Local Probes of Nanoscale Systems
We use our
Omicron-Zeiss Beetle STM/AFM for surface studies of nanotubes.
Single Wall Nanotubes can be successfully imaged with both, atomic
force and tunneling current feedback. In STM-Mode, we are also able
to probe their local electronic density of states. In any case,
sample preparation is crucial to obtain good imaging quality.
Single nanotubes as well as ropes containing up to 100
tubes can be found dispersed over the substrate. In our STM-experiments,
ropes are stable for many subsequent scans even with low tunneling
resistances. Individual tubes can be distinguished within the ropes
and their atomic structure can repeatedly be imaged with good tips
and some care in vibration damping (we use Pt-Ir tips from DI).
Single tubes tend to be less stable during scanning than ropes,
since they are often pushed away by the imaging tip. They can be
more easily imaged in AFM-(Tapping)-Mode where the tip sample
distance is usually larger than in STM-Mode.
Our STM studies reveal, that some tubes imbedded in ropes
exhibit a distortion in their hexagonal lattice (article
in PDF format). The angle between the armchair direction and the
zigzag direction is no longer 90, but differs by some degrees from
that value. A possible explanation for this phenomenon is a twist
distortion. If a tube is twisted, the direction perpendicular to the
tube axis stays the same, while the other directions are altered.
Twists might be introduced into tubes in ropes by their neighbors
during the growth process. They could have a strong impact on the
electronic properties of intrinsically metallic tubes. (E.g.
introducing isolator-like resistivity at low temperature). In this
field we are working closely with our
Our SPM is also capable of working in an AFM-Mode with a
Needle-Sensor put in place of the STM tip. the Needle-Sensor
consists of a quartz crystal that is driven at its resonant
frequency of ~1MHz. Conventional AFM tips (with their cantilevers)
are glued to the end of the crystal. We regulate by detecting the
phase change of the oscillation rather than an amplitude change. AFM
images of nanotubes obtained by Wilfried Clauss and David Bergeron
reveal the fantastic resolution in AFM-Mode that can be obtained
with our system.
Page last modified on November 5, 2005