Creation of Nanohillocks on CaF 2 Surfaces by Single Slow Highly Charged Ions

Institut für Allgemeine Physik, Vienna University of Technology, Vienna, Austria.
Physical Review Letters (Impact Factor: 7.73). 06/2008; 100(23):237601. DOI: 10.1103/PHYSREVLETT.100.237601
Source: PubMed

ABSTRACT Upon impact on a solid surface, the potential energy stored in slow highly charged ions is primarily deposited into the electronic system of the target. By decelerating the projectile ions to kinetic energies as low as 150 x q eV, we find first unambiguous experimental evidence that potential energy alone is sufficient to cause permanent nanosized hillocks on the (111) surface of a CaF(2) single crystal. Our investigations reveal a surprisingly sharp and well-defined threshold of potential energy for hillock formation which can be linked to a solid-liquid phase transition.

Download full-text


Available from: A. S. El-Said, Jun 19, 2015
1 Follower
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The status of the new EBIS-A irradiation facility constructed by the Dreebit GmbH company, Dresden, for the new laboratory at the Jan Kochanowski University (JKU) in Kielce designed for the studies of ion-matter interactions is presented. The facility will be used for the interdisciplinary studies involving atoms, molecules, plasmas, surfaces and cells by taking an advantage of low-energy highly charged ions (HCI) and x-ray spectroscopy techniques. The EBIS-A facility, consisting of an EBIT-type ion source, beam guiding and diagnostic system, double focusing analyzing magnet and multipurpose target chamber, offers new opportunities for performing the experiments on slow, highly charged ions colliding with matter, including such different phenomena as formation of nanostructures in ion-surface interactions, recombination processes in plasma, fragmentation of biomolecules by ion and electron impact and the radiobiological effects in living cells. In this paper a concept of the EBIT/X-ray laboratory, construction details of the EBIS-A facility, the physics program, based on our former experimental activities in the atomic and molecular collisions, and application of x-ray spectroscopy in materials science are discussed.
    Journal of Instrumentation 09/2010; 5(09):C09005. DOI:10.1088/1748-0221/5/09/C09005 · 1.53 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The ion-induced pressure instability is a hard limitation for the maximum intensity, and hence the ultimate luminosity achievable in a proton accelerator. This instability is due to the interaction of high intensity proton beams with the residual gas generating positive ions. These ions, accelerated by the beam space charge, impact on the vaccuum chamber wall and lead to the desorption of gaseous species like $H_{2}, CH_{4}, C_{2}H_{4}, C_{2}H_{6}, CO$ and $CO_{2}$. These gases can in turn be ionized by the circulating beam, and initiate a pressure run-away process causing the loss of the stored beam. This phenomenon was first registered right at the beginning of operation of the Intersecting Storage Rings (ISR) at CERN in 1970. Later on, a long term evolution of the pressure was recorded for a stable stored beam current where a change of the residual gas composition was measured. In order to adapt the pumping speed and the surface treatments to the desired circulating beam currents, mathematical tools (e.g. VASCO code) exist to calculate pressure profiles in accelerator vacuum systems. A key input for these programs is the desorption yield of the surface, i.e. the number of molecules released by incoming ions and one of the limitations of these programs results from the lack of data concerning the ion-induced desorption yields dependence on the nature and mass of the incident ions. To improve our knowledge of these desorption yields, the ion-induced desorption of Oxygen-Free High Conductivity (OFHC) copper samples has been studied at room temperature for various primary ions: noble gas ions and ions produced by the ionization of the common gases encountered in accelerator vacuum systems, i.e. $H^{+}_{2}, CH^{+}_{4}, CO^{+}$ and $CO^{+}_{2}$. The measured dependence of the desorption yields on the mass, energy and nature of the incident ions is presented and discussed. In this context, the decrease of the ion-induced desorption yield as a function of the incident ion dose (so called "beam cleaning") has been studied for OFHC-copper and other materials. From these measurements, desorption cross-sections have been calculated and are compared with results from corresponding measurements found in the literature. A model, which relates the sputter yield with the nuclear and electronic energy loss of ions in matter, has been applied to the ion-induced desorption: Conclusions concerning the influence of the mass and energy on the mechanism of desorption are presented.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In the present work thin films of CaF2 deposited on Si substrate by electron beam evaporation have been investigated for swift heavy ions induced sputtering and surface modifications. Glancing angle X-ray Diffraction (GAXRD) measurements show that the pristine films are polycrystalline in nature and the grain size increases with increase in film thickness. Rutherford backscattering spectrometry (RBS) of pristine as well as irradiated films was performed to determine the sputter yield of CaF2 and a decrease in sputter yield has been observed with increase in film thickness. Thermal spike model has been applied to explain this. The confinement of energy in the grains having size smaller than the electron mean free path (λ) results in a higher sputtering yield. Atomic force microscopy (AFM) studies of irradiated CaF2 thin films show formation of cracks on film surface at a fluence of 5 × 1012 ions/cm2. Also RBS results confirm the removal of film from the surface and more exposure of substrate with increasing dose of ions.
    Applied Surface Science 01/2014; 289:77–80. DOI:10.1016/j.apsusc.2013.10.102 · 2.54 Impact Factor