ERA NANOSCI: Sort Single Single-wall-nanotubes of Specific Sizes
Zusammenfassung der Projektergebnisse
Sorting of single-walled carbon nanotubes (SWCNTs) according to their type (semiconducting / metallic) is considered to be a top research priority in SWCNT science and research. Sorting nanotubes according to other relevant properties (length, diameter) is a research topic as well and might be mandatory for other sorting processes. For allowing such advanced sorting processes, the SWCNTs should be synthesized with well-defined and narrow-distributed properties. This requires the development of a suitable synthesis process together with doing some kind of 'pre-sortlng' during synthesis would be beneficial for the later sorting success. (1) We have developed post-synthesis sorting methods to separate metallic SWCNTs from semiconducting ones. In one approach, we have combined dielectrophoretic sorting with microfluidic flow to accomplish dynamic sorting of CNTs according to their type of electronic properties. This method is based on dielectrophoretic forces which differ considerably for semiconducting and metallic tubes. Depending on the applied surfactant, used to disperse the tubes, the semiconducting tubes experience either a much smaller or even counteracting force than the metallic ones, which is used to transfer the metallic tubes from a stream with high tube concentration into a parallel flow region without tubes. The two flows are separated at the end of the electromicrofluidic cell, which allows continuous sorting of nanotubes. The parameters important for the separation were thoroughly studied in experiments and verified by model calculations. These parameters consider both, particular electrical and flow conditions. So far, the achieved sorting efficiency is relatively low. We assume that this is caused by the fact that the applied electrical field - which is the driving force of separation - does not extend far enough into the microfluidic channels to get efficient separation over the whole cross section of the flow. Thus, further improvement is expected by application of three-dimensional field gradients. In another approach, we have used density gradient ultracentrifugation (DGU) to enrich the semiconducting fraction of tubes up to about 90%. This result was achieved in an improved two-step ultracentrifugation. We have developed methods for the self-assembly of field-effect transistors with a high electrical performance by dielectrophoresis. When using unsorted tubes, the self-assembly procedure requires one step where the metallic connections are burned to get high ON/OFF ratios of the transistor. This step is not necessary anymore, when DGU enriched semiconducting tubes are applied. In this case, field-effect transistors can be assembled in one step. Furthermore, we have applied a combined deposition of CNTs and metal ions to reduce the contact resistance of CNTs at the metallic contacts. Finally, we developed a sorting method based on preferential destruction (burning) of metallic or semiconducting SWCNTs by different laser wavelengths which induce different heating processes in nanotubes of different electronic type in an oxidizing atmosphere. This method worked quite well for thin SWCNT layers on surfaces. A 100 % selectivity hasn't been achieved up to now. (2) We have up-scaled an evaporation-based approach to synthesize SWCNTs to deliver up to 500 g SWCNTs each day. A special emphasis has been placed on narrow-distributed properties (especially diameter) to allow for high-quality SWCNTs for all sorting processes of this project. Ways to manipulate and to property characterize length and chirality distributions have been explored. In particular, the length (with the synthesis being optimized to deliver >10 μm SWCNTs) could be adjusted to sizes down to 100 nm. This up-scaled method was then used to explore the preferential synthesis of both metallic and semiconducting SWCNTs. By doing a thorough investigation into a large number of physical and chemical synthesis parameters it was possible to get substantial quantities of SWCNT containing material, in which the SWCNTs are up to 70% metallic - or - with other synthesis parameters, up to 80% semiconducting.
Projektbezogene Publikationen (Auswahl)
- High-Yield Synthesis of Single-Walled Carbon Nanotubes With a Pulsed Arc-discharge Technique. phys. stat. sol. (b) 2007;244(11):3907-3910
Roch A, Jost O, Schultrich B, Beyer E
- Self-assembly of high-performance multi-tube carbon nanotube field-effect transistors by ac dielectrophoresis. Int. J. Mat. Res. 2007;98(8):742-748
Taeger S, Mertig M
- Dielectrophoretically assembled carbon nanotube-metal hybrid structures with reduced contact resistance. phys. stat. sol. (b) 2008;24S(10):2311-2314
Ranjan N, Mertig M
- Multi-component catalysts for the synthesis of SWCNT. phys. stat. sol. (b) 2009;246(11):2511-2513
Roch A, Märcz M, Richter U, Leson A, Beyer E, Jost O
- Oielectrophoretic growth of metallic nanowires and microwires: theory and experiments. Langmuir 2009;26(1):S52-559
Ranjan N, Mertig M, Cuniberti G, Pompe W
- The arc/oven method for the synthesis of SWCNT - surprising (?) results and their consequences. The Fourth NASA - Air Force Research Laboratory and Rice University Workshop on Nucleation and Growth Mechanisms of Single Wall Carbon Nanotubes, San Antonio, Texas, April 2009
Jost O
- Bridging the gap between nano and micro by self-assembly. SALVE Seminar, University Ulm, April, 2010
Mertig M
- Improved sorting of carbon nanotubes according to electronic type by density gradient ultracentrifugation. phys. stat. sol. (b) 2010;247(11-12):2687-2690
Posseckardt J, Battie Y, Fleurier R, Lauret J, Loiseau A, Jost O, Mertig M
- Influence of growth technique and sorting of CNTs for efficient mode-locking of fiber lasers. ChemOnTubes, Arcachon (France), April 2010
Cabasse A, Khadour A, Märtet G, Tretout B, Maine S, Loiseau A, Fleurier R, Lauret, J-S Ambrosio, A, Maddalena P, Grossi V, Passacantando M, Santucci S, Jost O, Mertig M, Posseckardt J
- Molecular designed biological coatings - Intelligente Beschichtungen. Dresdner Transferbrief 2010;1(10):12-13
Rödel G, Ostermann, K, Pompe W, Mertig M, Cuniberti G
- Optical trapping and measurements on carbon nanotubes fibers. ChemOnTubes, Arcachon (France), April 2010
Romano C, Ambrosio A, Maddalena P, Cabasse, A, Khadour A, Martel, G., Lauret J-S, Grossi V, Passacantando M, Santucci S, Jost O, Mertig M, Posseckardt J
