance electrodes. In the resulting configuration, reduced graphene offers continuous conductive channels for electron/ion transfer and high specific surface area to accommodate the volume expansion of copper ferrites. Consequently, the sheet-on-sheet CuFeO2@rGO electrode exhibits a high reversible capacity (587 mAh g−1 after 100 cycles at 200 mA g−1). In particular, Cu/CuFe2O4@rGO hybrid, which combines the advantages of nano-copper and reduced graphene, manifests a significant enhancement in lithium storage properties. It reveals superior rate capability (723 mAh g−1 at 800 mA g−1; 560 mAh g−1 at 3200 mA g−1) and robust cycling capability (1102 mAh g−1 after 250 cycles at 800 mA g−1). This unique structure design provides a strategy for the development of multivalent metal oxides in lithium storage device applications.

Two-dimensional layered K4Nb6O17 (KN) was easily formed as a secondary phase caused by the volatilization of alkali metal ions, when preparing ferroelectric K x Na1−x NbO3 based ceramics and films. In this work, it was believed that KN film is with weak ferroelectricity and has a little effect on the ferroelectric properties of K x Na1−x NbO3 based films. Moreover, temperature dependent (77–500 K) dielectric functions of KN film have been firstly extracted by fitting ellipsometric spectra with the Adachi dielectric function model and a four-phase layered model. The high-frequency dielectric constant linearly increases and optical band gap slightly decreases with increasing the temperature. We also research its photoelectrochemical properties and its application in high-efficient light-induced H2 evolution. In addition, X-ray photoelectron spectroscopy, Raman scattering, temperature dependent transmittance and infrared reflectance spectra, and first-principles calculation were conjointly performed to further reveal the intrinsic optoelectronic features and relevant mechanisms of KN.

The enhanced light-harvesting capacity and effective separation of photogenerated carriers in fantastic hierarchical heterostructures enjoy striking attention for potential applications in the field of solar cells and photocatalysis. A three-dimensional (3D) dandelion-shaped hierarchical Bi2S3 microsphere compactly decorated with wing-shaped few layered MoS2 lamella (D-BM) was fabricated via a facile hydrothermal self-assembly process. Especially, polyethylene glycol (PEG) has been proven as the vital template to form D-BM microsphere. Importantly, the as-prepared D-BM microsphere presents pH-dependent superior adsorption behavior and remarkable visible light photocatalytic activity for degradation of organic dyestuffs (Rhodamine B/RhB and Methylene blue/MB), far exceeding those for the pure Bi2S3 and MoS2. It is understandable that D-BM with high surface area possesses more active sites and promotes light utilization due to the unique porous structure with outspread wings. Besides, based on the experiments and theoretical calculations, the staggered type II band alignment of D-BM permits the charge injection from Bi2S3 to MoS2, subsequently accelerates the separation and restrains the recombination of carriers, leading to excellent photocatalytic activity, as well as the photoconductance and photoresponse performance (with Ilight/Idark ratio 567).

The interlayer interaction of vertically stacked heterojunctions is very sensitive to the interlayer spacing, which will affect the coupling between the monolayers and allow band structure modulation. Here, with the aid of density functional theory (DFT) calculations, an interesting phenomenon is found that MoS2-WS2, MoS2-WSe2, and WS2-WSe2 heterostructures turn into direct-gap semiconductors from indirect-gap semiconductors with increasing the interlayer space. Moreover, the electronic structure changing process with interlayer spacing of MoS2-WS2, MoS2-WSe2, and WS2-WSe2 is different from each other. With the help of variable-temperature spectral experiment, different electronic transition properties of MoS2-WS2, MoS2-WSe2, and WS2-WSe2 have been demonstrated. The transition transformation from indirect to direct can be only observed in the MoS2-WS2 heterostructure, as the valence band maximum (VBM) at the Γ point in the MoS2-WSe2 and WS2-WSe2 heterostructure is less sensitive to the interlayer spacing than those from the MoS2-WS2 heterostructure. The present work highlights the significance of the temperature tuning in interlayer coupling and advance the research of MoS2-WS2, MoS2-WSe2, and WS2-WSe2 based device applications.

The optical properties and structural variations of silicon (Si) doped Sb2Te (SST) films as functions of temperature (210–620 K) and Si concentration (0–33%) have been investigated by the means of temperature dependent Raman scattering and spectroscopic ellipsometry experiments. Based upon the changes in Raman phonon modes and dielectric functions, it can be concluded that the temperature ranges for intermediates and transition states are estimated to 150, 120, 90 and 0 K, corresponding to ST, SST25%, SST28% and SST33% films, respectively. The phenomenon also can be summarized by the thermal evolutions of interband electronic transition energies (En) and partial spectral weight integral (I). The disappearance of intermediate (INT) state for SST33% film between amorphous (AM) and hexagonal (HEX) phases can be attributed to the acceleratory crystallization of HEX phase by Si introduction. It illustrates that the risk of phase separation (Sb and Te) during the cyclic phase-change processes decreases with the increasing Si concentration. The enhanced crystallization behaviors can optimize the data retention ability and the long term stability of ST by Si doping, which are important indicators for phase change materials. The performance improvement has been analyzed qualitatively from the optical perspective.

The enhanced light-harvesting capacity and effective separation of photogenerated carriers in fantastic hierarchical heterostructures enjoy striking attention for potential applications in the field of solar cells and photocatalysis. A three-dimensional (3D) dandelion-shaped hierarchical Bi2S3 microsphere compactly decorated with wing-shaped few layered MoS2 lamella (D-BM) was fabricated via a facile hydrothermal self-assembly process. Especially, polyethylene glycol (PEG) has been proven as the vital template to form D-BM microsphere. Importantly, the as-prepared D-BM microsphere presents pH-dependent superior adsorption behavior and remarkable visible light photocatalytic activity for degradation of organic dyestuffs (Rhodamine B/RhB and Methylene blue/MB), far exceeding those for the pure Bi2S3 and MoS2. It is understandable that D-BM with high surface area possesses more active sites and promotes light utilization due to the unique porous structure with outspread wings. Besides, based on the experiments and theoretical calculations, the staggered type II band alignment of D-BM permits the charge injection from Bi2S3 to MoS2, subsequently accelerates the separation and restrains the recombination of carriers, leading to excellent photocatalytic activity, as well as the photoconductance and photoresponse performance (with Ilight/Idark ratio 567).