Electronic sputtering of solid nitrogen and oxygen by keV hydrogen ions has been studied at two low-temperature setups. The yield of the sputtered particles has been determined in the energy regime 4–10 keV for H+, H 2+ and H3+ ions. The yield for oxygen is more than a factor of two larger than that for nitrogen. The energy distributions of the sputtered N2 and O2 molecules were measured for hydrogen ions in this energy regime as well. The yields from both solids turn out to depend on the sum of the stopping power of all atoms in the ion. The yield increases as a quadratic function of the stopping power for oxygen, but slightly slower for nitrogen. The energy distributions do not exhibit strong features, but are similar to those published earlier for electron sputtering.

Solid N2 has been bombarded by 0.5 keV electrons. Mass spectrometry and time of flight measurements were performed for the sputtered neutral particles. The dominant component is molecular N2, but also N-atoms and a small number of N3- and N4-molecules were observed. The energy distribution of N2 and N indicates that the sputtering is caused by non-radiative transitions that release up to more than 6 eV. The important non-radiative transitions in solid N2 are discussed.

Sputtering of Si in a Cl2 environment by Ar+ and Xe+ ions with energies down to 75 eV has been investigated. Mass spectra and time-of-flight distributions of the sputtered species have been measured. Under 75-eV Ar+-ion bombardment of the Si target, SiCl, SiCl2, SiCl3, and/or SiCl4 are sputtered. When increasing the ion energy the SiCl4 contribution decreases in comparison with SiCl. This is caused by the fact that the newly formed Si-Cl compounds are sputtered at a high rate compared to the rate of SiCl4 formation. Time-of-flight distributions indicate that under 100-eV Ar+-ion bombardment the species are not sputtered by a collision-cascade mechanism. The spectra can be fitted by Maxwell–Boltzmann distributions at a high (>2000 K) temperature. Increasing the Ar+-ion energy to approximately 250 eV the time-of-flight spectra of the sputtered species change from Maxwell–Boltzmann-like into spectra as expected for a collision-cascade mechanism. For low-energy Xe+ ion bombardment the sputtered species also show Maxwell–Boltzmann time-of-flight distributions. The change from Maxwell–Boltzmann to collision-cascade distributions occurs at higher ion energies than for Ar+-ion bombardment. The results obtained for low ion energies are discussed in terms of evaporation from an ion-induced hot spot.

Ar and Xe solids have been bombarded by 0.5 keV electrons. Mass spectrometry and time of flight measurements were made of the ejected neutral particles. The former measurements indicate that only atoms are emitted from the surface in contrast to sputtering by ions in which also clusters are found. The time of flight distribution of Ar atoms shows features distinctly different from those for Xe. The results are explained by creation of excitations, their transport towards the surface and subsequent decay of molecular excitons to a repulsive state.

Time-of-flight distributions of sputtered Au atoms have been measured under 4 ke V ${\mathrm{I}}^{+}$ and 8 keV ${\mathrm{I}}_{2}^{+}$ impact. The results show that a developing thermal spike contributes to the sputtering yield. It is higher under ${\mathrm{I}}_{2}^{+}$ bombardment but the measured temperature obtained from Maxwell-Boltzmann fits is lower, suggesting a lower effective surface binding energy ${U}_{0}$ for ${\mathrm{I}}_{2}^{+}$ bombardment. A correlation between spike temperatures and ${U}_{0}$ is discussed.

Si sputtering yields and Si to SiO2 etch rate ratios have been determined by measuring the depth of the etched craters after Ar+ ion bombardment. The experiments have been performed with energies down to 50 eV both with and without Cl2. Surprisingly high Si sputtering yields are obtained in a Cl2 environment by low-energy Ar+ ions. Hence, the influence of Cl2 on the Si sputtering mechanism is much larger for low ion energies than for high ion energies. Whereas the Si sputtering yield is enhanced by the presence of Cl2, the SiO2 sputtering yield is hardly affected. Therefore, large differences in the etch rate (high selectivities) between Si and SiO2 are obtained at low ion energies.

SiO2 has been bombarded by 3 keV Ar+ ions under simultaneous exposure to a thermal beam of Cl2 or XeF2. Mass spectra and time-of-flight distributions of the sputtered species have been measured. It is observed that during XeF2 exposure the sputtering yield of SiO2 is enhanced with a factor of 2.3. After ionizing the neutral ejected Si species, we have detected SiF+x (x=0–4) and SiOF+y ( y=0–2). The kinetic energy distributions of these particles indicate that the newly formed species have been bound loosely to the lattice and that they are sputtered predominantly by a collision cascade mechanism. The results are explained by assuming that adsorbed F atoms are mixed into subsurface layers in which Si–F bond formation takes place. Hardly any chemical enhancement of the sputtering yield of SiO2 is observed when Cl2 is added. In this case the Si species are detected as SiCl+x and SiOCl+y (x, y=0–2). The chlorine peak (Cl+) is an order of magnitude higher. The kinetic energy distribution of Cl shows that most of the chlorine is in the lattice chemically unbound. From the measurements it is concluded that the heat of formation determines that in the collision cascade Si–F bonds are formed while Si–Cl bonds are not. Differences in the enhancement of the sputtering yield between silicon and SiO2 can also be explained by differences in heat of formation.

Condensed layers ot methane at 20 K have been bombarded by 6–8 keV Ar+, He+ and H2+ ions. Mass spectra and Kinetic energy distributions of neutral species sputtered from these layers have been measured. We have found sputtered species with masses up to 72 amu and thus with at least 5 carbon atoms. In addition to this an involatile residue was formed. Analysis by pyrolysis mass spectrometry showed this residue to contain species with masses up to at least 170 amu which therefore contain at least 12 carbon atoms. The kinetic energy distributions of sputtered methane molecules lie between those of a Maxwell-Boltzmann distribution and a collision cascade. Higher values are reached for Ar+ than for the light ions. From these observations we conclude: for both light and heavy ions radicals are formed, which combine to new molecules. These exothermic reactions produce heat which causes desorption. The high energy tail for bombardment with argon ions shows that part of the sputtering is caused by momentum transfer.

Experiments show that silicon at 100 K can be etched by 1 keV electrons, when simultaneously exposed to a beam of thermal (300 K) SF6. A yield has been found of approximately 0.4 Si atoms per incoming electron. The etch mechanism has been investigated by mass spectrometry and time-of-flight measurements of the ejected species. The results indicate that during etching SiF4 is formed, which subsequently evaporates. In addition, species are sputtered from the target with relatively high energies. Mechanisms for the formation of these energetic particles are discussed.

Condensed layers of methane at 20 K. have been bombarded by electrons with an energy of 265 and 515 eV. The neutral sputtered flux was analyzed for mass and kinetic energy. Besides CH4 also larger molecules are sputtered. During this process an involatile residue is formed. The kinetic energy distributions for methane, obtained from the times of flight, fit a Maxwell-Boltzmann distribution curve with T = 170 K. These results are explained by exothermic chemical processes which are initiated by the electrons and which lead to spots with a higher temperature. Large molecules which do not desorb are subjected to chemical reactions which ultimately lead to a nonvolatile residue.

Etching of silicon by SF6 induced by keV Ar+ ions has been investigated as a function of target temperature and flux of SF6 molecules. The emitted species have been identified by mass spectrometry and their energy distributions have been determined by time-of-flight measurements. The results indicate that new products are formed, predominantly by reactions of silicon with F atoms formed upon dissociation of SF6 molecules. The effective binding energies are obtained for SiFx (x = 1−4) and SiS. It can be concluded that the newly formed products are present in an amorphized modified top layer of the silicon, and are subsequently sputtered by a collision-cascade-like mechanism. For SiFx-compounds evaporation is only important for SiF4 molecules.

Sputtering of silicon by 3-keV Ar+ ions in the presence of a molecular SF6 beam has been investigated by mass spectrometry and time-of-flight measurements. At temperatures below 100 K chemical reactions are induced between the silicon and an adsorbed layer of SF6 under ion bombardment leading to newly formed molecular products. The main products formed are SiFx′ (x=0–4) and a small amount of SiSFy compounds (y=0–2). The kinetic energies of these molecular species are for the major part in the 0.1-eV region which excludes evaporation at substrate temperature to be a dominant mechanism for erosion. An effective sputtering yield for silicon of approximately 15 is obtained.

The sputtering yield of Si when bombarded with a flux φAr+ of low‐energy Ar+ ions may be enhanced a few times when the Si surface is exposed simultaneously to Cl2 fluxes φCl2 about one order of magnitude larger than φAr+. The mechanism of this synergistic etching has been studied, using mass spectroscopy and time‐of‐flight techniques, for a φAr+ of about 5×1014 Ar+ cm−2 s−1 at Ar+ ion energies (Ep) from 0.25 to 5 keV, Cl2 fluxes between 1015 and 5×1016 Cl2 cm−2 s−1 and T in the range 300–625 K. As has been shown previously [J. Vac. Sci. Technol. A 2, 487 (1984)] the main products of the synergistic reaction are atomic Si and Cl and molecular SiCl and SiCl2; the kinetic energy distributions of the molecular products consist of two parts, a Maxwell–Boltzmann and a collision cascade‐like distribution. The Maxwell–Boltzmann part decreases relative to the collision cascade‐like part when T and/or Ep are increased and/or φCl2 is decreased. At the same time the collision cascade‐like part shifts to higher kineti...

The reaction of Si with Cl2 alone and under simultaneous exposure to an Ar+ ion beam is investigated as a function of target temperature and Ar+ ion energy using mass spectrometry and time-of-flight studies. The main products of the thermal reaction are SiCl4 at low and SiCl2 at higher temperatures. The main products of combined exposure are atomic Si and Cl and molecular SiCl and SiCl2. The contributions of atoms and molecules are of a comparable order of magnitude. It appears that the main fraction of the products of the combined exposure results from sputtering and not from stimulation of the thermal reaction path by ion bombardment. The results strongly suggest that a modification of the top atomic layers of the Si, from which the products are sputtered, by incorporation of significant quantities of Cl plays a dominant part in the reaction mechanism.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSynthesis and sputtering of newly formed molecules by kiloelectron volt ionsA. E. De Vries, R. A. Haring, A. Haring, F. S. Klein, A. C. Kummel, and F. W. SarisCite this: J. Phys. Chem. 1984, 88, 20, 4510–4512Publication Date (Print):September 1, 1984Publication History Published online1 May 2002Published inissue 1 September 1984https://pubs.acs.org/doi/10.1021/j150664a014https://doi.org/10.1021/j150664a014research-articleACS PublicationsRequest reuse permissionsArticle Views40Altmetric-Citations20LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access options Get e-Alerts

Beams of small molecular clusters of H2O, NH3, CO and CH4 have been produced by a nozzle system. The beams were analyzed using a quadrupole mass spectrometer with an electron impact ionizer. The fragment-ion distributions have been determined. By studying their behaviour vs. nozzle pressure or temperature, fragment ions could be assigned to specific clusters.

Ever since the first description of the synthesis of molecules by impinging protons on ices1, the possibility of formation of various molecules on cold surfaces by particle radiation has been widely discussed2–5. Because fluxes of light ions with energies of ∼1 keV AMU−1 exist in a wide variety of astrophysical sites6 there has been a dispute over whether molecules in space are formed by such a process or by gaseous reactions7. We have recently studied sputtering of species by bombarding simple frozen gases such as water, carbon monoxide and ammonia with light ions2. With these substances, only rather simple molecules were found. However, when bombarding methane, we detected much larger molecules in the sputtered beam—hydrocarbons containing up to at least 13 atoms. We propose, therefore, that bombardment of frozen methane by keV protons may produce large molecules in the Solar system.