Synthesis, characterization, and sensing applications of silicon nanowires and nanotubes

This thesis pursues the objective to advance and enhance existing achievements made in the field of nanowire-based sensing by studying new approaches for sensor design aiming both at a facilitation of device assembly and at an expansion of their application area. For that purpose, different technologies are combined to establish sensor concepts that profit from the emerging synergies. A combination of bottom-up nanowire synthesis and beam-induced material deposition is investigated in order to make it useful for the assembly of silicon nanowire (SiNW)-based sensing devices by circumventing certain obstacles in nanowire integration and device assembly. In particular, platinum (Pt) catalysts are chosen for SiNW synthesis because of the opportunity to create Pt structures by beam-induced deposition. The feasibility of this approach is shown by using it successfully for the modification of atomic force microscopy probes. From the insights gained during the investigation of the underlaying Pt-catalyzed SiNW growth mechanism, a second sensing application of Pt-catalyzed SiNWs is derived in form of single nanowire electrode arrays. These arrays can be fabricated with minimal technological effort by utilizing peculiarities of the Pt-catalyzed growth. Additional to these device assembly strategies, the electrical properties and the sensing abilities of the Pt-catalyzed SiNWs are determined. Corresponding to existing SiNW-based lab-on-chip sensor designs, a silicon nanotube (SiNT)-based biosensing concept is investigated. Therefore, also the synthesis of SiNTs from radial germanium/silicon heterostructures is studied. The synthesized structures are characterized electrically and their eligibility as biosensor is examined. In addition to the determination of their properties, a technological platform for the integration of the SiNTs is designed that allows both individual electrical and fluidical connections in an analyte flow-through configuration. The study on the suitability of this approach is completed by a brief experimental study of fluidic transport in and through SiNTs. All approaches are unified by the ambition to make use of the respective silicon nanostructures’ unique properties in sensing by simultaneously reducing the technological effort of the device assembly. As the synthesis of nanowires and nanotubes depends strongly on process parameters, the appendix contains all relevant data to ensure and facilitate reproduction. Also, as a significant part of the experiments involve steps of microfabrication, all relevant processing details are listed and summarized there as well.