Technische Universität Darmstadt
Electronic Type Separation of Single-walled Carbon Nanotubes by Weak Field Centrifugation.
Degree: PhD, Material Science, 2017, Technische Universität Darmstadt
The potential of semiconducting single–walled carbon nanotubes (SWCNTs) to outperform silicon in electronic application was finally realized in terms of on-state current density in September of 2016. High purity semiconducting SWCNT arrays were necessary to exceed the performance of silicon. But the desired semiconducting nanotubes cannot be grown exclusively without their metallic counterparts. Since electronic application requires predictable and uniform performance, strategies are sought for effective post synthesis separation of SWCNTs.
The identification of scalable processes that transfer random mixtures of SWCNTs into fractions featuring a high content of semiconducting species is therefore crucial for future application of SWCNTs in high-performance electronics.
Established separation methods employ SWCNT dispersions with polymeric dispersants and typically provide high semiconducting purity samples with narrow diameter distribution, i.e. almost single chiralities. But for a wide range of applications high purity mixtures of small and large diameters are sufficient or even required. The requirement of large quantities of organic solvents additionally hampers the scaling of these methods.
Herein a highly efficient and simple separation method is demonstrated that relies on selective interactions between tailor-made amphiphilic polymers and semiconducting SWCNTs in the presence of low viscosity separation media. The separation method relies on weak field centrifugation (WFC), i.e. <10,000 x g, of a SWCNT dispersion with a polymeric dispersant. In this work non-selective and strong adsorption of polymeric polyarylether dispersants on nanostructured carbon surfaces is demonstrated, which enables simple separation of diverse raw materials with different SWCNT diameter.
High purity individualized semiconducting SWCNTs or even self-organized semiconducting sheets are separated from an as-produced SWCNT dispersion via a single WFC run. Absorption and Raman spectroscopy are applied to verify the high purity of the obtained SWCNTs.
In addition and for the first time, increased temperatures were demonstrated to enable higher purity separation. Additionally it is shown that the mode of action behind this electronic enrichment is unique, i.e. strongly connected to both colloidal stability and protonation.
Furthermore SWCNT - network field-effect transistors (FETs) were fabricated, which exhibit high ON/OFF ratios (105) and field-effect mobilities (17 cm²/Vs). In addition to demonstrating the feasibility of high purity separation by a novel low complexity process, the WFC method can be readily transferred to large scale production and provide economical relevance to SWCNTs of any diameter.
Advisors/Committee Members: Krupke, Ralph (advisor), Weitz, Thomas (advisor).
to Zotero / EndNote / Reference
APA (6th Edition):
Reis, W. (2017). Electronic Type Separation of Single-walled Carbon Nanotubes by Weak Field Centrifugation. (Doctoral Dissertation). Technische Universität Darmstadt. Retrieved from http://tuprints.ulb.tu-darmstadt.de/6034/
Chicago Manual of Style (16th Edition):
Reis, Wieland. “Electronic Type Separation of Single-walled Carbon Nanotubes by Weak Field Centrifugation.” 2017. Doctoral Dissertation, Technische Universität Darmstadt. Accessed June 24, 2017.
MLA Handbook (7th Edition):
Reis, Wieland. “Electronic Type Separation of Single-walled Carbon Nanotubes by Weak Field Centrifugation.” 2017. Web. 24 Jun 2017.
Reis W. Electronic Type Separation of Single-walled Carbon Nanotubes by Weak Field Centrifugation. [Internet] [Doctoral dissertation]. Technische Universität Darmstadt; 2017. [cited 2017 Jun 24].
Available from: http://tuprints.ulb.tu-darmstadt.de/6034/.
Council of Science Editors:
Reis W. Electronic Type Separation of Single-walled Carbon Nanotubes by Weak Field Centrifugation. [Doctoral Dissertation]. Technische Universität Darmstadt; 2017. Available from: http://tuprints.ulb.tu-darmstadt.de/6034/