@article{MazareiPenschkeSaalfrank2023, author = {Mazarei, Elham and Penschke, Christopher and Saalfrank, Peter}, title = {Band gap engineering in two-dimensional materials by functionalization}, series = {ACS Omega}, volume = {8}, journal = {ACS Omega}, number = {24}, publisher = {American Chemical Society}, address = {Washington}, issn = {2470-1343}, doi = {10.1021/acsomega.3c02068}, pages = {22026 -- 22041}, year = {2023}, abstract = {Graphene is well-knownfor its unique combination of electricaland mechanical properties. However, its vanishing band gap limitsthe use of graphene in microelectronics. Covalent functionalizationof graphene has been a common approach to address this critical issueand introduce a band gap. In this Article, we systematically analyzethe functionalization of single-layer graphene (SLG) and bilayer graphene(BLG) with methyl (CH3) using periodic density functionaltheory (DFT) at the PBE+D3 level of theory. We also include a comparisonof methylated single-layer and bilayer graphene, as well as a discussionof different methylation options (radicalic, cationic, and anionic).For SLG, methyl coverages ranging from 1/8 to 1/1, (i.e.,the fully methylated analogue of graphane) are considered. We findthat up to a coverage theta of 1/2, graphene readily accepts CH3, with neighbor CH3 groups preferring trans positions. Above theta = 1/2, the tendency to accept further CH3 weakens and the lattice constant increases. The band gapbehaves less regularly, but overall it increases with increasing methylcoverage. Thus, methylated graphene shows potential for developingband gap-tuned microelectronics devices and may offer further functionalizationoptions. To guide in the interpretation of methylation experiments,vibrational signatures of various species are characterized by normal-modeanalysis (NMA), their vibrational density of states (VDOS), and infrared(IR) spectra, the latter two are obtained from ab initio moleculardynamics (AIMD) in combination with a velocity-velocity autocorrelationfunction (VVAF) approach.}, language = {en} } @article{KleinpeterKoch2023, author = {Kleinpeter, Erich and Koch, Andreas}, title = {The multiple bond character of the carbon-boron bond in boron trapped N-heterocyclic carbenes (NHCs) and cyclic(alkyl)(amino) carbenes (CAACs) on the magnetic criterion}, series = {Tetrahedron}, volume = {140}, journal = {Tetrahedron}, publisher = {Elsevier}, address = {Oxford}, issn = {0040-4020}, doi = {10.1016/j.tet.2023.133469}, pages = {13}, year = {2023}, abstract = {Geometry, 11B, 13C chemical shifts and the spatial magnetic properties (Through-Space NMR Shieldings -TSNMRS) of both cations and anions of boron-trapped N-heterocyclic carbenes (NHCs) and cyclic (alkyl)(amino)carbenes (CAACs) and of the corresponding diborane/diborene/diboryne dis-carbene adducts have been calculated using the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept; the TSNMRS results are visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction. The ICSS of the TSNMRS (actually the anisotropy effects measurable in 1H NMR spectroscopy) are employed to qualify and quantify the present multiple bond character of the Carbene-Boron bond in the trapped NHCs and CAACs. Results are confirmed by bond length and 11B/13C chemical shift variations. Thus the partial multiple bond character of the Carbene-Boron bond cannot be expressed by the arrow of weak, much longer dative bonds and should be omitted as in other covalent lone pair-it or triel bonds. \& COPY; 2023 Elsevier Ltd. All rights reserved.}, language = {en} } @article{SchlappaBresselReichetal.2023, author = {Schlappa, Stephanie and Bressel, Lena and Reich, Oliver and M{\"u}nzberg, Marvin}, title = {Advanced particle size analysis in high-solid-content polymer dispersions using photon density wave spectroscopy}, series = {Polymers}, volume = {15}, journal = {Polymers}, number = {15}, publisher = {MDPI}, address = {Basel}, issn = {2073-4360}, doi = {10.3390/polym15153181}, pages = {17}, year = {2023}, abstract = {High-solid-content polystyrene and polyvinyl acetate dispersions of polymer particles with a 50 nm to 500 nm mean particle diameter and 12-55\% (w/w) solid content have been produced via emulsion polymerization and characterized regarding their optical and physical properties. Both systems have been analyzed with common particle-size-measuring techniques like dynamic light scattering (DLS) and static light scattering (SLS) and compared to inline particle size distribution (PSD) measurements via photon density wave (PDW) spectroscopy in undiluted samples. It is shown that particle size measurements of undiluted polystyrene dispersions are in good agreement between analysis methods. However, for polyvinyl acetate particles, size determination is challenging due to bound water in the produced polymer. For the first time, water-swelling factors were determined via an iterative approach of PDW spectroscopy error (X-2) minimization. It is shown that water-swollen particles can be analyzed in high-solid-content solutions and their physical properties can be assumed to determine the refractive index, density, and volume fraction in dispersion. It was found that assumed water swelling improved the reduced scattering coefficient fit by PDW spectroscopy by up to ten times and particle size determination was refined and enabled. Particle size analysis of the water-swollen particles agreed well with offline-based state-of-the-art techniques.}, language = {en} } @article{XuDongJieetal.2022, author = {Xu, Yaolin and Dong, Kang and Jie, Yulin and Adelhelm, Philipp and Chen, Yawei and Xu, Liang and Yu, Peiping and Kim, Junghwa and Kochovski, Zdravko and Yu, Zhilong and Li, Wanxia and LeBeau, James and Shao-Horn, Yang and Cao, Ruiguo and Jiao, Shuhong and Cheng, Tao and Manke, Ingo and Lu, Yan}, title = {Promoting mechanistic understanding of lithium deposition and solid-electrolyte interphase (SEI) formation using advanced characterization and simulation methods: recent progress, limitations, and future perspectives}, series = {Avanced energy materials}, volume = {12}, journal = {Avanced energy materials}, number = {19}, publisher = {Wiley}, address = {Weinheim}, issn = {1614-6832}, doi = {10.1002/aenm.202200398}, pages = {22}, year = {2022}, abstract = {In recent years, due to its great promise in boosting the energy density of lithium batteries for future energy storage, research on the Li metal anode, as an alternative to the graphite anode in Li-ion batteries, has gained significant momentum. However, the practical use of Li metal anodes has been plagued by unstable Li (re)deposition and poor cyclability. Although tremendous efforts have been devoted to the stabilization of Li metal anodes, the mechanisms of electrochemical (re-)deposition/dissolution of Li and solid-electrolyte-interphase (SEI) formation remain elusive. This article highlights the recent mechanistic understandings and observations of Li deposition/dissolution and SEI formation achieved from advanced characterization techniques and simulation methods, and discusses major limitations and open questions in these processes. In particular, the authors provide their perspectives on advanced and emerging/potential methods for obtaining new insights into these questions. In addition, they give an outlook into cutting-edge interdisciplinary research topics for Li metal anodes. It pushes beyond the current knowledge and is expected to accelerate development toward a more in-depth and comprehensive understanding, in order to guide future research on Li metal anodes toward practical application.}, language = {en} } @article{MayerLeverPicconietal.2022, author = {Mayer, Dennis and Lever, Fabiano and Picconi, David and Metje, Jan and Ališauskas, Skirmantas and Calegari, Francesca and D{\"u}sterer, Stefan and Ehlert, Christopher and Feifel, Raimund and Niebuhr, Mario and Manschwetus, Bastian and Kuhlmann, Marion and Mazza, Tommaso and Robinson, Matthew Scott and Squibb, Richard J. and Trabattoni, Andrea and Wallner, M{\aa}ns and Saalfrank, Peter and Wolf, Thomas J. A. and G{\"u}hr, Markus}, title = {Following excited-state chemical shifts in molecular ultrafast x-ray photoelectron spectroscopy}, series = {Nature communications}, volume = {13}, journal = {Nature communications}, number = {1}, publisher = {Nature Research}, address = {Berlin}, issn = {2041-1723}, doi = {10.1038/s41467-021-27908-y}, pages = {9}, year = {2022}, abstract = {Imaging the charge flow in photoexcited molecules would provide key information on photophysical and photochemical processes. Here the authors demonstrate tracking in real time after photoexcitation the change in charge density at a specific site of 2-thiouracil using time-resolved X-ray photoelectron spectroscopy. The conversion of photon energy into other energetic forms in molecules is accompanied by charge moving on ultrafast timescales. We directly observe the charge motion at a specific site in an electronically excited molecule using time-resolved x-ray photoelectron spectroscopy (TR-XPS). We extend the concept of static chemical shift from conventional XPS by the excited-state chemical shift (ESCS), which is connected to the charge in the framework of a potential model. This allows us to invert TR-XPS spectra to the dynamic charge at a specific atom. We demonstrate the power of TR-XPS by using sulphur 2p-core-electron-emission probing to study the UV-excited dynamics of 2-thiouracil. The method allows us to discover that a major part of the population relaxes to the molecular ground state within 220-250 fs. In addition, a 250-fs oscillation, visible in the kinetic energy of the TR-XPS, reveals a coherent exchange of population among electronic states.}, language = {en} } @article{RotheZhaoMuelleretal.2021, author = {Rothe, Martin and Zhao, Yuhang and M{\"u}ller, Johannes and Kewes, G{\"u}nter and Koch, Christoph T. and Lu, Yan and Benson, Oliver}, title = {Self-assembly of plasmonic nanoantenna-waveguide structures for subdiffractional chiral sensing}, series = {ACS nano}, volume = {15}, journal = {ACS nano}, number = {1}, publisher = {American Chemical Society}, address = {Washington}, issn = {1936-0851}, doi = {10.1021/acsnano.0c05240}, pages = {351 -- 361}, year = {2021}, abstract = {Spin-momentum locking is a peculiar effect in the near-field of guided optical or plasmonic modes. It can be utilized to map the spinning or handedness of electromagnetic fields onto the propagation direction. This motivates a method to probe the circular dichroism of an illuminated chiral object. In this work, we demonstrate local, subdiffraction limited chiral coupling of light and propagating surface plasmon polaritons in a self-assembled system of a gold nanoantenna and a silver nanowire. A thin silica shell around the nanowire provides precise distance control and also serves as a host for fluorescent molecules, which indicate the direction of plasmon propagation. We characterize our nanoantenna-nanowire systems comprehensively through correlated electron microscopy, energy-dispersive X-ray spectroscopy, dark-field, and fluorescence imaging. Three-dimensional numerical simulations support the experimental findings. Besides our measurement of far-field polarization, we estimate sensing capabilities and derive not only a sensitivity of 1 mdeg for the ellipticity of the light field, but also find 10(3) deg cm(2)/dmol for the circular dichroism of an analyte locally introduced in the hot spot of the antenna-wire system. Thorough modeling of a prototypical design predicts on-chip sensing of chiral analytes. This introduces our system as an ultracompact sensor for chiral response far below the diffraction limit.}, language = {en} } @article{NingYuMeietal.2022, author = {Ning, Jiaoyi and Yu, Hongtao and Mei, Shilin and Sch{\"u}tze, Yannik and Risse, Sebastian and Kardjilov, Nikolay and Hilger, Andr{\´e} and Manke, Ingo and Bande, Annika and Ruiz, Victor G. and Dzubiella, Joachim and Meng, Hong and Lu, Yan}, title = {Constructing binder- and carbon additive-free organosulfur cathodes based on conducting thiol-polymers through electropolymerization for lithium-sulfur batteries}, series = {ChemSusChem}, volume = {15}, journal = {ChemSusChem}, number = {14}, publisher = {Wiley}, address = {Weinheim}, issn = {1864-5631}, doi = {10.1002/cssc.202200434}, pages = {10}, year = {2022}, abstract = {Herein, the concept of constructing binder- and carbon additive-free organosulfur cathode was proved based on thiol-containing conducting polymer poly(4-(thiophene-3-yl) benzenethiol) (PTBT). The PTBT featured the polythiophene-structure main chain as a highly conducting framework and the benzenethiol side chain to copolymerize with sulfur and form a crosslinked organosulfur polymer (namely S/PTBT). Meanwhile, it could be in-situ deposited on the current collector by electro-polymerization, making it a binder-free and free-standing cathode for Li-S batteries. The S/PTBT cathode exhibited a reversible capacity of around 870 mAh g(-1) at 0.1 C and improved cycling performance compared to the physically mixed cathode (namely S\&PTBT). This multifunction cathode eliminated the influence of the additives (carbon/binder), making it suitable to be applied as a model electrode for operando analysis. Operando X-ray imaging revealed the remarkable effect in the suppression of polysulfides shuttle via introducing covalent bonds, paving the way for the study of the intrinsic mechanisms in Li-S batteries.}, language = {en} } @article{LauLiuMaieretal.2021, author = {Lau, Skadi and Liu, Yue and Maier, Anna and Braune, Steffen and Gossen, Manfred and Neffe, Axel T. and Lendlein, Andreas}, title = {Establishment of an in vitro thrombogenicity test system with cyclic olefin copolymer substrate for endothelial layer formation}, series = {MRS communications / a publication of the Materials Research Society}, volume = {11}, journal = {MRS communications / a publication of the Materials Research Society}, number = {5}, publisher = {Springer}, address = {Berlin}, issn = {2159-6867}, doi = {10.1557/s43579-021-00072-6}, pages = {559 -- 567}, year = {2021}, abstract = {In vitro thrombogenicity test systems require co-cultivation of endothelial cells and platelets under blood flow-like conditions. Here, a commercially available perfusion system is explored using plasma-treated cyclic olefin copolymer (COC) as a substrate for the endothelial cell layer. COC was characterized prior to endothelialization and co-cultivation with platelets under static or flow conditions. COC exhibits a low roughness and a moderate hydrophilicity. Flow promoted endothelial cell growth and prevented platelet adherence. These findings show the suitability of COC as substrate and the importance of blood flow-like conditions for the assessment of the thrombogenic risk of drugs or cardiovascular implant materials.}, language = {en} } @article{NeusserSunTanetal.2022, author = {Neusser, David and Sun, Bowen and Tan, Wen Liang and Thomsen, Lars and Schultz, Thorsten and Perdigon-Toro, Lorena and Koch, Norbert and Shoaee, Safa and McNeill, Christopher R. and Neher, Dieter and Ludwigs, Sabine}, title = {Spectroelectrochemically determined energy levels of PM6:Y6 blends and their relevance to solar cell performance}, series = {Journal of materials chemistry : C, Materials for optical and electronic devices}, volume = {10}, journal = {Journal of materials chemistry : C, Materials for optical and electronic devices}, number = {32}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {2050-7526}, doi = {10.1039/d2tc01918c}, pages = {11565 -- 11578}, year = {2022}, abstract = {Recent advances in organic solar cell performance have been mainly driven forward by combining high-performance p-type donor-acceptor copolymers (e.g.PM6) and non-fullerene small molecule acceptors (e.g.Y6) as bulk-heterojunction layers. A general observation in such devices is that the device performance, e.g., the open-circuit voltage, is strongly dependent on the processing solvent. While the morphology is a typically named key parameter, the energetics of donor-acceptor blends are equally important, but less straightforward to access in the active multicomponent layer. Here, we propose to use spectral onsets during electrochemical cycling in a systematic spectroelectrochemical study of blend films to access the redox behavior and the frontier orbital energy levels of the individual compounds. Our study reveals that the highest occupied molecular orbital offset (Delta E-HOMO) in PM6:Y6 blends is similar to 0.3 eV, which is comparable to the binding energy of Y6 excitons and therefore implies a nearly zero driving force for the dissociation of Y6 excitons. Switching the PM6 orientation in the blend films from face-on to edge-on in bulk has only a minor influence on the positions of the energy levels, but shows significant differences in the open circuit voltage of the device. We explain this phenomenon by the different interfacial molecular orientations, which are known to affect the non-radiative decay rate of the charge-transfer state. We compare our results to ultraviolet photoelectron spectroscopy data, which shows distinct differences in the HOMO offsets in the PM6:Y6 blend compared to neat films. This highlights the necessity to measure the energy levels of the individual compounds in device-relevant blend films.}, language = {en} } @article{TungSunWangetal.2021, author = {Tung, Wing Tai and Sun, Xianlei and Wang, Weiwei and Xu, Xun and Ma, Nan and Lendlein, Andreas}, title = {Structure, mechanical properties and degradation behavior of electrospun PEEU fiber meshes and films}, series = {MRS advances : a journal of the Materials Research Society (MRS)}, volume = {6}, journal = {MRS advances : a journal of the Materials Research Society (MRS)}, number = {10}, publisher = {Springer Nature Switzerland AG}, address = {Cham}, issn = {2059-8521}, doi = {10.1557/s43580-020-00001-0}, pages = {276 -- 282}, year = {2021}, abstract = {The capability of a degradable implant to provide mechanical support depends on its degradation behavior. Hydrolytic degradation was studied for a polyesteretherurethane (PEEU70), which consists of poly(p-dioxanone) (PPDO) and poly(epsilon-caprolactone) (PCL) segments with a weight ratio of 70:30 linked by diurethane junction units. PEEU70 samples prepared in the form of meshes with average fiber diameters of 1.5 mu m (mesh1.5) and 1.2 mu m (mesh1.2), and films were sterilized and incubated in PBS at 37 degrees C with 5 vol\% CO2 supply for 1 to 6 weeks. Degradation features, such as cracks or wrinkles, became apparent from week 4 for all samples. Mass loss was found to be 11 wt\%, 6 wt\%, and 4 wt\% for mesh1.2, mesh1.5, and films at week 6. The elongation at break decreased to under 20\% in two weeks for mesh1.2. In case of the other two samples, this level of degradation was achieved after 4 weeks. The weight average molecular weight of both PEEU70 mesh and film samples decreased to below 30 kg/mol when elongation at break dropped below 20\%. The time period of sustained mechanical stability of PEEU70-based meshes depends on the fiber diameter and molecular weight.}, language = {en} }