On April 20, sixty participants will take part in LION’s triannual meeting for high school physics teachers, to deepen their knowledge of physics and astronomy and to explore new teaching methods. This edition marks a special occasion, as it is More info
the last meeting organized by Bert van der Hoorn, who will retire in November.
Astronomy group leader Elena Maria Rossi opens the evening with a lecture on her study of the Milky Way using the fastest stars in the Universe. After the dinner break, Henk Buisman will evaluate the first full operational year of his online experimental physics course KwantumWereldExperimenten. He is followed by students Thijs de Buck and Margot Leemker, who present their Bachelor thesis research on respectively Research in a living lab and High-frequency amplifiers for STM microscopy. Hannie van den Bergh, founder and creative director of Studio BH, closes the evening by explaining how her company researches and develops future materials. She works together with scientific institutes to address new developments in materials science.
Physicists image individual molecules by watching them absorb light
Molecules are extremely hard to see in visible light, especially without using fluorescence. Leiden physicists have now made their optical technique sensitive enough to image the molecules of their interest in all More info
What do ships, bats and torpedoes have in common? They navigate by emitting sound waves and registering listening where those get absorbed or reflected. Humans do the same with light waves, except that they rely on external sources like the sun for the original emission. However when looking at something as small as a single molecule this becomes problematic, as light waves, not to mention sound waves, are bigger than the object itself.
Two light beams
In 2010, Leiden physicist Michel Orrit became the first to optically image large single organic molecules at room temperature without using fluorescence. Now, he and his group have made their technique much more sensitive, enabling them to image their subjects objects of interest—light-sensitive conducting polymer molecules—of all sizes. Just like bats, they control their own source of waves and use varying frequencies. Their first light beam has a specific color which only the targeted molecules can absorb. This causes them to heat up a bit. And because of thermal expansion this changes the refractive index of the surrounding liquid, so that a second beam will be scattered differently at the exact places where the molecules of interest are hiding.
Still, this is easier said than done. Conducting polymers are quickly damaged by light, so scientists have to be extremely careful to only use very low intensities. But those are not nearly strong enough for the absorb-and-heat technique in regular liquids. Fortunately, so-called critical fluids are exceedingly sensitive to temperature changes within a small temperature range. In that regime, even the slightest heating power will alter the liquid’s refractive index by a large amount. So Orrit and his group used critical fluids and made sure temperature and pressure were precisely set during their experiment.
Locate them all
‘Until now we could only image the largest polymer molecules through absorption,’ says Orrit. ‘But because of our sensitivity enhancement, we can locate all of them. And this also gives us information on the brightness of each molecule. That is very important if you want to optimize their optoelectronic applications.’
Lei Hou, Subhasis Adhikari, Yuxi Tian, Ivan G. Scheblykin, and Michel Orrit, 'Absorption and Quantum Yield of Single Conjugated Polymer Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) Molecules', Nanoletters
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While they are excited by a first light beam, single conducting polymer molecules heat their surroundings, leading to altered scattering of a second light beam at their location (red spots). The intensity of the signal scales with the absorption, and thus the size of each individual molecule.
Nanoparticles are widely used, but their effect on the environment is unclear because they are hard to track. Leiden physicists have developed a new method to detect conducting nanoparticles. Aquiles Carattino successfully defended his PhD thesis on the subject.
are composed of just tens to thousands of molecules, which give them vastly different properties from bulk materials built up by quintillions of the exact same molecules. For example, copper nanowires are transparent. Manufacturers utilize these special properties in products like sunscreen, tires, clothing and plasters. But their tiny size also poses a problem; they are very difficult to track, so it is still unknown to what extent they harm the environment.
Leiden physicist Aquiles Carattino and his colleagues have developed a new way to track conducting nanoparticles using fluorescence. They shine a laser on a particle using light of a particular wavelength, matching the particle’s so-called plasma resonance. Surprisingly, the particle will give off some light with an even higher energy than it received. This gives it a sharper contrast against the background.
To develop a new detection technique based on this phenomenon, Carattino used a filter to get rid of the surrounding background light. In this way, nanoparticles are easier to detect because scientists can scan for one specific, clear signal. It gives environmental researchers a method for tracking nanoparticles and investigating their effect on nature.
The European Physical Society (EPS) has awarded the Gero Thomas Commemorative Medal 2017 to Jo Hermans, emeritus Professor in Physics. He wins the award for his role as Science Editor of Europhysics News and his numerous contributions to education and More info
public understanding of physics.
The prize was created in 2000 to honour the memory of G. Thomas, who was the Secretary General of the EPS from 1973 to 1997 and played an essential role in the growth and the development of the Society. The Commemorative Medal is awarded to individuals for their outstanding service to the Society.
Askes SH, Leeuwenburgh VC, Pomp W, Arjmandi-Tash H, Tanase S, Schmidt T, Bonnet S (2017) Water-Dispersible Silica-Coated Upconverting Liposomes: Can a Thin Silica Layer Protect TTA-UC against Oxygen Quenching?, ACS Biomater Sci Eng, 3, 322-334. [Abstract][DOI][pdf]
C. Cirillo, S. Voltan, E.A. Ilyina, J.M. Hernández, A. García-Santiago, J. Aarts and C. Attanasio (2017) Long-range proximity effect in Nb-based heterostructures induced by a magnetically inhomogeneous permalloy layer, New J. Phys., 19, 023037. [DOI]
24 April, 11:00, Gorlaeus DM.1.09
van Marum Colloquium Prof. Peter Saalfrank (Workgroup Theoretical Chemistry, Univ. Potsdam): Non-adiabatic molecular dynamics at metal surfaces host: Geert-Jan Kroes,
26 April, 15:00, Academy building, Rapenburg 73
Thesis Defense Paul Baireuther - Instituut-Lorentz: "On Transport Properties of Weyl Semimetals" Promotor: Prof.dr. C.W.J. Beenakker
4 May, 09:00, HL 207
BSM Seminar Dr. Giorgos Gkouridis, Groningen University: Bulk biochemical coupled to single-molecule investigations allow to understand life