Mishra, N., Boeckl, J.J., Tadich, A., Jones, R.T., Pigram, P.J., Edmonds, M., Fuhrer, M.S., Nichols, B.M. & Iacopi, F. 2017, 'Solid source growth of graphene with Ni-Cu catalysts: Towards high quality in situ graphene on silicon', Journal of Physics D: Applied Physics, vol. 50, no. 9.View/Download from: Publisher's site
© 2017 IOP Publishing Ltd. We obtain a monolayer graphene on epitaxial silicon carbide on silicon substrates via solid source growth mediated by a thin Ni-Cu alloy. Raman spectroscopy consistently shows an I D /I G band ratio as low as 0.2, indicating that the graphene obtained through this method is to-date the best quality monolayer grown on epitaxial silicon carbide films on silicon. We describe the key steps behind the graphene synthesis on the basis of extensive physical, chemical and morphological analyses. We conclude that (1) the oxidation, amorphisation and silicidation of the silicon carbide surface mediated by the Ni, (2) the liquid-phase epitaxial growth of graphene as well as (3) the self-limiting graphitization provided the molten Cu catalyst, are key characteristics of this novel synthesis method.
Mishra, N., Boeckl, J., Motta, N. & Iacopi, F. 2016, 'Graphene growth on silicon carbide: A review', Physica Status Solidi (A) Applications and Materials Science, vol. 213, no. 9, pp. 2269-2269.View/Download from: Publisher's site
Mishra, N., Boeckl, J., Motta, N. & Iacopi, F. 2016, 'Graphene growth on silicon carbide: A review', Physica Status Solidi (A) Applications and Materials Science, vol. 213, no. 9, pp. 2277-2289.View/Download from: Publisher's site
© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Graphene has been widely heralded over the last decade as one of the most promising nanomaterials for integrated, miniaturized applications spanning from nanoelectronics, interconnections, thermal management, sensing, to optoelectronics. Graphene grown on silicon carbide is currently the most likely candidate to fulfill this promise. As a matter of fact, the capability to synthesize high-quality graphene over large areas using processes and substrates compatible as much as possible with the well-established semiconductor manufacturing technologies is one crucial requirement. We review here, the enormous scientific and technological advances achieved in terms of epitaxial growth of graphene from thermal decomposition of bulk silicon carbide and the fine control of the graphene electronic properties through intercalation. Finally, we discuss perspectives on epitaxial graphene growth from silicon carbide on silicon, a particularly challenging area that could result in maximum benefit for the integration of graphene with silicon technologies.
Pradeepkumar, A., Mishra, N., Kermany, A.R., Boeckl, J.J., Hellerstedt, J., Fuhrer, M.S. & Iacopi, F. 2016, 'Catastrophic degradation of the interface of epitaxial silicon carbide on silicon at high temperatures', Applied Physics Letters, vol. 109, no. 1.View/Download from: UTS OPUS or Publisher's site
© 2016 Author(s). Epitaxial cubic silicon carbide on silicon is of high potential technological relevance for the integration of a wide range of applications and materials with silicon technologies, such as micro electro mechanical systems, wide-bandgap electronics, and graphene. The hetero-epitaxial system engenders mechanical stresses at least up to a GPa, pressures making it extremely challenging to maintain the integrity of the silicon carbide/silicon interface. In this work, we investigate the stability of said interface and we find that high temperature annealing leads to a loss of integrity. High-resolution transmission electron microscopy analysis shows a morphologically degraded SiC/Si interface, while mechanical stress measurements indicate considerable relaxation of the interfacial stress. From an electrical point of view, the diode behaviour of the initial p-Si/n-SiC junction is catastrophically lost due to considerable inter-diffusion of atoms and charges across the interface upon annealing. Temperature dependent transport measurements confirm a severe electrical shorting of the epitaxial silicon carbide to the underlying substrate, indicating vast predominance of the silicon carriers in lateral transport above 25 K. This finding has crucial consequences on the integration of epitaxial silicon carbide on silicon an d its potential applications.
Pradeepkumar, A., Mishra, N., Kermany, A.R., Boeckl, J.J., Hellerstedt, J., Fuhrer, M.S. & Iacopi, F. 2016, 'Response to 'Comment on 'Catastrophic degradation of the interface of epitaxial silicon carbide on silicon at high temperatures'', Applied Physics Letters, vol. 109, no. 19.View/Download from: UTS OPUS or Publisher's site
Gupta, B., Notarianni, M., Mishra, N., Shafiei, M., Iacopi, F. & Motta, N. 2015, 'Erratum: Corrigendum to ''Evolution of epitaxial graphene layers on 3C SiC/Si (111) as a function of annealing temperature in UHV'' [Carbon 68 (2014) 563-572]', Carbon, vol. 84, no. 1, p. 280.View/Download from: Publisher's site
Gupta, B., Placidi, E., Hogan, C., Mishra, N., Iacopi, F. & Motta, N. 2015, 'The transition from 3C SiC (1 1 1) to graphene captured by Ultra High Vacuum Scanning Tunneling Microscopy', Carbon, vol. 91, pp. 378-385.View/Download from: UTS OPUS or Publisher's site
© 2015 Elsevier Ltd. All rights reserved. In this paper we clarify the transformation mechanism of 3C-SiC into graphene upon thermal decomposition, by a combination of high resolution Scanning Tunneling Microscopy (STM) images and first principle calculations. We studied the transition from 3C-SiC to graphene by high temperature annealing of C-terminated 3C SiC (1 1 1)/Si (1 1 1) samples in Ultra High Vacuum. By using STM we were able to observe very clear atomic resolution images of the transition from SiC (33)R30°to a new intermediate stage SiC (3/23)R30°(very close to the graphene (2 2) reconstruction) after annealing at 1250°C. We also obtained images of the transformation of the intermediate structure into a (1 1) monolayer graphene, caused by further sublimation of atoms in the subsurface layer. We have interpreted the results by using Density Functional Theory - Local Density Approximation calculations, which give full account of the SiC (33)R30°reconstruction, but fail to describe the SiC (3/23)R30°structure due to its incommensurability with the 3C-SiC (1 1 1) lattice.
Iacopi, F., Mishra, N., Cunning, B.V., Goding, D., Dimitrijev, S., Brock, R., Dauskardt, R.H., Wood, B. & Boeckl, J. 2015, 'A catalytic alloy approach for graphene on epitaxial SiC on silicon wafers', Journal of Materials Research, vol. 30, no. 5, pp. 609-616.View/Download from: UTS OPUS or Publisher's site
© Materials Research Society 2015. We introduce a novel approach to the synthesis of high-quality and highly uniform few-layer graphene on silicon wafers, based on solid source growth from epitaxial 3C-SiC films. Using a Ni/Cu catalytic alloy, we obtain a transfer-free bilayer graphene directly on Si(100) wafers, at temperatures potentially compatible with conventional semiconductor processing. The graphene covers uniformly a 2 silicon wafer, with a Raman I D /I G band ratio as low as 0.5, indicative of a low defectivity material. The sheet resistance of the graphene is as low as 25 /square, and its adhesion energy to the underlying substrate is substantially higher than transferred graphene. This work opens the avenue for the true wafer-level fabrication of microdevices comprising graphene functional layers. Specifically, we suggest that exceptional conduction qualifies this graphene as a metal replacement for MEMS and advanced on-chip interconnects with ultimate scalability.
Cunning, B.V., Ahmed, M., Mishra, N., Kermany, A.R., Wood, B. & Iacopi, F. 2014, 'Graphitized silicon carbide microbeams: wafer-level, self-aligned graphene on silicon wafers.', Nanotechnology, vol. 25, no. 32, p. 325301.View/Download from: UTS OPUS or Publisher's site
Currently proven methods that are used to obtain devices with high-quality graphene on silicon wafers involve the transfer of graphene flakes from a growth substrate, resulting in fundamental limitations for large-scale device fabrication. Moreover, the complex three-dimensional structures of interest for microelectromechanical and nanoelectromechanical systems are hardly compatible with such transfer processes. Here, we introduce a methodology for obtaining thousands of microbeams, made of graphitized silicon carbide on silicon, through a site-selective and wafer-scale approach. A Ni-Cu alloy catalyst mediates a self-aligned graphitization on prepatterned SiC microstructures at a temperature that is compatible with silicon technologies. The graphene nanocoating leads to a dramatically enhanced electrical conductivity, which elevates this approach to an ideal method for the replacement of conductive metal films in silicon carbide-based MEMS and NEMS devices.
Gupta, B., Notarianni, M., Mishra, N., Shafiei, M., Iacopi, F. & Motta, N. 2014, 'Evolution of epitaxial graphene layers on 3C SiC/Si (1 1 1) as a function of annealing temperature in UHV', Carbon, vol. 68, pp. 563-572.View/Download from: UTS OPUS or Publisher's site
The growth of graphene on SiC/Si substrates is an appealing alternative to the growth on bulk SiC for cost reduction and to better integrate the material with Si based electronic devices. In this paper, we present a thorough in situ study of the growth of epitaxial graphene on 3C SiC (1 1 1)/Si (1 1 1) substrates via high temperature annealing (ranging from 1125 to 1375 C) in ultra high vacuum (UHV). The quality and number of graphene layers have been investigated by using X-ray Photoelectron Spectroscopy (XPS), while the surface characterization have been studied by Scanning Tunnelling Microscopy (STM). Ex-situ Raman spectroscopy measurements confirm our findings, which demonstrate the exponential dependence of the number of graphene layers on the annealing temperature. © 2013 Elsevier Ltd. All rights reserved.
Kermany, A.R., Brawley, G., Mishra, N., Sheridan, E., Bowen, W.P. & Iacopi, F. 2014, 'Microresonators with Q -factors over a million from highly stressed epitaxial silicon carbide on silicon', Applied Physics Letters, vol. 104, no. 8.View/Download from: UTS OPUS or Publisher's site
We utilize the excellent mechanical properties of epitaxial silicon carbide (SiC) on silicon plus the capability of tuning its residual stress within a large tensile range to fabricate microstrings with fundamental resonant frequencies (f 0 ) of several hundred kHz and mechanical quality factors (Q) of over a million. The fabrication of the perfect-clamped string structures proceeds through simple silicon surface micromachining processes. The resulting f Q product in vacuum is equal or higher as compared to state-of-the-art amorphous silicon nitride microresonators. We demonstrate that as the residual epitaxial SiC stress is doubled, the f Q product for the fundamental mode of the strings shows a four-fold increase. © 2014 AIP Publishing LLC.
Mishra, N., Hold, L., Iacopi, A., Gupta, B., Motta, N. & Iacopi, F. 2014, 'Controlling the surface roughness of epitaxial SiC on silicon', Journal of Applied Physics, vol. 115, no. 20.View/Download from: UTS OPUS or Publisher's site
The surface of cubic silicon carbide (3C-SiC) hetero-epitaxial films grown on the (111) surface of silicon is a promising template for the subsequent epitaxial growth of III-V semiconductor layers and graphene. We investigate growth and post-growth approaches for controlling the surface roughness of epitaxial SiC to produce an optimal template. We first explore 3C-SiC growth on various degrees of offcut Si(111) substrates, although we observe that the SiC roughness tends to worsen as the degree of offcut increases. Hence we focus on post-growth approaches available on full wafers, comparing chemical mechanical polishing (CMP) and a novel plasma smoothening process. The CMP leads to a dramatic improvement, bringing the SiC surface roughness down to sub-nanometer level, though removing about 200 nm of the SiC layer. On the other hand, our proposed HCl plasma process appears very effective in smoothening selectively the sharpest surface topography, leading up to 30% improvement in SiC roughness with only about 50 nm thickness loss. We propose a simple physical model explaining the action of the plasma smoothening. © 2014 AIP Publishing LLC.