Index
Nanostructured carbon and advanced carbon films
ARC Discovery Project DP0666866 (2006-2008)
ARC Discovery Project DP0986713 (2009-2011)
RMIT University Team
- Prof. Dougal McCulloch, Team Leader
- Dr. Jim Partridge, Research Fellow
- Dr. Matthew Taylor, Research Fellow
- Mr Ali Moafi, PhD Student
- Mr Desmond Lau, PhD Student
- Mr Mark Ryan, Masters Student
University of Sydney
- Prof. David McKenzie
- Dr Rebecca Powles
Curtin University
- Dr Nigel Marks
International Collaborator
- Prof. Ben Kang Tay, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore
RMIT’s filtered cathodic arc deposition system
Carbon films are produced using a filtered cathodic arc deposition system which employs an energetic plasma to produce coatings. By controlling the deposition conditions, the fraction of diamond-like to graphite-like bonding can be varied resulting in dramatically different properties.
RMIT’s filtered cathodic vacuum arc deposition system
Exploring the properties of films as a function of energy and temperature
We have identified the conditions under which thin films containing vertically oriented sp2 bonded sheets can be deposited at room temperature using energetic ions. Important parameters for orienting the graphene sheets are the ion energy and intrinsic stress within the film. Computer simulations reveal the mechanisms behind this phenomenon at the atomic level.
 (a) Cross-section Transmission Electron Microscope (TEM) image of an oriented amorphous carbon film. This image was taken with an objective aperture centred on a bright arc corresponding to a graphitic {002} reflection (see arrow in inset A). Inset B shows a high resolution image of the 0.335 nm graphite-like planes aligned perpendicular to the surface of the film. |  (b) Schematic representation of the arrangement of oriented sp2 sheets energetically preferred in a biaxial stress field indicated by arrows. |  (c) Snapshot of a molecular dynamics simulation showing an abrupt change in growth mode between amorphous carbon and oriented sp2 sheets. Light atoms are sp2 while dark atoms are sp3. |
We have recently shown that a sharp phase boundary exists between the sp2-rich (graphite-like) and sp3-rich (diamond-like) forms of amorphous carbon, analogous to the boundary between graphite and diamond. We demonstrate that when the biaxial stress in a film is increased above a critical value of 6 ± 1 GPa during growth at room temperature, the sp3-rich phase known as tetrahedral amorphous carbon ta-C is formed. This confirms the role of stress in the formation of this important material which has applications as a protective and optical coating. In the vicinity of the transition stress, a highly oriented graphite-like material is formed at energies more than 300 eV which exhibits low electrical resistance. The highly oriented transition phase provides a low-resistance Ohmic contact to silicon with potential application for high conductance interconnects in electronics.
Stress induced transition in amorphous carbon films.
Self assembly of graphitic nanostructures
We have investigated the formation of carbon onions both experimentally using ultra fast laser ablation and theoretically using MD simulations. We have shown that the amount of argon is critical to the formation of well ordered onions in two different ways. First, sufficient argon is required to encourage atoms to cluster and form large enough precursors. Second, the level of argon has to be low enough to allow the carbon precursors to anneal at high enough temperatures for long enough to order the precursors into carbon onions. MD simulations were performed to investigate the formation mechanism of carbon onions from a various precursor clusters. It was found that spherical onions form from the outer layer first through a process of rearrangement of atoms to form concentric spheres of curved graphite. The simulations confirm that annealing time is critical in forming well ordered onions, as found experimentally.
TEM image and computer simulation of carbon onions
Graphene based nanostructures for high performance devices
Graphene sheets are the building blocks of graphite and a huge variety of carbon based nanostructures. Stacked graphene sheets have the unique property of the highest known thermal conductivity. By manipulating grapheme sheets into three-dimensional channels and interconnects, vastly increased heat fluxes can be extracted from sensitive nanoscale devices such as microprocessors and micro electro mechanical systems. The potential of stacks of graphene as electrical contacts and interconnects will also be explored. By combining thermal and electrical functions, graphene will allow more efficient use of valuable space on future devices. The outcome will be more efficient nanoscale devices to meet ever increasing performance demands.
This work employs a combination of theoretical modelling, novel synthesis and advanced characterization methods to develop stacked graphene sheets onto electrical devices.
Concept for an electrical interconnect between Si and a metallization layer made using oriented graphene
Publications
Lau, D.W.M., McCulloch, D.G., Taylor, M.B., Partridge, J.G., McKenzie, D.R., Marks, N.A., Teo, E.H.T. & Tay, B.K. (2008). Abrupt Stress Induced Transformation in Amorphous Carbon Films with a Highly Conductive Transition Phase. Physical Review Letters 100(17), 176101-4
Lau, D.W.M., McCulloch, D.G., Marks, N.A., Madsen, N.R. & Rode, A.V. (2007). High-temperature formation of concentric fullerene-like structures within foam-like carbon: Experiment and molecular dynamics simulation. Physical Review B (Condensed Matter and Materials Physics) 75(23), 233408-4
Conference Presentations
D. Lau, “Stress Induced Transformation of Amorphous Carbon Thin Films”, 20th Australian Conference on Microscopy and Microanalysis, Perth
M. Taylor, “The Formation of Highly Oriented Graphitic Films Using Cathodic Arc Deposition”, 20th Australian Conference on Microscopy and Microanalysis, Perth