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LEEM/PEEM

The SPECS LEEM instrument FE-LEEM P90 is a next generation Low Energy Electron Microscope with unsurpassed 5 nm resolution for dynamic LEEM microscopy experiments. With this instrument, based on the design of Dr. Rudolf Tromp, nanometer scale processes on surfaces can be observed in real-time. The instrument is always equipped with an energy filter for spectromicroscopy and is available in a standard version, an aberration corrected version for lateral LEEM resolutions below 2 nm and as a Near Ambient Pressure version for studies in pressures up to 1 mbar.

FE-LEEM/PEEM P90 forms a state-of-the-art surface electron microscope reaching highest resolution in an easy-to-use compact design. Key features are fast specimen exchange, low vibration measurements, and in situ studies on dynamic surface processes. The base system is the PEEM P90 (without electron source) or the FE-LEEM P90 (equipped with a cold field emission electron source). Both are turnkey multichamber systems with an energy filter, sample storage and all necessary vacuum equipment. The system can also be upgraded with an optional aberration corrector for improved transmission and resolution. The FE-LEEM/PEEM is also available in a near ambient pressure version enabling operando studies under pressure conditions of up to 1 mbar.

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APPLICATION NOTES

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PUBLICATIONS

  1. (2014) Buffer layer free graphene on SiC(0001) via interface oxidation in water vapor

    Intercalation of various elements has become a popular technique to decouple the buffer layer of epitaxial graphene on SiC(0 0 0 1) from the substrate. Among many other elements, oxygen can be used to passivate the SiC interface, causing the buffer layer to transform into graphene. Here, we study a gentle oxidation of the interface by annealing buffer layer and monolayer graphene samples in water vapor. X-ray photoelectron spectroscopy demonstrates the decoupling of the buffer layer from the SiC substrate. Raman spectroscopy is utilized to investigate a possible introduction of defects. Angle-resolved photoemission spectroscopy shows that the electronic structure of the water vapor treated samples. Low-energy electron microscopy (LEEM) measurements demonstrate that the decoupling takes place without changes in the surface morphology. The LEEM reflectivity spectra are discussed in terms of two different interpretations.



    M. Ostler, F. Fromm, R.J. Koch, P. Wehrfritz, F. Speck, H. Vita, S. Böttcher, K. Horn, T. Seyller
    Carbon 70, pp. 258-265
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  2. (2013) Direct growth of quasi-free-standing epitaxial graphene on nonpolar SiC surfaces

    During the graphitization of polar SiC(0001) surfaces through thermal decomposition, a strongly bound carbon-rich layer forms at the graphene/SiC interface. This layer is responsible for the system's high electron-doping and contributes to the degradation of the electrical properties of the overlying graphene. In this study, with the aid of photoelectron spectroscopy, low-energy electron microscopy, low-energy electron diffraction, and the density functional theory, we show that if the graphitization process starts from the nonpolar (11¯20) and (1¯100) surfaces instead, no buffer layer is formed. We correlate this direct growth of quasi-free-standing graphene over the substrate with the inhibited formation of tetrahedral bonds between the nonpolar surface and the carbon monolayer.



    M. Ostler, I. Deretzis, S. Mammadov, F. Giannazzo, G. Nicotra, C. Spinella, Th. Seyller, A. La Magna
    Phys. Rev. B 88, 085408
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  3. (2017) Growth and Intercalation of Graphene on Silicon Carbide Studied by Low‐Energy Electron Microscopy

    Based on its electronic, structural, chemical, and mechanical properties, many potential applications have been proposed for graphene. In order to realize these visions, graphene has to be synthesized, grown, or exfoliated with properties that are determined by the targeted application. Growth of so‐called epitaxial graphene on silicon carbide by sublimation of silicon in an argon atmosphere is one particular method that could potentially lead to electronic applications. In this contribution we summarize our recent work on different aspects of epitaxial graphene growth and interface manipulation by intercalation, which was performed by a combination of low‐energy electron microscopy, low‐energy electron diffraction, atomic force microscopy and photoelectron spectroscopy.



    F. Speck, M. Ostler, S. Besendörfer, J. Krone, M. Wanke, T. Seyller
    Annalen der Physik, 529 (11), 1700046
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  4. (2014) Healing of graphene on single crystalline Ni(111) films

    The annealing of graphene layers grown on 150 nm thick single crystal Ni(111) films was investigated in situ by low energy electron microscopy and photoemission electron microscopy. After growth, by means of chemical vapor deposition of ethylene, the graphene layers consist of several domains showing different orientations with respect to the underlying Ni surface and also of small bilayer areas. It is shown that, in a controlled process, the rotated domains can be transformed into lattice-aligned graphene, and the bilayer areas can be selectively dissolved, so that exclusively the aligned monolayer graphene is obtained. The ordering mechanism involves transport of C atoms across the surface and solution in the bulk.



    P. Zeller, F. Speck, M. Weinl, M. Ostler, M. Schreck, T. Seyller, J. Wintterlin
    Appl. Phys. Lett. 105, 191612
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  5. (2017) Single Crystalline Metal Films as Substrates for Graphene Growth

    Single crystalline metal films deposited on YSZ‐buffered Si(111) wafers were investigated with respect to their suitability as substrates for epitaxial graphene. Graphene was grown by CVD of ethylene on Ru(0001), Ir(111), and Ni(111) films in UHV. For analysis a variety of surface science methods were used. By an initial annealing step the surface quality of the films was strongly improved. The temperature treatments of the metal films caused a pattern of slip lines, formed by thermal stress in the films, which, however, did not affect the graphene quality and even prevented wrinkle formation. Graphene was successfully grown on all three types of metal films in a quality comparable to graphene grown on bulk single crystals of the same metals. In the case of the Ni(111) films the originally obtained domain structure of rotational graphene phases could be transformed into a single domain by annealing. This healing process is based on the control of the equilibrium between graphene and dissolved carbon in the film. For the system graphene/Ni(111) the metal, after graphene growth, could be removed from underneath the epitaxial graphene layer by a pure gas phase reaction, using the reaction of CO with Ni to give gaseous Ni(CO)4.



    P. Zeller, M. Weinl, F. Speck, M. Ostler, A.-K. Henß, T. Seyller, M. Schreck, J. Wintterlin
    Annalen der Physik, 529 (11), 1700023
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