Upcoming seminars

Seminars at DIFFER cover a wide range of topics and are held on Thursdays at 11.15 AM in the seminar room of the institute (unless otherwise stated). Seminars are open to everybody. If you are interested in visiting a DIFFER seminar or want to subscribe to our mailing list, please follow the instructions for external visitors.

List all past seminars organized at DIFFER

Celso de Mello Donega
January 31st 2019
11:15 to 12:15
Colloidal semiconductor nanocrystals are versatile nanomaterials, whose properties are determined by their size, shape (quantum dots and nanorods, nanosheets, nanowires), composition, and compositional profile (i.e., single component, gradient or homogeneous alloy, doped, heterostructured). Heterostructured semiconductor nanocrystals (hetero-NCs) are particularly attractive, since they allow the spatial localization of photogenerated charge carriers to be manipulated by controlling the band offsets between the materials that are combined at the heterointerface. This has a dramatic impact on several optoelectronic properties. Moreover, the colloidal nature of these nanomaterials allows one to take full advantage of nanoscale effects to combine size-, shape- and composition-dependent properties with easy surface manipulation and solution processing. These characteristics have turned colloidal semiconductor NCs and hetero-NCs into promising materials for a myriad of applications (e.g., LEDs, solar cells, catalysis, biomedical imaging, etc.), motivating extensive research into their synthesis and optoelectronic properties. In our group, we have applied a multistage preparation strategy that allows the combination of different synthesis techniques in a sequential manner in order to achieve the targeted preparation of colloidal nanocrystals. This has allowed us to systematically investigate the optical properties of a variety of nanocrystal and hetero-nanocrystal compositions. In this seminar, I will discuss a selection of examples, chosen in order to illustrate specific synthesis strategies, as well as to show that composition, size, and shape control can be used to tailor nanoscale excitons, and consequently the optical properties of colloidal nanocrystals.
Bob van der Zwaan
February 7th 2019
11:15 to 12:15
Solar energy driven processes with H2O and CO2 as basic feedstocks can produce ‘‘solar fuels’’ that could substitute their fossil based counterparts. This presentation summarizes the main findings of techno-economic research on systems that can generate different types of fuels with renewable energy as starting point. These ‘‘renewable fuels’’ could potentially play a key role in future energy systems, both as a storage medium in the power sector and as an energy carrier in e.g. the transport sector, or deliver fundamental building blocks for the chemical industry. We determine whether, how, and when renewable fuels might become competitive alternatives for fossil fuels. The technologies required to produce renewable fuels are analyzed by the application of learning curves associated with individual system components. We thereby make projections for possible decreases in investment costs and reductions in fuel production costs. In an optimistic scenario we find that competitivity could be reached between 2025 and 2048 for all renewable energy production pathways that we investigate, for hydrogen, syngas, methanol, and diesel. Two techniques yield break-even costs before 2050 even in a conservative base case scenario: H2 production through electrolysis and diesel production by Fischer–Tropsch synthesis. Both processes use solid oxide electrolysis, which profits from rapid cost reductions and high efficiency.
Josefine Proll
February 14th 2019
11:15 to 12:15
Stellarators, the twisted siblings of the axisymmetric fusion experiments called tokamaks, have historically suffered from confining the heat of the plasma insufficiently compared with tokamaks and were therefore considered to be less promising candidates for a fusion reactor. This has changed, however, with the advent of stellarators in which the laminar transport is reduced by shaping the magnetic field accordingly. As in tokamaks, the turbulent transport remains as the now dominant transport channel. In this talk I want to give a brief overview of what we know about turbulence and the underlying instabilities in the - rather complicated - geometry of stellarator plasmas. I will show that some stellarators with a particular magnetic field are more stable towards the turbulence-causing instabilities than others, and discuss what is still missing before these findings can be translated into accurate turbulence predictions for general geometry. Ultimately, these predictions will be necessary to allow us to optimise stellarators not only for laminar, but also for turbulent transport.
Wybren Jan Buma
February 21st 2019
11:15 to 12:15
Absorption of light brings molecules into an activated state. From this state radiative processes can occur, but much more interesting are the nonradiative, dark processes in which the photon energy is transformed into other forms such as mechanical and chemical energy. We aim to control these light-to-activity pathways as they allow us to use photon energy to drive targeted applications such as energy conversion, photocatalysis, photon-driven molecular nanotechnology, as well as optogenetics and photopharmacology. Key to tailoring photoactivity are studies of the potential energy surfaces of electronically excited states. This is not trivial because photoactivity is generally associated with (ultra)fast conversions of energy. Using eye-catchers from molecular nanotechnology, health care, and various areas where photochromic compounds are employed, we have shown in recent years how ‘slow’ spectroscopies can map the excited-state potential energy surfaces and reveal the dynamics that occur on these surfaces. This is exciting as there is a huge amount of photoresponsive systems that so far have been deemed inaccessible because of their short excited-state lifetimes. There is thus still much to be learnt on the dark side of the forces that act upon molecules after light absorption!