Comprehensive new study in the journal "Structural Dynamics" looking at thin films helps to make sense of physical and chemical properties of a wide range of materials
A research team from Germany developed an analytical model to describe the structural dynamics of photoexcited thin films and verified it by ultrafast X-ray diffraction.
Time-resolved X-ray diffraction on a laser-excited thin film which is transiently split in an expanded and a compressed sub layer due to coherent lattice dynamics.
Lattice dynamics, atomic movements in a crystal structure, can influence the physical and chemical properties of a material. The phenomenon can be directly studied using ultrafast X-ray diffraction, in which femtosecond X-ray pulses take snapshots of the atomic positions in a crystal by interacting with the structure at the core electronic level.
However, no comprehensive study has yet been carried out to characterize the photoexcited lattice dynamics of an opaque thin film on a semi-infinite transparent substrate. As a result, ultrafast X-ray diffraction data for such samples can be challenging to interpret.
Now a new study in the journal Structural Dynamics, from AIP Publishing, builds a model to help interpret such data.
To study this common scenario, the researchers excited a thin film of metallic SrRuO3 deposited on a transparent SrTiO3 substrate with femtosecond near infrared laser pulses and subsequently probed the atomic structure with equally short hard X-ray pulses. By comparing the resulting time-resolved diffractograms for different film thicknesses and excitation conditions, they found that the lattice dynamics of the system depended on only four parameters: the thickness of the film, its longitudinal acoustic sound velocity, a scaling factor and a shape factor.
“The coherent lattice dynamics are involved in nearly any ultrafast experiment on laser-excited thin films and their time scale is mainly determined by the film thickness and its longitudinal sound velocity,” said Daniel Schick, a researcher at the University of Potsdam. They then incorporated these factors into an analytical model that can be used to explain the observed variation in the X-ray diffraction of different thin films.
Their model allows them to describe a rather puzzling finding: although a thin film is essentially heated by the laser excitation and should rapidly expand, a significant part of the film is compressed for a short time of only a few picoseconds after the laser pulse hits the sample. In the ultrafast X-ray diffraction this manifests in a transient “splitting” of the thin film’s Bragg peak, which provides direct information on the average atomic distances in the film. This observation can be directly linked to the spatial excitation profile of the thin opaque film, which is, in the simplest case, given by the optical absorption length of the laser light and is included as the shape factor in the analytical model.
After developing their model using this relatively simple model system, the researchers have applied it to study more complex ones, such as with a strong coupling of the lattice to charge or spin degrees of freedom in ferroelectric and magnetic materials.
The article, “Ultrafast lattice response of photoexcited thin films 1 studied by X-ray diffraction,” by Daniel Schick, Marc Herzog, André Bojahr, Wolfram Leitenberger, Andreas Hertwig, Roman Shayduk and Matias Bargheer appears in the journal Structural Dynamics on November 18, 2014 (DOI: 10.1063/1.4901228). After that date, it can be accessed at: http://scitation.aip.org/content/aip/journal/sdy/1/6/10.1063/1.4901228
The authors on this paper are affiliated with the Institute for Physics and Astronomy in Potsdam, Germany; the Helmholtz-Zentrum Berlin for Materials and Energy in Berlin; the Fritz Haber Institute of the Max Planck Society in Berlin; the BAM Federal Institute for Materials Research and Testing and the Deutsches Elektronen-Synchrotron.
ABOUT THE JOURNAL
Structural Dynamics is a journal devoted to research on the methods, techniques and understand of time-resolved changes in chemical, biological and condensed matter systems. See: http://sd.aip.org/
Jason Socrates Bardi, AIP
Jason Socrates Bardi | newswise
Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously
17.01.2017 | Sonderforschungsbereich 668
Manchester scientists tie the tightest knot ever achieved
13.01.2017 | University of Manchester
Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.
While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...
Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales
Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...
Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.
As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...
At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).
Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...
Many pathogens use certain sugar compounds from their host to help conceal themselves against the immune system. Scientists at the University of Bonn have now, in cooperation with researchers at the University of York in the United Kingdom, analyzed the dynamics of a bacterial molecule that is involved in this process. They demonstrate that the protein grabs onto the sugar molecule with a Pac Man-like chewing motion and holds it until it can be used. Their results could help design therapeutics that could make the protein poorer at grabbing and holding and hence compromise the pathogen in the host. The study has now been published in “Biophysical Journal”.
The cells of the mouth, nose and intestinal mucosa produce large quantities of a chemical called sialic acid. Many bacteria possess a special transport system...
10.01.2017 | Event News
09.01.2017 | Event News
05.01.2017 | Event News
17.01.2017 | Earth Sciences
17.01.2017 | Materials Sciences
17.01.2017 | Architecture and Construction