Events: Fysik events at Chalmers University of TechnologyWed, 21 Nov 2018 11:03:48 +0100 Advanced TEM/STEM School 19-21 November 2018<p>Kollektorn, lecture room,</p><p>​Learn about recent developments in advanced electron microscopy techniques from leading experts.</p>​The School will concentrate on advanced techniques for high-resolution electron microscopy of interest to scientists currently using transmission electron microscopes for materials science studies. Laboratory sessions will highlight state-of-the-art instrumentation. People attending the school should preferably have some basic understanding of conventional electron microscope operation.<br /><br /> by Alessandro Tredicucci<p>Kollektorn, lecture room,</p><p>The Graphene Center at Chalmers (GCC) will organize a monthly GCC seminar on the recent advances in the field of graphene and 2D materials.  Welcome to attend! Lecturer: Alessandro Tredicucci, University of Pisa, Italy​ Title of talk: Between photonics and electronics: is THz the promised land of graphene technologies?</p><h4 class="chalmersElement-H4">Abstract:</h4> <div>Graphene is attracting considerable attention for a variety of photonic applications, including fast photodetectors, transparent electrodes in displays and photovoltaic modules, and saturable absorbers. Owing to its high carrier mobility, gapless spectrum, tunable chemical potential, and frequency-independent absorption coefficient, it has been recognized as a very promising element for the development of detectors and modulators operating in the Terahertz (THz) region of the electromagnetic spectrum, which is still severely lacking in terms of solid-state devices.</div> <div> </div> <div>In the last few years, progress in the realization of graphene-based THz photonic devices has advanced very rapidly. In this talk I will focus in particular on the realization of THz detectors based on antenna-coupled graphene field-effect transistors (FETs), discuss the various mechanisms involved in their operation, and examine extension to other 2D materials and integration into future THz cameras. I will also address the development and applications of electrically switchable metamaterial devices as well as the prospects for the use of graphene in a new generation of THz sources, either directly as active element, or as waveguide optical component (for instance acting as saturable absorber in laser mode-locking). Finally, schemes to implement coherent control of absorption in graphene and the possible entailing device / diagnostic applications will be analysed.</div> ​ Physics Colloquium by the Nobel Prize Laureate Takaaki Kajita​<p>Gustaf Dalén-salen, lecture hall,</p><p>Welcome to attend the Physics Colloquium by Takaaki Kajita, University of Tokyo​​. Title of talk: Neutrino researches at Kamioka ​​</p><div><p class="chalmersElement-P"><strong><img src="/SiteCollectionImages/Institutioner/F/350x305/1_Takaaki_Kajita_350x305.jpg" class="chalmersPosition-FloatRight" alt="" style="margin:5px;width:240px;height:216px" />About Takaaki Kajita​'s research</strong><br />Neutrinos are elusive particles that were created at the birth of the Universe and are created today in nuclear processes, both in the Cosmos and in our laboratories, as well as in nuclear reactors.</p></div> <div>There are three types (flavors) of known neutrinos and they comprise some of the basic building blocks of our current theory of particle physics, the Standard Model. Originally assumed to be massless, they have been shown to have a small but non-zero mass and this discovery has had profound implications on e.g. stellar structure and cosmology. </div> <div> </div> <div><br /></div> <div> </div> <div>Professor Takaaki Kajita has been leading the experiments Kamiokande and its successor, Super-Kamiokande in Japan, aimed at study, amongst other things, neutrino oscillations, that is the transmutations between neutrino flavors that is predicted to occur by virtue of them not being massless. <br /><br /><strong>Awarded the Nobel prize 2015</strong><br />For this groundbreaking work he, together with Professor Arthur McDonald has been awarded the 2015 Nobel Prize <em>&quot;For the discovery of neutrino oscillations, which shows that neutrinos have mass”. </em><br />In his talk he is giving an account of the fascinating journey which led to this groundbreaking discovery.<br /><br /><a href=""><span><img class="ms-asset-icon ms-rtePosition-4" src="/_layouts/images/icgen.gif" alt="" />​</span> Read an article about Takaaki Kajita in conjunction with his visit to Chalmers</a><br /></div> <div><a href="" style="outline:0px"><img class="ms-asset-icon ms-rtePosition-4" src="/_layouts/images/icgen.gif" alt="" /></a> <a href="">M​ore facts about Takaaki Kajita​</a> (Nobel Prize organisation web page)<br /><br />Image credit: Bengt Nyman/Wikimedia commons<br /><br />The lecture by Professor Takaaki Kajita will be open to the public. No registration is needed.<br />Coffee and cake will be served in the entrance hall, (Gustaf Dalén lecture hall) before the lecture from 14.45.​<br /></div> <div> </div> view on ultrafast exciton dynamics in atomically thin materials<p>PJ, lecture hall,</p><p>​​ Promotion lecture by Ermin Malic, for the title as Professor, Department of Physics.</p><h4 class="chalmersElement-H4">​Abstract:</h4> <img src="/SiteCollectionImages/Institutioner/F/Blandade%20dimensioner%20inne%20i%20artikel/150px_ermin_malic.jpg" class="chalmersPosition-FloatRight" alt="" style="margin:5px" /><div>​<span style="background-color:initial">The remarkably rich exciton landscape in atomically thin nanomaterials and related heterostructures presents </span><span style="background-color:initial">a challenge for fundamental research, where formation and dynamics of excitons has remained in the dark. The focus of my research is to shed light on elementary many-particle processes behind the optical fingerprint and the ultrafast dynamics of excitons. Using the density matrix formalism with semiconductor Bloch equations in its core, we are able to track - in time and energy - the dynamics of the full spectrum of bright and dark, intra- and interlayer, as well as free and localized excitonic states. The vision is to exploit the fundamental insights to predict novel exciton-based technology concepts for optical sensing, light emission and light harvesting. </span><div> </div> <div> </div> <div> </div> <div>In this talk, I will give a flavor of our research by showing the exciton relaxation cascade, by demonstrating signatures of dark excitons and by suggesting a possible technological application in dark-exciton-based molecule sensors. </div></div> lecture: Charge Transfer and Reactions at Surfaces<p>PJ, lecture hall,</p><p>​ Promotion lecture by Anders Hellman, for the title as Professor, Department of Physics.​</p><h4 class="chalmersElement-H4">​Abstract: </h4> <div><span style="background-color:initial">Charge transfer and surface reactions are key in many important technologies, such as, after-treatment systems, sensors, batteries, solar and chemical energy conversion, etc. I will show a few examples where these concepts come into play and also how seemingly different charge transfer processes and surface reactions actually are related. Furthermore, I will indicate some future directions where the same concepts will be crucial.  </span></div> lecture<p>PJ, lecture hall,</p><p>Promotion lecture by Christian Forssén, for the title as full Professor at the Department of Physics.​</p> Day<p>PJ, lecture hall,</p><p>​​</p><div>Welcome to listen to the presentations by our recently promoted colleagues at Department of Physics. </div> <span style="background-color:initial"><br /></span><div><h4 class="chalmersElement-H4"></h4> <h4 class="chalmersElement-H4" style="font-family:&quot;open sans&quot;, sans-serif">Schedule for Physics' Promotion Day<br /><strong style="background-color:initial;color:rgb(51, 51, 51);font-family:&quot;open sans&quot;, sans-serif;font-size:14px">14.30</strong><span style="background-color:initial;color:rgb(51, 51, 51);font-family:&quot;open sans&quot;, sans-serif;font-size:14px"> Coffee and cake will be served outside PJ lecture hall.<br /></span><strong style="background-color:initial;color:rgb(51, 51, 51);font-size:14px">14.45</strong><span style="background-color:initial;color:rgb(51, 51, 51);font-size:14px"> </span><span style="background-color:initial;color:rgb(51, 51, 51);font-size:14px">Welcome by Thomas Nilsson<br /></span></h4> <div><span style="background-color:initial"><strong>​14.50 Christian Forssén</strong></span><span style="background-color:initial">, </span><span style="background-color:initial"> for the title as full P</span><span style="background-color:initial">rofessor</span><span style="background-color:initial"><br /></span></div></div> <div>Abstract of talk: To be announced.<br /><br /><span style="background-color:initial"><strong>15.15 Anders Hellman</strong>, </span><span style="background-color:initial"> for the title as P</span><span style="background-color:initial">rofessor</span><br /></div> <div>Abstract of talk: ​<a href="/en/departments/physics/calendar/Pages/Promotion_lecture_Anders_Hellman_1811291116-1692.aspx">Charge Transfer and Reactions at Surfaces​​</a><br /><br /></div> <div><strong style="background-color:initial">15.35 Ermin Malec</strong><span style="background-color:initial">,</span><span style="background-color:initial"> </span><span style="background-color:initial">for the title as P</span><span style="background-color:initial">rofessor​ ​</span><br /></div> <div><span style="background-color:initial">Abstract of talk: </span><span style="background-color:initial"><a href="/en/departments/physics/calendar/Pages/Promotion_lecture_Ermin_Malec_181129.aspx">Microscopic view on ultrafast exciton dynamics in atomically thin materials ​</a><br /><br /><strong>16.00-16.20</strong> </span><span style="background-color:initial">Martha</span><span style="background-color:initial"> McCartney and </span><span style="background-color:initial"></span><span style="background-color:initial">David J. Smith,</span><span style="background-color:initial">​ guest P</span><span style="background-color:initial">rofessors at </span><span style="background-color:initial">Eva Olsson Group, will present their research.</span></div> <div><span style="background-color:initial"></span></div> <div><span style="background-color:initial"></span><span style="background-color:initial">​</span></div> quantum electronics<p>PJ, lecture hall,</p><p>​ Seminar by Attila Geresdi, QuTech &amp; Kavli Institute of Nanoscience, Delft University of Technology</p><h4 class="chalmersElement-H4">Abstract:</h4> <div><span style="background-color:initial">The Andreev level is a key concept in mesoscopic superconductivity providing a fundamental description of the flow of the dissipationless supercurrent. In this talk, I will discuss the foundations of a radically new platform for solid state quantum electronics, which is based on the Andreev levels in semiconductor nanostructures attached to superconducting leads. </span></div> <div> </div> <div>These hybrid systems are interesting from the fundamental physics point of view as they are the most studied platform of topologically protected electronic states, and can serve as a versatile analog quantum simulator as well. In addition, they have a great potential in quantum information processing: several novel quantum bit (qubit) architectures, such as the gateable transmon (gatemon), Andreev spin qubits and topological qubits use them as building blocks.</div> <div> </div> <div>I will discuss the synergetic connection between the recent developments in the materials science of the superconductor-semiconductor nanostructures and novel measurement techniques as well as device designs, all instrumental for the scientific breakthroughs in the field of Andreev quantum electronics.</div> <div> </div> seminar: Daniel Andrén<p>PJ, lecture hall,</p><p>​Title of thesis: Optical manipulation and heating of gold nanoparticles near interfaces.</p><h4 class="chalmersElement-H4">Abstract: </h4> <div><span style="background-color:initial">By focusing laser light to small volumes, its momentum can be used to trap and manipulate objects in the size range from cells down to single atoms. Devices using this effect are called optical tweezers, and have found use in measuring and applying minuscule forces and torques, contributed to deepening our knowledge of molecular motors, unraveling the mechanics of cells and DNA, and better understand statistical mechanics and hydrodynamic interactions at the nanoscale. In short, the optical tweezer is a crucial component in our aspiration to understand and unlock the potential of nano-scaled objects.</span></div> <div> </div> <div><br /></div> <div> </div> <div>One class of nano-elements worth devoting special attention to are nanoparticles supporting plasmonic resonances. These present strongly enhanced light-matter interactions and may find use in as diverse fields as high-density data storage, single molecule detection, and personalized medicine. One potential use of plasmonic nanorods is as rotary nanomotors. These are capable of reaching record rotation frequencies of several tens of kilohertz when optically trapped in water against a glass surface. This thesis focuses on studying vital questions related to such rotary nanomotors, which are interesting to resolve from both a fundamental and from an applied point of view.</div> <div> </div> <div><br /></div> <div> </div> <div>It is well-known that metallic nanoparticles are efficiently heated by light. This will give rise to several photothermal effects affecting the nanoparticle and its surrounding. How these influence the performance of the nanomotor is evaluated. Through spectroscopic measurements, morphological changes induced by atomic migration is observed. Moreover, the elevated thermal environment around the nanoparticle is probed using two separate techniques, and temperatures above $200^\circ$C are routinely reached, but could be kept as low as a few degrees above ambient under the right circumstances.</div> <div> </div> <div><br /></div> <div> </div> <div>The gold nanoparticle is trapped at a small, but hitherto unknown, distance from a glass interface. The vicinity to a surface can affect several of a nanoparticles properties, including its diffusion and thermal environment, and knowing this distance is hence critical for any claims about the nanomotors' performance. Therefore, total internal reflection microscopy is performed on the trapped nanoparticles and it is found that they are confined less than 100 nm from the surface. The distance can be controlled by altering the radiation pressure, or Coulomb repulsion.</div> <div> </div> <div><br /></div> <div> </div> <div>In summary, the work performed in this thesis present important building blocks towards a complete understanding of this highly promising rotary motor system.}</div> <div> </div> <div> </div> <div> <strong>Keywords:</strong> <em>optical tweezers, plasmonics, gold nanorod, nanomotor, photothermal effects, thermal reshaping, LSPR spectroscopy, Brownian dynamics, TIRM, particle-surface separation distance.</em></div> <div><em></em></div> Lindgren: Materials Science<p>PJ, lecture hall,</p><p>T​itle of doctoral thesis: &quot;Effects of Irradiation and Thermal Ageing on the Nanoscale Chemistry of Steel Welds</p><div><h4 class="chalmersElement-H4">Abstract:</h4> <div>Structural materials of nuclear power plants degrade during operation due to thermal ageing and irradiation from the reactor core. Effects on the materials are an increase in hardness and tensile strength, and a decrease in ductility and fracture toughness, i. e. embrittlement. The degradation of the mechanical properties stems from changes in the microstructure. In this thesis, the effects of thermal ageing and irradiation on the nanoscale chemistry has been studied using atom probe tomography (APT).</div></div> <div><br /></div> <div>During irradiation, nanometre sized clusters are formed in the reactor pressure vessel (RPV) welds. As the RPV is a life-limiting part of a nuclear power plant, neutron irradiation with high flux is attractive for accelerated studies. Here, the effect of high flux is found to result in a higher number density of smaller NiMnSi-rich clusters for the high Ni and Mn - low Cu welds from Ringhals R4, resulting in similar hardening compared to surveillance material. It is also found that there are some stable matrix defects formed in the high flux material, contributing to the embrittlement. The cluster evolution showed no signs of late blooming phases (an accelerated degradation at high fluences). Furthermore, thermal ageing during operation for 28 years of a weld from the former Ringhals R4 pressurizer with similar composition is found to result in  clusters forming mainly on dislocations, hardening the weld metal.</div> <div><br /></div> <div>In ferrite with higher Cr-content, such as the ferritic parts of the mainly austenitic welds from the core barrel of the decommissioned Spanish reactor José Cabrera, spinodal decomposition occurs as well as G-phase (Ni16Si7Mn6) precipitation. Weld metals irradiated up to 2 dpa are compared with thermally aged welds, confirming that the irradiation is considerably contributing to the changes in the microstructure. After 0.15 dpa, the spinodal decomposition was well developed, and the Cr concentration in the ferrite was found to influence the wavelength more than the difference in irradiation (0.15 to 2 dpa). The G-phase precipitates were more well-developed after 1 dpa neutron irradiation, but no difference could be distinguished between the material irradiated to 1 and 2 dpa.</div> <div><br /></div> <div><br /></div> <div>Keywords: <em>reactor pressure vessel, irradiation damage, thermal ageing, clustering, atom probe tomography, low alloy steel, core barrel, spinodal decomposition </em></div> <div><em></em><br /></div> seminar: Lajos Nagy<p>Raven and the Fox, multifunctional room, Fysik forskarhus</p><p>​ Title: Campbell formulae for compound Poisson processes with applications in nuclear safeguards.</p><div><h4 class="chalmersElement-H4">Abstract:</h4> <div>Multiplicity counting is a widely used non-destructive assay method for estimating unknown parameters (primarily the mass) of samples of spontaneously fissioning materials (e.g.~plutonium). Traditionally, measurements are performed with thermal neutron detectors operating in pulse counting mode. The method is based on determining the first three lowest order moments of the number of particles emitted simultaneously from the sample, through measuring the so-called singles, doubles and triples detection rates from the counting statistics of the detectors, from which the sought sample parameters can be unfolded with algebraic inversion. The main difficulty with multiplicity counting is its inherent sensitivity to dead time effects, which poses a major constraint on the ability to extract correlated neutron counts.</div></div> <div><br /></div> <div>To overcome this difficulty, a new method of multiplicity counting has been developed, which is based on the statistics of the time-resolved signals of detectors operating in current mode. Specifically, the method utilizes information in the auto and cross cumulants of the stationary signals of different groups of detectors. Based on a stochastic theory of fission chamber signals, expressions were derived for the one-, two- and three-point (in time) cumulants of the detector currents. It was shown how the traditional multiplicity count rates can be recovered from the detector currents with the help of these relationships. Although the new approach needs a more involved calibration, its main advantage is that it is insensitive to dead time effects. As a result, no dead-time corrections are required and the sample parameters can be extracted from three (or even fewer) detectors.</div> turbulence (blobs) in the Wendelstein 7-X stellarator<p>PJ, lecture hall,</p><p>Seminar by Sandor Zoletnik, Wigner Research Center for Physics, Budapest, Hungary</p><h4 class="chalmersElement-H4">​Abstract:</h4> <div>Filaments or blobs are well known phenomena at the edge of tokamak plasmas. They represent a plasma filament detaching from the edge and propagating through the Scrape Off Layer (SOL) due to polarisation caused ExB drift. In the SOL filaments are the major cross-field transport mechanism. On the Wendelstein 7-X stellarator similar features have been seen from the first experiments and they seem to play an important role in the edge-SOL transport. In the standard configuration of this 3D device the edge is defined by a chain of magnetic islands, therefore the situation is much more complex than  in a tokamak. The talk presents multi-diagnostic observation of filaments, their response to changes in magnetic configuration and edge plasma conditions.</div> seminar: Mathias Hoppe<p>PJ, lecture hall,</p><p>​ T​itle of thesis: Simulation and analysis of ofradiation from runaway electrons</p><strong><br />A​bstract: </strong>To be announced