Eighth Condensed Phase and Interfacial Molecular Science (CPIMS)

100 kHz amplifier, SE-FSRS was successfully demonstrated on Au plasmonic nanoantennas
with approximately 0.5 monolayers of trans-1,2-bis(4-pyridyl)ethylene (BPE) as the adsorbate.
(2) Single molecule tip-enhanced Raman spectroscopy (SM-TERS): A second
experimental advance is the application of the isotopologue proof for single molecule SERS
(SM-SERS) to SM-TERS. Two isotopologues of Rhodamine 6G with unique vibrational
signatures were used for this proof. A combination of experimental and theoretical studies
provides a detailed view of the isotopic response of Rhodamine 6G–d0 (R6G–d0) and Rhodamine
6G–d4 (R6G–d4) in the 600 – 800 cm -1 region. The single molecule nature of the TERS
experiment is confirmed through two lines of evidence. First, the vibrational signature of only
one isotopologue was observed from multiple spectra. Second, spectral wandering of the peak
location was observed, consistent with the observation of only a single molecule.
(3) Ultra-high vacuum tip-enhanced Raman spectroscopy (UHV-TERS) integrated with
molecular-resolution ultra-high vacuum scanning tunneling microscopy (UHV STM): The third
experimental accomplishment is the acquisition of Raman spectra consisting of multiple
vibrational modes using UHV-TERS. Using a plasmonic Ag tip and 633 nm continuous wave
(CW) laser illumination of the UHV STM tip-sample junction, eight vibrational modes were
resolved in the TER spectra for copper phthalocyanine (CuPc) adlayers on Ag (111).
Concurrently, sub-nanometer molecular resolution STM images were obtained, revealing subtle
features in the CuPc adlayer, including the orientation and boundaries between ordered
molecular domains. Furthermore, density-functional theory (DFT) calculations were carried out
that allow quantitative identification of eight different vibrational modes in the TER spectra
2.2. Molecular-Resolution Characterization and Manipulation of Surface Chemistry
This SISGR program is actively exploring UHV STM methods for characterizing and
manipulating chemical reactions at the molecular scale. For example, electron-driven and
photon-driven chemistries are being studied on the surfaces of electronic materials such as
silicon and graphene. Specific accomplishments include:
(1) Characterization and manipulation of organic molecules on epitaxial graphene:
Organic adlayers of 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA), N,N′-dioctyl-
3,4,9,10-perylenedicarboximide (PTCDI-C8), 10,12 pentacosadiynoic acid (PCA), 4-nitrophenyl
diazonium (4-NPD) tetrafluoroborate, and C60 have been assembled and characterized at the
molecular scale with UHV STM and STS on epitaxial graphene on SiC(0001). In particular,
FCL has been employed to form heteromolecular nanostructures of PTCDA and PTCDI-C8,
while graphene nanoribbons have been nanopatterned by FCL on 4-NPD functionalized surfaces.
In addition, ultraviolet photopolymerization has been characterized at the molecular scale for
one-dimensionally ordered PCA monolayers. For C60 adsorbed to epitaxial graphene, the
molecular adlayer was found to be decoupled/shielded from any significant charge transfer from
the underlying SiC(0001) surface states.
(2) Characterization and manipulation of inorganic atomic adsorbates on epitaxial
graphene: In this work, epitaxial graphene on SiC(0001) is oxidized at room temperature in
UHV using atomic oxygen. Atomic resolution characterization with STM is quantitatively
compared to density functional theory, showing that UHV oxidization results in uniform epoxy
functionalization. Furthermore, this oxidation is shown to be fully reversible at temperatures as
low as 260ºC. Similar results have also been obtained for atomic hydrogen on graphene.
(3) Preparation and characterization of chemical vapor deposition (CVD) graphene on
copper: In this work, graphene is grown via chemical vapor deposition on copper. In particular,
graphene grown on Cu foil via ex situ CVD was studied at the atomic scale. In addition, a
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