Excitation Of Localized Surface Plasmons Research Articles

Ge(Sn) nano-island/Si heterostructure photodetectors with plasmonic antennas

We report on photodetection in deep subwavelength Ge(Sn) nano-islands on Si nano-pillar substrates, in which self-aligned nano-antennas in the Al contact metal are used to enhance light absorption by means of local surface plasmon resonances. The impact of parameters such as substrate doping and device geometry on the measured responsivities are investigated and our experimental results are supported by simulations of the three-dimensional distribution of the electromagnetic fields. Comparatively high optical responsivities of about 0.1 A W−1 are observed as a consequence of the excitation of localized surface plasmons, making our nano-island photodetectors interesting for applications in which size reduction is essential.

Multi-band MIM refractive index biosensor based on Ag-air grating with equivalent circuit and T-matrix methods in near-infrared region

In this paper, a multi-band metal-insulator-metal (MIM) perfect absorber with refractive index sensing capability has been investigated in near-infrared region. The proposed structure has been studied for biomedical applications such as detection of solution of glucose in water, diagnosis of different stages of malaria infection, bacillus bacteria and cancer cells. The MIM configuration improves the sensing parameters of the biosensor due to the good interaction with the analyte. The high sensitivity and figure of merit of 2000 nm/RIU and 100 RIU−1 have been achieved, respectively. Also, the Ag-air grating in the suggested plasmonic sensor helps the localized surface plasmons excitation and makes the structure sensitive to the incident lightwave polarization. Therefore, the presented biosensor behaves like a polarization switch with the high extinction ratio and fast response time of 25.15 dB and 100 fs, respectively. The methods of equivalent circuit model and transmission matrix have been utilized to verify the simulation results, as a new challenge in near-infrared region. The new idea of multi-application plasmonic devices, the feasibility of fabrication for the presented structure and utilizing mentioned analytical methods in near-infrared region could pave the way for the future of plasmonic structures.

Inhibiting the Segregation of Germanium in Silver Nanolayers

It is generally acknowledged that using germanium as a wetting film for silver nanolayers decreases the surface roughness of the metal. However, germanium atoms also tend to segregate towards the surface of silver films, increasing ohmic losses in the structure. Here we propose an Au/Ge/Ag based structure where the segregation of germanium in silver is inhibited. X-ray photoelectron spectroscopy (XPS) results show that for the Au/Ge/Ag system, the surface concentration of germanium drops by an order of magnitude relative to multilayers containing only one type of metal (Ag or Au). We have also observed that the time-dependent decrease in the reflectivity due to localized surface plasmon excitation is less prominent in the case of the Au/Ge/Ag structure than in the case of Ag/Ge/Ag. We provide XPS as well as optical reflectometry results to support that claim.

Selective excitation of multipolar surface plasmon in a graphene-coated dielectric particle by Laguerre Gaussian beam

Localized surface plasmonic resonance has attracted extensive attention since it allows for great enhancement of local field intensity on the nanoparticle surface. In this paper, we make a systematic study on the excitation of localized surface plasmons of a graphene coated dielectric particle. Theoretical results show that both the intensity and frequency of the plasmonic resonant peak can be tuned effectively through modifying the graphene layer. Furthermore, high order localized surface plasmons could be excited and tuned selectively by the Laguerre Gaussian beam, which is induced by the optical angular orbital momentum transfer through the mutual interaction between the particle and the helical wavefront. Moreover, the profiles of the multipolar localized surface plasmons are illustrated in detail. The study provides rich potential applications in the plasmonic devices and the wavefront engineering nano-optics.

Using plasmonically generated carriers as redox equivalents

Abstract

Optical Device Based on a Nanopillar Array by the Pattern Transfer of an Anodic Aluminum Oxide Membrane.

A simple and convenient nanofabrication method is proposed to achieve nanopillar arrays by the pattern transfer of an anodic aluminum oxide membrane, profiting from the rapid and efficient preparation process and regular hexagonal lattice patterns of the anodic aluminum oxide template. The taper angle of the nanopillar is affected by the distribution of the vapor particles during the deposition process, which is highly dependent on the material and deposition power. Based on this method, a novel scheme employing aluminum nanopillar arrays is demonstrated to realize the color tuning feature by simply varying the thickness of the top dielectric layer within a large range. The nanopillar arrays are completely covered by the thick dielectric layer atop due to the great conformality of the atomic layer deposition method that is used for the dielectric deposition. In addition, the color devices present good angular insensitivity up to 45°, resulting from the excited localized surface plasmon resonance within the metallic patches. The simple fabrication method is of great advantage to produce periodic nanostructures over large areas, which are widely used in designs and verifications of optical metasurfaces for various applications, including optical communication, imaging, sensing, and so forth.

Resolving the Correlation between Tip-Enhanced Resonance Raman Scattering and Local Electronic States with 1 nm Resolution.

Low-temperature tip-enhanced Raman spectroscopy (TERS) enables chemical identification with single-molecule sensitivity and extremely high spatial resolution even down to the atomic scale. The large enhancement of Raman scattering obtained in TERS can originate from physical and/or chemical enhancement mechanisms. Whereas physical enhancement requires a strong near-field through excitation of localized surface plasmons, chemical enhancement is governed by resonance in the electronic structure of the sample, which is also known as resonance Raman spectroscopy. Here we report on tip-enhanced resonance Raman spectroscopy (TERRS) of ultrathin ZnO layers epitaxially grown on a Ag(111) surface, where both enhancement mechanisms are operative. In combination with scanning tunneling spectroscopy (STS), it is demonstrated that the TERRS intensity strongly depends on the local electronic resonance of the ZnO/Ag(111) interface. We also reveal that the spatial resolution of TERRS is dependent on the tip–surface distance and reaches nearly 1 nm in the tunneling regime, which can be rationalized by strong-field confinement resulting from an atomic-scale protrusion on the tip apex. Comparison of STS and TERRS mapping clearly shows a correlation between resonantly enhanced Raman scattering and the local electronic states at near-atomic resolution. Our results suggest that TERRS is a new approach for the atomic-scale optical characterization of local electronic states.

Silver nanoparticles in organic photovoltaics: Finite size effects and optimal concentration

Using Transfer Matrix method combined with Effective Medium Approximation as well as Finite-Difference Time-Domain calculations we have determined the light absorption in organic solar cells with silver nanoparticles embedded in the active layer. In calculations, we introduced additional terms in permittivity of the nanoparticles due to their finite size. Our results show, that the optimal nanoparticle concentration in such a system is about 30% greater than when assuming that the permittivity of the Ag nanoparticles equates that of a continuous silver layer. We have found, that although the absorption curves for both models (with and without the finite size contribution) are similar, the dominant mechanism of absorption enhancement is different. When assuming that the permittivity of silver nanoparticles is that of a continuous Ag layer, the light scattering on the surface of the nanoparticles seems to dominate over localized surface plasmon (LSP) excitation, while when considering the finite sizes of the nanoparticles the opposite is true.

Modifying graphene\u2019s lattice dynamics by hot-electron injection from single gold nanoparticles

Two-dimensional layered materials like graphene pave the way to advanced (opto-) electronic devices. Their extraordinary properties can be further controlled employing plasmonic nanostructures. The interplay between two-dimensional material and plasmonic nanostructures yields enhanced light focusing, large absorption cross sections, and hot-carrier generation due to the excitation and decay of localized surface plasmons. However, this interplay strongly depends on the particle’s environment and geometry mandating the investigation of individual structures. Here, we show that Raman spectroscopy reveals locally resolved information about charge transfer, temperature, and strain distribution of graphene sheets in the vicinity of individual spherical gold nanoparticles. Hot-electrons are efficiently injected into graphene under resonant excitation of the localized surface plasmons of the gold nanoparticle. Additionally, heating of the graphene sheet and its intrinsic strain can be separated and quantified. Hence, the presented analysis provides unprecedented insights into the underlying microscopic physics enabling better device design in the future.

Plasmonic Implanted Nanogrooves for Optical Beaming

Surface plasmon polaritons are electromagnetic surface waves, which, due to their nanoscale nature, are efficiently used for modifying an output of optical field through a metallic nanoslit, e.g., extraordinary optical transmission and beaming of light. Herein, the phenomenon of optical beaming by employing a regular array of semicylinder-shaped grooves around a nanoslit has been investigated based on numerical simulations. By analyzing the behavior of Poynting vectors in near surroundings of the slit, we have successfully demonstrated that grooves which are embedded on the layer at the exit side of the slit produce enhanced directionality of the output light than the unembedded ones. In case of semicylinder-shaped grooves, the calculated intensity of the output beam was 1.5-times, at near and far distances, higher than that of the grating grooves. Our analysis shows that positioning of the groove right at the exit of the slit is crucial for the enhancement of the beaming effect. This is due to the conversion of surface plasmon polaritons into a freely propagating field and the possible excitation of localized surface plasmons because of the presence of nanogroove. Furthermore, the proposed geometries are made of Aluminum, which is a plasmonic material and commonly applied for the fabrication of optical nanostructures. Manipulating of light (beaming, focusing/guiding, and splitting) by nanoslit can be beneficial to several applications such as nano-resolution optical imaging, sensors, and plasmonic circuits.

A broadband plasmonic light absorber based on a tungsten meander-ring-resonator in visible region

We present the design and numerical simulations of a broadband plasmonic light absorber (PLA) based on a tungsten meander-ring-resonator (MRR) structure in visible region. The proposed PLA is composed of a periodic MRR array and a continuous tungsten (W) film separated by a dielectric substrate. Simulation results indicate that the absorbance of our PLA is up to 99.9% at 538 THz, and it is over 90% from 370 to 854 THz across the whole visible region. The simulated electric field distributions reveal that the stronger broadband absorption is caused by the excitation of localized surface plasmon (LSP), propagating surface plasmon (PSP) and guide mode resonances. Further simulation indicates that designed PLA is polarization insensitive and has a wide angle for both transverse electric (TE) and transverse magnetic (TM) modes. In addition, the impact of the geometric parameters of the designed PLA on the absorption spectrum was also studied systematically. Owing to its superior performance, the proposed PLA based on tungsten MRR can be a potential application in thermal imaging, emissivity control and solar energy harvesting.

Photothermal properties of plasmonic nanoshell-blended nanofluid for direct solar thermal absorption

The excitation of localized surface plasmon at the metal nanoparticles can significantly enhance the absorption of solar energy. However, the absorption peak is sharp at the resonant frequency. To achieve a broadband absorption, the blended nanofluid formed by SiO2/Ag nanoshells of different core size and shell thickness is employed. The blended nanofluid has a good solar absorption property, whose extinction spectrum matches the solar spectrum well. The transient temperature response of the nanofluid is simulated. It is found that the photothermal performance of the solar thermal collector is related to the geometric parameters and operation conditions of the solar collector, and the optical and thermophysical properties of nanofluid. As the flow velocity increases, the outlet temperature is gradually reduced. But, the collector efficiency is increased since less heat is lost to the environment via convection as nanofluid flows fast in the channel. In order to obtain a large outlet temperature at high velocity, it can be considered to elongate the channel length. Due to the strong extinction properties of the blended nanofluid, the required volume fraction can be significantly reduced, only 1/10 of that of Ag nanofluid for an equal temperature increases.

Probing nanoscale interfaces with electrochemical surface-enhanced Raman scattering

Surface-enhanced Raman scattering (SERS) is a powerful tool for studying nanoscale molecule-metal interfaces across a range of electrochemical applications. SERS combines molecular-level information with a high degree of surface specificity, making it an ideal tool for understanding interfacial processes, from understanding how analytes and electrolytes organize near metal surfaces to following surface-mediated reactions in real time. However, because SERS relies on the excitation of localized surface plasmons, additional effects such as the production of hot charge carriers and photothermal heating can impact electrochemical SERS signals. These effects must also be considered when using SERS for quantitative electrochemical studies.

Simulation study of electron beam induced surface plasmon excitation at nanoparticles

Phenomenon of localized surface plasmon excitation at nanostructured materials has attracted much attention in recent decades for their wide applications in single molecule detection, surface-enhanced Raman spectroscopy and nano-plasmonics. In addition to the excitation by external light field, an electron beam can also induce the local surface plasmon excitation. Nowadays, electron energy loss spectroscopy (EELS) technique has been increasingly employed in experiment to investigate the surface excitation characteristics of metallic nanoparticles. However, a present theoretical analysis tool for electromagnetic analysis based on the discrete dipole approximation (DDA) method can only treat the case of excitation by light field. In this work we extend the DDA method for the calculation of EELS spectrum for arbitary nanostructured materials. We have simulated EELS spectra for different incident locations of an electron beam on a single silver nanoparticle, the simulated results agree with an experimental measurement very well. The present method then provides a computation tool for study of the local surface plasmon excitation of metallic nanoparticles induced by an electron beam.

Correlation Between Surface Charge Distribution and Circular Dichroism of Elementary Planar Nanoparticles

A correlation is observed between surface charge distributions and the circular dichroism (CD) signature of nanoparticles excited by circularly polarized waves. These surface charge distributions arise as a result of charge separation and depend on the polarization of the externally excited light. This correlation can be observed by deriving the surface charge distribution profile of excited localized surface plasmon polaritons (SPPs) in elementary metal nanoparticles under the influence of circularly polarized light. Nanoparticles with strong CD signatures are especially desired for sensing of chiral biomolecules as well as to aid in photochemical catalysis. We also found out that CD signatures can even be induced via angular rotation. This is true for elementary non-rotated nanoparticles which do not possess a CD signature. The use of elementary nanoparticles for sensing poses a huge advantage over complex nanostructures due to the ease of fabrication. The observed CD signature can also be validated in accordance with theory and simulation results.

Single-Photon-Single-Electron Transition for Interpretation of Optical Spectra of Nonspherical Metal Nanoparticles in Aqueous Colloidal Solutions

Noble metal nanoparticles—especially shape anisotropic particles—have pronounced resonances in the optical spectrum. These sensitive absorption modes attract great interest in various fields of application. For nonspherical particles, no analytic description of the absorption spectra according to the commonly used Mie theory is possible. In this work, we present a semi-empirical approach for the explanation of the optical spectra of shape anisotropic particles such as silver nanoprisms and gold nanorods. We found an interpretation of the optical absorption spectra which is based on a single-photon-single-electron transition. This model is in a better agreement with the basic assumptions of quantum mechanics than the electrodynamic model of a localized surface plasmon excitation. Based on microfluidically obtained Ag nanoprisms and Au nanorods with very high ensemble homogeneities, dependencies between the geometrical properties of the shape anisotropic noble metal nanoparticles and the spectral position of the longitudinal absorption mode could be derived, which show that the assumption of a composed relative permittivity and the inclusion of the Rydberg constant is sufficient to describe the optical properties of the shape anisotropic particles. Within the scope of the measuring accuracy, the calculations furthermore lead to the value of the refractive index of the particle-surrounding medium.

Tailorable Au Nanoparticles Embedded in Epitaxial TiO2 Thin Films for Tunable Optical Properties.

The unique property of plasmonic materials to localize light into deep sub-wavelength regime has greatly driven various applications in the field of photovoltaics, sensors, and photocatalysis. Here, we demonstrate the one-step growth of an oxide-metal hybrid thin film incorporating well-dispersed gold (Au) nanoparticles (NPs) with tailorable particle shape and diameters (ranging from 2 to 20 nm) embedded in highly epitaxial TiO2 matrix, deposited using pulsed laser deposition. Incorporation of Au NPs reduces the band gap of TiO2 and enhances light absorption in the visible regime owing to the excitation of localized surface plasmons. Optical properties, including the plasmonic response and permittivity, and photocatalytic activities of the Au-TiO2 hybrid materials are effectively tuned as a function of the Au NP sizes. Such optical property tuning is well captured using full-field simulations and the effective medium theory for better understanding of the physical phenomena. The tailorable shape and size of Au NPs embedded in TiO2 matrix present a novel oxide-metal hybrid material platform for optical property tuning and highly efficient plasmonic properties for future oxide-based photocatalytic sensors and devices.

Plasmon-Directed Photocatalytic Deposition of Platinum Onto Gold Nanorods Via Hot Electrons

Targeted, reductive photodeposition of catalytic metals via plasmonic hot electrons excited on an electrode is a promising, economical approach to manufacturing plasmon-sensitized photoelectrodes for catalysis applications. This work examines liquid-phase, anisotropic photodeposition of Pt(0) co-catalysts from chloroplatinic acid, Pt(IV), onto suspended Au nanorods under localized surface plasmon (LSP) excitation. Photochemical Pt(0) nucleation is initiated by plasmonic hot electrons, which migrate to the Au surface according to the plasmon polarity. In situ, time-resolved absorbance monitoring of the photochemical reaction elucidated Au nanorod surface functionalization with Pt(IV), Pt(0) growth kinetics under Au LSP excitation, and the evolving light-matter interactions. Energy dispersive spectroscopy (EDS) mappings show preferential Pt(0) deposition on the Au nanorod ends, consistent with the laser-induced LSP dipoles. Discrete dipole approximation (DDA) of Maxwell’s equations corroborated measured optical responses and allows a priori design of hot electron energetics. Electronic valence band structure of the Pt-functionalized Au nanorod was measured by x-ray photoelectron spectroscopy (XPS) and calculated by density functional theory (DFT) to enumerate the energy distribution of carriers accessible for surface chemistry. Together, these techniques and analyses accelerate development of plasmon-sensitized photoelectrodes for solar fuel generation. Figure 1

Investigation of optical properties by localized surface plasmon excitation of nanoparticle arrays in photodetectors

We investigate absorption in the active medium by localized surface plasmon excitation of metal nanoparticle arrays. Calculations show for each specific application of the photodetector, which size of the metal nanoparticles should be deposited on photodetector. We show that the power absorption in the active medium in the presence of silver nanoparticle arrays in a certain wavelength range is more than gold nanoparticle arrays. Presence of nanoparticle arrays on surface of active medium can lead to dependence of absorption on wavelength and distance from nanoparticle arrays. Absorption cross-section in active medium strongly depends on distance from nanoparticle array that should be considered in design of embedded semiconductor quantum dots in the active medium.

Leveraging coffee‐ring effect on plasmonic paper substrate for sensitive analyte detection using Raman spectroscopy

AbstractRaman spectroscopy has demonstrated immense promise as a molecular fingerprinting tool in biomedical diagnostics. However, the utility of conventional Raman scattering for ultrasensitive measurements of biofluids is limited by intrinsically weak signals and has spurred advances in and wider applications of plasmon‐enhanced measurements. Here, we propose a label‐free methodology that leverages drop coating deposition on a silver ink‐based plasmonic paper substrate with tunable hydrophobic attributes to combine two distinct sources of enhancement, namely, solute preconcentration and excitation of localized surface plasmons. The facile modulation of the hydrophobicity of the plasmonic silver paper facilitates investigations into the coffee‐ring effect that results from the interplay of contact line pinning, solvent evaporation, and capillary flow. We show that the Raman spectra acquired from the hydrated ring deposits show clear enhancement beyond that obtained from surface‐enhancement owing to the presence of the silver nanofilm. In light of the superior sensitivity and lack of substantive sample preparation requirements, our findings open the door for a complementary low‐cost paper‐based analytical device for molecular sensing.