Abstract:
Numerous experiments on defect formation in insulators, metals, alloys, and amorphous semiconductors
have shown that these materials are sensitive to track formation when they are bombarded by swift
heavy ions (SHI).
Detail understanding of the basic processes of materials modification by SHI will help to construct materials
with preassigned properties.
Tracks were examined like a chain of deal spherical regions; it was assumed that each incident ion creates
one such chain. In this model, we assume that the track is formed randomly, but in that place of the
ion path, where the energy value, which loses each ion to the unity of the way, is above some threshold
value.
As a result of irradiation the number of tracks will continue to grow, areas of the single tracks modified
substance continue to overlap, form of modified matter becomes more complicated, creating branched
structure.
Based on the scaling hypothesis large-scale curve were constructed, critical exponents for this percolation
model was established. Two such curves were evaluated: in the case of non-equiprobable distribution
of tracks regions in depth with ratio of critical exponents ( / )s 0.68 and in the case with equiprobable
distribution of tracks regions in depth, so-called model of continuous percolation with ratio of critical exponents
( / )e 0.41.
Differences between critical exponents of this model and the continuous percolation model indicate
that the dependence of the modified structure area on the dose and the angle related with the correlation
between individual tracks. It results in next effect: angular dependence of the surface area of the branched
structure has maximum value at certain «critical» angle of ions incidence.
