13 research outputs found
Monitoring Chemical Reactions with Terahertz Rotational Spectroscopy
Rotational spectroscopy is introduced as a new in situ method for monitoring gas-phase reactants and products during chemical reactions. Exploiting its unambiguous molecular recognition specificity and extraordinary detection sensitivity, rotational spectroscopy at terahertz frequencies was used to monitor the decomposition of carbonyl sulfide (OCS) over an aluminum nanocrystal (AlNC) plasmonic photocatalyst. The intrinsic surface oxide on AlNCs is discovered to have a large number of strongly basic sites that are effective for mediating OCS decomposition. Spectroscopic monitoring revealed two different photothermal decomposition pathways for OCS, depending on the absence or presence of H_2O. The strength of rotational spectroscopy is witnessed through its ability to detect and distinguish isotopologues of the same mass from an unlabeled OCS precursor at concentrations of <1 nanomolar or partial pressures of <10 ÎŒTorr. These attributes recommend rotational spectroscopy as a compelling alternative for monitoring gas-phase chemical reactants and products in real time
Single Particle Cathodoluminescence Spectroscopy with Sub-20 nm, Electron-Stable Phosphors
Plasmonic Copper Nanoparticles for Photocatalytic Dry Methane Reforming: Synthesis, Surface, and Performance - Poster
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Communicating Science Concepts to Individuals with Visual Impairments Using Short Learning Modules
Of the 6.7 million individuals in the United States who are visually impaired, 63% are unemployed, and 59% have not attained an education beyond a high school diploma. Providing a basic science education to children and adults with visual disabilities can be challenging because most scientific learning relies on visual demonstrations. Creating resources to help teachers and service organizations better communicate science is thus critical both to the education of sighted students as well as to the continuing education of individuals with blindness or low vision (BLV). Here, 4 new scientific learning activities that last 5â15 min each are described. These simple exercises are designed to educate the general public, including both those who are sighted and those with BLV. The modules use tactile and auditory approaches to convey basic concepts including the metric system, material strength and deformation, transparency, and the electromagnetic spectrum. These modules were tested on 20 adults with BLV during a science outreach event. Answers to learning assessment questions indicate that the modules conveyed information about the scientific concepts presented and increased an interest in science for most participants
Communicating Science Concepts to Individuals with Visual Impairments Using Short Learning Modules
Of the 6.7 million individuals in the United States who are visually impaired, 63% are unemployed, and 59% have not attained an education beyond a high school diploma. Providing a basic science education to children and adults with visual disabilities can be challenging because most scientific learning relies on visual demonstrations. Creating resources to help teachers and service organizations better communicate science is thus critical both to the education of sighted students as well as to the continuing education of individuals with blindness or low vision (BLV). Here, 4 new scientific learning activities that last 5â15 min each are described. These simple exercises are designed to educate the general public, including both those who are sighted and those with BLV. The modules use tactile and auditory approaches to convey basic concepts including the metric system, material strength and deformation, transparency, and the electromagnetic spectrum. These modules were tested on 20 adults with BLV during a science outreach event. Answers to learning assessment questions indicate that the modules conveyed information about the scientific concepts presented and increased an interest in science for most participants
Bright InfraredâtoâUltraviolet/Visible Upconversion in Small Alkaline EarthâBased Nanoparticles with Biocompatible CaF 2
Upconverting nanoparticles (UCNPs) are promising candidates for photon-driven reactions, including light-triggered drug delivery, photodynamic therapy, and photocatalysis. Herein, we investigate the NIR-to-UV/visible emission of sub-15 nm alkaline-earth rare-earth fluoride UCNPs (M(1âx)Ln(x)F(2+x) MLnF) with a CaF(2) shell. We synthesize 8 alkaline-earth host materials doped with Yb(3+) and Tm(3+), with alkaline-earth (M) spanning Ca, Sr, and Ba, MgSr, CaSr, CaBa, SrBa, and CaSrBa. We explore UCNP composition, size, and lanthanide doping-dependent emission, focusing on upconversion quantum yield (UCQY) and UV emission. UCQY values of 2.46% at 250 W cm(â2) are achieved with 14.5 nm SrLuF@CaF(2) particles, with 7.3% of total emission in the UV. In 10.9 nm SrYbF:1%Tm(3+)@CaF(2) particles, UV emission increased to 9.9% with UCQY at 1.14%. We demonstrate dye degradation under NIR illumination using SrYbF:1%Tm(3+)@CaF(2), highlighting the efficiency of these UCNPs and their ability to trigger photoprocesses
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Transition-Metal Decorated Aluminum Nanocrystals.
Recently, aluminum has been established as an earth-abundant alternative to gold and silver for plasmonic applications. Particularly, aluminum nanocrystals have shown to be promising plasmonic photocatalysts, especially when coupled with catalytic metals or oxides into "antenna-reactor" heterostructures. Here, a simple polyol synthesis is presented as a flexible route to produce aluminum nanocrystals decorated with eight varieties of size-tunable transition-metal nanoparticle islands, many of which have precedence as heterogeneous catalysts. High-resolution and three-dimensional structural analysis using scanning transmission electron microscopy and electron tomography shows that abundant nanoparticle island decoration in the catalytically relevant few-nanometer size range can be achieved, with many islands spaced closely to their neighbors. When coupled with the Al nanocrystal plasmonic antenna, these small decorating islands will experience increased light absorption and strong hot-spot generation. This combination makes transition-metal decorated aluminum nanocrystals a promising material platform to develop plasmonic photocatalysis, surface-enhanced spectroscopies, and quantum plasmonics
From tunable core-shell nanoparticles to plasmonic drawbridges: Active control of nanoparticle optical properties
The optical properties of metallic nanoparticles are highly sensitive to interparticle distance, giving rise to dramatic but frequently irreversible color changes. By electrochemical modification of individual nanoparticles and nanoparticle pairs, we induced equally dramatic, yet reversible, changes in their optical properties. We achieved plasmon tuning by oxidation-reduction chemistry of Ag-AgCl shells on the surfaces of both individual and strongly coupled Au nanoparticle pairs, resulting in extreme but reversible changes in scattering line shape. We demonstrated reversible formation of the charge transfer plasmon mode by switching between capacitive and conductive electronic coupling mechanisms. Dynamic single-particle spectroelectrochemistry also gave an insight into the reaction kinetics and evolution of the charge transfer plasmon mode in an electrochemically tunable structure. Our study represents a highly useful approach to the precise tuning of the morphology of narrow interparticle gaps and will be of value for controlling and activating a range of properties such as extreme plasmon modulation, nanoscopic plasmon switching, and subnanometer tunable gap applications
AlâPd Nanodisk Heterodimers as AntennaâReactor Photocatalysts
Photocatalysis
uses light energy to drive chemical reactions. Conventional industrial
catalysts are made of transition metal nanoparticles that interact
only weakly with light, while metals such as Au, Ag, and Al that support
surface plasmons interact strongly with light but are poor catalysts.
By combining plasmonic and catalytic metal nanoparticles, the plasmonic
âantennaâ can couple light into the catalytic âreactorâ.
This interaction induces an optical polarization in the reactor nanoparticle,
forcing a plasmonic response. When this âforced plasmonâ
decays it can generate hot carriers, converting the catalyst into
a photocatalyst. Here we show that precisely oriented, strongly coupled
AlâPd nanodisk heterodimers fabricated using nanoscale lithography
can function as directional antennaâreactor photocatalyst complexes.
The light-induced hydrogen dissociation rate on these structures is
strongly dependent upon the polarization angle of the incident light
with respect to the orientation of the antennaâreactor pair.
Their high degree of structural precision allows us to microscopically
quantify the photocatalytic activity per heterostructure, providing
precise photocatalytic quantum efficiencies. This is the first example
of precisely designed heterometallic nanostructure complexes for plasmon-enabled
photocatalysis and paves the way for high-efficiency plasmonic photocatalysts
by modular design
Heterometallic antenna-reactor complexes for photocatalysis.
Metallic nanoparticles with strong optically resonant properties behave as nanoscale optical antennas, and have recently shown extraordinary promise as light-driven catalysts. Traditionally, however, heterogeneous catalysis has relied upon weakly light-absorbing metals such as Pd, Pt, Ru, or Rh to lower the activation energy for chemical reactions. Here we show that coupling a plasmonic nanoantenna directly to catalytic nanoparticles enables the light-induced generation of hot carriers within the catalyst nanoparticles, transforming the entire complex into an efficient light-controlled reactive catalyst. In Pd-decorated Al nanocrystals, photocatalytic hydrogen desorption closely follows the antenna-induced local absorption cross-section of the Pd islands, and a supralinear power dependence strongly suggests that hot-carrier-induced desorption occurs at the Pd island surface. When acetylene is present along with hydrogen, the selectivity for photocatalytic ethylene production relative to ethane is strongly enhanced, approaching 40:1. These observations indicate that antenna-reactor complexes may greatly expand possibilities for developing designer photocatalytic substrates