@misc{KostoTschammerMoralesetal., author = {Kosto, Yuliia and Tschammer, Rudi and Morales, Carlos and Henkel, Karsten and Flege, Jan Ingo and Ratzke, Markus and Fischer, Inga Anita and Costina, Ioan and Alvarado Chavarin, Carlos and Wenger, Christian}, title = {Rational design and development of room temperature hydrogen sensors compatible with CMOS technology: a necessary step for the coming renewable hydrogen economy}, series = {Proceedings of iCampus Conference Cottbus 2024}, journal = {Proceedings of iCampus Conference Cottbus 2024}, publisher = {AMA Service GmbH}, address = {Wunstorf}, isbn = {978-3-910600-00-3}, doi = {10.5162/iCCC2024/P21}, pages = {182 -- 185}, abstract = {The transition towards a new, renewable energy system based on green energy vectors, such as hydrogen, requires not only direct energy conversion and storage systems, but also the development of auxiliary components, such as highly sensitive hydrogen gas sensors integrated into mass devices that operate at ambient conditions. Despite the recent advances in nanostructured metal oxide thin films in terms of simple fabrication processes and compatibility with integrated circuits, high sensitivity, and short response/recovery times usually require the use of expensive noble metals or elevated tem-peratures (>250 ºC), which results in high power consumption and poor long-term stability. This article presents the first steps of the work on developing a novel resistive hydrogen gas sensor based on ultrathin cerium oxide films, compatible with complementary metal oxide semiconductor technology and capable of operating at room temperature. Here, we show a multidisciplinary bottom-up approach combining different work areas for the sensor development, such as sensor architecture, sensing mechanism and deposition strategy of the active layer, electrical contact design depending on the desired electrical output, and fast testing under controlled environments.}, language = {en} } @misc{ImamHarfoucheAbdelghanyetal., author = {Imam, Neama Gomaa and Harfouche, Messaoud and Abdelghany, Amr Mohamed and Flege, Jan Ingo}, title = {Effect of Cu incorporation in silicate and modified borate bioglass materials for health applications: insights from synchrotron-based x-ray absorption spectroscopy}, series = {Discover Materials}, volume = {4}, journal = {Discover Materials}, number = {1}, publisher = {Springer Science and Business Media LLC}, issn = {2730-7727}, doi = {10.1007/s43939-024-00103-8}, abstract = {This contribution investigates the effect of variable copper incorporation (x = 0.2, 1.0, 2.0, and 4.0) in silicate (45 SiO2, 24.5 CaO, 24.5 Na2O, 6P2O5wt\%) and modified borate (45 B2O3, 24.5 CaO, 24.5 Na2O, 6P2O5wt\%) bioglass materials to be used for bone bonding applications. X-ray absorption fine structure spectroscopy (XAFS) has been used to determine the oxidation states and local coordination structure of Cu atoms in silicate-based and borate-based glasses at the Cu K-edge (~ 8979 eV). The oxidation states of Cu atoms have been determined by near-edge XAFS (XANES) fingerprinting employing reference standard compounds of Cu. Cu (I) and Cu (II) XANES spectra of the standard reference compounds were linearly combined to fit the normalized μ(E) data of the collected XANES spectra using linear combination fitting (LCF approach). The obtained results prove that most of the silicate glass samples contain Cu2O almost exclusively, while modified borate glass samples contain a significant mixture of Cu2O and CuO phases. According to the literature, the remarkable coexistence of Cu2O and CuO phases within the borate sample, particularly when x = 4, promotes the conversion process to allow the more facile formation of hydroxy carbonate apatite (HCA). The best fit structural parameters derived from extended-XAFS (EXAFS) fitting show that the ratio between Cu (I) and Cu (II) in borate glass agreed well with that extracted from XANES analysis. XANES and EXAFS conclude that borate glass with x = 4 is the most suitable composition for bone bonding applications.}, language = {en} } @misc{MoralesPlateMarthetal., author = {Morales, Carlos and Plate, Paul and Marth, Ludwig and Naumann, Franziska and Kot, Małgorzata and Janowitz, Christoph and Kus, Peter and Z{\"o}llner, Marvin Hartwig and Wenger, Christian and Henkel, Karsten and Flege, Jan Ingo}, title = {Bottom-up design of a supercycle recipe for atomic layer deposition of tunable Indium Gallium Zinc Oxide thin films}, series = {ACS Applied Electronic Materials}, volume = {6}, journal = {ACS Applied Electronic Materials}, number = {8}, publisher = {American Chemical Society (ACS)}, issn = {2637-6113}, doi = {10.1021/acsaelm.4c00730}, pages = {5694 -- 5704}, abstract = {We present a successful bottom-up approach to design a generic plasma-enhanced atomic layer deposition (PEALD) supercycle recipe to grow high-quality indium gallium zinc oxide (IGZO) thin films with tunable composition at a relatively low temperature of 150 °C. In situ real-time ellipsometric characterization in combination with ex situ complementary techniques has been used to optimize the deposition process and quality of the films by identifying and solving growth challenges such as degree of oxidation, nucleation delays, or elemental composition. The developed supercycle approach enables facile control of the target composition by adapting the subcycle ratios within the supercycle process. Compared to other low-temperature deposition techniques resulting in amorphous films, our PEALD-IGZO process at 150 °C results in nearly amorphous, nanocrystalline films. The preparation of IGZO films at low temperature by a supercycle PEALD approach allows controlling the thickness, composition, and electrical properties while preventing thermally induced segregation.}, language = {en} } @misc{BussZamborliniSulaimanetal., author = {Buß, Lars and Zamborlini, Giovanni and Sulaiman, Cathy and Ewert, Moritz and Cinchetti, Mirko and Falta, Jens and Flege, Jan Ingo}, title = {Hexagons on rectangles: Epitaxial graphene on Ru(10-10)}, series = {Carbon}, volume = {231}, journal = {Carbon}, publisher = {Elsevier BV}, issn = {0008-6223}, doi = {10.1016/j.carbon.2024.119600}, pages = {10}, abstract = {Ruthenium is emerging as a promising candidate to replace copper in highly integrated electronics by enabling barrierless metallization in ultrathin interconnects. From this perspective, the study of graphene growth on such surface templates is of paramount importance as a platform for graphene integration in electronic devices. In particular, graphene growth on the Ru (10-10) surface allows selective growth of different graphene orientations, one-dimensional structures, and reduced substrate interaction compared to the well-established hexagonal Ru(0001) substrate. Real-time growth observations using low-energy electron microscopy and micro-diffraction highlight the influence of substrate symmetry on graphene growth, leading to the formation of rectangular islands with distinct zigzag- or armchair-terminated edges. Bilayer formation on Ru(10-10) occurs by nucleation of graphene nanoribbons under the monolayer. Micro-spot angle-resolved photoemission spectroscopy shows significantly less charge-transfer doping in these freestanding, zigzag-terminated bilayer graphene nanoribbons, indicating reduced graphene-substrate interaction and hence more effective decoupling as compared to graphene/Ru(0001). Our results show that the growth of graphene on non-hexagonal substrates opens new pathways for tailoring the graphene-substrate interaction at the interface, and thus the properties of graphene beyond the limits imposed by hexagonal substrates.}, language = {en} } @misc{GawlińskaNęcekKotStarowiczetal., author = {Gawlińska-Nęcek, Katarzyna and Kot, Małgorzata and Starowicz, Zbigniew and Janusz-Skuza, Marta and Panek, Piotr and Marth, Ludwig and Plate, Paul and Flege, Jan Ingo}, title = {Reaction dynamics between formamidinium lead iodide and Copper Oxide}, series = {ACS Applied Materials \& Interfaces}, volume = {16}, journal = {ACS Applied Materials \& Interfaces}, number = {42}, publisher = {American Chemical Society (ACS)}, issn = {1944-8244}, doi = {10.1021/acsami.4c12990}, pages = {57878 -- 57887}, abstract = {Copper oxide (CuOx) has been announced as a very promising hole-transporting layer for perovskite solar cells. However, in our previous work, we have shown that once a formamidinium lead triiodide (FAPI) perovskite is spin-coated on a spray-coated cuprous oxide (Cu2O) substrate, the Cu2O diffuses into and reacts with the FAPI film. In order to verify if the degradation products are related to the oxidation state of CuOx and/or its preparation method, in this work, we first prepared CuOx films by thermal oxidation at temperatures ranging from 120 to 300 °C. While increasing the process temperature, a transformation from copper I (Cu2O) to copper II (CuO) oxidation states was observed. For both oxidation states of copper, FAPI perovskite degradation was found; however, some alterations in the reaction products were noticed. In contrast to our expectations, the introduction of an ultrathin plasma-enhanced atomic layer deposited Al2O3 layer in between both films only partially blocked the CuOx migration into the FAPI film. It can be concluded that regardless of the chemical composition and/or preparation method of CuOx, the overlayered FAPI film gets decomposed. In order to use CuOx as a hole-transporting layer in solar cells, new strategies must be developed to limit these unwanted chemical reactions.}, language = {en} } @misc{MerteBraudBussetal., author = {Merte, Lindsay R. and Braud, Nicolas and Buß, Lars and Bisbo, Malthe Kj{\ae}r and Wallander, Harald J. and Krisponeit, Jon-Olaf and Flege, Jan Ingo and Hammer, Bj{\o}rk and Falta, Jens and Lundgren, Edvin}, title = {Oxygen Storage by Tin Oxide Monolayers on Pt3Sn(111)}, series = {The Journal of Physical Chemistry. C}, volume = {127}, journal = {The Journal of Physical Chemistry. C}, number = {6}, issn = {1932-7447}, doi = {10.1021/acs.jpcc.2c09041}, pages = {2988 -- 2994}, abstract = {The high performance of platinum-tin catalysts for oxidation reactions has been linked to the formation of tin oxides at the metal surface, but little is known about the structure of these oxides or the chemical behavior that determines their catalytic properties. We show here how surface oxides on Pt3Sn(111) incorporate oxygen at the metal interface, which may be subsequently removed by reaction with CO. The storage mechanism, where oxygen uptake occurs without loss of interfacial Pt-Sn bonds, is enabled by the peculiar asymmetrical coordination state of Sn2+. O atoms are bound at pocket sites in the 2D oxide sheet between these outward-buckled Sn atoms and metallic Sn in the alloy surface below.}, language = {en} } @misc{ZuoMalekshahiByranvandKodalleetal., author = {Zuo, Weiwei and Malekshahi Byranvand, Mahdi and Kodalle, Tim and Zohdi, Mohammadreza and Lim, Jaekeun and Carlsen, Brian and Friedlmeier, Theresa Magorian and Kot, Małgorzata and Das, Chittaranjan and Flege, Jan Ingo and Zong, Wansheng and Abate, Antonio and Sutter-Fella, Carolin M. and Li, Meng and Saliba, Michael}, title = {Coordination Chemistry as a Universal Strategy for a Controlled Perovskite Crystallization}, series = {Advanced Materials}, volume = {35}, journal = {Advanced Materials}, number = {39}, issn = {0935-9648}, doi = {10.1002/adma.202302889}, abstract = {The most efficient and stable perovskite solar cells (PSCs) are made from a complex mixture of precursors. Typically, to then form a thin film, an extreme oversaturation of the perovskite precursor is initiated to trigger nucleation sites, e.g., by vacuum, an airstream, or a so-called antisolvent. Unfortunately, most oversaturation triggers do not expel the lingering (and highly coordinating) dimethyl sulfoxide (DMSO), which is used as a precursor solvent, from the thin films; this detrimentally affects long-term stability. In this work, (the green) dimethyl sulfide (DMS) is introduced as a novel nucleation trigger for perovskite films combining, uniquely, high coordination and high vapor pressure. This gives DMS a universal scope: DMS replaces other solvents by coordinating more strongly and removes itself once the film formation is finished. To demonstrate this novel coordination chemistry approach, MAPbI3 PSCs are processed, typically dissolved in hard-to-remove (and green) DMSO achieving 21.6\% efficiency, among the highest reported efficiencies for this system. To confirm the universality of the strategy, DMS is tested for FAPbI3 as another composition, which shows higher efficiency of 23.5\% compared to 20.9\% for a device fabricated with chlorobenzene. This work provides a universal strategy to control perovskite crystallization using coordination chemistry, heralding the revival of perovskite compositions with pure DMSO.}, language = {en} } @misc{BussBraudEwertetal., author = {Buß, Lars and Braud, Nicolas and Ewert, Moritz and Jugovac, Matteo and Mentes, Tevfik Onur and Locatelli, Andrea and Falta, Jens and Flege, Jan Ingo}, title = {In-situ growth characterization of 2D heterostructures: MoSe2 on intercalated graphene/Ru(0001)}, series = {Verhandlungen der DPG}, journal = {Verhandlungen der DPG}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, abstract = {Despite the great fundamental interest in 2D heterostructures, most of the investigated 2D heterostructures were realized by mechanical exfoliation or chemical vapor deposition in the millibar range, preventing true in-situ characterization of the growth process. Here, we have investigated the growth of MoSe2 on single-layer graphene on Ru(0001) via real-time in-situ low-energy electron microscopy and micro-diffraction. After preparation of the graphene by standard procedures from an ethylene precursor, MoSe2 has been prepared via co-deposition of Mo and Se. Prior Se intercalation of the graphene appears to enhance the subsequent growth of MoSe2 on the graphene. At elevated temperatures, rotational ordering of the MoSe2 is facilitated by the strongly enhanced mobility of single-domain MoSe2 islands that align with the high symmetry orientations of the underlying graphene, indicating a non-negligible interaction between the two van-der-Waals materials. Micro-spot angle-resolved photoemission proves the monolayer nature of the as-grown MoSe2 as well as the free-standing character of the Se-intercalated graphene underneath.}, language = {en} } @misc{KostoMoralesDevietal., author = {Kosto, Yuliia and Morales, Carlos and Devi, Anjana and Henkel, Karsten and Flege, Jan Ingo}, title = {Activity of cerium oxide thin films prepared by atomic layer deposition using custom and commercial precursors}, series = {Verhandlungen der DPG}, journal = {Verhandlungen der DPG}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, abstract = {Atomic layer deposition (ALD) allows preparation of conformal coatings with possibility to control their thickness at the submonolayer level, making it a good tool for depositing active layers on 3D structures. Our group is working on cerium oxide-based materials for hydrogen detection, which is difficult at ambient conditions due to the low sensitivity and long response time of the sensors. The cerium oxide layers prepared by ALD contain a lot of defects and provide an opportunity to overcome these complications. Thickness and morphology of the oxide films play an important role in defining the Ce3+/Ce4+ ratio, as well as the interface with the used substrate. Here, we compare cerium oxide thin films deposited by ALD techniques on SiO2 and Al2O3 substrates. The results reveal that the interface to the substrate can considerably influence the reactivity of the cerium oxide toward hydrogen and oxygen. Preparation of the oxides using two different precursors (commercial Ce(thd)4 and custom Ce(dpdmg)3) has been demonstrated to affect the redox properties of the films, their reactivity, and the reversibility.}, language = {en} } @misc{KotKediaPlateetal., author = {Kot, Małgorzata and Kedia, Mayank and Plate, Paul and Marth, Ludwig and Henkel, Karsten and Flege, Jan Ingo}, title = {Application of plasma enhanced atomic layer deposition process of alumina on perovskite film boosts efficiency of solar cells}, series = {Verhandlungen der DPG}, journal = {Verhandlungen der DPG}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, abstract = {It is assumed that plasma-enhanced atomic layer deposition (PEALD) cannot be used to prepare thin films on sensitive organic-inorganic perovskites because the plasma destroys the perovskite film and thus deteriorates its photophysical properties. Here, we prove that using an appropriate geometry of the ALD system (SENTECH SI PEALD system) and suitable process parameters it is possible to coat perovskites with alumina by PEALD. Spectromicroscopy followed by electrical characterisation reveal that as long as the PEALD process is not optimized (too long plasma pulses) one gets degradation of the perovskite as well as dissociation of the created iodine pentoxide (during PEALD) under light that causes a valence band maximum (VBM) shift to the Fermi level and thus significantly decreases the solar cell efficiency. However, once the PEALD process parameters are optimized, no VBM shift is observed. Moreover, the solar cell efficiency depends inversely on process temperature and layer thickness.}, language = {en} }