V. Zaporojtchenko

Design of a Perfect Black Absorber at Visible Frequencies Using Plasmonic Metamaterials

The design and fabrication of a plasmonic black absorber with almost 100% absorbance spanning a broad range of frequencies from ultraviolet (UV) to the near infrared (NIR) is demonstrated. The perfect plasmonic absorber is achieved by a combination of a metal film with suitable metal/dielectric nanocomposites. Our fabrication technique is simple, versatile, cost-effective, and compatible with current industrial methods for solar absorber production.

Plasmonic properties of Ag nanoclusters in various polymer matrices

Nanocomposite films containing Ag nanoparticles embedded in a polymer matrix of Teflon AF, poly(methyl methacrylate) (PMMA) and Nylon 6 were prepared by vapour phase co-deposition in high vacuum. A large variation of the particle plasmon resonance frequency in the visible region was obtained by increasing the Ag volume fraction from 4-80%. The metal volume fraction was measured by energy dispersive x-ray spectrometry (EDX) and the film thickness was measured by surface profilometry. The position, width and strength of the plasmon resonance depend strongly on the metal filling factor, cluster size and interparticle distance. The microstructure of the nanocomposites (shape, size, size distribution and interparticle separation of metal clusters) was determined by transmission electron microscopy. The effect of the surrounding dielectric medium on the optical properties of nanocomposites was investigated by comparing the Teflon AF/Ag, PMMA/Ag and Nylon/Ag composites.

Tunable multiple plasmon resonance wavelengths response from multicomponent polymer-metal nanocomposite systems

A method of vapor phase codeposition has been used at elevated target temperature coupled with selective masking technique to produce a multicomponent optical material with seven different ultraviolet-visible optical active planes. Such a system consists of different nanocomposites of Teflon AF/Ag, Teflon AF/Au, and Teflon AF/Cu with sharp interfaces. The fabricated system has regions of single nanocomposite plane together with multilayer structures facilitating tunable multiple particle plasmon resonance wavelength response from a single system. Distinct double and triple plasmon wavelength resonance absorptions could be obtained from such interfaces forming multilayers of either two or three nanocomposite structures.

Physico-chemical and antimicrobial properties of co-sputtered Ag?Au/PTFE nanocomposite coatings

In this work, we used co-sputtering of noble metals together with polytetrafluorethylene (PTFE) as a method for producing antibacterial metal/polymer nanocomposite coatings, where the precious metals are only incorporated in a thin surface layer. Moreover, they are finely dispersed as nanoparticles, thus saving additional material and providing a very large effective surface for metal ion release. Nanocomposite films with thickness between 100 and 300 nm were prepared with a wide range of metal filling between 10 and 40%. The antimicrobial effect of the nanocomposite coatings was evaluated by means of two different assays. The bactericidal activity due to silver release from the surface was determined by a modification of conventional disc diffusion methods. Inhibition of bacterial growth on the coated surface was investigated through a modified proliferation assay. Staphylococcus aureus and S. epidermidis were used as test bacteria, as these species commonly cause infections associated with medical polymer devices. The antibacterial efficiency of the coatings against different bacteria was demonstrated at extremely small noble metal consumption: Au: ~1 mg m−2 and Ag: ~0.1 g m−2. The maximum ability for having an antibacterial effect was shown by the Ag–Au/PTFE nanocomposite, followed by the Ag/PTFE nanocomposite.

Controlled syntheses of Ag?polytetrafluoroethylene nanocomposite thin films by co-sputtering from two magnetron sources

Co-sputtering from two independent magnetron sources was used to prepare polymer?metal nanocomposite films. Both gradient films with increasing metal fraction and homogeneous composite films were produced from polytetrafluoroethylene?(PTFE) and silver targets using a rotatable sample holder. The structure of the pure sputtered polymer as well as the composite structure was studied. Electrical properties of the composite material near the percolation threshold show the expected, sharp change in the resistivity from 107???cm atsmall silver content to 10?3???cm after percolation. The optical absorption in the visible region due to surface plasmon resonances also has a strong dependence on the metal content, showing a red shift of the absorption peak from 405?nm to more than 500?nm at higher silver content.

Metal/polymer interfaces with designed morphologies

The morphology of a metal/polymer interface is important for many properties, e.g. its adhesional strength. Starting from the basic processes occurring in the initial stages of metal/polymer interface formation, it is possible to obtain different morphologies by variation of the preparation conditions. In this report we present selected examples from our own work of how metal/polymer interfaces with different morphologies can be prepared by evaporating noble metals (Au, Ag, Cu) onto chemically different polymers, i.e. bisphenol-trimethyl cyclohexane polycarbonate (TMC-PC), pyromellitic dianhydride-oxydianiline (PMDA-ODA) polyimide (PI), and on Teflon AF 1601. The interfaces were characterized using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The combination of these techniques allows one to determine morphological parameters such as the concentration and distribution of metal clusters at the surface and in the near-surface region. Using low deposition rates and elevated temperatures, spread-out metal/polymer interfaces can be formed, whereas the use of high deposition rates and moderate temperatures results in relatively sharp interfaces. Another approach to obtain a defined morphology is to form large metal clusters of 10-30 nm diameter on the polymer surface and embed them into the polymer in a controlled manner by a subsequent annealing process. First experiments on the macroscopic adhesion of Au and Cu on TMC-PC showed that the initially low peel strength could be increased substantially by subsequent annealing above the glass transition temperature.

Nanostructured magnetic Fe–Ni–Co/Teflon multilayers for high-frequency applications in the gigahertz range

Thin multilayer films of sputtered polytetrafluoroethylene (Teflon) and Fe54Ni27Co19 with different layer thicknesses were prepared by vapor-phase tandem deposition. The films show ferromagnetic resonance frequencies from 3.0to4.7GHz and a high-frequency permeability in the range from 100 to 175, while having negligible losses up to 700MHz and a quality factor Q up to 12 at 1GHz. Thus these films could be promising candidates as high-frequency components used, for example, in mobile communication electronics.

Condensation coefficients and initial stages of growth for noble metals deposited onto chemically different polymer surfaces

The initial stages of growth of noble metals deposited onto untreated as well as Ar+ beam-treated polymer surfaces were investigated by means of X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and radiotracer methods. Condensation coefficients C of the metals on the polymer surfaces were determined by comparison of the XPS signals of the metals with the nominal thicknesses measured by a quartz microbalance during deposition. These measurements were combined with radiotracer measurements, which allow to determine C independently with high accuracy and sensitivity. C was found to depend strongly on the chemical composition of the polymer surface, e.g., at room temperature, C varies between 0.95 for PMDA-ODA polyimide and 0.002 for Teflon AF. By ion beam treatment of the latter, C was raised considerably. During nucleation of the metal on the polymer surface, C increases strongly with metal coverage. C also depends on the deposition rate of the metal and decreases strongly at elevated temperatures.

Functional Polymer Nanocomposites

While extensive research has been carried out in the field of structural polymer-based nanocomposites much less investigations have been concerned with polymer nanocomposites for functional applications. Among the functional nanomaterials, nanocomposites consisting of metal nanoparticles dispersed in a dielectric matrix are of particular interest due to their novel functional properties offering hosts of new applications. Here, polymers are attractive as matrix, and several approaches have been reported to incorporate metal nanoparticles into polymers. The present review is concerned with the preparation of polymer-based nanocomposites by vapor phase co-and tandem deposition and the resulting functional properties. The techniques involve evaporation and sputtering, respectively, of metallic and organic components and inter alia allow the preparation of composites which contain alloy clusters of well defined composition. Emphasis is placed on soft-magnetic high frequency materials with cut-off frequencies well above 1 GHz and on optical composites with tuned plasmon resonances suitable for ultra thin color filters, Bragg reflectors, and other devices. In addition, antibacterial coatings and sensors for organic vapors are addressed. The latter take advantage of the steep drop of the electrical resistivity at the percolation threshold. First results are also reported on the incorporation of photo-switchable molecules into nanocomposites near the percolation threshold. Moreover, a novel approach to produce magnetic nanorods is presented.

Formation of metal-polymer interfaces by metal evaporation: influence of deposition parameters and defects

Abstract Metal–polymer interfaces with different but well defined morphologies were prepared by evaporating noble metals (Au, Ag, Cu) onto chemically different polymers, i.e. bisphenol-trimethyl cyclohexane polycarbonate (TMC-PC), pyromellitic dianhydride-oxydianiline (PMDA-ODA) polyimide (PI), polystyrene (PS) and the low-k dielectric Teflon AF 1601. The interfaces were characterised using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The combination of these techniques allowed one to determine morphological parameters such as concentration and distribution of metal clusters at the surface and in the near-surface region. In addition, radiotracer measurements yielded exact metal condensation coefficients C and was used to determine the extent of diffusion of metal atoms into the polymers. First experiments on the macroscopic adhesion of Cu on TMC-PC showed that the initially low peel strength can be increased substantially by subsequent annealing above the polymer glass transition temperature, T g .