SPUTTERING OF IONIC WATER CLUSTERS

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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