title: SPUTTERING OF IONIC WATER CLUSTERS
text: 396
  SPUTTERING OF IONIC WATER CLUSTERS
  K.Otabaeva, D.Xudaynazarova
  Urganch State University, H.Olimjon str.14, Urganch,Uzbekistan
  Secondary ion mass spectrometry (SIMS) is a wonderful technique for
  providing mass spectrometric information of molecules on surfaces [1].
  Theoretical studies of the keV bombardment of organic films on metallic
  surfaces have contributed to our understanding of the mechanisms governing
  these processes. Many experiments of keV bombardment, however, are
  performed both the thick and thin targets [2-4]. In this paper, we present
  molecular dynamics (MD) simulations aimed at obtaining such a microscopic
  picture and mass spectrum of sputtering clusters. Because of the importance of
  solvent H
  2
  O in many of the experiments, we have chosen it as our system. The
  interaction potentials available for MD simulations of H
  2
  O are sufficiently
  reliable such that a quantitative analysis of the simulation results can be directly
  related to the parameters of water. From the variety of substrate materials used
  in different experiments, we have chosen to perform our simulations using Au.
  This substance is chosen to match preliminary experiments with the selective
  killing of cells by inserted Au nanoparticles and because of the availability of
  good interaction potentials for gold. Below we give our choices for the
  interaction potentials for the H
  2
  O-H
  2
  O, Au-Au, and Au-H
  2
  O components of the
  system. The interaction potential employed to describe the H
  2
  O-H
  2
  O interaction
  is the simple-point-charge (SPC) water potential developed by Berendsen et al.
  This potential has been used extensively to study the properties of H
  2
  O as a
  solid. It has been shown that the SPC potential is able to reproduce many of the
  properties of bulk H
  2
  O. The Au-Au interactions are represented by the
  MD/Monte Carlo corrected effective medium (MD/MC-CEM) potential
  function for fcc metals. For metal- water systems has been developed a potential
  by Spohr. The Spohr potential consist a Morse function combined with a
  corrugation term defining various surface sites for the oxygen-surface
  interaction and a repulsive term for the hydrogen –surface interaction. For our
  calculation we used modified Spohr function.
  Fundamental fanlarni rivojlantirish istiqbollari
  Международная научно-техническая конференция «Практическое применение технических и
  цифровых технологий и их инновационных решений», ТАТУФФ, Фергана, 4 мая 2023 г.
  397
  This ion-water interaction results in re-orientation of water dipoles in the
  vicinity of the ion, thus disrupting the hydrogen bond network. Consequently,
  the local structure can almost be characterized as a pre-formed ion with the
  weak bonding to the remaining liquid forms.
  When on the surface are present atoms as Na, K and Li, they form with
  analyte by molecules quasi- ions. Imaging of MALDI samples shows that the
  position of analyte molecules and alkali ions highly correlated. The information
  of alkali attached ions is additionally dependent on the chemical structure of
  anylite molecule. We have chosen 4 layers of water with atom Na. This system
  equilibrated 20 ps. The first case when atom Na is on the surface, and the second
  one between layers 2-3. The computational results show that on the mass
  spectrum a few intensive peaks are observed. At the mass spectrum are observed
  high intensive peak corresponds to molecule H
  2
  O. In the mass spectrum also
  observed peaks which corresponded to the water clusters and Au atoms. The
  water clusters are consists 2ionic water clusters. This is a case when ions Na+ located on the top of water
  molecules which are shown in fig.2a. In this cluster Na ions formed bonds with
  H atoms. And large cluster are consists 32-45 water molecules. Our results
  shows that the preferred orientation of water molecules around a central cation,
  however, is similar to the orientation around a central water molecule, i.e., the
  cation in water does not introduce a large perturbation and the hydrogen bond
  network retains its structural identity near the cation. These results are
  interesting for mass spectrometry of molecules, study of surfaces and biological
  molecules.
  References
  1.B.J.Garrison, A.D.Delcorte, K.D.Krantzman.Acc.Chem.Res.33(2000)
  69.
  2. S.J.Stuart, A.B.Tutein, J.A.Harrison. J.Chem.Phys.112(2000) 6472.
  3. B.J.Garrison, D.Srivastava, P.B.S.Kodali. Modelling of Surface
  Processes as Exemplified by Hydrocarbon Reactions. Chem. Rev.
  1996, 96, 1327-1341.
  4. B.J.Garrison,D.Srivastava. Potential Energy Surfaces for Chemical
  Reactions at Solid Surfaces. Annu. Rev. Phys. Chem. 1995, 46, 373-
  394.
  Песпективы развития фундаментальных наук
  Международная научно-техническая конференция «Практическое применение технических и
  цифровых технологий и их инновационных решений», ТАТУФФ, Фергана, 4 мая 2023 г.
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