Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
1680934 | Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms | 2012 | 4 Pages |
Abstract
The self-organisation of periodic pattern on (0Â 0Â 1) Ge by bombardment with different heavy ion species (Bi+, Bi++, Bi2+, Bi3+, Bi3++) obtained from a liquid metal ion source in a mass separating 30Â kV FIB system was studied. Aspect ratios exceeding values reported so far for elemental semiconductors substantially were found after cluster irradiation. An excellent regular self-ordering of dots (40Â nm in height, interdistance of â¼50Â nm) and ripple pattern were achieved. Despite of high ion fluence, Raman measurements prove a crystalline surface layer. This result deviates drastically from monomer irradiation, where similar to former ion irradiation of Ge a spongy amorphous surface layer is formed. For the transition from the usual behaviour to the unexpected pronounced pattern formation a threshold of the energy density deposited by the collision cascade was identified: If the deposited energy density exceeds the melting threshold, dot or ripple pattern appear. In our model we assume that the ion-impact-induced deposition of energy per volume (estimated by SRIM) must exceed the energy needed for melting. Thus, Bi segregation during resolidification of the melted pool and the 5% volume difference between molten and solid Ge can cause the observed Bi separation and Ge patterning, respectively. A consistent, qualitative model will be discussed.
Keywords
Related Topics
Physical Sciences and Engineering
Materials Science
Surfaces, Coatings and Films
Authors
L. Bischoff, K.-H. Heinig, B. Schmidt, S. Facsko, W. Pilz,