  This dissertation presents an investigation into the electrical properties of
two types of G4-DNA and several DNA-based molecules, targeting them as
candidates for molecular wires and devices. Atomic force microscopy (AFM) and
electrostatic force microscopy (EFM) comparison of co-deposited tetra- and
intra-molecular G4-DNA reveals variations in morphology and different
sensitivity to the applied electric field, suggesting that the folding
orientation of the strands affects the molecular structure, i.e. either the
tetrad unit or the tetrad-tetrad stacking or both, and therefore the charge
mobility. Tetra-molecular G4-DNA is found to be twice as polarizable as
intra-molecular G4-DNA, suggesting it has greater charge mobility. These
promising results motivated direct electrical transport measurements on
tetra-molecular G4-DNA using a special conductive AFM setup, profiling the
conductance along the molecule. Reproducible currents of tens to over 100 pA
were measured in many tetra-molecular G4-DNA molecules over distances ranging
from tens to over 100 nm. The measured charge transport is compatible with
long-range thermally activated hopping between multi-tetrad segments. To form
the stationary electrical contact, a new variant of stencil lithography was
developed, based on reversible electrostatic clamping, overcoming indeterminate
blurring effects associated with the problem of metal penetration in standard
mask patterning techniques. This method enabled to demonstrate full mask
compliance in scanning electron microscopy (SEM) and AFM measurements. The
pull-in instability was demonstrated inside an SEM chamber and was confirmed by
a non-linear transient response computation. New mechanisms were proposed for
the replica formation and the blurring effect based on cluster evaporation and
mobile source decay, explaining the ultimate resolution of the masking
technique and its limitations.
