Veranstaltungen

Seminar "Physical and Theoretical Chemistry”

Junctions and Contacts in 2D semiconductor devices

Aleksandar Matkovic

Chair of Physics, Department Physics, Mechanics and Electrical Engineering, Montanuniversitaet Leoben, Austria

As the 2D materials based electronics develop towards very large-scale integrated circuits, one of the major challenges is to obtain high quality contact to 2D semiconductors. Carrier injection barriers, metal induced gap states, and consequently Fermi level pinning at the electrode interfaces hinder the integration of 2D semiconductors. Intrinsic properties of the channel 2D material are rarely accessible as usually majority of the bias intended for the carrier transport is used to overcome the contact ¬related junctions. Further, in the case of polycrystalline films and assembled nanosheet networks also junctions between adjacent domains and nanosheets govern the macroscopic response of the devices.

This talk will focus on single crystalline MoS2, WSe2, PtSe2, and on liquid phase-exfoliated and liquid-liquid interface assembled MoS2 nanosheet networks. We will review several possible electrode choices, from organic self-assembled monolayers functionalized conventional metals, to van der Waals semi-metallic contacts. The focus will be on ways to evaluate contact related losses considering macroscopic electrical measurements, device modelling, and local probing of the electrostatic potential by in operando Kelvin Probe Force Microscopy. We will see how contact engineering can enhance the properties of 2D semiconductor devices, and also tailor carrier injection into 2D channels.

[1]   Matković, A., et.al., Interfacial band engineering of MoS2/gold interfaces using pyrimidine‐containing self‐assembled monolayers: toward contact‐resistance‐free bottom‐contacts. Advanced Electronic Materials 6, 2000110, 2020.
2]  Murastov, G., et.al.,  Multi-Layer Palladium Diselenide as a Contact Material for Two-Dimensional Tungsten Diselenide Field-Effect Transistors. Nanomaterials 14, 481, 2024.
[3] Gabbett, C., et.al., Understanding how junction resistances impact the conduction mechanism in nano-networks. Nature Communications 15, 4517, 2024.
[4] Aslam, M.A., et.al., All van der Waals Semiconducting PtSe2 Field Effect Transistors with Low Contact Resistance Graphite Electrodes. Nano Letters 24, 6529, 2024.

Friday, 28^th March 2025, 2.00 pm

Lecture hall HS 10.01, Heinrichstraße 28, ground floor

Seminar "Physical and Theoretical Chemistry”

Beneath the Surface: Neutron Reflectometry in Physics, Chemistry and Biology

Maximilian Skoda

Rutherford Appleton Lab, UK

Neutron reflectometry (NR) is a powerful analytical tool that provides nanoscale insights into the structure and composition of thin films and interfaces. This presentation will introduce the fundamental principles of NR and its applications to solving key challenges in physical chemistry, soft matter, and related fields. By analysing how neutrons reflect off surfaces at varying angles, NR allows for precise measurements of layer thickness, density, roughness, and composition in complex systems.

NR can investigate a wide range of layered systems at the nanoscale. Examples to be discussed include both fundamental research and more applied topics, such as batteries, fuel cell materials, and corrosion.

When applied to the physical chemistry of the atmosphere, for instance, NR has revealed the behaviour of atmospheric aerosols, pollutant adsorption on surfaces, and the properties of thin water and ice films. For example, it has elucidated how coatings on aerosol particles influence cloud formation and climate, as well as how surface reactions affect air quality and pollutant dynamics.

In soft matter chemistry, NR is essential for studying the arrangement and interactions of polymers, surfactants, and colloidal systems at interfaces—knowledge that underpins advances in coatings, adhesives, and nanotechnology. Similarly, in biochemistry, NR provides unparalleled insights into biomembranes, protein adsorption, and lipid structures, with implications for drug delivery and biosensor development.

The non-invasive nature of NR, its exceptional sensitivity to isotopic composition, and its ability to probe interfaces at atomic resolution make it a unique and versatile technique. This presentation will showcase key studies across chemistry-related disciplines, illustrating how NR contributes to our understanding of complex interfacial phenomena and supports innovation in science and technology.

Friday, 10^th January 2025, 2.00 pm

Lecture hall HS 10.01, Heinrichstraße 28, ground floor

Seminar "Physical and Theoretical Chemistry”

Nanoreactor Molecular Dynamics extended to Periodic Boundary Conditions

Jan Meisner 

Heinrich Heine University Düsseldorf, Institute for Physical Chemistry

Recent developments of efficient computational methods make it possible to discover chemical reactions starting from basic principles and elucidate reaction entire reaction networks autonomously, enabling a complete investigation of chemical systems with all their elementary steps, intermediates, and side reactions which might otherwise have been overlooked. Computational discovery of chemical reactions based on ab initio molecular dynamics (MD) simulations accelerated by different external forces, so-called nanoreactor molecular dynamics (MND) was recently applied to a broad variety of fields, such as combustion chemistry, atmospheric chemistry, and catalysis.

The combination of NMD with periodic boundary conditions is shown using the example of selective catalytic reduction (SCR), a substantial process reducing toxic nitrogen oxides to nitrogen. However, SCR produces the long-lasting greenhouse gas nitrous oxide (N₂O) as an undesirable by-product with an unknown formation mechanism. This study aims at investigating the N₂O formation mechanism in the SCR catalyzed by copper-containing zeolites by means of NMD. The workflow of automated reaction discovery and reaction detection is presented. The chemical reaction network contains the main reaction forming N₂ as well as side reactions forming N₂O for which a reaction mechanism could be deducted. This reaction mechanism might explain the formation of N₂O as side product in SCR and can lead to an improvement of automotive catalyst design in the future to reduce N₂O emission.

Friday, 29. November 2024, 2.00 pm

Besprechungsraum, Heinrichstraße 28, 5^th floor

Seminar "Physical and Theoretical Chemistry”

Battling the elements: Rethinking Strategies for Characterising Nano- and Microstructures

David Clases, Thomas Lockwood, Matthias Elinkmann, Lhiam Paton, Lukas Schlatt, Marko Simic, Christian Neuper, Christian Hill, Raquel Gonzalez de Vega

Universität Graz

Nano- and microstructures play a fundamental role in basic biology and geology but are often neglected. In the past, one reason for this was a lack of suitable methods to provide complementary perspectives on integrated and discrete structures and to establish models on parameters such as sizes, masses, composition and number concentrations. Inductively coupled plasma – mass spectrometry (ICP-MS) and its associated techniques initiated a paradigm shift for the investigation of micro- and nanostructures. In its single particle (SP) mode, it is capable to count individual particles rapidly whilst estimating critical particles features in a bottom-up fashion. In conjunction with laser ablation (LA), it provides opportunities to inquire the spatial distribution of elements in micro-scaled microstructures.

This presentation will provide a general overview of ICP-MS principles in both SP and LA-ICP-MS and consider relevant instrumental and methodical facets. New approaches for the characterisation of small and heterogenous structures are covered subsequently and a focus is directed to the analysis of low abundant particles in complex matrices. A second focus is set on the hyphenation of ICP-MS and the implementation of new instrumentation, specifically optical traps and single particle Raman spectroscopy, providing new opportunities to characterise single particles from various perspectives and to create new, more comprehensive bottom-up models.

Friday, 22. November 2024, 2.00 pm

!Besprechungsraum, Heinrichstraße 28, 5^th floor!

Seminar "Physical and Theoretical Chemistry”

New Strategies for Quantum Control of Nuclear Spins in Molecules 

Johannes K. Krondorfer, Matthias Diez and Andreas W. Hauser

TU Graz

Two recently proposed strategies for the manipulation of nuclear spins are presented and evaluated on a theoretical level via a combination of quantum simulation and electronic structure theory.^1,2,3 Both suggestions attempt to overcome the problem of addressing specific, single nuclear spins, a problem intrinsic to any method involving magnetic fields.  

The first method identifies the vibrational excitation of pseudorotational motions in suitable, highly symmetric molecules as a possible way to generate localized magnetic fields. With the help of these local magnetic fields, even spin states of identical atoms within the same molecule might become individually addressable. The second method exploits the nuclear electric quadrupole moment of non-spherical nuclei to access nuclear spin states through time-dependent electric fields.

Both methods have in common, that they aim for a link between individual nuclear spin manipulation and well established technologies such as microelectronics and quantum optics. On the long run, by introducing pulsed lasers in the optical or IR regime as a tool for spin control, the long coherence times of the nuclear spin degrees of freedom might become accessible via known and proven technology standards.

References  

1. Wilhelmer, R.; Diez, M.; Krondorfer, J. K.; Hauser, A. W. Molecular Pseudorotation in Phthalocyanines as a Tool for Magnetic Field Control at the Nanoscale. J. Am. Chem. Soc. 2024, 146 (21), 14620–14632. https://doi.org/10.1021/jacs.4c01915.

2. Krondorfer, J. K.; Diez, M.; Hauser, A. W. Optical Nuclear Electric Resonance in LiNa: Selective Addressing of Nuclear Spins through Pulsed Lasers. Phys. Scr. 2024, No. 99, 075307. https://doi.org/10.1088/1402-4896/ad52fe.

3. Krondorfer, J. K.; Hauser, A. W. Nuclear Electric Resonance for Spatially Resolved Spin Control via Pulsed Optical Excitation in the UV-Visible Spectrum. Phys. Rev. A 2023, 108, 053110. https://doi.org/10.1103/physreva.108.053110.

Friday, 15. November 2024, 2.00 pm

Lecture hall HS 10.01, Heinrichstraße 28, ground floor