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ACS Nano. 2018 Dec 26;12(12):12733-12740. doi: 10.1021/acsnano.8b07761. Epub 2018 Dec 7.

Anomalous K-Point Phonons in Noble Metal/Graphene Heterostructure Activated by Localized Surface Plasmon Resonance.

Author information

1
Imaging Device Laboratory , Samsung Advanced Institute of Technology , Suwon , Gyeonggi-do 16419 , South Korea.
2
Center for Integrated Nanostructure Physics , Institute for Basic Science (IBS) , Suwon 16419 , Republic of Korea.
3
Department of Energy Science , Sungkyunkwan University (SKKU) , Suwon 16419 , Republic of Korea.
4
Department of Physics , Ulsan National Institute of Science and Technology (UNIST) , Ulsan 689-798 , South Korea.
5
School of Integrative Engineering , Chung-Ang University , Seoul 156-756 , South Korea.
6
Samsung Advanced Institute of Technology , Suwon , Gyeonggi-do 16419 , South Korea.

Abstract

The metal/graphene interface has been one of the most important research topics with regard to charge screening, charge transfer, contact resistance, and solar cells. Chemical bond formation of metal and graphene can be deduced from the defect induced D-band and its second-order mode, 2D band, measured by Raman spectroscopy, as a simple and nondestructive method. However, a phonon mode located at ∼1350 cm-1, which is normally known as the defect-induced D-band, is intriguing for graphene deposited with noble metals (Ag, Au, and Cu). We observe anomalous K-point phonons in nonreactive noble metal/graphene heterostructures. The intensity ratio of the midfrequency mode at ∼1350 cm-1 over G-band (∼1590 cm-1) exhibits nonlinear but resonant behavior with the excitation laser wavelength, and more importantly, the phonon frequency-laser energy dispersion is ∼10-17 cm-1 eV-1, which is much less than the conventional range. These phonon modes of graphene at nonzero phonon wave vector (q ≠ 0) around K points are activated by localized surface plasmon resonance and not by the defects due to chemical bond formation of metal/graphene. This hypothesis is supported by density functional theory (DFT) calculations for noble metals and Cr along with the measured contact resistances.

KEYWORDS:

K-point phonon; Raman; graphene; localized surface plasmon; noble metal

PMID:
30516949
DOI:
10.1021/acsnano.8b07761

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