Small metallic particles studied by optical and electron-optical spectroscopy

Abstract

Electron energy loss spectroscopy (EELS) in a transmission electron microscope (TEM) and photoacoustic spectroscopy (PAS) has been used to study the electronic structure of small Ag, In and Au particles, deposited on thin carbon foils, quartz supports or as self-supporting layers, respectively.In the low energy-loss region the EELS spectra of Ag particles with diameters of ca. 50 nm are different from the spectra of the homogeneous Ag layers, mainly owing to the influence of the carbon foil. By decreasing the packing density of the Ag particles, a shift of the plasma losses to lower energies is observed in the energy region 10eV. The optical behaviour of homogeneous metallic and small particle layers on thin quartz supports was studied by PAS in the ultraviolet/visible (UV/VIS) spectral region. The homogeneous layers, e.g. of Ag, show, in the UV range, the well known change of reflectance due to an interband transition of bare silver. For Ag particle layers surface plasma resonances are excited. With increasing packing density of the particles the absorption peak observed is red-shifted and becomes broader, whereas the results of EELS in the low energy-loss region revealed a shift to higher energies.To obtain additional information investigations of In and Au particles were performed.

Sonochemical Deposition of Silver Nanoparticles on Silica Spheres

“…Photoacoustic Spectroscopy (PAS) Studies. In our previous work, the PAS method was used to study semiconductor nanoparticles, in order to measure their electronic properties (e.g., band gap). − As far as we know, there are only a few published studies where PAS was used to measure surface plasmon resonance (SPR), − and none of these papers described SPR measurements of small nanoparticles of the size described in this report. PAS may be very useful for the study of such particles, because in the case of analogous semiconductors, nanoparticle PAS was a superior technique, relative to other optical methods such as diffuse reflectance and absorption spectroscopy. , …”

“…27,28 The electronic properties of the products were studied by measurement of the optical absorption spectra (interband transitions) using photoacoustic spectroscopy (see Figure 7a,b). From previous studies using UV-vis absorption, it is known that the height and position of the peaks depend on various parameters: (1) the amount of Ag (affects the height of the peak); 8 (2) particle size (increased diameter causes a red shift); 29 (3) packing density of the particles (increased packing density causes a red shift); 24 and (4) oxidation level of the particles (increased oxidation level causes a blue shift). 30 The PAS spectrum of sample 2h shows two peaks (see Figure 7a), at 429 and 460 nm.…”

Study of Quasi-Fractal Many-Particle-Systems and Percolation Networks by Zero-Loss Spectroscopic Imaging, Electron Energy-Loss Spectroscopy and Digital Image Analysis

“…Unfortunately, the spectrum was governed in the low-loss region by the carbon plasmon contribution from the support. A shift of the plasmon peak at 21.5 eV to lower energy-losses compared with the value 25 eV for pure carbon film probably was due to the contribution of surface plasmons excited in the aggregated particles and in the PVA layer [5]. Fig.…”

“…Volume and surface plasmon excitations, in particular, are determined both by properties of the individual particles and by collective effects due to interaction among the particles densely packed in aggregates. To understand how fractal geometry affects electronic properties of aggregated matter, electron-optical and optical methods can be applied [3,5].…”