Distinctly Improved Photocurrent and Stability in TiO₂ Nanotube Arrays by Ladder Band Structure

Introducing a ternary interlayer into binary heterostructures to construct a ladder band structure provides a promising way for photoelectrochemical water splitting. Here, we design and fabricate a sandwich structure on TiO₂ nanotubes using CdS_<i>x</i>Se_1–<i>x</i> as the interlayer to obtain a matching band alignment. The photoelectrochemical (PEC) properties of composite photoanodes are optimized by the order of sensitization and elements ratio, wherein the TiO₂/CdS/CdS_0.5Se_0.5/CdSe photoanode shows a significantly enhanced photocurrent of 14.78 mA cm^–2 at −0.2 V vs SCE, exhibiting a nearly 15-fold enhancement, over 1 order of magnitude. The quantum efficiency apparently increases to 40% at a range of 400–520 nm, resulting from the fact that a sensitizing layer with a matching band alignment can facilitate the separation of photogenerated electron–hole pairs and also extend the absorption range to the visible region due to its narrow bandgaps. Furthermore, its stability was distinctly improved by coating MoS₂ on the surface of the TiO₂/CdS/CdS_0.5Se_0.5/CdSe photoanode. Our findings provide a novel route toward developing a highly efficient photoelectrode for water splitting

Self-Assembling VO₂ Nanonet with High Switching Performance at Wafer-Scale

Technologically controlling nanostructures is essential to tailoring the functionalities and properties of nanomaterials. Various methods free from lithography-based techniques have been employed to fabricate 2D nanostructures; however it is still hard to achieve a well interconnected 2D regular nanostructure. Here, we demonstrate a facile chemical solution method to self-assemble a regular and interconnected VO₂ nanonet on the wafer scale. The nanonet shows a well-defined 2D truss network constructed by VO₂ nanorods with twinning relationships. The growth direction and crystallographic orientation of nanorods are synchronously controlled, leading to horizontally epitaxial growth of nanorods along three symmetric directions of the (001) single-crystal sapphire substrate. The unique nanonets enable the acquisition of excellent resistance switching properties and dramatic fatigue endurance. A large resistance change of near 5 orders with a 1.7 °C width of the hysteresis loop is characterized comparably to the properties of single crystals without detectable degradation after 500 cycles over the metal-to-insulator transition. It indicates that the nanonet can serve as an exceptional candidate for practical application in switching functional devices. Our findings offer a novel pathway for self-assembly of 2D ordered nanostructures, which would provide new opportunities for the bottom-up integration of nanodevices

Highly Efficient Microwave Absorption of Magnetic Nanospindle–Conductive Polymer Hybrids by Molecular Layer Deposition

Oxidative molecular layer deposition (oMLD) was applied to fabricate conductive polymer–magnetic material core–shell microwave absorbers in this work. One dimensional Fe₃O₄–poly­(3,4-ethylenedioxythiophene) (PEDOT) nanospindles with controllable PEDOT thickness were successfully synthesized. Their absorption performance was evaluated in the 2–18 GHz frequency range. With the advantage of oMLD, PEDOT shell thicknesses can be controlled precisely. Because the permittivity of Fe₃O₄–PEDOT nanospindles obviously increases while their permeability decreases slightly with the PEDOT cycles, the properties can be tuned effectively by only adjusting the PEDOT cycle number. With a proper PEDOT shell thickness, excellent reflection characteristics can be obtained. Remarkably high absorption strength (−55.0 dB at 16.2 GHz) and good absorption bandwidth (4.34 GHz less than −10 dB) were realized. Such excellent performance is better than that reported previously for most magnetic material-based absorbers. Considering the precise controllability and excellent absorption performance of the prepared microwave absorbers, we believe that oMLD is a facile synthetic route for microwave absorbers

Evolution of Structural and Electrical Properties of Oxygen-Deficient VO₂ under Low Temperature Heating Process

Structural stability and functional performances of vanadium dioxide (VO₂) are strongly influenced by oxygen vacancies. However, the mechanism of metal–insulator transition (MIT) influenced by defects is still under debate. Here, we study the evolution of structure and electrical property of oxygen-deficient VO₂ by a low temperature annealing process (LTP) based on a truss-structured VO₂ nanonet. The oxygenation process of the oxygen-deficient VO₂ is greatly prolonged, which enables us to probe the gradual change of properties of the oxygen-deficient VO₂. A continuous lattice reduction is observed during LTP. No recrystallization and structural collapse of the VO₂ nanonet can be found after LTP. The valence-band X-ray photoelectron spectroscopy (XPS) measurements indicate that the oxygen deficiency strongly affects the energy level of the valence band edge. Correspondingly, the resistance changes of the VO₂ films from 1 to 4.5 orders of magnitude are achieved by LTP. The effect of oxygen vacancy on the electric field driven MIT is investigated. The threshold value of voltage triggering the MIT decreases with increasing the oxygen vacancy concentration. This work demonstrates a novel and effective way to control the content of oxygen vacancies in VO₂ and the obvious impact of oxygen vacancy on MIT, facilitating further research on the role of oxygen vacancy in structure and MIT of VO₂, which is important for the deep understanding of MIT and exploiting innovative functional application of VO₂