Roman Pedrys

Sputtering yields and energy distributions from nonoverlapping subspikes in ion bombarded volatile solids

Abstract The yields and energy distributions of particles sputtered from rare gas solids bombarded by keV ions have been studied. The experimental yields are typically much larger than those predicted from linear collision cascade theory, but the dependence on the nuclear stopping power is similar. This discrepancy is explained by a sputtering model based on nonoverlapping elastic subspikes. The predictions from this model agree well with the experimental results for helium ions incident on solid neon and argon as well as nitrogen ions on solid xenon. The analysis of the collision regime demonstrates that the subspikes do not overlap at the primary energies considered.

Sputtering of frozen gases by molecular hydrogen ions

Abstract Measurements of the energy dependence of the electronic sputtering yield from solid nitrogen and deuterium bombarded by 4.5–10 keV atomic and molecular hydrogen ions are reported. The yield depends on the total energy deposition at the surface of the solid by the molecule. The behaviour in this energy range agrees well with that observed for electronic sputtering of water ice for energies at the high-energy side of the stopping power maximum.

Sputtering of solid nitrogen by keV helium ions

Abstract Solid nitrogen has become a standard material among the frozen molecular gases for electronic sputtering. We have combined measurements of sputtering yields and energy spectra from nitrogen bombarded by 4–10 keV helium ions. The data show that the erosion is electronic rather than knockon (collisional) sputtering. The sputtering yields induced by 3 He + and 4 He + ions of equal velocity are almost the same. The magnitude of the yields is about 20 N 2 molecules/He + ion. Most of the sputtered particles are molecules, but also atoms are emitted. For molecules, the energy distribution is similar to that for electron incidence, but differs considerably from that of bombardment by medium mass ions.

Sputtering of solid deuterium by He-ions

Abstract Sputtering of solid deuterium by bombardment of 3 He + and 4 He + ions was studied. Some features are similar to hydrogen ion bombardment of solid deuterium, but for the He-ions a significant contribution of elastic processes to the total yield can be identified. The thin-film enhancement is more pronounced than that for hydrogen projectiles in the same energy range.

Time-of-flight study of water ice sputtered by slow xenon ions

Abstract Sputtering of heavy water ice by 1–9 keV Xe ions was studied. The relative yield of sputtered D 2 O molecules and the energy distribution of the D 2 O molecules were measured in this energy range. In these energy distributions there is a distinct contribution from linear collision-cascade sputtering, which decreases relatively to the contribution from other sputtering mechanisms with primary energy. A clear change of the sputtering yield from linear to non-linear (elastic spike) sputtering was found as well.

Sputtering of the most volatile solids: the solid hydrogens

Abstract Electronic sputtering of the three stable hydrogenic solids, H 2 , HD and D 2 by keV hydrogen and deuterium ions has been studied at the low-temperature setup at Riso. The yield of the sputtered particles has been determined for hydrogenic films of thicknesses ranging from 0.1 × 10 18 up to 10 × 10 18 molecules/cm 2 and for 4–10 keV H + , H 2 + , H 3 + and D 3 + ions. The yield increases with decreasing film thickness for solid hydrogen as well as for deuterium. This behavior agrees with the trend observed for other volatile gases. For thick films the yield decreases to a constant value. This thick-film yield can be approximated fairly well by a quadratic function of the stopping power except for a somewhat steeper dependence for proton-bombarded deuterium. The yield increases strongly with decreasing sublimation energy from one isotope to another. No existing theory can account for the dependence of the yield on the electronic stopping power as well as the sublimation energy.

Synthesis and characterisation of PEG-peptide surfaces for proteolytic enzyme detection.

AbstractPeptide surfaces were obtained by the covalent immobilisation of fluorescently labelled pentapeptides carboxyfluorescein–glycine–arginine–methionine–leucine–glycine, either directly or through a poly(ethylene glycol) (PEG) linker on modified silicon wafers. Each step during the preparation of the peptide surfaces was confirmed by several surface characterisation techniques. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy were used to determine the surface composition, the wafers philicity was measured by contact angle and atomic force microscopy was used to investigate the surface morphology. Exposure of the peptide surfaces to trypsin resulted in the release of a fluorescently labelled peptide product, which allowed the kinetics of the enzymatic reaction to be followed with the aid of fluorescence spectroscopy. The electrospray ionisation mass spectrometry analysis of the post-digestion solution confirmed that the pentapeptides attached to the solid support undergo specific trypsin hydrolysis at the C-terminus of the arginine residues. Detailed surface analyses before and after the enzyme action was performed using ToF-SIMS. Because of the limited accessibility of the short peptide directly attached to the surface, a quantitative yield of enzymatic hydrolysis was observed only in case when the peptide was bound through the PEG linker. The insertion of the PEG linker increased the number of immobilised peptides and the rate of enzymatic digestion which consequently improved the quality of the enzyme assays. The described approach may be used for different peptide sequences designed for other proteases. FigureMonitoring of trypsin hydrolysis on PEG-peptide surface

Sputtering of carbon monoxide ice by hydrogen ions

Carbon monoxide is an important constituent of comet comae, of icy surfaces of planetary bodies, and of interstellar grains. We present new laboratory studies of sputtering of frozen CO by hydrogen ions for energies below 10 keV. The sputtering yield turned out to depend critically on the energy and the electronic stopping power, (dE/dx) e , for the ions. The yield for a 9 keV H + incident on solid CO was ∼34 CO/H + . For proton bombardment the yield is proportional to (dE/dx) 1,3 e , similar to the behavior of the sputtering yield for water ice. It means that the particle ejection occasionally requires species from two ionization/excitation events. For molecular ions the yield for CO ice increases with the square of the stopping power (dE/dx) e . The distribution of the sputtered CO molecules exhibits a maximum at 13 meV and falls off strongly with ejection energy E 1 . A complicating feature is the formation of a residue, possibly CO 2 ice, during bombardment of solid CO. The sputtering yield depends slightly on the initial residue, similar to the case of sputtering by keV electrons. The sputtering yield and the chemical efficiency are high compared to similar properties of solid N 2 , which means that mixtures of these solids are preferentially depleted of CO.

Sputtering by excitonic and elastic processes from solid neon by He ion bombardment

Abstract Sputtering of solid neon by keV He+ ions and 0.2 keV electrons has been studied. We have measured the energy distributions of neon atoms emitted from neon during bombardment by these particles. The ion-induced distributions show features from knockon (elastic) as well as electronic (inelastic) sputtering processes. The electronic components have been identified on the basis of the distribution from electron impact.

Water ice as a matrix for film production by matrix-assisted pulsed laser evaporation (MAPLE)

We have studied water ice as a matrix for the production of PEG (polyethylene glycol) films by MAPLE at 355 nm. The deposition rate is small compared with other matrices typically used in MAPLE, but the deposition of photofragments from the matrix can be avoided. At temperatures above −50°C of the target holder the deposition rate increases strongly, but the evaporation pressure in the MAPLE chamber also increases drastically.