In this study, an ultraviolet photodetector (UV-PD) based on TiO2/water solid-liquid heterojunction (SLHJ) is reported. The SLHJ UV-PD exhibits a high photosensitivity, excellent spectral selectivity, linear variations in photocurrent, and fast response. In addition, it is suggested that the spectral response can be tailored and that the performance can be improved through deliberate design of the active layer, electrolyte, and substrate of the SLHJ UV–PD. Moreover, we anticipate this work to be a starting point for more sophisticated commercial photon detection using an SLHJ device.

In this paper, a novel space-limited crystal growth mechanism of TiO 2 films on a Si substrate by ALD is presented. The results show that two distinct grain-growth behaviors are observed at two different growth temperature ranges. At 300-500 °C, grain growth of the films has a conventional temperature dependence with an activation energy of about 12.39 kJ/mol. However, the grain growth has an unconventional temperature dependence, as the grain size decreases with increasing growth temperature for films grown at temperatures between 150 and 250 °C. This TiO 2 growth is dominated by the surface nucleation of the films. It is suggested that this interesting phenomenon may also occur for other materials grown by ALD. In addition, the nucleating kinetics of ALD-TiO 2 films has also been investigated, and the nucleating activation energy of films is approximately 48.25 kJ/mol.

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Vanadium dioxide (VO2) is a multifunctional material with semiconductor-to-metal transition (SMT) property. Organic vanadium compounds are usually employed as ALD precursors to grow VO2 films. However, the as-deposited films are reported to have amorphous structure with no significant SMT property, therefore a postannealing process is necessary for converting the amorphous VO2 to crystalline VO2. In this study, an inorganic vanadium tetrachloride (VCl4) is used as an ALD precursor for the first time to grow VO2 films. The VO2 film is directly crystallized and grown on the substrate without any postannealing process. The VO2 film displays significant SMT behavior, which is verified by temperature-dependent Raman spectrometer and four-point-probing system. The results demonstrate that the VCl4 is suitably employed as a new ALD precursor to grow crystallized VO2 films. It can be reasonably imagined that the VCl4 can also be used to grow various directly crystallized vanadium oxides by controlling the ALD-process parameters.

The recent progress in plasmonic metasurfaces gives rise to an intense evolution of controlling light properties such as phase, amplitude, polarization, and frequency. In this work, a new paradigm is established to control the light properties centered on low‐loss toroidal multipoles with high field enhancement in contrast to most of the previous plasmonic metasurfaces that are optimized through electric and magnetic multipolar resonances. Through a proof‐of‐concept demonstration, a linear cross‐polarization conversion efficiency reaching 22.9%, remarked as the optimal value that can exist in a single‐layer plasmonic metasurface in the near‐infrared spectrum, is experimentally realized. A polarization‐insensitive toroidal response, that previously was accessible only in isotropic high‐index metasurfaces, is also observed. Furthermore, a giant anisotropic (polarization‐sensitive) generation of the second‐harmonic frequency is demonstrated with the proposed polarization‐independent toroidal metasurface that provides different levels of electric energy storage within the metasurface. These findings open a new path for keeping low‐efficiency plasmonic components on track when one engineers a metasurface based on the toroidal multipole family.