X-ray Photoelectron Spectroscopy (XPS) is well established to study surfaces and interfaces. In particular, Parallel Angle Resolved XPS (PAR-XPS) may be seen as an ultimate tool to study 2D materials as it allows for analyzing surfaces and interfaces by means of probing non-destructive depth profiles within the information depth of less than 10 nm [1,2,3]. The Figure depicts an example of PAR-XPS survey spectra obtained from a self-assembled monolayer (SAM) on hafnium oxide substrate. The increased intensities of the F1s lines with increased surface sensitivity may indicate an upright position of the molecules on the substrate.

[Translate to English:] PAR-XPS

© Annette Foelske

Left: PAR-XPS survey spectra of a SAM on a HfO2 substrate. Surface sensitivity increases from bottom to top as the photoelectrons are collected at different escape angles with respect to the surface normal. Right: Analyzer chamber: (1) entrance slit to lens system, (2) flood gun, (3) UV-Source, (4) sputter gun, arrows mark the possible directions for manipulation of the sample (x, y, z, θ, φ).

Goals

(i) Analyze commercial, functionalized and CVD/ALD grown 2D Mat /substrate interfaces for obtaining a sound PAR-XPS database [M1]. (ii) Manipulate the materials with heat, electrons and ions and investigate changes in XP spectra, e.g. chemical changes, charging phenomena, van der Waals interactions, thermal desorption of adsorbates [M4]. (iii) Fabricate 2D Mat electronic devices for in situ PAR-XPS of the 2D Mat /dielectric interface in the analyzer chamber of the UHV System. (iv) Characterize and manipulate device performance and correlate results in situ with PAR-XPS data.

Methods

For PAR-XPS measurements a novel XPS instrument (SPECS GmbH, Berlin, Germany) of the Analytical Instrumentation Center at TU Wien will be used. The unique prototype is equipped with an energy and angle dispersive 2D detector system (Phoibos WAL analyzer). The instrumented sample holder (Figure 1b) allows heating and contacting two electrodes and ground. A preparation chamber that may be equipped with additional UHV tools and a glovebox for inert sample storage is available too. In addition, a fine focusing (< 10 µm beam diameter) XPS and an Auger Electron Spectrometer will be installed in 2022 providing multiple more opportunities (e.g. Argon Cluster Gun, RHEELS etc.) to study 2D Mat . The 2D Mat electronic device will be designed following [4].

Collaborations

CVD growth, device fabrication and data interpretation will be conducted in close collaboration with the groups of Mueller and Grasser. Artificial 2D heterostructures will be provided by the group of Aumayr, ALD grown ones D. Eder, and exfoliated and/or functionalized ones by Holzer.

Supervisor

Annette Foelske is a physical chemist. She is head of the Analytical Instrumentation Center (AIC) at TU Wien and responsible for surface analysis by means of electron spectroscopy (PAR-XPS, Scanning XPS and AES). Her area of responsibility is operating measurements as well as the extension and maintenance of three state-of-the-art electron spectrometer. Her research interest is focused on application of surface analytical methods to study novel materials and interfacial reactions. The goal is to enhance the fundamental understanding of interfacial processes leading to an improvement of devices.

Website

Group of Prof. Foelske

Literature

  1. A. Foelske-Schmitz. X-ray photoelectron spectroscopy in electrochemistry research. In Encyclopedia of Interfacial Chemistry, pages 591–606. Elsevier, (2018). DOI: 10.1016/b978-0-12-409547-2.11549-5.
  2. R. N. S. Sodhi, P. Brodersen, L. Cademartiri, M. M. Thuo, and C. A. Nijhuis. Surface and buried interface layer studies on challenging structures as studied by ARXPS. Surface and interface Analysis 49, 1309–1315 (2017). DOI: 10.1002/sia.6270.
  3. A. Foelske-Schmitz and M. Sauer. About charging and referencing of core level data obtained from x-ray photoelectron spectroscopy analysis of the ionic liquid/ultrahigh vacuum interface. Journal of Electron Spectroscopy and Related Phenomena 224, 51–58 (2018). DOI: 10.1016/j.elspec.2017.06.007.