Monolayer Of Metal Nanoparticles Research Articles

Ellipsometry of monolayers of metallic nanoparticles taking into account depolarization

Spectroscopic ellipsometry of disordered monolayers of gold nanoparticles on oxidized silicon prepared by thermal flash-annealing of thin sputtered gold films was performed taking into account depolarization and accompanied by scanning electron microscopy. It allows to compare optical properties of samples with their structure and to demonstrate that depolarization registered in far-field zone carries the information about near-field interparticle interactions.

Lasing action in multilayers of alternating monolayers of metallic nanoparticles and dielectric slabs with gain

By employing a rigorous multiple-scattering electrodynamic approach we study the loss compensation and lasing action in photonic crystals formed as alternating layers of active dielectric slabs and two-dimensional planes of plasmonic (metallic) spheres. The strong dispersion of the plasmonic bands and the efficient trapping of light among the dielectric slabs (the cavity effect) triggers lasing action for thin slabs of the photonic crystal and for a moderate amount of gain, with quality factors of the order of 103. Below and above the lasing threshold, gain compensates losses, promising significant improvement of the imaging properties of plasmonic photonic crystals.

Effect of carrier injection process in the organic field-effect transistor by introducing metal nanoparticle monolayer

Silver nanoparticles (NPs) self-assembled monolayer (SAM) was deposited on pentacene organic field-effect transistors (OFET) via modified Langmuir-Schaffer (horizontal lifting) technique and its effect was being investigated by steady-state method which is current-voltage measurements. Here we focus on its effect to the carrier injection. The contact resistance, drain-source current, trapped charges and threshold voltage analysis revealed that OFET with SAM exhibited significant charge trapping effect due to the space charge field formed by immobile/ trapped charges and further influenced the carrier injection.

Charged Metal Nanoparticle Monolayers on Semiconductor Substrates

The present work demonstrates selective charging of metal nanoparticles on semiconductor substrates, exploiting the Fermi level difference. Monolayers of surfactant-free silver nanoparticles (AgNP) were prepared by electroless reduction as well as vapor deposition on high conductivity n- and p-type Si substrates. The selective charging of the AgNP was investigated using electric force microscopy (EFM). As deduced from EFM, polarity and magnitude of the nanoparticle charge can be controlled by varying the Fermi level difference. The present study also reveals the impact of charging on the growth and coalescence of AgNP during chemical reduction. We also demonstrate that the monolayers of charged AgNP can be employed as charge-selective Raman scattering (i.e., surface-enhanced Raman scattering) substrates.

Charged Metal Nanoparticle Monolayers on Semiconductor Substrates

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Generalized Fabrication of Surfactant-Stabilized Anisotropic Metal Nanoparticles to Amino-Functionalized Surfaces: Application to Surface-Enhanced Raman Spectroscopy

A universal and facile approach for the self-assembly of surfactant-coated anisotropic metal nanoparticles on the amino-functionalized planar and spherical surfaces based on electrostatic attraction has been explored. Large-scale and different surface coverage of monolayer film and metallodielectric core-shell nanostructures of anisotropic metal nanoparticles, including Au nanorods, Au(core)Ag(shell) nanorods and Ag nanoprisms, have been fabricated. The optical response in the visible and the near infrared (NIR) of resulting nanostructures can be easily controlled by varying the concentration of the anisotropic nanoparticle, the amount of silica particles, and the immersion time of the substrates. Large-scale anisotropic metal nanoparticle monolayer films with subtle control over the surface coverage and tunable plasmon resonance as surface-enhanced Raman spectroscopy (SERS) substrates for probing 4-aminothiophenol were investigated, which exhibited high SERS activity, stability and reproducibility.

Concentration-related enhancement of the sensitivity of surface plasmon resonance of metallic nanoparticles to the characteristics of a dielectric environment

We present the results of theoretical and experimental studies of the optical attenuation spectra of planar nanocomposites consisting of close-packed monolayers of metallic nanoparticles placed in different dielectric matrices. We have analyzed the dependence of the spectral position of the collective surface plasmon resonance (collective SPR) on the refractive index of the dielectric environment. The experimental samples were created by successive thermal vaporization under vacuum of a metal and a dielectric. The theoretical calculations were performed using the quasicrystal approximation of multiple wave scattering theory. We have shown that an increase in the concentration of nanoparticles of noble metals shifts the maximum of the collective SPR band toward longer wavelengths, and significantly increases the sensitivity of its spectral position to the refractive index of the dielectric environment.

Direct and Stepwise Energy Transfer from Excitons to Plasmons in Close-Packed Metal and Semiconductor Nanoparticle Monolayer Films

We studied the dynamics of photoluminescence (PL) and energy transfer in close-packed monolayer films of CdSe and Au nanoparticles (NPs) assembled using the Langmuir-Blodgett technique. The PL intensity and dynamics depended on the ratio of CdSe to Au NPs in the mixed films. The PL quenching of CdSe NPs occurs through rapid energy transfer from excitons in CdSe NPs to plasmons in Au NPs. The PL decay curves of the mixed NPs monolayers are determined by three decay rates: the direct energy transfer between the nearest-neighbor CdSe and Au NPs (CdSe-->Au), the stepwise energy transfer from CdSe to CdSe to Au NPs (CdSe-->CdSe-->Au), and the radiative recombination in CdSe NPs.

In situ monitoring of metal nanoparticle self-assembly on protein-functionalized glass by broadband optical waveguide spectroscopy

Broadband, time-resolved optical waveguide (OWG) spectroscopy has been used for in situ, real-time investigation into the self-assembly of metal nanoparticle monolayers. The OWG spectroscopy makes it possible to use the transverse electric (TE) and transverse magnetic (TM) modes to measure surface plasmon absorption of immobilized metal nanoparticles in two directions, parallel and normal to the waveguide surface. Therefore, this technique can provide direction-dependent information on the metal nanoparticles at the interface. In this paper, a 50-μm-thick glass plate was used as a slab waveguide and the kinetics of Au nanoparticle adsorption on a hemoglobin-functionalized glass substrate was examined in the early stage of self-assembly. The findings show that with the TE mode the surface plasmon resonance (SPR) behavior for immobilized Au nanoparticles is different from that with the TM mode.

Charge injection and lateral conductivity in monolayers of metallic nanoparticles

Scanning electrochemical microscopy has been used to quantify both the charge injection energetics between a solution redox couple and a monolayer of hexanethiol stabilised gold nanoparticles and the subsequent lateral charge transport in the monolayer.

The spatial ordering effect on spectral properties of close-packed metallic nanoparticle monolayers

In the frame of the theory of multiple scattering of waves we have studied transmission spectra of monolayers of monodisperse spherical metallic nanoparticles surrounded by dielectric matrix at different nanoparticle arrangement types. The method being used takes into account collective effects of the coherent nature and electrodynamic coupling between particles. The effect of the particle correlation degree on the surface plasmon absorption band has been investigated for random close-packed, polycrystalline quasiregular and chain-like planar particle arrays. We have established that the spatial ordering is mostly pronounced in transmission spectra of metal nanoparticle chain-like monolayers. Binary interactions in these structures cause the structure modification and the polarization dependence of the surface plasmon–polariton resonance.

Coupled Plasmon Modes in an Ordered Hexagonal Monolayer of Metal Nanoparticles: A Direct Observation

We report on the experimental observation of STM-induced photon emission in ultrahigh vacuum on a network of 4-nm silver spheres. The spheres are covered by a dielectric, electrically insulating, organic layer and deposited on Au(111). The bias-dependent spatial distribution of the photon emission rates reveals the electric-field distribution of the different coupled plasmon modes in this model.