7 research outputs found
Enhancing the photocurrent and photoluminescence of single crystal monolayer MoS2ďž with resonant plasmonic nanoshells
Monolayer molybdenum disulfide (MoS2) produced by controlled vapor-phase synthesis is a commercially promising new two-dimensional material for optoelectronics because of its direct bandgap and broad absorption in the visible and ultraviolet regimes. By tuning plasmonic core-shell nanoparticles to the direct bandgap of monolayer MoS2 and depositing them sparsely (<1% coverage) onto the material's surface, we observe a threefold increase in photocurrent and a doubling of photoluminescence signal for both excitonic transitions, amplifying but not altering the intrinsic spectral response
Reinventing the International Space Station Payload Integration Processes and Capabilities
The fundamental ISS payload integration philosophy, processes and capabilities were established in the context of how NASA science programs were conducted and executed in the early 1990 s. Today, with the designation of the United States (US) portion of ISS as a National Lab, the ISS payload customer base is growing to include other government agencies, private and commercial research. The fields of research are becoming more diverse expanding from the NASA centric physical, materials and human research sciences to test beds for exploration and technology demonstration, biology and biotechnology, and as an Earth and Space science platform. This new customer base has a broader more diverse set of expectations and requirements for payload design, verification, integration, test, training, and operations. One size fits all processes are not responsive to this broader customer base. To maintain an organization s effectiveness it must listen to its customers, understand their needs, learn from its mistakes, and foster an environment of continual process improvement. The ISS Payloads office is evolving to meet these new customer expectations
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 (â3.5 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 PlasmonâPhonon 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 plasmonâphonon interaction
using a quantum mechanical approach based on the FranckâCondon
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 excitationsî¸plasmons and phononsî¸in molecules
Hot Hole Photoelectrochemistry on Au@SiO<sub>2</sub>@Au Nanoparticles
There is currently
a worldwide need to develop efficient photocatalytic
materials that can reduce the high-energy cost of common industrial
chemical processes. One possible solution focuses on metallic nanoparticles
(NPs) that can act as efficient absorbers of light due to their surface
plasmon resonance. Recent work indicates that small NPs, when photoexcited,
may allow for efficient electron or hole transfer necessary for photocatalysis.
Here we investigate the mechanisms behind hot hole carrier dynamics
by studying the photodriven oxidation of citrate ions on Au@SiO<sub>2</sub>@Au coreâshell NPs. We find that charge transfer to
adsorbed molecules is most efficient at higher photon energies but
still present with lower plasmon energy. On the basis of these experimental
results, we develop a simple theoretical model for the probability
of hot carrierâadsorbate interactions across the NP surface.
These results provide a foundation for understanding charge transfer
in plasmonic photocatalytic materials, which could allow for further
design and optimization of photocatalytic processes
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