Research Highlights


 

Low-Temperature Exfoliation of Multilayer-Graphene Material from FeCl3 and CH3NO2 Co-Intercalated Graphite Compound

Wujun Fu,a Jim Kiggans,b Steven H. Overbury,a,c Viviane Schwartz,a and Chengdu Lianga

aCenter for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee
bMaterials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee
cChemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee

Achievement
We have developed a novel scalable method for the synthesis

of high quality graphene materials via low-temperature exfoliation of graphite under mild chemical conditions. The method preserves energy and chemicals used in the generation of graphene materials that used to be an energy consuming and chemical wasteful process. We found that FeCl3 and nitromethane (CH3NO2) co-intercalated graphite can be readily exfoliated to graphene sheet at the boiling temperature of water by heating in a microwave (MW) oven. The essence of this method is the rapid decomposition of nitromethane to gaseous products expanding within the galleries of graphene sheets. The mechanical force from the gas expansion overcomes the already weakened van der Waals forces and thus leads to the formation of graphene sheets.

Significance
The large demand for high quality graphene materials makes the synthesis of graphene one of the key steps to meet various research needs. The chemical or physical exfoliation of graphite is a straightforward method to produce graphene with least synthesis effort, since it takes advantage of the existing graphene structure in crystalline graphitic materials.

We demonstrate the exfoliation of graphite intercalation compounds (GIC) by a method that circumvents the dramatic structural changes of graphene brought about by irreversible chemical functionalization. The method holds the promise for massive production of graphene with a low concentration of defects via a low-temperature, mild exfoliation approach.

Credit: This work was published in Chemical Communications DOI: 10.1039/C1CC10508F. This research was supported by the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Office of Basic Energy Sciences, U. S. Department of Energy.

 



Phonon Softening and Metallization of a Narrow-Gap Semiconductor by Thermal Disorder

O. Delaire,1 K. Marty,1 M. B. Stone,1 P. R. C. Kent,1 M. S. Lucas,2 D. L. Abernathy,1 D. Mandrus,1 B. C. Sales1

1Oak Ridge National Laboratory, One Bethel Valley Road, Oak Ridge, TN 37831
2
Air Force Research Laboratory, Wright-Patterson AFB, OH 45433

Achievement
We have shown how, in some materials, there can be a surprisingly strong coupling between certain features of the electronic structure and the way the atoms in a solid vibrate. This insight should help us understand better how heat is transported in a solid. Inelastic neutron scattering measurements of Fe1-xCoxSi alloys were combined with quantum mechanics based calculations to show why the alloys exhibit unusual softening as the temperature is increased. Our results show that for alloys with a rapidly changing concentration of electrons near the chemical potential, there are likely to be strong temperature-dependent interactions between the atom vibrations and electrons.

(Left) Phonon dispersions of FeSi measured via time-of-flight inelastic neutron scattering, compared with calculations (light blue lines) provides clear evidence of the unusual softening of atomic motion with increasing temperature. (Right) Phonon density of states for FeSi and CoSi from ab initio molecular dynamics simulations. A large phonon softening in FeSi between 300K and 1200K is predicted.

Significance
By combining extensive neutron scattering based analysis with the results of first principles molecular dynamics calculations, we have clearly demonstrated a strong coupling between the phonon and electron states when there are sharp electronic features around the Fermi level. These effects are likely to be common to many narrow gap materials including some superconductors, heavy-Fermion compounds, and many thermoelectric materials. Our results demonstrate the importance of including these effects in predicting or optimizing heat flow in these materials.

Credit: This work was published in Proceedings of the National Academy of Sciences (7 March 2011, 2010-14869RR, doi: 10.1073/pnas.1014869108). Research at ORNL’s Spallation Neutron Source, High Flux Isotope Reactor, and Center for Nanophase Materials Sciences (PRCK) was sponsored by the U. S. Department of Energy Scientific User Facilities Division. Computations by PRCK used resources of the National Energy Research Scientific Computing Center, which is supported by the Office of Science, U.S. Department of Energy.


 

Characterization and Carbonization of Highly-Oriented Poly(diiododiacetylene) Nanofibers

Liang Luo,1 Christopher Wilhelm,1 Christopher N. Young,2 Clare P. Grey,1 Gary P. Halada,2 Kai Xiao,3 Ilia N. Ivanov,3 Jane Y. Howe,4 David B. Geohegan,3 and Nancy S. Goroff1

1Department of Chemistry, State University of New York, Stony Brook, NY 11794
2Department of Material Science and Engineering, State University of New York, Stony Brook, NY 11794
3Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, 37831
4Materials Sciences and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831

Achievement
Nanofibers (10-50 nm in diameter) of poly(diiododiacetylene) (PIDA) were synthesized by topochemical polymerization of diiodobutadiyne within host guest cocrystals. PIDA is a novel conjugated polymer with an all-carbon backbone which was shown to align within the nanofibers using polarized Raman spectroscopy. The PIDA nanofibers were stable at room temperature, but could be easily induced to irreversibly convert to sp2–hybridized carbon by a variety of processing treatments, including irradiation with a 532-nm laser beam. The mechanism of the transformation was found to be the release of iodine, which permits cross-linking between individual polymer chains within the nanofibers, transforming them to sp2–hybridized carbon.

Significance
One dimensional carbon nanomaterials are of broad interest for applications in batteries, fuel cells, hydrogen storage, and nanoscale electronics, however synthesizing them under mild conditions remains a challenge. Common synthesis techniques require transition metal catalysis and/or high temperature processing. This work describes a new low-energy pathway for the synthesis of one-dimensional carbonized nanofibers through the alignment of precursor polymers with iodine atoms which can be easily released to permit cross-linking of the individual polymer chains within the fiber.

Credit: This work was web published in Macromolecules March 25, 2011. Research was sponsored by the National Science Foundation (CHE-9984937, CHE-0446749, CHE-0453334, and DMR0804737). A portion of this research was conducted as a user project at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Office of Basic Energy Sciences, U.S. Department of Energy.

Citation for Highlight: L. Luo, C. Wilhelm, C. N. Young, C. P. Grey, G. P. Halada, K. Xiao, I. N. Ivanov, D. B. Geohegan, and N. S. Goroff, Characterization and Carbonization of Highly Oriented Poly(diiododiacetylene) Nanofibers, Macromolecules (published April 26, 2011, DOI: 10.1021/ma102324r).