Amorphous silicon monoxide (∼100 nm thick), prepared by evaporation on rock salt, was bombarded with 80 keV He+ ions. Examination by transmission electron microscopy revealed that crystalline regions up to 15 nm diameter were produced throughout the amorphous matrix when the ion flux was greater than 2.0 × 10l8 ions/m2-sec in which the sample temperature was 850 ± C due to beam heating. Heating unirradiated samples to this temperature did not cause crystallization. The crystalline precipitates were identified as silicon using electron diffraction. The Si precipitates are thought to be initially present in unirradiated SiO and grow to an observable size during bombardment. The crystallization process followed nucleation and growth kinetics, and was found to saturate after .8% of the SiO had transformed to crystalline Si at a dose of 1.5 × 1022 ions/m2. Silicon monoxide fits into a group with other amorphous nonmetallic solids that have a crystallization to melting temperature ratio (Tc/Tm) greater than 0.30 and partially crystallize under ion bombardment. These materials form crystalline precipitates by an extended diffusion of atoms, and in compounds the stochiometry of the precipitate is typically lower than that of the initial amorphous matrix due to preferential sputtering effects on one of the species. On the other hand amorphization of crystalline nonmetals withTc/Tm>0.30 and crystallization of amorphous nonmetals withTc/Tm < 0.30 are not diffusional processes but rather transform in a localized region surrounding the individual ion paths.

A series of laboratory experiments has been performed to investigate the role of sulfur ion implantation on the differences in the reflectivity of Europa's “leading” and “trailing” hemispheres in the UV and visible. The lower reflectivity of Europa's trailing hemisphere at around 0.28 μm can be attributed to a SO band which is caused by either the implantation of sulfur ions from Jupiter's magnetosphere into the water-ice surface of Europa's trailing hemisphere or by the preferential condensation of SO2 from volcanism on the trailing side. Laboratory measurements of the strength of this absorption band allow an estimate of the column density of 2 × 1017 cm−2 SO bonds within the sampling depth of the photons reflected from Europa's trailing hemisphere. Under the conditions tested in the laboratory, sulfur implantation or SO2 deposition cannot account for the general “reddening” in the UV of the trailing hemisphere relative to the leading hemisphere, a feature which we previously showed can be produced by fast penetrating ions.

Ion and electron beam-induced deposition (BID) of thin (1–4 μm), conductive films is accomplished by dissociating and removing the nonmetallic components of an adsorbed, metal-based, molecular gas [SnCl4 and (CH3)4Sn]. Previous research has focused primarily on room-temperature (monolayer adsorption) BID using electrons and slow, heavy ions. This study investigates low-temperature (120 K) BID in which the condensation rate of the precursor gas is well controlled. The residual metallic films are produced by using as incident beams either 2-keV electrons, 25-keV H2+, or 50-keV H2+, all of which provide predominantly electronic energy deposition, or 30-keV Ar+, which provides predominantly nuclear energy deposition. Residual films are analyzed ex situ by scanning electron microscopy, mechanical thickness measurements, resistivity measurements, Rutherford backscattering spectroscopy, and infrared spectrometry. A model is developed that considers bulk and surface dissociation mechanisms and sputtering to describe the BID process. The derived cross sections for the formation of a residue from condensed (CH3)4Sn are nonlinearly related to the total deposited energy approximately to the 1.4 power. The lowest electrical resistivity values of the residues (650 μΩ cm) are obtained only by significant loss of carbon, which is strongly dependent on the nuclear stopping power.

Measurements were made of the forward scattered secondary electron yield from thin carbon foils bombarded by heavy ions in the energy range from 2 to 100 keV/amu. The ratio, LAMBDA-f, of the forward scattered yield to the stopping power is constant from 2 to 10 keV/amu at 3.6 electrons cm2/(eV-mu-g) but as the ion energy is increased above 10 keV/amu, LAMBDA-f decreases to near 2.2 electrons cm2/(eV-mu-g).

Satellite in the Jovian and Saturnian system exhibit differences in reflectivity between their 'leading' and 'trailing' surfaces which can affect the local vapor pressure. Since these differences are thought to be due to differences in the flux of bombarding magnetospheric ions, the influence of ion impact on the UV-visible reflectance of water ice surfaces (20-90 K) by keV ion bombardment was studied. An observed decrease in reflectance in the UV is attributed to rearrangement processes that affect the physical microstructure and surface 'roughness'. The ratio in reflectance of bombarded to freshly deposited films is compared to the ratio of the reflectance of the leading and trailing hemispheres for Europa and Ganymede.

Satellites in the Jovian and Saturnian system exhibit differences in reflectivity between their "leading" and "trailing" surfaces which can affect the local vapor pressure. Since these differences are thought to be due to differences in the flux of bombarding magnetospheric ions, we studied the influence of ion impact on the UV-visible reflectance of water ice surfaces (20-90 K) by keV ion bombardment. An observed decrease in reflectance in the UV is attributed to rearrangement processes that affect the physical microstructure and surface "roughness." The ratio in reflectance of bombarded to freshly deposited films is compared to the ratio of the reflectance of the leading and trailing hemispheres for Europa and Ganymede.

We have bombarded condensed CO “ice” films with keV and MeV ions at low temperatures to investigate the physical sputtering mechanisms and chemical modifications of the ice. The sputtering yield measured for keV and MeV H+ and He+ ions indicates that the yield has a quadratic dependence on the electronic stopping power of the ions. Energy spectra of CO molecules sputtered by bombardment with 53 keV He+ and 34 keV Ar+ ions are very similar and show a collision-cascade-like behavior. We explore the origin of this quadratic dependence in terms of several models proposed for sputtering by electronic excitation and conclude that the quadratic dependence is intrinsic to the electronic relaxation process for CO. RBS measurements of the residue produced from sputtering various thicknesses of the initial CO film (∼ (3–25) × 1017 CO/cm2) indicate the production of the residue is approximately proportional to the initial thickness, accounts for ∼ 2% of the initial mass, and has a stoichiometric composition of approximately C3O. The production and composition of the residue is discussed in terms of existing mechanisms for the radiolysis of gas phase CO.

Ejected-atom kinetic energy spectra from electronically excited Ar, Kr, and Xe have been interpreted in terms of two mechanisms: the first due to exciton decay in the surface layer and the second due to exciton decay in the subsurface layers. We use the absolute ejection yields for the surface component to determine the efficiency of the surface layer in trapping excitons produced by incident energetic ions and electrons. Estimates of the ratio of surface-to-bulk exciton trapping efficiencies are 4.7, 6.5, and 3.9 for Ar, Kr, and Xe, respectively, at 15 K.

Abstract Experimental results for the kinetic energy spectra of atoms ejected from rare gas solids as a result of electronic excitation are reviewed and analyzed in terms of the ejection processes and energy states involved. These analyses are aided by classical dynamics simulations of the motion of atoms and dimers in the surface region of the solid. The results indicate that an important process is the ejection of an excited dimer with small kinetic energy, followed by its radiative decay and the subsequent repulsion of the two atoms. For incident He+ on Xe we explore the contribution to sputtering from both the electronic and nuclear energies deposited in the solid.

Measurements have been made of the total yield and sputtered particle time-of-flight spectra for the sputtering of solid argon, krypton, and xenon films by 33 keV Ne+, Ar+, Kr+, and Xe+. A careful extrapolation for low energy (long flight-time) particles was made and the resulting time-of-flight spectra were normalized to the experimentally determined total yield, giving absolute yields that are differential in the ejected atom energy. The shape and magnitude of these absolute energy spectra were then compared with earlier experiments and models for sputtering. For the high energy end of the energy spectra the absolute yields are smaller than that predicted from collision cascade theory using the standard parameterization even when the total yields greatly exceed the cascade result. Also it is found from the low energy spectra that, for any ejection model, planar binding is not justified even for the lowest yield case studied here.

Experimental results on the molecular species ejected from condensed S8 at low temperatures by 10–60 keV H+, He+, N+, Ne+, Ar+, Kr+, and Xe+ are presented. Net erosion rates and mass and energy spectra of the ejected species were measured. The net surface erosion rate measured at 15 K was found to exhibit two distinct regimes. For the heavier ions starting with N+ the sputtering yield increased linearly with the collisional energy deposited at the surface. For incident keV H+ the sputtering yield was determined by electronic excitations and when combined with MeV He+ data exhibited a roughly quadratic dependence on the electronic stopping power. For keV He+ the expected contributions to the yield from electronic and collisional energy deposition were comparable. The mass spectra for the ejected sulfur species Si, i = 1–8, by incident 34 keV Ne+, Ar+, Kr+ and Xe+ showed that, whereas the overall yield was nearly linear in the energy deposited at the surface, the relative yields of each molecular species varied from linear for the smallest, S1 and S2, to nearly quadratic for S8, S4 was the only exception to this trend. Its dependence on the surface deposited energy was also nearly quadratic indicating that it came predominantly from vibrationally dissociated S8. Correcting the mass spectrometer signal to account for various instrumental sensitivities, we found that ∼ 66% of the total yield corresponded to S2 ejection. The ejected molecule energy spectrum for S1 had the usual 1/E2 dependence at higher energies (∼ 1 eV) associated with the linear cascade model but S2, S3, and S5 fell off more rapidly with increasing energy. These results are compared to previous measurements of sulfur sputtering and discussed in terms of current ideas concerning the sputtering of monatomic and multicomponent targets.

A number of the icy satellites of the outer planets exhibit interesting hemispherical differences in brightness1–5 which have been attributed to enhanced bombardment by the local plasma of one hemisphere. The plasma bombardment is thought to erode the icy surfaces and implant species, thereby altering the surface reflectance spectra2,3, as well as producing fresh plasma6. Here we present the first results of laboratory measurements of the wavelength dependence of the alteration of the visible reflectance spectra of H2O ice irradiated by keV ions. When the implanted species is chemically neutral, absorption is slightly enhanced below 0.55 μm. For an incident species containing sulphur, a strong absorption feature is produced at 0.4 μm corresponding (probably) to S3. This occurs at too large a wavelength to account for the absorption feature observed at Europa by Voyager and therefore casts doubt on the recent interpretations7–9 of the reflectance data of Europa.

Measurements have been made of the sputtering yields, the mass spectra of ejected molecules, and ejection rates for various kiloelectronvolt ions incident on sodium sulfide (Na2S). The sputtering yields were small compared to those measured earlier for the more volatile sulfur (S8) and SO2 due to the strong ionic bonding in the solid. The mechanism of sputtering for the corotating sulfur and oxygen ions in Jupiter's magnetosphere is due to a cascade of quasi-elastic collisions initiated by the incident ion. The mass spectrum indicated that sodium is ejected predominantly as a molecule with a lesser amount ejected as atomic sodium. Making several assumptions it seems unlikely that the sputtering of Na2S by magnetospheric ions can maintain the observed neutral cloud densities. Instead, the sodium probably exists as a larger polysulfide for which we show that the sputtering yield should be greater.

Measurements of total yields, temperature dependences, mass spectra, and energy spectra of molecules sputtered from condensed sulfur (S8) at low temperatures by keV ions are reported and results are given for Jovian plasma ion bombardment of Io. A change in the reflectance of the sulfur, which can be removed by annealing, is produced by the most penetrating ions and may be connected with the darker, colder polar regions on Io. The measured sputtering yields are much lower than those estimated earlier for room temperature sulfur films but are comparable to previous measurements of keV ion sputtering of SO2 at low temperatures. The corrected mass spectrum indicates that ≈66% of the total yield corresponds to S2 ejection while only 5 and 16% correspond to S and S3, respectively. Therefore, if ions reach the surface of Io its atmosphere will have a non-negligible sulfur component of primarily S2. The ejection of S and S2 is temperature independent for temperatures characteristic of most of the surface of Io. The energy spectrum for S has an approximate 1/E2 dependence at high ejection energies, whereas S2 and S3 fall off more rapidly. Assuming 50% coverage of both sulfur and SO2 and a thin atmosphere (e.g., nightside and polar region) the direct sputter injection of sulfur atoms and molecules into the Jovian plasma torus and the indirect injection due to coronal processes are estimated. These injection rates for sulfur are compared to those for SO2 showing that injection from sulfur deposits contributes 13% to the total mass injection rate of ∼2–3 × 1029 amu/sec.

The sputtering of D2O and CO solids by keV ions has been studied by measuring the absolute sputtering yield and the masses of ejected particles. The yield results for several ions on D2O indicate that for the case where the energy deposited in nuclear motion is comparable to that deposited electronically, the sputtering yield is still determined to a large extent by the electronic energy. The mass spectra ejected from D2O by 30 keV Kr+ ions have a behavior very much like those produced by MeV ions. The bombardment of CO by kr+ results in the rapid production of a dark residue, stable at room temperature, and the ejection of CO, CO2, O2, O, C2 and (CO)2.