Nanoscience and nanotechnology both take key positions in the improvement of societal needs towards better life conditions in the 21st century whereby proper knowledge and understanding of the material interactions at surfaces and (most often buried) interfaces has become a key element in boosting their performance. For more than 5 decades, X-ray photoelectron spectroscopy (XPS) using soft X-rays (1.5keV) was one of the prime approaches giving access to that information as it probes chemical compositions and material interactions directly, be it within a sampling depth of typically 2-5nm. The availability of lab-scale instrumentation created its widespread industrial (and academic) use and exploitation for routine, easily accessible high volume analysis. Whereas its high surface sensitivity is on the one hand favorable as it confines the sampling volume to a shallow depth, the limited information depth does represent in many cases also a major hurdle as the detailed analysis of deeper lying layers and interfaces is not possible without (destructive) ion beam sputtering which may cause severe bond degradation such that nearly all chemical information is lost. Such limitations arise when trying to study metal gate high-k stacks, interfaces of metallization contacts, photovoltaics, catalysis, protective coatings, batteries, etc. The only resource to overcome this problem is to rely on higher X-ray energies as provided by synchrotron sources which lack the flexibility and availability for daily use and industrial applications.
The recent emergence of lab-based instrumentation providing high (hard) energy XPS (HAXPES) is a game changer as materials analysis with X-ray energies up to 9 keV becomes routinely possible. The increased X-ray energy leads to a larger information depth (from 2 up to 30-50 nm) allowing for non-destructive chemical analysis of complex structures and even the gate stack in a (3D) GAA device.
Imec is one of the first labs worldwide equipped with HAXPES instruments covering a photon energy from 20 eV to 9keV (4 energies will be available), supplying the analysis capabilities from synchrotron centers to the lab-based research.
However to enable such industrial use, the fundamental parameters for quantitative analysis with HAXPES (photoionization cross sections, transmission functions, sensitivity factors, attenuation lengths,..) and insight in the underlying physics of high energy photoemission (e.g. many-particle final-state effects) need to be investigated.
Having established the basics of HAXPES the second part of the thesis will be devoted to a number of application areas:
- Electronic structure at interfaces: Electronic structure at interface is critical to devices performances (band alignment, work functions, ...). This is for instance critical in the case for gate stack analysis including passivation layers, multiple layer oxide stacks and metal gates or 2D materials (Chalcogenide).
- Batteries materials: A very important application area of HAXPES, is the study of battery materials, where the Solid-Electrolyte-Interphase (SEI) layer is utmost important for the functioning of an anode material in a Li-ion battery as it is decisive for battery lifetime. The SEI layer is typically at a depth beyond the reach of conventional XPS but not of HAXPES.
- 3D structures: Present technologies include a continuously increasing number of 3D-structures (nanowires etc) often in dimensions preventing the characterization of individual structures by many chemical analysis methods. The larger information depth of HAXPES may overcome this limitation as photoelectron from all sides can be detected. Novel data interpretation algorithms are required to apply this concept in a quantitative manner.
Required background: Master physics/chemistry/materials science/nanotechnology
Type of work: 75% Experimental, 25% Theory
Supervisor: Wilfried Vandervorst
Daily advisor: Thierry Conard
The reference code for this position is 1812-02. Mention this reference code on your application form.