Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Self-organization of Ge nanopattern under erosion with heavy Bi monomer and cluster ions

Bischoff, L.; Heinig, K.-H.; Schmidt, B.; Facsko, S.; Pilz, W.

The self-organisation of periodic pattern on (001)Ge by bombardment with different heavy ion species (Bi+, Bi++, Bi2+, Bi3+, Bi3++) obtained from a liquid metal ion source in a mass separating 30 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 dot (40 nm in height, interdistance of ~50 nm) and ripple pattern was 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 re-solidification 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: Bi-cluster; germanium; FIB; nanopattern

Related publications

  • Poster
    17th International Conference on Ion Beam Modification of Material - IBMM 2010, 22.-27.08.2010, Montreal, Canada
  • Nuclear Instruments and Methods in Physics Research B 272(2012), 198-201
    DOI: 10.1016/j.nimb.2011.01.064
    Cited 28 times in Scopus

Publ.-Id: 14400