Seminar by Prof. Arne Rosén, Molecular Physics (4 June)
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Seminar ‘Experimental and theoretical analysis of carbon nanotubes grown from catalytic nanoparticles of defined size distribution. Enabling Materials for Printed Electronics-A Decade of Progress’
Speaker: Prof. Arne Rosén, Molecular Physics, Molecular Physic
Date: 4 June 2012 (Mon)
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1. We report use of a dip-coating method to prepare catalyst particles (mixture of iron and cobalt) with a controlled diameter distribution on silicon wafer substrates by changing the solution concentration and withdrawal velocity. The size and distribution of the prepared catalyst particles were analyzed by atomic force microscopy. Carbon nanotubes were grown by chemical vapor deposition, CVD, on the substrates with the prepared catalyst particles. By decreasing the particle size, the growth of carbon nanotubes can be tuned from few walled carbon nanotubes, with homogeneous diameters, to highly pure single walled carbon nanotubes, SWNT. Analysis of the Raman radial breathing mode, showed a relatively broad diameter distribution (0.8-1.4 nm) of single walled carbon nanotubes, SWNT, with different chiralities. By changing the size and composition of the catalyst particles but maintain the growth parameters, the chiralities of SWNT were reduced to mainly four different types: (12,1), (12.0), (8,5) and (7,5) of which quantity is 70 % of all the nanotubes.
2. A deeper understanding of the growth mechanism of nanotubes by the CVD is usually done using a modified version of the established vapor-liquid-solid (VLS) method for production of nanowires. For successful growth the catalytic metal particles should be able to: (i) decompose the feed-stock gas, (ii) form graphitic caps at their surface and (iii) stabilize of the growing open end to maintain the hollow structure. Recently criterion (iii) was identified and shown to be fulfilled using Density Functional Theory, DFT, calculations when the metal-carbon bond is strong enough to make the dissociation of the catalytic particle and the SWNT unfavorable. Too week metal-carbon bond cannot stabilize the open CNT end. For investigation of the relative stability of hydrogen terminated SWNTs and open-ended SWNT fragments of varying diameter and chirality were analyzed using electronic structure DFT calculations. Calculations for open-ended segments of (n+m) =9, 10 and 11 tubes show that the armchair tubes are the most stable followed in sequence by chiral index up to the least stable zigzag segments. These calculations are now extended to (n+m) = 12 and 13 tubes for comparison with the above mentioned experimental results.
Arne Rosén, PhD of Physics, graduated from Physics Department, University of Gothenburg in 1973. He has been employed as Associate Professor University of Gothenburg 1977-1986, University Lecturer 1986-1988 and Professor in Molecular Physics since 1988 and Professor emeritus from September 2006. He has been working in theoretical and experimental atomic physics focused on hyperfine structure studies using the ABMR method and laser spectroscopy and relativistic SCF calculations. The research has been extended to SCF calculations for molecular systems with in particular a 4 component relativistic method. The research has also been extended to MD simulations of metal clusters, and the growth of carbon nanotubes, which has been extended to DFT calculations. He has also worked experimentally with production of metal clusters and studies of their reactivity. Different spectroscopic techniques have been used for studies of catalytic reactions, flames, sprays in engines and detection of skin cancer. He has published more than 200 papers.
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