Nanoscience Colloquia 2024

Open, advanced talks on nanoscience

2024 Colloquia

19 December 2024

Franz J. Giessibl – Scanning Tunneling- and Atomic Microscopy with High Resolution

Abstract:

The scanning tunneling microscope (STM) has enabled us to “see” and move single atoms. STM relies on vacuum tunneling with an exponential increase of a tunneling current between two biased conductive electrodes at a factor of ten per Å (100 pm). If a tip has one atom that sticks out one Å more than all the others, this front atom carries ten times more current than the other atoms. The monotonic decrease of current with distance facilitates distance feedback and allows to scan the tip across a sample with atomic precision. In 1986, Binnig, Gerber and Quate introduced atomic force microscopy (AFM), a method that also images insulators by relying on forces. Unlike the current, the force between tip and sample is non-monotonic and includes long- and short-range components. AFM has been inferior in resolution to STM for a long time. Today, AFM exceeds STM in spatial resolution by utilizing Pauli repulsion forces that change even stronger with distance than the tunneling current. That progress was enabled by advances in measuring small forces and by the isolation of chemical bonding forces from strong background forces. The special challenges of AFM are met by the qPlus sensor,1 a quartz force sensor that measures force gradients by frequency changes and was initially based on tuning forks used in Swatch wristwatches. Using the outstanding precision of frequency measurements, we can today measure the forces that act in atomic manipulation, measure exchange interactions with sub-pN sensitivity, image metal clusters (see figure) and molecules with atomic resolution and single adatoms with subatomic resolution. Highest precision measurements require vacuum and low temperatures, and measuring the deflection of a force sensor usually introduces heat. Nevertheless, we could show that the tip of a qPlus sensor remains superconductive during its operation.3 Tips that are electrically conductive allow to measure the tunneling current (moving electrons with energies close to the Fermi level) and the forces (electrons at rest, ranging from van-der-Waals attraction to bond formation and Pauli repulsion), including spin dependent forces4 and a direct measurement on the influence of tip-sample forces on the eigenfrequencies of molecules that are detected by inelastic electron tunneling spectroscopy.5 An exciting possibilities of AFM with qPlus sensors is its capability to obtain subatomic resolution, i.e. the measurement of the angular dependence of chemical bonding forces shown in Fig. C. The quantum corral, introduced by Crommie, Lutz and Eigler in 1993, was revisited by AFM in 2021, showing that the 102 electrons that the corral contains can be viewed as the shell of a two-dimensional atom with similar bonding properties to AFM tips as a natural atom.7

References

1. F. J. Giessibl, Rev. Sci. Instrum. 90, 011101 (2019)
2. M. Emmrich et al., Science 348 308 (2015)
3. A. Peronio et al., Phys. Rev. B 94 094503 (2016)
4. F. Pielmeier et al., Phys. Rev. Lett. 110 266101 (2013)
5. N. Okabayashi et al., PNAS 115 4571 (2018)
6. F. Huber et al., Science 366 235 (2019)
7. F. Stilp et al., Science 372 1196 (2021)

3 October 2024

Magnus Jonsson - Dynamic control of light and heat with conducting polymers

Abstract:

Conducting polymers offer unique ways to control light and heat, which I will illustrate using examples from our recent research. I will first demonstrate that conducting polymers enable a new type of dynamically tuneable plasmonic nanoantennas.1-5 Such optical nanoantennas form the basis for important applications like optical metasurfaces, but they are traditionally static. By contrast, the optical response of conducting polymer nanoantennas can be dynamically tuned by varying the oxidation state of the polymer, thereby opening for redox-tunable metasurfaces and applications like dynamic flat lenses and video holograms.

Next, I will introduce novel means for dynamic structural coloration for reflective colour displays.6-7 Reflective displays form an energy-efficient complement to emissive displays and provide additional benefits such as being suitable for use in bright light. I will describe how we can achieve materials with tunable structural colour for such devices by combining dynamic electroactive functions of conducting polymers with interference effects in thin films.

In the third example, we utilize the coldness of outer space to passively cool objects on Earth via thermal radiation. This concept, called passive radiative cooling, is explored world-wide as a sustainable complement to energy-consuming cooling methods which currently consume around 10% of all electricity used globally. Our recent research shows that conducting polymers can be used to electrically tune the radiative cooling power, offering temperature regulation of objects at ambient conditions by tuning their ability to radiate heat.8-9 The concept is based on modulating the infrared emissivity of our devices, which also offer means for adaptable camouflage and anticounterfeiting.10

References:

1. S. Chen et al. Nature Nanotechnology 2020, 15, 35-40.
2. A. Karki et al. Advanced Materials 2022, 34, 13, 2107172
3. A. Karki et al. Communications Materials 2022, 2022, 3, 48
4. S. Chen and M. P. Jonsson. ACS Photonics 2023, 10, 3, 571–581
5. Y. Duan, et al. Advanced Materials 2023, 35, 51, 2303949.
6. S. Rossi et al. Advanced Materials 2021, 33, 40, 2105004
7. S. Chen et al. Advanced Materials 2021, 33, 33, 2102451
8. M. Liao, et al. Advanced Science 2023, 10, 2206510
9. D. Banerjee et al. Cell Reports Physical Science, 2023, 4, 101274
10. C. Kuang et al. npj Flexible Electronics 2024, in press

13 September 2024

Jani Oksanen - Diffusion driven semiconductor devices and energy conversion

Abstract:

Diffusion plays a critical role in both electronics and optoelectronics, influencing how charge carriers and dopants behave in semiconductor materials. It is essential for the operation of LEDs and solar cells and can also enable other energy conversion processes.

In this talk I will overview the role of diffusion in selected semiconductor devices, and introduce our group's activities touching on the topic. In particular I will discuss the role of drift and diffusion, and how to harness diffusion to create new (and old) types of devices and energy converters; For LEDs diffusion driven devices can be expected to provide very low resistive losses and enable fully back contacted devices leading to very high efficiency LEDs, ideally breaking thermodynamic barriers converting LEDs into optical refrigerators. Some of these prospects also apply to III-V solar cells, and even to new types of elecrochemical energy converters. While the possibilities or diffusion driven devices especially in optoelecronics are substantial, fabrication of optimal devices sets new requirements for device dimensions and calls for fabrication methods that have not been readily available for III-V materials.

13 June 2024

Birte Höcker - Learning from nature how to design new proteins

Abstract:

Proteins are the machines of life. These diverse macromolecules are essential for all cellular processes. Nature has generated an impressive set of proteins through evolution. Many protein structures and even more protein sequences are known by now. This enormous set of data can be used on the one hand to learn about the evolutionary history and how different proteins came about. On the other hand, we can extract information to be applied in the design of new tailor-made proteins. The ability to design custom proteins, such as reagent antibodies, biosensors or enzymes, is a major goal in protein biochemistry and will be necessary to tackle global challenges that we face today. Here I will discuss different approaches and show some highlights from our work on designing complex proteins.

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23 May 2024

Agustín Mihi - Scalable Photonic Architectures by Nanoimprinting Unconventional Materials

Abstract:

Photonic and plasmonic architectures can concentrate the electric field through resonances, increase the light optical path by strong diffraction and exhibit many other interesting optical phenomena that cannot be achieved with traditional lenses and mirrors. The use of these structures within actual devices will be most beneficial for enhanced light absorption solar cells, photodetectors and improved new sensors and light emitters. However, emerging optoelectronic devices rely on large area and low-cost fabrication routes to cut manufacturing expenses and increase the production throughput. If the exciting properties exhibited photonic structures are to be implemented in these devices, then they too have to be processed in a similar fashion as the devices they intend to improve.
In this presentation, I will illustrate how the technique of soft nanoimprinting lithography provides an exciting opportunity for the fabrication of nanostructures in a scalable, fast and inexpensive way. In our group, we use pre-patterned soft elastomeric stamps to induce a nanostructure in a variety materials from conductive polymers to cellulose1. We also use our patterned stamps to induce the long range ordering of metal colloids2 and perovskite nanocrystals3 in what is known as template-induced self-assembly. In all cases, the resulting photonic architectures can exhibit a resolution below 100 nm while covering an area of 1 cm2. This fabrication route allows us to combine the photonic properties of the pattern with those of the original material resulting in a new generation of inexpensive photonic components such as biodegradable photonic films, highly efficient SERS platforms for sensing, chiral metamaterials,4 improved efficiency solar cells and more.

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18 April 2024

Jos Haverkort - Direct bandgap hexagonal SiGe nanowires

Abstract:

It has been a holy grail for several decades to observe efficient direct bandgap emission from silicon. Unfortunately, cubic silicon has an indirect bandgap, thus impeding the efficient emission of light. The VLS growth method allows to grow III/V nanowires in either the cubic (zincblende) or hexagonal (wurtzite) crystal phase. This allows to grow hexagonal crystal phase SiGe nanowire shells that feature a direct bandgap in the spectral region between 1.5 and 3.4 µm. This material shows efficient light emission and a subnanosecond radiative recombination lifetime. Moreover, by transferring these nanowires to an AlN substrate, we observe a nonlinear increase of the Fabry-Perot cavity modes, thus providing a clear prove of stimulated emission in hex-SiGe. Our recent research is focused on hex-Ge/SiGe nanoshells which feature type I band alignment. Moreover, the quantum well emission spectra show clear quantum confinement effects. The realization of these quantum heterostructures in hex-SiGe is a first step towards quantum well lasers and hex-SiGe single photon emitters.

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11 January 2024 14:00

Very welcome to this mini-symposium with with Giovanni Volpe and Pawel Sikorski!

Agenda

14:00-14:45 Pawel Sikorski: Nanotechnology meets bioengineering with some examples from nano-, microfabrications and biomaterials.

14:45:15:15 Coffee Break

15:15-16:00 Giovanni Volpe: Deep Learning for Imaging and Microscopy

Speaker information and abstracts

Pawel Sikorski, Professor at the Department of Physics, Norwegian University of Science and Technology (NTNU)

Nanotechnology meets bioengineering with some examples from nano-, microfabrications and biomaterials.

In this presentation, I aim to highlight connections between bioengineering, biomaterials, and nanotechnology. I will introduce nanoscale effects that can be important for bioengineering research and technology development. Nanotechnology has the potential to contribute to biomedical research by providing new tools and new experimental methods. Compared to traditional approaches, these techniques often allow for miniaturization and better control of the experimental system. In our research, we are interested in the fabrication of nanostructured and microstructured surfaces that are easy and inexpensive to make, and that are compatible with typical workflows in biomedical research. I will describe two different fabrication approaches and how they are used to study biological systems.

Giovanni Volpe, Professor at the Department of Physics, University of Gothenburg

Deep Learning for Imaging and Microscopy

Video microscopy has a long history of providing insights and breakthroughs for a broad range of disciplines, from physics to biology. Image analysis to extract quantitative information from video microscopy data has traditionally relied on algorithmic approaches, which are often difficult to implement, time consuming, and computationally expensive. Recently, alternative data-driven approaches using deep learning have greatly improved quantitative digital microscopy, potentially offering automatized, accurate, and fast image analysis. However, the combination of deep learning and video microscopy remains underutilized primarily due to the steep learning curve involved in developing custom deep-learning solutions. To overcome this issue, we have introduced a software, currently at version DeepTrack 2.1, to design, train and validate deep-learning solutions for digital microscopy.