ADVERTISEMENT RETURN TO ISSUEEditorialNEXTAdvancing Research at the Nation’s 101 HBCUs and Their Role in Maintaining the Nation’s Competitiveness in Science and TechnologyMichael L. Curry*Michael L. CurryTuskegee UniversityNorfolk State UniversityOak Ridge Associate UniversitiesFounder and Sr. International Affairs & STEM Advisor to the TMCF PresidentMore by Michael L. Curryhttps://orcid.org/0000-0001-7026-9724, Carl BonnerCarl BonnerTuskegee UniversityNorfolk State UniversityOak Ridge Associate UniversitiesFounder and Sr. International Affairs & STEM Advisor to the TMCF PresidentMore by Carl Bonnerhttps://orcid.org/0000-0002-8595-3286, Desmond StubbsDesmond StubbsTuskegee UniversityNorfolk State UniversityOak Ridge Associate UniversitiesFounder and Sr. International Affairs & STEM Advisor to the TMCF PresidentMore by Desmond Stubbs, and N. Joyce PayneN. Joyce PayneTuskegee UniversityNorfolk State UniversityOak Ridge Associate UniversitiesFounder and Sr. International Affairs & STEM Advisor to the TMCF PresidentMore by N. Joyce PayneCite this: Acc. Chem. Res. 2023, 56, 11, 1251–1252Publication Date (Web):June 6, 2023Publication History Received13 April 2023Published online6 June 2023Published inissue 6 June 2023https://doi.org/10.1021/acs.accounts.3c00218Copyright © Published 2023 by American Chemical SocietyRIGHTS & PERMISSIONSArticle Views571Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (957 KB) Get e-AlertscloseSUBJECTS:Biology,Biomaterials,Biosensing,Chemical engineering and industrial chemistry,Students Get e-Alerts

Conspectus Plasmonic nanolayers and laminarmetallic/dielectric multilayers were originally developed for opticalcloaking applications and lensing applications that could potentiallyimage objects whose size was below the diffraction limit. These assemblieswere initially formed from gold or silver nanorods grown within analumina mesh. However, more recently, assemblies with similar propertieshave also been prepared by sequential thin-layer deposition of alternatinglayers of gold and magnesium fluoride (MgF2). These metal/dielectriccomposite materials enable control of the dielectric constant in thedirections perpendicular to the layers and balance the real and imaginarydielectric constants of the assembly such that the speed and the amplitudeof the waves traveling through the assembly are not attenuated. In this Account, we will also focus on a few of the applicationsranging from surface wetting to fluorescence quenching to enhancementof photochemical reactions. First, we will share an introduction toprocesses used to create these materials, which are combinations oflow refractive index metals and transparent higher index materialsarranged in a scalable repeating fashion. Two fabrication methodswere employed: an electrochemical deposition of Ag nanorods intoan anodized alumina matrix which produced materials with an anisotropicnegative refractive index material within the plane of the film andlamellar metal/dielectric layers in which the negative index perpendicularto the growth direction. These alternating layers of plasmonic metalsand dielectric materials were ultimately chosen to prepare films forfurther testing, because of their relative ease of fabrication. Wewill continue with a discussion of a few of the applications of bothof these nonlocal dielectric composite materials including more specializedplasmonic, composite, and hyperbolic metamaterials including fluorescencequenching, photochemical reactions, and surface wetting. In each ofthese applications, the unique response caused by the enhancementof the electric field and the interface between hyperbolic materialsand plasmonic materials as they interact photophysically with theirnear neighbors is presented. In each of the applications, the enhancedelectric field extends from the composite substrate layer to interactwith its near neighbors and beyond. The presence of this extendedinteraction can be observed in the form of decreased emission lifetime,enhancement of photochemical reaction rates, and changes in the surfaceenergies measured by contact angle goniometry. In this Account, all of these situations will be addressed. Finally,we will conclude with a summary and vision for the future as wellas a discussion of the unique challenges and opportunities availableas research active faculty at an HBCU.

One of the ways to mitigate the world energy crisis is to harvest clean and green energy from waste-heat, which is abundant, ubiquitous, and free. Energy harvesting of this waste-heat is one of the most encouraging methods to capture freely accessible electrical energy. Ferroelectric materials can be used to harvest energy for low power electronic devices, as they exhibit switchable polarization, excellent piezoelectric and pyroelectric properties. The most important characteristic of ferroelectric materials, in the context of energy harvesting, is their ability to generate electric power from a time-dependent temperature change. In this work, we grew highly c-axis oriented heterostructures of BaZr 0.2 Ti 0.8 O 3 (barium zirconium titanate, BZT)/Ba 0.7 Ca 0.3 TiO 3 (barium calcium titanate, BCT) on SrRuO 3 (strontium ruthenate, SRO) and deposited on SrTiO 3 (strontium titanate, STO) single crystalline substrate using pulsed laser deposition (PLD) technique. We investigated the structural, electrical, dielectric, and pyroelectric properties of the above-mentioned fabricated heterostructures. The wide range of θ–2θ X-ray diffraction (XRD) patterns only shows ( 00l ) reflection peaks of heterostructures and the substrate which confirmed that the films are highly c-axis oriented. We are also capable to convert the low-grade waste-heat into electrical energy by measuring various temperature-dependent ferroelectric hysteresis loops of our nanostructure films via pyroelectric Ericsson cycles and the structures show an energy conversion density ~ 10,970 kJ/m 3 per cycle. These devices exhibit a large pyroelectric current density of ~ 25 mA/m 2 with 11.8 °C of temperature fluctuation and the corresponding pyroelectric coefficient of 3425 μC/m 2 K. Our research findings suggest that these lead-free relaxor-ferroelectric heterostructures might be the potential candidates to harvest electrical energy from waste low-grade thermal energy.

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 emission kinetics in dye-doped polymeric films (HITC:PMMA), deposited on top of glass and silver and embedded in Fabry–Perot cavities (metal-insulator-metal waveguides). For highly doped films on glass, we observed strong concentration quenching, as evidenced by a dramatic shortening of the emission kinetics, consistent with our previous studies. However, for the same dye-doped films on top of silver, slower emission kinetics were observed despite the high decay rates of individual dye molecules near the metallic surface. The concentration quenching rates in Fabry–Perot cavities were nearly identical to those of HITC:PMMA films deposited on top of silver. These findings are explained within a theoretical model for the inhibition of Förster energy transfer near a metallic surface. Furthermore, the emission kinetics of the dye-doped films on top of silver were approximately single exponential—consistent with the strong coupling of excited molecules with propagating surface plasmons.

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 Förster 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

Abstract We have studied the dependence of concentration quenching of luminescence (donor–acceptor energy transfer) on the thickness d of dye-doped polymeric films (HITC:PMMA) and found its strong inhibition at small values of d. This phenomenon is tentatively explained by a limited number of acceptors, which donors’ excitation can reach in thin samples, if the film’s thickness is comparable to the diffusion length of the energy transfer. The latter mechanism, along with effective reduction of the dye concentration, is responsible for an inhibition of the concentration quenching of dye molecules impregnating porous alumina membranes. The elongation of emission kinetics in thick (≥3 μm) HITC:PMMA films is cautiously attributed to the samples’ crystallinity.

We have studied the dependence of concentration quenching of luminescence on the thickness d of dye-doped polymeric films (HITC:PMMA) and found a strong inhibition of the donor-acceptor energy transfer (concentration quenching) at small values of d .

We found that inhibition of concentration quenching of HITC dye in Fabry-Perot cavities is almost similar to that on top of silver. Low convexity of the emission kinetics suggests strong coupling mediated by surface plasmons.

We report on the optical properties of nanoporous gold leaf (NPGL) metamaterials consisting of single and multiple-fold layers, and having different pore and ligament sizes. Due to their complex structure, such metamaterials have a unique optical property, which distinguishes them from homogeneous gold films. Thus, the transmission spectra of NPGLs feature two characteristic peaks positioned at ~ 490 nm and ~560 nm to 605 nm. The most notable result of this study is that the optical properties of NPGLs can be tuned by changing the dielectric environment and by applying voltage in an electrochemical cell.

We have studied emission kinetics of HITC laser dye on top of glass, smooth Au films, and randomly structured porous Au nanofoams. The observed concentration quenching of luminescence of highly concentrated dye on top of glass (energy transfer to acceptors) and the inhibition of the concentration quenching in vicinity of smooth Au films were in accord with our recent findings. Intriguingly, the emission kinetics recorded in different local spots of the Au nanofoam samples had a spread of the decay rates, which was large at low dye concentrations and became narrower with increase of the dye concentration. We infer that in different subvolumes of Au nanofoams, HITC molecules are coupled to the nanofoams weaker or stronger. The inhibition of the concentration quenching in Au nanofoams was stronger than on top of smooth Au films. This was true for all weakly and strongly coupled subvolumes contributing to the spread of the emission kinetics. The experimental observations were explained using theoretical model accounting for change in the Förster radius caused by the strong energy transfer to metal.

Combining two materials in a nanoscale level can create a composite with new functionalities and improvements in their physical and chemical properties. Here we present a high-throughput approach to produce a nanocomposite consisting of metal nanoparticles and semiconductor oxide nanostructures. Volmer-Weber growth, though unfavorable for thin films, promotes nucleation of dense and isolated metal nanoparticles on crystalline oxide nanostructures, resulting in new material properties. We demonstrate such a growth of Au nanoparticles on SnO 2 nanostructures and a remarkable sensitivity of the nanocomposite for detecting traces of analytes in surface enhanced Raman spectroscopy. Au nanoparticles with tunable size enable us to modify surface wettability and convert hydrophilic oxide surfaces into super-hydrophobic with contact angles over 150°. We also find that charge injection through electron beam exposure shows the same effect as photo-induced charge separation, providing an extra Raman enhancement up to an order of magnitude.

We show that concentration quenching of emission of dye molecules - an energy transfer to quenching centers - is inhibited in subwavelength Fabry-Perot cavities (or metal-insulator-metal, MIM, waveguides). © 2019 The Author(s)

In this Perspective, we make the case that (meta) material platforms that were originally designed to control the propagation of light can affect scores of physical and chemical phenomena, which are often thought to lie outside of the traditional electrodynamics domain. We show that nonlocal metal-dielectric environments, which can be as simple as metal-dielectric interfaces, can control spontaneous and stimulated emission, Forster energy transfer, wetting contact angle, and rates of chemical reactions. The affected phenomena can occur in both strong and weak coupling regimes and the large coupling strength seems to enhance the effects of nonlocal environments. This intriguing field of study has experienced a rapid growth over the past decade and many exciting discoveries and applications are expected in the years to come.

We studied emission kinetics of HITC dye in disordered metal-dielectric environments and found that the latter, contrary to expectations, can reverse emission kinetics shortening in highly concentrated dyes, caused by a combination of relaxation processes. © 2019 the Author(s)

We explore color switching properties of thin polyaniline (PANI) films deposited on plasmonic nanomesh structures in comparison with the films deposited on flat gold. The nanostructured systems show a much steeper color switching with increasing voltage than the films prepared on flat substrates. A strong difference between nanostructured and flat systems is also observed at small voltages, where nanostructured samples often demonstrate an additional feature in cyclic voltammetry curves and nonmonotonous changes in optical properties. Possible origins of the observed effects are discussed in terms of acceleration of charge transport in nanostructured plasmonic environment and interface-related effects. The results can provide opportunities for enhancing and controlling the electrochromic polymer performance in smart windows or display applications.

We have experimentally studied the non-resonant enhancement of spontaneous emission of HITC laser dye in metal-insulator-metal (MIM) waveguides (also referred to as Fabry–Perot cavities). We have found that in the cavities, whose size was too small to support a fundamental or any higher order resonance, the emission decay rate increased, by nearly an order of magnitude, with reduction of the cavity size. At the same time, the emission intensity increased when the cavity size was reduced from ∼200 to ∼30  nm and dropped sharply when the cavity was smaller than ∼30  nm. This emission enhancement, consistent with the perpendicular orientation of the emitting dipole with respect to the mirrors, is in a good agreement with the theoretical predictions known from the literature.

The long-range inhibition of the luminescence concentration quenching in heavily doped HITC:PMMA polymeric films in the vicinity of lamellar hyperbolic metamaterials and metallic surfaces is tentatively explained in terms of the strong exciton-plasmon coupling.