Achieving sub-100 nm resolution over a broad visible bandwidth has long been an elusive goal in the nano-imaging of cell-surface interfaces. While metamaterial super-lenses and near-field optics have ...been previously demonstrated, these techniques can operate only at one wavelength, and do not provide accesses to the cell-surface interfaces. Here, we investigate a broadband 2D lens comprised of an oblate spheroidal dielectric cavity embedded just beneath a planar metal surface. The lens operates by adiabatically focusing asymmetric plasmon energies at sub-100 nm scale on the low-index side of the thin metal film formed between the cavity top and the planar metal surface. We then proposed the use of our lens in a high-resolution far-field confocal microscopy setup. Due to the surface-field nature of our lens, the presented system holds potential as an indispensable tool for cell-surface interfacial studies that require sub-100 nm hyper-spectral imaging analysis.
In solar energy harvesting using solar cells and photocatalysts, the photoexcitation of electrons and holes in semiconductors is the first major step in the solar energy conversion. The lifetime of ...carriers, a key factor determining the energy conversion and photocatalysis efficiency, is shortened mainly by the recombination of photoexcited carriers. We prepared and tested a series of ZnO/TiO2-based heterostructures in search of designs which can extend the carrier lifetime. Time-resolved photoluminescence tests revealed that, in ZnO/TiO2 core–shell structure the carrier lifetime is extended by over 20 times comparing with the pure ZnO nanorods. The performance improved further when Ag nanoparticles were integrated at the ZnO/TiO2 interface to construct a Z-scheme structure. We utilized these samples as photoanodes in a photoelectrochemical (PEC) cell and analyzed their solar water splitting performances. Our data showed that these modifications significantly enhanced the PEC performance. Especially, under visible light, the Z-scheme structure generated a photocurrent density 100 times higher than from the original ZnO samples. These results reveal the potential of ZnO-Ag-TiO2 nanorod arrays as a long-carrier-lifetime structure for future solar energy harvesting applications.
WxC and Pt-WxC (x=1 or 2) nano-catalysts supported on carbon black were synthesized using a simple co-impregnation and thermal reduction method. An enhanced performance in the electro-reduction of ...oxygen in an alkaline media is achieved when Pt is incorporated into the WxC catalyst. In the presence of WxC, Pt loading in carbon-supported Pt-WxC catalysts can be reduced to as low as 5% while the oxygen reduction reaction (ORR) performance of the Pt-WxC catalyst remains comparable to that of a commercially available 20% Pt/C catalyst. This indicates that the Pt-WxC composite material is more cost-efficient in ORR than the conventional Pt catalysts since WC is three orders of magnitude less expensive than Pt. WxC alone is not an excellent ORR catalyst, but its addition can greatly enhance the ORR activity of Pt where it serves as an electronic promoter by preventing Pt from oxidation and modifying Pt d-band structure via charge flow from W2C to Pt which is confirmed by XPS and UPS. It is found by XRD and TEM characterizations that WxC may play a role as a structural promoter by preventing agglomeration of Pt particles. On the other hand, Pt is found to promote the formation of WxC during the synthesis and also to stabilize the WxC during ORR. The findings on the synergistic effects of this hybrid material are important in assisting the future design of more efficient and durable ORR catalysts.
Display omitted
► Pt-WxC catalyst was synthesized via simple co-impregnation and thermal reduction. ► Enhanced ORR performance achieved due to the synergistic effects between Pt and W2C. ► Pt loading in Pt-WxC was reduced by 75% compared to commercial catalyst.
The Bernal (ABA)-stacked graphene trilayer is presumed to be thermodynamically more stable than the rhombohedral (ABC) counterpart. However, the thermal transformation from ABC to ABA domains does ...not occur at a temperature lower than 1,000 °C. Here we report that ABC-stacked trilayers are transformed to ABA-stacked layers after an organic molecule triazine is evaporated onto graphene surfaces at 150 °C. The transformation is found to always initiate at the ABA-ABC domain boundaries. Simulations based on density function theory considering the van der Waals interaction suggest that after triazine decoration the energy difference between ABA and ABC domains is larger, providing a driving force for stacking transformation. The molecular dynamics simulation results further suggest that the triazine decoration on the wrinkles at the ABC-ABA domain boundary activates the wrinkle sliding toward the ABC domains, leading to the stacking transformation from ABC to ABA.
After a brief introduction to the fundamental properties of graphene, this book focuses on synthesis, characterization and application of various types of two-dimensional (2D) nanocarbons ranging ...from single/few layer graphene to carbon nanowalls and graphene oxides. Three major synthesis techniques are covered: epitaxial growth of graphene on SiC,
In this paper, we present a new technique for determining the angle of incident light using an image sensor. This technique makes use of two distinct pixel types for simultaneous coarse angle ...estimation and fine angle detection. A new type of pixel structure, the quadrature pixel cluster is introduced, which produces response that varies linearly with incident light angle. The proposed technique greatly reduces the overall sensor complexity and is very area efficient compared with the previous work on angle detection. The sensor is fabricated in 65-nm mixed-signal CMOS process and can accurately distinguish between angles in the range from -35° to +35°.
Herein is reported a study of Co‐assisted crystallographic etching of graphite in hydrogen environment at temperatures above 750 °C. Unlike nanoparticle etching of graphite surface that leaves ...trenches, the Co could fill the hexagonal or triangular etch‐pits that progressively enlarge, before finally balling‐up, leaving well‐defined etched pits enclosed by edges oriented at 60° or 120° relative to each other. The morphology and chirality of the etched edges have been carefully studied by transmission electron microscopy and Raman analysis, the latter indicating zigzag edges. By introducing defects to the graphite using an oxygen plasma or by utilizing the edges of graphene/graphite flakes (which are considered as defects), an ability to define the position of the etched edges is demonstrated. Based on these results, graphite strips are successfully etched from the edges and graphitic ribbons are fabricated which are enclosed by purely zigzag edges. These fabricated graphitic ribbons could potentially be isolated layer‐by‐layer and transferred to a device substrate for further processing into graphene nanoribbon transistors.
Cobalt‐assisted crystallographic etching is explored to pattern graphene/graphite at predefined positions. The etching leaves well‐defined zigzag edges oriented at 60° or 120° relative to each other. The significant D‐peak contrast in the Raman map demonstrates that the quality of Co‐etched edges is much higher than edges produced by conventional lithography/plasma etching method.
Surface Enhanced Raman Spectroscopy (or SERS) has received tremendous attention in the past three decades. However, the extremely-confined probe volume (1 nm) of the plasmonic hot-spots occurring on ...a conventional roughened SERS-active metallic surface has limited value in macro-molecular studies. In this article, we show the plausibility of generating large SERS hot-spot volumes on an atomically-flat metal surface based upon a special 3D adiabatic plasmonic nano-focusing effect brought about by an array of nano-scale superlenses. We experimentally demonstrate the feasibility of this particular approach and report, for the first time, the acquisition of whole-protein SERS spectra of a layer of test protein, Cytochrome-c, using a custom-made Otto-Raman spectroscopy system equipped with nano-fluidics. Our study shows the potential of whole-protein SERS spectroscopy as a useful analytical tool that complements surface probe microscopies.
The application of plasma-enhanced chemical vapour deposition (PECVD) in the production and modification of carbon nanotubes (CNTs) will be reviewed. The challenges of PECVD methods to grow CNTs ...include low temperature synthesis, ion bombardment effects and directional growth of CNT within the plasma sheath. New strategies have been developed for low temperature synthesis of single-walled CNTs based the understanding of plasma chemistry and modelling. The modification of CNT surface properties and synthesis of CNT hybrid materials are possible with the utilization of plasma.
PDF
