Comparative electron spectroscopic studies of surface segregation on SiC(0001) and SiC(0001̄)

Muehlhoff, L.; Choyke, W. J.; Bozack, M. J.; Yates, John T.

doi:10.1063/1.337068

Cited by 285 publications

(128 citation statements)

References 30 publications

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“…19,20 The overall intensity of the C 1s emission increased after the 530°C annealing step, presumably due to an insufficient outgassing of the heating stage prior to the experiment. The shape of the C 1s emission after the 530°C anneal was similar to the shape of the C 1s signal observed for the CH 3 -Si(111) surface after a 530°C anneal, indicating that a similar decomposition reaction product formed at this temperature in both cases.…”

Section: Surface Symmetry Of C 2 H 5 -Functionalized Si(111)mentioning

confidence: 99%

High-Resolution Synchrotron Photoemission Studies of the Electronic Structure and Thermal Stability of CH₃- and C₂H₅-Functionalized Si(111) Surfaces

et al. 2007

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The relative coverage, thermal stability, and electronic properties of CH 3 -and C 2 H 5 -functionalized Si(111) surfaces prepared by a two-step chlorination/alkylation procedure have been compared using high-resolution synchrotron photoemission spectroscopy. Whereas the CH 3 -terminated Si(111) surface showed only one C 2s peak for the occupied σ orbitals, the C 2s spectra of C 2 H 5 -terminated Si(111) surfaces showed a symmetric splitting of the occupied σ orbitals, as expected for an ethyl moiety bonded to the surface. The C 2 H 5 termination resulted in an unpinning of the Si surface Fermi level, with a band bending of ∼0.2 eV, and produced a surface dipole potential step of -0.23(15) eV. The observed close-to-flat-band condition is similar to that of CH 3 -Si(111) and is consistent with H termination of the non-alkylated Si atop sites in the two-step chlorination/ alkylation process. The C 2 H 5 -functionalized Si(111) surfaces decomposed at temperatures >300°C, whereas CH 3 -Si(111) surfaces were stable up to at least 440°C. The data clearly highlight the similarities and identify some significant differences between the behavior of the CH 3 -and C 2 H 5 -functionalized Si(111) surfaces.

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Section: Surface Symmetry Of C 2 H 5 -Functionalized Si(111)mentioning

confidence: 99%

High-Resolution Synchrotron Photoemission Studies of the Electronic Structure and Thermal Stability of CH₃- and C₂H₅-Functionalized Si(111) Surfaces

et al. 2007

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“…113 The segregation of the graphite from the newly deposited film is consistent with the phase diagram.…”

Section: Section 52 Discussionsupporting

confidence: 62%

Synthesis and Oxidation of non-Stoichiometric Tungsten Carbide Studied by Scanning Tunneling Microscopy/Spectroscopy

McClimon¹

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Tungsten Carbide (WC) is a promising catalyst material for applications where cost is paramount, such as microbial fuel cells. Unfortunately, oxidation depresses performance which is a critical problem with respect to long term performance. In this work, non-stoichiometric carbon-rich WC is investigated to infer whether an excess of carbon near the surface can reduce or be utilized to repair oxidation of the active catalytic surface. The carbides are synthesized via a physical vapor deposition of metallic tungsten and C 60 , which allows fine control over the composition of the resulting film. The films are studied predominantly via Scanning Tunneling Microscopy/Spectroscopy (STM/STS).Prior to synthesizing the carbide, a number of RT depositions are performed onto graphite substrates to understand the interactions between the C 60 and W prior to thermallyinduced destruction of the C 60 cage and formation of the carbides. These experiments showed a surprising lack of interaction between small W clusters and adjacent C 60 molecules. This result contrasts with literature of analogous experiments showing significant charge transfer from W to C 60 and strong interaction as a result. For W deposited on top of C 60 layers, it is found that isolated W atoms diffuse easily into the interstices of the C 60 matrix and that for high coverages, interactions between the W and C 60 induce a significant reduction in the C 60 bandgap. These interactions can also stabilize very small islands of C 60 on graphite that otherwise require hundreds of molecules before a stationary C 60 island can form.Intermediate annealing at 400-500C of C 60 on epitaxial W/MgO(100) produces novel nanostructures with a very similar size and shape to C 60 but with metallic conductivity, a unique atomic-scale stripe pattern on their surface, occasional mobility under the influence of the STM iv tip, and show signs of evolving towards WO 3 under oxidation. These structures increase in diameter and slowly dissolve into the W surface under increasing annealing temperatures.Carbide thin films are synthesized by codeposition onto MgO substrates held above 600˚C. These thin films are determined to be predominantly metastable, cubic WC 1-x phase. At a C/W ratio of 60/40 and above, carbon is observed to surface segregate and form graphite on the surface of the film. At a ratio of 60/40 the surface is heavily populated with graphene, rather than graphite.Oxidation of the films at elevated temperatures in UHV shows that morphological changes, even at atomic resolution, were absent. STS shows that signs of oxidation overspread the surface immediately but that WO 3 nucleates well-defined islands which grow in size with harsher oxidation conditions. For the graphite covered surfaces, graphite appears to protect the underlying carbide from oxidation, and between 300 and 400˚C, O 2 begins to etch the graphite.The underlying carbide appears to oxidize similarly to films without a graphitized surface.Overall, the WC films oxidize much less rapidly than W cluste...

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“…At about 3 eV above the C 1s peak is a broad additional feature. Others have noted the appearance of a similar feature from single crystal SiC wafers that have been subjected to high temperature anneals above 1100K and attribute the feature to graphite formation on top of the SiC [8]. We therefore suggest that the high energy feature observed in the C 1s spectrum is due to the formation of a SiCO "amalgam" following oxidation of the SiC surface.…”

Section: Discussionmentioning

confidence: 81%

“…6. The narrow high energy peak is the expected C 1s signal from bulk SiC [8]. At about 3 eV above the C 1s peak is a broad additional feature.…”

Section: Discussionmentioning

confidence: 96%

Profiling of the SiO₂ - SiC Interface Using X-ray Photoelectron Spectroscopy

et al. 2000

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The implementation of SiC based sensors and electronics for operation in chemically harsh, high temperature environments depends on understanding the SiO 2 /SiC interface in field effect devices. We have developed a technique to fabricate wedge polished samples (angle 1 x10 -4 rad) that provides access to the SiO 2 /SiC interface via a surface sensitive probe such as xray photoelectron spectroscopy (XPS). Lateral scanning along the wedge is equivalent to depth profiling. Spatially resolved XPS images of the O 1s and Si 2p core levels were obtained of the interfacial region. Samples consist of device-quality thermally grown oxides on 4H-SiC single crystal substrates. The C 1s spectrum suggests the presence of a graphitic layer on the nominally bare SiC surface following thermal oxidation.

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Comparative electron spectroscopic studies of surface segregation on SiC(0001) and SiC(0001̄)

Cited by 285 publications

References 30 publications

High-Resolution Synchrotron Photoemission Studies of the Electronic Structure and Thermal Stability of CH₃- and C₂H₅-Functionalized Si(111) Surfaces

High-Resolution Synchrotron Photoemission Studies of the Electronic Structure and Thermal Stability of CH₃- and C₂H₅-Functionalized Si(111) Surfaces

Synthesis and Oxidation of non-Stoichiometric Tungsten Carbide Studied by Scanning Tunneling Microscopy/Spectroscopy

Profiling of the SiO₂ - SiC Interface Using X-ray Photoelectron Spectroscopy

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Comparative electron spectroscopic studies of surface segregation on SiC(0001) and SiC(0001̄)

Cited by 285 publications

References 30 publications

High-Resolution Synchrotron Photoemission Studies of the Electronic Structure and Thermal Stability of CH3- and C2H5-Functionalized Si(111) Surfaces

High-Resolution Synchrotron Photoemission Studies of the Electronic Structure and Thermal Stability of CH3- and C2H5-Functionalized Si(111) Surfaces

Synthesis and Oxidation of non-Stoichiometric Tungsten Carbide Studied by Scanning Tunneling Microscopy/Spectroscopy

Profiling of the SiO2 - SiC Interface Using X-ray Photoelectron Spectroscopy

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High-Resolution Synchrotron Photoemission Studies of the Electronic Structure and Thermal Stability of CH₃- and C₂H₅-Functionalized Si(111) Surfaces

High-Resolution Synchrotron Photoemission Studies of the Electronic Structure and Thermal Stability of CH₃- and C₂H₅-Functionalized Si(111) Surfaces

Profiling of the SiO₂ - SiC Interface Using X-ray Photoelectron Spectroscopy