Optical Excitation Of Surface Plasmons Research Articles

Enhancement of Terahertz Radiation by Surface Plasmons Based on CdTe Thin Films.

Terahertz (THz) time-domain spectroscopy (TDS) is a powerful tool used to characterize the surface/interface of materials, and semiconductor/metal interfaces can generate THz emission through ultrafast optical excitation, which can be further improved through the optical excitation of surface plasmons. Here, we assembled cadmium telluride (CdTe) on an AuAg alloy (Au25Ag75, wt.%) substrate and obtained five times stronger THz emission compared with silicon substrate, and found that the enhancement can be tuned by controlling the thickness of the semiconductor materials and plasmonic metal substrates. We believe that our results not only promote the development of THz emission enhancement, but also provide a straightforward way of producing small, thin, and more efficient terahertz photonic devices.

Plasmon-Driven C–N Bond Cleavage Across a Series of Viologen Derivatives

The optical excitation of surface plasmons leads to the generation of highly enhanced nanoscale local fields and an abundance of harvestable hot carriers. When certain analytes are positioned within these unique environments, surface plasmons may be able to induce chemical reactions that are energetically unfavorable under standard conditions. Sometimes, the plasmonic environments can initiate entirely new reaction pathways for the chemical adsorbates. Here, we investigate the nature of plasmon-driven reactions on three viologen derivatives: methyl viologen, ethyl viologen, and benzyl viologen. Viologens have traditionally been employed as excellent redox agents due to their ability to reversibly stabilize additional electrons in their molecular structures. However, by using surface-enhanced Raman spectroscopy, we were able to directly observe a C–N bond cleavage on benzyl and ethyl viologen to form 4,4′-bipyridine on the surface of gold film-over-nanosphere substrates. Surprisingly, methyl viologen does ...

Optical excitation of surface plasmons and terahertz emission from metals

We propose a microscopic theory of terahertz (THz) radiation generation on metal gratings under the action of femtosecond laser pulses. In contrast to previous models, only low-frequency currents inside the metal are considered without involving electron emission. The presented model is based on plasmon-enhanced thermal effects and explains the resonant character of optical-to-THz conversion giving an adequate estimation for the full signal energy. Numerical modeling reproduces specific experimental features like delayed character of THz response and low conversion efficiency when the grating depth is too large.

Surface-Plasmon-Driven Hot Electron Photochemistry.

Visible-light-driven photochemistry has continued to attract heightened interest due to its capacity to efficiently harvest solar energy and its potential to solve the global energy crisis. Plasmonic nanostructures boast broadly tunable optical properties coupled with catalytically active surfaces that offer a unique opportunity for solar photochemistry. Resonant optical excitation of surface plasmons produces energetic hot electrons that can be collected to facilitate chemical reactions. This review sums up recent theoretical and experimental approaches for understanding the underlying photophysical processes in hot electron generation and discusses various electron-transfer models on both plasmonic metal nanostructures and plasmonic metal/semiconductor heterostructures. Following that are highlights of recent examples of plasmon-driven hot electron photochemical reactions within the context of both cases. The review concludes with a discussion about the remaining challenges in the field and future opportunities for addressing the low reaction efficiencies in hot-electron-induced photochemistry.

Surface Plasmon Scattering in Exposed Core Optical Fiber for Enhanced Resolution Refractive Index Sensing.

Refractometric sensors based on optical excitation of surface plasmons on the side of an optical fiber is an established sensing architecture that has enabled laboratory demonstrations of cost effective portable devices for biological and chemical applications. Here we report a Surface Plasmon Resonance (SPR) configuration realized in an Exposed Core Microstructured Optical Fiber (ECF) capable of optimizing both sensitivity and resolution. To the best of our knowledge, this is the first demonstration of fabrication of a rough metal coating suitable for spectral interrogation of scattered plasmonic wave using chemical electroless plating technique on a 10 μm diameter exposed core of the ECF. Performance of the sensor in terms of its refractive index sensitivity and full width at half maximum () of SPR response is compared to that achieved with an unstructured bare core fiber with 140 μm core diameter. The experimental improvement in , and therefore the detection limit, is found to be a factor of two (75 nm for ECF in comparison to 150 nm for the large core fiber). Refractive index sensitivity of 1800 nm/ was achieved for both fibers in the sensing range of aqueous environment (1.33–1.37) suitable for biosensing applications.

Plasmon-enhanced terahertz emission from a semiconductor/metal interface

Terahertz emission by ultrafast optical excitation of semiconductor/metal interfaces strongly depends on the strength of the depletion-field. Here, we report on the strong enhancement of the emission after optical excitation of surface plasmons at these interfaces. The enhancement is caused by the plasmonic localization of the pump light near the metal surface, where the depletion-field is the strongest. Compared to the case where no surface plasmons are excited, a terahertz field enhancement of more than an order of magnitude is obtained for a particular thickness of cuprous oxide layer on gold, where localized surface plasmons are excited at the interface.

Molecular Plasmonics for Biology and Nanomedicine

The optical excitation of surface plasmons in metal nanoparticles leads to nanoscale spatial confinement of electromagnetic fields. The confined electromagnetic fields can generate intense, localized thermal energy and large near-field optical forces. The interaction between these effects and nearby molecules has led to the emerging field known as molecular plasmonics. Recent advances in molecular plasmonics have enabled novel optical materials and devices with applications in biology and nanomedicine. In this article, we categorize three main types of interactions between molecules and surface plasmons: optical, thermal and mechanical. Within the scope of each type of interaction, we will review applications of molecular plasmonics in biology and nanomedicine. We include a wide range of applications that involve sensing, spectral analysis, imaging, delivery, manipulation and heating of molecules, biomolecules or cells using plasmonic effects. We also briefly describe the physical principles of molecular plasmonics and progress in the nanofabrication, surface functionalization and bioconjugation of metal nanoparticles.

Scattering matrix method for optical excitation of surface plasmons in metal films with periodic arrays of subwavelength holes

We present the formulation of a scattering matrix method for the study of light-scattering properties of metal films. The method is employed for the study of the optical excitation of surface plasmons in a gold film of 15-230 nm thickness, patterned periodically with subwavelength nanoholes. The gold film is placed on a thick SiO2 wafer, and the nanoholes as well as the top side of the gold film are filled with H2O. Light is incident on the gold film from either the SiO2 or the H2O side. The extinction and reflectance spectra of the system, as well as the electromagnetic field distributions at certain characteristic wavelengths, are calculated. The extinction spectra show, depending on system parameters, one or several peaks in the visible wavelength range. The extinction peaks are found to be caused by surface plasmons. A simple model based on the dispersion relation for surface plasmons in an unperforated gold film is shown to predict the peak positions of the extinction for thick perforated films very well. Even for thin films, this simple model, which includes coupling of surface plasmons on both surfaces of the film, predicts peak positions of the extinction well if the hole diameter is small enough. As the hole diameter increases, the extinction peaks of thin films show redshifts. Extinction peaks caused by surface plasmons at the SiO2/Au interface in thick films exhibit strong redshifts when the film thickness is decreased. However, the extinction peaks caused by surface plasmons at the H2O/Au interface in thick films show a completely different behavior. In this case, the extinction peaks do not move noticeably when the film thickness is decreased. Instead, they are weakened and finally disappear. It is also found that each extinction peak is accompanied by an extinction dip and that a reflectance dip is located in the wavelength between the extinction peak and the dip. This arrangement of an extinction peak, a reflectance dip, and an extinction dip is a general property of the surface-plasmon excitation. The calculated electromagnetic field distributions in both thick and thin films show clearly the signature of the excitation of surface plasmons at the extinction peaks, the extinction dips, and the reflectance dips. In thick films with small holes, the electric-field strength in the vicinity of the holes is weak at wavelengths for which surface plasmons are excited. In contrast to this, for thin films at the surface-plasmon excitations, a much stronger electric field is seen in the vicinity of the holes. (Less)

Plasmonics: An Emerging Field Fostered by Nano Letters

While studies of surface plasmons on metals have been pursued for decades, the more recent appearance of nanoscience has created a revolution in this field with "Plasmonics" emerging as a major area of research. The direct optical excitation of surface plasmons on metallic nanostructures provides numerous ways to control and manipulate light at nanoscale dimensions. This has stimulated the development of novel optical materials, deeper theoretical insight, innovative new devices, and applications with potential for significant technological and societal impact. Nano Letters has been instrumental in the emergence of plasmonics, providing its readership with rapid advances in this dynamic field.

Surface Plasmon Mediated Interference Phenomena in Low-Q Silver Nanowire Cavities

Optical excitation of surface plasmons in wet-chemically grown monocrystalline silver nanowires ( approximately 100 nm diameter and up to a few tens of micrometers length) is studied by broadband imaging spectroscopy. Surface plasmons excited by an incident light beam in the so-called Kretschmann-Raether configuration give optical interference phenomena in the spectral domain. These spectral oscillations are interpreted in terms of Fabry-Perot cavity modes for surface plasmons in silver nanowires and allow for a direct experimental determination of the surface plasmon group velocity and cavity losses.

A spectroscopic investigation of the shape dependency of gold nanoparticles grown on roughened surfaces

We present an investigation of the optical excitation of surface plasmons on Au films deposited on roughened surfaces by using a glancing angle deposition technique. By adjusting the deposition parameters of calcium fluoride and Au thin films, the spectral position of the surface plasmon resonances can be shifted through the green and into the near infrared region. In particular, we find that a rougher surface with obliquely deposited Au produces distinct spheroid-shaped nanoparticles (NPs). This results in stronger resonances with narrower linewidths, whereas smoother films result in broad red-shifted absorption. Imaging with an atomic force microscope and a scanning electron microscope provides information of NP geometry which are used as inputs for theoretical simulations of the observed spectra. The consequence of geometry distributions and inter-particle interactions are discussed. The ability to control the shape, therefore the optical response, of Au NPs over an arbitrarily large active area is of paramount importance in nano-science, especially in biological sensing applications and surface enhanced Raman scattering.

Modeling of optical and geometrical data of Al thin films on GaAs

In this paper, we show how optical excitation of surface plasmons (SPs) can be used to obtain optical and geometrical parameters of specific layers in multilayered thin film systems. The optimum coupling phenomenon between incoming p-polarized light and SPs appears as a minimum in the reflectance that is calculated using a standard matrix formalism. The sensitive dependence of the reflectance minimum on optical and geometrical parameters suggests that they can be determined accurately by fitting the measured attenuated total reflectance (ATR) to the matrix-calculated reflectance using the Simplex minimization method. The procedure is applied to the multilayered system: Prism/Air gap/Al-oxide/Al/GaAs. At fixed incident light wavelength, the fitting parameters are the Al-oxide optical constant and the thickness of the air gap, Al-oxide and Al layers. Fortran codes are implemented for the reflectance calculations and the fitting procedures. The results show that the theoretical reflectance fits well the measured ATR at 633-nm wavelength. Moreover, the modeled Al-oxide optical constant at this wavelength agrees well with the literature. However, the reflectance fits are less good at 590- and 458-nm wavelengths and their modeled Al-oxide optical constants show a dispersion effect in disagreement with the literature. The modeled geometrical parameters are consistent with the nominal values.

Surface Plasmons for Probing Optical Data of Multi- Layered Thin Films

In this paper, we show how optical excitation of surface plasmons (SPs) can be used to obtain optical and geometrical parameters of specific layers in multi-layered thin film systems. The optimum coupling phenomenon between incoming p-polarized light and SPs appears as a minimum in the reflectance that is calculated using a standard matrix formalism. The sensitive dependence of the reflectance minimum on optical and geometrical parameters suggests that they can be determined accurately by fitting the measured attenuated total reflectance (ATR) to the matrix-calculated reflectance using the Simplex minimization method. The procedure is applied to the multi-layered system: Prism / Air gap / Al-oxide / Al / GaAs. At fixed incident light wavelength, the fitting parameters are the Al-oxide optical constant and the thickness of the air gap, Al-oxide and Al layers. Fortran codes are implemented for the reflectance calculations and the fitting procedures. The results show that the theoretical reflectance fits well the measured ATR at 633 nm wavelength. Moreover, the modeled Al-oxide optical constant at this wavelength agrees well with the literature. However, the reflectance fits are less good at 590 nm and 458 nm wavelengths and their modeled Al-oxide optical constants show a dispersion effect in disagreement with the literature. The modeled geometrical parameters are consistent with the nominal values.

Imaging of Cell/Substrate Contacts of Living Cells with Surface Plasmon Resonance Microscopy

We have developed a new method for observing cell/substrate contacts of living cells in culture based on the optical excitation of surface plasmons. Surface plasmons are quanta of an electromagnetic wave that travel along the interface between a metal and a dielectric layer. The evanescent field associated with this excitation decays exponentially perpendicular to the interface, on the order of some hundreds of nanometers. Cells were cultured on an aluminum-coated glass prism and illuminated from below with a laser beam. Because the cells interfere with the evanescent field, the intensity of the reflected light, which is projected onto a camera chip, correlates with the cell/substrate distance. Contacts between the cell membrane and the substrate can thus be visualized at high contrast with a vertical resolution in the nanometer range. The lateral resolution along the propagation direction of surface plasmons is given by their lateral momentum, whereas perpendicular to it, the resolution is determined by the optical diffraction limit. For quantitative analysis of cell/substrate distances, cells were imaged at various angles of incidence to obtain locally resolved resonance curves. By comparing our experimental data with theoretical surface plasmon curves we obtained a cell/substrate distance of 160 ± 10 nm for most parts of the cells. Peripheral lamellipodia, in contrast, formed contacts with a cell substrate/distance of 25 ± 10 nm.

Optical excitation of surface plasmons: An introduction

Abstract Beginning from low level concepts the basic understanding for the optical excitation of surface plasmons is developed. Prism coupling using the attenuated total reflection technique is discussed as well as the less traditional grating coupling technique. A brief discussion of some recent developments using twisted gratings is also presented. Finally a short summary of the potential device applications is given.

Surface plasmon enhanced transient thermoreflectance

Ahct. It is shown that optically excited surface plasmons can k used for measurements of the surface temperature of a metal with nanosecond the resolution. This method is closely related to transient thermoreflectance, but its sensitivity is considerably higher. We give a survey on the mechanisms involved, briefly discussing the dependence on the sample properties. Experimental confirmation of the proposed sensitivity enhancement as well as the time resolution is presented. PACS: 07.60, 42.80, 61.80 Transient thermoreflectance is a well established technique for observing temperature changes at a metal surface with high temporal resolution [I, 21. It employs as a probe the thermally induced change in the optical constants of the metal by measuring the intensity of a Iight beam being reflected at the surface under consideration. However, since the optical constants of the metal are not very sensitive to the temperature, signals obtained are usually small, and enhancement of the sensitivity of the method would be desirable. In this paper we demonstrate a modified transient thermoreflectance setup using an attenuated total reflectance technique. When the conditions for optical excitation of surface plasmons are fulfilled, the thermoreflectance signal becomes resonantly enhanced, thus increasing the sensitivity of the measured light intensity to changes of the surface temperature. We elaborate on the feasibility of this effect for performing fast high sensitivity measurements of temperature changes at a metal surface. 1. Theory Optical excitation of surface plasmons by means of the socalled Kretschmann setup has been described by many authors [3-51: the sample is formed by a metal fdm with a thickness of several tens of nanometers, evaporated onto the base of a glass prism. The surface to be studed is the interface between the metal and the vacuum. On illu

Optical excitation of surface plasmons

Optical excitation of surface plasmon polaritons provides a simple method for localizing an electromagnetic field at an interface. This field, and hence the optical response of the interface, is very sensitive to small changes in the dielectric properties of a region very close to the interface. Because the surface plasmon polariton is resonantly excited there is also substantial field enchancement at the surface. The sensitivity to small changes at the surface as well as the field enhancement have recently produced a revival of interest in this field and this article is aimed at briefly reviewing this revival and examining potential further development.

“Fresnelian” sensors

The title “Fresnelian” sensors in this work indicates sensors in which the conversion of non-electrical quantities into electrical ones is based on the light reflection and refraction at the interface between optical media. The detection and determination of the non-electrical quantity in these sensors consists of electrical measurement of the reflectance by use of standard semiconductor devices. Conversion is possible of all those variables which act either on the refractive index of the substance in contact with the sensor or on the light incident angle or on the flux of the so called evanescent wave. Optical excitation of surface plasmons in thin metallic films and the changes in the plasmon resonance due to their absorption on the surface can also be used as a sensor effect. The general analysis, supported by the examples previously elaborated indicates that on the basis of the effects mentioned many new types of sensor can be designed.

Optical excitation of surface plasmons on Ag based alloys

Nous avons etudie les proprietes optiques d’alliages dilues Ag1-xNix (x 0,15) par excitation des plasmons de surface par reflexion totale attenuee. Les echantillons sont prepares par pulverisation cathodique radiofrequence et caracterises par microscopie electronique de transmission, fluorescence X et sonde ionique. Les courbes de dispersion des plasmons de surface ont ete analysees en liaison avec les niveaux lies virtuels qui peuvent exister dans le cas d’impuretes d dans une matrice s-p. Cette analyse nous a permis d’evaluer l’energie moyenne de ce niveau lie virtuel a 2,2 eV et sa largeur a 0,35 eV.

Preparation and characterization of opto-electrochemical Ag/Al composite electrodes

We describe the preparation of a opto-electrochemical electrode designed for in-situ studies of the metal-electrolyte interface by optical excitation of surface plasmons up to the UV region. The samples are very thin Ag-layers evaporated onto Al films on quartz substrates under UHV conditions to avoid alumina formation. SIMS and transmission electron microscope measurements show the continuous epitaxial growth of the 5 nm Ag layers on the alumina free Al film. The stability of the system in air and in the electrolyte has been tested optically and electrochemically.