TY - GEN A1 - Ewert, Moritz A1 - Schmidt, Thomas A1 - Flege, Jan Ingo A1 - Heidmann, Inga A1 - Grzela, Tomasz A1 - Klesse, Wolfgang Matthias A1 - Förster, M. A1 - Aballe, Lucia A1 - Schröder, Thomas T1 - Morphology and Chemical Composition of Co Germanide islands on Ge(001): in-situ nanoscale insights into contact formation for Ge-based device technology T2 - Nanotechnology Y1 - 2016 SN - 1361-6528 SN - 0957-4484 VL - 27 IS - 32 SP - 325705 ER - TY - GEN A1 - Bignardi, Luca A1 - Lizzit, Daniel A1 - Bana, Harsh A1 - Travaglia, Elisabetta A1 - Lacovig, Paolo A1 - Sanders, Charlotte E. A1 - Dendzik, Maciej A1 - Michiardi, Matteo A1 - Bianchi, Marco A1 - Ewert, Moritz A1 - Buß, Lars A1 - Falta, Jens A1 - Flege, Jan Ingo A1 - Baraldi, Alessandro A1 - Larciprete, Rosanna A1 - Hofmann, Philip A1 - Lizzit, Silvano T1 - Growth and structure of singly oriented single-layer tungsten disulfide on Au(111) T2 - Physical Review Materials N2 - A singly oriented, single layer of tungsten disulfide (WS2) was epitaxially grown on Au(111) and characterized at the nanoscale by combining photoelectron spectroscopy, photoelectron diffraction, and low-energy electron microscopy. Fast x-ray photoelectron spectroscopy revealed that the growth of a single crystalline orientation is triggered by choosing a low W evaporation rate and performing the process with a high temperature of the substrate. Information about the single orientation of the layer was obtained by acquiring x-ray photoelectron diffraction patterns, revealing a 1H polytype for the WS2 layer and, moreover, determining the structural parameters and registry with the substrate. The distribution, size, and orientation of the WS2 layer were further ascertained by low-energy electron microscopy. KW - tungsten disulfide (WS2) KW - Au (111) KW - photoelectron spectroscopy KW - photoelectron diffraction KW - low-energy electron microscopy Y1 - 2019 U6 - https://doi.org/10.1103/PhysRevMaterials.3.014003 SN - 2475-9953 VL - 3 IS - 1 ER - TY - GEN A1 - Schmidt, Thomas A1 - Buß, Lars A1 - Ewert, Moritz A1 - Schönhoff, Gunnar A1 - Wehling, Tim Oliver A1 - Falta, Jens T1 - Adsorption of sulfur on Si(111) T2 - Surface Science N2 - The adsorption of S on Si(111)- 7 × 7 has been investigated for different preparation schemes and parameters. S was supplied from an electrochemical Ag2S cell. For room temperature adsorption and subsequent annealing, no ordered S induced reconstruction can be observed with spot profile analysis low-energy electron diffraction (SPALEED). S deposition at temperatures above about 400°C, however, leads to a well-ordered reconstruction. Judging from the LEED pattern, the same reconstruction was already observed by Metzner et al. [Surf. Sci. 377–379(1997) 71–74] who identified it as 4 × 4 reconstruction. The upper temperature limit for the pre-paration of this superstructure depends on S flux, which is needed to compensate for desorption. Prolonged S exposure leads to surface roughening, as observed with SPALEED and scanning tunneling microscopy (STM), pointing to surface etching by S. From our SPALEED data, we can conclude that the observed reconstruction is not a 4 × 4 reconstruction, but a 20/12 superstructure with a rectangular unit cell that exists in three rotational domains, as confirmed by STM. Different structural trial models have been assessed with density functional theory. Among these model structures, a configuration with dimers adsorbed on bridging sites, with a S coverage of 1 monolayer, is most likely, since it is energetically favorable and is in agreement with all experimental results. KW - Passivation KW - Low-energy electron diffraction KW - Scanning tunneling microscopy KW - Density functional theory KW - Auger electron spectroscopy Y1 - 2020 U6 - https://doi.org/10.1016/j.susc.2019.121561 SN - 0039-6028 SN - 1879-2758 VL - 694 ER - TY - GEN A1 - Ewert, Moritz A1 - Buß, Lars A1 - Braud, Nicolas A1 - Kundu, Asish K. A1 - Sheverdyaeva, Polina M. A1 - Moras, Paolo A1 - Genuzio, Francesca A1 - Menteş, Tevfik Onur A1 - Locatelli, Andrea A1 - Falta, Jens A1 - Flege, Jan Ingo T1 - The Transition From MoS2 Single-Layer to Bilayer Growth on the Au(111) Surface T2 - Frontiers in Physics N2 - The transition from single-layer to bilayer growth of molybdenum disulfide on the Au(111) surface is investigated by in situ low-energy electron and photoemission microscopy. By mapping the film morphology with nanometer resolution, we show that a MoS2 bilayer forms at the boundaries of single-layer single-domain MoS2 islands and next to merging islands whereas bilayer nucleation at the island centers is found to be suppressed, which may be related to the usage of dimethyl disulfide as sulfur precursor in the growth process. This approach, which may open up the possibility of growing continuous films over large areas while delaying bilayer formation, is likely transferable to other transition metal dichalcogenide model systems. KW - molybdenum disulfide (MoS2) KW - bilayer KW - in situ low-energy electron microscopy (LEEM) KW - in situ photoemission microscopy (PEEM) KW - micro-ARPES (angle-resolved photoelectron spectroscopy) KW - Au step bunches Y1 - 2021 U6 - https://doi.org/10.3389/fphy.2021.654845 SN - 2296-424X VL - 9 ER - TY - GEN A1 - Ewert, Moritz A1 - Buß, Lars A1 - Lauritsen, Jeppe V. A1 - Falta, Jens A1 - Flege, Jan Ingo T1 - Growth Mechanism of Single-Domain Monolayer MoS2 Nanosheets on Au(111) Revealed by In Situ Microscopy: Implications for Optoelectronics Applications T2 - ACS Applied Nano Materials N2 - The nucleation and growth of single-layer molybdenum disulfide single-domain nanosheets is investigated by in situ low-energy electron microscopy. We study the growth of micrometer-sized flakes and the correlated flattening process of the gold surface for three different elevated temperatures. Furthermore, the influence of surface step edges on the molybdenum disulfide growth process is revealed. We show that both nanosheet and underlying terrace grow simultaneously by pushing the surface step in the expansion process. Our findings point to an optimized growth procedure allowing for step-free, single-domain, single-layer islands of several micrometers in size, which is likely transferable to other transition-metal dichalcogenides (TMDs), offering a very fine degree of control over the TMD nanosheet structure and thickness. KW - in situ methods KW - low-energy electron microscopy and diffraction KW - molybdenum disulfide KW - 2D material KW - epitaxial growth mechanism KW - Au(111) Y1 - 2022 U6 - https://doi.org/10.1021/acsanm.2c03584 SN - 2574-0970 VL - 5 IS - 12 SP - 17702 EP - 17710 ER - TY - GEN A1 - Buß, Lars A1 - Zamborlini, Giovanni A1 - Sulaiman, Cathy A1 - Ewert, Moritz A1 - Cinchetti, Mirko A1 - Falta, Jens A1 - Flege, Jan Ingo T1 - Hexagons on rectangles: Epitaxial graphene on Ru(10-10) T2 - Carbon N2 - 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. KW - low-energy electron microscopy (LEEM) KW - angle-resolved photoelectron spectroscopy (ARPES) KW - Nanoribbons KW - Graphene KW - Ruthenium Y1 - 2025 U6 - https://doi.org/10.1016/j.carbon.2024.119600 SN - 0008-6223 VL - 231 PB - Elsevier BV ER - TY - GEN A1 - Buß, Lars A1 - Braud, Nicolas A1 - Ewert, Moritz A1 - Jugovac, Matteo A1 - Menteş, Tevfik Onur A1 - Locatelli, Andrea A1 - Falta, Jens A1 - Flege, Jan Ingo T1 - Unraveling van der Waals epitaxy: A real-time in-situ study of MoSe2 growth on graphene/Ru(0001) T2 - Ultramicroscopy N2 - In the present work we investigate the growth of monolayer MoSe2 on selenium-intercalated graphene on Ru(0001), a model layered heterostructure combining a transition metal dichalcogenide with graphene, using low energy electron microscopy and micro-diffraction. Real-time observation of MoSe2 on graphene growth reveals the island nucleation dynamics at the nanoscale. Upon annealing, larger islands are formed by sliding and attachment of multiple nanometer-sized MoSe2 flakes. Local micro-spot angle-resolved photoemission spectroscopy reveals the electronic structure of the heterostructure, indicating that no charge transfer occurs within adjacent layers. The observed behavior is attributed to intercalation of Se at the graphene/Ru(0001) interface. The unperturbed nature of the proposed heterostructure therefore renders it as a model system for investigations of graphene supported TMD nanostructures. KW - Graphene KW - transition metal dichalcogenides (TMDs) KW - angle-resolved photoemission spectroscopy (ARPES) KW - Heterostructures KW - low energy electron microscopy (LEEM) KW - low energy electron diffraction (LEED) Y1 - 2023 U6 - https://doi.org/10.1016/j.ultramic.2023.113749 SN - 0304-3991 SN - 1879-2723 VL - 250 ER - TY - GEN A1 - Pożarowska, Emilia A1 - Pleines, Linus A1 - Ewert, Moritz A1 - Prieto, Mauricio J. A1 - Tănase, Liviu Christian A1 - Souza Caldas, Lucas de A1 - Tiwari, Aarti A1 - Schmidt, Thomas A1 - Falta, Jens A1 - Krasovskii, Eugene A1 - Morales, Carlos A1 - Flege, Jan Ingo T1 - Preparation and stability of the hexagonal phase of samarium oxide on Ru(0001) T2 - Ultramicroscopy N2 - We have used low-energy electron microscopy (LEEM), micro-illumination low-energy electron diffraction (µLEED) supported by ab initio calculations, and X-ray absorption spectroscopy (XAS) to investigate in-situ and in real-time the structural properties of Sm2O3 deposits grown on Ru(0001), a rare-earth metal oxide model catalyst. Our results show that samarium oxide grows in a hexagonal A-Sm2O3 phase on Ru(0001), exhibiting a (0001) oriented-top facet and (113) side facets. Upon annealing, a structural transition from the hexagonal to cubic phase occurs, in which the Sm cations exhibit the +3 oxidation state. The unexpected initial growth in the A-Sm2O3 hexagonal phase and its gradual transition to a mixture with cubic C-Sm2O3 showcases the complexity of the system and the critical role of the substrate in the stabilization of the hexagonal phase, which was previously reported only at high pressures and temperatures for bulk samaria. Besides, these results highlight the potential interactions that Sm could have with other catalytic compounds with respect to the here gathered insights on the preparation conditions and the specific compounds with which it interacts. KW - Samarium oxide (Sm2O3) KW - low-energy electron microscopy (LEEM) KW - X-ray photoemission electron microscopy (XPEEM) KW - Facets KW - Epitaxy KW - Hexagonal phase Y1 - 2023 U6 - https://doi.org/10.1016/j.ultramic.2023.113755 SN - 0304-3991 SN - 1879-2723 VL - 250 ER - TY - GEN A1 - Angrick, Christian A1 - Henriksen, Annika A1 - Edossa, Nicole A1 - Reimann, Andre A1 - Ewert, Moritz A1 - Buß, Lars A1 - Falta, Jens A1 - Flege, Jan Ingo A1 - Donath, Markus T1 - Transition metal dichalcogenide surfaces as scattering targets in spin-polarization detectors : a case study of MoS₂ T2 - Physical review B N2 - The suitability of transition metal dichalcogenides (TMDCs) for the use as scattering targets in electron spin-polarization detectors is put to a paradigmatic test: a case study of MoS₂ is performed. Therefore, the electron reflectivity, the Sherman function, and the figure of merit are measured for the following samples: a single layer of MoS₂ on Au(111) and cleaved MoS₂ single-crystal surfaces. MoS₂ offers promising features for the use in spin-polarization detection: working points with a reversed sign of the Sherman function and a long-term target stability. To overcome the low figure of merit of MoS₂, the closely-related 2D material WS₂ with higher spin-orbit interaction is proposed, which may resemble the promising features with higher Sherman function. This study demonstrates the potential suitability of 2D materials such as TMDCs as scattering targets in spin-polarization detectors. KW - Magnetism KW - Spin polarization KW - Spin-orbit coupling KW - Low-energy electron diffraction KW - Spin-resolved photoemission spectroscopy Y1 - 2025 U6 - https://doi.org/10.1103/fln2-pf6n SN - 2469-9950 VL - 112 IS - 23 SP - 1 EP - 11 PB - American Physical Society (APS) CY - College Park, Maryland ER -