Low Energy Cluster Beam Deposition (LECBD) is considered an intriguing technique to obtain thin layers with well defined structures at the nano- and meso-scale levels, allowing novel optical, electronic and magnetic properties. The produced layers are highly porous and extremely reactive due to the high surface to volume ratio and must be characterized with “in situ” techniques in order to study their original composition and their evolution once exposed to reactive gases. In this work we present a general overview and some results on the formation evolution and deposition of silicon and carbon cluster beams produced using a laser vaporization source.

The study of the structures and properties of small elemental clusters has been an extremely active area of current research, due to the peculiar behavior of these species halfway between that of single atoms and of the bulk phase. In this work silicon nanoclusters are generated by ablation of a high purity polycrystalline rod with a pulsed laser vaporization source and then deposited on a support. Their structure is studied both in the gas phase by means of Time of Flight Mass Spectrometry and in the solid phase through in situ Raman and Infrared Spectroscopy. The spectra reveal that the as deposited clusters are hydrogenated with negligible amount of oxide. Degradation of silicon nanoclusters has been studied after gas exposure. In the gas of air a consistent modification was observed, leading to a near-infrared luminescent silicon nanoparticles. In the second part of the work, density functional theory is applied to investigate the geometrical structure of silicon clusters and their interaction, in term of structure and energy, with different gases. The calculations were performed with the Gaussian 03 program suite, adopting the B3LYP functional to calculate the exchange and correlation energy. Si8 has been chosen as model cluster to study the degradation of silicon clusters both kinetically and thermodynamically, in order to explain the experimental evidences. Experimental and calculated infrared spectra are compared.

In this paper we present a study on the formation of gold colloids by laser ablation of a gold metal target in alkanes and thiol-alkane solutions. The results show a decrease of the gold particles' size up to 2 nm when thiol molecules are present in the liquid environment. In summary, we observed that laser ablation of gold targets in thiol-alkane solutions leads to the formation of stable gold clusters with size smaller than those obtained in the corresponding pure alkane. This result is a consequence of the competition between the aggregation of gold species in the plume (which allows a gold embryo to be formed and to grow) and the tendency of the dispersed thiol molecules to bond at each embryo surface stopping their growth.

Nanostructured amorphous carbon thin films deposited by a Low Energy Carbon Cluster Beam Deposition technique have been characterized by Raman spectroscopy and Electron Spin Resonance (ESR). This study focuses on the correlation between carbon cluster structure and sp2 related defects. The ESR spectrum of as prepared and thermally annealed carbon clusters is a single line located near the free electron g-factor. Resonance lines were accurately fitted by a single line symmetric and narrow Lorentzian line. The resonance line parameters (line position, line amplitude, and line width) were found to be extremely sensitive to the thermal treatment of the as deposited samples. The paramagnetic centres are randomly distributed and correlated with the nanosized nature of the investigated system. The absence of the resonance line asymmetry, typical for the ESR spectra of conducting carbaceneous materials, confirms the small size of carbon nanoclusters and indicates poor electrical contacts between them. The resonance line parameters (position, intensity, and width) are not affected by the orientation of the carbon cluster film relative to the direction of the external magnetic field. The evolution of the ESR signal upon thermal treatments is sensitive to the increase of the sp2 average domain size as revealed by Raman spectroscopy. The Raman spectrum of as obtained and thermally annealed carbon clusters, in the domain 1000 cm−1 to 2000 cm−1 shows two Lorentzian lines located at 1300 cm−1 and 1550 cm−1 representing the D and G bands. The position and amplitude of these lines were found to be affected by thermal annealing.

In this paper, we present a study on the formation of gold colloids by laser ablation of a gold metal target in alkanes and thiol-alkane solutions. The results show a decrease of the gold particles’ size up to 2 nm when thiol molecules are present in the liquid environment. The observation of a blue-shift of the surface plasmon resonance is discussed together with transmission electron microscopy analyses accounting the cluster size decrease and the stabilization of the obtained suspensions.

A Lie subalgebra L of [gfr ][lfr ][ ](V) is said to be finitary if it consists of elements of finite rank. We study the situation when L acts irreducibly on the infinite-dimensional vector space V and show: if Char [ ] > 7, then L has a unique minimal ideal I. Moreover I is simple and L/I is solvable.

In this paper we study the problem of the existence on non-inner automorphisms for the class of torsion-free supersolvable groups, answering a question raised by Robinson.

1991 Mathematics Subject Classification 20F16, 20F28.

1. Introduction

A class [Xscr] of groups is said to be countably recognizable, if every group all of whose countable subgroups are contained in countable [Xscr]-subgroups is itself an [Xscr]-group. Many examples of such classes are discussed in section 8·3 of [20]. In the present work we are concerned with the question of how far countable recognizability can be obtained for classes of finitary linear groups. Recall that a group is said to be finitary []-linear if it is isomorphic to a subgroup of FGL[](V), the group of all invertible []-linear transformations α of the []-vector space V with the property that the image of the endomorphism α−idV has finite []-dimension. This generalizes the notion of linearity. A survey about features of finitary linear groups is given in [18].

In his celebrated paper [3] Gaschiitz proved that any finite non-cyclic p-group always admits non-inner automorphisms of order a power of p. In particular this implies that, if G is a finite nilpotent group of order bigger than 2, then Out (G) = Aut(G)/Inn(G) =≠1. Here, as usual, we denote by Aut (G) the full group of automorphisms of G while Inn (G) stands for the group of inner automorphisms, that is automorphisms induced by conjugation by elements of G. After Gaschiitz proved this result, the following question was raised: “if G is an infinite nilpotent group, is it always true that Out (G)≠1?”

Three-dimensional chemical maps by Secondary Ion Mass Spectrometry (3D-SIMS), XPS spectroscopy, and SEM-EDAX microscopy were employed in order to investigate the effects of accelerated fatigue tests on crack formation in 95.5% Pb–2% Sn–2.5% Ag and 95% Pb–5% Sn solder joints. These alloys are used in the die bonding of electronic power device assemblies. The results show that cracks form by Sn-depletion from the inner regions of the soldered joint. Simultaneously, there is a recrystallization of the Pb-rich phase in the same regions of the joint. The crack occurs at a critical number of cycles when a Sn-depleted region is formed, yielding weaker inner layers with lower shear strength. A possible explanation of the Sn-depletion is also discussed.

Ultra-thin films of polyamic acid (BTDA-ODA type) are prepared by spin coating a very dilute solution onto bare or metallized silicon wafers (estimated thickness 25 ± 5 Å). The XPS analysis of the various polymer/metal interfaces suggests the occurrence of acid-base type interaction between the carboxylic groups of the polymer and the oxides and hydroxides that cover the Ni and Cr surfaces. When these systems are in situ cured, the XPS analysis shows the occurrence of a variety of chemical interfacial reactions. In particular: (i) when the substrate is a naturally passivated Ni layer, the complete destruction of the polymer is observed; (ii) when the substrate is a naturally passivated Si wafer, no relevant interaction occurs; (iii) for a naturally passivated Cr and an oxidized Ni surface, partial decomposition of the polymer is observed. The above effects are explained in terms of the acid or basic properties of the oxidized layers that cover the metal surfaces, and in terms of their stability toward heating.

The paper presents a study of three polyimide-oxide interfaces. The Cr-oxide-PI interface seems to undergo a drastic topographical structural rearrangement. The case of the Ni surface is indicative of heavy decomposition of the Ni oxide which induces the decomposition of the polymer film. On the contrary the stabilized Ni surface behaves in a normal manner indicating that the driving force for the decomposition is the instability of the oxide.

The paper presents a study of three polyimide-oxide interfaces. The Cr-oxide-PI interface seems to undergo a drastic topographical structural rearrangement. The case of the Ni surface is indicative of heavy decomposition of the Ni oxide which induces the decomposition of the polymer film. On the contrary the stabilized Ni surface behaves in a normal manner indicating that the driving force for the decomposition is the instability of the oxide.

The formation of an insoluble gel under ion-beam bombardment is governed by ion-beam parameters and target parameters. Here reported is a study of the influence of the target molecular parameters on the sol–gel transition of ion-bombarded polystyrene with particular emphasis for the number-average molecular weight $\overline M$n. It is shown that the main parameter is the number of macromolecules of the film so that by adopting a “corrected” fluence F/n (ions per macromolecule), the different curves of the various polymers collapse in only one universal curve. The importance of the “corrected” fluence is shown also at molecular level and the MWD of the various polymers is similar at equal F/n values. An experimental model is outlined which explains the sol–gel transition on the basis of transition from an isolated-track regime to an overlap regime where the formation of insoluble giant macromolecules occurs.