Plasmonic Layer Research Articles

A study on the effect of low energy ion beam irradiation on Au/TiO2 system for its application in photoelectrochemical splitting of water

Nanostructured TiO2 thin films were deposited on indium tin oxide (ITO) substrate via sol–gel technique and were modified by plasmonic Au layer. The plasmonic Au modified TiO2 (Au/TiO2) thin films were then irradiated with 500keV Ar2+ ion beam at different ion fluences viz. 1×1016, 3×1016 and 1×1017 to study the effect of nuclear energy deposition on the morphology, crystallinity, band gap, surface plasmon resonance (SPR) peak exhibited by Au particles and photoelectrochemical properties of the system. Prepared thin films were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), Rutherford backscattering spectrometry (RBS) measurements and UV–visible spectroscopy. The photoelectrochemical measurements revealed that both Au/TiO2 and Au/TiO2 thin film irradiated at 1×1016 fluence exhibits enhanced photoelectrochemical response in comparison to pristine TiO2. The film irradiated at 1×1016 fluence offered maximum applied bias photon-to-current efficiency (ABPE) and shows 6 times increment in photocurrent density which was attributed to more negative flat band potential, maximum decrease in band gap, high open circuit voltage (Voc) and reduced charge transfer resistance.

Plasmonic layer enhanced photoelectrochemical response of Fe2O3 photoanodes

Present experimental study focuses on the influence of plasmonic layer in Zr-doped Fe2O3 (Z-F) thin film based photoanodes deposited in different configurations for photo splitting of water. The Au nanoparticles (plasmonic layer) as bottom layer and surface (top) layer are incorporated in the spray pyrolytically deposited Z-F thin layer. In addition to this, fabrication of Z-F sandwiched between two plasmonic Au layers (Au/Z-F/Au) as well as plasmonic Au layer sandwiched between two Z-F layers (Z-F/Au/Z-F) are also undertaken. All configurations using plasmonic layer show enhanced photoresponse in comparison to the pristine Z-F samples. The Z-F sandwiched between two plasmonic layers shows the most significant increase in photocurrent density at 0.8 V/SCE (Saturated Calomel Electrode) and also improved optical absorption due to the presence of two palsmonic layers which promote charge transfer and inhibit charge recombination. The obtained results are supported by characterization techniques viz. X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Analysis (EDAX), UV-Visible absorption spectroscopy, Photoelectrochemical properties, Mott-Schottky analysis and efficiency measurements of photoelectrochemical (PEC) sytstem.

Metamaterial Fabry–Perot cavity implementation for gain and bandwidth enhancement of THz dipole antenna

In this article, Metamaterial layer is implemented to improve radiation characteristic of dipole antenna at THz domain. Also, cavity back reflector is studied in order to gain enhancement and pattern shaping; in fact, combination of both structures is known as Fabry–Perot cavity. Return loss is modified at 486–654GHz for less than −10dB and also Q factor is calculated in presence of Metamaterial layer. The absorption and shield factors are simulated and showed at 0.55THz. Antenna gain is increased more than 120% and bandwidth is amended around 82%. By achieved simulation result, −14.85dB shield factor is obtained for proposed metamaterial layer. The dipole antenna contains silver line on silicon lossless material with n=2.43 and the plasmonic layer is modeled by deposition of silver wire in silicon. In addition, Glass (n=1.65) and SiN (n=1.87) are used for metamaterial part and it is shown that increase in the permittivity leads to decrease the plasmonic permittivity; thus, more bandwidth of the structure is obtained. Also, effect of change in radius of the metamaterial micro wire on bandwidth of the antenna is considered.

Optimization of Magneto-Optical Kerr Effect in Cu/Fe/Cu Nano-structure

We use an analytical approach to describe the optical response of a magnetoplasmonic structure upon surface plasmon polariton (SPP) excitation in glass/Cu/Fe/Cu multilayer. The proposed structure is based on Kretschmann prism couplers, Fe layer as magneto-optical (MO) medium, and Cu layer as plasmonic metal layer, to enhance the MO effects thanks to the resonant excitation of surface plasmons. The influence of constituent layer thicknesses and layer order is investigated to obtain the maximum MO Kerr signal and figure of merit (FOM) in polar geometry. In addition, we show a range of parameters to determine the maximum Kerr rotation accompanied by minimum Kerr ellipticity which is desirable for data storage applications. Results demonstrate the important role of film thicknesses and incidence angle distribution on resonant excitation of surface plasmons.

Copper-Graphene-Based Photonic Crystal Fiber Plasmonic Biosensor

We propose a photonic crystal fiber surface plasmon resonance biosensor where the plasmonic metal layer and the sensing layer are placed outside the fiber structure, which makes the sensor configuration practically simpler and the sensing process more straightforward. Considering the long-term stability of the plasmonic performance, copper (Cu) is used as the plasmonic material, and graphene is used to prevent Cu oxidation and enhance sensing performance. Numerical investigation of guiding properties and sensing performance is performed by using a finite-element method. The proposed sensor shows average wavelength interrogation sensitivity of 2000 nm/refractive index unit (RIU) over the analyte refractive indices ranging from 1.33 to 1.37, which leads to a sensor resolution of $5\times 10^{-5} \text{RIU}$ . Due to the simple structure and promising results, the proposed sensor could be a potential candidate for detecting biomolecules, organic chemicals, and other analytes.

Supramolecular Organic Nanowires as Plasmonic Interconnects

Metallic nanostructures are able to interact with an incident electromagnetic field at subwavelength scales by plasmon resonance which involves the collective oscillation of conduction electrons localized at their surfaces. Among several possible applications of this phenomenon, the theoretical prediction is that optical circuits connecting multiple plasmonic elements will surpass classical electronic circuits at nanoscale because of their much faster light-based information processing. However, the placement and coupling of metallic elements smaller than optical wavelengths currently remain a formidable challenge by top-down manipulations. Here, we show that organic supramolecular triarylamine nanowires of ≈1 nm in diameter are able to act as plasmonic waveguides. Their self-assembly into plasmonic interconnects between arrays of gold nanoparticles leads to the bottom-up construction of basic optical nanocircuits. When the resonance modes of these metallic nanoparticles are coupled through the organic nanowires, the optical conductivity of the plasmonic layer dramatically increases from 259 to 4271 Ω(-1)·cm(-1). We explain this effect by the coupling of a hot electron/hole pair in the nanoparticle antenna with the half-filled polaronic band of the organic nanowire. We also demonstrate that the whole hybrid system can be described by using the abstraction of the lumped circuit theory, with a far field optical response which depends on the number of interconnects. Overall, our supramolecular bottom-up approach opens the possibility to implement processable, soft, and low cost organic plasmonic interconnects into a large number of applications going from sensing to metamaterials and information technologies.

Enhanced electroluminescence of an organic light-emitting diode by localized surface plasmon using Al periodic structure

In this work, we investigate the emission enhancement of an organic light-emitting diode (OLED) by increasing the internal quantum efficiency of the organic materials thanks to localized surface plasmon resonance (LSPR). We, particularly, consider periodic arrays of Al nanorods fabricated by e-beam lithography. The intrinsic parameters of the nanoparticles (NPs) are optimized using 3D finite-difference time-domain numerical simulations in order to match the emission wavelength of the Alq3-based OLED (520 nm) with the LSPR of the NPs. The periodic structures were fabricated on top of an indium titanium oxide anode. Our results indicate that the luminance and the current density of the OLED incorporating the Al arrays is drastically increased with an overall luminance increase of 20% compared to the standard OLED without a NP plasmonic layer.

Increased short-circuit current density and external quantum efficiency of silicon and dye sensitised solar cells through plasmonic luminescent down-shifting layers

Luminescent down-shifting (LDS) is a purely optical method to improve the short-wavelength response of photovoltaics by red-shifting the incident solar spectrum. This work is the first to investigate plasmonic LDS (pLDS) layers applied to c-Si and DSSC solar cells. The addition of pLDS composite layers containing core–shell quantum dots CdSe/ZnS was demonstrated to increase the short circuit current density (Jsc) of c-Si and DSSC devices between 300 and 500nm, where the QDs is most absorbing. Up to ∼22% (relative) increase has been achieved for both cells when compared with cells with no pLDS layers. External quantum efficiency measurements have shown significant enhancement where the solar cells have poor optical response, below 500nm, while increased efficiency was confirmed with current–voltage (I–V) measurements.

Au–Cu Alloyed Plasmonic Layer on Nanostructured GaN for SERS Application

The main aim of this work was developing a novel technology for producing platforms for surface enhanced Raman scattering (SERS) measurements on photoetched (nanostructured) GaN with Au–Cu thin film as surface plasmonic layer. Dealloying of deposited Au–Cu films gives very stable and SERS-active platforms. Influence of percentage of copper in the alloyed Au–Cu layer on the SERS enhancement factor (EFSERS) was examined. SERS measurements were performed using pyridine and 4-mercaptobenzoic acid. Corresponding GaN platforms covered with Au and Au–Ag layers were used as a reference. It was also shown that the formation of even relatively large (above 1 μm) and very regular etch pits on the GaN surface may significantly increase the SERS enhancement factor.

Enhancement of P3HT:PCBM Photovoltaic Shells Efficiency Incorporating Core-shell Au@Ag Plasmonic Nanoparticles

We report on a simple and scalable process for the synthesis of core-shell Au@Ag (Gold core @ Ag shell) bimetallic plasmonic nanoparticles (NPs) with an average size in the range of 40nm, endowing a remarkable improvement of the power conversion efficiency (PCE) of air processed organic photovoltaics (OPVs) upon being deposited onto the active layer. The beauty of the current work lies on the fact that the spin coated OPV devices; exhibiting a normal architecture consisting of a Glass/ITO (Indium Tin Oxide) anode, a poly-3,4-ethylenedioxy-thiophene:poly(styrenesulfonic-acid) (PEDOT:PSS) hole transport layer (HTL), a poly(3-hexylthiophene) (P3HT) and methanofullerene derivative (PCBM) bulk heterojunction (BHJ) photoactive blend layer (P3HT:PCBM), a Au@Ag plasmonic NPs layer, a Calcium (Ca) electron transport layer (ETL), and an Aluminium (Al) cathode, were processed in ambient conditions. The plasmonic NP layer, which was deposited onto the active layer after a short period of O2 plasma treatment to enhance the adhesion of the water based NP dispersion (limited time of plasma treatment for 20sec at a pressure of 1.12 mbar and at 10 Watts power), resulted in a 20.1% enhancement of the PCE compared to reference devices. Namely, the PCE was enhanced from 2.24 to 2.69%. The spin coating parameters for the optimum film morphology, thickness, optical properties, etc of all the OPV layers, as well as the desirable morphology at the nanometer scale of the BHJ have been followed according to previous established protocols. Ultraviolent visible (UV-vis) spectroscopy demonstrated the localised surface plasmon resonance (LSPR) peak of the plasmonic NPs. Scanning and transmission electron microscopy (SEM, TEM) depicted the distribution and the surface coverage of Au@Ag NPs above the active layer as well as their geometry and size, respectively. This study shows for the first time the utilization of plasmonic NPs as a means to improve the PCE of air processed OPVs, which is known to get deteriorated by ambient conditions processing.

Sub-diffraction demagnification imaging lithography by hyperlens with plasmonic reflector layer

The sub-diffraction demagnification imaging of hyperlens with plasmonic reflector was demonstrated experimentally in lithography performance at 365 nm light wavelength.

Prediction of transmittance spectra for transparent composite electrodes with ultra-thin metal layers

Recent interest in indium-free transparent composite-electrodes (TCEs) has motivated theoretical and experimental efforts to better understand and enhance their electrical and optical properties. Various tools have been developed to calculate the optical transmittance of multilayer thin-film structures based on the transfer-matrix method. However, the factors that affect the accuracy of these calculations have not been investigated very much. In this study, two sets of TCEs, TiO2/Au/TiO2 and TiO2/Ag/TiO2, were fabricated to study the factors that affect the accuracy of transmittance predictions. We found that the predicted transmittance can deviate significantly from measured transmittance for TCEs that have ultra-thin plasmonic metal layers. The ultrathin metal layer in the TCE is typically discontinuous. When light interacts with the metallic islands in this discontinuous layer, localized surface plasmons are generated. This causes extra light absorption, which then leads to the actual transmittance being lower than the predicted transmittance.

Nanoantenna-induced fringe splitting of Fabry-Perot interferometer: a model study of plasmonic/photonic coupling.

In this paper, we present a simple approach to study the coupling mechanisms between a plasmonic system consisting of bowtie nanoantennas and a photonic structure based on a Fabry-Perot interferometer. The nanoantenna array is represented by an equivalent homogeneous layer placed at the interferometer surface and yielding the effective dielectric function of the NA resonance. A phase matching model based on thin film interference is developed to describe the multi-layer interferences in the device and to analyze the fringe variations induced by the introduction of the plasmonic layer. The general model is validated by an experimental system consisting of a bowtie nanoantenna array and a porous-silicon-based interferometer. The optical response of this hybrid device exhibits both the enhancement induced by the nanoantenna resonance and the fringe pattern of the interferometer. Using the phase matching model, we demonstrate that strong coupling can occur in such a system, leading to fringe splitting. A study of the splitting strength and of the coupling behavior is given. The model study performed in this work enables to gain deeper understanding of the optical behavior of plasmonic/photonic hybrid devices.

Perfect plasmonic absorbers for photovoltaic applications

A novel regime of perfect absorption in a thin plasmonic layer corresponds to a collective mode of an array of plasmonic nanospheres. In our theoretical study we show that the absorption of the incident light occurs mainly in the semiconductor material hosting plasmonic nanospheres, whereas the absorption in the metal is very small. The regime survives when the uniform host layer is replaced by a practical photovoltaic cell. Trapping the light allows the thickness of the doped semiconductor to be reduced to values for which the degradation under light exposure should be insufficient. The light-trapping regime is compatible with both the metal-backed variant of the photovoltaic cell and its semitransparent variant when both electrodes are preformed of a conductive oxide. Negligible parasitic losses, a variety of design solutions and a reasonable operational band make our perfect plasmonic absorbers promising for photovoltaic applications.

Tunable surface-plasmon-polariton-like modes based on graphene metamaterials in terahertz region

Plasmonic response in graphene-based metamaterials show great potential for terahertz (THz) wave manipulation. In this work, we study the tunable surface-plasmon-polariton-like modes based on graphene complementary split ring resonators (CSRRs) in THz region. Our study suggests that these modes can be generated by graphene plasmonic metamaterials due to the diffraction coupling of surface plasmon and propagating electromagnetic (EM) wave. Furthermore, the modes can be tuned by stacking graphene plasmonic metamaterials layers or by changing the graphene Fermi level with electric field. Our results suggest graphene plasmonic metamaterials for both physical understanding and novel applications in THz region.

Opto-Electrical Performance Improvement of Mono c-Si Solar Cells Using Dielectric–Metal–Dielectric (D-M-D) Sandwiched Structure-Based Plasmonic Anti-Reflector

Mono c-Si solar cells based on plasmonic anti-reflector, an ultra-thin silver (Ag) film sandwiched between silicon nitride (SiNx) layers on non-textured c-Si surface, have been explored. Prior to solar cell fabrication, the plasmonic anti-reflector structure was optimized separately by varying different thicknesses of top and bottom SiNx layers and the sandwiched ultra-thin Ag film. For broad wavelength range (300–1200 nm), minimum weighted reflectance was observed in the range of 8–9 %, for the top and bottom SiNx layers having 70–80-nm thickness. The refractive index of top and bottom SiNx layers was in the range of 1.77–1.80 and 1.92–1.96, respectively. A 180-μm non-textured mono c-Si solar cell is fabricated with plasmonic anti-reflector, having top and bottom SiNx layer thickness of 80-nm and 8–9-nm sandwiched ultra-thin Ag layer, resulted in 17 % solar cell efficiency. The measured efficiency was 1.8 % higher compared to 180-μm mono c-Si solar cell with standard 80 nm SiNx anti-reflector. The short circuit current density (J sc) extracted from external quantum efficiency (EQE) has shown 0.5 mA/cm2 enhancement for the dielectric–metal–dielectric (D-M-D) sandwiched structure (plasmonic anti-reflector)-based solar cell compared to standard SiNx anti-reflection coating (ARC) structure-based solar cell. EQE enhancement was seen for all wavelengths above 700 nm with maximum 25–26 % enhancement at around 1125 nm. Also, in UV wavelength region (300–400 nm), EQE enhancement was seen with maximum 25 % enhancement at around 370 nm. Possible phenomenon for improved anti-reflection and EQE in D-M-D-based plasmonic anti-reflector has been discussed.

Surface Plasmon Resonance Photonic Crystal Fiber Biosensor: A Practical Sensing Approach

We propose a simple, two rings, hexagonal lattice photonic crystal fiber biosensor using surface plasmon resonance phenomenon. An active plasmonic gold layer and the analyte (sample) are placed outside the fiber structure instead of inside the air-holes, which will result in a simpler and straight forward fabrication process. The proposed sensor exhibits birefringent behavior that enhances its sensitivity. Numerical investigation of the guiding properties and sensing performance are conducted by finite element method. Using wavelength and amplitude interrogation methods, the proposed sensor could provide maximum sensitivity of 4000 nm/RIU and 320 RIU <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , respectively. The resolutions of the sensor are 2.5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> and 3.125 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> RIU for wavelength and amplitude interrogation modes. The proposed sensor design shows promising results that could be used in biological and biochemical analytes detection.

Electromagnetic wave transmission through a subwavelength nano-hole in a two-dimensional plasmonic layer.

An integral equation is formulated to describe electromagnetic wave transmission through a subwavelength nano-hole in a thin plasmonic sheet in terms of the dyadic Green's function for the associated Helmholtz problem. Taking the subwavelength radius of the nano-hole to be the smallest length of the system, we have obtained an exact solution of the integral equation for the dyadic Green's function analytically and in closed form. This dyadic Green's function is then employed in the numerical analysis of electromagnetic wave transmission through the nano-hole for normal incidence of the incoming wave train. The electromagnetic transmission involves two distinct contributions; one emanates from the nano-hole, and the other is directly transmitted through the thin plasmonic layer itself (which would not occur in the case of a perfect metal screen). The transmitted radiation exhibits interference fringes in the vicinity of the nano-hole, and they tend to flatten as a function of increasing lateral separation from the hole, reaching the uniform value of transmission through the sheet alone at large separations.

Fluorescence in nonlocal dissipative periodic structures

We present an approach for the description of fluorescence from optically active material embedded in layered periodic structures. Based on an exact electromagnetic Green's tensor analysis, we determine the radiative properties of emitters such as the local photonic density of states, Lamb shifts, line widths etc. for a finite or infinite sequence of thin alternating plasmonic and dielectric layers. In the effective medium limit, these systems may exhibit hyperbolic dispersion relations so that the large wave-vector characteristics of all constituents and processes become relevant. These include the finite thickness of the layers, the nonlocal properties of the constituent metals, and local-field corrections associated with an emitter's dielectric environment. In particular, we show that the corresponding effects are non-additive and lead to considerable modifications of an emitter's luminescence properties.

Progress in Pulse Plating Atomic Layer Deposition (PP-ALD)

A family of absorber materials of interest for high volume production of photovoltaics is referred to as CZTS, or Cu2ZnSn(S,Se)4. The primary advantages of these materials are that they are made from nontoxic earth abundant elements. This group has been working on electrochemical atomic layer deposition (E-ALD) as a method for the formation of PV absorber materials for many years. E-ALD involves the use of surface limited reactions to form deposits an atomic layer at a time, in order to achieve atomic layer control during the growth process. E-ALD has been based on the alternating of precursor solutions of the desired elements and the use of UPD to limit growth to an atomic layer at a time. The E-ALD method has important advantages for the formation of nanofilms of materials, including: conformal growth, atomic layer control over deposition, room temperature deposition, and scalable principles. There are a range of new PV designs involving nanostructured electrodes and plasmonic layers where the absorber layer thickness can be considerably thinner than the 4 µm used for say the formation of CdTe based thin layer photovoltaics. However, even a µm of CdTe formed using present E-ALD technology would take at least 100 time longer then the presently used industrial methods. Present E-ALD technology is can be used to grow films from a nm up, but is most applicable to where conformal, high quality nanofilms are needed. The rate of growth using E-ALD is presently limited by the time it takes to change solutions, and the solution should be changed at least twice per atomic layer. The present report involves efforts by this group to develop of a variant of E-ALD based on changing the potential, pulsing, rather than solution exchanges, greatly decreases the cycle time. Presently, the Authors referred to it as potential pulse ALD (PP-ALD). Preliminary results on the formation of Cu2Se, ZnS, and other possible binary compounds which could serve as components of a CZTS absorber layer will be discussed.