TY - GEN A1 - Grönke, Martin A1 - Pohflepp, Danny A1 - Schmidt, Peer A1 - Valldor, Martin A1 - Oswald, Steffen A1 - Wolf, Daniel A1 - Hao, Qi A1 - Steiner, Udo A1 - Büchner, Bernd A1 - Hampel, Silke T1 - Simulation and synthesis of alpha-MoCl₃ nanosheets on substrates by short time chemical vapor transport T2 - Nano-Structures & Nano-Objects N2 - Alpha-molybdenum(III) chloride (MoCl₃) belongs to layered van-der-Waals materials, which are in focus to exhibit interesting properties due to their weak chemical and magnetic interactions. Especially the structure of alpha-MoCl₃ has been discussed in terms of symmetry breaking dimerization of Mo atoms at room temperature, which might led to exotic ground states. By exploiting the 2D materials characteristics, an investigation of physical properties on the nanoscale is intended. We herein demonstrate the probably first approach to synthesize phase pure, as-grown alpha-MoCl₃ few-layer nanosheets by means of a pure short time chemical vapor transport (CVT) process. Vapor growth benefits from a one-step deposition of high crystalline alpha-MoCl₃ nanosheets without stacking faults on a substrate. Thus, mostly applied subsequent delamination, associated with the introduction of structural defects, becomes redundant. According to the CVT process thermodynamic simulations of gas phase equilibria have been performed and the synthesis conditions could be optimized based on the calculation results. By CVT the as-grown nanolayers are deposited on sapphire (Al₂O₃) substrates by applying a temperature gradient of 70 K from 743 K to 673 K. Single crystalline sheets with thicknesses ≤75 nm down to five layer (3 nm) could be obtained by using a pure CVT process. According to the deposited nanostructures we approve the desired composition, morphology, phase purity and high crystallinity by using several microscopy and spectroscopy techniques. Furthermore, we show micro-RAMAN measurements which hint at a slight increase in phonon energies for nanosheets in comparison to the corresponding bulk phase. KW - Crystal growth KW - Chemical vapor transport KW - 2D layered compounds KW - Halides Y1 - 2019 UR - https://www.sciencedirect.com/science/article/pii/S2352507X18304888?via%3Dihub#! U6 - https://doi.org/10.1016/j.nanoso.2019.100324 SN - 2352-507X IS - 19 SP - 1 EP - 7 ER - TY - GEN A1 - Grönke, Martin A1 - Arrozi, Ubed S. F. A1 - Bronkalla, Nadine A1 - Schmidt, Peer A1 - Valldor, Martin A1 - Oswald, Steffen A1 - Woodcock, Thomas G. A1 - Eckert, Victoria A1 - Hao, Qi A1 - Plüschke, Laura A1 - Lederer, Albena A1 - Nielsch, Kornelius A1 - Büchner, Bernd A1 - Kaskel, Stefan A1 - Hampel, Silke T1 - Layered α-TiCl₃: Microsheets on YSZ Substrates for Ethylene Polymerization with Enhanced Activity T2 - Chemistry of Materials N2 - The transition metal halide α-titanium(III) chloride (α-TiCl₃) is a layered two-dimensional compound and a well-established Ziegler–Natta catalyst for the polymerization of ethylene. A new synthesis technique is used to obtain thin sheets of α-TiCl₃ that show exceptional physical properties in contrast to their bulk counterparts, due to an enlarged surface-to-volume ratio. Chemical vapor transport (CVT) of α-titanium(III) chloride directly on substrates results in microsheets that exhibit an improved catalytic effect. For rational planning of synthesis conditions, thermodynamic simulations of occurring gas-phase equilibria were performed. Based on these calculation results, crystal growth was achieved by adding GaCl₃via pure short term CVT in a temperature gradient of 700–600 K on yttrium-stabilized zirconia (YSZ) substrates. Phase pure, as-grown, single crystal sheets with high crystallinity and a thickness of around 4 μm were obtained. These thin sheets of α-TiCl₃ on YSZ substrates were implemented as catalysts for the ethylene polymerization reaction. A significant improvement of catalytic activity of 16% was achieved, probably due to an increased surface-to-volume ratio. As a highlight, the as-grown microsheets were exfoliated subsequently to a thickness lower than 200 nm and an even higher catalytic activity of up to 24% was confirmed experimentally due to delamination effects. This is the first time that an improved catalytic effect of α-TiCl₃ is observed as a result of downscaling from bulk to microsheets by CVT. KW - Crystal growth KW - Chemical vapor transport KW - Thermodynamic modeling KW - 2D layered compounds KW - Halides KW - Nanocrystals (1) Y1 - 2019 UR - https://pubs.acs.org/doi/10.1021/acs.chemmater.9b01818 U6 - https://doi.org/10.1021/acs.chemmater.9b01818 VL - 31 IS - 14 SP - 5305 EP - 5313 ER - TY - GEN A1 - Grönke, Martin A1 - Buschbeck, Benjamin A1 - Schmidt, Peer A1 - Valldor, Martin A1 - Oswald, Steffen A1 - Hao, Qi A1 - Lubk, Axel A1 - Wolf, Daniel A1 - Steiner, Udo A1 - Büchner, Bernd A1 - Hampel, Silke T1 - Chromium Trihalides CrX₃(X = Cl, Br, I): Direct Deposition of Micro‐ and Nanosheets on Substrates by Chemical Vapor Transport T2 - Advanced Materials Interfaces N2 - The experimental observation of intrinsic ferromagnetism in single layered chromium trihalides CrX₃ (X = Cl, Br, I) has gained outstanding attention recently due to their possible implementation in spintronic devices. However, the reproducible preparation of highly crystalline chromium(III) halide nanolayers without stacking faults is still an experimental challenge. As chromium trihalides consist of adjacent layers with weak interlayer coupling, the preparation of ultrathin CrX₃ nanosheets directly on substrates via vapor transport proves as an advantageous synthesis technique. It is demonstrated that vapor growth of ultrathin highly crystalline CrX₃ micro‐ and nanosheets succeeds directly on yttrium stabilized zirconia substrates in a one‐step process via chemical vapor transport (CVT) in temperature gradients of 100 K (600°C → 500°C for CrCl₃ and 650°C → 550°C for CrBr₃ or CrI₃) without a need for subsequent delamination. Due to simulation results, optimization of synthesis conditions is realized and phase pure CrX₃ nanosheets with thicknesses ≤25 nm are obtained via short term CVT. The nanosheets morphology, crystallinity, and phase purity are analyzed by several techniques, including microscopy, diffraction, and spectroscopy. Furthermore, a potential subsequent delamination technique is demonstrated to give fast access to CrX₃ monolayers using the example of CrCl₃ . KW - 2D layered compounds KW - Crystal growth KW - Chemical vapor transport KW - Halides KW - Nanocrystals KW - Thermodynamic modeling Y1 - 2019 UR - https://onlinelibrary.wiley.com/doi/epdf/10.1002/admi.201901410 U6 - https://doi.org/10.1002/admi.201901410 SN - 2196-7350 VL - 6 IS - 24 ER -