Projectile Incidence Angle Research Articles

A PRINCIPLE FOR MICRO-REGION SUPERPOSITING OF ION SPUTTERING

Solid surfaces subjected to energetic ion bombardment generally develop chara-cteristic structures, which may significantly change total and differential sputtering yields. The change is due to several competing effects, for instance, change of the effective projectile incidence angle, recapture of obliquely ejected particles (shadow effect), and element local-enrichment in different micro-region on the alloy surface. From these, we have now developed an efficient new theoretical method for covering all of the above effects exactly. This method and its application to the analysis of experimental results of element (Cd) and alloy system (ＡｌxSn１００－x)targets are de-scribed in detail.

Ion-photon emission of CuZn alloy

Some CuZn alloy targets of different known concentrations were investigated using the ion-induced photon emission (IIPE) technique. The influence of the projectile energy and incidence angle on the ratio of the intensities of CuI (324.7 nm) and ZnI (481.1 nm) emission lines was measured. The theory of the quantitative analysis of two-component alloys based on standards and taking into consideration the matrix effects is discussed.

Convoy-electron emission in 20-100-keV grazing proton bombardment of Cu(100).

We investigate the convoy-electron (CE) emission produced during grazing bombardment of a Cu(100) surface with 20--100-keV protons. At 0.5\ifmmode^\circ\else\textdegree\fi{} of incidence the CE peak measured at projectile energies below 50 keV along the direction of specular reflection of the ions presents the same width and shape as the CE peak corresponding to ${\mathrm{H}}^{+}$-He collisions and is considerably narrower than that observed in transmission through thin foils. This finding shows that CE's are mainly subjected to the Coulomb potential of the scattered ion when the velocity resolutions are high enough to localize electron states close to the ion velocity. A strong variation of the CE peak shape with the projectile incidence angle was also observed. This finding can be explained by a calculation that takes into account the angular distribution of the reflected ions.

Study of atomic excitations in sputtering with targets partially covered with oxygen

We bombarded pure elemental targets of beryllium, boron, magnesium, aluminium, silicon, titanium and gold with 80 keV Ar + ions and studied the excitation of sputtered atoms or ions under ultrahigh vacuum conditions as well as with oxygen present at the target surface. The measurements on magnesium, aluminium, silicon and titanium were made at projectile incidence angles from 0° to 85°. Excitation probabilities for gold were found to be very little influenced by oxygen, but for beryllium, boron, magnesium, aluminium, silicon and titanium the excitation probabilities were in many, but not all, cases found to depend strongly on the oxygen pressure as well as on the beam current density. This indicates that the excitation mechanism is markedly dependent on the initial electronic conditions in the solid.

Heavy-ion-induced secondary electron emission from magnesium, aluminium and silicon partially covered with oxygen

We bombarded magnesium, aluminium and silicon with 80 keV Ar + ions and measured the secondary electron emission yields at projectile incidence angles from 0° to 85° with oxygen present at the target as well as under ultrahigh vacuum conditions. The total secondary electron emission yields were found to depend markedly on the amount of oxygen present. The three elements studied show relatively large individual variations. For all three elements, and with as well as without oxygen present, the relative secondary electron emission yield was observed to vary as 1/cos v where v is the angle of incidence of the projectiles. This seems to indicate that the secondary electron production is initiated uniformly along the projectile path in the solid, in a region close to the surface. The results are discussed, and it is tentatively suggested that the increase in secondary electron emission caused by the presence of oxygen originates from electron loss from sputtered oxygen which initially is present as O 2− ions.

Study of atomic excitation in sputtering as a function of the projectile incidence angle

Solid targets of beryllium, boron and magnesium have been bombarded with 80 keV Ar + ions. Intensities of photons emitted from sputtered particles have been measured as functions of the angle of incidence of the projectile. Generally, the excitation intensities increase with increasing angle of incidence, but a few levels show much stronger angular variations than the majority of levels do. The results are discussed. It is concluded that whereas the common increase in excitation is caused by the general increase in the number of swift, sputtered atoms, a few levels are in addition selectively excited through molecular-orbital electron-promotion processes taking place in binary collisions.

Study of secondary electron emission from Be, B, Mg, and Au as a function of the projectile incidence angle

Solid targets of elemental boron, beryllium, magnesium and gold have been bombarded with 80 keV Ar + ions. In addition, gold was also bombarded with 80 keV Xe + ions. The emission of secondary electrons has been measured as a function of the incidence angle of the projectile. The results are discussed.

Study of atomic excitation in sputtering as a function of the projectile incidence angle

Solid targets of elemental beryllium, boron, magnesium, and gold have been bombarded with 80-keV ${\mathrm{Ar}}^{+}$ ions. Intensities of photons emitted from sputtered particles have been measured as functions of the angle of incidence of the projectile. Generally, the excitation intensities increase with increasing angle of incidence, but a few levels show much stronger angular variations than the majority of levels do. The results are discussed. It is concluded that whereas the common increase in excitation is caused by the general increase in the number of swift, sputtered atoms, a few levels are in addition selectively excited through molecular-orbital electron-promotion processes taking place in binary collisions.

The influence of surface structures on sputtering: Angular distribution and yield from faceted surfaces

Solid surfaces subject to energetic particle bombardment generally develop characteristic structures, which may significantly change the total and differential sputtering yield. The change is due to two competing effects, a yield-increase by an enhanced effective projectile incidence angle, and a yield-reduction by recapture of obliquely ejected particles. Both effects have been included in calculations of the sputtering yields from faceted surfaces in the regime where the plane surface yield follows a cos−v dependence on the incidence angle. Except at very low energies, the total sputtering yield is always increased by faceting. The angular distribution function is mainly influenced at large polar angles and may significantly deviate from that of the corresponding flat surface. This has important consequences both in comparisons between experimental and theoretical distribution functions as well as in applications such as thin film production, plasma contamination, secondary ion mass spectrometry etc.

High resolution Cherenkov and range detectors for balloon-borne cosmic-ray experiment

We have proposed a novel combination of an active Cherenkov detector and passive range detectors for the high resolution measurement of isotopic composition in the neighborhood of iron in the galactic cosmic rays. Here we describe tests both of a large area (4300 cm 2) Cherenkov counter, and of passive range detectors, built for an experiment based on this principle, the University of California IRIS experiment. Tests with heavy ions (2.1 GeV/amu 12C, 289 MeV/amu 40Ar, and 594 MeV/amu 20Ne) at the Lawrence Berkeley Bevalac have shown the spatial uniformity of response of the Cherenkov counter to be better than 1% peak-to-peak. Light collection efficiency is independent of projectile energy and incidence angle to within at least 0.5%. We believe this measured uniformity of response as a function of position, energy and angle to be the best reported to date. The counter, a 1.27 cm slab of Pilot 425, produces 35.3 Z 2 sin 2 θ cphotoelectrons/cm of Cherenkov signal from the primary ion (i.e., scintillation by the primary or by delta rays, and Cherenkov emission by delta rays are excluded) where Z is the projectile charge number, and θ c the Cherenkov angle. In addition, using 594 MeV/amu 20Ne, we tested the capability of passive Lexan track recorders to measure range in the presence of the nuclear interaction background which results from stopping particles through 0.9 interaction lengths of matter. We find that nuclear interactions produce an effective range straggling distribution only ∼75% wider than that expected from range straggling alone. The combination of these tested techniques makes possible high mass resolution in the neighborhood of iron. We discuss the implications of these measurements on the expected mass resolution of the IRIS experiment.

2.2.6 Microcraters Produced by Oblique Incidence of Projectiles

Using a Van de Graaff dust accelerator an experimental program has been carried out in order to study crater parameters as a function of projectile incidence angle. Iron particles were shot into quartz glass targets. The angle of incidence which is the angle between target normal and the impact direction of the projectile has been varied from 0° to 70° in steps of 10°. Projectile masses ranged from 10−11 to 10−13g with velocities between 3 and 20 km/sec and projectile masses at 10−2 g with 4 km/sec impact velocity using a light gas gun at the Ernst-Mach-Institut, Freiburg i.Br. The so called circularity index which is the ratio of the crater area to the area of the smallest circle around the crater is a measure of the asymmetry of a crater. The circularity index decreases linearly with increasing angle of incidence. Also a small increase of the circularity index with increasing projectile velocity has been found i.e. the craters have a rounder shape with increasing velocity at the same angle. The circularity index appears to be independent from the projectile mass in the mass range from 10−11 to 10−2 g for stainless steel targets.