The process of sputtering by bombardment with gas cluster ions was investigated from the perspective of the kinetic energy per constituent atom (E atom ) of an incident cluster ion, which determines the threshold for the formation of craterlike defects by irradiation of an argon gas cluster ion beam (Ar-GCIB) onto a graphite surface. Furthermore, DNA molecules adsorbed on a graphite surface were preferentially sputtered by adjusting E atom of the Ar-GCIB down to this threshold, while the substrate graphite surface retained its carbon lattice structure without the formation of craterlike defects. These results indicate that a GCIB could be used as a primary ion beam for secondary ion mass spectrometry (SIMS), which would enable the preferential analysis of an adsorbed layer on a substrate without causing damage to the substrate.
A cluster ion irradiation system with cluster size selection has been developed to study the effects of the cluster size in surface processing using cluster ions. A permanent magnet with a magnetic field of 1.2 T was installed for size separation of large cluster ions. Traces formed on a graphite surface by the impact with Ar cluster ions under an acceleration energy of 30 keV were investigated by scanning tunneling microscopy. The nature of the traces is strongly affected by the number of constituent atoms of the irradiating cluster ion. When the cluster ion is composed of 100–3000 atoms, crater like traces are observed on the irradiated surfaces. In contrast, such traces are not observed at all with the irradiation of the cluster ions composed of over 5000 atoms. This behavior is discussed on the basis of the kinetic energy per constituent atom of the cluster ion.
We have calculated the Raman spectrum of strained Ge 0.11 Si 0.89 wires sandwiched between Si layers. Because of the relatively large width and penetration depth of the laser beam the volume sampled by the beam is large. Using the strain components calculated by the finite element method, the strain induced Raman shifts and Raman spectra were calculated at each point in the volume sampled. The final spectrum obtained by superposing these spectra shows excellent agreement with the observed spectrum. The strain induced shift measured by micro Raman in nonuniformly strained solids does not give strain values in a straightforward manner.
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