"Advances in the Chemical State Analysis of Functional Oxides by Combining Soft and Hard X ray Photoelectron Spectroscopy"
Presented by:
Short bio:
Dr. Lars Jeurgens was born in the Netherlands and obtained his PhD in materials sciences at the Delft University of Technology in 2001. After a 2-years postdoctoral period working for the Dutch technology foundation (STW), he moved to the Max Planck Institute for Metals Research in Stuttgart (Germany) in 2003, to lead a research group on “Reactions and Phase Transformations at Surfaces and Interfaces”. At the same time, he was responsible for the surface analysis equipment and services at the institute. His research on the initial oxidation of metals and alloys during this period was honoured with the Masing Gedächtnispreis of the Deutsche Gesellschaft für Materialkunde (DGM) in 2008. Lars joined the Empa, as the head of the new laboratory for “Joining Technologies and Corrosion”, since February 2012. His research interest comprise the surface and interface engineering of metals, alloys, oxides and their coating systems for joining and corrosion management, (ii) the tailoring of microstructure-property relationships of functional oxide films, as well as (iii) the interfacial design and application of nanostructured materials for novel micro- and nano-joining technologies.
Since 2020, his Empa laboratory runs the only laboratory-based Hard X-ray Photoelectron Spectrometer in Switzerland. Accordingly, his recent research is focussed on chemical state studies of functional oxide films by combing soft and hard X-ray Photoelectron Spectroscopy, which is also the topic of today's talk.
Abstract:
The recent development of commercial lab-based XPS/HAXPES systems, equipped with both soft Al-Ka and hard Cr-Ka (or Ga-Ka) X-ray sources, opens unique opportunities for investigating the chemical and electronic structure of functional oxides in a routine laboratory environment [1]. Surface-sensitive deep core-level photoelectron lines and respective Auger transitions can be measured using the hard X-ray source, whereas more bulk-sensitive shallow core-levels can be excited using either the hard or soft X-ray source. Combined access to deep core-level lines (e.g. 1s) and respective sharp core-core Auger transitions (e.g. KLL) in a single XPS/HAXPES setup allows full chemical state analysis of both the cations and anions in various oxides on the basis of the respective Auger parameter [1-3]. Exemplary cases are given for the combined chemical state analysis of cations and anions in different amorphous and crystalline TiO2 and Al2O3 thin films, as prepared by various synthesis methods, such as thermal oxidation, anodization, atomic layer deposition (ALD) and pulsed-laser deposition (PLD). It is shown that differently synthesized am-Al2O3 polymorphs with identical stoichiometric compositions, but with different densities and optical constants, can be well distinguished by their shift in the Al Auger parameter [1-2]. Chemical state analysis can even disclose the effect of H incorporation during the ALD process on the local chemical states of Al and O in am-Al2O3 ALD barrier films [2]. Molecular dynamics simulations were performed to correlate the measured Auger parameter shifts to the change in the O ligand polarizability due to the formation of covalent –OH hydroxyl bonds in the nearest-coordination sphere of Al: see Fig. 1 [3]. As revealed by a combination of atomistic and electrostatic modeling, the measured Al Auger parameter shift as function of the H content and oxide density depends on the complex correlations between local coordination, bond lengths, bond angles, and ligand type(s) around the core-ionized atoms [3].
References
[1] Concepts for chemical state analysis at constant probing depth by lab-based XPS/HAXPES combining soft and hard X-ray sources, Surf. & Interf. Anal. 52 (2020) 802.
[2] Effect of Hydrogen on the Chemical State, Stoichiometry and Density of Amorphous Al2O3 Films Grown by Thermal Atomic Layer Deposition, Surf. & Interf. Anal. 56 (2024) 293
[3] Effect of hydrogen on the local chemical bonding states and structure of amorphous alumina by atomistic and electrostatic modeling of Auger parameter shifts (2024), submitted; see arXiv.2408.08255.