DEPARTMENT OF EARTH AND ENVIRONMENTAL SCIENCES
LMU MÜNCHEN
Scanning Probe Microscope (SPM) for
the International Space Station ISS
P. Hix, M. Reiter, W.M. Heckl
Design and fuction of a SPM
Parabolic flight test as feasibility study
Conventional microscopes generate an image of an inspected sample by utilising
the wave properties of matter or radiation. A scanning probe microscope avoids
the resolution limits of such methods by scanning the surface of a sample with a
fine tip, converting atomic-scale physical properties of the surface into an image.
The resulting magnification enables the visualisation of single molecules and
atoms. Various instruments have been developed in the last 20 years in order to
record different properties, two of which are to be combined in this instrument:
A series of imaging tests was conducted on a parabolic flight as a feasibility study
for the use of a SPM in a microgravity environment. In these tests an aircraft flies
a series of parabolic arcs. During acceleration and deceleration phases the
gravitational force is almost twice that on Earth, whilst in the apex of the flight path
microgravity is achieved for a duration of approximately 20 seconds.
The scanning tunneling microscope (STM) utilises an electrically conductive probe
– usually an atomically fine metal tip. A voltage is then applied between the
scanning tip and the sample, resulting in the flowing of a tunnelling current which
is then converted into an image of the surface.
8500 m
The atomic force microscope (AFM) generally uses a fine tip attached to a
miniature cantilever to record the attractive (van-der-Waals) and repulsive
(electromagnetic interactive) forces of the surface of a sample. These forces
cause a bending of the cantilever which is recorded, and then converted into an
image of the surface.
Scanning tunneling microscopy
Scan-generator
lateraler Piezo
vertikaler Piezo
Ut
z
Piezo-Höhe
Feedbacksignal It
Wolframspitze
Feedback
10,6 nm
Left: schematic functioning principle of
a scanning tunneling microscope:
The distance between tip and sample
is kept at a constant value by the
electronics,
thus
generating
a
topographical image of the sample
surface.
altitude
45°
7600 m
6000 m
gravitation (g)
20 s
25 s
20 s
1,8 g micro- 1,8 g
gravitation
2
1
22 s
Diagrams of the flight path of the Airbus A300 during parabolic arcs and of the
resulting gravitation.
y
x
Optimisation of a SPM for the ISS
Right: It is not only possible to image with
an SPM, but also to manipulate single
molecules (PTCDA on HOPG).
Advantages of microgravity on the ISS
The utilisation of scanning probe microscopy in the microgravity environment on board the
International Space Station ISS has many advantages – especially in interdisciplinary studies. In
cooperation with other projects the surface structures of biological specimens can be determined, for
example, or the properties of new materials, or defects in crystals grown on board the ISS. A SPM is
an excellent instrument for complementing scientific microscopic studies.
During the development of a SPM for use on board the
International Space Station ISS the following specific
requirements, amongst others, were considered:
- straightforward construction, enabling simple operation and
maintenance
- compact dimensions and low weight
- imaging process automated as far as possible
- remote operating capability
- integrated CCD-camera for optical sample monitoring
- vibration damping suspension optimised for microgravity, with
incorporated locking system
Working prototype of a
scanning probe microscope
optimised for use on board
the International Space
Station ISS.
The future
ISS data:
-Span:
-Length:
-Height:
-Internal volume:
-Weight:
-Altitude:
-Orbit:
-Orbit time:
-First occupation:
-life span:
-Total cost:
108,6 m
79,9 m
88,0 m
1140 cum
450 Tons
400 km
51,6° declination
90 min
1999
ca. 10 years
ca. 100 billion €
A completely new instrument will be developed, incorporating the
advantages of the present prototype whilst eliminating the
shortcomings.
The main developmental focus will be the incorporation of atomic
force microscopic capability, as the present prototype is only
capable of performing scanning tunneling microscopy.
Furthermore, the vibration damping suspension and the locking
system will be optimised for simpler adjustment and improved
reliability.
The prospective launch date is in the year 2005.
Large image:
Small image:
the ISS over the Caribbean
russian cosmonaut preparing
an experiment
This SPM development project is in cooperation with KayserThrede GmbH, and is sponsored by the European Space
Agency ESA.