@misc{EwertBussBraudetal., author = {Ewert, Moritz and Buß, Lars and Braud, Nicolas and Kundu, Asish K. and Sheverdyaeva, Polina M. and Moras, Paolo and Genuzio, Francesca and Mente{\c{s}}, Tevfik Onur and Locatelli, Andrea and Falta, Jens and Flege, Jan Ingo}, title = {The Transition From MoS2 Single-Layer to Bilayer Growth on the Au(111) Surface}, series = {Frontiers in Physics}, volume = {9}, journal = {Frontiers in Physics}, issn = {2296-424X}, doi = {10.3389/fphy.2021.654845}, abstract = {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.}, language = {en} } @misc{JugovacMenteşGenuzioetal., author = {Jugovac, Matteo and Mente{\c{s}}, Tevfik Onur and Genuzio, Francesca and Lachnitt, Jan and Feyer, Vitaliy and Flege, Jan Ingo and Locatelli, Andrea}, title = {Sensitivity to crystal stacking in low-energy electron microscopy}, series = {Applied Surface Science}, volume = {566}, journal = {Applied Surface Science}, issn = {0169-4332}, doi = {10.1016/j.apsusc.2021.150656}, abstract = {In this work we demonstrate the general characteristics of hcp and fcc stacking in low-energy electron reflectivity for transition metal surfaces, by following the restacking during homoepitaxial growth in real-time. For this purpose, the stacking of a model system, single-crystalline Ag islands during layer-by-layer growth at high temperature on O/W(110), is chosen. Multiple scattering calculations are used to model the relation between electron reflectivity and the crystal geometry. The changes in the electron reflectivity are shown to derive from the changes in the stacking sequence of the topmost surface layers. The results allow to distinguish between the hcp and fcc crystalline arrangements at a surface based on typical differences in the reflectivity curves, making the Ag results relevant for a variety of materials with hexagonal surface geometry. In particular, the multiplet structure within the first Bragg peak in the very low electron energy regime is identified with the fcc structure and thus it can be utilized as a fingerprint to determine the stacking sequence.}, language = {en} } @misc{BraudBussLundgrenetal., author = {Braud, Nicolas and Buß, Lars and Lundgren, Edvin and Merte, Lindsay R. and Wallander, Harald J. and Krisponeit, Jon-Olaf and Locatelli, Andrea and Mentes, Tevfik Onur and Jugovac, Matteo and Flege, Jan Ingo and Falta, Jens}, title = {Cleaning and tailoring the Pt3Sn(111) surface for surface experiments}, series = {Surface Science}, volume = {732}, journal = {Surface Science}, issn = {0039-6028}, doi = {10.1016/j.susc.2023.122281}, abstract = {The cleaning process of the bimetallic Pt3Sn(111) surface has been studied by means of low-energy electron microscopy (LEEM), microspot low-energy electron diffraction (-LEED), and X-ray photoemission electron microscopy (XPEEM). Different cleaning procedures, performed under ultra-high vacuum conditions (UHV), including sputtering with argon ions and repeated cycles of annealing up to 1500 K were investigated. In this work, we show that a clean Pt3Sn(111) surface of high structural quality with a sharp and brilliant (2 × 2) bulk reconstruction in LEED as well as a perfectly smooth surface with terraces of micron size can be achieved by sputtering, annealing at very high temperatures, followed by a subsequent slow (0.09 K/s) and careful cooling procedure. Additionally, we show the possibility of tailoring the Sn concentration in the topmost layers of Pt3Sn(111) as a function of annealing temperature and subsequent cooling rate. Structural changes of the surface are induced by Sn segregation combined with a surface order-disorder transition at 1340 K. Moreover, two new surface reconstructions depending on the cooling rate are reported.}, language = {en} } @misc{BussBraudEwertetal., author = {Buß, Lars and Braud, Nicolas and Ewert, Moritz and Jugovac, Matteo and Mente{\c{s}}, Tevfik Onur and Locatelli, Andrea and Falta, Jens and Flege, Jan Ingo}, title = {Unraveling van der Waals epitaxy: A real-time in-situ study of MoSe2 growth on graphene/Ru(0001)}, series = {Ultramicroscopy}, volume = {250}, journal = {Ultramicroscopy}, issn = {0304-3991}, doi = {10.1016/j.ultramic.2023.113749}, pages = {7}, abstract = {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.}, language = {en} } @misc{FerbelVeronesiMentesetal., author = {Ferbel, Letizia and Veronesi, Stefano and Mentes, Tevfik Onur and Buß, Lars and Rossi, Antonio and Mishra, Neeraj and Coletti, Camilla and Flege, Jan Ingo and Locatelli, Andrea and Heun, Stefan}, title = {Rubidium intercalation in epitaxial monolayer graphene}, series = {Nanoscale}, volume = {17}, journal = {Nanoscale}, number = {19}, publisher = {Royal Society of Chemistry (RSC)}, address = {London}, issn = {2040-3364}, doi = {10.1039/D5NR00417A}, pages = {12465 -- 12472}, abstract = {Alkali metal intercalation of graphene layers has been of particular interest due to potential applications in electronics, energy storage, and catalysis. Rubidium (Rb) is one of the largest alkali metals and among the least investigated as an intercalant. Here, we report a systematic investigation, with a multi-technique approach, of the phase formation of Rb under epitaxial monolayer graphene on SiC(0001). We explore a wide phase space with two control parameters: the Rb density (i.e., deposition time) and sample temperature (i.e., room and low temperature). We reveal the emergence of (2 × 2) and [sqrt(3) x (sqrt3)] R30° structures formed by a single alkali metal layer intercalated between monolayer graphene and the interfacial C-rich reconstructed surface, also known as the buffer layer. Rb intercalation also results in strong n-type doping of the graphene layer. Upon progressively annealing to higher temperatures, we first reveal the diffusion of Rb atoms, which results in the enlargement of intercalated areas. As desorption sets in, intercalated regions progressively shrink and fragment. Eventually, at approximately 600 °C, the initial surface is retrieved, indicating the reversibility of the intercalation process.}, language = {en} } @misc{BussSulaimanSanchezBarquillaetal., author = {Buß, Lars and Sulaiman, Cathy and S{\´a}nchez-Barquilla, Raquel and Cojocariu, Iulia and Szpytma, Marcin and Mente{\c{s}}, Tevfik Onur and Locatelli, Andrea and Falta, Jens and Flege, Jan Ingo}, title = {Rise and fall of 1T-TaS₂ : epitaxial growth of monolayer TaS₂ on Au(111)}, series = {Physical review materials}, volume = {9}, journal = {Physical review materials}, number = {7}, publisher = {American Physical Society (APS)}, address = {College Park, MD}, issn = {2475-9953}, doi = {10.1103/1bxg-yvw2}, pages = {1 -- 9}, abstract = {Monolayer tantalum disulfide epitaxially grown on Au(111) is studied in real time during molecular beam epitaxy using low-energy electron microscopy and microdiffraction. Complementary x-ray photoelectron emission microscopy provides insight into the chemical and electronic structure of the grown layers. Our study reveals a previously unreported growth mechanism where the formation of 2⁢H-TaS2 proceeds via a transient 1⁢T-TaS2 phase. The 1⁢T-TaS2 phase exhibits a significantly higher growth rate than the 2⁢H-TaS2 phase, with growth proceeding mainly in the 1T phase. By comparison with TaSe2 on Au(111), we find that this growth mechanism is common to other Ta-based transition-metal dichalcogenides on Au(111). Furthermore, we find spectroscopic evidence for the presence of charge-density-wave order in 1⁢T-TaS2 on Au(111). These findings provide perspectives on the growth dynamics and phase control of TaS2, opening up avenues for tailoring its electronic properties through substrate interaction and phase engineering.}, language = {en} }