TY  - THES
AB  - The forces between surfaces determine the properties of many biological systems. This
makes them an important field of study. With an atomic force microscope (AFM) such
surface forces can be measured easily. In such measurements the AFM tip and the sample
are approached and the force on the tip is recorded. It was the objective of this work
to investigate the ubiquitous jumps of the tip towards the substrate both theoretically
and experimentally. It is known that jumps occur if the gradient of an attractive force
exceeds the spring constant of the cantilever. In this work a nucleation theory was developed
that describes the jumps on a two-dimensional liquid film on a surface. These
jumps correspond to the penetration of the tip through the liquid layer. The penetration
is thermally activated. Theory predicts that the force at which the penetration occurs
increases if the approach velocity between AFM tip and substrate increases. Parameters
of the theory are the jump rate of the tip and an activated volume. Two different systems
were investigated experimentally. A thermally activated jump was found for double
layers of two model lipids, adsorbed on mica in electrolyte solution. Contrastingly,
for the interaction between AFM tip and mica and graphite, both immersed in nalcohols
with 2 to 8 carbon atoms, a periodic force profile was found. This force leads
to a jump that is not thermally activated. Models for the structure of the alcohol molecules
on the substrates are proposed that are based on the force profile.
AU  - Franz, Volker
DA  - 2001
KW  - Rasterkraftmikroskopie
KW  - Lipiddoppelschichten
KW  - Solvatationskräfte
LA  - eng
PY  - 2001
TI  - Measurement of surface forces of adsorbed layers on smooth substrates
UR  - https://nbn-resolving.org/urn:nbn:de:hbz:467-1504
Y2  - 2024-11-21T23:05:41
ER  -