HICS: Highly charged ion collisions with surfaces
Abstract The layout of a new instrument designed to study the interaction of highly charged ions with surfaces, which consists of an ion source, a beamline including charge separation and a target chamber, is presented here. By varying the charge state and impact velocity of the projectiles separately, the dissipation of potential and kinetic energy at or below the surface can be studied independently. The target chamber offers the use of tunable metal–insulator–metal devices as detectors for internal electronic excitation, a time-of-flight system to study the impact induced particle emission and the possibility to transfer samples in situ to an ultra high vacuum (UHV) scanning probe microscope. Samples and detectors can be prepared in situ as well. As a first example data on graphene layers on SrTiO3 which have been irradiated with Xe36+ are presented.
Electron emission induced by multiply charged Ar ions impinging on a tungsten surface
Abstract We have investigated collisions of Ar q+ ions on a clean polycrystalline tungsten surface at collision energies between 35 eV and 250 keV by analysis of the ejected secondary electrons. We report total electron yields as well as highly resolved energy spectra of electrons for different primary projectile charge states up to q = 12, for different collision energies and for different ejection angles. Special emphasis is given to the production mechanisms of electrons with energies above ≈ 100 eV. A relatively sharp structure near 212 eV, occurring for q ⩾ 8 predominantly at collision energies below ≈ 2 keV, is ascribed to Auger transitions in the neutralized projectile on its way to the surface. A broad structure between 125 and 175 eV, occurring predominantly at collision energies above ≈ 2 keV, can be interpreted as being due to target Auger processes, induced by vacancy transfer from the projectiles to the target atoms.
Modeling of chemical reactors—XXIX mixing-cell model for packed bed reactors. Steady state considerations. Problems of multiplicity
Abstract The axial heat and mass transfer in tubular catalytic reactors may be described by mixing-cell model and diffusion model as well. The diffusion description yields for a strong exothermic reaction and adiabatic conditions three steady state profiles, on the other hand the mixing-cell model gives rise to more than three steady states. A simple numerical and graphical analysis for mixing-cell model is presented.