A thermalized ion explosion model for high energy sputtering and track registration

A velocity spectrum of neutral sputtered particles as well as a low resolution mass spectrum of sputtered molecular ions was measured for 4.74 MeV F-19(+2) incident of 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. A thermalized ion explosion model is proposed for high energy sputtering which is 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

Fabrication and characterization of thin, self‐supporting germanium single crystals

Thin Gesingle crystals (≤1 μm) up to 4 mm in diameter have been fabricated from epitaxialGefilmsgrown by atmospheric pressurechemical vapor deposition on Si(100) wafers. The thin Ge windows are formed by chemically etching away both the Si substrate and the region of the Gefilm near the interface that contains misfit dislocations associated with heteroepitaxialgrowth and relaxation of the Gefilms. The resulting Gefilms are comparable in crystalline quality to bulk Ge wafers, as indicated by ion channeling studies

Coulomb Explosion and Thermal Spikes

A fast ion penetrating a solid creates a track of excitations. This can produce displacements seen as an etched track, a process initially used to detect energetic particles but now used to alter materials. From the seminal papers by Fleischer et al. [Phys. Rev. 156, 353 (1967)] to the present [C. Trautmann, S. Klaumunzer and H. Trinkaus, Phys. Rev. Lett. 85, 3648 (2000)], `Coulomb explosion' and thermal spike models are treated as conflicting models for describing ion track effects. Here molecular dynamics simulations of electronic-sputtering, a surface manifestation of ion track formation, show that `Coulomb explosion' produces a `heat' spike so that these are early and late aspects of the same process. Therefore, differences in scaling are due to the use of incomplete spike models.Comment: Submitted to PRL. 4 pages, 3 figures. For related movies see: http://dirac.ms.virginia.edu/~emb3t/coulomb/coulomb.html PACS added in new versio

International Consensus Statement on Rhinology and Allergy: Rhinosinusitis

Background: The 5 years since the publication of the first International Consensus Statement on Allergy and Rhinology: Rhinosinusitis (ICAR‐RS) has witnessed foundational progress in our understanding and treatment of rhinologic disease. These advances are reflected within the more than 40 new topics covered within the ICAR‐RS‐2021 as well as updates to the original 140 topics. This executive summary consolidates the evidence‐based findings of the document. Methods: ICAR‐RS presents over 180 topics in the forms of evidence‐based reviews with recommendations (EBRRs), evidence‐based reviews, and literature reviews. The highest grade structured recommendations of the EBRR sections are summarized in this executive summary. Results: ICAR‐RS‐2021 covers 22 topics regarding the medical management of RS, which are grade A/B and are presented in the executive summary. Additionally, 4 topics regarding the surgical management of RS are grade A/B and are presented in the executive summary. Finally, a comprehensive evidence‐based management algorithm is provided. Conclusion: This ICAR‐RS‐2021 executive summary provides a compilation of the evidence‐based recommendations for medical and surgical treatment of the most common forms of RS

Sputtering of uranium tetrafluoride in the electronic stopping region

We have studied the sputtering of ^(235)U from UF_4 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 ^(19)F ions at energies ranging from 1/16 MeV/amu to 1½ Mev/amu exhibit a peak of S = 7.1 ± 1.5 for ^(19)F^(+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 ^(19)F^(+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 UF_4 by ^(4)He, ^(16)O and ^(20)Ne. Experiments with ^(16)O and ^(20)Ne beams at 100 keV show that the Sigmund theory adequately describes the sputtering of UF_4 in the nuclear stopping region

Sputtering of UF_4 by high energy heavy ions

The sputtering of UF_4 targets by energetic beams of ^(16)O, ^(19)F, and ^(35)Cl 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 ^(35)Cl ions; in both cases the spectrum has a Maxwellian form. The data obtained are compared with several models of the high energy sputtering process

The sputtering of insulating materials by fast heavy ions

In this paper we review recent experimental results from our laboratory on sputtering of UF_4 and H_2O (ice) by fast heavy ions. Measurements have been made of the dependence of the sputtering yield on the incident ion type, charge state and energy. In the case of UF_4 the energy spectra of neutral sputtered particles have been obtained as well. There is a clear dependence of the sputtering yield on the electronic part of the stopping power, and the yield is strongly affected by the charge state of the incident ion, which shows that in the near-surface region from which sputtered particles arise the charge state of the incident ion has not reached equilibrium. The shape of the energy spectra observed for UF_4 targets is that expected from a thermal distribution rather than that of the collision cascade from typical of ordinary sputtering. A model of the sputtering-track registration process that has arisen from these data is shown to provide a framework for understanding the close relationship of our observations to the “plasma desorption” of macromolecules

Fabrication and characterization of thin, self‐supporting germanium single crystals

Thin Gesingle crystals (≤1 μm) up to 4 mm in diameter have been fabricated from epitaxialGefilmsgrown by atmospheric pressurechemical vapor deposition on Si(100) wafers. The thin Ge windows are formed by chemically etching away both the Si substrate and the region of the Gefilm near the interface that contains misfit dislocations associated with heteroepitaxialgrowth and relaxation of the Gefilms. The resulting Gefilms are comparable in crystalline quality to bulk Ge wafers, as indicated by ion channeling studies