CRC-colloquia

Monday, 11th of November 2024
12:15 o'clock ZOOM and Lecture Hall: H33, INF/AI

Prof. Christine M. Aikens, Kansas State University, USA 

Theoretical Studies of Optical and Photoluminescent Properties of Noble Metal Nanoclusters: Alloy and Ligand Effects

Atomically-precise noble metal nanoclusters have unique chemical and physical properties and are of interest for applications in photonics, sensing, hot-electron-enhanced photocatalysis, etc. In hot-electron-enhanced photocatalysis, a photoexcited nanocluster transfers electrons (or holes) to a neighboring adsorbate or metal oxide system.  Thus, understanding what happens upon photoexcitation of these systems is key to elucidating the mechanism of this interesting phenomenon.  Using density functional theory (DFT) and time-dependent DFT (TDDFT) calculations, we have recently elucidated the optical absorption and photoluminescence spectra of Au25(SR)18- and related nanoparticles. Significant changes in the geometric and electronic structure of this system are observed upon photoexcitation.  Alloying the system with silver atoms leads to tuning of the photoluminescence, but does not change the underlying photoluminescence mechanism.  However, doping the system with other transition metals can lead to a loss of photoluminescence, and we determine that this arises because of changes in the number of filled electronic shells in the system.  Recently, work in atomically-precise nanoclusters has moved from traditional thiolate- and phosphine- stabilized nanoclusters to include a vast array of other types of ligands, including stibine and alkynyl ligands and metal oxide ions.  In this work, we employ TDDFT to examine how the ligands affect the optical absorption and luminescence properties of the metal nanoclusters.  Finally, we examine electron dynamics after photoexcitation in order to understand the spatial locations of the electrons and holes during this process. Overall, photoexcitation in atomically-precise gold nanoparticles is greatly affected by the specific size and composition of the system, leading to many opportunities to tune the photoluminescence.

Monday, 28th of October 2024
12:15 o'clock ZOOM and Lecture Hall: H33, INF/AI

Prof. Sally Brooker, University of Otago, New Zealand

He Honoka Hauwai / German-New Zealand Green Hydrogen centre for research, networking and outreach 

The increasingly severe impacts of climate change demand us to: (a) reduce energy use (b) decarbonise existing high emissions industrial processes and (c) rapidly replace of our present range of carbon-emitting fossil fuels (coal, oil, natural gas) by a suite of carbon-zero and carbon-neutral fuels. The best carbon-zero fuel is direct electrification (from renewable generation), followed by batteries and green hydrogen, both of which are also carbon-zero fuels. New Zealand is very well placed to take up this amazing economic opportunity, and become an exporter of green, energy-intense, high value products.

After setting the scene, I will introduce the German-New Zealand Green Hydrogen Centre / He Honoka Hauwai and our activities, as well as presenting a range of industry green hydrogen activities across NZ. If time permits I will also include some of my own team’s research into improved catalysts for H₂ production from water and CO₂ reduction into commodity chemicals.

Monday, 7th of October 2024
12:15 o'clock ZOOM and Lecture Hall: H33, INF/AI

Prof. Bartlomiej Graczykowski, Adam Mickiewicz University in Poznan, Poland 

Mechanical and Thermal Engineering of Functional Nanomembranes

Continuous miniaturization of electronics, increasing computing power and data transmission speed, an alternative to silicon-based electronics, and obtaining new sources of clean energy are among the most vital challenges in physics, chemistry, and material engineering. The search for new materials, structures, and composites that can meet these requirements has contributed to the spectacular development of nanoscience and nanotechnology in the last two decades. What is essential, the search for new nanomaterials with application potential is often a compromise between excellent properties and incurred energy and environmental costs.

In this talk, I will present the results of experimental research focused on such topics as (i) nature-inspired membranes for ultra-fast light-to-motion conversion1–3, (ii) silicon thermal diode4, (iii) elastic size effect in MoSe25, (iv) GHz signal filtering in 2D Phononic Crystals6 and (v) mechanical reinforcement of colloidal crystals by a cold soldering process based on polymer plasticization using supercritical fluids7,8.

References:

1. Vasileiadis, T. et al. Fast Light-Driven Motion of Polydopamine Nanomembranes. Nano Lett. 22, 578–585 (2022).

2. Krysztofik, A. et al. Fast Photoactuation and Environmental Response of Humidity-Sensitive pDAP-Silicon Nanocantilevers. Advanced Materials 36, 2403114 (2024).

3. Krysztofik, A. et al. Multi-responsive poly-catecholamine nanomembranes. Nanoscale (2024) doi:10.1039/D4NR01050G.

4. Kasprzak, M. et al. High-temperature silicon thermal diode and switch. Nano Energy 78, 105261 (2020).

5. Babacic, V. et al. Thickness-Dependent Elastic Softening of Few-Layer Free-Standing MoSe2. Advanced Materials 33, 2008614 (2021).

6. Graczykowski, B., Vogel, N., Bley, K., Butt, H.-J. & Fytas, G. Multiband Hypersound Filtering in Two-Dimensional Colloidal Crystals: Adhesion, Resonances, and Periodicity. Nano Lett. acs.nanolett.9b05101 (2020) doi:10.1021/acs.nanolett.9b05101.

7. Varghese, J. et al. Size-dependent nanoscale soldering of polystyrene colloidal crystals by supercritical fluids. Journal of Colloid and Interface Science 633, 314–322 (2023).

8. Babacic, V. et al. Mechanical reinforcement of polymer colloidal crystals by supercritical fluids. Journal of Colloid and Interface Science 579, 786–793 (2020).

Monday, 15th of July 2024

12:15 o'clock ZOOM and Lecture Hall: H33, INF/AI

Dr. Sebastian Reparaz, Materials Science Institute of Barcelona, ICMAB-CSIC, Barcelona, Spain

Modern Approaches to Study Thermal Anisotropy and In-plane Heat Transport Using a One-Dimensional Optical Heat Source

The study of the thermal conductivity (or diffusivity) tensor (κij) in bulk and low dimensional materials has gained considerable momentum in recent years. A large number of experimental methods to study the out-of-plane components of the thermal conductivity have been developed and successfully demonstrated using different methodologies, e.g., based on electrical or optical methods. On the other hand, the study of in-plane thermal transport is comparatively more challenging due to the lack of sensitivity to this component of most developed methods, among other reasons. We demonstrate two complementary original experimental approaches with enhanced sensitivity to thermal anisotropy and in-plane heat transport, which are based on using a 1D heat source with uniform power distribution along its long axis.2,3 We show that the 1D geometry of the heat source leads to a slower spatial decay of the temperature field as compared to 0D heat sources, hence, allowing to probe the temperature field at relatively large spatial distances from the heat source. The present approach is based on measuring the phase lag between the thermal excitation and the thermal detection spot for different excitation frequencies of the heat source, hence, rendering the thermal diffusivity of the studied samples. We have applied the previous methods to study the thermal properties of a large variety of samples, with special focus on determining the thermal conductivity tensor elements. We have investigated: βGa2O3 and -Ga2O3; highly oriented pyrolytic graphite (HOPG); suspended silicon and polymer membranes with different thicknesses; bismuth, silicon, glass, AlN, GaN, ZnO, and ZnS substrates; and several Van der Waals materials such as PdSe2,3 hence, demonstrating their excellent performance and rather simple data analysis procedure.

References:

1. Luis A. Pérez, Kai Xu, Markus R. Wagner, Bernhard Dörling, Aleksandr Perevedentsev, Alejandro R. Goñi, Mariano Campoy-Quiles, M. Isabel Alonso, and Juan Sebastián Reparaz, Review of Scientific Instruments 93, 034902 (2022) 2. Kai Xu, Jiali Guo, Grazia Raciti, Alejandro R. Goni, M. Isabel Alonso, Xavier Borrise, Ilaria Zardo, Mariano Campoy-Quiles, and Juan Sebastian Reparaz, International Journal of Heat and Mass Transfer 214, 124376 (2023) 3. Kai Xu, Luis Martínez Armesto, Josef Světlík, Juan F. Sierra, Vera Marinova, Dimitre Dimitrov, Alejandro R. Goñi, Adam Krysztofik, Bartlomiej Graczykowski, Riccardo Rurali, Sergio O. Valenzuela, Juan Sebastián Reparaz, Accepted in 2D materials (2024)

Monday, 24th of June 2024
12:15 o'clock ZOOM and Lecture Hall: H33, INF/AI

Prof. Lianzhou Wang, The University of Queensland, Australia

Nanomaterials for photoelectrochemical energy conversion

Semiconductor nanomaterials hold the keys for efficient solar energy harvesting and conversion processes like photocatalysis and photoelectrochemical reactions. In this talk, we will give a brief overview of our recent progress in designing semiconductor nanomaterials for photoelectrochemical energy conversion including solar hydrogen generation and low-cost solar cells. In more details, we have been focusing on a few aspects; 1) photocatalysis mechanism, light harvesting, charge separation and transfer and surface reaction engineering of low-cost metal oxide based semiconductors including TiO2, BiVO4 as efficient photoelectrode for photoelectrochemical hydrogen production; 2) the working mechanism and stability improvement of perovskite quantum dots for high efficient solar cells; 3). The design of ultra-stable composites of perovskite-MOF with improved light emitting performance.1-7 The resultant material systems exhibited efficient photocatalytic performance and improved power conversion efficiency in solar cells, which underpin sustainable development of solar-energy conversion application.

References：

[1]     Angew. Chem, 2019, doi/10.1002/anie.201810583

[2]     Angew. Chem., 2020, doi: 10.1002/anie.202001148 

[3]     Nature Energy, 2020, 5, 79-88.

[4]     Nature Commun, 2020, https://doi.org/10.1038/s41467-020-15993-4.

[5]     Science, 2021, 374, 621.

[6]     Adv. Mater., 2022, 34 (10), 2106776.

[7]     Nature Commun, 2023, articles/s41467-023-35830-8

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Monday, 3rd of June 2024
12:15 o'clock ZOOM and Lecture Hall: H33, INF/AI

Prof. Radha Boya, University of Manchester, Manchester, UK

Ionic selectivity and memory under angstrom-scale confinement

Understanding molecular transport in nano/angstrom scale channels has practical relevance in applications such as membrane desalination, blue energy, supercapacitors and batteries, as well as in understanding ionic flow through biological channels. Synthetic Å-channels are now a reality with the emergence of several cutting-edge bottom-up and top-down fabrication methods. In particular, the use of atomically thin 2D-materials and nanotubes as components to build fluidic conduits has pushed the limits of fabrication to the Å-scale. In this talk, I will discuss about angstrom (Å)-scale capillaries which are rectangular slit-shaped channels and are created by extracting one-atomic layer out of a crystal [1].

The Å-capillary is an antipode of graphene and can be dubbed as “2D-nothing”. What is intriguing here is, the dimensions of the thinnest channels being comparable to the size of a water molecule. The Å-capillaries have helped probe several intriguing molecular-scale phenomena experimentally, including: water flow under extreme atomic-scale confinement [1] complete steric exclusion of ions [3,5], specular reflection and quantum effects in gas reflections off a surface [2,7], voltage gating of ion flows [4] translocation of DNA [6]. I will present ionic flows induced by stimuli (electric, pressure, concentration gradient) and discuss the importance of ionic parameters that are often overlooked in the selectivity between ions [7], along with ionic memory effects [8].

[1] B. Radha et al., Nature 538, 222 (2016).

[2] A. Keerthi et al., Nature (2018), 558, 420.

[3] A. Esfandiar et al., Science 358, 511 (2017).

[4] T. Mouterde et al., Nature 567, 87 (2019).

[5] K. Gopinadhan et al., Science 363, 145 (2019).

[6] Y. You, A.Ismail et al., Annual Reviews for Materials Research 52, 189, (2022).

[7] S. Goutham et al., Nature Nanotechnology 2023, 18, 596.

[8] P. Robin et al., Science (2023), 379, 161.

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Monday, 27 May 2024
12:15 o'clock ZOOM and Lecture Hall: H33, INF/AI

Prof. Bradley Chmelka, University of California, Santa Barbara, USA

New mesostructured materials for energy conversion and storage: Understanding and design at the atomic level

Advances in synthesis and characterization capabilities enable the atomic-scale features and properties of engineering materials to be measured, understood, and controlled in ways that have not previously been possible. Technologically important examples include new mesoporous nitrogen-carbon electrocatalysts for fuel cells or batteries and mesostructured silica-surfactant materials with ion-conducting membrane proteins that are promising for solar-to-electrochemical energy conversion applications. The properties of such materials have been challenging to understand and control, due in part to their non-stoichiometric compositions and complicated structures that have important influences on their transport and reaction properties. By using a combination of X-ray diffraction, electron microscopy, solid-state NMR spectroscopy, molecular modeling, and bulk property analyses, such materials can be probed over multiple length scales to obtain insights on that local bonding environments and interactions that account for their macroscopic properties. Recent results will be presented on understanding and optimizing the atomic-level compositions and structures of materials for energy-related applications, in particular the influences that distributions of functional species in mesostructured N-carbons and silica-proteorhodopsin materials have on their transport and reaction properties. The analyses provide guidance for the rational design and engineering of these materials for electrochemical or photochemical device applications.

Friday, 17 May 2024
10:30 o'clock ZOOM and Lecture Hall: H18, NWII

Prof. Thalappil Pradeep, Indian Institute of Technology Madras (IITM), Chennai, India

Matter in Confinement: Atomically Precise Clusters and Microdroplets

Research in the recent past has resulted in a large number of nanoparticles whose properties depend on the number and spatial arrangement of their constituent atoms. This distinct atom-dependence of properties is particularly noticeable in ligand protected atomically precise clusters of noble metals, which I will refer to as nanomolecules in this lecture. They show unusual properties such as luminescence in the visible and near-infrared regions. Their molecule-like behavior is evident from their atom- and structure conserving-chemical reactions. Several clusters, which are archetypal nanoparticles, Ag25(SR)18 and Au25(SR)18 (-SR = alkyl/aryl thiolate) have been used for such reactions. Despite their geometric robustness and electronic stability, reactions between them in solution at room temperature produce alloys AgmAun(SR)18 (m+n = 25), keeping their M25(SR)18 composition, structure and topology intact. We captured one of the earliest events of the process, namely the formation of the dianionic adduct, [Ag25Au25(SR)36]2-, by electrospray ionization mass spectrometry. Numerous new ‘molecules’ of this kind have been synthesised in the recent past and they are being taken to practical applications. This work is closely connected to the mission of “clean water for all using advanced materials”. Glimpses of this work will also be presented.

Work in the recent past has shown that new phenomena occur in microdroplets of common solvents. Often, these are related to reaction acceleration. Our work has shown that unusual materials can be synthesized using microdroplets in millisecond timescales. I will illustrate this with various examples involving nanoparticles, functional materials and devices. I will conclude the presentation with an outline of our most recent work on the spontaneous weathering of minerals forming nanoparticles in charged water microdroplets.

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Monday, 05 February 2024
12:00 o'clock ZOOM and Lecture Hall: H18, NWII

Prof. Denis Morineau, Institute of Physics of Rennes, CNRS, University of Rennes, France

Liquids under Nanoscale Confinement: How Different are they?

Spatially confined fluids in nanometer-sized geometry exhibit unique fundamental properties that have no equivalent in corresponding bulk systems. In order to illustrate this statement, I will present an overview of studies we have conducted the recent years on different types of liquids, including binary mixtures, water and aqueous solutions, when confined in carefully designed nanoporous materials.The impacts of confinement on their thermodynamics, structure and dynamics over a wide range of time scales will be discussed based on the combination of experimental and numerical methods, encompassing temporal and spatial windows that range from the molecular to the macroscopic scales.