Uniform Gold-Nanoparticle-Decorated {001}-Faceted Anatase TiO₂ Nanosheets for Enhanced Solar-Light Photocatalytic Reactions

The {001}-faceted anatase TiO₂ micro-/nanocrystals have been widely investigated for enhancing the photocatalysis and photoelectrochemical performance of TiO₂ nanostructures, but their practical applications still require improved energy conversion efficiency under solar-light and enhanced cycling stability. In this work, we demonstrate the controlled growth of ultrathin {001}-faceted anatase TiO₂ nanosheets on flexible carbon cloth for enhancing the cycling stability, and the solar-light photocatalytic performance of the synthesized TiO₂ nanosheets can be significantly improved by decorating with vapor-phase-deposited uniformly distributed plasmonic gold nanoparticles. The fabricated Au–TiO₂ hybrid system shows an 8-fold solar-light photocatalysis enhancement factor in photodegrading Rhodamine B, a high photocurrent density of 300 μA cm^–2 under the illumination of AM 1.5G, and 100% recyclability under a consecutive long-term cycling measurement. Combined with electromagnetic simulations and systematic control experiments, it is believed that the tandem-type separation and transition of plasmon-induced hot electrons from Au nanoparticles to the {001} facet of anatase TiO₂, and then to the neighboring {101} facet, is responsible for the enhanced solar-light photochemical performance of the hybrid system. The Au–TiO₂ nanosheet system addresses well the problems of the limited solar-light response of anatase TiO₂ and fast recombination of photogenerated electron–hole pairs, representing a promising high-performance recyclable solar-light-responding system for practical photocatalytic reactions

Hierarchical Core–Shell Structure of ZnO Nanorod@NiO/MoO₂ Composite Nanosheet Arrays for High-Performance Supercapacitors

A hierarchical core–shell structure of ZnO nanorod@NiO/MoO₂ composite nanosheet arrays on nickel foam substrate for high-performance supercapacitors was constructed by a two-step solution-based method involving two hydrothermal processes followed by a calcination treatment. Compared to one composed of pure NiO/MoO₂ composite nanosheets, the hierarchical core–shell structure electrode displays better pseudocapacitive behaviors in 2 M KOH, including high areal specific capacitance values of 1.18 F cm^–2 at 5 mA cm^–2 and 0.6 F cm^–2 at 30 mA cm^–2 as well as relatively good rate capability at high current densities. Furthermore, it also shows remarkable cycle stability, remaining at 91.7% of the initial value even after 4000 cycles at a current density of 10 mA cm^–2. The enhanced pseudocapacitive behaviors are mainly due to the unique hierarchical core–shell structure and the synergistic effect of combining ZnO nanorod arrays and NiO/MoO₂ composite nanosheets. This novel hierarchical core–shell structure shows promise for use in next-generation supercapacitors

Sensitive Surface-Enhanced Raman Scattering Detection Using On-Demand Postassembled Particle-on-Film Structure

Highly sensitive and low-cost surface-enhanced Raman scattering (SERS) substrates are essential for practical applications of SERS. In this work, we report an extremely simple but effective approach to achieve sensitive SERS detection of molecules (down to 10^–10 M) by using a particle/molecule/film sandwich configuration. Compared to conventional SERS substrates which are preprepared to absorb analyte molecules for detection, the proposed sandwich configuration is achieved by postassembling a flexible transparent gel tape embedded with plasmonic nanoparticles onto an Au film decorated with to-be-detected analyte molecules. In such a configuration, the individual plasmonic gel tape and Au film have low or no SERS activity but the final assembled sandwich structure shows strong SERS signal due to the formation of numerous hot spots at the particle–film interface, where the analyte molecules themselves serve as both spacer and signal probes. Because of its simple configuration, we demonstrate that the proposed SERS substrate can be obtained over a large area with extremely low cost. Particularly, because of the on-demand nature and the flexibility, such a postassembly strategy provides an ideal solution to detect the pesticide residue on fruit surfaces with significantly enhanced sensitivity

Rapid Focused Ion Beam Milling Based Fabrication of Plasmonic Nanoparticles and Assemblies <i>via</i> “Sketch and Peel” Strategy

Focused ion beam (FIB) milling is a versatile maskless and resistless patterning technique and has been widely used for the fabrication of inverse plasmonic structures such as nanoholes and nanoslits for various applications. However, due to its subtractive milling nature, it is an impractical method to fabricate isolated plasmonic nanoparticles and assemblies which are more commonly adopted in applications. In this work, we propose and demonstrate an approach to reliably and rapidly define plasmonic nanoparticles and their assemblies using FIB milling <i>via</i> a simple “sketch and peel” strategy. Systematic experimental investigations and mechanism studies reveal that the high reliability of this fabrication approach is enabled by a conformally formed sidewall coating due to the ion-milling-induced redeposition. Particularly, we demonstrated that this strategy is also applicable to the state-of-the-art helium ion beam milling technology, with which high-fidelity plasmonic dimers with tiny gaps could be directly and rapidly prototyped. Because the proposed approach enables rapid and reliable patterning of arbitrary plasmonic nanostructures that are not feasible to fabricate <i>via</i> conventional FIB milling process, our work provides the FIB milling technology an additional nanopatterning capability and thus could greatly increase its popularity for utilization in fundamental research and device prototyping

Modulating the Electronic Properties of Monolayer Graphene Using a Periodic Quasi-One-Dimensional Potential Generated by Hex-Reconstructed Au(001)

The structural and electronic properties of monolayer graphene synthesized on a periodically reconstructed substrate can be widely modulated by the generation of superstructure patterns, thereby producing interesting physical properties, such as magnetism and superconductivity. Herein, using a facile chemical vapor deposition method, we successfully synthesized high-quality monolayer graphene with a uniform thickness on Au foils. The hex-reconstruction of Au(001), which is characterized by striped patterns with a periodicity of 1.44 nm, promoted the formation of a quasi-one-dimensional (1D) graphene superlattice, which served as a periodic quasi-1D modulator for the graphene overlayer, as evidenced by scanning tunneling microscopy/spectroscopy. Intriguingly, two new Dirac points were generated for the quasi-1D graphene superlattice located at −1.73 ± 0.02 and 1.12 ± 0.12 eV. Briefly, this work demonstrates that the periodic modulation effect of reconstructed metal substrates can dramatically alter the electronic properties of graphene and provides insight into the modulation of these properties using 1D potentials

Observation and Manipulation of Visible Edge Plasmons in Bi₂Te₃ Nanoplates

Noble metals, like Ag and Au, are the most intensively studied plasmonic materials in the visible range. Plasmons in semiconductors, however, are usually believed to be in the infrared wavelength region due to the intrinsic low carrier concentrations. Herein, we observe the edge plasmon modes of Bi₂Te₃, a narrow-band gap semiconductor, in the visible spectral range using photoemission electron microscopy (PEEM). The Bi₂Te₃ nanoplates excited by 400 nm femtosecond laser pulses exhibit strong photoemission intensities along the edges, which follow a cos⁴ dependence on the polarization state of incident beam. Because of the phase retardation effect, plasmonic response along different edges can be selectively exited. The thickness-dependent photoemission intensities exclude the spin–orbit induced surface states as the origin of these plasmonic modes. Instead, we propose that the interband transition-induced nonequilibrium carriers might play a key role. Our results not only experimentally demonstrate the possibility of visible plasmons in semiconducting materials but also open up a new avenue for exploring the optical properties of topological insulator materials using PEEM

Contrast between Surface Plasmon Polariton-Mediated Extraordinary Optical Transmission Behavior in Epitaxial and Polycrystalline Ag Films in the Mid- and Far-Infrared Regimes

In this Letter we report a comparative study, in the infrared regime, of surface plasmon polariton (SPP) propagation in epitaxially grown Ag films and in polycrystalline Ag films, all grown on Si substrates. Plasmonic resonance features are analyzed using extraordinary optical transmission (EOT) measurements, and SPP band structures for the two dielectric/metal interfaces are investigated for both types of film. At the Si/Ag interface, EOT spectra show almost identical features for epitaxial and polycrystalline Ag films and are characterized by sharp Fano resonances. On the contrary, at the air/Ag interface, dramatic differences are observed: while the epitaxial film continues to exhibit sharp Fano resonances, the polycrystalline film shows only broad spectral features and much lower transmission intensities. In corroboration with theoretical simulations, we find that surface roughness plays a critical role in SPP propagation for this wavelength range