Wilfried Schulze

Chemiluminescence in the Agglomeration of Metal Clusters

The agglomeration of copper or silver atoms in a matrix of noble gas atoms to form small clusters may be accompanied by the emission of visible light. Spectral analysis reveals the intermediate formation of electronically excited atoms and dimers as the source of the chemiluminescence. A mechanism is proposed, according to which the gain in binding energy upon cluster formation may even lead to the ejection of excited fragments as a result of unstable intermediate configurations. A similar concept was introduced in the field of nuclear reactions by Niels Bohr 60 years ago.

Fluorescence and excitation spectra of Ag4 in an argon matrix

We report the fluorescence and excitation spectra of size selected Ag4 deposited in an argon matrix. The main fluorescence peak for Ag4 is observed at 458 nm. The excitation spectrum for this emission is in good agreement with recent theoretical calculations and photodepletion experiments.

Absorption and fluorescence spectra of Ar-matrix-isolated Ag3 clusters

The absorption and fluorescence spectra of silver trimers isolated in an Ar matrix show the existence of three distinct lattice sites whereby the population of each site depends on the conditions of matrix preparation. Irradiation of certain absorption bands of the trimer isolated in one of these sites results in an irreversible reorganization of the surrounding matrix and population of another site. The experiments were performed with matrices prepared either by the matrix isolation/aggregation method or by soft landing of size-selected Ag/sub 3/ species.

Composition and lattice structure of fivefold twinned nanorods of silver

Multiply twinned silver particles of rod-like shape and nanometer dimensions prepared by inert-gas aggregation technique have been studied by high-resolution electron microscopy. These pentagonal nanorods exhibit aspect ratio between 1.8 and 6 with the length of their fivefold axis ranging from 22 to 132 nm. Digital image processing and evaluation was utilised to characterise composition and lattice structure of the nanorods. Measuring the spacings of lattice plane fringes of nanorod subunits in various orientations revealed no deviation from the face centred cubic lattice type. There was also no indication of extended lattice defects found. Instead, a certain extent of non-regular lattice distortions recognised in the surface regions of the nanorods apparently is an effective means to achieve sufficient space filling.

LIGHT EMISSION DURING THE AGGLOMERATION OF SILVER CLUSTERS IN NOBLE GAS MATRICES

The agglomeration of small silver clusters in noble gas matrices to form larger ones may be accompanied by the emission of light. Spectral analysis reveals that part of radiation intensity can be attributed to fluorescence from excited metal atoms, dimers and trimers the formation of which results from cluster/cluster agglomeration as a consequence of the gain in binding energy. The remaining spectral features must be assigned to excited clusters Agn, with n⩾4.

Growth of rodlike silver nanoparticles by vapor deposition of small clusters

A beam of silver clusters of 3 nm average diameter is produced by the gas-aggregation technique and deposited onto the NaCl (100) surface. Subsequent agglomeration leads in part to the growth of rodlike particles with the structure of truncated decahedra of typical dimensions 70 nm long and 10 nm diameter and a fivefold symmetry, as shown in the picture. A growth mechanism is inferred from a detailed analysis of electron microscopy data.

The surface plasmon resonance of free and embedded Ag-clusters in the size range 1,5 nm D 30 nm

It is experimentally proven that the size dependence of the surface plasmon resonance of large spherical silver clusters is related to the surface optical properties of Ag. It is also demonstrated that there is a minimum size, below hich this approach fails as expected, and that there is a maximum size, above which the surface contribution can be neglected such that classical optics applies.

Absorption spectra of small silver clusters Agn (n⩾3)

A novel preparation technique enables the generation of small silver clusters Agn in an argon matrix in the otherwise hardly accessible size range 3⩽n<40. Apart from the previously known absorption spectra around 350 nm, further bands at wavelengths up to 900 nm were detected. These features exhibit very low intensities and are attributed to low-energetic single electron–hole excitations.

Light emission in the agglomeration of silver clusters

Abstract Small noble-gas droplets are generated by adiabatic expansion and travel over a heated crucible where evaporated Ag atoms are picked up. The subsequent agglomeration of these Ag atoms to clusters is associated with light emission. This effect is caused by the gain in binding energy by the clustering process leading to the ejection, preferably, of excited trimers. The heat released by condensation and coagulation of the Ag atoms on the droplets causes continuous evaporation of the noble-gas atoms, so that under suitable conditions even light emission from the decay of free Ag 3 ∗ species could be observed and analyzed.

The light emission observed from small palladium particles during passage of electronic current

Light emission spectra were measured from separate Pd particles excited by the passage of electrical current through them. As the particle size decreases or input power increases the intensities of peaks increase more strongly in the high-energy part of the spectra than in the low-energy part. Moreover, new peaks can appear in the high-energy region. The color of an emission center changes from red to blue upon an increase in electric power fed into the Pd particle. This process is reversible and can be observed visually. On a further increase in feeding power, the Pd particle can be brought to a premolten state and can even melt. The integral intensity of light emission then increases dramatically, and the light emission spectrum changes and corresponds to thermal radiation. This latter process is irreversible.