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 - 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 - 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 - Putze, Philipp A1 - Ritschel, Tobias A1 - Chekhonin, Paul A1 - Geck, Jochen A1 - Wolf, Daniel A1 - Popov, Alexey A1 - Büchner, Bernd A1 - Schmidt, Peer A1 - Hampel, Silke T1 - Creating chirality in WSe₂ through screw dislocations by chemical vapor transport T2 - Nanoscale horizons N2 - Screw dislocation-driven nanostructures of two-dimensional transition metal dichalcogenides (2D TMDs) can feature chirality that enables prominent asymmetric optical properties. One of the outstanding representatives is WSe₂ as it can exhibit intriguing new size and shape-dependent chemical and physical properties compared to its bulk counterpart. Crystal growth control in nanostructures with screw dislocation-driven growth is central for exploiting their structure-related properties. However, bottom-up syntheses of 2D TMDs usually contain ‘trial and error’ approaches. Here we report on the rational synthesis planning and realizing for the binary system W:Se to achieve chirality in nano-scale crystals by chemical vapor transport (CVT). For that purpose, key parameters were modelled based on thermodynamic datasets. Thus, crystal growth by CVT under addition of SeCl4 succeeds for right-handed spiral nanocrystals from 850 °C to 800 °C with a dwell time of 60 min, while left-handed spirals are obtained from 915 °C to 860 °C. Surface-fused SiO₂ nanoparticles on an Si(100) substrate served as potential nucleation points. Chirality of screwed WSe₂ was unprecedentedly investigated by circular-polarized Raman Spectroscopy and showed an intensity increase of the E¹₂g mode of 29% and 15% for right and left-handed spirals, respectively. Pyramid-like WSe2 analyzed by atomic force microscopy exhibits step heights of around 10 nm. Electron backscatter diffraction patterns reveal a convex curvature for WSe₂ with the curvature radii determined as Rx = (270 ± 32) μm and Ry = (141 ± 9) μm, respectively. KW - Chrystal growth KW - Chemical vapor transport KW - Thermodynamic modeling KW - 2D layered compounds KW - Chalcogenides Y1 - 2025 UR - https://pubs.rsc.org/en/content/articlelanding/2025/nh/d4nh00567h U6 - https://doi.org/10.1039/D4NH00567H VL - 10 IS - 5 SP - 944 EP - 956 PB - Royal Society of Chemistry CY - Cambridge ER - TY - GEN A1 - Putze, Philipp A1 - Wolf, Daniel A1 - Chekhonin, Paul A1 - Popov, Alexey A1 - Ritschel, Tobias A1 - Lubk, Axel A1 - Geck, Jochen A1 - Büchner, Bernd A1 - Schmidt, Peer A1 - Hampel, Silke T1 - Twisted and screw dislocation-driven growth of MoSe₂ nanostructures by chemical vapor transport T2 - Nano research N2 - Twisted multilayers of two-dimensional materials attract widespread research interest due to their intriguing electronic and optical properties related to their chiral symmetry breaking and Moiré effects. The two-dimensional transition metal dichalcogenide MoSe₂ is a particular promising material for twisted multilayers, capable of sustaining Moiré excitons. Here, we report on a rational bottom-up synthesis approach for twisted MoSe₂ flakes by chemical vapor transport (CVT). Screw dislocation-driven growth was forced by surface-fused SiO₂ nanoparticles on the substrates that serve as potential nucleation points in low supersaturation condition. Thus, crystal growth by in-situ CVT under addition of MoCl₅ leads to bulk 2H-MoSe₂ in a temperature gradient from 900 °C to 820 °C with a dwell time of 96 h. Hexagonally shaped 2H-MoSe₂ flakes were grown from 710 °C to 685 °C with a dwell time of 30 min on SiO₂@Al₂O₃(0001) substrates. Electron backscatter diffraction as well as electron microscopy reveals the screw dislocation-driven growth of triangular 3R-MoSe₂ with individual step heights between 0.9 nm and 2.9 nm on SiO₂@Si(100) under the same conditions. Finally, twisted MoSe₂ flakes exhibiting a twist angle of 19° with respect to the [010] zone axis could be synthesized. KW - Chrystal growth KW - Chemical vapor transport KW - Thermodynamic modeling KW - 2D layered compounds KW - Chalcogenides Y1 - 2025 UR - https://www.sciopen.com/article/10.26599/NR.2025.94908020 U6 - https://doi.org/10.26599/NR.2025.94908020 SN - 1998-0000 IS - 18 SP - 1 EP - 23 PB - Tsinghua University Press ER -