Controlled surface manipulation at the nanometer scale based on the atomic force microscope

The object of this thesis is the development of theoretical and
experimental methods for the controlled manipulation of surfaces at
the nanometer scale, including the design, construction and
experimental demonstration of an atomic force microscope (AFM)
based manipulator. The transfer function description of an AFM
system not only offers a theoretical dynamic characterization but,
additionally, it is appropriate for the analysis of stability and
controllability of different system configurations, i.e. different
inputs and outputs. In this thesis, transfer functions are derived
that correspond to a realistic model of the AFM sensor, including
all its resonance modes and the tip-sample interaction. This
theoretical description is then validated using the frequency
response along an AFM cantilever. Different experimental and
control techniques have been combined in the NanoManipulator system
to optimize AFM lithography. Optical video microscopy allows a fast
recognition of the sample and exact positioning of the AFM tip in
the particular region of interest, while UV-laser ablation offers
the possibility of noncontact manipulation of a wide range of
materials, including biological specimens. Two different control
approaches have been implemented in the NanoManipulator system: (i)
automated control using a vector-scan module, and (ii) interactive
control based on the use of a haptic interface. Using the
NanoManipulator, the two different standard AFM lithography
techniques based on dynamic methods (namely dynamic and modulated
plowing) are compared by performing nanopatterning on thin resist
films. The results reflect that modulated plowing, where the AFM
tip is in permanent contact with the resist surface while the force
is being modulated, offers the highest reliability, minimizing
undesired side effects. The isolation and extraction of localized
regions of human metaphase chromosomes represents a promising
alternative to standard methods for the analysis of genetic
material. The NanoManipulator is an excellent tool for such
application, as it is here illustrated by comparing AFM based
mechanical dissection and noncontact ablation on side by side
chromosomes. The results are analyzed in situ using AFM imaging,
revealing the high precision of mechanical dissection. Acoustical
force nanolithography is a novel method for AFM based lithography
where the cantilever is actuated using an acoustic wave coupled
through the sample surface. The influence of acoustic wave
frequency and magnitude, along with the preloading force of the
cantilever are studied in detail. Acoustical force nanolithography
can be used as a stand alone method or as a complement for the fine
adjustment of manipulation forces.