Auger electron spectroscopy | EPFL Graph Search

Auger electron spectroscopy (AES; pronounced oʒe in French) is a common analytical technique used specifically in the study of surfaces and, more generally, in the area of materials science. It is a form of electron spectroscopy that relies on the Auger effect, based on the analysis of energetic electrons emitted from an excited atom after a series of internal relaxation events. The Auger effect was discovered independently by both Lise Meitner and Pierre Auger in the 1920s. Though the discovery was made by Meitner and initially reported in the journal Zeitschrift für Physik in 1922, Auger is credited with the discovery in most of the scientific community. Until the early 1950s Auger transitions were considered nuisance effects by spectroscopists, not containing much relevant material information, but studied so as to explain anomalies in X-ray spectroscopy data. Since 1953 however, AES has become a practical and straightforward characterization technique for probing chemical and comp

Transfer of Graphene under Ultra-High Vacuum

Darius Constantin Merk

This thesis reports on a novel method for graphene transfer that is fully UHV compatible, which has remained a challenge for a long time due to the necessity of supporting graphene for transfer and most often requiring supporting layer removal post-transfer. Our graphene transfer method is based on the wafer-bonding approach, where graphene is stamped onto a target surface, from a support to which it is weakly bound. We use a bilayer of graphene supported by a teflon tape for the low adhesion between graphene layers and the flexibility of teflon tape to allow adaptability to the target surface.We demonstrate successful transfer onto Cu(100) and Ir(111) single crystal surfaces as well as on gr/Ir(111), thus forming a (partial) graphene bilayer on Ir(111). For in-situ characterization, we use Auger electron spectroscopy and STM. Auger measurements confirm that we are able to transfer an average 0.8-0.9 ML of carbon, by comparison to CVD grown samples. After transfer onto Ir(111), we show that by annealing to 1000 °C, we are able to observe by STM the characteristic moiré pattern formed by CVD grown graphene on Ir(111). Auger spectra show that the graphene-Iridium interaction undergoes a change from physisorption to chemisorption upon annealing. XAS and Raman spectroscopy demonstrate that the annealing step taken post transfer to observe the moiré by STM is only necessary to induce a change in interaction strength but not to heal graphene defects, to increase its domain size, or to make it flat. After transfer onto Cu(100), Raman spectra show that the transferred graphene is of the same quality as the CVD grown graphene before transfer, without further annealing. Comparison of synchrotron based high resolution XAS spectra of transferred gr/Ir(111) to CVD grown samples confirms that the transferred graphene is flat on top of the Ir(111) crystal surface.This enables sample and device fabrication, usually hampered by impurities, to be carried out in UHV leading to fully reproducible results. Clean twisted bilayer graphene samples can be made and studied in UHV. Further, surface science can be extended to the third dimension, by capping layers and continuing growth, etc., all under clean conditions.

EPFL2022

A methodology for characterizing the electrochemical stability of DLC coated interlayers and interfaces

Roland Hauert, Emilija Ilic, Stefano Mischler, Patrik Schmutz

DLC coatings are often deposited on Si and Cr based adhesion-promoting interlayers to mitigate stress at the DLC/substrate interface. Interlayers reduce the likelihood of mechanical coating delamination. However, their chemical stability at miniature DLC coating defects, such as pores and micro-pinholes, may be adversely affected in a corrosive environment, such as the human body where DLC coated implants are envisaged. An experimental methodology is presented for accessing and characterizing the electrochemical reactivity of buried interlayers and interfaces. The interlayer, with its interfaces, is revealed by ion beam polishing at an angle, forming a wedge-like profile of the substrate/interlayer/DLC system. The chemical binding and composition of the interlayer/interface is determined by Auger electron spectroscopy (AES), and the susceptibility of the different interfaces to carbide formation and oxidation is identified. It is shown that pure interlayer/interface materials can be obtained for the model Co interlayer. On the other hand, for more reactive materials such as Si, Ti and Cr, the formation of new interface phases was observed. These different new materials are characterized for their corrosion susceptibility with a local-electrochemical microcapillary technique both at open circuit potential (OCP) and under potentiodynamic polarization. Cr and Si-DLC based interlayers presented good passive behavior, while a Si interlayer corroded in bovine-based wear test fluid (HyClone (R) WTF). An analogous degradation is found after a long-term immersion experiment and failed implant cases. The influence of coating defects distribution on the current response of DLC surfaces during electrochemical measurements was also investigated by varying the exposed area (from the cm(2) to the mu m(2) range). Microscale characterization allowed for a better representation of the intrinsic reactivity of DLC, while larger areas were highly dependent on the underlying interlayer.

ELSEVIER SCIENCE SA2019

Oxygen Distribution of Fluorine-doped Tin Oxide Films Coated on Float Glass along Depth Before and After Heat Treatment

Juan Kiwi, César Pulgarin

Fluorine-doped tin oxide (FTO) films were deposited on float glass to create low-emissivity glass (low-E glass) by atmospheric pressure chemical vapor deposition (APCVD). Heat treatments were carried out to assess its antioxidant properties. The surface morphology, crystal structure, and the oxygen and tin concentrations in the FTO films were investigated by scanning electron microscope (SEM), X-ray diffraction (XRD), Auger electron spectrometer (AES), and X-ray photoelectron spectroscopy (XPS), respectively. The results indicated that the electrical properties determined by the four-point probe method remained constant up to 600 degrees C with increasing temperature. The FTO films exhibited nonstoichiometry with a ratio of [O]/[Sn] >2 on the top surface and

Wiley Periodicals, Inc2013