Directed Microwave‐Assisted Self‐Assembly of Au–Graphene–Au Plasmonic Dimers for SERS Applications

Abstract

photodetection [5,6] and photocatalysis. [7] While random aggregates of silver nano particles can result in very high enhance ment, thereby facilitating the detection of single molecules through Raman scat tering; [8] for technological applications, a greater control and reproducibility over the junction dimensions and therefore enhancements will be necessary. Past efforts include using dielectric spacers, made with SiO 2 [9,10] and Al 2 O 3 [11] of con trolled thickness, as well as graphene. [5,[12][13][14] The existing fabrication techniques to realize these strategies often involves multi step microfabrication processes involving expensive patterning techniques such as ebeam lithography, [15,16] nanosphere lithography, [17] nanoimprint lithography [18] or vacuum based deposition [19] techniques.Among various spacer layers, single layer graphene provides an attractive platform due to its atomic layer thickness, broadband photo responsivity and ease of integration over large areas. This was recently demonstrated by Paria et al., [5] who used a graphene monolayer as a separator between 70 nm Ag spheres. The field enhancement at the junction was calculated to be very large, and this was confirmed through Raman measurements of the graphene layer. In addition, the graphene photoresponsivity was found to be significantly enhanced, and found to be much larger than other plasmonically sensitized graphene photo detectors. [5,6,20,21] Li et al. have developed Cu NPs-graphene-Cu film system by directly depositing Cu nanoparticles on the CVD grown graphene which showed strong nearfield coupling between Cu NPs and Cu films. [22] Enhancement dependence on the laser incident angle was demonstrated and an optimum incident angle of 60° was identified for maximum enhance ment. Similarly, there have been other efforts to use graphene as separators between nanowires, [14] nanodimers, [12,23] photonic nanocrystals, and nanocavities for a multitude of applications. These graphenebased hybrids [13,18,22,24] show excellent Raman signal enhancement and hence have created a new pathway in the field of biosensing through surfaceenhanced Raman spectroscopy.In this paper, we report a new fabrication strategy involving selfassembly that exploits selective heterogenous nucleation to create graphene separated Au dimers. The most important observation is the existence of a window in the growth condi tions that yields preferential heterogeneous nucleation of a Noble metal dimers with sub-nanometer separation support strong electromagnetic field enhancement which has practical applications in surface enhanced Raman scattering (SERS), photodetection, and photocatalysis. Monolayer graphene is an excellent spacer material to practically realize uniform separation between the dimers. Here, directed microwave-assisted self-assembly of Au nanoparticle dimers is reported, separated by graphene monolayer over 1 cm 2 substrates. Detailed analytical models of Au particle formation kinetics explain the experimentally observed control of the density and sel...

Application of Novel Plasmonic Nanomaterials on SERS

“…The other is from the abundant rough structures on the nanorices and flakes surface. The contribution of surface roughness to near-field enhancement on a mesostructure has also been confirmed by previous experiments and simulations [71][72][73]. Numerical simulations were also performed to help visualize the enhancement contributions from gaps and rough surface.…”

“…where N A is Avogadro's number, and V Analyte , d Analyte , and M Analyte were the effective volume of analyte in the laser beam, the density, and molecular weights of the related analyte (Table 2), respectively. The EFs were then estimated using Equation ( 1) for the different analytes ( [70,71]. These authors linked the large EF values to multiple enhancement contributions, and that charge transfer between the g-C 3 N 4 and the metal surface protected the Ag NPs from oxidation.…”

“…Studies have reported combining semiconductor NPs (such as TiO 2 ) with plasmonically active NPs to stabilize and enhance the performance of SERS substrates [67][68][69]. Jiang et al described a hybrid Ag/gCN material with a stable high-performance SERS activity, demonstrating strong optoelectronic interactions that promote the SERS enhancement along with charge transfer effects that protect the Ag NPs from oxidation [70,71]. Here we applied pulsed laser ablation of a Cu target coated with acetonitrile (CH 3 CN) to create Cu/gCN hybrid nanomaterials that were characterized using a range of spectroscopic, diffraction, and imaging techniques, and we studied their SERS/SERRS activity for the probe analyte molecules crystal violet (CV), methylene blue (MB), and rhodamine 6G (R6G).…”

Latest Novelties on Plasmonic and Non-Plasmonic Nanomaterials for SERS Sensing

“…Ghosh et al showed that plasmonic dimers with subnanometer gap enabled to reach enhancement factor of 10 7 and a Rhodamine 6G (R6G) detection at the ppb level. These plasmonic nanostructures were realized by directed microwave-assisted self-assembly and segregated by a graphene monolayer [ 71 ].…”

Hydrophobic Paper-Based SERS Sensor Using Gold Nanoparticles Arranged on Graphene Oxide Flakes

“…To fabricate a stable metal-nanoparticle platform, graphene oxide (GO) was used as a support for the arrangement of AuNPs. Graphene and graphene-based substrates are considered a promising material for SERS sensors owing to their large surface area and excellent molecule adsorption ability, and therefore, a number of graphene-based SERS devices have been proposed [7,[18][19][20][21][22][23][24][25][26]. In addition, GO plays a crucial role as a fluorescence quencher and molecular stabilizer that render GO-metal NPs as hybrid platforms [27].…”