Jahresbericht 2005 - IPHT Jena

84
As a new field of research at IPHT, silicon
nanowires are grown by thermal and plasma
enhanced CVD from SiH 4 or electron beam evaporation
via a gold nanodot supported vapor-liquid-solid
mechanism. This work is performed in
close cooperation with the universities of Jena
and Halle as well as the Max-Planck-Institute of
Microstructural Physics at Halle. Evidently the
nanowire growth conditions now can be sufficiently
controlled to achieve well oriented epitaxial
silicon wires with diameters ranging from
50 nm to 1 µm (Fig. 4.2).
Fig. 4.2: Silicon nanowires grown by CVD on
Si(111), Si(100), and Si(110) surfaces (top to
bottom).
LASERTECHNIK / LASER TECHNOLOGY
Laser ablation
(Gudrun Andrä, Fritz Falk, Joachim Bergmann,
A. Bochmann)
Femtosecond (fs) laser ablation for micromachining
of hard metal tools as a spin-off from an
InnoRegio project was presented at the LASER
2005 fair at Munich. The potential of fs laser
micromachining could, in addition, be demonstrated
in case of a diamond tip sharpened by fs
laser ablation (Fig. 4.3). This result demonstrates
the importance of nonlinear processes as diamond
has an indirect bandgap of 5.48 eV (direct:
7.3 eV) which is very large in comparison to the
laser photon energy of 1.6 eV.
Fig. 4.3: Diamond tip sharpened by fs laser ablation.
4.2.2 Laser diagnostics
The Laser Diagnostics section applies different
types of lasers as remote and contactless probes
particularly to characterise optical materials,
components, and thin films and to investigate
flames. Some years ago, the development of
solid state lasers dedicated to flame diagnostics
has been successfully established.
In 2005 two high ranking PhD theses were
submitted to the Friedrich-Schiller-University:
Ch. Mühlig could considerably improve the
understanding of the ArF laser pulse absorption
by fused silica and CaF 2 (magna cum laude). In
both materials laser absorption is related to the
generation and annealing of defects. T. Scheidt
revealed 5 new laser induced effects at the technologically
important Si/SiO 2 interface applying
the surface second harmonic generation (SSHG)
method using fs laser pulses (summa cum
laude). He performed his experiments at the
Laser Research Institute at the University of Stellenbosch,
South Africa, after having built up the fs
laser laboratory from scratch.