Understanding Electromagnetic Interactions and Electron Transfer in Ga Nanoparticle–Graphene–Metal Substrate Sandwich Systems

Abstract

Plasmonic metal nanoparticle (NP)–graphene (G) systems are of great interest due their potential role in applications as surface-enhanced spectroscopies, enhanced photodetection, and photocatalysis. Most of these studies have been performed using noble metal NPs of silver and gold. However, recent studies have demonstrated that the noble metal–graphene interaction leads to strong distortions of the graphene sheet. In order to overcome this issue, we propose the use of Ga NPs that, due to their weak interaction with graphene, do not produce any deformation of the graphene layers. Here, we analyze systems consisting of Ga NP/G/metal sandwich coupling structures, with the metal substrate being, specifically, copper (Cu) and nickel (Ni), i.e., Ga NP/G/Cu and Ga NPs/G/Ni. We experimentally show through real-time plasmonic spectroscopic ellipsometry and Raman spectroscopy measurements of the quenching of the Ga NP localized surface plasmon resonance (LSPR) depending on the wetting of the graphene by the Ga NPs and on the electron transfer through graphene. Theoretical finite-difference time-domain (FDTD) simulations supportively demonstrate that the LSPR in such sandwich structures strongly depends on the contact angle of the NP with graphene. Finally, we also provide evidence of the electron transfer from the Ga NPs into the graphene and into the metal substrate according to the work function alignments. These considerations about the contact angle and, consequently, geometry and wetting of the metal NPs on graphene, are useful to guide the design of those plasmonic systems to maximize electromagnetic enhancement.

Investigation of the Importance of the Electronic Enhancement Mechanism for Surface-Enhanced Raman Scattering (SERS)

“…While most of the work related to SERS is focusing on the more practical aspect of reaching as high as possible enhancement ratios, a better fundamental understanding of the processes remains to be achieved. Although the interplay of different mechanisms is difficult to be explained using simple theories, mostly due to the considerable diversity of the results obtained by different research groups, both experimentalists and theorists are converging to an agreement that the enhancement mainly arises from two contributions, the electromagnetic (EME) and electronic or chemical (CE) enhancement mechanisms. − It has been confirmed that surface plasmon polaritons (SPPs) play a crucial role by drastically increasing the intensity of the local electromagnetic field of the exciting laser light as well as the inelastically scattered Raman signal for the EME to be observed. In addition to the EME, which due to its nature should be independent of the molecules under investigation, there is clear evidence that there is a second enhancement mechanism, which works independently and contributes to a signal enhancement in parallel to the EME.…”

A Review on the Development of Tunable Graphene Nanoantennas for Terahertz Optoelectronic and Plasmonic Applications

“…In addition, the surface conductivity matrix of magnetized graphene is applied for the infinitesimally thin graphene sheet. The localized surface plasmon resonance in the graphene-based sandwich structure is demonstrated using the FDTD simulation and provides the strong interaction of graphene with metals having higher EM wave confinement [89].…”

Nitrides as Alternative Materials for Plasmonics

“…Nitrides are used as alternative materials as these are refractory materials, have high electron conductivity, mobility, high melting points and also CMOS compatibility. These properties make nitrides as good candidates in optical sensors, heat-assisted recording magnetic (HAMR) [8][9][10][11][12]. As both the imaginary part (loss) and the real part of the permittivity are critical factors to consider when developing alternative plasmonic materials, It is shown by comparing permittivities of Au, Ag, TiN and ZrN that nitrides are best plasmonics in infrared region.…”