Abstracts Category : Other

Group 14 and 15 elements as building blocks for low dimensional functional nanostructures

by Sandeep Yadav

Carbon nanotubes (CNTs) are an interesting allotrope of carbon which can have a wide range of applications as they have extraordinary mechanical, electrical and thermal properties. All this makes CNTs an interesting nanomaterial for different applications ranging from mechanical sensors to electrical microelectrodes and even biological applications due to their biological compatibility.Beside the excellent material properties, the use of special structuring of these materials is of great importance. The random orientation of CNTs cannot be controlled which usually leads to irreproducible material which is not suitable for real world applications. Therefore, the controlled growth of vertically aligned carbon nanotubes (VACNTs) is considered in this work.VACNTs have been grown on Si/SiO2 substrates using a water-assisted chemical vapor deposition technique. By this technique highly crystalline, pure, low-layer multiwalled CNTs with a vertical orientation to the substrate are obtained. The parameters for the growth are optimized and even structuring of the VACNTs is possible obtaining VACNTs with different heights in one synthesis step. This structuring is the used to construct a nano-microstructured artificial-hair-cell-type sensor as an example for a mechanical sensor which can measure three-dimensional forces by the changing contact resistance between neighboring CNT bundles of different heights.Because to the excellent electrical properties together with the highly-increased surface area due to the vertical alignment of VACNTs, they are compared to randomly oriented CNTs for microelectrode applications. In this, the advantage of vertical alignment becomes clear in the dramatic decrease in impedance and enormous increase in capacity. These microelectrodes are then tested for biological applications for which the compatibility and growth pattern of cortical neurons on VACNTs is studied.While CNTs represent one-dimensional systems, also two-dimensional materials related to carbon such as graphene oxide and reduced graphene oxide are studied and used for gas-adsorption as well as liquids absorbents in combination with bacterial cellulose in the form of aerogels.Finally, phosphorene as an example of a two-dimensional material closely related to graphene is synthesized. Phosphorene, although structurally similar to graphene, it has a band gap in contrast to graphene which makes it an interesting material field-effect transistor devices as shown in this work.Advisors/Committee Members: Schneider, Jrg J (advisor), Yilmazoglu, Oktay (advisor).