Electron-surface interactions plasma

Fig. 2.1. Representation of the parameter problem in plasma-surface interaction. n,-electron density, f(E)-electron energy distribution, N-gas density, x-residence time for gas molecules in plasma volume...

When the electrons are removed from the nucleus at a high temperature, a gas of ions and electrons forms as plasma. In this case, the kinetic energy exceeds the potential energy between each particle (electrons and metal ions). When they are very near, the electron and nucleus get attracted and the density of states increases, whereas the opposite repulsion energy occurs in electron interactions. In the first case, the number of charged particles, n, of the volumetric charge densities, p, produces the surface polarization, P. This property exhibits the polarizability tensor, a, in an electric field, E ... 

The principal aim of the present work was to study the modification of polymer surfaces by plasma treatment as well as the interaction of a metal film with these treated surfaces by surface analytical techniques. As shown above, the results indeed show increased interaction after surface treatment under certain conditions. However, ultimately, improved adhesion should also be observed. For this purpose preliminary expenments with aluminum films on plasma treated polypropylene were carried out. These films were not evaporated under in-situ conditions, but in a separate electron beam evaporator under identical conditions for the different polymer surfaces. A simple Scotch tape test was performed in order to characterize the adhesion qualitatively. In agreement with the surface analytical results, the as-received polypropylene surfaces show poor adhesion as the aluminum film and can be peeled off completely. A five second nitrogen plasma treatment however leads to a film which adheres well and cannot be lifted off by the same tape. Hnally, a 120 s ocatment in a nitrogen plaana leads to an oveitreatmcntof the surface characterized by a low adherion again. 

Note that another very important problem, in addition to the plasma/surface interactions and the osdllations, is that of the electron transport, in a direction transversal to the magnetic field lines. 

VLEED (with E < 16 eV, or lower than the plasma excitation energy) spectral collects simultaneously comprehensive yet nondestructive information from the outermost two atomic layers about the bond geometry, surface potential barrier (SPB), valence electrons (DOS features), Brillouin zones, and work function, reaction dynamics [69, 70]. VLEED is very insensitive to dislocations of atoms in the third layer and below [69, 70]. In the VLEED, electron beams interact with the valence electrons of atoms in the outermost two layers and resonant within the barrier of surface potential. 

The reaction mechanisms of plasma polymerization processes are not understood in detail. Poll et al [34] (figure C2.13.6) proposed a possible generic reaction sequence. Plasma-initiated polymerization can lead to the polymerization of a suitable monomer directly at the surface. The reaction is probably triggered by collisions of energetic ions or electrons, energetic photons or interactions of metastables or free radicals produced in the plasma with the surface. Activation processes in the plasma and the film fonnation at the surface may also result in the fonnation of non-reactive products. 

In this Section we want to present one of the fingerprints of noble-metal cluster formation, that is the development of a well-defined absorption band in the visible or near UV spectrum which is called the surface plasma resonance (SPR) absorption. SPR is typical of s-type metals like noble and alkali metals and it is due to a collective excitation of the delocalized conduction electrons confined within the cluster volume [15]. The theory developed by G. Mie in 1908 [22], for spherical non-interacting nanoparticles of radius R embedded in a non-absorbing medium with dielectric constant s i (i.e. with a refractive index n = Sm ) gives the extinction cross-section a(o),R) in the dipolar approximation as ... 

Along with atom particles and radicals, ions and electrons play an important role in radiation and plasma chemical processes. Ions and electrons are being produced and interact actively with irradiated matter both in gases and, especially, at the surfaces of solids (vessel walls, adsorbents, etc.). 

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