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The transmission of terahertz (THz) waves in vanadium dioxide (VO2) films decreases with the decrease in resistivity caused by the insulator-to-metal transition. Doping of VO2 films with Cu leads to a narrowing of the hysteresis width and a decrease in the transition temperature. However, Cu doping affects both electrical properties and THz optical properties in such a way that for films with different doping ratios it is not possible to obtain similar resistivities and similar THz transmissions simultaneously. The investigations reported here reveal both the substitutional and interstitial roles of Cu doping, with the latter, in particular, leading to Cu separation. Further analysis shows that the conditions at grain boundaries mainly influence resistivity, while crystal quality significantly affects THz optical properties. Consequently, although the variations in resistivity and optical properties show similar trends, the ranges of variation are different. This can be attributed to the fact that, according to the Drude model, the relaxation time and static conductivity depend on the conditions at grain boundaries. The results are used to explore the possibility of balancing the electrical and THz optical performances of THz devices. [ABSTRACT FROM AUTHOR]

GeSe, a black phosphorus analogue, has great potential in the applications of optoelectronic devices due to its distinct optical properties and air stability. Developing techniques that can boost the photoresponsivity of GeSe‐based photodetectors is essential to promoting their practical applications. Herein, ferroelectric PbZrxTi1−xO3 (PZT) gating is introduced as an effective method to enhance the performance of GeSe‐based transistors. Comparative study on the performance of conventional Si/SiO2‐ and PZT‐gated GeSe phototransistors demonstrates a 3.1 times increase in photoresponsivity under zero gate voltage by ferroelectric gating. Furthermore, the PZT‐gated photodetector shows a rise time of 52 ms and a maximal external quantum efficiency (EQE) of 45% across the visible and near‐infrared range. These results indicate that ferroelectric gating is a promising methodology to enhance the performance of GeSe‐based photodetectors. This work paves a new pathway toward developing high‐performance photodetectors. [ABSTRACT FROM AUTHOR]

Se doped silicon is fabricated by femtosecond-laser irradiation in the presence of Si/Se bilayer films. The enhancement in infrared absorption and carrier density is achieved by sputtering a Si thin film onto the Se film before femtosecond-laser irradiation. The effects of laser micro-structuring conditions (scanning speed and laser fluence) on surface morphology, optical and electronic properties of Se doped silicon are also studied. With the decrease of scanning speed, the absorptance increases at wavelengths from 0.4 to 2.2 µm, while the carrier density and mobility follow an opposite tendency. The optical absorption and sheet carrier density for sample fabricated at the fluence of 4.5 kJ/m 2 are greater than that of samples prepared at other fluence. This experimental method facilitates the application of hyperdoping of silicon with Se in optoelectronic devices. [ABSTRACT FROM AUTHOR]

A flower-like ZnO microstructure with an average diameter of 3 μm was successfully synthesized by assembly of nanosheets. The morphology, microstructure, and optical properties of the ZnO product was characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffractometry, UV-visible spectrophotometry, and photoluminescence spectroscopy. A possible mechanism of growth of the flower-like ZnO microstructure is tentatively proposed. Furthermore, the flower-like ZnO microstructure had very high photocatalytic activity in the decomposition of rhodamine B under ultraviolet light irradiation. [ABSTRACT FROM AUTHOR]

In this paper, the optical properties of black silicon have been studied. The black silicon samples were fabricated by alkaline etching and metal assisted etching. The micro-columns and nanopores on the silicon surface were obtained in KOH and Au-induced HF/HO solution, respectively. The height and diameter of micro-columns prepared by KOH etching is about 470 nm and 2 μm. In the Au-induced HF/HO etching, the metallic nuclei behave as a cathode and their surrounding area acts as an anode, resulting in nanopores with diameters ranging from 80 to 120 nm. These microstructures formed in the etching process directly affect the optical properties of black silicon such as reflectance, transmittance and absorptance. According to the measurement of integrating sphere detector, the absorptance of the black silicon produced by wet etching remains roughly 90% from 250 to 1,000 nm wavelength, which is almost 150% of the absorptance of conventional silicon. However, the reflectance of black silicon is less than 13% and the transmittance is less than 4%. [ABSTRACT FROM AUTHOR]

Reactive direct current magnetron sputtering and in situ thermal oxidation were used to prepare vanadium oxide (VO X ) thin films with different oxygen contents. X-ray diffraction, Fourier transform infrared spectroscopy and a field emission scanning electron microscope were employed to characterize the films. The optical properties of the VO X films at room temperature and 90 °C were investigated by applying an spectroscopic ellipsometer with a three-layer model of BEMA/Brendel–Bormann oscillator/substrate. It was demonstrated that the vanadium–oxygen bonds were strengthened, the film thickness and roughness decreased, while the grain size increased with increasing oxygen content. The increase in oxygen content had the effect of decreasing the near-infrared reflectance and free-electron concentration of the film at 90°C due to the decrease in the amount of VO2. [ABSTRACT FROM PUBLISHER]

Abstract: Amorphous thin films of titanium oxide (TiOx) have been deposited on K9 glass substrates by dc reactive magnetron sputtering from a pure titanium target at different oxygen partial pressure. The structure and composition of these films have been characterized by x-ray diffraction (XRD), and x-ray photoelectron spectroscopy (XPS), respectively. The effects of the oxygen partial pressure on the composition and optical properties of amorphous TiOx thin films have been mainly investigated. Analyses of transmittance, reflectance, optical band gap of the films demonstrate that the oxygen partial pressure during the sputtering plays a very important role in their optical properties. [Copyright &y& Elsevier]

Abstract: Nanostructured vanadium oxide (nano-VOX) thin films were prepared by direct current magnetron reactive sputtering in mixed O2/Ar discharges and subsequent annealing in oxygen atmosphere. X-ray diffraction and field emission scanning electron microscope were employed to characterize the crystal structures and morphologies, respectively. Fourier transform infrared spectroscopy was applied to analyze the vanadium–oxygen bonds of films. X-ray photoelectron spectroscopy revealed the compositions of the surface and inner portion of nano-VOX thin films. It was shown that the as-deposited films were amorphous, and in-situ annealing of these films in ambient oxygen for 10min can lead to the growth of nano-VOX thin films. Results of electrical studies indicated that the absolute values of temperature coefficient of resistance and activation energy of films increased significantly after oxygen annealing. Optical investigations carried out in the UV-visible range showed that the absorption edges of nano-VOX films exhibited large red shifts compared with as-deposited film, and that dual optical absorptions were observed in nano-VOX films. [Copyright &y& Elsevier]

Abstract: Applying reactive direct current (DC) magnetron sputtering method, nanoparticle vanadium pentoxide thin films were deposited onto glass slides and KBr substrates at different substrate temperatures. The films were characterized by X-ray photoelectron spectroscopy and atomic force microscope. Infrared spectra were recorded with a Fourier transform infrared spectrophotometer. It was found that, excepting the compositions, the film growth and vanadium oxygen bonds were strongly affected by the substrate temperature. Electrical measurements indicated that the square resistances of films showed an exponential decrease from 46 MΩ/□ to 33 kΩ/□ with substrate temperature increasing from 433 K to 593 K, and that the square resistance–temperature curves of films exhibited typical semiconducting behavior. Optical investigations were carried out in the near infrared and ultraviolet–visible range. Transmittance varied from about 95 to 55% in near-infrared range when the substrate temperature was elevated. In ultraviolet–visible range, optical band gaps and refractive indexes of films were deduced according to the transmission and reflection spectra. [ABSTRACT FROM AUTHOR]

• The long-term natural aging characteristics of the VO X films were studied in details. • Aging was found to cause a dramatic change in surface composition rather than optical properties. • An aging mechanism involving interface aging and diffusion aging was proposed. • The results provided valuable information for improving the atmospheric durability of VO X films. We experimentally investigate the long-term atmospheric durability of thermochromic vanadium oxide (VO X) films. The VO X films were deposited on glass substrates by reactive direct current magnetron sputtering and were then in-situ annealed at the preparation temperature ≤350 °C. The X-ray photoelectron spectroscopy (XPS) was applied to investigate the surface compositions of the natural aged films, while the optical properties of the films were characterized by the spectrophotometer and spectroscopic ellipsometry. The XPS results reveal that the oxygen-deficient VO X (X < 2.5) components possessing remarkable chemical changes is preferred to react with the O 2 and H 2 O in the air and become high oxidation state compounds. However, it is worth to note that the optical properties of the films shows extra-low variation performance (e.g. linear increasing rate of transmittance ~0.00448% per day @ λ = 600 nm). The aging mechanism of the VO X films in air was interpreted in terms of the interface aging and the diffusion-reaction aging on basis of the above experimental results. This study would provide valuable experience of the natural aging of VO X films. [ABSTRACT FROM AUTHOR]