Proceedings Article | 17 September 2018
KEYWORDS: Plasmonics, Gold, Metals, Nanostructures, Graphene, Optoelectronics, Nanoparticles, Surface plasmons, Plasmons, Fluorescence resonance energy transfer
Surface Plasmons has been recognized as a promising platform that premises the advance of diverse optoelectronic materials and devices. Very recently it is noted that the potential of plasmonics is rapidly extended to wider scientific areas. In this presentation, we introduce our recent efforts to utilize plasmonics for versatile applications and understand its fundamental nature. Plasmonic effects have been proposed as a solution to overcome the limited light absorption of thin film photovoltaic devices and diverse types of plasmonic solar cells have been developed. We demonstrate a viable and promising optical engineering technique enabling the development of high-performance plasmonic organic photovoltaic devices. Laser interference lithography was explored to fabricate metal nanodot (MND) arrays with elaborately controlled dot size as well as periodicity. MND arrays with ~91 nm dot size and ~202 nm periodicity embedded in poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) hole transport layer remarkably enhanced the average power conversion efficiency (PCE) from 7.52% up to 10.11%, representing one of the highest PCE and degree of enhancement (~34.4%) levels compared to the pristine device among plasmonic OPVs reported to date.
The development of highly sensitive and selective photodectors has been an interesting issue yet to be resolved, for which we introduce a simple protocol for the fabrication of wavelength-selective photodiodes or high-gain photoconductors at low voltage. Herein, size-controlled silver nanoparticles (AgNPs), gold nanoparticles (AuNPs) and gold nanorods (AuNRs) have been introduced into polymer photodiodes. The evaluated devices exhibit remarkable photocurrent enhancement at corresponding plasmon resonant wavelengths, directly resulting in the photosensitivity increase. When compared with a pristine photodiode, AgNPs-, AuNPs- and AuNRs-mediated devices unveil maximum enhancement of 46, 49 and 65% for responsivity and 39, 30 and 54% for detectivity for blue (450 nm), green (525 nm) and red (620 nm) light detection, respectively. We also integrated a uniformly-distributed layer of Au nanorods (AuNRs) into vertically-structured perovskite photoconductive photodetectors and report, as a result, perovskite-AuNR hybrid photodetectors that exhibit significant photocurrent enhancements. The high responsivity and low driving voltage place this device among the highest-performing perovskite-based thin-film photoconductive photodetectors reported.
Unique features can be observed if the characteristics of the light emitters and metal nanoparticles are integrated. Photoluminescence (PL) can be enhanced or quenched by the presence of neighboring plasmonic metal nanostructures. An unambiguous study of the mechanism behind the enhancement and the quenching of emission is necessary to obtain new insight to the interaction between light and metal-fluorophore nanocomposites. The core aspect of combining plasmonic metal nanostructures with fluorophores is discussed by considering various functional roles of plasmonic metals in modifying the PL property. A few representative applications of SPR mediated luminescence are also discussed. We demonstrate the surface-plasmon-induced enhancement of Förster resonance energy transfer using a model multilayer core-shell nanostructure consisting of an Au core and surrounding FRET pairs, i.e., CdSe quantum dot donors and S101 dye acceptors. The multilayer configuration was demonstrated to exhibit synergistic effects of surface plasmon energy transfer from the metal to the CdSe and plasmon-enhanced FRET from the quantum dots to the dye. With precise control over the distance between the components in the nanostructure, significant improvement in the emission of CdSe was achieved by combined resonance energy transfer and near-field enhancement by the metal, as well as subsequent improvement in the emission of dye induced by the enhanced emission of CdSe. Consequently, the Förster radius was increased to 7.92 nm and the FRET efficiency was improved to 86.57% in the tailored plasmonic FRET nanostructure compared to the conventional FRET system (22.46%) without plasmonic metals.
Metal-free purely organic phosphorescent molecules are attractive alternatives to organometallic and inorganic counterparts because of their low cost and readily tunable optical properties through a wide chemical design window. However, their weak phosphorescent intensity due to inefficient spin-orbit coupling and consequently prevailing non-radiative decay processes limits their practical applicability. Here, we systematically studied phosphorescence emission enhancement of a purely organic phosphor system via plasmon resonance energy transfer. By precisely tuning the distance between purely organic phosphor crystals and plasmonic nanostructures using layer-by-layer assembled polyelectrolyte multilayers as a dielectric spacer, maximum 2.8 and 2.5 times enhancement in photoluminescence intensity was observed when the phosphor crystals were coupled with ~55 nm AuNPs and ~7 nm AgNPs, respectively, at the distance of 9.6 nm. When the distance is within the range of 3 nm, a dramatic decrease in phosphorescence intensity was observed while at a larger distance the plasmonic effect diminished rapidly. The distance-dependent plasmon-induced phosphorescence enhancement mechanism was further investigated by time-resolved photoluminescence measurements. Our results reveal the correlation between the amplification efficiency and plasmonic band, spatial factor, and spectral characteristics of the purely organic phosphor, which may provide an insightful picture to extend the utility of organic phosphors by using surface plasmon-induced emission enhancement scheme.
Surface plasmon based optical biosensors constitute a well-established model that efficiently realized the activity of plasmonics for viable optoelectronics. A massive amount of approaches was demonstrated to enhance the sensitivity via combined localized and propagating modes, and more recently an increasing attention has been paid to graphene plasmons. Hybrid plasmonic nanostructures comprising gold nanoparticle (AuNP) arrays separated from Au substrate through a temperature-sensitive poly(N-isopropylacrylamide) (PNIPAM) linker layer were constructed, and a unique plasmonic-coupling-based surface plasmon resonance (SPR) sensing properties was investigated. We also investigated for the first time the dependence of the coupling behavior in AuNPs with controlled density on the temperature in a quantitative manner in terms of the change in SPR signals. The device containing AuNPs with optimized AuNP density showed 3.2-times enhanced sensitivity compared with the control Au film-PNIPAM sample. The refractive index sensing performance of the Au film-PNIPAM-AuNPs was greater than that of Au film-PNIPAM by 19% when the PNIPAM chains have a collapsed conformation above LCST.
The use of graphene in conventional plasmonic devices was suggested by several theoretic researches. However, the existing theoretic studies are not consistent one another and the experimental studies are still at the initial stage. In order to reveal the role of graphenes on the plasmonic sensors, graphene oxide (GO) and reduced graphene oxide (rGO) thin films were deposited on Au films and their refractive index (RI) sensitivity was compared for the first time in SPR-based sensors. The deposition of GO bilayers with number of deposition L from 1 to5 was carried out by alternative dipping of Au substrate in positively- and negatively-charged GO solutions. The fabrication of layer-by-layer self-assembly of the graphene films was monitored in terms of the SPR angle shift. GO-deposited Au film was treated with hydrazine to reduce the GO. For the rGO-Au sample, 1 bilayer sample showed a higher RI sensitivity than bare Au film, whereas increasing the rGO film from 2 to 5 layers reduced the RI sensitivity. In case of GO-deposited Au film, the 3 bilayer sample showed the highest sensitivity. The biomolecular sensing was also performed for the graphene multilayer systems using BSA and anti-BSA antibody. We also suggest a paradigm to better understand the mechanism of the enhanced performance of coupled graphene and surface plasmon based sensors in terms of surface potential and work function.
Plasmon metal nanoparticles can induce an improvement of the catalytic efficiency of rationally designed composite catalysts. Despite efforts to combine the plasmonic effect and the catalytic fingerprints in metal-based catalytic systems, corresponding mechanistic studies based on electrochemical methods have remained challenging to date. In this context, the transition from plasmon metals to catalytic metals based core-shell heterostructures in plasmonic photo-electrocatalysis provides a sustainable route to high-value catalytic activity and confirm the practical potential of plasmon-mediated electrocatalytic performance. Here we report an enhancement of the catalytic activity toward an improved generation of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) on Au nanoparticles (AuNPs) using visible light. Materials characterization and enhanced catalytic activity of both H2 and O2 generation using visible light inferred the advantageous incorporation of rGO with tuned layer thickness. This model system allows us to decisively separate the optical and catalytic function of the hybrid nanomaterial and determine that the flow of energy is strongly biased towards the excitation of energetic charge carriers in the Pd shell. For photo-electrocatalytic properties of AuNP@rGO@Pd nanostructures during reaction, in-situ observation was utilized to advance our understanding of the fundamental physical and chemical properties of high-performance. Lastly, we introduce an unprecedented strategy to rationally quantify the plasmonic effects on electro-/-photo-catalysis using modified Kreschmann setup and KPFM study.
