ISBN 978-3-8439-2338-5

978-3-8439-2338-5, Reihe Nanotechnologie

Muhammed Ihab Schukfeh
Semiconducting electrodes for molecular nanoelectronics

176 Seiten, Dissertation Technische Universität Braunschweig (2015), Softcover, A5

Zusammenfassung / Abstract

This dissertation reports on the utilization of organic molecules and proteins as active components in semiconductor - molecule - semiconductor junctions, introducing two novel approaches. In both cases the separation between the two electrodes is defined by a (sacrificial) separation layer. The nanogap devices were thoroughly characterized and exhibited excellent electrical properties, allowing to use them for the investigation of charge transport along long conjugated molecules, and across proteins, respectively. Nanometer-spaced semiconductor electrodes were fabricated using two distinct novel techniques. For the first approach, indium arsenide (InAs) nanowires with an embedded short indium phosphide (InP) segment were used as electrodes. A photo-assisted etching procedure based on hydrobromic acid (HBr) was developed that allowed the selective removal of InP segments, yielding nanogaps in InAs nanowires as short as 11 nm. For electrical measurements on semiconductor - molecule - semiconductor junctions, oligo(phenylene vinylene) (OPV) derivative molecules with a conjugated backbone and a thioacetyl termination group were surface-bound to InAs nanowires comprising a 5 nm InP segment. The ~12 nm long OPVs were used to bridge the InP barrier. The device architecture allowed for the application of a backgate voltage, making the presented device the first gateable, all-semiconductor-contacts molecular device.

Additionally, silicon on insulator (SOI) based vertical nanogap devices (VNDs) were fabricated using selective wet etching techniques, resulting in tower-like, 3 µm high and 600 µm long, p+ Si top electrodes, and one global p+ Si bottom electrode, separated from each other by 4 nm or 8 nm buried oxide. The buried oxide was slightly recess-etched, exposing a nanogap. Cytochrome c was deposited inside the 4 or 8 nm Si nanogaps. This way, a hitherto not reported semiconductor - protein - semiconductor nano-junction was realized and electrically characterized at room temperature as well as with temperature-dependent measurements.

The techniques proposed in the scope of this dissertation may offer elegant methods to directly contact organic molecules or protein molecules using semiconducting electrodes, each with unique advantages.