AgBi₂I₇ thin film is one of the important candidates for constructing heterojunction ultraviolet photodetectors, due to their great optoelectronic properties and environmental stability. In this study, AgBi₂I₇ thin films were prepared by solution method and their photodetecting properties were investigated. By optimizing technological parameters such as concentration of the precursor solution and type of solvent (n-butylamine and DMSO), their photodetecting performance were investigated. AgBi₂I₇ thin films were fabricated on wide-bandgap GaN by optimal scheme to construct an AgBi₂I₇/GaN heterojunction. The heterojunction has a great selective detection of UVA-ray of which full width at half maximum is about 30 nm. Under 3 V bias and 350 nm UV irradiation, the On/Off ratio of the device exceeds 5 orders of magnitude, achieving a high responsivity of 27.51 A/W and a high detection rate of 1.53×10¹⁴ Jones. Therefore, the present research indicates that AgBi₂I₇ thin films prepared by solution method are promising to be applied to construct high-performance heterojunction ultraviolet photodetectors.

X-ray detection has been widely used in medical imaging, security inspection, and industrial non-destructive tests. Halide perovskite X-ray detectors have attracted increasing attention due to their high sensitivity and low detection limit, but the notorious ion migration leads to poor operational stability. It is reported that the low dimensional structure can effectively suppress the ion migration of perovskites, thus greatly improving the stability of the detectors. This review introduces the working mechanism, key performance parameters of perovskite X-ray detectors, and summarizes the recent progress of low-dimensional perovskite materials and their application in direct X-ray detectors. The relationship between the structural characteristics of low-dimensional perovskite materials and their X-ray detection performance was systematically analyzed. Low-dimensional perovskite is a promising candidate for the preparation of X-ray detectors with both high sensitivity and stability. Further optimization of detection material and device structure, preparation of large-area pixelated imaging devices, and study of working mechanism in-depth of the detector are expected to promote the practical application of perovskite X-ray detectors.

Two-dimensional (2D) perovskite displays great potential in optoelectronic applications due to its inherent quantum well structure, large exciton binding energy and good stability. However, facile preparation of high-quality 2D perovskite films with low cost remains a huge challenge. In this work, high-quality two-dimensional perovskite (PEA)₂PbI₄ films were prepared by solution method at low annealing temperature(80 ℃) without other special treatments, and further applied in the field of photodetectors. The results show that this photodetector possessed a low dark current (10^-11 A), good responsiveness illuminated at a wavelength of 450 nm (107 mA·W^-1), high detection rate (2.05×10¹² Jones) and fast response time (250 μs/330 μs). After 1200 s continuous illumination, the device maintains 95% initial photocurrent. In addition, the photocurrent remains almost unchanged after storage for 30 d. This work provides promising strategy to develop stable and high-performance optoelectronic devices.

Nickel molybdate (NiMoO₄) is a material with excellent performance in the field of energy storage and catalysis, but lacking of further explorations in the field of electrochromism. In this work, porous NiMoO₄ films were grown on transparent conductive glasses by hydrothermal method without using seed layer. Crystalline phase and micromorphology of NiMoO₄ nanosheet films were characterized by grazing incidence X-ray diffractometer (GIXRD) and field-emission scanning electron microscope (FESEM), and the electrochromic and electrochemical properties were also investigated by using a UV-Vis-NIR spectrophotometer and an electrochemical workstation. The results show that the NiMoO₄ electrochromic films have a porous structure, which can provide sufficient channels for ion migration and reactive sites for the dynamic process of ion intercalation/deintercalation into NiMoO₄ film. Therefore, the NiMoO₄ films exhibit excellent electrochromic performance, including large optical modulation of 79.6% at 480 nm and high coloring efficiency of 86.2 cm²·C^-1. Meanwhile, the coloration and bleaching response time of the NiMoO₄ films are 9.5 and 12.7 s, respectively. Interestingly, there is a two-step process in the bleached process of NiMoO₄ electrochromic films, including a fast process and a slow process. And the optical modulation can still be maintained at 99.7% of the maximum optical modulation after 100 cycles. In addition, the NiMoO₄ films exhibit a large area specific capacitance of 49.59 mF·cm^-2 at 0.3 mA·cm^-2. These excellent properties support NiMoO₄ nanosheet films with promising application in high-performance electrochromic devices. And the next step is to focus on finding the suitable electrolyte and matched counter electrodes in the device assembly.

Electrochromic materials have been applied in energy-saving buildings, intelligent displays, and other fields, recognized as one of the most promising intelligent materials for research. Liquid phase method for preparation of WO₃ electrochromic thin filmscan construct complex polychromies structures, showing great potential in modulation amplitude and short response time, especially in large area and low cost preparation. This study aims to develop a low-cost, easy-to-scale WO₃ nanocrystalline liquid phase coating process, and improve cycle stability and preparation process. WO₃ electrochromic films with high modulation amplitude, rapid response and fatigue resistance were prepared. Optimized the annealing process, WO₃ nanopowders were synthesized with low aggregation and high crystallinity, and then WO₃ nanocrystalline coating solution was prepared by ball milling dispersion. Thin film microstructure and coating solution crystallinity were optimized. The obtained thin electrochromic films of WO₃ show high tuning amplitude (82%), short response time (t_c/t_b: 8 s/4.2 s), high colouring efficiency (81.5 cm²·C^-1), and high cycling stability (> 1000 times). In this work, the crystallization and dispersion properties of WO₃ nano-powder were modified to comprehensively improve the performance of WO₃ electrochromic films prepared by nanocrystalline liquid phase coating technology. All results above demonstrate that the WO₃ electrochromic film prepared by the liquid phase method is expected to be used in the future with high color-changing performance and cycle stability.

Electrochromic materials are energy-saving and environmentally friendly materials that can reduce energy use by adjusting sunlight and solar-heat. In particular, transition metal oxides with stable chemical properties have been widely studied as electrochromic materials. Recently, bimetallic oxides with two variable valence states of metal ions have received increasing attention due to their better electrochemical activity. In this study, Ti₂Nb₁₀O₂₉ films were successfully prepared on conductive glasses, and the effect of the atomic ratio of niobium to titanium in the precursor on the electrochromic properties of the thin films was investigated. The results show that the thin film prepared from precursors with an atomic ratio of niobium to titanium of 3 : 1 possesses the best electrochromic properties. It is worth noting that the thin film achieves a large optical modulation in the wavelength range of 300-1100 nm, and the transmittance in the bleached state is nearly 90%, appearing grayish blue under the action of −1.6 V, colorless state under the action of 0.4 V, and achieving a maximum optical modulation of 69.4% at the wavelength of 750 nm. After a square-wave potential of -1.6 V for 60 s and 0.4 V for 15 s, the film shows response time of 29.8 s for coloring and 5.9 s for bleaching. Coloration efficiency of the as-prepared film is 68.3 cm²·C^-1. The above results indicate that the successfully prepared Ti₂Nb₁₀O₂₉ thin film enriches variety of bimetallic oxide electrochromic materials and has widely application prospect.

Wearable instruments are functional devices that can be worn on human body, sensing, transmitting and processing body or environmental information in real time, and show broad application prospects in medical health, especially artificial intelligence, sports and entertainment. With the development of wearable instruments, various flexible sensors have emerged. Flexible mechanical sensors based on piezoelectric effect have attracted much attention because of their advantages of wide sensing frequency, fast response, good linearity, and self-power supply. However, traditional piezoelectric materials are mostly brittle ceramics and crystalline materials, which limit their application in flexible devices. With the deepening of research, more and more flexible piezoelectric materials and piezoelectric composites continue to emerge, injecting new development vitality into flexible wearable mechanical devices. This article mainly summarizes the cutting-edge progress of flexible wearable piezoelectric devices, including piezoelectric principle, preparation and performance improvement methods of flexible piezoelectric materials. In addition, the main application directions of flexible wearable piezoelectric devices, including medical health and human-computer interaction, as well as the challenges and opportunities encountered, are summarized.

As a colossal magnetoresistance material, the perovskite manganese oxide La_1–xSr_xMnO₃ (LSMO) has broad application prospects in magnetic sensors and other fields. However, it is difficult to obtain a significant colossal magnetoresistance effect at a low magnetic field at room temperature. To improve its magnetoresistance effect and transition temperature, La_0.8Sr_0.2Mn_1–xAl_xO₃ (0≤x≤0.25) (LSMAO) polycrystalline samples were prepared by traditional solid-state reaction method in present work. Effects of Al³⁺ doping on the electrical transport property and magnetoresistance of LSMO were systematically analyzed. The X-ray diffraction (XRD) results indicate that all samples crystallize in a single rhombohedral structure with the space group of $\text{R}\bar{3}\text{C}$. Result of electrical transport property shows that resistivity of the samples increases exponentially with the increment of Al³⁺ doping amount, and the metal-insulator transition temperature is increased by an external magnetic field. This phenomenon may be attributed to dilution of the Mn³⁺/Mn⁴⁺ ions network by Al³⁺, which increases the magnetic disorder but reduces the number of carriers. In addition, the conduction mechanism of LSMAO ceramics change from the small polaron hopping model (SPH) to the variable range hopping model (VRH) after doping of Al³⁺, reflecting that the non-magnetic Al³⁺ weakens the carrier exchange between the ferromagnetic clusters. As a result, the thermally activated neighbor transition of small polarons is suppressed. Magnetoresistance effect of LSMAO is enhanced from 21.03% to 59.71% with x increasing from 0 to 0.25, which proves that the doping of Al³⁺can effectively enhance the magnetoresistance effect of LSMAO.

The outbreak of corona virus disease 2019 (COVID-19) has aroused great attention around the world. SARS-CoV-2 possesses characteristics of faster transmission, immune escape, and occult transmission by many mutation, which caused still grim situation of prevention and control. Early detection and isolation of patients are still the most effective measures at present. So, there is an urgent need for new rapid and highly sensitive testing tools to quickly identify infected patients as soon as possible. This review briefly introduces general characteristics of SARS-CoV-2, and provides recentl overview and analysis based on different detection methods for nucleic acids, antibodies, antigens as detection target. Novel nano-biosensors for SARS-CoV-2 detection are analyzed based on optics, electricity, magnetism, and visualization. In view of the advantages of nanotechnology in improving detection sensitivity, specificity and accuracy, the research progress of new nano-biosensors is introduced in detail, including SERS-based biosensors, electrochemical biosensors, magnetic nano-biosensors and colorimetric biosensors. Functions and challenges of nano-materials in construction of new nano-biosensors are discussed, which provides ideas for the development of various coronavirus biosensing technologies for nanomaterial researchers.

The pandemic outbreak of COVID-19 has posed a threat to public health globally, and rapid and accurate identification of the viruses is crucial for controlling COVID-19. In recent years, nanomaterial-based electrochemical sensing techniques hold immense potential for molecular diagnosis with high sensitivity and specificity. In this review, we briefly introduced the structural characteristics and routine detection methods of SARS-CoV-2, then summarized the associated properties and mechanisms of the electrochemical biosensing methods. On the above basis, the research progress of electrochemical biosensors based on gold nanomaterials, oxide nanomaterials, carbon-based nanomaterials and other nanomaterials for rapid and accurate detection of virus were reviewed. Finally, the future applications of nanomaterial-based biosensors for biomolecular diagnostics were pointed out.

Ammonia leak is one of the key factors for air pollution, which may cause acute edema, respiratory failure and other diseases harmful to human health. Nowadays, the development of high-performance ammonia sensors has become one of the important means of real-time monitoring and safety warning of ammonia. In this work, three types of molybdenum disulfide with different morphologies of nanoflower, nanosphere and nanosheet were prepared by the hydrothermal method, and three types of MoS₂ ammonia sensors were constructed. The results of gas-sensing experiments showed that among these MoS₂ ammonia sensors with different morphologies, the NH₃ gas sensor made of nanoflowers MoS₂ performed the best performance with a high response value of 7.41% to 10×10^-6 NH₃, while those of the nanosheets MoS₂ and nanospheres MoS₂ sensors under the same NH₃ concentration were 2.01% and 5.11%, respectively. In addition, the nanoflowers MoS₂ sensor also exhibited excellent repeatability, stability and selectivity. The reason for the superior response performance of the nanoflower MoS₂ ammonia sensor is mainly due to the larger surface area, which could provide more active sites for the adsorption of ammonia. This study demonstrates an effective way to prepare high-performance NH₃ sensors with using MoS₂ as the substrate material.