This work is devoted to the study of plasmon-enhanced
Raman scattering
by the fundamental vibrational modes of multilayered graphene films.
The film thickness was ∼3.5 nm, which corresponds to ∼10
monolayers. Multilayered graphene films were placed on a plasmonic
substrate consisting of arrays of gold nanodisks (50–250 nm
in diameter). Surface-enhanced Raman scattering by the main vibrational
modes of multilayered graphene film placed on an array of Au nanodisks
of various sizes was implemented. The measurements were performed
at excitation wavelengths of 532, 638, and 785 nm. A resonant SERS
enhancement of the main vibrational modes of multilayered graphene
by a factor of 25 was achieved for nanodisks with a diameter of 103
nm upon excitation at 638 nm. A stronger local enhancement of Raman
scattering in multilayered graphene (by a factor of 50) placed on
Au nanodisk array is achieved using gap-mode tip-enhanced Raman scattering
(gap-mode TERS). Nanofolds in the graphene film appeared due to the
corrugated surface of the plasmonic substrate were visualized with
nanometer spatial resolution. It is shown that the frequency positions
of G and 2D modes of nanofolds decrease with respect to the corresponding
values in flat multilayered graphene manifesting mechanical stresses
in the nanofolds up to 0.7%. The results obtained shed light on the
effects of the interaction of multilayered graphene with metal nanostructures
and are important in creating hybrid metal/graphene plasmonic substrates.
In this work, approaches for fabrication metal coated probes for Tip Enhanced Raman Spectroscopy (TERS) are considered. It was proposed to use optical characterization of probes to achieve the effective TERS of semiconductor nanoobjects. The shape and size of the metal cluster at the tip apex determines the position of the localized surface plasmon resonance, the electromagnetic field enhancement and, thus, TERS performance. The possibility of optimizing the characteristics of the probes for TERS studies of nanoobjects has been investigated.
In
this work, the phonon spectra of core/shell CdSe/CdS nanoplatelets
with different shell thicknesses were studied using IR and Raman spectroscopies.
Nanoplatelets are rectangular plates, with lateral dimensions of tens
of nanometers and thicknesses of core and shell layers of a few nanometers.
Longitudinal optical (LO) and surface optical (SO) phonon modes in
the CdSe core and the CdS shell dominate in the Raman spectra at frequencies
of approximately 200–210 and 250–300 cm–1, respectively, while transverse optical (TO) modes in the nanoplatelets
(NPLs) are active in the IR reflection/absorption spectra near 170
and 240 cm–1. The LO modes can be additionally activated
in the IR spectra measured at an oblique angle of light incidence
that provides a component of the electric field perpendicular to the
surface. As the shell thickness increases, the phonon modes reveal
frequency shifts of optical modes, which are explained in terms of
the stress state in the core and shell, as well as the influence of
phonon confinement. Low-frequency peaks of bare CdSe and core–shell
CdSe/CdS platelets were observed in the Raman spectra, and their frequencies
were compared with both literature data and the results of calculations
within a two-phase model.
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