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The surface cracking behavior of vitreous fused silica (suprasil II) induced by MeV35C1 and19F ions was observed. The crack density increases with ion fluence, reaches a maximum (for 17 MeV35C1 at 1 × 1013 35Cl/cm2 and for 17 MeV19F at 5 × 1013 19F/cm2) and then declines. The cracks close up for subsequent higher ion fluences. The surface cracking occurs in different ion fluence ranges with ion mass, for 17 MeV35C1 5xl012-lxl014 35Cl/cm2; for 17 MeV19F, 1 × 1013-3 × 1014 19F/cm2. No surface cracks were observed for 2 MeV H+ for the ion fluence range of 5 × 10,4-1017 ‘H/cm2. The measurements of the defects in silica samples with EPR indicate that the surface cracking occurs in the transition region where the ion damage tracks partly overlap. We tentatively suggest that the surface cracking may result from heavy ion tracks in the insulating materials, and cracks close up at higher ion fluence due to the compaction of the irradiated area. [ABSTRACT FROM PUBLISHER]

We develop a new, quantitative model describing the electronically mediated erosion of dielectric materials by fast ion bombardment. This model is based on the concept that the effective inter-molecular lattice potential is transiently but significantly modified in some restricted region about the primary ion path, due to intense electronic excitation. The acceleration of the nuclei in this modified lattice potential transfers appreciable energy to molecular motion. Sputtering yields are calculated without the introduction of adjustable parameters or arbitrary normalization, and the results compare favorably with the available data. Sputtering induced by both heavy and light ions, on both refractory dielectric materials and condensed volatiles may be treated. The model calculations are consistent with observed yields ranging over three orders of magnitude. There are possible applications of the model to related radiation effects, including track registration and the soft failure of solid state computer devices. [ABSTRACT FROM PUBLISHER]

The energy and angular distributions of copper atoms ejected by 5 keV incident Ar ions have been simulated using the multiple interaction molecular dynamics technique. Calculations carried out with two independently written computer codes yielded essentially identical results. As in previous simulation studies of low to medium energy sputtering, virtually all ejected atoms came from the first layer or second layer. Two different ion-atom potentials were used in the simulations. Absolute sputtering yields depended strongly on the choice of potential; relative yields and angular distributions were found to be insensitive to the choice of potential. For Ar ions normally incident on the (100), (110), and (111) faces of a fcc Cu crystallite, ejected atoms from the second layer of the crystallite exited preferentially in the forward direction compared to those sputtered from the first layer. The energy spectra of atoms ejected from the second layers were harder than those of the first layer atoms. [ABSTRACT FROM PUBLISHER]

We have measured sputtering yields of H2O films with 19F ions at bombarding energies from 1.6 to 25 MeV. The sputtering yield was found to be very sensitive to the incident charge state of the beam, and insensitive to the thickness of the ice film for thicknesses ranging from approximately 20 to 80×l016H2O/cm2. The yield was independent of the target substrate temperature from 10 to 60 K and independent of the F beam current density from < 1 to approximately 5.5 particle nanoamps/mm2. There are several models proposed to explain enhanced sputtering of dielectrics; we have discussed their relevance to our data. [ABSTRACT FROM PUBLISHER]

Sputtering yields of solid SO2 by high energy ions were measured in order to study the mechanism for sputtering dielectrics with ions in the electronic stopping power region. The incident ions were helium and fluorine with energies ranging from 1.5 MeV to 25 MeV. Yields as high as 7000 SO2 molecules/incident F ion were measured; the 1.5 MeV 4He beam had a sputtering yield of 50. The data are compared to yield measurements made on UF4 and H2O targets. There is a striking similarity in the yield as a function of the incident F energy for all three targets. The data compare favorably with theoretical yield curves based on a new model for the sputtering which considers the electronic excitations induced in the target by the incident beam. Measurements and calculations of this sort are also useful in understanding processes which occur on the surface of Jupiter's satellite Io, which is covered with SO2 frost and bombarded by energetic ions trapped in the Jovian magnetosphere. [ABSTRACT FROM PUBLISHER]

The sputtering of UF4 targets by energetic beams of 16O, 19F, and 35Cl ions has been investigated for beam energies in the range 0.12 to 1.5 MeV/amu. The sputtering yields, which follow the same trend as the electronic part of the projectile energy loss in the material, are observed to have a strong dependence on the charge state of the incident ions. Data have been taken both in transmission and reflection (0° and 180° to the incident beam direction, respectively). Energy spectra of the neutral sputtered particles have been obtained for 5 MeV 19F ions and for 13 MeV 35Cl ions; in both cases the spectrum has a Maxwellian form. The data obtained are compared with several models of the high energy sputtering process. [ABSTRACT FROM PUBLISHER]

A velocity spectrum of neutral sputtered particles as well as a low resolution mass spectrum of sputtered molecular ions has been measured for 4.74 MeV 19F+2 incident on UF4. The velocity spectrum is dramatically different from spectra taken with low energy (keV) bombarding ions, and is shown to be consistent with a hot plasma of atoms in thermal equilibrium inside the target. We propose a “thermalized ion explosion” model for high energy sputtering which is also expected to describe track formation in dielectric materials. The model is shown to be consistent with the observed total sputtering yield and the dependence of the yield on the primary ionization rate of the incident ion. [ABSTRACT FROM PUBLISHER]

Using a double-spike, mass spectrometric technique, we have measured the absolute isotopic composition of Ca sputtered from several Ca minerals by normally incident, low energy, nitrogen beams (130 keV N+ and 100 keV N+ 2). The precision in the 40Ca/44Ca ratio is 0.05% for samples as small as 10−7 g, corresponding to a resolution of possible mass dependent isotope fractionation effects of ∼0.01% per unit mass difference. In general, the material sputtered first was isotopically light by up to 2% in the isotopic ratio 40Ca/44Ca when compared with the measured isotopic composition of the target; as the bombardment progressed, the isotopic composition became less light and approached the initial composition of the target. We have demonstrated that, after prolonged bombardment, a surface layer develops on the target with a distinctly heavy isotopic composition; the thickness of the layer is a significant fraction of the range of the bombarding ions. Angular distributions of the sputtered material show that, throughout the bombardment, the material ejected back along the beam direction was isotopically light relative to the material ejected at oblique angles; the difference in the isotopic ratio 40Ca/44Ca over the angular range was ∼ 1.5%. This fractionation with angle of ejection persisted even when a quasi-steady state was reached after heavy bombardment, when the isotopic composition of the material averaged over angle had become essentially indistinguishable from that of the pristine target. These results indicate that sputtering produces isotope fractionation and that there is a marked angular dependence in the effects. This suggests that solar wind sputtering of the lunar surface may contribute to the isotopic and elemental enrichments observed for the surface layers of soil grains. [ABSTRACT FROM PUBLISHER]

We have studied the sputtering of 235U from UF4 surfaces by ions with energies in the electronic stopping region. The observed sputtering yields are very large and are associated with the electronic stopping power. Measured yields produced by 19F ions at energies ranging from 1/16 MeV/amu to 1½ Mev/amu exhibit a peak of S = 7.1 ± 1.5 for 19F+3 at an energy of ¼ MeV/amu. The data suggest that the yield depends on the charge state of the incident ion. The yields are independent of target temperature in the range between 70°C and 170°C. The energy spectrum of the neutral component of the sputtered particles produced by ¼ MeV/amu 19F+2 has been measured with the mechanical time-of-flight spectrometer developed by Weller and Tombrello. The spectrometer data indicate that a large fraction of the sputtered particles is charged. We also describe the behavior of high energy sputtering of UF4 by 4He, 16O and 20Ne. Experiments with 16O and 20Ne beams at 100 keV show that the Sigmund theory adequately describes the sputtering of UF4 in the nuclear stopping region. [ABSTRACT FROM PUBLISHER]

The sticking probabilities for sputtered atoms of 93Nb and 103Rh incident on Al2O3 surfaces have been measured using the backscattering of MeV heavy ions. In the circumstance where the collecting surface has become thickly covered, the sticking probabilities integrated over the energy distribution of sputtered atoms are 0.97 ± 0.01 and 0.95 ± 0.01 for 93Nb and 103Rh, respectively. In the limit of negligible areal coverage of the collector. the accuracy is less; in this case the sticking probabilities are 0.97+ 0.08 and 0.95+0.05 0.08. [ABSTRACT FROM PUBLISHER]

We have measured the energy dependence of the trapping probability for sputtered 235U atoms striking an oxidized aluminum collector surface at energies between 1 eV and 184 eV. At the lowest energies approximately 10% of the uranium atoms are not trapped, while above 10 eV essentially all of them stick. In addition, we present trapping probabilities averaged over the sputtered energy distribution for uranium incident on gold and mica. [ABSTRACT FROM PUBLISHER]

The fission track technique for detecting 235U has been used in conjunction with a mechanical time-of-flight spectrometer in order to measure the energy spectrum in the region 1 eV to 1 keV of material sputtered from a 93% enriched 235U foil by 80 keV 40Ar+ ions. The spectrum was found to exhibit a peak in the region 2–4 eV and to decrease approximately as E –1.77 forE ≳ 100 eV. The design, construction and resolution of the mechanical spectrometer are discussed and comparisons are made between the data and the predictions of the random collision cascade model of sputtering. [ABSTRACT FROM PUBLISHER]

A fission track technique was employed to study the sputtering of uranium by 1H+, 4He+, and 40Ar+ ions with energies up to 120 keV. The technique involves detection of fission tracks produced in mica by 235U sputtered onto collector foils which are subsequently irradiated with thermal neutrons. This method is extremely sensitive and allowed measurement of sputtering yields less than 10−4 atoms per ion. It also made possible a detailed study of the emission of chunks from the uranium targets during sputtering. Mass distributions of chunks emitted during bombardment by 40-120 keV protons and by 80 keV argon are presented. Angular distributions of sputtered material and total sputtering yields for uranium metal under bombardment by 13-120 keV protons and by 40-120 keV 4He+ are also presented. Sputtering yields for 40 and 80 keV 40Ar+ were measured as well. Comparisons are made between the experimental results and those predicted by the collision cascade model. [ABSTRACT FROM PUBLISHER]

We have measured the yields of 90 keV 40Ar+ and V4He+ sputtering of Mo and V samples by the use of a new radio-tracer technique. This technique involves activating the samples by high-energy charged-particle irradiation before sputtering, and using conventional γ-ray counting methods to analyze the material subsequently sputtered onto collector foils. We have also measured angular distributions of the sputtered material, and compared these results and our total sputtering yields with the predictions of Sigmund's sputtering theory. Further comparisons between our radiotracer results and those obtained for 40Ar+ sputtering of unactivated Mo and V samples, determined from elastic backscattering measurements using 12 MeV 16O ions, show that the techniques give consistent results. [ABSTRACT FROM PUBLISHER]

Experimental energy loss measurements were made for protons of energy 0.5 to 1.6 MeV channeling through 1 μm thick silicon targets along the (110), (11l), and (211) axial directions, and the {l00}, {110}, (1ll}, and (211) planar directions. These data have a precision of ±5% and are presented graphically along with an extensive summary of other data in the literature. The new data cover a wider range of channels than has previously been examined with protons and are in agreement with the helium data of Eisen et 01.' A standard theory of energy loss is summarized and ampli- tied, and straggling is calculated theoretically. Local electron densities for various channels in silicon are extracted from plane and row averaged Thomas Fermi potentials via v ▿2 V = 4 πρ, and are used in the theoretical energy loss and straggling equations. The results agree with the experimental data to within 5%. The need for more precise measure-ments in order to make a decisive test of the theory is discussed. [ABSTRACT FROM PUBLISHER]

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