Publications at the Institute of Physics

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Paszuk, Agnieszka; Nandy, Manali; Kleinschmidt, Peter; Hannappel, Thomas;
In situ monitoring of As-P exchange on Ge(100) surfaces in GaAs-rich CVD reactors for low-defect III-V multijunction solar cells. - In: 2021 48th IEEE Photovoltaic Specialists Conference (PVSC), (2021), S. 339-341
Nandy, Manali; Paszuk, Agnieszka; Feifel, Markus; Koppka, Christian; Kleinschmidt, Peter; Dimroth, Frank; Hannappel, Thomas;
Reduction of defects in GaP layers grown on Si(100) by MOCVD. - In: 2021 48th IEEE Photovoltaic Specialists Conference (PVSC), (2021), S. 1344-1347
Mehler, Alexander; Néel, Nicolas; Voloshina, Elena; Dedkov, Yuriy; Kröger, Jörg;
Second floor of flatland: epitaxial growth of graphene on hexagonal boron nitride. - In: Small, ISSN 1613-6829, Bd. 17 (2021), 36, 2102747, insges. 9 S.

In the studies presented here, the subsequent growth of graphene on hexagonal boron nitride (h-BN) is achieved by the thermal decomposition of molecular precursors and the catalytic assistance of metal substrates. The epitaxial growth of h-BN on Pt(111) is followed by the deposition of a temporary Pt film that acts as a catalyst for the fabrication of the graphene sheet. After intercalation of the intermediate Pt film underneath the boron-nitride mesh, graphene resides on top of h-BN. Scanning tunneling microscopy and density functional calculations reveal that the moiré pattern of the van-der-Waals-coupled double layer is due to the interface of h-BN and Pt(111). While on Pt(111) the graphene honeycomb unit cells uniformly appear as depressions using a clean metal tip for imaging, on h-BN they are arranged in a honeycomb lattice where six protruding unit cells enframe a topographically dark cell. This superstructure is most clearly observed at small probe-surface distances. Spatially resolved inelastic electron tunneling spectroscopy enables the detection of a previously predicted acoustic hybrid phonon of the stacked materials. Its' spectroscopic signature is visible in surface regions where the single graphene sheet on Pt(111) transitions into the top layer of the stacking.
Cretu, Andrea; Mattea, Carlos; Stapf, Siegfried;
Low-field and variable-field NMR relaxation studies of H2O and D2O molecular dynamics in articular cartilage. - In: PLOS ONE, ISSN 1932-6203, Bd. 16 (2021), 8, e0256177, insges. 34 S.
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Zhang, Keyu; Cui, Dingfang; Huang, Xiaopeng; Liang, Feng; Gao, Geng; Song, Tingyu; Zhang, Libo; Yao, Yaochun; Lei, Yong;
Insights into the interfacial chemistry and conversion mechanism of iron oxalate toward the reduction by lithium. - In: The chemical engineering journal, ISSN 1873-3212, Bd. 426 (2021), 131446

The origin of excellent lithium storage ability and high irreversible capacity is probably the least understood component for transition-metal oxalates as anode materials in lithium-ion batteries. Considerable efforts have been put into understanding their electrochemical reaction mechanisms, but these insights have mostly been unilateral and unsystematic. Herein, the interface characteristic between iron oxalate anode and electrolyte and detailed conversion process were investigated to explore the source of irreversible Li+ storage. In particular, a gelatinous "organic" layer identified oxygen, fluorine and phosphorus as the main chemical elements can be re-oxidized and exhibits an obviously reversible conversion between sedimentation and decomposition during its initial lithiation process, despite the general belief that it shows similar electrochemically inert to solid-electrolyte interphase (SEI). Meanwhile, this special interface layer leads to higher ability of Li+ ions diffusion and smaller charge-transfer resistance, which is the vital role for excellent rate capability. Furthermore, ex situ FTIR analysis confirms the formation and residue of new intermediate compound of Li2Fe(C2O4)2, thus making a part of initial irreversible capacity. It is also found that the iron oxalate electrode with larger capacitive contribution still has more widely application in energy storage of supercapacitors in future.
Wu, Xiaocui; Wiame, Frédéric; Maurice, Vincent; Marcus, Philippe;
Molecular scale insights into interaction mechanisms between organic inhibitor film and copper. - In: npj Materials degradation, ISSN 2397-2106, Bd. 5 (2021), 22, insges. 8 S.

A model experimental approach, providing molecular scale insight into the build up mechanisms of a corrosion inhibiting interface, is reported. 2-mercaptobenzimidazole (2-MBI), a widely used organic inhibitor, was deposited from the vapor phase at ultra-low pressure on copper surfaces in chemically-controlled state, and X-ray photoelectron spectroscopy was used in situ to characterize the adsorption mechanisms upon formation of the inhibiting film. On copper surfaces prepared clean in the metallic state, the intact molecules lie flat at low exposure, with sulfur and both nitrogen atoms bonded to copper. A fraction of the molecules decomposes upon adsorption, leaving atomic sulfur on copper. At higher exposure, the molecules adsorb in a tilted position with sulfur and only one nitrogen bonded to copper, leading to a densification of 2-MBI in the monolayer. A bilayer is formed at saturation with the outer layer not bonded directly to copper. In the presence of a pre-adsorbed 2D oxide, oxygen is substituted and the molecules adsorb intactly without decomposition. A 3D oxide prevents the bonding of sulfur to copper. The molecular film formed on metallic and 2D oxide pre-covered surfaces partially desorbs and decomposes at temperature above 400 ˚C, leading to the adsorption of atomic sulfur on copper.
Wu, Xiaocui; Wiame, Frédéric; Maurice, Vincent; Marcus, Philippe;
Effects of water vapour on 2-mercaptobenzothiazole corrosion inhibitor films deposited on copper. - In: Corrosion science, Bd. 189 (2021), 109565

The effects of water on 2-mercaptobenzothiazole (2-MBT) film pre-formed on copper at low pressure and room temperature was investigated in situ by X-ray photoelectron spectroscopy. Upon exposure to water vapour at 5×10 6 mbar, the 2-MBT molecules not directly bonded to copper desorb, until only one monolayer remains adsorbed. Further exposure leads to cleavage of the bond between exocyclic sulphur and copper, whereas nitrogen remains bonded to copper. Dissociative adsorption of water is observed, without copper oxidation for exposure up to 3×106L. This work brings new molecular scale insight into corrosion inhibition mechanisms in water-containing environments.
Zhang, Huanming; Zhou, Min; Guo, Yaqiong; Yu, Zhenjiang; Xu, Rui; Wen, Liaoyong; Wang, Yi; Zhao, Huaping; Lei, Yong;
Gas-flow-assisted wrinkle-free transfer of a centimeter-scale ultrathin alumina membrane onto arbitrary substrates. - In: ACS applied materials & interfaces, ISSN 1944-8252, Bd. 13 (2021), 29, S. 35124-35132

The transfer of an ultrathin membrane onto arbitrary substrates is important in different practical fields. Conventional wet-transfer methods inevitably induce wrinkle defects as a result of the large contact angle of the trapped droplet between the membrane and the substrate. Here, we demonstrate a gas flow-assisted method (GFAM) to transfer centimeter (cm)-scale ultrathin membranes onto arbitrary substrates (including a curved substrate) without wrinkles. GFAM makes use of contact angle hysteresis to bulge the trapped droplet between the substrate and the ultrathin membrane and simultaneously stretch the ultrathin membrane during rapid dewetting driven by gas flow. Moreover, GFAM can be easily fulfilled by using compressed air for seconds. Compared with conventional hydrophilic treatments or organic liquid wetting, this method has no durability concern and does not change the surface nature of substrates. Taking a widely used ultrathin anodic aluminum oxide (AAO) membrane as an example, we successfully demonstrate the application of a large-area wrinkle-free ultrathin AAO membrane to defect-free ordered nanostructure array fabrication and investigate the micro-scale details of macro-scale wrinkles generated by the conventional ways. In addition, its corresponding superiority over the defective counterpart is further studied in optical sensing. This method is highly valuable for promoting the simplicity of large-area ultrathin membrane transfer in practice.
Halle, Johannes; Néel, Nicolas; Kröger, Jörg;
Monolayer and bilayer graphene on Ru(0001): layer-specific and moiré-site-dependent phonon excitations. - In: The journal of physical chemistry letters, ISSN 1948-7185, Bd. 12 (2021), 29, S. 6889-6894

Graphene phonons are excited by the local injection of electrons and holes from the tip of a scanning tunneling microscope. Despite the strong graphene-Ru(0001) hybridization, monolayer graphene unexpectedly exhibits pronounced phonon signatures in inelastic electron tunneling spectroscopy. Spatially resolved spectroscopy reveals that the strength of the phonon signal depends on the site of the moiré lattice with a substantial red-shift of phonon energies compared to those of free graphene. Bilayer graphene gives rise to more pronounced spectral signatures of vibrational quanta with energies nearly matching the free graphene phonon energies. Spectroscopy data of bilayer graphene indicate moreover the presence of a Dirac cone plasmon excitation.
Lauer, Kevin; Brokmann, Geert; Bähr, Mario; Ortlepp, Thomas;
Determination of piezo-resistive coefficient π44 in p-type silicon by comparing simulation and measurement of pressure sensors. - In: AIP Advances, ISSN 2158-3226, Bd. 11 (2021), 8, 085005, insges. 6 S.