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We demonstrate room temperature coherent hybridization of the A- and B-excitons in few-layer MoS2, mediated by simultaneous strong coupling to surface plasmon polaritons. Few-layer MoS2 was placed ...

This work studies photogenerated carrier dynamics in gold nanoparticle (AuNP)-decorated mono- to few-layer transition metal dichalcogenide (TMD) nanosheets using transient absorption spectroscopy (...

The electronic structure of few-layer MoS2 is studied by in situ and operando spectroelectrochemistry in conditions relevant to its use as an electrocatalyst. We show that electron injection into the conduction band is coupled with a redshift of the exciton resonance, the magnitude of which depends on the number of vertical MoS2 layers. In addition, the applied electric field/electronic doping imparts uniaxial tensile strain evidenced by broadening Raman signals, indicating that under conditions of electrocatalysis, the system is structurally different from equilibrium. We demonstrate that field/carrier induced changes to the electronic structure of MoS2 alter the band edge positions which changes the fundamental thermodynamic driving force for charge transfer. This property is a function of the applied potential, an effect unique to 2D semiconductors. The dynamic band edge potentials change the relevant interfacial energetics for charge transfer and have strong implications for the mechanistic understanding of (photo)catalytic fuel-forming reactions using two-dimensional systems.

By understanding how the environmental composition impacts the optoelectronic properties of transition metal dichalcogenide monolayers, we demonstrate that simple photoluminescence (PL) measurements of tungsten disulfide (WS2) monolayers can differentiate relative humidity environments. In this paper, we examine the PL and photoconductivity of chemical vapor deposition grown WS2 monolayers under three carefully controlled environments: inert gas (N2), dry air (O2 in N2), and humid nitrogen (H2O vapor in N2). The WS2 PL is measured as a function of 532 nm laser power and exposure time and can be decomposed into the exciton, trion, and lower energy state(s) contributions. Under continuous illumination in either O2 or H2O vapor environment, we find dramatic (and reversible) increases in PL intensity relative to the PL in an inert environment. The PL bathochromically shifts in an O2 environment and is dominated by increased trion emission and diminished exciton emission. In contrast, the WS2 PL increase in a H2O environment results from an overall increase in emission from all spectral components where the exciton contribution dominates. The drastic increases in PL are anticorrelated with corresponding decreases in photoconductivity, as measured by time-resolved microwave conductivity. The results suggest that both O2 and H2O react photochemically with the WS2 monolayer surface, modifying the optoelectronic properties, but do so via distinct pathways. Thus, we use these optoelectronic differences to differentiate the amount of humidity in the air, which we show with 0%, 40%, and 80% relative humidity environments. This deeper understanding of how ambient conditions impact WS2 monolayers enables novel humidity sensors as well as a better understanding of the correlation between TMDC surface chemistry, light emission, and photoconductivity. Moreover, these WS2 measurements highlight the importance of considering the impact of the local environment on reported results.

Two-dimensional tungsten disulfide (WS2) is an emerging semiconducting photocatalyst featuring high optical absorption, carrier mobility, and catalytic activity toward hydrogen evolution. While characterization of its optical and electrocatalytic properties has advanced, less is known about its ultrafast carrier dynamics and intrinsic photocatalytic activity in aqueous systems producing hydrogen. This work removed extraneous variables often found in photoelectrochemical systems, thereby allowing the intrinsic proton reduction rate for monolayer-rich WS2 nanosheets to be estimated via transient absorption lifetimes and a developed kinetic scheme. Addition of a hole scavenger, ascorbic acid (AA), resulted in a 3-fold increase in carrier lifetimes following photoexcitation. Longer electron lifetimes with AA yielded a 14-fold increase in hydrogen production. An intrinsic proton reduction rate constant was extracted that may be extended to any photoelectrochemical or electrochemical hydrogen evolution scheme i...

Layered transition metal dichalcogenides (TMDs) represent a diverse, emerging source of two-dimensional (2D) nanostructures with broad application in optoelectronics and energy. Chemical functionalization has evolved into a powerful tool to tailor properties of these 2D TMDs; however, functionalization strategies have been largely limited to the metallic 1T-polytype. The work herein illustrates that 2H-semiconducting liquid-exfoliated tungsten disulfide (WS2) undergoes a spontaneous redox reaction with gold (III) chloride (AuCl3). Au nanoparticles (NPs) predominantly nucleate at nanosheet edges with tuneable NP size and density. AuCl3 is preferentially reduced on multi-layer WS2 and resulting large Au aggregates are easily separated from the colloidal dispersion by simple centrifugation. This process may be exploited to enrich the dispersions in laterally large, monolayer nanosheets. It is proposed that thiol groups at edges and defects sides reduce the AuCl3 to Au0 and are in turn oxidized to disulfides. Optical emission, i.e. photoluminescence, of the monolayers remained pristine, while the electrocatalytic activity towards the hydrogen evolution reaction is significantly improved. Taken together, these improvements in functionalization, fabrication, and catalytic activity represent an important advance in the study of these emerging 2D nanostructures.

Photoinduced generation of mobile charge carriers is the fundamental process underlying many applications, such as solar energy harvesting, solar fuel production, and efficient photodetectors. Monolayer transition-metal dichalcogenides (TMDCs) are an attractive model system for studying photoinduced carrier generation mechanisms in low-dimensional materials because they possess strong direct band gap absorption, large exciton binding energies, and are only a few atoms thick. While a number of studies have observed charge generation in neat TMDCs for photoexcitation at, above, or even below the optical band gap, the role of nonlinear processes (resulting from high photon fluences), defect states, excess charges, and layer interactions remains unclear. In this study, we introduce steady-state microwave conductivity (SSMC) spectroscopy for measuring charge generation action spectra in a model WS

Thermal dissipation of plasmon energy from gold nanoparticles (AuNPs) dispersed in transparent polymers is important to biotherapeutics, optoelectronics, sensing, and chemical separations. This work assessed heat dissipated from power extinguished by 16 nm AuNPs with negligible Rayleigh scattering cross-sections dispersed into subwavelength, 70 nm polyvinylpyrrolidone (PVP) films at interparticle separations much less than the resonant wavelength. In contrast to super-wavelength films with particles at separations near the resonant wavelength, measured optical extinction and temperature increase per NP (°C per NP) decreased as AuNP concentration increased: °C per NP decreased 22% and optical extinction per NP decreased 35% as AuNP concentration increased from 1.01 to 5.06 × 1015 NP per cm3. The trend and magnitude of measured values were consistent with those from a priori description of optical extinction per NP from Maxwell Garnett effective medium theory (EMT) and from coupled dipole approximation (CDA). Optical power extinguished by the films exhibited a trend and magnitude consistent with finite element analysis (FEA) of thermal dissipation from subwavelength films at particle separations of 130 to 76 nm. Comparing measured values with results from EMT, CDA, and FEA distinguished contributions to plasmon-resonant optical extinction and heat dissipation. These results support design and adaptive control of thermal dissipation from plasmonic films.

Polymer films containing plasmonic nanostructures are of increasing interest for development of responsive energy, sensing, and therapeutic systems. The present work evaluates heat dissipated from power absorbed by resonant gold (Au) nanoparticles (NP) with negligible Rayleigh scattering cross sections randomly dispersed in polydimethylsiloxane (PDMS) films. Finite element analysis (FEA) of heat transport was coordinated with characterization of resonant absorption by Mie theory and coupled dipole approximation (CDA). At AuNP particle separation greater than resonant wavelength, correspondence was observed between measured and CDA-predicted optical absorption and FEA-derived power dissipation. At AuNP particle separation less than resonant wavelength, measured extinction increased relative to predicted values, while FEA-derived power dissipation remained comparable to CDA-predicted power absorption before lagging observed extinguished power at higher AuNP content and resulting particle separation. Effects of isolated particles, for example, scattering, and particle-particle interactions, for example, multiple scattering, aggregation on observed optothermal activity were evaluated. These complementary approaches to distinguish contributions to resonant heat dissipation from isolated particle absorption and interparticle interactions support design and adaptive control of thermoplasmonic materials for a variety of implementations.

Layered transition metal dichalcogenides (TMDs) represent a diverse, emerging source of two-dimensional (2D) nanostructures with broad application in optoelectronics and energy. In particular, tungsten disulfide (WS2) is an efficient visible light absorber with relatively high carrier mobilities and catalytic activity towards hydrogen evolution. While explanation of the quantum confinement and excitonic effects governing TMD optoelectronic properties has progressed in recent years, less is known about the ultra-fast photoresponse and carrier dynamics following light excitation. This work utilizes transient absorption spectroscopy, with pump tunability and broadband visible probing, to monitor the carrier dynamics of both CVD-grown monolayer and solution exfoliated WS2. Picosecond-scale features include simultaneous bleaching of excitonic states and a red-shifted absorption spectrum attributed to bandgap renormalization, while free carriers, defect trapped carriers, and recombination signatures are apparent at increasing pico- to nanosecond lifetimes. Features associated with excitons, trions, and photo-excited carriers exhibit strong dependence on local environmental factors. Moisture, oxygen, chemical dopants, and dielectric environment strongly affect the strength and decay lifetimes of these photo-excited species. These results highlight the importance of understanding and controlling these local environmental factors to the rational design and implementation of 2D TMDs optoelectronic device platforms.

Surface plasmon resonant nanoantennas can confine incident energy onto two-dimensional (2D) transition metal dichalcogenides (TMD) to enhance efficiency of harmonic conversion to higher energies, which is otherwise limited by the intrinsic A-scale interaction length. Second harmonic generation (SHG) from nanoantenna-decorated 2D TMD was heuristically examined with hyper Rayleigh scattering (HRS), multi-photon microscopy, electron energy loss spectroscopy (EELS), and discrete dipole computation. HRS experimentally quantified the frequency dependence of the second-order nonlinear susceptibility, χ (2) , for liquid-exfoliated WS2. Measured χ(2) fell within 21% of independent density functional theory (DFT) calculations, overcoming the known 100-1000x overestimation of microscopy approaches. EELS supported design of nanoantennas for integration with TMD. Overall SHG conversion efficiencies from chemical vapor-deposited (CVD) 4×105 nm2 MoS2 crystals on silicon dioxide were enhanced up to 0.025 % W-1 in the presence of by single 150 nm Au nanoshell monomers and dimers, ostensibly due to augmented local plasmonic fields.

Embedding soft matter with nanoparticles (NPs) can provide electromagnetic tunability at sub-micron scales for a growing number of applications in healthcare, sustainable energy, and chemical processing. However, the use of NP-embedded soft material in temperature-sensitive applications has been constrained by difficulties in validating the prediction of rates for energy dissipation from thermally insulating to conducting behavior. This work improved the embedment of monodisperse NPs to stably decrease the inter-NP spacings in polydimethylsiloxane (PDMS) to nano-scale distances. Lumped-parameter and finite element analyses were refined to apportion the effects of the structure and composition of the NP-embedded soft polymer on the rates for conductive, convective, and radiative heat dissipation. These advances allowed for the rational selection of PDMS size and NP composition to optimize measured rates of internal (conductive) and external (convective and radiative) heat dissipation. Stably reducing the distance between monodisperse NPs to nano-scale intervals increased the overall heat dissipation rate by up to 29%. Refined fabrication of NP-embedded polymer enabled the tunability of the dynamic thermal response (the ratio of internal to external dissipation rate) by a factor of 3.1 to achieve a value of 0.091, the largest reported to date. Heat dissipation rates simulated a priori were consistent with 130 μm resolution thermal images across 2- to 15-fold changes in the geometry and composition of NP-PDMS. The Nusselt number was observed to increase with the fourth root of the Rayleigh number across thermally insulative and conductive regimes, further validating the approach. These developments support the model-informed design of soft media embedded with nano-scale-spaced NPs to optimize the heat dissipation rates for evolving temperature-sensitive diagnostic and therapeutic modalities, as well as emerging uses in flexible bioelectronics, cell and tissue culture, and solar-thermal heating.

Thermal response rates of plasmonic nanocomposite materials limit their capacity for adaptive control and scalable implementation. This work examines thermal dynamics in insulating and conductive dielectrics containing two- and three-dimensional disordered distributions of plasmonic gold nanoparticles (AuNP). It is shown that a balance of micro- and macroscale internal and external dissipation rates can model overall thermal dynamics and dissipation rates measured for widely varying composite materials to within a few percent using independent geometric and thermodynamic parameters. The independent estimates are within 2.6% of values measured for isolated colloid AuNP suspensions, between 0.15 to 13.4% for randomly sized AuNP embedded in polymer films, and within 5.4 to 30.0% for AuNP deposited on conductive ceramics. Estimated thermal dynamics for AuNP embedded in thin polymer film are higher than AuNP in fluid or on ceramic substrates. This modeling approach could guide design and deployment of thermall...

Chemical functionalization of low-dimensional nanostructures has evolved as powerful tool to tailor the materials’ properties on demand. For two-dimensional transition metal dichalcogenides, functionalization strategies are mostly limited to the metallic 1T-polytype with only few examples showing a successful derivatization of the semiconducting 2H-polytype. Here, we describe that liquid-exfoliated WS2 undergoes a spontaneous redox reaction with AuCl3. We propose that thiol groups at edges and defects sites reduce the AuCl3 to Au0 and are in turn oxidized to disulfides. As a result of the reaction, Au nanoparticles nucleate predominantly at edges with tuneable nanoparticle size and density. The drastic changes in nanosheet mass obtained after high loading with Au nanoparticles can be exploited to enrich the dispersions in laterally large, monolayered nanosheets by simple centrifugation. The optical properties (for example photoluminescence) of the monolayers remain pristine, while the electrocatalytic activity towards the hydrogen evolution reaction is significantly improved. Defect engineering of WS2 nanosheets via redox chemistry in liquid phase yields enhanced catalytic activity and monolayer enrichment. A team led by Claudia Backes at Ruprecht-Karls University demonstrated that liquid-phase exfoliated WS2 undergoes a spontaneous redox reaction with AuCl3, whereby thiol groups occurring at edges and defect sites reduce the AuCl3 to Au0. The reaction causes Au nanoparticles to nucleate at WS2 edges, and in turn such Au nanoparticle loading determines a substantial change in the nanosheet mass. As the Au decoration preferentially occurs at the edges of incompletely exfoliated WS2 flakes, the dispersions can be further enriched with monolayers by means of centrifugation. While the optical properties of Au-decorated WS2 sheets remain unaltered, their electrocatalytic activity is highly enhanced, showing promise for applications in hydrogen evolution reactions.

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Optical properties and thermal relaxation dynamics of resonantly excited plasmons are important in applications for optoelectronics, biomedicine, energy, and catalysis. Geometric optics of polydimethylsiloxane (PDMS) thin films containing uniformly or asymmetrically distributed polydisperse reduced AuNPs or uniformly distributed monodisperse solution-synthesized AuNPs were recently evaluated using a compact linear algebraic sum. Algebraic calculation of geometric transmission, reflection, and attenuation for AuNP-PDMS films provides a simple, workable alternative to effective medium approximations, computationally expensive methods, and fitting of experimental data. This approach allows for the summative optical responses of a sequence of 2D elements comprising a 3D assembly to be analyzed. Thin PDMS films containing 3-7 micron layers of reduced AuNPs were fabricated with a novel diffusive-reduction synthesis technique. Rapid diffusive reduction of AuNPs into asymmetric PDMS thin films provided superior photothermal response relative to thicker films with AuNPs reduced throughout, with a photon-to-heat conversion of up to 3000°C/watt which represents 3-230-fold increase over previous AuNP-functionalized systems. Later work showed that introduction of AuNPs into PDMS enhanced thermoplasmonic dissipation coincident with internal reflection of incident resonant irradiation. Measured thermal emission and dynamics of AuNP-PDMS thin films exceeded emission and dynamics attributable by finite element analysis to Mie absorption, Fourier heat conduction, Rayleigh convection, and Stefan-Boltzmann radiation. Refractive-index matching experiments and measured temperature profiles indicated AuNP-containing thin films internally reflected light and dissipated power transverse to the film surface. Enhanced thermoplasmonic dissipation from metal-polymer nanocomposite thin films could affect opto- and bio-electronic implementation of these systems.

An optical phenomena based on the incident light absorption and transduction to the detectable thermal signal by plasmonic bimetallic Ag and Au nanocages (Ag@AuNCs) has been researched on free standing layer-by-layer (LbL) films of poly(vinyl alcohol) (PVA) and poly(vinyl pyrrolidone) (PVPON), (PVA/PVPON_Ag@AuNCs). Unlike well-studied monometallic Au nanocages (NCs), which possess a photothermal response in the near-infrared region, the bimetallic nanocages show a pronounced photothermal response in the visible range (532 nm) and near-infrared range (780 nm) due to the presence of two characteristic peaks at both wavelength ranges. The photothermal response in the visible range (532 nm) is distinguishable. Specifically increasing the laser power to 100 mW led to visual burning of the free standing film (temperature increased greater than >150 °C). The photothermal response by (PVA/PVPON_Ag@AuNCs)n films increases in proportion to the number (n) of bilayers (bl). It also increases as the molar concentration of the Ag@AuNCs introduced to the PVPON layer is increased. Therefore the molar concentration of the plasmonic Ag@AuNCs in (PVA/PVPON_Ag@AuNCs)n films is a primary factor that affects the photothermal dynamic response along with Ag@AuNCs distribution. This is supposed to result from the Ag@AuNCs assembled in a layer that leads to electromagnetic field enhancement. The unusual observation in multilayered (PVA/PVPON_Ag@AuNCs)n films is that the UV-visible spectra (extinction efficiency) and photothermal response (Tmax) do not rely on the content of the adjacent layer of PVA and show a comparable (by value in magnitude) photothermal response at a different PVA composition of 2 mg ml−1 and 20 mg ml−1 at the same Ag@AuNCs concentration in the PVPON layer.

Hyper Rayleigh scattering (HRS) was used to measure the second-order nonlinear susceptibility, χ

Thermal relaxation dynamics of resonantly excited plasmons is important in optoelectronic, medical, and catalytic applications. This work shows introducing gold nanoparticles (AuNPs) into thin polydimethylsiloxane (PDMS) films enhanced thermoplasmonic dissipation coincident with internal reflection of incident resonant irradiation. Measured thermal emission and dynamics of AuNP–PDMS thin films exceeded emission and dynamics attributable by finite element analysis to Mie absorption, Fourier heat conduction, Rayleigh convection, and Stefan–Boltzmann radiation. Refractive-index matching experiments and measured temperature profiles indicated AuNP-containing thin films internally reflected light and dissipated power transverse to the film surface. Enhanced thermoplasmonic dissipation from metal–polymer nanocomposite thin films could affect opto- and bioelectronic implementation of these systems.

Layered transition metal dichalcogenides (TMDs) represent a diverse, emerging source of two-dimensional (2D) nanostructures with intriguing optoelectronic and catalytic properties. Gold nanoparticles (AuNPs), supporting localized surface plasmon resonances, can complement TMDs, allowing their optoelectronic properties to be tuned for use in a broad range of applications. Plasmonic AuNPs offer an extraordinary ability to concentrate electromagnetic fields and confine light to sub-wavelength dimensions. While non-plasmonic enhancement of electrocatalytic HER performance in AuNP-decorated TMDs has been reported, light-induced plasmonic excitation and dissipation mechanisms and their effect on light absorption, charge transfer, and band structure in adjacent TMDs are of keen interest. Mechanisms of plasmon-active enhancement includes light scattering, local field confinement, resonant energy transfer, and interfacial charge transfer pathways. This work utilizes transient absorption spectroscopy, with pump tunability and broadband visible probing, to monitor the carrier excitation and dynamics in various AuNP-TMD heterostructures. In particular, a combination of both time-resolved and steady-state optical spectroscopies unveils the presence of a sub-gap absorption feature in AuNP-decorated molybdenum diselenide (MoSe2) nanosheets. Optical excitation of this low-energy feature generates long-lived, energetic carriers in MoSe2. This development could represent an important advance in the design and implementation of hybrid metal NP-TMD heterostructures for use in photoelectrochemistry.

Polymer films containing plasmonic nanostructures are of increasing interest for development of responsive energy, sensing, and therapeutic systems. A series of novel gold nanoparticle (AuNP)-polydimethylsiloxane (PDMS) films were fabricated to elucidate enhanced optical extinction from diffractive and scattering induced internal reflection. AuNPs with dramatically different scattering-to-absorption ratios were compared at variable interparticle separations to differentiate light trapping from optical diffraction and Mie scattering. Description of interfacial optical and thermal effects due to these interrelated contributions has progressed beyond Mie theory, Beer’s law, effective media, and conventional heat transfer descriptions. Thermal dissipation rates in AuNP-PDMS with this interfacial optical reflection was enhanced relative to films containing heterogeneous AuNPs and a developed thermal dissipation description. This heuristic, which accounts for contributions of both internal and external thermal dissipations, has been shown to accurately predict thermal dissipation rates from AuNP-containing insulating and conductive substrates in both two and three-dimensional systems. Enhanced thermal response rates could enable design and adaptive control of thermoplasmonic materials for a variety of implementations.

Augmented plasmonic damping of dipole-resonant gold (Au) nanoparticles (NP) physicochemically bonded onto edges of tungsten disulfide (WS2) nanosheets, ostensibly due to hot electron injection, is quantified using electron energy loss spectroscopy (EELS). EELS allows single-particle spatial resolution. A measured 0.23 eV bandwidth expansion of the localized surface plasmon resonance upon covalent bonding of 20 nm AuNP to WS2 edges was deemed significant by Welch’s t-test. Approximately 0.19 eV of the measured 0.23 eV expansion went beyond conventional radiative and nonradiative damping mechanisms according to discrete dipole models, ostensibly indicating emergence of hot electron transport from AuNP into the WS2. A quantum efficiency of up to 11±5% spanning a 7 fs transfer process across the optimized AuNP-TMD ohmic junction is conservatively calculated. Putative hot electron transport for AuNP physicochemically bonded to TMD edges exceeded that for AuNP physically deposited onto the TMD basal plane. This arose from contributions due to (i) direct physicochemical bond between AuNP and WS2; (ii) AuNP deposition at TMD edge sites; and (iii) lower intrinsic Schottky barrier. This improves understanding of photo-induced doping of TMD by metal NP which could benefit emerging catalytic and optoelectronic applications.

Polymer thin films embedded with plasmonic gold nanoparticles (AuNPs) are of significant interest in biomedicine, optics, photovoltaic, and nanoelectromechanical systems. Thin polydimethylsiloxane (PDMS) films containing 3-7 micron layers of AuNPs that were fabricated with a novel diffusive-reduction synthesis technique attenuated up to 85% of incoming laser light at the plasmon resonance. Rapid diffusive reduction of AuNPs into asymmetric PDMS thin films provided superior optothermal capabilities relative to thicker films in which AuNPs were reduced throughout. A photonto- heat conversion of up to 3000°C/watt was demonstrated, which represents a 3-230-fold increase over previous AuNPfunctionalized systems. Optical attenuation and thermal response increased in proportion to order of magnitude increases in tetrachloroaurate (TCA) solution concentration. Optical and thermoplasmonic responses were observed with and without an adjacent mesh support, which increased attenuation but decreased thermal response. Morphological, optical, and thermoplasmonic properties of asymmetric AuNP-PDMS films varied significantly with diffusive TCA concentration. Gold nanoparticles, networks, and conglomerates were formed via reduction as the amount of dissolved TCA increased across a log 10 -scale. Increasing TCA concentrations caused polymer surface cratering, leading to a larger effective surface area. This method, utilizing the diffusion of TCA into a single exposed partially cured PDMS interface, could be used to replace expensive lithographic or solution synthesis of plasmon-functionalized systems.

Interest in the optical properties of plasmonic nanoparticles embedded in transparent polymers is expanding due to potential uses in sustainability, biomedicine, and manufacturing. Geometric optics of polydimethylsiloxane (PDMS) thin films containing uniformly or asymmetrically distributed polydisperse reduced gold nanoparticles (AuNPs) or uniformly distributed monodisperse solution synthesized AuNPs were recently evaluated using a compact linear algebraic sum. Algebraic calculation of geometric transmission, reflection, and attenuation for AuNP-PDMS films provides a simple, workable alternative to effective medium approximations, computationally expensive methods, and fitting of experimental data. Generally, transmission and reflection increased with AuNP isotropy and particle density, as displayed on a novel ternary diagram. Irregular AuNP morphology and size distribution caused optical attenuation from polydisperse films to increase in proportion to log 10 increases in gold content, resulting in lower attenuation per gold mass when compared to monodisperse AuNPs. Uniform monodisperse AuNP-PDMS films attenuated light in proportion to gold content, with films attenuating 0.15 fractional units per 0.1 mass-percent AuNPs. Thin layers of concentrated AuNPs attenuated light more efficiently. A 25 micron thick layer of 1.2 mass-percent AuNPs attenuated 0.5 fractional units, the same number as a 130 micron thick 0.6 mass-percent film. Measured optical responses from asymmetric AuNP-PDMS films with an adjacent back-reflector and pairs of uniformly distributed films were predictable within 0.04 units of linear algebraic estimates based on geometric optics. This approach allows for the summative optical responses of a sequence of 2D elements comprising a 3D assembly to be analyzed.

Opto-electronic coupling of plasmonic nano-antennas in the near infrared water window in vitro and in vivo is of growing interest for imaging contrast agents, spectroscopic labels and rulers, biosensing, drug-delivery, and optoplasmonic ablation. Metamaterials composed of nanoplasmonic meta-atoms offer improved figures of merit in many applications across a broader spectral window. Discrete and coupled dipole approximations effectively describe localized and coupled resonance modes in nanoplasmonic metamaterials. From numeric and experimental results have emerged four design principles to guide fabrication and implementation of metamaterials in bio-related devices and systems. Resonance intensity and sensitivity are enhanced by surface-to-mass of meta-atoms and lattice constant. Fano resonant coupling is dependent on meta-atom polarizability and lattice geometry. Internal reflection in plasmonic metaatom- containing polymer films enhances dissipation rate. Dimensions of self-assembled meta-atoms depend on balancing electrochemical and surface forces. Examples of these principles from our lab compare computation with images and spectra from ordered metal-ceramic and polymeric nanocomposite metamaterials for bio/opto theranostic applications. These principles speed design and description of new architectures for nanoplasmonic metamaterials that show promise for bioapplications.

Polymer thin films containing gold nanoparticles (AuNPs) are of growing interest in photovoltaics, biomedicine, optics, and nanoelectromechanical systems (NEMs). This work has identified conditions to rapidly reduce aqueous hydrogen tetrachloroaurate (TCA) that is diffusing into one exposed interface of a partially cured polydimethylsiloxane (PDMS) thin film into AuNPs. Nanospheroids, irregular gold (Au) networks, and micrometer-sized Au conglomerates were formed in a ∼5 μm layer at dissolved TCA contents of 0.005, 0.05, and 0.5 mass percent, respectively. Multiscale morphological, optical, and thermal properties of the resulting asymmetric AuNP-PDMS thin films were characterized. Reduction of TCA diffusing into the interface of partially cured PDMS film increased AuNP content, robustness, and scalability relative to laminar preparation of asymmetric AuNP-PDMS thin films. Optical attenuation and thermoplasmonic film temperature due to incident resonant irradiation increased in linear proportion to the order of magnitude increases in TCA content, from 0.005 to 0.05 to 0.5 mass percent. At the highest TCA content (0.05 mass percent), an asymmetric PDMS film 52-μm-thick with a 7 μm AuNP-containing layer was produced. It attenuated 85% of 18 mW of incident radiation and raised the local temperature to 54.5 °C above ambient. This represented an increase of 3 to 230-fold in photon-to-heat efficiency over previous thermoplasmonic AuNP-containing systems.

Plasmonic nanoparticles embedded in polymer films enhance optoelectronic properties of photovoltaics, sensors, and interconnects. This work examined optical extinction of polymer films containing randomly dispersed gold nanoparticles (AuNP) with negligible Rayleigh scattering cross-sections at particle separations and film thicknesses less than (sub-) to greater than (super-) the localized surface plasmon resonant (LSPR) wavelength, λ LSPR . Optical extinction followed opposite trends in sub- and superwavelength films on a per nanoparticle basis. In ∼ 70 - nm -thick polyvinylpyrrolidone films containing 16 nm AuNP, measured resonant extinction per particle decreased as particle separation decreased from ∼ 130 to 76 nm, consistent with trends from Maxwell Garnett effective medium theory and coupled dipole approximation. In ∼ 1 - mm -thick polydimethylsiloxane films containing 16-nm AuNP, resonant extinction per particle plateaued at particle separations ≥ λ LSPR , then increased as particle separation radius decreased from ∼ 514 to 408 nm. Contributions from isolated particles, interparticle interactions and heterogeneities in sub- and super- λ LSPR films containing AuNP at sub- λ LSPR separations were examined. Characterizing optoplasmonics of thin polymer films embedded with plasmonic NP supports rational development of optoelectronic, biomedical, and catalytic activity using these nanocomposites.

Optical properties of polymer films embedded with plasmonic nanoparticles (NPs) are important in many implementations. In this work, optical extinction by polydimethylsiloxane (PDMS) films containing gold (Au) NPs was enhanced at resonance compared to AuNPs in suspensions, Beer?Lambert law, or Mie theory by internal reflection due to optical diffraction in 16 nm AuNP?PDMS films and Mie scattering in 76 nm AuNP?PDMS films. Resonant extinction per AuNP for 16 nm AuNPs with negligible resonant Mie scattering was enhanced up to 1.5-fold at interparticle separation (i.e., Wigner?Seitz radii) comparable to incident wavelength. It was attributable to diffraction through apertures formed by overlapping electric fields of adjacent, resonantly excited AuNPs at Wigner?Seitz radii equal to or less than incident wavelengths. Resonant extinction per AuNP for strongly Mie scattering 76 nm AuNPs was enhanced up to 1.3-fold at Wigner?Seitz radii four or more times greater than incident wavelength. Enhanced light trapping from diffraction and/or scattering is relevant to optoelectronic, biomedical, and catalytic activity of substrates embedded with NPs.

Interest in optical properties of plasmonic nanoparticles embedded in transparent dielectrics is growing due to potential uses in biomedicine, sustainable energy, and manufacturing. This work evaluates geometric optics in polymer thin films containing mono- or polydisperse gold nanoparticles (AuNP) using a compact linear algebraic sum. Reflection and transmission from polydimethylsiloxane (PDMS) films containing uniformly- or assymetrically-distributed monodisperse or polydisperse AuNPs decreased with AuNP morphological isotropy and particle density. In PDMS, monodisperse AuNPs increased optical attenuation linearly with gold content, while polydisperse AuNPs reduced from hydrogen tetrachloroaurate (TCA) increased optical attenuation in proportion to order-of-magnitude rises in gold content. Polydisperse AuNP concentrated asymmetrically at one film interface exhibited higher attenuation. Cumulative optical responses from AuNP-PDMS films paired with another film or reflective element were within 0.04 units on average from values predicted for transmission, reflection, or attenuation using linear algebra. These results support design of NP-containing dielectric films to integrate into biochemical, microelectromechanical, and optoelectronic devices and systems.