Verlag des Forschungszentrums Jülich
JUEL-4242
Schwaab, Daniel
Surface patterning by means of Soft Lithography for Molecular and Bio-Electronics
II, 202 S., 2007
The aim of this thesis was establishing Soft Lithography, mainly Microcontact
Printing, as a powerful patterning technique for Molecular and Bio-Electronics. Especially
patterns having sub 100 nm dimensions were subject of this thesis. Therefore
a main issue addressed was the adoption of stamp materials with a Young's modulus
larger than 100MPa that allowed the transfer of patterns with low critical dimensions.
The Young's modulus of these materials was more than an order of magnitude larger
than that of materials commonly used. From a functional point of view emphasis was
laid on the transfer of proteins. A process was to be developed that allowed the transfer
of fully functional protein patterns. In addition the influence of Contact Inking
on the functionality of transferred proteins was investigated. Beside that, protein patterns
were used to demonstrate the influence of sub 1 μm patterns on the cell culture of
neurons. Another major object of this thesis was the establishment of a technique to
transfer metal patterns to arbitrary surfaces. Commonly used methods only work with
a specific choice of stamp material, metal and target surface. The concept proposed
and demonstrated in this thesis was more universal. Crossbar junctions having molecular
interlayers were demonstrated as one application for this process.
A special design was developed based on lines and spaces with variable widths and
gaps, which allowed the detailed investigation of various scaling issues. This pattern
was used as template for the fabrication of masters. A process compromising Electron-
Beam Lithography of PMMA resist and megasonic development followed by a Reactive
Ion Etching process using a hydrogen-bromide plasma to etch into polysilicon
provided best results. Ideal passivation of masters was obtained by vapor deposition
of a perfluoro-octyl-trichlorosilane. It formed a smooth monolayer on the master's
surface prohibiting sticking of the stamp. PDMS stamps were fabricated by casting
the liquid pre-polymer against the master. Since PDMS has got a rather low Young's
modulus defects such as Pairing were observed for the pattern design used. Thermoplastic
material Affinity VP polyolefin was used as stamp material patterned by Hot
Embossing. Although its Young's modulus is fifty times higher than that of PDMS
Pairing was observed. Therefore thermoplastic materials with an even higher Young's
modulus were used, namely polyolefins Zeonor, Zeonex, Topas, ionomere Surlyn and
methacrylate Plexiglas. All these materials could be used to obtain defect free replications
of the master. For Surlyn the edges were slightly rounded, while for the other
materials the shape of the stamp pattern were rectangular.
Alkanethiols served as model molecules to investigate the printing process since
they are commonly used in various applications and widely studied. For printing octadecanethiol
Contact Inking was performed. Diffusion of the molecules for printing
with PDMS stamps was found in agreement with previous publications. For Affinity
VP stamps however, the diffusion was found to be less pronounced due to the different
composition of the stamp material. For printing with Surlyn, which is rather
hydrophilic compared to PDMS or Affinity, a special wetting behavior was observed.
A transfer was only observed at the edges of the patterns resulting in 60 nm patterns.
Redox-active proteins cytochrome c and azurin served as model molecules with a
very specific, easy accessible, fragile functionality. Laminin was used as model system
with a binding functionality. ECM gel and polylysine were used as model molecules
for cell adhesion proteins. Beside their functionality they were used to demonstrate
the printing of sub 100 nm patterns, since their mobility at surfaces is rather low due
to the huge mass. For the first time Contact Inking was demonstrated with proteins
using various stamp materials. A longer transfer time was found to be necessary for a
complete transfer. The binding functionality of laminin was proven to be unchanged.
However, the redox activity of cyt c was lost, but this is also true for Wet Inking.
Therefore a novel process called In-situ μCP was developed. It was shown, that this
process allows to transfer cyt c in a patterned manner without loosing the functionality.
The applicability of the protein transfer for the guiding of neuron growth with sub
1 μm patterns was demonstrated. The direction of neurite growth was dominated by
the pattern direction. Larger patterns were preferred against thinner lines. First results
indicate, that certain patterns might initiate a splitting of neurite bundles or a change
of growth direction.
Surlyn was used for the printing of octadecanthiol and various proteins by applying
an extra load in the 0.1MPa range. Its Young's modulus is higher than any other
stamp material used in μCP so far. In order to use materials with an even higher
Young's modulus and in order to achieve very homogeneous printing results a novel
process called Air-Cushion μCP was introduced. For the first time usability of stamp
materials with a Young's modulus larger 100MPa was demonstrated. Small defects
and inhomogeneities in the stamps patterns were compensated. With these hard stamp
materials protein pattern transfer smaller than 40 nm was demonstrated.
A novel process called Shuttle-Transfer Printing was developed in order to transfer
pre-patterned metal films with low kinetic energy to arbitrary substrates. The applicability
of this process for the formation of Crossbar junctions was demonstrated.
Therefore molecular layers were sandwiched between two gold electrodes. For alkanethiol
molecules a tunneling like behavior was found, as expected. For long thiols the
tunneling parameters were in agreement with various publications, while for shorter
molecules the characteristic was dominated by the roughness of the electrodes. For
junction with a cytochrome c interlayer also a tunneling behavior was observed. The
tunneling parameters indicate, that the Superexchange mechanism makes major contributions
to the charge transfer process.
Neuerscheinungen
Schriften des Forschungszentrums Jülich
Ihre Ansprechperson
Heike Lexis
+49 2461 61-5367
zb-publikation@fz-juelich.de