Au@Cu Nanoarrays with Uniform Long-Range Ordered Structure: Synthesis and SERS Applications

The nanostructures with uniform long-range ordered structure are of crucial importance for performance standardization of high-quality surface-enhanced Raman scattering (SERS) spectra. In this paper, we described the fabrication and SERS properties of Au decorated Cu (Au@Cu) nanoarrays. The Cu nanoarrays with uniform long-range ordered structure were first synthesized by in-situ electrochemistry assembly on insulated substrate. The Cu nanoarrays can reach a size of centimeters with strictly periodic nano-microstructure, which is beneficial for the production and performance standardization of SERS substrates. Then Au nanoparticals were decorated on the Cu nanoarrays by galvanic reaction without any capping agent. The obtained Au@Cu nanoarrays exhibit excellent SERS activity for 4-Mercaptopyridine, and the sensitivity limit is as low as 10⁻⁸ M. Therefore, this facile route provides a useful platform for the fabrication of SERS substrates based on nano ordered arrays.

Spectroscopically forbidden infra-red emission in Au-vertical graphene hybrid nanostructures

Implementation of Au nanoparticles (NPs) is a subject for frontier plasmonic research due to its fascinating optical properties. Herein, the present study deals with plasmonic assisted emission properties of Au NPs-vertical graphene (VG) hybrid nanostructures. The influence of effective polarizability of Au NPs on the surface enhanced Raman scattering and luminescence properties is investigated. In addition, a remarkable infra-red emission in the hybrid nanostructures is observed and interpreted on the basis of intra-band transitions in Au NPs. The flake-like nanoporous VG structure is invoked for the generation of additional confined photons to impart additional momentum and a gradient of confined excitation energy towards initiating the intra-band transitions of Au NPs. Integrating Au plasmonic materials in three-dimensional VG nanostructures enhances the light-matter interactions. The present study provides a new adaptable plasmonic assisted pathway for optoelectronic and sensing applications.

Optical coupling of gold nanoparticles on vertical graphenes to maximize SERS response

Gold particle interaction with few-layer graphenes is of interest for the development of numerous optical nanodevices. The results of numerical studies of the coupling of gold nanoparticles with few-layer vertical graphene sheets are presented. The field strengths are computed and the optimum nanoparticle configurations for the formation of surface enhanced Raman spectroscopy (SERS) hotspots are obtained. The nanoparticles are modeled as 8 nm diameter spheres atop 1.5 nm (five layers) graphene sheet. The vertical orientation is of particular interest as it is possible to use both sides of the graphene structure and potentially double the number of particles in the system. Our results show that with the addition of an opposing particle a much stronger signal can be obtained, as well as the particle the number of atomic carbon layers can control separation. These results provide further insights and contribute to the development of next-generation plasmonic devices based on nanostructures with hybrid dimensionality.

Selective decoration of Au nanoparticles on monolayer MoS2 single crystals

We report a controllable wet method for effective decoration of 2-dimensional (2D) molybdenum disulfide (MoS₂) layers with Au nanoparticles (NPs). Au NPs can be selectively formed on the edge sites or defective sites of MoS₂ layers. The Au-MoS₂ nano-composites are formed by non-covalent bond. The size distribution, morphology and density of the metal nanoparticles can be tuned by changing the defect density in MoS₂ layers. Field effect transistors were directly fabricated by placing ion gel gate dielectrics on Au-decorated MoS₂ layers without the need to transfer these MoS₂ layers to SiO₂/Si substrates for bottom gate devices. The ion gel method allows probing the intrinsic electrical properties of the as-grown and Au-decorated MoS₂ layers. This study shows that Au NPs impose remarkable p-doping effects to the MoS₂ transistors without degrading their electrical characteristics.

Plasma break-down and re-build: same functional vertical graphenes from diverse natural precursors

Plasmas, the 4(th) state of matter, uniformly transform natural precursors with different chemical composition in solid, liquid, and gas states into the same functional vertical graphenes in a single-step process within a few minutes. Functional vertical graphenes show reliable biosensing properties, strong binding with proteins, and improved adhesion to substrates.

Si-compatible cleaning process for graphene using low-density inductively coupled plasma

We report a novel cleaning technique for few-layer graphene (FLG) by using inductively coupled plasma (ICP) of Ar with an extremely low plasma density of 3.5 × 10(8) cm(-3). It is known that conventional capacitively coupled plasma (CCP) treatments destroy the planar symmetry of FLG, giving rise to the generation of defects. However, ICP treatment with extremely low plasma density is able to remove polymer resist residues from FLG within 3 min at a room temperature of 300 K while retaining the carbon sp(2)-bonding of FLG. It is found that the carrier mobility and charge neutrality point of FLG are restored to their pristine defect-free state after the ICP treatment. Considering the application of graphene to silicon-based electronic devices, such a cleaning method can replace thermal vacuum annealing, electrical current annealing, and wet-chemical treatment due to its advantages of being a low-temperature, large-area, high-throughput, and Si-compatible process.