Igor A. Wojciechowski

Distortion of H2 potentials by embedding into an electron gas at molecule scattering by a metal surface

Abstract A screening action of electrons from the selvage of a solid on a molecule scattered by a solid surface at grazing incidence is considered. Electronic states of a neutral hydrogen molecule in the vicinity of a metal surface are calculated using the screened Hulthen potential. Results of the calculations give a dependence of the molecule potential energies on the electron density.

Theoretical study of mechanisms responsible for emission of highly excited metal atoms

Abstract Using a molecular dynamics technique we demonstrate that the formation of holes in the d-shell can be a mechanism initiating sputtering of metastable metal atoms with a closed outer s-shell. The formation of d-holes is a result of electron promotion in the energetic collisions in the cascade developing in solid under fast ion bombardment.

Effect of mass and incidence angle of keV energy polyatomic projectiles in silicon sputtering

Recent experiments of bombardment of silicon targets show that keV energy polyatomic projectiles can greatly increase both the total yield and the secondary silicon ion emission, especially complex secondary ions. This effect is more pronounced for the heavy polyatomic projectiles than for light ones. To understand why the heavy projectiles increase the non-linear enhancement of the yields, molecular dynamics simulations of the bombardment of a Si(1 0 0)– (2 � 1) surface by Aln (n ¼ 1, 2) and Aun (n ¼ 1, 2) projectiles with E0 ¼ 1:5 keV/atom at the incident angles of h ¼ 0� and h ¼ 45� have been carried out. It is shown that oblique bombardment by heavy dimer projectiles at this initial energy leads to an increase of the number of trajectories with a very high yield of ejected atoms. A microscopic analysis of the events is given and also the influence of the high yield events on the energy distributions of the sputtered silicon atoms is described. � 2002 Elsevier Science B.V. All rights reserved.

THE BROADENING OF ENERGY SPECTRA OF ATOMS SCATTERED BY A SOLID SURFACE UNDER MOLECULAR ION BOMBARDMENT

Abstract The broadening of energy spectra of atoms scattered by a metal surface under molecular ion bombardment are calculated taking into account the molecular ions to suffer dissociative neutralization on the initial part of their scattering trajectory. The results of the calculations explain the experimental data for scattering of hydrogen atoms from aluminum, palladium and palladium covered by potassium surfaces under bombardment with H2+.

Ionization and fragmentation of clusters sputtered from a metal surface by fast ions

Abstract A mechanism of ionization of clusters sputtered from a metal surface by keV-ion bombardment is proposed. The mechanism is based on the idea of a partial transfer of the internal nuclear cluster energy into it the electronic subsystem and following ionization. In terms of such an approach the dependence of degrees of cluster ionization on n , the number of atoms in a cluster, is calculated. The obtained results are in a qualitive agreement with the measurements.

Mechanism of metal cationization in organic SIMS

A scenario of metal cationization in which the organic molecule combines with a neutral excited metal atom is proposed. Ionization of the nascent complex occurs via ejection of an electron during the association process. Electron structure calculations for the model systems C6H6+Me (Me=Ag, Cu, Au) using the density functional theory give a strong argument in favor of the proposed mechanism.

On non-binary nature of the collisions of heavy hyperthermal particles with solid surfaces

Abstract The limits of applicability of the binary collision approximation for a description of scattering of atomic particles by a solid surface are discussed. The experimental data of energy losses of atoms of hyperthermal energies (HT) scattered by a solid surface were found to bring in evidence for the non-binary nature of collisions in the hyperthermal energy region (1–30 eV). The dependence of the energy losses on the initial energy of the particles and their angles of incidence was shown to be well described by the following model: the particle is being single-scattered by certain complex of surface atoms forming an effective mass. A contribution of the non-binary collisions to the processes of atomic and cluster sputtering is also discussed.

Dissociation of fast N-2 molecules scattered from different fcc(110) surfaces

The dissociation of fast nitrogen molecules with kinetic energies ranging from 200 to 2000 eV/atom was studied for grazing collisions with various fcc surfaces. At these energies, the dissociation is caused by vibrational and rotational excitation, the latter being favored for scattering along the surface semichannels. N2 is chemically inert and interacts mainly elastically with the surfaces. A controversial question is the role of the dynamic screening of the molecular constituents by the bulk electron gas during the dissociation process. Another interesting issue is the dependence of the dissociation probability on the azimuthal scattering angle—the fragmentation is highest for the low indexed direction. We treat both problems, by comparing results obtained from the different surfaces Pd(110), Ag(110), and Pt(110). The experimental data are compared to molecular dynamics simulations based on realistic interaction potentials as obtained from density functional theory calculations. The potentials are impr...

Non-additive effects in ion-photon emission

Abstract The excitation mechanisms of scattered atomic particles under molecular ion bombardment of solid surface have been studied. Some additional mechanisms of atomic excitation which are not realized in the case of atomic bombardment have been discussed. These new mechanisms result in the non-additivity of the excitation process under molecular bombardment.

The formation of singly and doubly cationized oligomers in SIMS

The cationization of sputtered organic species via metal particle adduction is investigated using poly-4-methylstyrene molecules in combination with Cu, Pd, Ag and Au substrates. Metal-cationization occurs for these four substrates. The cationized molecule yields vary with the considered substrate and they are not correlated with the metal ion yields. In addition, double cationization with two metal particles is observed with a very significant intensity for Cu, Ag and Au supports. We interpret the results with an emission scheme in which excited molecules and metal atoms recombine above the surface and decay via electron emission, thereby locking the complex in the ionic state.