Improved Thermal Stability of Graphene-Veiled Noble Metal Nanoarrays as Recyclable SERS Substrates

The ability to enhance the heat resistance of noble metals is vital to many industrial and academic applications. Because of its exceptional thermal properties, graphene was used to enhance the thermal stability of noble metals. Monolayer graphene-covered noble metal triangular nanoarrays (TNAs) showed excellent heat resistance, which could maintain their original triangular nanoarrays at high temperatures, whereas bare noble metal TNAs all agglomerate into spherical nanoparticles. On the basis of this mechanism, we obtained a universal recyclable surface-enhanced Raman scattering (SERS) substrate; after 16 cycles, the SERS substrate still worked well. The improvement of the heat resistance of noble metals by graphene has a great significance to the working reliability and service life of electronic devices and the single-use problem of traditional SERS substrates

Controllable Synthesis, Magnetic Properties, and Enhanced Photocatalytic Activity of Spindlelike Mesoporous α-Fe₂O₃/ZnO Core–Shell Heterostructures

Mesoporous spindlelike iron oxide/ZnO core–shell heterostructures are successfully fabricated by a low-cost, surfactant-free, and environmentally friendly seed-mediate strategy with the help of postannealing treatment. The material composition and stoichiometry, as well as these magnetic and optical properties, have been examined and verified by means of high-resolution transmission electron microscopy and X-ray diffraction, the thickness of ZnO layer can be simply tailored by the concentration of zinc precursor. Considering that both α-Fe₂O₃ and ZnO are good photocatalytic materials, we have investigated the photodegradation performances of the core–shell heterostructures using organic dyes Rhodamin B (RhB). It is interesting to find that the as-obtained iron oxides/ZnO core–shell heterostructures exhibited enhanced visible light or UV photocatalytic abilities, remarkably superior to the as-used α-Fe₂O₃ seeds and commercial TiO₂ products (P25), mainly owing to the synergistic effect between the narrow and wide bandgap semiconductors and effective electron–hole separation at the interfaces of iron oxides/ZnO

Ultrasensitive Au Nanooctahedron Micropinball Sensor for Mercury Ions

Mercury ion (Hg²⁺) is one of the most toxic heavy metals that has severe adverse effects on the environment and human organs even at very low concentrations. Therefore, highly sensitive and selective detection of Hg²⁺ is desirable. Here, we introduce plasmonic micropinball constructed from Au nanooctahedron as a three-dimensional surface-enhanced Raman spectroscopy (SERS) platform, enabling ultrasensitive detection of trace Hg²⁺ ions. Typically, strong SERS signals could be obtained when the single-stranded DNA structure converts to the hairpin structure in the presence of Hg²⁺ ions, due to the formation of thymine (T)–Hg²⁺–T. As a result, the detection limit of Hg²⁺ ions is as low as 1 × 10^–16 M, which is far below compared to that reported for conventional analytical strategies. Moreover, to achieve rapid multiple detection, we combine the micropinball sensors with microflow tube online detection. Our platform prevents cross-talk and tube contamination, allowing multiassay analysis, rapid identification, and quantification of different analytes and concentrations across separate phases

Template and Silica Interlayer Tailorable Synthesis of Spindle-like Multilayer α‑Fe₂O₃/Ag/SnO₂ Ternary Hybrid Architectures and Their Enhanced Photocatalytic Activity

Our study reports a novel iron oxide/noble metal/semiconductor ternary multilayer hybrid structure that was synthesized through template synthesis and layer-by-layer deposition. Three different morphologies of α-Fe₂O₃/Ag/SiO₂/SnO₂ hybrid architectures were obtained with different thicknesses of the SiO₂ interlayer which was introduced for tailoring and controlling the coupling of noble metal Ag nanoparticles (NPs) with the SnO₂ semiconductor. The resulting samples were characterized in terms of morphology, composition, and optical property by various analytical techniques. The as-obtained α-Fe₂O₃/Ag/SiO₂/SnO₂ nanocomposites exhibit enhanced visible light or UV photocatalytic abilities, remarkably superior to commercial pure SnO₂ products, bare α-Fe₂O₃ seeds, and α-Fe₂O₃/SnO₂ nanocomposites. Moreover, the sample of α-Fe₂O₃/Ag/SiO₂/SnO₂ also exhibits good chemical stability and recyclability because it has higher photocatalytic activity even after eight cycles. The origin of enhanced photocatalytic activity on the multilayer core–shell α-Fe₂O₃/Ag/SiO₂/SnO₂ nanocomposites was primarily ascribed to the coupling between noble metal Ag and the two semiconductors Fe₂O₃ and SnO₂, which are proven to be applied in recyclable photocatalysis

3D Flowerlike α‑Fe₂O₃@TiO₂ Core–Shell Nanostructures: General Synthesis and Enhanced Photocatalytic Performance

The 3D flowerlike α-Fe₂O₃@TiO₂ core–shell nanocrystals with thorhombic, cubic, and discal morphologies are synthesized for photocatalytic application. α-Fe₂O₃ nanocrystals were prepared via a Cu²⁺, Zn²⁺, and Al³⁺ ion-mediated hydrothermal route. The α-Fe₂O₃@TiO₂ core–shell nanocrystals are obtained via a hydrothermal and annealing process. The shape-dependent photocatalytic activities of these as-obtained α-Fe₂O₃@TiO₂ core–shell nanocrystals are measured. The results reveal that the discal α-Fe₂O₃@TiO₂ nanocrystals exhibit the best photocatalytic activity relative to the other two core–shell nanocrystals because the discal α-Fe₂O₃ nanocrystals possess more rough surface and surface defects. The fast interfacial charge-transfer process and the wide spectral response could be the driving force for the enhanced photocatalytic performance. These core–shell architectures provide a positive example for synthesis of novel composite nanomaterial

Rational Design of Amorphous Indium Zinc Oxide/Carbon Nanotube Hybrid Film for Unique Performance Transistors

Here we report unique performance transistors based on sol–gel processed indium zinc oxide/single-walled carbon nanotube (SWNT) composite thin films. In the composite, SWNTs provide fast tracks for carrier transport to significantly improve the apparent field effect mobility. Specifically, the composite thin film transistors with SWNT weight concentrations in the range of 0–2 wt % have been investigated with the field effect mobility reaching as high as 140 cm²/V·s at 1 wt % SWNTs while maintaining a high on/off ratio ∼10⁷. Furthermore, the introduction SWNTs into the composite thin film render excellent mechanical flexibility for flexible electronics. The dynamic loading test presents evidently superior mechanical stability with only 17% variation at a bending radius as small as 700 μm, and the repeated bending test shows only 8% normalized resistance variation after 300 cycles of folding and unfolding, demonstrating enormous improvement over the basic amorphous indium zinc oxide thin film. The results provide an important advance toward high-performance flexible electronics applications

Micro–Nanosized Nontraditional Evaporated Structures Based on Closely Packed Monolayer Binary Colloidal Crystals and Their Fine Structure Enhanced Properties

Interest in monolayer binary colloidal crystals (bCCs) has long been motivated by their wide applications. Large-area various monolayer bCC patterns are self-assembled in air–water interface and reveal that the structure of closely packed large polystyrene (PS) colloidal spheres is vital to the formation of bCCs. Small spheres may have very limited influence on the final close-packed structure of large spheres; therefore, the periodically ordered bCC patterns can be designed by choosing large colloidal spheres with the needed size. After oxygen plasma treatment, various controllable morphologies of nanoparticles can be achieved by the etched spheres acting as a template during the metal deposition. On the basis of the complex bCC patterns and subsequent oxygen plasma processing, this work points to a new method of designing the dimension and separation of nontraditional evaporated structures, including dot, strip, and block, which demonstrate fine structure enhanced performance. The experimental results are further supported by theoretical calculations

Controllable Electrical Properties of Metal-Doped In₂O₃ Nanowires for High-Performance Enhancement-Mode Transistors

In recent years, In₂O₃ nanowires (NWs) have been widely explored in many technological areas due to their excellent electrical and optical properties; however, most of these devices are based on In₂O₃ NW field-effect transistors (FETs) operating in the depletion mode, which induces relatively higher power consumption and fancier circuit integration design. Here, n-type enhancement-mode In₂O₃ NW FETs are successfully fabricated by doping different metal elements (Mg, Al, and Ga) in the NW channels. Importantly, the resulting threshold voltage can be effectively modulated through varying the metal (Mg, Ga, and Al) content in the NWs. A series of scaling effects in the mobility, transconductance, threshold voltage, and source–drain current with respect to the device channel length are also observed. Specifically, a small gate delay time (0.01 ns) and high on-current density (0.9 mA/μm) are obtained at 300 nm channel length. Furthermore, Mg-doped In₂O₃ NWs are then employed to fabricate NW parallel array FETs with a high saturation current (0.5 mA), on/off ratio (>10⁹), and field-effect mobility (110 cm²/V·s), while the subthreshold slope and threshold voltage do not show any significant changes. All of these results indicate the great potency for metal-doped In₂O₃ NWs used in the low-power, high-performance thin-film transistors

Obviously Angular, Cuboid-Shaped TiO₂ Nanowire Arrays Decorated with Ag Nanoparticle as Ultrasensitive 3D Surface-Enhanced Raman Scattering Substrates

In recent years, surface-enhanced Raman scattering (SERS) has received renewed attention, because of its nondestructive, ultrasensitive, and rapid analysis, detection, and imaging. Development of SERS substrates with high sensitivity and excellent stability is of great importance to realize its practical applications in trace analysis, bio diagnosis, and in vivo studies. In this work, we demonstrate wafer-scale Ag-nanoparticle-decorated, obviously angular, quasi-vertically aligned cuboid-shaped TiO₂ nanowire arrays (TiO₂-NWs), as ultrasensitive and uniform 3D SERS substrates. A detection limit of 10^–15 M rhodamine 6G molecules and an analytical enhancement factor of 10¹² were achieved on the cuboid-shaped TiO₂-NWs arrays with 9 min Ag-sputtering. This is the best result obtained among the literature values on Ag-modified semiconductor SERS substrates. More importantly, the optimized TiO₂-Ag also exhibits excellent stability and uniformity. The excellent SERS performance is attributed to the “cusp” and “gaps” formed on the Ag-NPs coated TiO₂ nanowire arrays, which create a huge number of SERS “hot spots”. The experimental results were further confirmed by theoretical calculations of the spatial distributions of electromagnetic field intensity. The prepared TiO₂-Ag SERS substrates with such low detection limit and high sensitivity will provide a promising candidate for practical chemical and biological detection

Tube-Like Ternary α‑Fe₂O₃@SnO₂@Cu₂O Sandwich Heterostructures: Synthesis and Enhanced Photocatalytic Properties

Heterogeneous photocatalysis is of great interest for environmental remediation applications. However, fast recombination of photogenerated electron–hole pair and a low utilization rate of sunlight hinder the commercialization of currently available semiconductor photocatalysts. In this regard, we developed a unique ternary single core-double shell heterostructure that consists of α-Fe₂O₃@SnO₂@Cu₂O. This heterostructure exhibits a tube-like morphology possessing broad spectral response for the sunlight due to the combination of narrow bandgap and wide bandgap semiconductors forming a p–n heterojunction. To fabricate such a short nanotube (SNT), we used an anion-assisted hydrothermal route for deposition of α-Fe₂O₃, a seed-mediated deposition strategy for SnO₂, and finally an aging process to deposit a Cu₂O layer to complete the tube-like ternary α-Fe₂O₃@SnO₂@Cu₂O single core-double shell heterostructures. The morphology, composition, and photocatalytic properties of those ternary core–shell–shell heterostructures were characterized by various analytical techniques. These ternary heterostructures exhibited enhanced photocatalytic properties on the photodegradation of the organic dye of Rhodamine B (RhB) under simulated sunlight irradiation. The origin of enhanced photocatalytic activity is due to the synergistic effect of broad spectral response by combining narrow bandgap and wide bandgap semiconductors and, hence, an efficient charge separation of photogenerated electron–hole pairs facilitated through the p–n heterojunction. Furthermore, our unique structure provides an insight on the fabrication and controlled preparation of multilayer heterostructural photocatalysts that have intriguing properties