Publications by authors named "Bernd Szyszka"

3 Publications

  • Page 1 of 1

Plasma Assisted Reduction of Graphene Oxide Films.

Nanomaterials (Basel) 2021 Feb 3;11(2). Epub 2021 Feb 3.

Institute of High-Frequency and Semiconductor System Technologies, Technische Universität Berlin, HFT 5-2, Einsteinufer 25, 10587 Berlin, Germany.

The past decade has seen enormous efforts in the investigation and development of reduced graphene oxide (GO) and its applications. Reduced graphene oxide (rGO) derived from GO is known to have relatively inferior electronic characteristics when compared to pristine graphene. Yet, it has its significance attributed to high-yield production from inexpensive graphite, ease of fabrication with solution processing, and thus a high potential for large-scale applications and commercialization. Amongst several available approaches for GO reduction, the mature use of plasma technologies is noteworthy. Plasma technologies credited with unique merits are well established in the field of nanotechnology and find applications across several fields. The use of plasma techniques for GO development could speed up the pathway to commercialization. In this report, we review the state-of-the-art status of plasma techniques used for the reduction of GO-films. The strength of various techniques is highlighted with a summary of the main findings in the literature. An analysis is included through the prism of chemistry and plasma physics.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3390/nano11020382DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7913195PMC
February 2021

Vibrational dynamics in lead halide hybrid perovskites investigated by Raman spectroscopy.

Phys Chem Chem Phys 2020 Mar;22(10):5604-5614

Institute of Solid State Physics, Technische Universitat Berlin, Hardenbergstr. 36, 10623 Berlin, Germany.

Lead halide perovskite semiconductors providing record efficiencies of solar cells have usually mixed compositions doped in A- and X-sites to enhance the phase stability. The cubic form of formamidinium (FA) lead iodide reveals excellent opto-electronic properties but transforms at room temperature (RT) into a hexagonal structure which does not effectively absorb visible light. This metastable form and the mechanism of its stabilization by Cs+ and Br- incorporation are poorly characterized and insufficiently understood. We report here the vibrational properties of cubic FAPbI3 investigated by DFT calculations on phonon frequencies and intensities, and micro-Raman spectroscopy. The effects of Cs+ and Br- partial substitution are discussed. We support our results with the study of FAPbBr3 which expands the identification of vibrational modes to the previously unpublished low frequency region (<500 cm-1). Our results show that the incorporation of Cs+ and Br- leads to the coupling of the displacement of the A-site components and weakens the bonds between FA+ and the PbX6 octahedra. We suggest that the enhancement of α-FAPbI3 stability can be a product of the release of tensile stresses in the Pb-X bond, which is reflected in a red-shift of the low frequency region of the Raman spectrum (<200 cm-1).
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c9cp06568gDOI Listing
March 2020

Crystallisation Phenomena of In₂O₃:H Films.

Materials (Basel) 2019 Jan 15;12(2). Epub 2019 Jan 15.

Institute of High-Frequency and Semiconductor System Technologies, Technical University Berlin, Einsteinufer 25, 10587 Berlin, Germany.

The crystallisation of sputter-deposited, amorphous In₂O₃:H films was investigated. The influence of deposition and crystallisation parameters onto crystallinity and electron hall mobility was explored. Significant precipitation of metallic indium was discovered in the crystallised films by electron energy loss spectroscopy. Melting of metallic indium at ~160 °C was suggested to promote primary crystallisation of the amorphous In₂O₃:H films. The presence of hydroxyl was ascribed to be responsible for the recrystallization and grain growth accompanying the inter-grain In-O-In bounding. Metallic indium was suggested to provide an excess of free electrons in as-deposited In₂O₃ and In₂O₃:H films. According to the ultraviolet photoelectron spectroscopy, the work function of In₂O₃:H increased during crystallisation from 4 eV to 4.4 eV, which corresponds to the oxidation process. Furthermore, transparency simultaneously increased in the infraredspectral region. Water was queried to oxidise metallic indium in UHV at higher temperature as compared to oxygen in ambient air. Secondary ion mass-spectroscopy results revealed that the former process takes place mostly within the top ~50 nm. The optical band gap of In₂O₃:H increased by about 0.2 eV during annealing, indicating a doping effect. This was considered as a likely intra-grain phenomenon caused by both (In⁰) and (OH) point defects. The inconsistencies in understanding of In₂O₃:H crystallisation, which existed in the literature so far, were considered and explained by the multiplicity and disequilibrium of the processes running simultaneously.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3390/ma12020266DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6356562PMC
January 2019