Research Highlight 20th April 2018

Research Highlight 20th April 2018

Note: Soft X-ray transmission polarizer based on ferromagnetic thin films.

2018 Mar;89(3):036103. doi: 10.1063/1.5018396.

 

Author information

1 Deutsches Elektronen-Synchrotron DESY, FS-CXS, 22607 Hamburg, Germany.
2 Deutsches Elektronen-Synchrotron DESY, FS-PE, 22607 Hamburg, Germany.
3 SCI Materials Physics, KTH Royal Institute of Technology, Electrum 229, 16440 Kista, Sweden.
4 Department of Physics, Universität Hamburg, 22761 Hamburg, Germany.
5 Universität Hamburg, Center for Hybrid Nanostructures, 22761 Hamburg, Germany.
6 European XFEL, 22869 Schenefeld, Germany.
7 MAX IV Laboratory, Lund University, 22100 Lund, Sweden.

Abstract

A transmission polarizer for producing elliptically polarized soft X-ray radiation from linearly polarized light is presented. The setup is intended for use at synchrotron and free-electron laser beamlines that do not directly offer circularly polarized light for, e.g., X-ray magnetic circular dichroism (XMCD) measurements or holographic imaging. Here, we investigate the degree of ellipticity upon transmission of linearly polarized radiation through a cobalt thin film. The experiment was performed at a photon energy resonant to the Co L3-edge, i.e., 778 eV, and the polarization of the transmitted radiation was determined using a polarization analyzer that measures the directional dependence of photo electrons emitted from a gas target. Elliptically polarized radiation can be created at any absorption edge showing the XMCD effect by using the respective magnetic element.

PMID:
29604789
DOI:
10.1063/1.5018396

Self-cleaning and surface chemical reactions during hafnium dioxide atomic layer deposition on indium arsenide.

2018 Apr 12;9(1):1412. doi: 10.1038/s41467-018-03855-z.

Author information

1 Division of Synchrotron Radiation Research, Department of Physics, and NanoLund, Lund University, Box 118, 221 00, Lund, Sweden. rainer.timm@sljus.lu.se.
2 Division of Synchrotron Radiation Research, Department of Physics, and NanoLund, Lund University, Box 118, 221 00, Lund, Sweden.
3 Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA.
4 Division of Solid State Physics, Department of Physics, and NanoLund, Lund University, Box 118, 221 00, Lund, Sweden.
5 MAX IV Laboratory, Lund University, Box 118, 221 00, Lund, Sweden.

Abstract

Atomic layer deposition (ALD) enables the ultrathin high-quality oxide layers that are central to all modern metal-oxide-semiconductor circuits. Crucial to achieving superior device performance are the chemical reactions during the first deposition cycle, which could ultimately result in atomic-scale perfection of the semiconductor-oxide interface. Here, we directly observe the chemical reactions at the surface during the first cycle of hafnium dioxide deposition on indium arsenide under realistic synthesis conditions using photoelectron spectroscopy. We find that the widely used ligand exchange model of the ALD process for the removal of native oxide on the semiconductor and the simultaneous formation of the first hafnium dioxide layer must be significantly revised. Our study provides substantial evidence that the efficiency of the self-cleaning process and the quality of the resulting semiconductor-oxide interface can be controlled by the molecular adsorption process of the ALD precursors, rather than the subsequent oxide formation.

PMID:
29651110
PMCID:
PMC5897406
DOI:
10.1038/s41467-018-03855-z

Anomalous surface behavior of hydrated guanidinium ions due to ion pairing.

2018 Apr 14;148(14):144508. doi: 10.1063/1.5024348.

 

Author information

1 Department of Physics and Astronomy, Uppsala University, P.O. Box 516, SE-751 20 Uppsala, Sweden.
2 Rudjer Bošković Institute, Bijenička cesta 54, 10000 Zagreb, Croatia.
3 Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nám. 2, CZ-16610 Prague 6, Czech Republic.
4 Physical Chemistry, Department of Chemistry, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden.
5 Department of Cell and Molecular Biology, Computational Biology and Bioinformatics, Uppsala University, P.O. Box 596, SE-751 24 Uppsala, Sweden.
6 MAX IV Laboratory, Lund University, P.O. Box 118, SE-221 00 Lund, Sweden.

Abstract

Surface affinity of aqueous guanidinium chloride (GdmCl) is compared to that of aqueous tetrapropylammonium chloride (TPACl) upon addition of sodium chloride (NaCl) or disodium sulfate (Na2SO4). The experimental results have been acquired using the surface sensitive technique X-ray photoelectron spectroscopy on a liquid jet. Molecular dynamics simulations have been used to produce radial distribution functions and surface density plots. The surface affinities of both TPA+ and Gdm+ increase upon adding NaCl to the solution. With the addition of Na2SO4, the surface affinity of TPA+ increases, while that of Gdm+ decreases. From the results of MD simulations it is seen that Gdm+ and SO42- ions form pairs. This finding can be used to explain the decreased surface affinity of Gdm+ when co-dissolved with SO42- ions. Since SO42- ions avoid the surface due to the double charge and strong water interaction, the Gdm+-SO42-ion pair resides deeper in the solutions’ bulk than the Gdm+ ions. Since TPA+ does not form ion pairs with SO42-, the TPA+ ions are instead enriched at the surface.

PMID:
29655316
DOI:
10.1063/1.5024348