Patterned Organic Thin Films

Generalforsamlingen er torsdag den 30. september 2004 kl 19.00 og afholdes på DTU, bygning 101, mødelokale 1 (umiddelbart over Polyteknisk Boghandel). Dagsorden for generalforsamlingen er:

· Valg af dirigent

· Formanden aflægger beretning

· Kassereren fremlægger det reviderede regnskab

· Formanden forelægger bestyrelsens aktivitetsplaner for det kommende år. Bestyrelsen foreslår en nedsat mødefrekvens og deltagelse i et netværk med andre materialeforeninger. Dette er begrundet i en for lille tilslutning til foredragene.

· Kassereren forelægger budgetforslag og forslag til kontingent

· Valg af bestyrelsesmedlemmer, suppleanter og revisorer

· Eventuelt

Generalforsamlingen ventes at tage 45 minutter. Derefter er der foredrag ved prof. Gunther Wittstock, Dept. of Pure and Applied Chemistry and Institute of Chemistry and Biology of the Marine Environment, Oldenburg, Germany. Wittstock vil tale om mønstring af organisk tynd film og elektrokemisk scanning mikroskopi. Wittstock har forsknings interesser inden for organisk tynd film på uorganisk substrat, self-assembly på overflader, elektrokemi og kombination med klassiske overfladeanalyse. Efter foredraget vil der være øl og vand.

Patterned Organic Thin Films: Reactivity Imaging from Micrometer towards Nanometer Size Regimes with Scanning Electrochemical Microscopy

Gunther Wittstock

Carl von Ossietzky University Oldenburg, Dept. of Pure and Applied Chemistry and Institute of Chemistry and Biology of the Marine Environment, D‑26111 Oldenburg, Germany

Scanning electrochemical microscopy (SECM) has become an indispensable tool for the characterization of reactivities at interfaces. Among the reactions that have been studied by this technique are reactions of immobilized enzymes and other biomolecules [1]. The analysis is based on the detection of redox active species generated by an immobilized enzyme though conversion at the scanning ultramicroelectrode (UME). This mode is called generation-collection mode. Alternatively one can use the UME to locally produce a cofactor for an enzymatic reaction and observe the cofactor consumption of the enzyme by a change of the amperometric current at the UME (feedback mode).

In addition to localized analysis SECM instruments was used as tools for microstructuring [2]. The special advantage of such surface modification protocols are twofold: They can be applied in aqueous buffers, an environment that maintains the activity of delicate biochemical surface layers. By switching between microstructuring and reactivity imaging the success of individual preparation steps can be analysed forming the basis for the rational optimization of such processes.

Self-assembled monolayers (SAM) of alkanethiolates on gold can form a passivating inert film. By patterning such layers, a surface template can be formed into which enzymatically active layers can be immobilized. Patterned SAMs have been prepared by microcontact printing [3] and localized electrochemical desorption using SECM. By combination of both approaches complex patterns become available that contain two or more enzymes. Reaction chains and cofactor recycling between different active regions can be studied as a function of the pattern layout at such specimens [4].

The experiments described above have been performed in the micrometer range, i.e. the UME electrode used as local probe has diameters of 10-25 micrometer. Its extension limits the lateral resolution to about the same size. A much higher lateral resolution is needed for several application like the investigation of fuel cell catalysts. Such experiments require smaller probes, still having a suitable geometry. Rather extensive experiments in conjunction with digital simulations using the boundary element method (BEM) allowed to optimize an etching and coating procedure to give nanoelectrodes suitable for such experiments. Furthermore, SECM experiments in the nanometer regime require a mechanisms for guiding the UME in constant distance over the specimen surface because the surface roughness it at least in the size regime of the UME itself. In our setup the mechanism of a scanning tunneling microscope (ECSTM) is used to obtain topographic information of the sample. This information is then used position the UME in the SECM experiment [5].

1. G. Wittstock, Fresenius J. Anal. Chem. 2001, 370, 303-315.

2. T. Wilhelm, G. Wittstock; Electrochim. Acta 2001, 47, 275-281.

2. T. Wilhelm, G. Wittstock, Langmuir 2002, 18, 9486-9493.

3. T. Wilhelm, G. Wittstock, Angew. Chem., Int. Ed. Engl. 2003, 42, 2247.

4. T. H. Treutler. G. Wittstock, Electrochim. Acta 2003, 48, 2923.