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We have grown arrays of silver nanowires in pores of anodic alumina membranes (metamaterials with hyperbolic dispersion at λ ≥ 615 nm), spin coated them with the dye-doped polymer (HITC:PMMA), and studied the rates of radiative and nonradiative relaxation as well as the concentration quenching (Förster energy transfer to acceptors). The results were compared to those obtained on top of planar Ag films and glass (control samples). The strong spatial inhomogeneity of emission kinetics recorded in different spots across the sample and strong inhibition of the concentration quenching in arrays of Ag nanowires are among the most significant findings of this study.

We have studied the effects of planar, lamellar, and random nanostructured metal-dielectric environments on spontaneous emission and energy transfer concentration quenching of HITC laser dye. We found an inhibition of the concentration quenching in vicinity of metal, which was stronger in nanostructured substrates than in plain geometries. It was shown that the same substrates, which boosted spontaneous emission, also inhibited the concentration quenching. The effect is discussed in terms of the Forster radius affected by losses. Work at LLNL was performed under the auspices of the U.S. Department of Energy by LLNL under Contract DE-AC52-07NA27344

It is well known that dielectric coatings used in high energy laser systems for beam steering are susceptible to laser damage. The laser damage ensued in high refractive index materials, such as hafnia, is responsible for limiting the laser operation fluence and lifetime. Although hafnia is an ideal high refractive index material used in dielectric coatings for a broad range of laser wavelengths, defects developed during the deposition process leads to laser-induced damage. In order to increase the resistance to laser damage and improve laser performance, it is imperative to understand the underlying physics of laser damage in high index coating materials. Earlier work observed a substantial difference in laser damage thresholds for hafnia coatings produced by different deposition methods, yet the underlying mechanisms for the observed difference remains elusive. In this work we investigated the responses of single layer hafnia films produced by two deposition processes, electron beam (e-beam) evaporation and ion beam sputtering (IBS) methods upon UV ns-laser exposure. The films underwent laser damage testing using a 1-on-1 laser damage testing protocol with a beam size of 650 µm (1/e2) at 355 nm and 8 ns pulse duration. Both S and P polarizations were tested at a 45° angle of incidence. Chemical, structural and morphological characterizations of the films both pre- and post-laser damage were performed using Rutherford backscattering spectroscopy, glancing incidence X-Ray diffraction, and optical and scanning/transmission electron microscopy. We found that films deposited from the e-beam process had a higher damage onset threshold (4.4 +/- 0.1 J/cm2) than those deposited by IBS method (2.1 +/- 0.2 J/cm2). Furthermore, a polarization-dependent damage threshold onset was observed for the e-beam evaporated coatings but was not observed in IBS films. Although the typical size of the damage in general is larger for the e-beam produced films, the morphology shows similar foamy appearance in both films. The density of the damage sites, on the other hand, was much greater in the IBS produced films than that by the e-beam method. The observed difference can be attributed to their resulting structural/textural differences inherited in each method: porous in the e-beam films and dense with isolated nanobubbles in the IBS films, which can lead to a large difference in laser-defect coupling. The underlying physical mechanism will be discussed in detail. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. IM Release# LLNL-ABS-809117

Laser-induced damage in coating materials with a high index of refraction, such as hafnia, limits the performance of high power and high energy laser systems. Understanding the underlying physics responsible for laser damage holds the key for developing damage-resistant optical films. Previous studies have reported a substantial difference in laser damage onset for hafnia films produced by different deposition methods, yet the underlying mechanisms for the observed difference remain elusive. We combined laser damage testing with analytical characterizations and theoretical simulations to investigate the response of hafnia films produced by electron (e-) beam evaporation vs ion beam sputtering (IBS) methods upon UV ns-laser exposure. We found that e-beam produced hafnia films were overall more damage resistant; in addition, we observed a polarization anisotropy associated with the onset of damage in the e-beam films, while this effect was absent in the latter films. The observed differences can be attributed to the stark contrast in the pressure inside the pores inherent in both films. The high pressure inside the IBS-induced nanobubbles has been shown to reduce the threshold for laser-induced plasma breakdown leading to film damage. The polarization effects in the e-beam coatings can be related to the asymmetric electric field intensification induced by the columnar void structure. Our findings provide a fundamental basis for developing strategies to produce laser damage-resistant coatings for UV pulsed laser applications.

Understanding the behavior of metal ions in room temperature ionic liquids (ILs) is essential for predicting and optimizing performance for technologies like metal electrodeposition; however, many mechanistic details remain enigmatic, including the solvation properties of the ions in ILs and how they are governed by the intrinsic interaction between the ions and the liquid species. Here, we utilize first-principles molecular dynamics simulations to unravel and compare the key structural properties of Ag+ and Cu+ ions in a common room temperature IL, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate. We find that, when compared to Cu+, the larger Ag+ shows a more disordered and flexible solvation structure with a more frequent exchange of the IL species between its solvation shells. In addition, our simulations reveal an interesting analog in the solvation behavior of the ions in the IL and aqueous environments, particularly in the effect of the ion electronic structures on their solvation properties. This work provides fundamental understanding of the intrinsic properties of the metal ions in the IL, while offering mechanistic understanding and strategy for future selection of ILs for metal electrodeposition processes.

Enhancing electrical conductance in organic semiconductors has been a focus of intense research over last few decades. The improvement can be made by optimizing either the material or the device architecture. As it has been shown in [Orgiu et al., Nature Materials, 2015], strong coupling of organic molecules with a nanostructured plasmonic substrate can significantly improve the molecules’ electrical conductivity. In the present study, we searched for the effect of strong coupling with a Fabry-Perot cavity on the conductivity of the semiconducting Poly (3- hexylthiophene) (P3HT) polymer. Despite the observation of the strong coupling evidenced by a very large Rabi splitting of 1.0 eV, the increase of electrical conductivity with increase of the P3HT film thickness was primarily affected by an increase of the polymer’s order in thick P3HT films.

We present the novel metamaterial based on a nanoporous alumina membrane impregnated with R6G dye molecules. The splitting of the reflectance and emission bands at large dye concentration is discussed in terms of strong coupling.

We have studied photodegradation of the semiconducting polymer p3ht in the resonant cavity and the control samples. The nearly three-fold reduction of the reaction rate is attributed to the strong polymer-cavity coupling.

We studied chemiluminescence of rhodamine 6G (R6G) dye in a series of R6G:DNPO:PMMA films deposited onto a variety of metallic, metal–dielectric, and dielectric substrates. We found that chemiluminescence kinetics on top of Ag and Au films covered by an insulating MgF2 layer had longer decay times than those on top of purely dielectric substrates, MgF2 films on glass. We infer that Ag- and Au-based substrates with an insulating MgF2 layer on top affected the reaction rates by influencing polarization energies of reactants and surrounding molecular dipoles. At the same time, the chemiluminescence kinetics on top of Ag and Au surfaces (without an insulating MgF2 spacer) were substantially shorter than those on top of dielectric substrates, probably because of conventional chemical catalysis. The peak emission intensities on top of metallic substrates (with and without the MgF2 layer on top) were lower than those on top of purely dielectric substrates, likely due to inhibition of the energy transfer to acceptors (R6G dye molecules) known in the vicinity of metals. The further reduction of chemiluminescence intensity on top of lamellar metal–dielectric stacks could be due to preferential emission of light inside the volume of the metamaterial rather than outside.

Enhancing electrical conductance in organic semiconductors has been a focus of intense research over the last few decades. The improvement can be made by optimizing either the material or the device architecture. As it has been shown by Orgiu et al., strong coupling of organic molecules with a nanostructured plasmonic substrate can significantly improve the molecules’ electrical conductivity. We searched for the effect of strong coupling with a Fabry–Perot cavity on the conductivity of the semiconducting poly(3 hexylthiophene-2, 5-diyl) (P3HT) polymer. Despite the observation of the strong coupling evidenced by a very large Rabi splitting of 1.0 eV, the increase of electrical conductivity with increase of the P3HT film thickness was primarily affected by an increase of the polymer’s order in thick P3HT films.

Photonic structures are commonly designed to manipulate scattered or emitted light. However, in recent years, they were demonstrated to affect a variety of phenomena, including chemical reactions, which lie outside the traditional electrodynamics domain. In this work, we have studied the effect of a Fabry–Perot cavity on the chemical reaction of practical importance—photodegradation of the semiconducting polymer 2,5-poly(3-hexylthiophene) (P3HT), which is the material of choice in organic photovoltaics. Experimentally, Fabry–Perot cavities, composed of two silver mirrors and filled with P3HT polymer, were photoexposed over tens of hours, and the concentration of the remaining thiophene rings (composing P3HT) was studied as a function of time. It has been found that in the regime of strong coupling with the cavity, characterized by one of the largest values of the Rabi splitting reported in the literature (1.0 eV), the normalized rate of photodegradation is reduced threefold, substantially larger than in the weak coupling regime reported in our recent study. This result adds to the toolbox of strong coupling phenomena and paves the road towards long-range control of chemical reactions and catalysis.

We have studied strong exciton-plasmon coupling in the films of Ag nanoislands as well as in the layer-by-layer (LBL) deposited films of Au nanoparticles (NPs) coated with highly concentrated rhodamine 6G (R6G) dye. Their absorbance and the reflectance spectra featured the peaks or dips, which were not characteristic of dye or NPs/nanoislands taken separately. The positions of the spectral maxima (or minima) in the dye-doped films, plotted against those in pristine Ag nanoislands films, resulted in the dispersion curves comprised of three branches. They could be described by the analytical model based on the Hamiltonian accounting for the unperturbed energies of the surface plasmon (SP) resonance, the two bands composing the absorption spectrum of R6G dye, and the exciton-plasmon coupling energy Δ. Its value was larger in Ag nanoislands films deposited on hyperbolic metamaterials (0.221 eV) than on glass (0.165 eV). The minimal gap between the upper and the lower branches was equal to ≈3Δ. The dispersion curves in the Au NPs LBL films could be described with the Hamiltonian equation at relatively small dye concentrations. At larger concentrations of R6G molecules, the spectral peaks shifted and became more pronounced. The corresponding dispersion curve could not be described in terms of the existing model, indicating the need for further theoretical studies.

We studied photoinduced reduction of absorption and emission in p3ht semiconducting polymer and found that the rate of photodegradation does not correlate with the luminescence intensity and does not depend on the excited state concentration.

We have studied the spectroscopic properties of nanoporous alumina membranes impregnated with rhodamine 6G (R6G) dye molecules. At small dye concentrations, the reflectance spectra feature one minimum, corresponding to the absorption band of R6G. With increase of the dye concentration, the reflectance dip splits in two and the energy difference between the two minima increases. A similar behavior is shared by the emission spectral band. We explain these observations in terms of strong coupling of closely situated dye molecules inside the channels. At the same time, the experimentally observed angular dependence of the reflectance spectrum is consistent with a long-range collective behavior of dye molecules across an array of dye-impregnated channels.

Proximity to metallic surfaces, plasmonic structures, cavities and other inhomogeneous dielectric environments is known to control spontaneous emission, energy transfer, scattering and many other phenomena of practical importance. The aim of the present study was to demonstrate that, in spirit of the Marcus theory, the rates of chemical reactions can, too, be influenced by nonlocal dielectric environments, such as metallic films and metal/dielectric bilayer or multilayer structures. We have experimentally shown that metallic, composite metal/dielectric substrates can, indeed, control ordering as well as photodegradation of thin poly-3-hexylthiophene (p3ht) films. In many particular experiments, p3ht films were separated from metal by a dielectric spacer, excluding conventional catalysis facilitated by metals and making modification of the nonlocal dielectric environment a plausible explanation for the observed phenomena. This first step toward understanding of a complex relationship between chemical reactions and nonlocal dielectric environments is to be followed by the theory development and a broader scope of thorough experimental studies.

We show that photo-oxidation of organic semiconducting films can be controlled by geometry and composition of metallic and metal/dielectric substrates, in agreement with increase of the chemical reaction rate by the density of photonic states.