Exploring the Interface Landscape of Noble Metals on Epitaxial Graphene

Abstract

Understanding the interaction between noble metals (NMs) and epitaxial graphene is essential for the design and fabrication of novel devices. Within this framework, a combined experimental and theoretical investigation of the effect of vapor‐deposited NM (silver [Ag] and gold [Au]) nanostructures on the vibrational and electronic properties of monolayer epitaxial graphene (MLG) on 4H‐SiC is presented. Large sets of Raman scattering data are analyzed using supervised classification and statistical methods. This analysis enables identification of the specific Raman fingerprints of Au‐ and Ag‐decorated MLG originating from different dispersion interactions and charge transfer at the metal nanostructure/MLG interface. It is found that Raman scattering spectra of Au‐decorated MLG feature a set of allowed phonon modes similar to those in pristine MLG, whereas the stronger Ag physisorption triggers an activation of defect‐related phonon modes and electron doping of MLG. A principal component analysis (PCA) and linear discriminant analysis (LDA) are leveraged to highlight the features in phonon dispersion of MLG that emanate from the NM deposition process and to robustly classify large‐scale Raman spectra of metal‐decorated graphene. The present results can be advantageous for designing highly selective sensor arrays on MLG patches decorated with different metals.

Epitaxial Graphene on 4H-SiC (0001) as a Versatile Platform for Materials Growth: Mini-Review

“…The behavior of noble metals on epitaxial graphene is a matter of considerable interest, as its deep understanding may boost the development of new sensor designs based on nano-plasmonics. Our recent findings shed light on the interplay between two selected magnetron-sputtered noble metals (silver and gold as representatives of metals with best plasmonic activity) and epitaxial graphene on 4H-SiC [43,[47][48][49]. From the theoretical point of view, both considered metals interact with epitaxial graphene through weak van der Waals forces, which is confirmed by a low adsorption energy that is below the lower limit of chemisorption and small charge transfer from metals to graphene [49].…”

“…Our recent findings shed light on the interplay between two selected magnetron-sputtered noble metals (silver and gold as representatives of metals with best plasmonic activity) and epitaxial graphene on 4H-SiC [43,[47][48][49]. From the theoretical point of view, both considered metals interact with epitaxial graphene through weak van der Waals forces, which is confirmed by a low adsorption energy that is below the lower limit of chemisorption and small charge transfer from metals to graphene [49]. Concomitantly, silver atoms interact stronger with graphene surfaces compared to gold species.…”

“…Back to the silver case, the higher adsorption energy and the less negative cohesive energy seem to be sufficient factors to ensure a high density of small, separated Ag islands. It is interesting to note that the difference in the interaction strength characteristically manifests itself in Raman spectra of epitaxial graphene (Figure 8) [49]. Particularly, the Raman spectrum of pristine epitaxial graphene remains typically intact after gold deposition (except for small displacements of the main characteristic G and 2D peaks), while silver deposition causes substantial changes in Raman activity reflected in an appearance of defect-related Raman peaks (D, D', D + D', D + G, and D **) and huge red-shift of the 2D peak.…”

Computational Appraisal of Silver Nanocluster Evolution on Epitaxial Graphene: Implications for CO Sensing

“…Due to its high conductivity, large surface area, and high signal-to-noise ratio, epitaxial graphene on SiC has recommended itself as an effective electrical transducer for the sensing of toxic heavy metals and hazardous volatile organic compounds. − The key principle behind this sensing is that the epitaxial graphene resistance changes upon exposure to liquid or gas and returns to the initial resistance after the removal of the liquid or gas. Since the CO molecule by its properties is physically adsorbed onto bare epitaxial graphene, it is unlikely to affect measurably the epitaxial graphene resistance. In contrast, the decoration of epitaxial graphene with silver nanoparticles of cluster origin enables introducing additional reactive sites, thereby enhancing the adsorption capability and CO sensing performance.…”

Silver nanoparticle array on weakly interacting epitaxial graphene substrate as catalyst for hydrogen evolution reaction under neutral conditions

“…It is most likely that only exceedingly small sub-nanometer Ag clusters (with unpaired electrons) can effectively dope the monolayer epitaxial graphene, while the formation of large islands leads to reduced Ag/ MEG interaction that limits the charge transfer from Ag to MEG. 55,56 Furthermore, additionally to an obvious nanoisland coarsening, the de-wetting process also reduces the overall Ag-MEG contact area, as shown by SEM, thereby enlarging the area of deposit-free graphene regions with intrinsic carrier density affected only by SiC-related charge transfer.…”