Experimental identification of the out-of-plane phonon mode of a few layered graphene from individual Au nanoparticle-Au film junctions

Abstract

Detection of organic vapors by graphene films functionalized with metallic nanoparticles

Nano-Physical Characterization of Chemical Vapor Deposition-Grown Monolayer Graphene for High Performance Electrode: Raman, Surface-Enhanced Raman Spectroscopy, and Electrostatic Force Microscopy Studies

“…Optical characterization of CVD-MG by upright-type Raman spectroscopy is extensively used as a conventional method to understand the degree of doping [35], number of layers [36], and the influence of mechanical strain [6,34,35,37] predominantly employing in-plane phonon vibrations. Park and colleagues readily recognized the z-directional out-of-plane phonon vibrational modes, such as the RBLM and transverse nano-scroll-type defect modes of CVD-MG at each of the Au NP/Au film junctions via the SERS signal obtained using linearly polarized HeNe laser (633 nm) irradiation [20,21,25,26]. Generally, a 633 nm laser beam is utilized as the excitation source since it closely matches the localized surface plasmon (LSP) resonance of Au NPs and the coupled resonance surface plasmon polariton (SPP) of the Au NP-Au film junction system [18][19][20][21][22][23][24][25][26].…”

“…Park and colleagues readily recognized the z-directional out-of-plane phonon vibrational modes, such as the RBLM and transverse nano-scroll-type defect modes of CVD-MG at each of the Au NP/Au film junctions via the SERS signal obtained using linearly polarized HeNe laser (633 nm) irradiation [20,21,25,26]. Generally, a 633 nm laser beam is utilized as the excitation source since it closely matches the localized surface plasmon (LSP) resonance of Au NPs and the coupled resonance surface plasmon polariton (SPP) of the Au NP-Au film junction system [18][19][20][21][22][23][24][25][26]. Based on these studies, the un-polarized SERS signals identified along the z-axis were attributed to the xy-plane axially symmetric SERS signal distribution from a z-directional dipole emitter (corresponding to the Au NP-Au film coupling orientation).…”

“…The preparation of SERS-active metal nano-structures which provide predictable, reliable and intense Raman signals is extremely complex. This problem is still being overcome by methods such as by producing self-assembled nanoparticle-molecule monolayer-film junctions, called the Nanoparticle-on-Mirror (NPoM) system [18][19][20][21][22][23][24][25][26] that generates significantly reproducible SERS signals at the single-junction level. Moreover, exploring catalytic chemical reactions probed by plasmon-driven coupling has been done by Yoon and colleagues via NPoM system [53][54][55].…”

“…This results in a 5-6 orders of magnitude variation in the SERS intensity across hot spots even within identical specimens. Owing to the reproducibility of the SERS signal intensity, a nanoparticle-on-mirror (NPoM) system composed of Au NP/CVD-MG/Au films could be employed to comparatively explore the contribution of both in-plane and out-of-plane vibration modes at individual NPoMs according to the SERS intensity ratio [18][19][20][21][22][23][24][25][26]. It is worthwhile to note the significance of previous work by Park and coworkers pertaining to utilization of the Au NP/molecule/Au Film system [17,18].…”

“…As the EM enhancement factor of the Au NP/molecule/Au film was within ~106 and exhibited a nearly uniform intensity distribution, the NPoM-SERS system was utilized in this article. Due to the dipole-dipole interaction between Au NPs and the Au film, the SERS signal revealed the presence of the radial breathing-like mode (RBLM) associated with the normal-to-surface direction (z-axis) from spaced CVD-MG in the NPoM system, which was present in the low frequency region along with three nano-scroll-type defect peaks [20,21]. The peak intensity and position of the transverse 1, 2, 3 peaks below 700 cm −1 were also useful indicators of the tilted z-directional CVD-MG protrusion.…”