Partial disintegration and change of concentration profiles at ion bombarded Na silicate glass surfaces

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Abstract
From the observation of the change of photon emission intensities of sputtered excited atoms from glass surfaces by applying an ion beam of 5.6 keV Ar+ ions, the influence of the bond energy of the different atoms in the target on the sputtering behaviour can be investigated. Differences of bond energy constitute different masses effective in the collision cascade, which is developed by the impinging ions below the glass surface. The probability for sputtering of more weakly bound atoms in an excited state or for a transport ofthese atoms to deeper layers below the surface, depends on the angle of incidence β of the projectile ions. This is illustrated for Na atoms and Si atoms displaced in the collision cascade spread below the bombarded surface in the silica rich network of Na20.4 SiO2 glass by recording the changes of intensity of photon emission of the excited Na I and Si III lines. The Na concentration in thin layers at the surface of the ion bombarded glass is decreased during sputtering. The change of the energy spread in the collision cascade below the surface connected with the change of P causes maxima and minima in the recordings of the photon emission intensity observed during continuous ablation. The period of time which is needed for these changes indicated by these extrema immediately after a change of β depends on the amount of the change of β and on the bond energy of the constituents or on the effective masses M2 respectively in the glass target. This period characterizes therefore the short range order of this glass target with respect to the bonding of the constituents.