The research facilities of the Materials Research group at the GSI Helmholtz center for heavy ion research in Darmstadt provides the unique possibility to irradiate polymer foils (e.g., polyethylene-teraphthalate, polycarbonate, and polyimide) with an individual, high energy, heavy ion. Subsequent chemical track etching yields single nanochannels with excellent control of both pore geometry (e.g. cylindrical, conical, bullet-shaped) and size (diameter tunable between ~10 nm and few µm). The carboxyl groups present at the etched polymer surface facilitate the subsequent chemical functionalization of the channel surface. Functionalized solid state nanochannels exhibit unique ion transport properties including ion selectivity, ion current rectification, and responsive behavior to external stimuli such as pH value, temperature or concentration of a specific ion. Understanding their functionality is essential to develop novel sensing devices in chemistry, biology or medicine.
Nanochannel functionalization can be achieved by various techniques. By atomic layer deposition, polymer membranes can be conformably modified with oxides that exhibit e.g. different isoelectric points. Also, numerous chemical surface modification strategies can be applied to integrate functional chemical groups in the polymer nanochannels.
In addition, nanowire arrays and interconnected 3-D nanowire ensembles of various materials including metals (Cu, Au1-xAgx), semiconductors (ZnO and p-Cu2O) and semimetals (Bi1-xSbx) are synthesized at GSI by electrodeposition in multichannel polymer membranes. The assembly of nanowires and nanotubes into stable 3D architectures is important towards their implementation in e.g. thermoelectric, catalytic, photoelectrochemical, and biotechnological devices.
