Near-field interactions between metal nanoparticle surface plasmons and molecular excitons in thin-films: part I: absorption

In this and the following paper (parts I and II, respectively), we systematically study the interactions between surface plasmons of metal nanoparticles (NPs) with excitons in thin-films of organic media. In an effort to exclusively probe near-field interactions, we utilize spherical Ag NPs in a size-regime where far-field light scattering is negligibly small compared to absorption. In part I, we discuss the effect of the presence of these Ag NPs on the absorption of the embedding medium by means of experiment, numerical simulations, and analytical calculations, all shown to be in good agreement. We observe absorption enhancement in the embedding medium due to the Ag NPs with a strong dependence on the medium permittivity, the spectral position relative to the surface plasmon resonance frequency, and the thickness of the organic layer. By introducing a low index spacer layer between the NPs and the organic medium, this absorption enhancement is experimentally confirmed to be a near field effect In part II, we probe the impact of the Ag NPs on the emission of organic molecules by time-resolved and steady-state photoluminescence measurements

Gold nanoparticle-polymer nanocomposites synthesized by room temperature atmospheric pressure plasma and their potential for fuel cell electrocatalytic application

Conductive polymers have been increasingly used as fuel cell catalyst support due to their electrical conductivity, large surface areas and stability. The incorporation of metal nanoparticles into a polymer matrix can effectively increase the specific surface area of these materials and hence improve the catalytic efficiency. In this work, a nanoparticle loaded conductive polymer nanocomposite was obtained by a one-step synthesis approach based on room temperature direct current plasmaliquid interaction. Gold nanoparticles were directly synthesized from HAuCl4 precursor in poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS). The resulting AuNPs/PEDOT: PSS nanocomposites were subsequently characterized under a practical alkaline direct ethanol fuel cell operation condition for its potential application as an electrocatalyst. Results show that AuNPs sizes within the PEDOT: PSS matrix are dependent on the plasma treatment time and precursor concentration, which in turn affect the nanocomposites electrical conductivity and their catalytic performance. Under certain synthesis conditions, unique nanoscale AuNPs/PEDOT: PSS core-shell structures could also be produced, indicating the interaction at the AuNPs/polymer interface. The enhanced catalytic activity shown by AuNPs/PEDOT: PSS has been attributed to the effective electron transfer and reactive species diffusion through the porous polymer network, as well as the synergistic interfacial interaction at the metal/polymer and metal/metal interfaces.Funding Agencies|UK EPSRC [EP/K022237/1, EP/M024938/1, EP/P00394X/1, EP/I013229/1]; National Natural Science Foundation of China [51203135]; InvestNI [PoC-325]; Department of Employment Learning; EU-COST Action [TD1208]</p

Evaluation of the pH-sensitive swelling of a hydrogel by means of a plasmonic sensor substrate

The inline monitoring of parameters in aqueous liquids is facing an increasing demand in many different application areas. Hydrogels with pH-induced swelling and deswelling behavior offer a means to measure pH in such liquids. Here we investigate the optical interrogation of a pH-sensitive hydrogel which can be applied in the physiological pH range. For this, a nanostructured gold substrate supporting surface plasmon oscillations is coated with a HPMA/DMAEMA/TEGDMA/EG hydrogel. The gel swells in the pH range under investigation (here 4.5 to 6.5), and the resulting refractive index changes subsequently lead to a spectral shift of the plasmon resonance of the gold nanostructure. The spectral resonance position is determined from optical transmittance spectra of the sensor substrates, and the initial results for our hydrogel reported here indicate a nearly linear dependence between the swelling state and the plasmon resonance wavelength

Large field optical tomography system

Optical measurement technologies become more and more import in many fields of nondestructive testing. One of these technologies is the optical coherence tomography (OCT). By now mostly used in medical applications, such as ophthalmology and dermatology, relevance of OCT for testing of non-biological samples in manufacturing and research is increasing. For this reason new OCT measurement systems for fast volume inspection are needed. In this paper we present an automated high speed swept source based OCT system with a scan rate of 100.000 A-scans per second. The advantage of high scan rates of such systems until know lead into high costs for appropriate light sources. Furthermore the big size of available sources makes system integration and miniaturization difficult. With a new kind of MEMS-based light sources components with smaller dimensions and a cost reduction of more than 50% are possible. We combine the MEMS-based swept source OCT system with a table top robot for large-area inspections. The field of view of commercial systems is limited to few centimeters. Our new system is capable of measuring up to 400mm in square. With inherent software the acquisition of A-Scans at any position in the working area and of any quantity is possible. Once calibrated for a sample, the system can perform an automated measurement. Therefore our OCT system can be used as a tool for testing scenarios in research, for failure analyses and for semi-automated production processes

Time-resolved luminescence measurements on upconversion phosphors for electron beam sterilization monitoring

We present our recent investigations on time-resolved measurements of alterations in the temporal luminescence decay of upconversion phosphors induced by electron beam treatment. The latter is a promising alternative to low-temperature and dry sterilization of surfaces for sensitive packaging materials. Especially in the food and medical sector regulations concerning sterility are increasingly tightened. For this, a secure proof for electron-beam-assisted sterilization is required. However, no non-destructive and in situ method exists up to now. Our approach to provide a secure proof of sterilization is to place a suitable marker material based on rare-earth-doped phosphors inside or on top of the packaging material of the respective product. Upon electron irradiation the marker material changes its luminescent properties as a function of applied energy dose. We verified the energy dependence by means of time-resolved measurements of the luminescent decay of different upconversion materials. In our experimental realization short laser pulses in the near-infrared range excite the marker material. The emitted light is spectrally resolved in a monochromator, collected via a silicon photo diode, and analyzed with an oscilloscope. As the main results we observe a reduction of luminescence lifetime due to electron beam treatment dependent on the emission wavelength. Hence, the electron beam induces changes in the particles' up- and down-conversion properties from which the applied energy dose can be derived

Infrared optical properties of nanoantenna dimers with photochemically narrowed gaps in the 5 nm regime

In this paper, we report on the manipulation of the near-field coupling in individual gold nanoantenna dimers resonant in the infrared (IR) spectral range. Photochemical metal deposition onto lithographically fabricated nanoantennas is used to decrease the gap between the antenna arms down to below 4 nm, as confirmed by finite-difference time-domain simulations. The increased plasmonic coupling in the gap region leads to a shift of the surface plasmon resonances to lower energies as well as to the appearance of hybridized plasmonic modes. All of the occurring electron oscillation modes can be explained by the plasmon hybridization model. Besides the bonding combination of the fundamental resonances of individual antennas, also the antibonding combination is observed in the IR transmittance at normal incidence. Its appearance is due to both structural defects and the small gaps between the antennas. The detailed analysis of individual IR antennas presented here allows a profound understanding of the spectral features occurring during the photochemical manipulation process and therefore paves the way to a full optical process monitoring of sub-nanometer scale gaps, which may serve as model systems for experimental studies of quantum mechanical effects in plasmonics

Fabrication of two-dimensional Au@FePt core-shell nanoparticle arrays by photochemical metal deposition

In this report, we experimentally demonstrate that single platinum nanoparticles exhibit the necessary catalytic activity for the optically induced reduction of H[AuCl4] complexes to elemental gold. This finding is exploited for the parallel Au encapsulation of FePt nanoparticles arranged in a self-assembled two-dimensional array. Magnetic force microscopy reveals that the thin gold layer formed on the FePt particles leads to a strongly increased long-term stability of their magnetization under ambient conditions