No abstract

The industrial realization of graphene has so far been limited by challenges related to the quality, reproducibility, and high process temperatures required to manufacture graphene on suitable substrates. We demonstrate that epitaxial graphene can be grown on transition-metal-treated 6H-SiC(0001) surfaces, with an onset of graphitization starting around 450−500 °C. From the chemical reaction between SiC and thin films of Fe or Ru, sp 3 carbon is liberated from the SiC crystal and converted to sp 2 carbon at the surface. The quality of the graphene is demonstrated by using angle-resolved photoemission spectroscopy and low-energy electron diffraction. Furthermore, the orientation and placement of the graphene layers relative to the SiC substrate are verified by using angle-resolved absorption spectroscopy and energy-dependent photoelectron spectroscopy, respectively. With subsequent thermal treatments to higher temperatures, a steerable diffusion of the metal layers into the bulk SiC is achieved. The result is graphene supported on magnetic silicide or optionally, directly on semiconductor, at temperatures ideal for further large-scale processing into graphene-based device structures.

This is a repository copy of Versailles Project on Advanced Materials and Standards interlaboratory study on intensity calibration for x-ray photoelectron spectroscopy instruments using low-density polyethylene.

This paper extends a previous description of XPS survey spectra from low density polyethylene (LDPE), which was specific for a single type of geometry, to all geometries. Instrument geometries are specified by two angles. The first angle, a, is between the sample-to-monochromator vector and the sample-to-analyzer vector. The second angle, b, is the dihedral angle between the anode-monochromator-sample plane and the monochromator-sample-analyzer plane. The second angle is important because of the polarization induced by the monochromator. We show, using theory, that the XPS spectrum can be decomposed into a “magic angle” reference spectrum, I1, and an anisotropy correction spectrum, f. The geometry for LDPE at which photoemission intensity is equivalent to isotropic emission is shown to be a function of a and b with extreme values for a of 64.6° (b = 0 or 180°) and 57.5° (b = 90°). The deviation of these angles from the “magic angle” a = 54.7° is due to a combination of x-ray polarization and nondipole effects in photoemission. Intensity-calibrated data from a number of instruments with two geometries with b = 180°, one set with a = 60° and the other set with a = 45° are used to determine I1 and f, and these are fitted with simple functions to allow the reproduction of LDPE reference spectra for any instrument geometry. The spectra are taken from the Versailles Project on Advanced Materials and Standards, Technical Working Area 2: Surface Chemical Analysis study A27 and are traceable to the National Physical Laboratory, UK intensity calibration spectra for argon ion sputter-cleaned gold. The functions in this paper may be used in the calibration of XPS instruments with quartz-crystal-monochromated Al Kα x-rays by the comparison of the calculated reference spectrum to data from clean LDPE.

Graphene is now being produced on an industrial scale and there is a pressing need for rapid in-line measurements of particle size for Quality Assurance and Quality Control (QA/QC). Standardised...