Electron spectroscopy

Summary

Electron spectroscopy refers to a group formed by techniques based on the analysis of the energies of emitted electrons such as photoelectrons and Auger electrons. This group includes X-ray photoelectron spectroscopy (XPS), which also known as Electron Spectroscopy for Chemical Analysis (ESCA), Electron energy loss spectroscopy (EELS), Ultraviolet photoelectron spectroscopy (UPS), and Auger electron spectroscopy (AES). These analytical techniques are used to identify and determine the elements and their electronic structures from the surface of a test sample. Samples can be solids, gases or liquids. Chemical information is obtained only from the uppermost atomic layers of the sample (depth 10 nm or less) because the energies of Auger electrons and photoelectrons are quite low, typically 20 - 2000 eV. For this reason, electron spectroscopy is a technique for surface chemical analyzes. History The development of electron spectroscopy can be considered

Official source

https://en.wikipedia.org/wiki/Electron_spectroscopy

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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

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Nanoscale mapping of the distinct electronic phases characterizing the metal-insulator transition displayed by most of the rare-earth nickelate compounds is fundamental for discovering the true nature of this transition and the possible couplings that are established at the interfaces of nickelate-based heterostructures. Here, we demonstrate that this can be accomplished by using scanning transmission electron microscopy in combination with electron energy-loss spectroscopy. By tracking how the O K and Ni L edge fine structures evolve across two different NdNiO3/SmNiO3 superlattices, displaying either one or two metal- insulator transitions depending on the individual layer thickness, we are able to determine the electronic state of each of the individual constituent materials. We further map the spatial configuration associated with their metallic/insulating regions, reaching unit cell spatial resolution. With this, we estimate the width of the metallic/insulating boundaries at the NdNiO3/SmNiO3 interfaces, which is measured to be on the order of four unit cells.

AMER CHEMICAL SOC2021

The structural and electronic properties of a series of SrMnO3 thin films grown on different substrates leading to different biaxial strains are examined by means of aberration-corrected high-angle annular dark-field scanning transmission electron microscopy and electron energy-loss spectroscopy (EELS). Here, we report a comprehensive theoretical investigation on the impact of oxygen nonstoichiometry and strain on the O-K and Mn-L-2,L-3 electron energy-loss near-edge structures of SrMnO3 with the aid of the all-electron density functional theory code WIEN2K. Our experimental and theoretical EELS data reveal pronounced peak-height changes and energy shifts as a function of strain, which are ascribed to differences in the oxygen vacancy density rather than to a direct effect of lattice distortions. In addition, we find that the formation of oxygen vacancies in SrMnO3 is likely to be enhanced by tensile strain. Compared to the unstrained material, the vacancy formation energy is reduced by 0.25 eV under 3.78% tensile strain.

Amer Physical Soc2016

Transfer of Graphene under Ultra-High Vacuum

Darius Constantin Merk

EPFL2022