Experimental demonstration of two-dimensional hybrid waveguide-integrated plasmonic crystals on silicon-on-insulator platform

Nanoscale plasmonic structures can offer unique functionality due to extreme sub-wavelength optical confinement, but the realization of complex plasmonic circuits is hampered by high propagation losses. Hybrid approaches can potentially overcome this limitation, but only few practical approaches based on either single or few element arrays of nanoantennas on dielectric nanowire have been experimentally demonstrated. In this paper, we demonstrate a two dimensional hybrid photonic plasmonic crystal interfaced with a standard silicon photonic platform. Off resonance, we observe low loss propagation through our structure, while on resonance we observe strong propagation suppression and intense concentration of light into a dense lattice of nanoscale hot-spots on the surface providing clear evidence of a hybrid photonic plasmonic crystal bandgap. This fully integrated approach is compatible with established silicon-on-insulator (SOI) fabrication techniques and constitutes a significant step toward harnessing plasmonic functionality within SOI photonic circuits

Wafer-scale two-dimensional semiconductors from printed oxide skin of liquid metals

© The Author(s) 2017. A variety of deposition methods for two-dimensional crystals have been demonstrated; however, their wafer-scale deposition remains a challenge. Here we introduce a technique for depositing and patterning of wafer-scale two-dimensional metal chalcogenide compounds by transforming the native interfacial metal oxide layer of low melting point metal precursors (group III and IV) in liquid form. In an oxygen-containing atmosphere, these metals establish an atomically thin oxide layer in a self-limiting reaction. The layer increases the wettability of the liquid metal placed on oxygen-terminated substrates, leaving the thin oxide layer behind. In the case of liquid gallium, the oxide skin attaches exclusively to a substrate and is then sulfurized via a relatively low temperature process. By controlling the surface chemistry of the substrate, we produce large area two-dimensional semiconducting GaS of unit cell thickness (∼1.5 nm). The presented deposition and patterning method offers great commercial potential for wafer-scale processes

Corrigendum: Wafer-scale two-dimensional semiconductors from printed oxide skin of liquid metals.

Nature Communications 8: Article number: 14482; published: 17 February 2017; Updated: 22 March 2017 The original version of this Article contained a typographical error in the spelling of the author Omid Kavehei, which was incorrectly given as Omid Kevehei. This has now been corrected in both the PDF and HTML versions of the Article.</jats:p

Laser-Induced Dewetting for Precise Local Generation of Au Nanostructures for Tunable Solar Absorption

A precise and scalable method is introduced for realizing deeply subwavelength nanostructures through laser-induced dewetting. This fabrication method is used to realize a three layer planar absorber device that allows for highly tunable selective visible–IR light absorption. This large area laser dewetting method uses a 532 nm laser with a μm ranged focal spot on a translation stage allowing for fine pattern control. A range of laser powers from 60 to 130 mW is explored and it is found that three dramatically different structures, all aperiodic and random in nature are developed. An interconnected metallic nanowire network, partially connected nanowire networks, and spherical or elliptically shaped nanoparticles are observed for low, intermediate, and high laser powers, respectively. Optical absorptance spectra demonstrate a noticeable variation in response to the structures formed. A tunable absorption in the visible range is demonstrated and the partially connected nanowires show the greatest enhancement in broadband absorption compared to the other structures. Finite element simulations uncover plasmonic and magnetic resonances as the underlying mechanisms for the absorbing behavior. This high degree of control over the dewetting area makes this technique a suitable candidate for many photonic and solar applications allowing for precise engineering of the absorbing nanostructure design

2D WS2/carbon dot hybrids with enhanced photocatalytic activity

Two-dimensional (2D) tungsten disulfide (WS2) nanoflakes were synthesised and hybridised with carbon dots (CDs) using a facile two-step method of exfoliation of bulk tungsten disulphide followed by microwave irradiation of nanoflakes in a solution of citric acid. Physicochemical characterisation indicated that the hybrid consists of graphitic carbon dots with diameters of approximately 2-5 nm, attached to monolayer tungsten disulphide via electrostatic attraction forces. This synthesised hybrid material was investigated for photocatalytic applications. We found that within one hour approximately 30% more of the model organic dye was photodegraded by the hybrid material compared with the pristine 2D WS2. This enhancement was associated to the affinity of the CDs to the organic dye rather than heterojunctioning. Comparisons of the photocatalytic efficacy of this hybrid material with those of recently reported 2D transition metal dichalcogenides and their hybrids showed a significantly higher turnover frequency. Additionally, the presented microwave based synthesis method for developing hybrids of 2D WS2 and CDs, without making significant changes to the base 2D crystal structure and its surface chemistry, has not been demonstrated before. Altogether, the hybrid 2D material provides great potential for photocatalysis applications

Enhanced quantum efficiency from a mosaic of two dimensional MoS<inf>2</inf> formed onto aminosilane functionalised substrates

© 2016 The Royal Society of Chemistry. Developing scalable methods of growing two dimensional molybdenum disulphide (2D MoS2) with strong optical properties, on any desired substrates, is a necessary step towards industrial uptake of this material for optical applications. In this study, Si/SiO2 substrates were functionalised using self-assembled monolayers of three different aminosilanes with various numbers of amine groups and molecular lengths as underlayers for enhancing the adherence of the molybdenum precursor. The tetrahedral [MoS4]2- anion groups from the molybdenum precursor were bonded on these silanised Si/SiO2 substrates afterwards. The substrates were then treated with a combined thermolysis and sulphurisation step. The results showed that silanisation of the substrates using the longest chains and the largest number of amine groups provided a good foundation to grow quasi 2D MoS2 made from adjacent flakes in a mosaic formation. Microscopy and spectroscopy investigations revealed that these quasi 2D MoS2 formed using this long chain aminosilane resulted in flakes with lateral dimensions in micron and submicron ranges composed of adjoining MoS2 pieces of 20 to 60 nm in lateral dimensions, dominantly made of 3 to 5 MoS2 fundamental layers. The obtained quasi 2D MoS2 shows a high internal quantum efficiency of 2.6% associated with the quantum confinement effect and high stoichiometry of the adjoining nanoflakes that form the structure of the sheets. The synthesis technique in this study is reliable and facile and offers a procedure to form large, scalable and patternable quasi 2D MoS2 sheets on various substrates with enhanced optical properties for practical applications

Corrigendum: Wafer-scale two-dimensional semiconductors from printed oxide skin of liquid metals (vol 8, 14482, 2017)

Nature Communications 8: Article number: 14482; published: 17 February 2017; Updated: 22 March 2017 The original version of this Article contained a typographical error in the spelling of the author Omid Kavehei, which was incorrectly given as Omid Kevehei. This has now been corrected in both the PDF and HTML versions of the Article