M. Schosnig

Secondary-electron velocity spectra and angular distributions from ions penetrating thin solids☆

Abstract We present velocity spectra and angular distributions of secondary electrons emitted from cleaned surfaces of thin carbon and gold foils penetrated by H+ (Ep = 0.8 and 1.2 MeV), H2+ (Ep/Mp = 0.8 MeV/u) and C+ (Vp = 2.30− and 2.85 VB). Prominent structures in doubly differential velocity spectra d 2 n/ d E d Ω of secondary electrons (SE) are (1) the “true SE” peak at low electron energies Ee

Search for solitons in solids

Abstract It has been suggested that solitons might be created during radiation damage processes. Circumstantial evidence for such solitons has been found in the layered crystal muscovite. An attempt was made to detect such solitons by their inelastic scattering at a crystal surface in a single crystal of silicon.

Search for Fermi shuttle mechanisms in electron emission from atomic collision sequences

Abstract In electron spectra induced by slow heavy ion bombardment of solids a high energy tail can be observed, which is suggested to be explained by multiple collision sequences. In order to find those multiple collision effects like the “Fermi shuttle” acceleration mechanism we measured doubly differential electron emission cross sections for H+ (33.5–700 keV) impact on different targets (He, Ne, C and Au) as a function of projectile energy and electron emission angle. We observed a surprising target dependence of the electron emission within the range of electron energies close to that of the binary encounter electrons for all observed angles of emission.

Elemental composition of different types of wood

Abstract For the use of wood as an environmental sensor the average or normal elemental composition of wood has to be known (here with Z > 12). Since we find with PIXE that the elemental composition depends on the species, environmental influences can only be deduced indirectly from deviations from average elemental concentrations, which have to be known for each examined species. The average elemental composition was calculated from the concentrations of more than 10 samples from almost as many sites for beech and oak. Other species were also analysed but not from more than three different sites. Significant correlations between certain elemental concentrations were found (in particular between Ca and Mn), also studied was the influence of the growing site on the elemental concentrations.

Electron emission and desorption from frozen gases under fast (MeV) ion bombardment

Abstract First results of the adsorbate-thickness dependence of electron yields obtained with thin copper foils covered with solid CO 2 are presented. Absolute values of the CO 2 coverage were determined by Rutherford forward scattering. The erosion of frozen CO 2 by transmission of protons (1 MeV) was observed for the first time. The obtained CO 2 thickness was related to the yield of convoy electrons ( E e ≈ 540 eV) being emitted along the beam direction ( Θ = 0°) with a velocity ν c equal to the projectile velocity ν p and to the intensity of low energy “true” secondary electrons ( E e λ ( E e ). Our alternative interpretation is based on nonuniform erosion, which generates a modificaton of the bombarded and the contaminated target area with increasing irradiation time.

Convoy electrons accompanying neutral ejectiles in ion—solid interactions

Abstract Electron energy spectra (θ = 0°) induced by H+ (150 keV) and He+ impinging on thin carbon and copper foils (100–500 A) have been measured in coincidence with the emergent change states qf(H) = 0, 1 and qf(He) = 0, 1, 2 experiments were carried out in an ultrahigh vacuum chamber (P = 1.5×10−9 hPa), in order to minimise the charge changing of the ejectiles between the target and their detection in the novel charge state analysing detector UHLAND. The charge states were separated electrostatically and extreme care was taken to prevent them from overlapping. Convoy electrons accompanying the projectiles in low-lying continuum states were detected in coincidence not only with emerging charged ions, but also with neutral ejectiles. These measurements may help to clarify the discrepancies between recent data published by different groups.

Charge state analysis of heavy ions after penetration of uncleaned and sputter cleaned conducting surfaces

Abstract The evolution of the charge state distribution of fast ions inside a solid is of basic interest in various research fields as stopping power measurements etc. The existing models for the charge state evolution differ in the treatment of the projectile-exit-surface interaction, which has a strong influence on the final charge state distributions. We measured the charge state distributions for C+, N+, and O+ (30 ≤ E/M ≤ 130 keV u ) impact on thin C, Cu, and Au foils, where the surface properties were modified by sputter cleaning. The measurements show a pronounced change of the mean projectile charge state to lower values in the case of sputter cleaned surfaces. This result underlines the importance of the projectile-surface interaction for the generation of the outcoming charge state distribution.

Beam - foil convoy electrons emerging from uncleaned and cleaned surfaces in coincidence with charge-analysed projectiles including neutrals

We discuss measurements of convoy electrons performed with incident (50, 150 keV) and (100, 200, 400 keV) ions, in coincidence with charge-analysed projectiles emerging from thin (150 - ) C and Cu foils. A strong dependence of convoy electron yields on the projectile charge, as well as cusp-electron spectra in coincidence with neutrals are observed and compared with the characteristics of presently available models for beam - foil convoy electron emission. Measurements performed with sputter-cleaned target surfaces confirm that the transmission through the surface potential is important in determining both the coincident convoy electron yields and the final charge distribution of the emerging projectiles.

Deviation of the binary encounter electron energy from simple conservation laws in ion-atom and in ion-solid collisions

Abstract We have measured electron energy spectra from fast (0.4–2.0 MeV/u) light projectiles (H+, He+, H+2, H+3, H0) impinging on gaseous (He, Ar and Kr) and solid (C, Cu, Au, 600 A) targets under observation angles of 0° ⩽ Θ ⩽ 50° and Θ = 110°, 120°, 180°. Major interest was directed upon the position of the binary encounter and electron loss peaks, which are commonly assumed to follow simple kinematics. However, our measurements confirm recent results which show that the peaks are significantly shifted towards lower energies. For comparison we calculated double differential electron emission cross sections with different theoretical approaches.

Particle penetration through frozen gases

The energy deposition of swift charged particles penetrating solids is accompanied by such processes as particle (electrons, atoms, photons …) production or phase transition along the particle track. The electron yield obtained with thin copper foils covered with solid CO2 (or Xe) and the erosion of frozen CO2 (or Xe) by transmission of protons (1 MeV) was measured quantitatively. The obtained CO2 (or Xe) thickness was related 1. to the yield of convoy electrons (Ee ≃ 540eV) being emitted along the beam direction (Θ=O°) with a vector velocity ve equal to the projectile vector velocity vp and 2. to the intensity of low energy “true” secondary electrons (Ee < 50eV). The adsorbate thickness dependence of both electron yields is found to be independent of their electron transport lengths 1(Ee.