[en] Highlights: • Cu nanodots were decorated on TiO_2 surface through ball milling method. • Its size distribution was investigated in water and ethanolic medium. • Photocurrent response and hydrogen evolution was improved. • Performance was found to be dependent on size of Cu nanodots. - Abstract: Recently, copper species have been extensively investigated to replace Pt as efficient co-catalysts for the evolution of H_2 due to their low cost and relatively high activity. Cu nanoparticles less than 5 nm are successfully decorated on TiO_2 surface in this work by an easy and mild milling process. These Cu nanoparticles are highly dispersed on TiO_2 when the loading amount of Cu is no more than 10 wt%. The sizes of Cu nanoparticles can be controlled by changing the milling environment and decrease in the order of Cu-ethanol > Cu-water > Cu nanoparticles obtained through drying milling. The highest and stable hydrogen generation can be realized on Cu/TiO_2 with 2.0 wt% Cu and sizes of Cu nanoparticles ranging from 2 to 4 nm, in which high and stable photocurrent confirms promoted photogenerated charge separation. Smaller Cu clusters are demonstrated to be detrimental to hydrogen evolution at same Cu content. High loading of Cu nanoparticles of 2–4 nm will benefit photogenerated electron-hole recombination and thus decrease the activity of Cu/TiO_2. The results here demonstrate the key roles of Cu cluster size in addition to Cu coverage on photocatalytic activity of Cu/TiO_2 composite photocatalysts.

[en] Two dimensional (2D) nanomaterials are promising fundamental building blocks for use in the next-generation semiconductor industry due to their unique geometry and excellent (opto)-electronic properties. However, large scale high quality fabrication of 2D nanomaterials remains challenging. Thus, the development of controllable fabrication methods for 2D materials is essential for their future practical application. In this review, we will discuss the importance of the space-confined vapor deposition strategy in the controllable fabrication of 2D materials and summarize recent progress in the utilization of this strategy for the synthesis of novel materials or structures. Using this method, various high quality ultrathin 2D materials, including large-area graphene and boron nitride, ReS₂/ReSe₂, HfS₂, pyramid-structured multilayer MoS₂, and the topological insulators Bi₂Se₃ and Bi₂Te₃, have been successfully obtained. Additionally, by utilizing van der Waals epitaxy growth substrates such as mica or other 2D materials, patterned growth of 2D nanomaterials can be easily achieved via a surface-induced growth mechanism. Finally, we provide a short prospect for future development of this strategy. .

[en] 2D materials have shown great promise for next-generation high-performance photodetectors. However, the performance of photodetectors based on 2D materials is generally limited by the tradeoff between photoresponsivity and photodetectivity. Here, a novel junction field-effect transistor (JFET) photodetector consisting of a PdSe${}_2$ gate and MoS${}_2$ channel is constructed to realize high responsivity and high detectivity through effective modulation of top junction gate and back gate. The JFET exhibits high carrier mobility of 213 cm${}^2$ V${}^{-<!--\; ???\; -->1}$ s${}^{-<!--\; ???\; -->1}$. What is more, the high responsivity of 6 × 10${}^2$ A W${}^{-<!--\; ???\; -->1}$, as well as the high detectivity of 10${}^{11}$ Jones, are achieved simultaneously through the dual-gate modulation. The high performance is attributed to the modulation of the depletion region by the dual-gate, which can effectively suppress the dark current and enhance the photocurrent, thereby realizing high detectivity and responsivity. The JFET photodetector provides a new approach to realize photodetectors with high responsivity and detectivity. (© 2021 Wiley-VCH GmbH)

[en] Two-dimensional (2D) metal halide materials have recently attracted much attention due to their layered structures, direct bandgap, and high absorption coefficient, rendering them promising applications for electronics and optoelectronics. In addition, they have shown remarkable tunable magnetic properties depending on layer thickness and stacking order. In this letter, recent studies on 2D metal halides and their structural and optical properties, synthesis methods, and applications are reviewed. First, their layered crystal and electronic band structures are presented. Next, synthesis methods, such as mechanical exfoliation, liquid phase method, and vapor phase deposition, are summarized. Additionally, their device performance in field-effect transistors, photodetectors, spintronics, and 2D van der Waals heterostructures are presented. Finally, some conclusions and an outlook for future research are stated. (topical review)

[en] Platinum disulfide (PtS₂) is a newly emerging 2D material, which possesses relatively high carrier mobility, a widely tunable band gap from 0.25 to 1.6 eV, and ultra-high air stability, showing a potential in electronics and optoelectronics. Here, for the first time, we study the temperature-dependent Raman spectra on PtS₂ with different thicknesses. It was found that with the temperature increase from 80 to 298 K, the ${{\mathrm{A}}_{1\mathrm{g}}}^2$ and ${{\mathrm{E}}_{\mathrm{g}}}^1$ modes of all samples show linear softening. Moreover, the linear softening with temperature of PtS₂ is much smaller than other 2D transition metal dichalcogenides, which could be attributed to the stronger interlayer coupling in PtS₂. Our work gives fundamental temperature-dependent vibrational information of PtS₂, which will be useful in future PtS₂–based electronic devices. (paper)

[en] Two-dimensional (2D) materials with atomic thickness are promising candidates for the applications in future semiconductor devices, owing to their fascinating physical properties and superlative optoelectronic performance. Chemical vapor deposition (CVD) is considered to be an efficiënt method for large-scale preparation of 2D materials toward practical applications. However, the high melting points of metal precursors and the thermodynamics instabilities of metastable phases limit the direct CVD synthesis of plenty of 2D materials. The salt has recently been introduced into the CVD process, which proved to be effective to address these issues. In this review, we highlighted the latest progress in the salt-assisted CVD growth of 2D materials, including layered and non-layered crystals. Firstly, strategies of adding salts are summarized. Then, the salt-assisted growth of various layered materials is presented, emphasizing on the transition metal chalcogenides of stable and metastable phases. Furthermore, strategies to grow ultrathin non-layered materials are discussed. We provide viewpoints into the techniques of using salt, the effects of salt, and the growth mechanisms of 2D crystals. Finally, we offer the challenges to be overcome and further research directions of this emerging salt-assisted CVD technique.

[en] Physical vapor deposition (PVD) methods have been widely employed for high-quality crystal growth and thin-film deposition in semiconductor electronics. However, the fabrication of emerging low dimensional nanostructures is hitherto challenging in conventional PVD systems due to their large thermal mass and near-continuous operation which hinder flexible control of the nucleation and growth events. Herein, a pulsed PVD method is reported that features finely controllable temperature and heating time (down to milliseconds), which enables programming of the vapor supersaturation and decoupling of nucleation and growth events. Take tellurium as an example, the pulsed PVD allows transient source vaporization (≈1000 °C, 30 ms) for burst nucleation, followed by relatively low-temperature volatilization (≈600 °C, 5 min) for steady-state growth with well-suppressed random nucleation. As a result, uniform and high-density tellurium nanowires are obtained at the ultrathin thickness of sub-10 nm and length >10 µm, which is in sharp contrast to the randomly formed nanostructures in conventional PVD. When used in the field-effect transistor, the thin tellurium nanowires display a high on-off ratio of >10${}^4$ and hole mobility of ≈40 cm${}^2$ V${}^{-<!--\; ???\; -->1}$ s${}^{-<!--\; ???\; -->1}$, showing the potential for high-performance electronics. Pulsed PVD therefore enables to flexibly program and finely tailor the nucleation and growth events during vapor phase deposition, which are otherwise impossible in conventional PVD. (© 2022 Wiley‐VCH GmbH)

[en] As a structural analogue of the carbon nanotube (CNT), the boron nitride nanotube (BNNT) has become one of the most intriguing non-carbon nanostructures. However, up to now the pre-existing restrictions/limitations of BNNT syntheses have made the progress in their research rather modest. This work presents a new route toward the synthesis of highly pure ultrafine BNNTs based on a modified boron oxide (BO) CVD method. A new effective precursor-a mixture of Li₂O and B-has been proposed for the growth of thin, few-layer BNNTs in bulk amounts. The Li₂O utilized as the precursor plays the crucial role for the present nanotube growth. The prepared BNNTs have average external diameters of sub-10 nm and lengths of up to tens of μm. Electron energy loss spectrometry and Raman spectroscopy demonstrate the ultimate phase purity of the ultrafine BNNTs. Property studies indicate that the ultrafine nanotubes are perfect electrical insulators exhibiting superb resistance to oxidation and strong UV emission. Moreover, their reduced diameters lead to a dramatically decreased population of defects within the tube walls and result in the observation of near-band-edge (NBE) emission at room temperature.

[en] Intrinsically flexible photodetectors are compelling building blocks for next-generation wearable optoelectronic systems owing to their distinctive advantages of reliable structural durability and versatile scalability for large-scale production. However, their practical applications are still impeded by the inferior photodetection performance, irreversible device failure after breakage, and serious e-waste accumulation after service life. Herein, a high-performance intrinsically flexible, mechanically durable, self-healable, closed-loop recyclable, and screen-printable Te NWs/MoS${}_2$ nanosheets/polyimine nanocomposite-based photodetector are designed by engineering-ordered-bridged 1D/2D carrier percolation "fast lanes" in dynamic covalent polyimine matrix via a flow-designed solution-shearing method. Such a design provides a sixfold, 20.1-fold, and 6.9-fold enhancement in carrier mobility, responsivity (11.68 mA W${}^{-<!--\; ???\; -->1}$), and detectivity (1.145 × 10${}^{10}$ Jones), respectively, as well as stable photoresponse over eight months or after 50 000 bending-flattening times. Meanwhile, this photodetector presents excellent self-healing efficiency and repeatable recyclability for device reconfiguration. Furthermore, these merits can be fully integrated onto textile by assembling nacre-like Te NWs/MoS${}_2$/polyimine nanocomposite coatings on textiles via screen-printing processes, enabling programmable patterning of photodetection arrays for large-area image sensing. This work provides a viable approach for the design of shape-tunable optoelectronics with reliable mechanical durability and customizable functionalities, demonstrating the tremendous potential for large-scale applications in wearable optoelectronic systems. (© 2024 Wiley‐VCH GmbH)

[en] Nickel cobalt sulfides (Ni-Co-S) have attracted extensive attention for application in electronic devices owing to their excellent conductivity and high electrochemical capacitance. To facilitate the large-scale practical application of Ni-Co-S, the excellent rate capability and cyclic stability of these compounds must be fully exploited. Thus, hierarchical Ni-Co-S@Ni-W-O (Ni-Co-S-W) core/shell hybrid nanosheet arrays on nickel foam were designed and synthesized herein via a facile three-step hydrothermal method, followed by annealing in a tubular furnace under argon atmosphere. The hybrid structure was directly assembled as a free-standing electrode, which exhibited a high specific capacitance of 1,988 F·g⁻¹ at 2 A·g⁻¹ and retained an excellent capacitance of approximately 1,500 F·g⁻¹ at 30 A·g⁻¹, which is superior to the performance of the pristine Ni-Co-S nanosheet electrode. The assembled asymmetric supercapacitors achieved high specific capacitance (155 F·g⁻¹ at 1 A·g⁻¹), electrochemical stability, and a high energy density of 55.1 W·h·kg⁻¹ at a power density of 799.8 W·kg⁻¹ with the optimized Ni-Co-S-W core/shell nanosheets as the positive electrode, activated carbon as the negative electrode, and 6 M KOH as the electrolyte. .