Superlattices are artificial, periodic potentials which are used to confined particles and quasiparticles such as atoms, electrons, or excitons. If the trapped quasiparticles are allowed to interact, the resulting many-body state can capture essential behaviors of canonical quantum many-body theories (e.g. the Hubbard model). Such artificial quasiparticle lattices are often called analogue quantum simulators. A bit like a quantum wind tunnel, the quantum simulator serves as an engineerable scale model of a real physical system (electrons or other particles in a real crystalline solid) which allows us to probe complicated many-body physics with a high level of control. Such many-body physics are often hard to describe or predict theoretically, so our quantum simulators provide a route to benchmark leading theories and discover new phases of matter beyond current theoretical predictions.

Thin film semiconductors based on nitrides, oxynitrides, and oxides serve as versatile platforms for tailoring electronic and optical properties of materials. By leveraging advanced deposition techniques, such as reactive sputter deposition, molecular beam epitaxy, and solution-based processing, we explore novel material compositions with precisely controlled structures. A key focus of our research is the comprehensive characterization of these materials, including their elemental composition and atomic bonding environments, electronic structures, and excited state characteristics using a combination of lab- and synchrotron-based techniques. With this suite of complementary experimental tools, we investigate defects, doping strategies, and charge transport dynamics to understand and tune optical and electronic properties. These insights are crucial for controlling the functional properties of these materials for applications that include photoelectrochemical energy conversion, solar cells, and sustainable electronic devices. 

To unlock the full potential of functional materials, it is essential to study their properties under realistic operating conditions. Our research focuses on the development of in situ and operando spectroscopic techniques that provide real-time insights into the structural, electronic, and chemical dynamics of thin films, electrocatalysts, and semiconductor systems. In particular, we employ near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) to probe surface chemistry in reactive environments, transient absorption spectroscopy (TAS) to track charge carrier and electrochemical dynamics, Fourier-transform infrared (FTIR) spectroscopy to monitor molecular vibrations and reaction intermediates, and Raman spectroscopy to analyze structural transformations of materials driven away from equilibrium. These techniques allow us to correlate key energy conversion performance metrics with the electronic structure, defect states, and reaction mechanisms in dynamic environments. Our approach bridges fundamental materials science with innovative energy conversion concepts, enabling the design of more efficient and stable energy materials.

The performance of advanced energy materials is critically determined by their interfaces. In (photo)electrochemical systems, efficient charge transfer relies on the precise design of both solid-solid and solid-liquid interfaces. Our research focuses on tailoring these interfaces at the atomic- and nanoscale to precisely guide efficient energy conversion processes. A key aspect of this research is based on the alignment of energy levels at heterojunctions, which governs selective charge injection and extraction. In addition, we investigate semiconductor-liquid junctions, where interfacial electric fields and surface states play a crucial role in dictating reaction kinetics. Beyond material properties, we study how microenvironments around electrocatalysts – including local pH, ion distribution, and solvation effects – can influence reaction selectivity. These insights are applied to the development of materials for sustainable generation of chemicals from sunlight, with tailored interfacial properties enabling accelerated charge transfer, enhanced reaction selectivity, and improved conversion efficiency.

From tunable dielectrics integrated into nanoscale electronic devices to multifunctional coatings that promote efficient solar-to-chemical energy conversion, we make extensive use of atomic layer deposition (ALD) to precisely engineer interfaces, design novel heterostructures, and introduce defined functionalities at surfaces. Within this research, we develop novel ALD processes and materials, guided by in situ spectroscopic ellipsometry and mass spectrometry that offer real-time insights into nucleation dynamics, growth kinetics, defect formation, and film properties. Moving beyond traditional approaches, we explore advanced ALD strategies by, for example, integrating plasma-surface interactions to tune interfacial chemical and electronic properties, introducing external stimuli to achieve area-selective growth, and tailoring reaction conditions to shape nanoscale morphologies. By advancing ALD-based methods for precise interface and material control, our work contributes to the development of next-generation electronic, energy, and catalytic systems in which nanoscale structure-property relationships are critical.

While 2D semiconductors offer unique electronic and optical properties, realization of their full potential requires scalable growth and controlled integration into functional assemblies. In our research, we aim to create defined 2D/3D heterostructures using chemical vapor deposition (CVD) of transition metal dichalcogenides (TMDs) onto engineered substrates. These heterostructures include thin film junctions and laterally patterned substrates that enable precise spatial control of the 2D material and its electronic environment. In addition, we take advantage of low-temperature atomic layer deposition (ALD) processes to precisely tune interaction lengths and strengths between TMDs and their surroundings. A major emphasis of this work on 2D semiconductor assemblies is devoted to elucidating interfacial mechanisms that govern charge transfer pathways, energetic alignment, and structural and chemical interactions, providing a basis for future applications spanning from advanced optoelectronics to photocatalytic energy conversion.

By far the most important chip materials are silicon (Si) and germanium (Ge), accounting for ~90% of global demand, and entirely dominating the electronics industry. Silicon chips could be much faster and more energy efficient if they operated with light. Silicon, germanium, and their alloys do not efficiently emit light in their naturally occurring, cubic, crystal form due to their indirect bandgap.  However, a newly discovered allotrope of SiGe - hexagonal SiGe - efficiently emits light, holding much promise for silicon based classical and quantum photonic technologies. 

The overarching goal of the Munich Initiative for Cross-Correlative Spin Microscopy (MICroCoSM) is to facilitate the study of nanoscale quantum materials and hybrid quantum systems using the high-resolution - and crucially - the multi-modal spectroscopy offered by tip-based nitrogen vacancy (NV) quantum sensing.  The unique system installed in the labs of WSI moves the boundary of the experimental state-of-the-art by enabling tip-based, time resolved single spin spectroscopy at low temperatures in high magnetic fields.  This is done using a low-temperature version of the ProteusQ scanning NV microscope from Qnami as a Spin-based Quantum Light Microscope (SQLM).  It provides nanoscale access to magnetic properties of nano-materials subject to electrical / optical perturbations.  Feel free to reach out to Prof. Finley if you are interested!

Besides their spectacular optical, spin and electronic properties 2D materials can also exhibit ferroelectric order that arises as a consequence of the stacking order of van-der-Waals (vdW) layered materials and polarisation fields that emerge within the unit cell of the crystal.  Such ferroelectricity can be controlled by strain & sliding of the component vdW layers of the materials.  We explore high-quality 3R-stacked polytypes of TMDs that exhibit out-of-plane ferroelectricity.  In 3R-TMD bilayers, sliding one monolayer a few Ångströms over the other flips the ferroelectric polarisation, a new ‘slidetronics’ concept in condensed matter physics inspired by twistronics.  Such materials are deal for nanoscale systems in which ferroelectric order can be controlled with light, providing exciting new opportunities for optoelectronics, neuromorphic photonics, and sensing.