Deutsche Tagung f ¨ur Forschung mit ... - SNI-Portal

Nanostrukturen und Grenzflächen Poster: Do., 13:00–15:30 D-P315
Electronic structure of ultra-thin graphite layers on SiC(0001)
Thomas Seyller 1 , Konstantin Emtsev 1 , Florian Speck 1 , Lothar Ley 1 , Petar
Stojanov 2 , Eric Huwald 2 , John Riley 2 , Robert Leckey 2
1 Lehrstuhl für Technische Physik, Universität Erlangen-Nürnberg, Germany –
2 Department of Physics, La Trobe University, Australia
Graphene is a zerogap semiconductor with a linear dispersion of the π-bands at the
zone boundary. There electrons and holes can be considered massless and transport
should be governed by Diracs equation. Thus the mobility of 2D electron gases reach
high values (15,000cm 2 /Vs at 300K, 60,000 cm 2 /Vs at 4K) [1-2]. Similar behaviour
with smaller mobilities was observed for graphite/SiC(0001) [3]. It was suggested that
such a system could open up a route towards graphene based electronics. This requires
to understand the formation of thin graphite layers in detail.
Graphite on SiC(0001) is grown by sublimation of Si at T > 1150 ◦ C. The first carbon
rich structure in the growth sequence is a (6 √ 3×6 √ 3) structure. Chen [4] characterized
the (6 √ 3 × 6 √ 3) structure by STM and proposed a carbon nanomesh model which is
incompatible with the weak substrate-overlayer interaction proposed by Forbeaux [5]
based on undistorted π ∗ -bands.
We have studied the occupied electronic states of the (6 √ 3 × 6 √ 3) structure and
thin graphite layers by ARPES. Figure 1 compares the dispersion of the observed surface
states of the (6 √ 3 × 6 √ 3) structure with band structure calculations for graphite
[6]. The observed σ-bands match the calculation quite well but the π-bands are not
developed. Further results obtained at different coverages with graphite will be presented.
The development of the electronic structure of ultra-thin graphite layers with
increasing coverage is outlined.
[1] K. S. Novoselov et al., Nature 438 (2005) 197. [2] K. S. Novoselov et al., Science 306
(2004) 666. [3] C. Berger et al., Journal Of Physical Chemistry B 108 (2004) 19912. [4]
W. Chen et al., Surface Science 595 (2005) 107. [5] I. Forbeaux et al., Phys. Rev. B
58 (1998) 16396. [6] R. Ahuja et al., Phys. Rev. B 51 (1995) 4813.
Fig. 1: Comparison of the electronic states of the
(6 √ 3 × 6 √ 3) structure with the calculated band
structure of graphite [6]. Note that the latter has
been shifted downward in energy by 1eV in order
to match the observed σ-bands to the calculation.