E. Mora

Publications (5)15.06 Total impact

• Article: Reduced carbon solubility in Fe nanoclusters and implications for the growth of single-walled carbon nanotubes.

  A R Harutyunyan, N Awasthi, A Jiang, W Setyawan, E Mora, T Tokune, K Bolton, S Curtarolo
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  ABSTRACT: Fe nanoclusters are becoming the standard catalysts for growing single-walled carbon nanotubes via chemical vapor decomposition. Contrary to the Gibbs-Thompson model, we find that the reduction of the catalyst size requires an increase of the minimum temperature necessary for the growth. We address this phenomenon in terms of solubility of C in Fe nanoclusters and, by using first-principles calculations, we devise a simple model to predict the behavior of the phases competing for stability in Fe-C nanoclusters at low temperature. We show that, as a function of particle size, there are three scenarios compatible with steady state growth, limited growth, and no growth of single-walled carbon nanotubes, corresponding to unaffected, reduced, and no solubility of C in the particles.
  Physical Review Letters 05/2008; 100(19):195502. · 7.37 Impact Factor
• Source

  Available from: ArXiv

  Article: Reduced carbon solubility in Fe nano-clusters and implications for the growth of single-walled carbon nanotubes

  A. R. Harutyunyan, N. Awasthi, A. Jiang, W. Setyawan, E. Mora, T. Tokune, K. Bolton, S. Curtarolo
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  ABSTRACT: Various diameters of alumina-supported Fe catalysts are used to grow single-walled carbon nanotubes (SWCNTs) with chemical vapor decomposition. We find that the reduction of the catalyst size requires an increase of the minimum temperature necessary for the growth. We address this phenomenon in terms of solubility of C in Fe nanoclusters and, by using first principles calculations, we devise a simple model to predict the behavior of the phases competing for stability in Fe-C nano-clusters at low temperature. We show that, as a function particles size, there are three scenarios compatible with steady state-, limited- and no-growth of SWCNTs, corresponding to unaffected, reduced and no solubility of C in the particles. The result raises previously unknown concerns about the growth feasibility of small and very-long SWCNTs within the current Fe CVD technology, and suggests new strategies in the search of better catalysts. Comment: 4 pages, 3 figures. in press
  03/2008;
• Article: Liquid as a required catalyst phase for carbon single-walled nanotube growth

  A. R. Harutyunyan, T. Tokune, E. Mora
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  ABSTRACT: The evolution of the iron catalyst during carbon single-walled nanotube growth is studied using calorimetry, temperature-programmed oxidation and Raman measurements. Carbon-induced solid-liquid, and solid-liquid-solid phase transitions of the nanocatalyst during the synthesis were observed. We found that liquid phase is favored for the growth of nanotubes, while the solidification of the catalyst nearly terminates the growth. No growth was observed below the eutectic point, when the catalyst is in solid phase. Our results support a growth mechanism of single-walled carbon nanotubes on liquid catalyst particles.
  Applied Physics Letters 07/2005; 87(5):051919-051919-3. · 3.84 Impact Factor
• Article: Liquefaction of catalyst during carbon single-walled nanotube growth

  A. R. Harutyunyan, T. Tokune, E. Mora
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  ABSTRACT: Two groups of cobalt nanoparticles with spherical and disk shape were used to grow carbon single-walled nanotubes by chemical vapor deposition. To elucidate the synthesis conditions and for comparison purpose, a third group of cobalt catalyst prepared by common wet chemistry was used. After the synthesis, electron-microscopic studies revealed that the disk-shape particles with size less than 20 nm were transformed into spheres. Meanwhile, calorimetric measurements showed that the given synthesis temperature was lower than the melting point of the catalyst nanoparticles. Our result supports a growth concept based on the formation of nanotubes on carbon-induced liquefied metal nanoparticles.
  Applied Physics Letters 04/2005; 86(15):153113-153113-3. · 3.84 Impact Factor
• Article: Thermodynamics behind Carbon Nanotube Growth via Endothermic Catalytic Decomposition Reaction

  A. R. Harutyunyan, O. A. Kuznetsov, C. J. Brooks, E. Mora, G. G. Chen
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  ABSTRACT: Carbon filaments can be grown using hydrocarbons with either exothermic or endothermic catalytic decomposition enthalpies. By in situ monitoring the evolution of the reaction enthalpy during nanotube synthesis via methane gas, we found that although the decomposition reaction of methane is endothermic an exothermic process is superimposed which accompanies the nanotube growth. Analysis shows that the main contributor in this liberated heat is the radiative heat transfer from the surroundings, along with dehydrogenation reaction of in situ formed secondary hydrocarbons on the catalyst surface and the carbon hydrogenation/oxidation processes. This finding implies that nanotube growth process enthalpy is exothermic, and particularly, it extends the commonly accepted temperature gradient driven growth mechanism to the growth via hydrocarbons with endothermic decomposition enthalpy.
  Acs Nano. 3(2):379-385.