Papers by Author: Martin Hundhausen

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Authors: Felix Fromm, Martin Hundhausen, Michl Kaiser, Thomas Seyller
Abstract: Raman spectroscopy is commonly applied for studying the properties of epitaxial graphene on silicon carbide (SiC). In principle, the Raman intensity of a single graphene layer is rather low compared to the signal of SiC. In this work we follow an approach to improve the Raman intensity of epitaxial graphene on SiC by recording Raman spectra in a top-down geometry, i.e. a geometry in which the graphene layer is probed with the excitation through the SiC substrate [1]. This technique takes advantage of the fact, that most of the Raman scattered light of the graphene is emitted into the SiC substrate. We analyze in detail the top-down measurement geometry regarding the graphene and SiC Raman intensity, as well as the influence of aberration effects caused by the refraction at the air/SiC interface.
Authors: S. Rohmfeld, Martin Hundhausen, Lothar Ley
Authors: Markus Ostler, Roland J. Koch, Florian Speck, Felix Fromm, Hendrik Vita, Martin Hundhausen, Karsten Horn, Thomas Seyller
Abstract: Epitaxial graphene (EG) grown on SiC(0001) resides on the so-called buffer layer. This carbon rich (6√3×6√3)R30° reconstruction is covalently bound to the topmost silicon atoms of the SiC. Decoupling the graphene buffer layer from the SiC interface is a well studied topic since successful intercalation has been shown for hydrogen [1-3]. Recently, intercalation was also shown for oxygen [4, 5]. We present ARPES, XPS and Raman spectroscopy studies to determine the quality of oxygen intercalated buffer layer samples in terms of decoupling and integrity of the transformed graphene layer. The decoupling effect is demonstrated by ARPES measurements showing a graphene-like π band. XPS shows whether the oxidation takes place in the buffer layer or at the interface. Raman spectroscopy is well suited to investigate oxygen induced defects in graphene-like material.
Authors: Roland Püsche, S. Rohmfeld, Martin Hundhausen, Lothar Ley
Authors: Roland Püsche, Martin Hundhausen, Lothar Ley, Kurt Semmelroth, Gerhard Pensl, Patrick Desperrier, Peter J. Wellmann, Eugene E. Haller, J.W. Ager, Ulrich Starke
Abstract: We study electronic Raman scattering of phosphorus and nitrogen doped silicon carbide (SiC) as a function of temperature in the range 7K < T < 300K. We observe a series of peaks in the Raman spectra which we assign to electronic transitions at nitrogen and phosphorus donors on different lattice sites. These transitions are identified as valley orbit transitions of the 1s donor ground state. From the polarization dependence of the observed peaks, we find that all electronic Raman signals have E2-symmetry of C6v for the hexagonal polytypes (6H-SiC and 4H-SiC) and E-symmetry of C3v for 15R-SiC. We find a reduction of the intensities of all valley-orbit Raman signals with increasing temperature and ascribe this reduction to the decreasing occupation of donor states.
Authors: B. Herzog, S. Rohmfeld, Roland Püsche, Martin Hundhausen, Lothar Ley, Kurt Semmelroth, Gerhard Pensl
Authors: Jonas Röhrl, Martin Hundhausen, Konstantin V. Emtsev, Thomas Seyller, Lothar Ley
Abstract: We present a micro-Raman spectroscopy study on single- and few layer graphene (FLG) grown on the silicon terminated surface of 6H-silicon carbide (SiC). On the basis of the 2D-line (light scattering from two phonons close to the K-point in the Brillouin zone) we distinguish graphene mono- from bilayers or few layer graphene. Monolayers have a 2D-line consisting of only one component, whereas more than one component is observed for thicker graphene layers. Compared to the graphite the monolayer graphene lines are shifted to higher frequencies. We tentatively ascribe the corresponding phonon hardening to strain in the first graphene layer.
Authors: Kurt Semmelroth, Michael Krieger, Gerhard Pensl, Hiroyuki Nagasawa, Roland Püsche, Martin Hundhausen, Lothar Ley, M. Nerding, Horst P. Strunk
Authors: John W. Steeds, G.A. Evans, S.A. Furkert, Lothar Ley, Martin Hundhausen, Norbert Schulze, Gerhard Pensl
Authors: Peter J. Wellmann, Z.G. Herro, M. Selder, F. Durst, Roland Püsche, Martin Hundhausen, Lothar Ley, Albrecht Winnacker
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