TY - GEN A1 - Hansen, Felix A1 - Wels, Martin A1 - Froeschke, Samuel A1 - Popov, Alexey A1 - Wolf, Daniel A1 - Büchner, Bernd A1 - Schmidt, Peer A1 - Hampel, Silke T1 - Thermodynamic Evaluation and Chemical Vapor Transport of Few-Layer WTe2 T2 - Crystal Growth and Design N2 - Tungsten telluride WTe2 is the sole candidate of a group of two-dimensional layered transition metal dichalcogenides (TMDCs) MX2 with a thermodynamically stable 1T′-structure at room temperature. The binary system W/Te was audited with respect to a rational approach of planning and realization of a bottom-up synthesis of WTe2 nanostructures. Thus, the parameters of the synthesis via chemical vapor transports (CVT) were derived by thermodynamic simulations of the reaction pathway according to the Calphad method. Reflecting on the peritectic melting behavior at 1020 °C, the values of ΔfHm° (298 K) = −26.5 kJ·mol−1 and Sm° (298 K) = 132 J·mol−1 ·K−1 have been obtained. According to modeling, crystal growth by short time vapor transport is reasonable under the addition of bromine or TeBr4 in the temperature range between 650 and 750 °C. Experimental implementation of crystal growth of WTe2 nanosheets succeeded in a temperature gradient from 725 to 675 °C on yttria-stabilized zirconia (YSZ) (111) substrates, observing the deposition of single crystal sheets of high crystallinity with thicknesses of 15−20 nm (∼20−30 layers). The high crystallinity, pristine morphology, and overall quality of the deposited nanosheets is shown by means of atomic resolution transmission electron microscopy, selected area electron diffraction (SAED), and atomic force microscopy as well as profound double-polarized Raman spectroscopy. KW - Crystal growth KW - Chemical vapor transport KW - Thermodynamic modeling KW - 2D layered compounds KW - Chalcogenides KW - Phase diagram Y1 - 2020 UR - https://pubs.acs.org/doi/abs/10.1021/acs.cgd.0c01004 U6 - https://doi.org/10.1021/acs.cgd.0c01004 SN - 1528-7505 VL - 20 IS - 11 SP - 7341 EP - 7349 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 - TY - GEN A1 - Froeschke, Samuel A1 - Bestha, Kranthi Kumar A1 - Fucke, Rico A1 - Schiemenz, Sandra A1 - Popov, Alexey A1 - Naumann, Marco A1 - Knupfer, Martin A1 - Giebeler, Lars A1 - Wolf, Daniel A1 - Kizhake Malayil, Ranjith Kumar A1 - Sivan, Saramgi Chencheriparambil A1 - Grafe, Hans-Joachim A1 - Gräßler, Nico A1 - Corredor, Laura T. A1 - Wolter, Anja U. B. A1 - Büchner, Bernd A1 - Schmidt, Peer A1 - Hampel, Silke T1 - Structural and Magnetic Transitions Caused by Dimer Formation in the CrCl3–MoCl3 Solid Solution T2 - Chemistry of Materials N2 - In this work, we apply the concept of solid solutions to the two 2D transition metal trihalides CrCl3 and MoCl3. While CrCl3 belongs to the magnetically active CrX3 family, the magnetism in MoCl3 is intrinsically suppressed by the formation of aligned Mo–Mo dimers, which also distort the regular honeycomb lattice that is typical for the 2D transition metal trihalides. We report suitable synthesis conditions for the gapless solid solution and crystal growth by chemical vapor transport. The CrCl3–MoCl3 solid solution was initially synthesized at 650 °C for 100 h under addition of MoCl5 as mineralizer, and bulk crystals were subsequently grown by vapor transport in a temperature gradient from 600 °C → 550 °C for 60 h. The obtained solid solution exhibits multiple composition-dependent phase transitions at room temperature, as confirmed by powder X-ray diffraction measurements. The possible presence of Mo–Mo dimers in the solid solution was further investigated by infrared, Raman, electron energy loss, and nuclear quadrupole resonance spectroscopies. The combined results indicate that the Mo–Mo dimers are present over a wide range of compositions. Their orientation changes from parallel alignment for compositions from 70% ≤ c(Mo3+) ≤ 100% to random orientation for samples with c(Mo3+) < 70% content, which significantly affects the course of lattice parameters. Finally, the magnetic properties of the powder samples show a correlation between the Mo3+ content and the transition temperature into the low-temperature phase. Y1 - 2024 U6 - https://doi.org/10.1021/acs.chemmater.3c03109 SN - 0897-4756 SN - 1520-5002 VL - 36 IS - 9 SP - 4240 EP - 4253 ER -