TY - GEN A1 - Froeschke, Samuel A1 - Yasmen, Nadia A1 - Popov, Alexey A1 - Schiemenz, Sandra A1 - Wolf, Daniel A1 - Giebeler, Lars A1 - Hantusch, Martin A1 - Gräßler, Nico A1 - Büchner, Bernd A1 - Schmidt, Peer A1 - Hampel, Silke T1 - Controlled Nanoplatelet Deposition of 2D Chromium Trihalide Solid Solutions T2 - Chemistry of Materials N2 - The two-dimensional (2D) chromium trihalides CrCl3, CrBr3, and CrI3 are most famous for their exotic magnetic properties when their crystals get downscaled to nanometer dimensions. One way to tune the properties of such materials and to further increase their potential utility, e.g., in spintronics, is the formation of solid solutions. Here, we present a detailed theoretical and experimental study on the synthesis and nanoplatelet growth of CrBrxCl3–x and CrBrxI3–x solid solutions. Phase pure powder was obtained by tempering the respective parent compounds at 600 and 550 °C, using additional iodine in the case of CrBrxI3–x. The dominant stacking order changes at x = 1.8 for CrBrxCl3–x while remaining similar to CrI3 for the whole CrBrxI3–x series. A consecutive chemical vapor transport from 575 → 525 °C for 2 h (CrBrxCl3–x) or 600 → 550 °C for 3 h with 0.1 mmol additional iodine (CrBrxI3–x) resulted in the deposition of high-quality nanoplatelets on a substrate with only several nanometers in height. The composition can be controlled by the choice of the starting material, since only small shifts in the anion ratio occur during the transport. The deposited CrBrxCl3–x nanoplatelets can then be easily delaminated by ultrasonication in ethanol to reduce the height even further to few-layer dimensions. These nanoplatelets could potentially be used to investigate the property changes (e.g., in terms of magnetic response) for the downscaling of these solid solutions. We further demonstrate the quality of the deposited material by transmission electron microscopy, selected area electron diffraction, and X-ray photoelectron spectroscopy. Raman spectroscopy of the solid solution series reveals a complex evolution of vibrational modes. Photoluminescence measurements on solid solution samples show emission peaks in the near-infrared energy range with the specific energy and intensity being composition and temperature dependent. KW - 2D layered compounds KW - Chemical vapor transport KW - Crystal growth KW - Crystal structure KW - Halides KW - Thermodynamic modeling Y1 - 2023 UR - https://pubs.acs.org/doi/full/10.1021/acs.chemmater.2c03785 U6 - https://doi.org/10.1021/acs.chemmater.2c03785 SN - 1520-5002 SN - 0897-4756 VL - 35 IS - 11 SP - 4136 EP - 4148 ER - TY - GEN A1 - Froeschke, Samuel A1 - Schroth, Karl-Georg A1 - Steiner, Udo A1 - Popov, Alexey A1 - Schiemenz, Sandra A1 - Wolf, Daniel A1 - Giebeler, Lars A1 - Gräßler, Nico A1 - Büchner, Bernd A1 - Schmidt, Peer A1 - Hampel, Silke T1 - Understanding the chemistry of 2D rhodium trihalide solid solutions: tuning of optical properties and nanocrystal deposition T2 - 2D Materials N2 - In the search for novel 2D materials with potentially valuable properties, such as a tunable band gap for optoelectronic or catalytic applications, solid solutions hold the potential to significantly expand the inventory of available 2D nanomaterials. In this study, we present for the first time the synthesis of such 2D rhodium trihalide solid solutions: RhBrxCl3−x and RhBrxI3−x. We use thermodynamic simulations and simultaneous thermal analysis to predict conditions for their rational synthesis and to investigate suitable chemical vapor transport (CVT) parameters for these solid solutions. The evolution of the lattice parameters was investigated by powder x-ray diffraction, showing an isostructural relationship of the synthesized compounds and only minor deviation from Vegard's law. The optical band gap of these materials can be tuned in an energy range from 1.5 eV (RhCl3) to 1.2 eV (RhI3) by choosing the composition of the solid solution, while the samples also exhibit photoluminescence in similar energy ranges. Ultimately, the successful deposition of bulk as well as ultrathin 2D nanocrystals of RhBrxCl3−x by CVT from 925 °C to 850 °C is shown, where the composition of the deposited crystals is precisely controlled by the choice of the starting composition and the initial amount of material. The high quality of the obtained nanocrystals is confirmed by atomic force microscopy, high resolution transmission electron microscopy and selected area electron diffraction. For RhBrxI3−x, the CVT from 900 °C to 825 °C is more difficult and has only been practically demonstrated for an exemplary case. According to the observed properties, these novel solid solutions and nanocrystals show a great potential for an application in optoelectronic devices. KW - Crystal growth KW - Chemical vapor transport KW - Crystal structure KW - Thermodynamic modeling KW - 2D layered compounds KW - Halides Y1 - 2023 UR - https://iopscience.iop.org/article/10.1088/2053-1583/acd012 U6 - https://doi.org/10.1088/2053-1583/acd012 SN - 2053-1583 VL - 10 IS - 3 SP - 1 EP - 12 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 - TY - GEN A1 - Froeschke, Samuel A1 - Wolf, Daniel A1 - Hantusch, Martin A1 - Giebeler, Lars A1 - Wels, Martin A1 - Gräßler, Nico A1 - Büchner, Bernd A1 - Schmidt, Peer A1 - Hampel, Silke T1 - Synthesis of micro- and nanosheets of CrCl3–RuCl3 solid solution by chemical vapour transport T2 - Nanoscale N2 - Solid solutions of 2D transition metal trihalides are rapidly growing in interest for the search for new 2D materials with novel properties at nanoscale dimensions. In this regard, we present a synthesis method for the Cr1−xRuxCl3 solid solution and describe the behaviour of the unit cell parameters over the whole composition range, which in general follows Vegard's law in the range of a = 5.958(6)CrCl3 … 5.9731(5)RuCl3 Å, b = 10.3328(20)CrCl3 … 10.34606(21)RuCl3 Å, c = 6.110(5)CrCl3 … 6.0385(5)RuCl3 Å and β = 108.522(15)CrCl3 … 108.8314(14)RuCl3 °. The synthesized solid solution powder was subsequently used to deposit micro- and nanosheets directly on a substrate by applying chemical vapour transport in a temperature gradient of 575 °C → 525 °C for 2 h and 650 °C → 600 °C for 0.5 h as a bottom-up approach without the need for an external transport agent. The observed chromium chloride enrichment of the deposited crystals is predicted by thermodynamic simulation. The results allow for a nanostructure synthesis of this solid solution with a predictable composition down to about 30 nm in height and lateral size of several μm. When applying a quick consecutive delamination step, it is possible to obtain few- and monolayer structures, which could be used for further studies of downscaling effects for the CrCl3–RuCl3 solid solution. X-ray photoelectron spectroscopy, transmission electron microscopy and Raman spectroscopy were used to confirm the purity and quality of the synthesized crystals. KW - Crystal growth KW - Chemical vapor transport KW - Thermal analysis KW - Thermodynamic modeling KW - 2D layered compounds Y1 - 2022 UR - https://pubs.rsc.org/en/content/articlelanding/2022/NR/D2NR01366E U6 - https://doi.org/10.1039/D2NR01366E SN - 2040-3372 VL - 29 IS - 14 SP - 10483 EP - 10492 ER - TY - GEN A1 - Hansen, Felix A1 - Fucke, Rico A1 - Charvin, Titouan A1 - Froeschke, Samuel A1 - Wolf, Daniel A1 - Giraud, Romain A1 - Dufouleur, Joseph A1 - Gräßler, Nico A1 - Büchner, Bernd A1 - Schmidt, Peer A1 - Hampel, Silke T1 - Direct Deposition of (BixSb1–x)2Te3 Nanosheets on Si/SiO2 Substrates by Chemical Vapor Transport T2 - Crystal growth & design N2 - The tellurides of bismuth and antimony (Bi2Te3 and Sb2Te3) are prominent members of the V2VI3 material family that exhibit promising topological properties. We provide a method for the rational synthesis of mixed crystals of these materials ((BixSb1–x)2Te3 with x = 0.1, ..., 0.9) by means of a bottom-up chemical vapor transport (CVT) approach. Thermodynamic calculations showed the synthesis to be possible in the temperature range of 390–560 °C without significant enrichment of either component and without adding a transport agent. The starting materials were synthesized and verified by X-ray diffraction (XRD). Optimization experiments showed the ideal conditions for nanosheet synthesis to be T2 = 560 °C, T1 = 390 °C with a reaction time of t = 36 h. Crystals with heights of down to 12 nm (12 quintuple layers) were synthesized and analyzed by means of scanning electron microscopy, energy-dispersive X-ray spectrometry, and atomic force microscopy. High-resolution transmission electron microscopy confirmed the R3̅m crystal structure, high crystallinity, and overall quality of the synthesized (BixSb1–x)2Te3 nanosheets. Magnetotransport measurements revealed that such ternary compounds can have a significantly reduced carrier density compared to the binary parent compounds. KW - Crystal growth KW - Chemical vapor transport KW - Thermodynamic modeling KW - Chalcogenides Y1 - 2022 UR - https://pubs.acs.org/doi/abs/10.1021/acs.cgd.1c01446 U6 - https://doi.org/10.1021/acs.cgd.1c01446 SN - 1528-7505 SN - 1528-7483 VL - 22 IS - 4 SP - 2354 EP - 2363 ER - 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 -