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Effects of aluminum on epitaxial graphene grown on C-face SiC
Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
Lund University, Sweden.
Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.ORCID-id: 0000-0002-2837-3656
Vise andre og tillknytning
2015 (engelsk)Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 117, nr 19, s. 195306-Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

The effects of Al layers deposited on graphene grown on C-face SiC substrates are investigated before and after subsequent annealing using low energy electron diffraction (LEED), photoelectron spectroscopy, and angle resolved photoemission. As-deposited layers appear inert. Annealing at a temperature of about 400 degrees C initiates migration of Al through the graphene into the graphene/SiC interface. Further annealing at temperatures from 500 degrees C to 700 degrees C induces formation of an ordered compound, producing a two domain root 7 x root 7R19 degrees LEED pattern and significant changes in the core level spectra that suggest formation of an Al-Si-C compound. Decomposition of this compound starts after annealing at 800 degrees C, and at 1000 degrees C, Al is no longer possible to detect at the surface. On Si-face graphene, deposited Al layers did not form such an Al-Si-C compound, and Al was still detectable after annealing above 1000 degrees C.

sted, utgiver, år, opplag, sider
American Institute of Physics (AIP) , 2015. Vol. 117, nr 19, s. 195306-
HSV kategori
Identifikatorer
URN: urn:nbn:se:liu:diva-119250DOI: 10.1063/1.4921462ISI: 000355005600036OAI: oai:DiVA.org:liu-119250DiVA, id: diva2:820824
Merknad

Funding Agencies|Swedish Research Council [621-2011-4252]; Linnaeus Grant

Tilgjengelig fra: 2015-06-12 Laget: 2015-06-12 Sist oppdatert: 2017-12-04
Inngår i avhandling
1. Characterizations of as grown and functionalized epitaxial graphene grown on SiC surfaces
Åpne denne publikasjonen i ny fane eller vindu >>Characterizations of as grown and functionalized epitaxial graphene grown on SiC surfaces
2015 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

The superior electronic and mechanical properties of Graphene have promoted graphene to become one of the most promising candidates for next generation of electronic devices. Epitaxial growth of graphene by sublimation of Si from Silicon Carbide (SiC) substrates avoids the hazardous transfer process for large scale fabrication of graphene based electronic devices. Moreover, the operation conditions can potentially be extended to high temperatures, voltages and frequencies. This thesis is focused on characterizations of as grown and functionalized epitaxial graphene grown on both Si-face and C-face SiC. Synchrotron radiation-based techniques are employed for detailed investigations of the electronic properties and surface morphology of as grown and functionalized graphene.

Large area and homogeneous monolayer (ML) graphene has been possible to grow on SiC(0001) substrates by sublimation, but efforts to obtain multilayer graphene of similar quality have been in vain. A study of the transport behavior of silicon atoms through carbon layers was therefore performed for the purpose to gain a better understanding of the growth mechanism of graphene on Si-face SiC. It showed that a temperature of about 800°C is required for Si intercalation into the interface to take place. Intercalation of Si was found to occur only via defects and domain boundaries which probably is the reason to the limited growth of multilayer graphene. Annealing at 1000-1100°C induced formation of SiC on the surface and after annealing above 1200°C Si started to de-intercalate and desorb/sublimate.

Different alkali metals were found to affect graphene grown in SiC quite differently. Li started to intercalate already at room temperature by creating cracks and defects, while K, Rb and Cs were found unable to intercalate into the graphene/SiC interface. Effects induced by the alkali metal Na on graphene grown on both Si-face and C-face SiC were therefore studies. For the Si-face, partial intercalation of Na through graphene was observed on both 1 ML and 2 ML areas directly after Na deposition. Annealing at a temperature of about 75°C strongly promoted Na intercalation at the interface. The intercalation was confirmed to start at domain boundaries between 1 ML and 2 ML areas and at stripes/streaks on the 1 ML areas. Higher annealing temperature resulted in desorption of Na from the sample surface. Also for C-face graphene, a strong n-type doping was observed directly after Na deposition. Annealing at temperatures from around 120 to 300 °C was here found to result in a considerable π-band broadening, interpreted to indicate penetration of Na in between the graphene layers and at the graphene SiC interface.

The thermal stability of graphene based electronic devices can depend on the choice of contact material. Studies of the stability and effects induced by two commonly used metals (Pt and Al) on Si-face graphene were carried out after deposition and after subsequent annealing at different temperatures. Both Al and Pt were found to be good contact materials at room temperature. Annealing at respectively ~400 ºC and ~ 800 ºC was found to trigger intercalation of Al and Pt into the graphene/SiC interface, and induce quasi-free-standing bilayer electronic properties. Contacts of Pt can thus withstand higher temperatures than Al contacts. For Al inhomogeneous islands of different ordered phases were observed to form on the surface during annealing, while this was not the case for Pt. The initial single π-band structure was in the Al case restored after annealing at ~1200 ºC although some Al remained detectable from the sample. For Pt, the bilayer graphene electronic properties induced by intercalation were thermally stable up to 1200ºC. In the case of Al the stability and effects induced on C-face graphene were also investigated for comparison, and significant differences were revealed. An ordered Al-Si-C compound was found to form after annealing at temperatures between ca. 500ºC and 700ºC. Formation of this compound was accompanied with a large reduction of graphene in the surface region. Annealing at temperatures above 800°C resulted in a gradual decomposition of this compound and regrowth of graphene. No Al signal could be detected after annealing C-face graphene at 1000°C.

Graphene grown on C-face SiC has attracted high interest since its mobility has been reported to be one order of magnitude higher compared to Si-face graphene. C-face graphene has moreover been claimed to be fundamentally different compared to Si-face graphene. A rotational disorder between adjacent graphene layers has been suggested that effectively decouples the graphene layers and result in monolayer electronic properties of multilayer C-face graphene. The domain/grain size is typically much smaller for C-face graphene and the number of graphene layers less uniform than on Si-face graphene. Using LEEM and micro-LEED we showed that there is no rotational disorder between adjacent layers within the domains/grains but that they had different azimuthal orientations. Using nano-APRES, we recently also revealed that multilayer Cface graphene show multiple π-bands and Bernal stacking, similar to multilayer Si-face graphene.

sted, utgiver, år, opplag, sider
Linköping: Linköping University Electronic Press, 2015. s. 32
Serie
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1689
HSV kategori
Identifikatorer
urn:nbn:se:liu:diva-120893 (URN)10.3384/diss.diva-120893 (DOI)978-91-7685-998-8 (ISBN)
Disputas
2015-10-08, Planck, Fysikhuset, Campus Valla, Linköping, 10:15 (engelsk)
Opponent
Veileder
Tilgjengelig fra: 2015-08-28 Laget: 2015-08-28 Sist oppdatert: 2019-11-15bibliografisk kontrollert

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