4 research outputs found
Multicolor Electrochromic Devices Based on Molecular Plasmonics
Polycyclic aromatic
hydrocarbon (PAH) molecules, the hydrogen-terminated,
sub-nanometer-scale version of graphene, support plasmon resonances
with the addition or removal of a single electron. Typically colorless
when neutral, they are transformed into vivid optical absorbers in
either their positively or negatively charged states. Here, we demonstrate
a low-voltage, multistate electrochromic device based on PAH plasmon
resonances that can be reversibly switched between nearly colorless
(0 V), olive (+4 V), and royal blue (−3.5 V). The device exhibits
highly efficient color change compared to electrochromic polymers
and metal oxides, lower power consumption than liquid crystals, and
is shown to reversibly switch for at least 100 cycles. We also demonstrate
the additive property of molecular plasmon resonances in a single-layer
device to display a reversible, transmissive-to-black device. This
work illuminates the potential of PAH molecular plasmonics for the
development of color displays and large-area color-changing applications
due to their processability and ultralow power consumption
Molecular Plasmon–Phonon Coupling
Charged
polycyclic aromatic hydrocarbons (PAHs), ultrasmall analogs of hydrogen-terminated
graphene consisting of only a few fused aromatic carbon rings, have
been shown to possess molecular plasmon resonances in the visible
region of the spectrum. Unlike larger nanostructures, the PAH absorption
spectra reveal rich, highly structured spectral features due to the
coupling of the molecular plasmons with the vibrations of the molecule.
Here, we examine this molecular plasmon–phonon interaction
using a quantum mechanical approach based on the Franck–Condon
approximation. We show that an independent boson model can be used
to describe the complex features of the PAH absorption spectra, yielding
an analytical and semiquantitative description of their spectral features.
This investigation provides an initial insight into the coupling of
fundamental excitationsplasmons and phononsin molecules
Molecular Plasmonics
Graphene supports surface plasmons
that have been observed to be both electrically and geometrically
tunable in the mid- to far-infrared spectral regions. In particular,
it has been demonstrated that graphene plasmons can be tuned across
a wide spectral range spanning from the mid-infrared to the terahertz.
The identification of a general class of plasmonic excitations in
systems containing only a few dozen atoms permits us to extend this
versatility into the visible and ultraviolet. As appealing as this
extension might be for active nanoscale manipulation of visible light,
its realization constitutes a formidable technical challenge. We experimentally
demonstrate the existence of molecular plasmon resonances in the visible
for ionized polycyclic aromatic hydrocarbons (PAHs), which we reversibly
switch by adding, then removing, a single electron from the molecule.
The charged PAHs display intense absorption in the visible regime
with electrical and geometrical tunability analogous to the plasmonic
resonances of much larger nanographene systems. Finally, we also use
the switchable molecular plasmon in anthracene to demonstrate a proof-of-concept
low-voltage electrochromic device
Revealing the Size Effect of Ceria Nanocube-Supported Platinum Nanoparticles in Complete Propane Oxidation
The
elimination of propane is one of the key tasks in
reducing
volatile organic compounds (VOCs) and automotive exhaust emissions.
The platinum nanoparticle (NP) is a promising catalyst for propane
oxidation, while the study of its structural characteristics and functionality
remains in its infancy. In this work, we synthesized the nanocubes
CeO2 with a well-defined (100) facet supporting Pt NPs
with various sizes, from 1.3 to 7 nm, and systematically investigated
the effect of the Pt size on complete propane oxidation efficiency.
In particular, CeO2(100) supported Pt NPs smaller than
4 nm promote the formation of positively charged Pt sites, which hinder
the adsorption and activation of propane and reduce the intrinsic
activity for propane oxidation. Consequently, within this size range,
the catalytic performance is primarily influenced by the electronic
state of the Pt species, with metallic Pt being identified as the
active site for the reaction. Conversely, as the particle size exceeds
4 nm, metallic Pt particles become dominant and the geometric structure
starts to influence the activity as well. Such entanglement of electronic
and geometric factors gives rise to a volcano relationship between
reaction rates and Pt particle sizes ranging from 1.3 to 7 nm, while
an increased correlation can be observed between the turnover frequencies
and the particle sizes in this range. This knowledge can guide the
synthesis of highly active catalysts, enabling the efficient oxidation
of VOCs with reduced precious metal loadings