Open Positions
Neu für Herbst 2011:
Diploma-/Master’s thesis: Selective Area Epitaxy of III-Nitride Nanowires on Diamond
For further information please read SAE of III-nitride nanowires on diamond
Contact: Martin Stutzmann and Fabian Schuster
Diploma/Master's thesis: Graphene biosensors on flexible substrates
Due to their unique electronic structure, monolayers of sp2-bonded carbon – called graphene – exhibit properties, which are superior to any other electronic material, such as high mobility, excellent thermal conductivity, high chemical stability, and extreme sensitivity to environmental conditions and charge adsorption. Furthermore, the high mechanical sensitivity of graphene enables the fabrication of graphene devices on flexible substrates.
Among the applications requiring flexible electronics, graphene field effect transistors hold great promise for sensing in biological and chemical systems. In graphene, as in any 2D material, all processes are located directly at the surface, which can enable devices with very high sensitivity.
However, to pattern contacts and to provide mechanical stability, the graphene layers must be placed on a substrate, which not only influences the devices’ electronic performance but also has an effect on the usability in specific environments. As graphene itself shows a very high mechanical flexibility, we aim at the design of flexible sensors for medical implants, which, however, cannot be achieved with conventional, rigid substrates as silicon dioxide. Therefore, we intend to fabricate graphene solution-gated FETs (SGFETs) on flexible polymer substrates such as polyimides, which are well known for their chemical and mechanical stability.
This diploma thesis includes the preparation of graphene films by chemical vapor deposition (CVD) and the fabrication and optimization of graphene SGFETs on flexible polymeric substrates.
The fabricated devices shall be characterized by electrochemical and mechanical experiments and their performance shall be compared to transistors on conventional substrates such as SiO2.
For further information please contact Jose Antonio Garrido and Lucas Hess
Diplom-/Masterarbeit: Miniaturization of diamond solution-gated field effect transistors
Hydrogen-terminated diamond surfaces have been extensively studied in the past years as transducer materials in biosensing applications. One of the reasons is the high chemical and electrochemical stability of diamond which is required in physiological environments. Furthermore, diamond is reported to be particularly biocompatible. Another reason is the extraordinary surface conductivity of hydrogen-terminated diamond. This p-type surface conductivity can be modulated in an electrolyte by a voltage applied between a reference electrode and the diamond.
Based on this effect, our group has realized solution-gated field effect transistors (SGFET) which have been shown to work as sensors for pH and ionic strength. High specificity can be obtained by covalent attachment of biomolecules to the diamond surface. Recently, our group has demonstrated the suitability of diamond SGFETs for the extracellular detection of action potentials from cells [Figure a) and b)].
This thesis will focus on the fabrication of such devices with the goal of miniaturization down to the nanometer regime. The structures will have to be characterized regarding their performance as sensors in order to compare them to other available technologies (larger diamond devices, Si-based, GaN-based). Experimentally, this involves semiconductor device fabrication techniques like optical and electron beam lithography [Figure c)]. Furthermore, electronic and electrochemical characterization methods will be extensively used to assess the performance of the fabricated devices.
For further information please contact Moritz Hauf or Jose Antonio Garrido
Diploma/Master's thesis: Organic Field Effect Transistors for sensing applications