Size effect in cluster collision on solid surfaces
ABSTRACT New surface modification processes have been demonstrated using gas cluster ion irradiations. Multiple collision and high energy density collision of cluster ions are responsible for “non-linear phenomena”, which play an important role in the surface modification process. Because of the unique interaction between cluster ions and surface atoms, atomistic mechanisms of cluster ion bombardment must be understood for the further developments of this technology. Cluster size is a unique parameter for cluster ions. One of the fundamental questions in this surface modification technique is the cluster size effect. It is important to use appropriate cluster size in each process. Size dependence of sputtering yields and secondary ion yields with large Ar cluster (N>300) have been measured.
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ABSTRACT: Measurements are reported of the sputtering yields of gold using Arn+ gas cluster ion beams of energies E of 5, 10, and 20 keV with 100 ≤ n ≤ 5000. In measuring the sputtering yields for 30 nm gold layers on silicon wafers with a thin thermal oxide, the analysis is conducted using SIMS with 25 keV Bi3+ primary ions. The measured Aut– signals for 1 ≤ t ≤ 6 show an enhancement of intensity beyond the Au/SiO2 interface arising from the presence of the oxide on the Si wafer, but this intensity enhancement is reduced by a factor t–1.38 between the secondary ions so that it may be removed to establish the sputtering dose at the interface. The sputtering yield, Y, so determined, exhibits a consistent dependence of Y/n on E/n for all beam energies showing that their effects are linearly additive in this regime (i.e., doubling the number of atoms in the cluster at the same energy per atom doubles the total yield). An empirical description of these sputtering yields is provided for 100 ≤ n ≤ 5000. The trend at low n values is consistent with Sigmund and Claussen’s thermal spike model valid here for 1 ≤ n ≤ 10. This confirms that the maximum yields occur for 10 ≤ n ≤ 200. No indication of a threshold below which sputtering ceases was found.The Journal of Physical Chemistry C 10/2012; 116(44):23735–23741. · 4.84 Impact Factor
- Applied Surface Science 08/2014; 310:112-114. · 2.54 Impact Factor
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ABSTRACT: An analysis is made of the sputtering yields of materials for argon gas cluster ion beams used in SIMS and XPS as a function of the beam energy, E, and the cluster size, n. The analysis is based on the yield data for the elements Si and Au, the inorganic compound SiO2, and the organic materials Irganox 1010, the OLED HTM-1, poly(styrene), poly(carbonate), and poly(methyl methacrylate). The argon primary ions have cluster sizes, n, in the range 100–16 000 and beam energies, E, from 2.5 to 80 keV. It is found that the elemental and compound data expressed as the yields, Y, of atoms sputtered per primary ion may all be described by a simple universal equation: Y/n = (E/An)q/[1 + (E/An)q−1] where the parameters A and q are established by fitting. The sputtering yields of the three organic materials are given as yield volumes expressed in nm3. For these, an extra parameter B is included multiplying the right-hand side of the equation where B is found by fitting to be of the order (0.18 nm)3 to (0.26 nm)3. This universal equation exhibits no threshold energy, and no deviation was observed from the equation, indicating that any threshold energy would have to be significantly below E/n = 1 eV per atom. The equation also shows that doubling the cluster size at the same energy per atom simply doubles the sputtering yield so that in this sense, and probably this sense alone, the sputtering effects are linearly additive. The parameter A is related, inversely, to the mean sputtered fragment size, and the low A values for organic materials are indicative of high yield volumes. For materials with low A values, the universal equation is close to a linear dependence on energy, and if that linear dependence is assumed, an apparent threshold energy is predicted and observed experimentally.The Journal of Physical Chemistry C 06/2013; 117(24):12622–12632. · 4.84 Impact Factor