Metal Island Films Research Articles

Influence of drying treatment to electrochemically roughened Ag substrates on the corresponding surface-enhanced Raman scattering performances

For obtaining metal-island films on substrates with activity of surface-enhanced Raman scattering (SERS), a controllable and reproducible surface roughness can be easily generated by using electrochemical oxidation–reduction cycle (ORC) procedures. However, different preparation procedures could significantly change their corresponding SERS activities. In this study, SERS-active Ag substrates were prepared by using triangular-wave ORC procedures in 0.1 M KCl solutions. Before the adsorptions of probe molecules on these Ag substrates one substrate was further dried in a vacuum-dryer. Interestingly, the SERS activity of this dried Ag substrate is significantly reduced due to this additional treatment. Experimental results indicate that this phenomenon can be ascribed to the correspondingly significant decrease in content of Cl-containing complexes formed on the interface of the roughened Ag metal.

Induced Surface Enhancement in Coral Pt Island Films Attached to Nanostructured Ag Electrodes

Coral Pt islands films are deposited via electrochemical reduction on silica-coated nanostructured Ag electrodes. From these devices surface-enhanced (resonance) Raman [SE(R)R] signals of molecules exclusively attached to Pt are obtained with intensity up to 50% of the value determined for Ag. SE(R)R spectroscopic investigations are carried out with different probe molecules, silica-coating thicknesses, and excitation lines. Additionally, field enhancement calculations on Ag-SiO(2)-Pt support geometries are performed to elucidate the influence of the Pt island film nanostructure on the observed Raman intensities. It is concluded that the nonperfect coating of the Pt island film promotes the efficiency of the induced Pt SER activity. Comparison with similar measurements on Ag-SiO(2)-Au electrodes further suggests that the chemical nature of the deposited metal island film plays a minor role for the SE(R)R intensity.

Tailoring optical and non-optical properties of interference coating materials through the explicit use of small-scale optical inhomogeneities

Abstract Although optical coating deposition techniques have been perfected over decades to prepare optically homogeneous dense coatings with smallest surface roughness, nanostructuring of optical coatings has proven as an effective mechanism to further enhance their performance while reducing their thickness in special cases. Therefore, nanostructure effects can be tackled as additional degrees of freedom for coating design, and can even lead to useful property combinations that are inaccessible to ‘classical’ coatings prepared on the basis of the traditionally available coating materials. Examples include metal island films as building blocks for spectrally selective absorber coatings for color management or solar energy conversion purposes, as well as motheye structures for antireflection coatings and the combined optimization of optical and non-optical coating properties.

Computer simulation of surface-enhanced Raman scattering in nanostructured metamaterials

The simulation of local field fluctuations and surface-enhanced Raman scattering in percolation systems at the percolation threshold is described. An approximate real-space renormalization group method was used in the simulation. It allows one to radically reduce the computation time compared to an exact calculation and to obtain detailed information about the electromagnetic field. The local fields in real macroscopic systems can be calculated by using this approximation. A computer simulation of the local fields in metal island (percolation) films has been performed by the developed method. The calculation has confirmed the existence of giant local field fluctuations. In turn, the local electric field excites Raman scattering. The local fields of surface-enhanced Raman scattering have been calculated for the first time. The dependence of the Raman scattering enhancement factor on the reference frequency and Stokes shift has been derived. An experimental observation of this dependence could be considered as a confirmation of the electromagnetic nature of the enhancement.

Design and production of bicolour reflecting coatings with Au metal island films

Optical properties of metal island films (MIFs) can be combined with interference of dielectric coatings. A set of multilayer designs containing metal clusters reflecting different colours from front and back side of the coating was obtained by numerical optimization. The chosen designs presenting the range of feasible colours were deposited by electron beam evaporation. Spectrophotometric and ellipsometric measurements verified that the produced coatings present an excellent agreement with the optical performance calculated from the designs. Numerical optimization was verified as a useful method in designing of coatings containing MIFs. This approach can ease the implementation of metal clusters into multilayer designs and broaden the applications of MIFs.

Erratum to: “Calculation of the Electronic Structure of Metal Island Films”

Erratum to: “Calculation of the Electronic Structure of Metal Island Films”

Aligned metallic nanoparticles on rippled surfaces: Optical characterization using generalized ellipsometry

Oblique-angle deposition of metallic island films onto self-organized rippled surfaces results in arrays of particles and wires with characteristic dimensions below 50nm. Films of the noble metals exhibit distinct optical properties due to localized plasmon resonances. Here the films are characterized using generalized spectroscopic ellipsometry. Due to the small characteristic dimensions we can describe the optical properties using an effective medium approach. The dielectric properties are highly anisotropic and a biaxial dielectric tensor description is required. The plasmonic resonances provide a means to tune the form birefringence by adjusting the metal fraction, from aligned nanoparticles with anisotropic localized plasmon resonances, to arrays of nanowires with orthogonal metallic and dielectric properties. The deposition of the particles on one side of the ripple ridges causes additional anisotropy that shows a 2-fold symmetry upon rotation in the substrate plane. This is associated with a longitudinal plasmon resonance in the out-of-plane direction.

Plasmon Enhanced Spectroscopy of N,N′-Dialkylquinacridones Used as Codopants in OLEDs

Plasmon-enhanced Raman scattering and plasmon-enhanced fluorescence of the two molecules N,N′-dimethylquinacridone (DMQA) and N,N′-diisoamylquinacridone (DIQA) used as codopants in OLEDs (with improved stability) are reported. The work includes a complete vibrational characterization using Raman and infrared spectra supported by DFT calculations. Plasmon enhancement is achieved using silver and mixed Ag/Au nanostructures: colloids and metal island films, supporting localized surface plasmon resonances (LSPR). However, fine-tuning of the experimental conditions is necessary to attain surface-enhanced (resonance) Raman scattering (SERS/SERRS) of the two molecules with similar structures. SERRS spectra of DMQA are obtained on silver colloids and from a Langmuir–Blodgett (LB) monolayer deposited onto silver island films (SIF). High quality SERRS spectra of DIQA were only obtained from LB layers on mixed Ag/Au island films. Using spacer LB layers of arachidic acid (AA) to separate the fluorophore from the meta...

Calculation of the electronic structure of metal island films

The aim of our paper is to study the electronic structure of metal island films as examples of a nanosystem. Because the electronic structure is discrete, the charge exchange between atomic particles and nanosystems exhibits quantum-dimensional effects. We calculated the electronic structure of thin island films, which is required for solving and analyzing the problem of charge exchange with the film. The typical island dimensions are also estimated; in the case of dimensions exceeding them, the discreteness of the electronic structure becomes unimportant and quantum-dimensional effects disappear.

Effective permittivity of the system of metal nanoislands in strong electric fields

The effect of the electric field on the value and sign of the low-frequency effective permittivity of metal island films is studied. It is shown that the permittivity in island metal films can be both positive and negative. The permittivity of some samples changed sign with the polarity of the applied electric field. Film polarization mechanisms are considered.

Transmission through Ag/Organic Multilayers Using Continuous and Island Metal Films

We present the results of transmission spectrum measurements of Ag/tetraphenyldiphenyldiamine periodic multilayers, as well as Ag/SiO2 in the visible and near IR spectral range. Using continuous silver films, these one-dimensional multilayers transmit visible light in controllable bands and stop IR light. Using island metal films, surface plasmon modes are excited, which exhibits broad absorption features covering the entire visible spectral range. This work successfully extends the discussion of metal-dielectric one-dimensional photonic crystals to metal-organic cases and exhibits the linear optical properties of surface plasmon modes at the island metal/organic interface.

Electron exchange between atomic particle and thin metal island films

The resonant charge transfer between H − ion and thin island films was investigated by the instrumentality of the wave-packet propagation method. Under the fixed island film size the ion level width, which characterizes the efficiency of electron transfer, is found to decrease exponentially with ion–surface distance increase. On the other hand the ion level width shows quantum-size effect when the island film radius is changing. The quantum-size effect can be verified experimentally by measuring the yield of charged atomic particles scattered or sputtered from thin metal island films. The necessary conditions for the quantum-size effect observation are low projectile velocity (under 0.01 a.u.) and small island film radius (under 100 a.u.). The thin island films can be obtained by means of electron stimulated desorption from dielectric surfaces.

Optical fiber sensor based on oblique angle deposition

The technique of oblique angle deposition has been extended to the fabrication of nanostructured metal coatings on the tips of standard silica optical fibers by thermal evaporation. The coatings are initiated as metal island films, which grow into extended rodlike structures as the deposition continues. The nanorod coatings demonstrate excellent surface-enhanced Raman scattering performance with variability of less than 10% as shown by direct measurements off the fiber tip with thiophenol as a test analyte. However, in the remote sensing configuration, the nanorod structures perform no better than thin metal island films. This appears to be mainly due to reduced transmission when nanorod lengths exceed ~100 nm. Moreover, the variability of remote measurements is increased to 18%. This is believed to be due to variations in coupling efficiency.

Gradient silver nanoparticle layers in absorbing coatings—experimental study

Metal island films show a characteristic absorption peak related to the surface plasmon resonance of free electrons. This kind of film can be used in absorbing coatings, together with dielectric layers. Such absorbing multilayer coatings, with and without the gradient of the silver mass thickness in metal island films throughout the coating, have been deposited by electron beam evaporation. It is shown experimentally that coatings with a gradient in the mass thickness of silver nanoparticles have higher absorption than equivalent nongradient coatings with the same total mass thickness of silver nanoparticles.

Optical properties of gold island films—a spectroscopic ellipsometry study

Metal island films of noble metals are obtained by deposition on glass substrates during the first stage of evaporation process when supported metal nanoparticles are formed. These films show unique optical properties, owing to the localized surface plasmon resonance of free electrons in metal nanoparticles. In the present work we study the optical properties of gold metal island films deposited on glass substrates with different mass thicknesses at different substrate temperatures. The optical characterization is performed by spectroscopic ellipsometry at different angles of incidence and transmittance measurements at normal incidence in the same point of the sample. Fitting of the ellipsometric data allows determining the effective optical constants and thickness of the island film. A multiple oscillator approach was used to successfully represent the dispersion of the effective optical constants of the films.

Ultra thin films of gadolinium deposited by evaporation in ultra high vacuum conditions: Composition, growth and morphology

Ultra-thin gadolinium films with thicknesses between 8 and 101Å were deposited on AT-cut crystalline quartz substrates under ultra high vacuum conditions, and subsequently subjected to composition and morphologic characterization through X-ray photo-spectroscopy analysis and atomic force microscopy. Oxygen contamination is found on the samples, and its amount is estimated in terms of the thickness of an oxygen layer over the gadolinium films after subtracting the contribution to the XPS spectra of the underlying background. Atomic force microscope pictures provide evidence of having metal island films, with two growing regimes: the Volmer–Weber mode for the thinner films considered and the Stranski–Krastanov growing mode for the thicker ones. From evaluation of the sticking coefficient, the shape of the islands is approximated in terms of oblate spheroid caps and variation of the contact angle with film mass thickness is reported.

Surface enhanced infrared spectroscopy using gold nanoantennas

AbstractThe sensitivity of infrared (IR) vibration spectroscopy can be enhanced by several orders of magnitude if plasmonic electromagnetic nearfield enhancement is exploited. For maximum enhancement the plasmonic resonance needs to be strong, which cannot be achieved by randomly grown metal island films that on average may show already signal enhancement of the order of 1000. Metal nanowires may give sufficiently strong antenna‐like plasmonic resonances in the IR that can be adjusted to the molecular vibration frequencies of interest via the wire length. With individual gold nanowires we obtained vibration‐signal enhancement up to 500,000 for molecular monolayers adsorbed on gold nanowires. The already obtained enhancement is not a limit. Since antennae coupled via nanogaps should enable strong electromagnetic nearfield enhancement in these gaps, respective arrays would be ideal for surface enhanced IR spectroscopy. First experiments prove the tendency of increasing vibration‐signal enhancement with decreasing gap size.

Photoelectron emission from island metallic sodium films during the excitation of localized plasmon resonances

The photoelectron emission from island sodium films is studied under the action of radiation that is resonant to the collective electron excitations in the nanoparticles forming a film. Noticeable deviations from the Fowler law and an increase in the photoelectron yield are detected. The dependences of the photoeffect efficiency from these films on their structural parameters, the polarization vector, and the angle of radiation incidence are obtained.

Optical and structural characterization of silver islands films on glass substrates

Metal island films (MIFs) of Ag on glass substrates were fabricated by the e-beam evaporation technique. The dependence of the surface plasmon (SP) absorption properties on the deposition mass thickness and substrate temperature was quantified. The structural and optical characterization of the MIFs, obtained using spectrometry, grazing-incidence small-angle X-ray scattering (GISAXS) and atomic force microscopy (AFM) evidences the evolution of SP characteristics depending on the fabrication parameters: the red shift of the absorption peaks with the increase of deposition thickness accompanied by peak widening and the blue-shift of peaks with the increase of deposition temperature followed by the peak narrowing. These findings were explained by the differences in the concentration, shape and size of the obtained silver islands.

Effect of γ-irradiation on the frequency-independent parameters of an equivalent circuit for two-dimensional island platinum films

Four sets (A, B, C and D) of two-dimensional island platinum films [2D-I(Pt)Fs] were prepared by the thermal evaporation technique. The mass thicknesses for the films of such sets are 1, 5, 10 and 20 A, respectively. The frequency-independent parameters of one of the equivalent circuit for island metal films in general are R b, R g and C g where R b is the resistance of the islands themselves while R g is the resistance that accompanies the transfer of electrons across the gaps among islands and C g is the capacitance that results from the separated metallic islands. The least-square values of R b, R g and C g for our films were deduced via a computerized analysis. The stabilized films were exposed to γ-rays at doses 100, 200, 300, 500 and 700 Gy using 137Cs (0.662 MeV) radiation source of dose rate 0.5 Gy/min. It was found that (1) For any particular mass thickness: (a) R b and R g decreases with the increase in the dose of γ-rays while C g increases (b) the absolute value of the fractional change in R b, R g and C g increases with the increase in dose. (2) For any particular dose the increase in the fractional change in R b, R g and C g becomes more pronounced when the mass thickness increases. Qualitative interpretation for our results was given on the ground that γ-rays changed the island’s shape from spherical to prolate spheroid one and this has been checked experimentally via imaging the films by Atomic Force Microscope before and after γ-irradiations.