Search This Blog

Friday, December 30, 2011

Graphane, Hydrogen and Nickel Papers to Read

The evolving story of graphene
Aaron Bostwicka, Thomas Seyllerb, Eli Rotenberga, Carsten Enderlein, Yuriy Dedkov, and Karsten Horn

The “carbon rush” to investigate the physics, chemistry, and materials science of graphene, the single sheet of sp2-bonded carbon atoms arranged in a honeycomb lattice, has not yet abated, although the concept of “massless Dirac Fermions” has been preached in most major conferences, and even in the popular press. It is fair to say that the basic properties of graphene are quite well known, and as far as the electronic structure and the general surface science is concerned, the FHI – Erlangen – Berkeley collaboration has had some part in this, investigating in detail within the last two years the electronic structure (through photoelectron spectroscopy), growth morphology (through low energy electron microscopy1), and optimized layer preparation2. In cooperation with Roland Bennewitz’s group, the friction properties of graphene were addressed, and a connection with electron-phonon coupling was made3. Our interest has turned to the interaction between graphene and adsorbates, both from a “functionalization” point of view, and to study how defects affect its transport properties4. Hydrogen is a particularly important adsorbate since it converts the bonding in graphene from sp2 to sp3, creating a new material (“graphane”) in which the nature of the charge carriers changes completely and the conductivity is greatly reduced. The properties of interfaces between graphene and different substrates will continue to be addressed in order to find additional viable procedures for large-scale growth on insulating or electronically totally decoupled substrates. All of the work mentioned above has been carried out on graphene films prepared on silicon carbide, where it was demonstrated that large films with excellent structural perfection can be produced by an ex situ process under atmospheric pressure3.

Our interest has also turned to graphene films on metal surfaces, particularly ferromagnetic ones, since graphene layers may act as spin filters useful for applications in proposed spintronics devices. Among the possibilities are sandwich-like structures such as Ni/graphene/Ni, a system with a perfect lattice match. We have shown that the magnetic moment of nickel is partly transferred to the carbon atoms at the graphene/Ni interface where NEXAFS spectra have clarified the mechanism of the strong interaction between the Ni substrate and the graphene monolayer.

References 1. T. Ohta, F. E. Gabaly, A. Bostwick, J. L. McChesney, K. V. Emtsev, A. K. Schmid, Th. Seyller, K. Horn, and E. Rotenberg, New J. Phys. 10, 023034 (2007). 2. K. V. Emtsev, A. Bostwick, K. Horn, J Jobst, G. L. Kellogg, L. Ley, J. L. McChesney, T. Ohta, S. A. Reshanov, J. Röhrl, E. Rotenberg, A.K. Schmid, D. Waldmann, H. B. Weber, and Th. Seyller, Nature Materials 8, 203 (2009). 3. T. Filleter, J. L. McChesney, A. Bostwick, E. Rotenberg, K. V. Emtsev, Th. Seyller, K. Horn, and R. Bennewitz, Phys. Rev. Lett. 102, 086102 (2009). 4. A. Bostwick, J. L. McChesney, K. Emtsev, Th. Seyller, K. Horn, S. D. Kevan, and E. Rotenberg, Phys. Rev. Lett. 103, 056404 (2009). a Advanced Light Source, Lawrence Berkeley Laboratory, Berkeley, CA, USA b University of Erlangen, Erlangen, Germany 88



Annual Review of Materials Research

Vol. 36: 555-608 (Volume publication date August 2006)
First published online as a Review in Advance on April 24, 2006
DOI: 10.1146/annurev.matsci.36.090804.094451
A. Pundt and R. Kirchheim
Institut für Materialphysik, D-37077 Göttingen, Germany; email: ,
FULL-TEXT| PDFPDF (1192 KB)| Permissions
Web of Science ®: Related Records ®| Times Cited: 91
Cost: $20.00
Lattice strain effects in graphane and partially-hydrogenated graphene sheetsMorris, James R [ORNL]; Averill, Frank [ORNL]; He, Dr. Haiyan [University of Science and Technology of China]; Pan, Dr. Bicai [University of Science and Technology of China]; Cooper, Valentino R [ORNL]; Peng, L. [University of Tennessee]
This paper presents a brief review of recent developments in the studies of fully hydrogenated graphene sheets, also known as graphane, and related initial results on partially hydrogenated structures. For the fully hydrogenated case, some important discrepancies, specifically whether or not the graphene sheet expands or contracts upon hydrogenation, exist between published first-principles calculations, and between calculations and experiment. The lattice change has important effects on partially hydrogenated structures. In addition, calculations of the interfacial energy must carefully account for the strain energy in neighboring regions: For sufficiently large regions between interfaces, defects at the interface which relieve the strain may be energetically preferable. Our preliminary first-principles calculations of ribbon structures, with interfaces between graphane and graphene regions, indicate that the interfaces do indeed have substantial misfit strains. Similarly, our tight-binding simulations show that at ambient temperatures, segments of graphene sheets may spontaneously combine with atomic hydrogen to form regions of graphane. Here, small amounts of chemisorbed hydrogen distort the graphene layer, due to the lattice misfit, and may induce the adsorption of more hydrogen atoms.
Energy Technology Data Exchange (ETDEWEB)

Lassila, D. H.; Birnbaum, H.K. (Univ. of Illinois, Urbana (USA))

The dependence of the fracture mode of hydrogen charged nickel deformed in tension at 77 K on grain boundary segregation has been studied. In the absence of any segregation the fracture mode at 77 K is ductile rupture. It is shown that if a sufficient quantity of hydrogen is segregated at grain boundaries by aging at various temperatures the fracture mode changes from a ductile shear rupture mode to an intergranular mode. The binding enthalpy of hydrogen to nickel grain boundaries is determined based on the dependence of the fracture mode on aging temperature and hydrogen concentration.
Energy Technology Data Exchange (ETDEWEB)

Tight-binding molecular dynamics study of the hydrogen-induced structural modifications in tetrahedral amorphous carbon
Ukpong, A. M.
A tight-binding molecular dynamics study of the structural evolution in tetrahedral amorphous carbon networks under dynamic hydrogen saturation is presented. The incorporation of hydrogen results in higher degrees of network disorder in second-neighbour distances, and initiates orbital re-hybridization that relaxes network stress. Using the simulated structures, numerical tests are performed to verify the effectiveness of a new structural order parameter for tetrahedrally-bonded solids. It is found that the island of accessible information, within the order parameter field shows a linear dependence between the fluctuations in first- and second-nearest-neighbour distances at a preferred orientation of 36°. A comparison with similar studies on hydrogenated amorphous silicon suggests tha...
Electronic Table of Contents (ETOC) (United Kingdom)

No comments:

Post a Comment