Colloquium with Kartik Ayyer (Max Plank Institute - Hamburg) and Ermes Peci (VU Amsterdam)
12:30 - 12:50 Ermes Peci, Postdoc, PhotoConversion Materials, VU Amsterdam
Titel: Semiconducting 2D materials: who they are and what they do
Abstract: What happens to a semiconductor when it is only three atoms thick? This question has driven the growing interest in 2D transition metal dichalcogenides (TMDCs) over the past decade. These atomically thin semiconductors exhibit many remarkable physical phenomena, including tightly bound excitons that dominate their optical response, layer-dependent bandgaps, strong light-matter interactions, and coupled spin and valley physics. Understanding these effects is crucial not only for fundamental science but also for enabling next-generation optoelectronic devices. In this talk, I will begin with an overview of the electronic and optical properties that make 2D TMDCs so distinctive. I will then discuss how these three‑atom‑thick crystals can be fabricated and what can be learned by characterizing them with optical techniques, including less commonly used spectroscopic methods such as ellipsometry. Finally, I will present ongoing work on photothermal effects in hybrid systems composed of plasmonic nanoparticles and 2D semiconductors.
12:50 -13:45 Kartik Ayyer, Group Leader, Max Plank Institute for the Structure and Dynamics of Matter, Hamburg
Titel: Serial diffractive imaging to study nanoscale structural dynamics
Abstract: X-ray free electron lasers provide a unique opportunity to measure ultrafast, high resolution dynamics using diffractive imaging methods. In particular, I will focus on measurements on ensembles of nanosystems where the high peak brightness enables a serial (one-at-a-time) imaging approach which, when combined with modern machine learning analysis algorithms, provides much richer information than conventional ensemble measurements. Building upon our proof-of-concept studies understanding the structural landscape of gold nanoparticles [1, 2], I will talk about three problems where we use this method to observe hitherto unseen properties of nanosystems, (i) large polaron formation in CsPbBr3 quantum dots [3], (ii) dehydration dynamics on MS2 bacteriophage capsids using deep learning [4,5] and (iii) plasmon-induced structural deformations of gold nanorods. Finally, I will discuss the possibility of using such an approach to observe ultrafast dynamics where precise optical triggering is not possible.
References:
1. Ayyer, et al. Optica, 8(1), 15-23 (2021).
2. Shen, et al. ACS Nano, 18, 24, 15576-15589 (2024).
3. Shen, et al. ACS Nano 19, 31, 28372-28382 (2025).
4. Mall, et al. arXiv:2407.11687 (2024).
5. Zhuang et al. IUCrJ 9(2), 204-214 (2022).