@misc{WolfDoertStolzeetal., author = {Wolf, Adrian and Doert, Thomas and Stolze, Karoline and Schmidt, Peer}, title = {Modeling of Chemical Vapor Transport of Uranium Phosphide Telluride UPTe}, series = {Zeitschrift f{\"u}r Anorganische und Allgemeine Chemie}, volume = {640}, journal = {Zeitschrift f{\"u}r Anorganische und Allgemeine Chemie}, number = {11}, issn = {1521-3749}, doi = {10.1002/zaac.201490026}, pages = {2374}, abstract = {The crystallization mechanism of uranium phosphide telluride UPTe by chemical vapor transport reaction [1] is presented based on thermodynamic modelling using TRAGMIN program. Evaluation of standard data of all expected species was performed by modeling of the binary phase diagrams U/Te and U/P. Data of UPTe were deduced from known phosphide tellurides[2,3]. Identifying the viable composition area within the quaternary system U/P/Te/I the temperature depending transport equilibria could be obtained.}, language = {en} } @misc{Schmidt, author = {Schmidt, Peer}, title = {Rational Synthesis Design by Application of Electromotive Series of Solid Materials}, series = {Zeitschrift f{\"u}r Anorganische und Allgemeine Chemie}, volume = {640}, journal = {Zeitschrift f{\"u}r Anorganische und Allgemeine Chemie}, number = {11}, issn = {1521-3749}, doi = {10.1002/zaac.201490026}, pages = {2326}, abstract = {The concept of Electromotive Series of Solids presents an easy tool for prediction and interpretation of red-ox processes of inorganic solid materials. Thus, a rational synthesis design succeeds with low effort compared to complex thermodynamic considerations. The principle has been applied and validated for interpretation of known chemical systems as well for the development of new systems and processes.}, language = {en} } @misc{GroenkeSchmidtValldoretal., author = {Gr{\"o}nke, Martin and Schmidt, Peer and Valldor, Martin and Oswald, Steffen and Wolf, Daniel and Lubk, Axel and B{\"u}chner, Bernd and Hampel, Silke}, title = {Chemical vapor growth and delamination of α-RuCl3 nanosheets down to the monolayer limit}, series = {Nanoscale}, volume = {10}, journal = {Nanoscale}, number = {40}, issn = {2040-3372}, doi = {10.1039/C8NR04667K}, pages = {19014 -- 19022}, abstract = {2D layered honeycomb magnet α-ruthenium(III) chloride (α-RuCl3) is a promising candidate to realize a Kitaev spin model. As alteration of physical properties on the nanoscale is additionally intended, new synthesis approaches to obtain phase pure α-RuCl3 nanocrystals have been audited. Thermodynamic simulations of occurring gas phase equilibria were performed and optimization of synthesis conditions was achieved based on calculation results. Crystal growth succeeded via chemical vapor transport (CVT) in a temperature gradient of 973 K to 773 K on YSZ substrates. Single crystal sheets of high crystallinity with heights ≤ 30 nm were obtained via pure CVT. The crystal properties were characterized by means of optical and electron microscopy, AFM, SAED, micro-Raman and XPS proving their composition, morphology, crystallinity and phase-purity. A highlight of our study is the successful individualization of nanocrystals and the delamination of nanosheets on YSZ substrates down to the monolayer limit (≤ 1 nm) which was realized by means of substrate exfoliation and ultrasonication in a very reproducible way.}, language = {en} } @misc{GroenkeArroziBronkallaetal., author = {Gr{\"o}nke, Martin and Arrozi, Ubed S. F. and Bronkalla, Nadine and Schmidt, Peer and Valldor, Martin and Oswald, Steffen and Woodcock, Thomas G. and Eckert, Victoria and Hao, Qi and Pl{\"u}schke, Laura and Lederer, Albena and Nielsch, Kornelius and B{\"u}chner, Bernd and Kaskel, Stefan and Hampel, Silke}, title = {Layered α-TiCl₃: Microsheets on YSZ Substrates for Ethylene Polymerization with Enhanced Activity}, series = {Chemistry of Materials}, volume = {31}, journal = {Chemistry of Materials}, number = {14}, doi = {10.1021/acs.chemmater.9b01818}, pages = {5305 -- 5313}, abstract = {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.}, language = {en} } @misc{GroenkeBuschbeckSchmidtetal., author = {Gr{\"o}nke, Martin and Buschbeck, Benjamin and Schmidt, Peer and Valldor, Martin and Oswald, Steffen and Hao, Qi and Lubk, Axel and Wolf, Daniel and Steiner, Udo and B{\"u}chner, Bernd and Hampel, Silke}, title = {Chromium Trihalides CrX₃(X = Cl, Br, I): Direct Deposition of Micro- and Nanosheets on Substrates by Chemical Vapor Transport}, series = {Advanced Materials Interfaces}, volume = {6}, journal = {Advanced Materials Interfaces}, number = {24}, issn = {2196-7350}, doi = {10.1002/admi.201901410}, pages = {11}, abstract = {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 .}, language = {en} } @misc{HeinemannSchmidt, author = {Heinemann, Robert and Schmidt, Peer}, title = {Crystal Growth by Chemical Vapor Transport: Process Screening by Complementary Modeling and Experiment}, series = {Crystal Growth \& Design}, volume = {20}, journal = {Crystal Growth \& Design}, number = {9}, issn = {1528-7505}, doi = {10.1021/acs.cgd.0c00679}, pages = {5986 -- 6000}, abstract = {Despite chemical vapor transport (CVT) being a widely used method for crystal growth of inorganic substances, detailed mechanistic studies on the course of the crystallization process are rather few. In this study, an elaborated experimental screening run combined with sophisticated modeling of the respective heterogeneous equilibria is presented: Crystal growth of germanium by vapor transport with the addition of iodine has been chosen as a model system for validation of the applied method spectrum. In order to record the course and the interplay of heterogeneous equilibrium and non-equilibrium reactions in the system Ge-I, the experimental setup of high-temperature gas-balance (HTGB) is applied. Additionally, the observed evaporation processes are compared with saturation curves of corresponding volatile substances and, thus, can be assigned to individual species within the system. In this experimental screening, a phase sequence means to examine how the condensed phases undergo iodine depletion and how the gaseous phase undergoes a germanium enrichment when the temperature is increased. This phase screening combined with annealing experiments in the course of the phase sequence helps to analyze stepwise non-equilibrium products and to identify the characteristic species. Subsequently, for the evaluation of the composition of the gaseous phase, and for the deduction of the vapor transport mechanism, thermodynamic modeling by the CalPhaD method is performed. For the reference system, it is confirmed that iodine does not act as the transport agent. Instead, GeI4 is responsible for the volatilization of germanium, forming GeI2. Nevertheless, investigations clearly illustrate how GeI4 forms naturally in the phase sequence in the system Ge-I, which makes direct addition of it unnecessary. The recommended temperature range for vapor transport of germanium spans from 460 to 800 °C. Modeling shows that migration rates for germanium reaches a maximum at a mean temperature between 540 and 550 °C. Finally, vapor transport experiments were performed from 565 to 515 °C and from 690 to 590 °C. By increasing the deposition temperature, a slight decrease of the migration rate was observed, though a positive impact on the crystal's morphology was also found.}, language = {en} } @misc{HansenWelsFroeschkeetal., author = {Hansen, Felix and Wels, Martin and Froeschke, Samuel and Popov, Alexey and Wolf, Daniel and B{\"u}chner, Bernd and Schmidt, Peer and Hampel, Silke}, title = {Thermodynamic Evaluation and Chemical Vapor Transport of Few-Layer WTe2}, series = {Crystal Growth and Design}, volume = {20}, journal = {Crystal Growth and Design}, number = {11}, issn = {1528-7505}, doi = {10.1021/acs.cgd.0c01004}, pages = {7341 -- 7349}, abstract = {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.}, language = {en} } @techreport{SchmidtDonathWelsetal., author = {Schmidt, Peer and Donath, Ines and Wels, Martin and Pinnau, Sebastian and Grau Turuelo, Constantino and Breitkopf, Cornelia and Hack, Klaus and Baben, Moritz to and Reis, Bruno and M{\"u}ller, Michael and Sergeev, Dmitry and Qi, Jia}, title = {PCM Screening - Evaluierung eutektischer Gemische f{\"u}r den Einsatz als PCM: thermodynamische Modellierung und experimentelle Methoden : Energie Speicher: PCM-Screening : Schlussbericht}, publisher = {TIB - Leibniz-Informationszentrum Technik und Naturwissenschaften}, address = {Hannover}, doi = {10.2314/KXP:177643451X}, pages = {163}, abstract = {Ein wichtiges Ziel der Bundesregierung ist der Ausbau des Anteils erneuerbarer Energien an der gesamten Stromerzeugung. Die Entwicklung optimierter W{\"a}rme- und K{\"a}ltespeicher stellt einen wichtigen Baustein bei der Erreichung dieser Zielstellung dar. Elektrisch betriebene W{\"a}rmepumpen und Kompressionsk{\"a}ltemaschinen sowie dezentrale Klein-BHKW bieten in Verbindung mit entsprechend dimensionierten, thermischen Speichern ein großes Potential zum Lastmanagement in Smart Grids und somit zur Netzintegration von Strom aus erneuerbaren Energien. Die im Projekt entwickelte Methodik zur Suche nach neuen Latentspeichermedien kann f{\"u}r ein breites Anwendungsfeld von Heiz- und K{\"u}hlanwendungen in Geb{\"a}uden bis hin zur Kraftwerkstechnik eingesetzt werden. Innerhalb der F{\"o}rdermaßnahme „Anwendungsorientierte Forschung und Entwicklung zur nichtnuklearen Energieforschung" im 6. Energieforschungsprogramm der Bundesregierung wurde durch die Projektarbeiten das Schwerpunktthema Energiespeicher (3.8) adressiert, wobei der Aspekt der Entwicklung neuer Materialien mit reduzierten Kosten f{\"u}r einen wirtschaftlichen Betrieb im Vordergrund stand. Speziell wurden dabei die Unterpunkte 3.8.4 Thermische Speicher zur Weiterentwicklung, Optimierung und Erprobung von PCM sowie 3.8.5 {\"U}bergeordnete Themen mit Modellen und Simulationswerkzeugen f{\"u}r die Auswahl und Bewertung neuer Speichermaterialien adressiert. Die Projektergebnisse besitzen aber auch Ber{\"u}hrungspunkte mit den Schwerpunkten 3.12 Energieeffizienz in Industrie, Gewerbe, Handel und Dienstleistungen sowie 3.4 Solarthermische Kraftwerke, da mit der entwickelten Screening-Methode f{\"u}r diese Anwendungsf{\"a}lle neue W{\"a}rmespeichermaterialien auf der Basis wasserfreier Salze mit h{\"o}heren Prozesstemperaturen gefunden werden k{\"o}nnen. Durch den Einsatz von Methoden zur Modellierung und Simulation von Prozessen erfolgt gleichermaßen die Umsetzung einer energie- und ressourcenschonenden Forschungst{\"a}tigkeit. Das im Projekt entwickelte Vorgehen hilft dabei, einen {\"a}ußerst sparsamen Einsatz von Chemikalien, eine niedrige Belastung der Umwelt durch verringerten Entsorgungsaufwand der verbrauchten Stoffe sowie einen deutlich geringeren Aufwand und Energieeinsatz f{\"u}r die Messtechnik zu erm{\"o}glichen. Damit wurde zugleich das Schwerpunktthema 3.8.5 Modelle und Simulationswerkzeuge f{\"u}r die Auswahl und Bewertung neuer Speichermaterialien angesprochen.}, language = {de} } @misc{FroeschkeWolfHantuschetal., author = {Froeschke, Samuel and Wolf, Daniel and Hantusch, Martin and Giebeler, Lars and Wels, Martin and Gr{\"a}ßler, Nico and B{\"u}chner, Bernd and Schmidt, Peer and Hampel, Silke}, title = {Synthesis of micro- and nanosheets of CrCl3-RuCl3 solid solution by chemical vapour transport}, series = {Nanoscale}, volume = {29}, journal = {Nanoscale}, number = {14}, issn = {2040-3372}, doi = {10.1039/D2NR01366E}, pages = {10483 -- 10492}, abstract = {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 {\AA}, b = 10.3328(20)CrCl3 … 10.34606(21)RuCl3 {\AA}, c = 6.110(5)CrCl3 … 6.0385(5)RuCl3 {\AA} 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.}, language = {en} } @misc{HansenFuckeCharvinetal., author = {Hansen, Felix and Fucke, Rico and Charvin, Titouan and Froeschke, Samuel and Wolf, Daniel and Giraud, Romain and Dufouleur, Joseph and Gr{\"a}ßler, Nico and B{\"u}chner, Bernd and Schmidt, Peer and Hampel, Silke}, title = {Direct Deposition of (BixSb1-x)2Te3 Nanosheets on Si/SiO2 Substrates by Chemical Vapor Transport}, series = {Crystal growth \& design}, volume = {22}, journal = {Crystal growth \& design}, number = {4}, issn = {1528-7505}, doi = {10.1021/acs.cgd.1c01446}, pages = {2354 -- 2363}, abstract = {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.}, language = {en} } @misc{FroeschkeYasmenPopovetal., author = {Froeschke, Samuel and Yasmen, Nadia and Popov, Alexey and Schiemenz, Sandra and Wolf, Daniel and Giebeler, Lars and Hantusch, Martin and Gr{\"a}ßler, Nico and B{\"u}chner, Bernd and Schmidt, Peer and Hampel, Silke}, title = {Controlled Nanoplatelet Deposition of 2D Chromium Trihalide Solid Solutions}, series = {Chemistry of Materials}, volume = {35}, journal = {Chemistry of Materials}, number = {11}, issn = {1520-5002}, doi = {10.1021/acs.chemmater.2c03785}, pages = {4136 -- 4148}, abstract = {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.}, language = {en} } @misc{FroeschkeSchrothSteineretal., author = {Froeschke, Samuel and Schroth, Karl-Georg and Steiner, Udo and Popov, Alexey and Schiemenz, Sandra and Wolf, Daniel and Giebeler, Lars and Gr{\"a}ßler, Nico and B{\"u}chner, Bernd and Schmidt, Peer and Hampel, Silke}, title = {Understanding the chemistry of 2D rhodium trihalide solid solutions: tuning of optical properties and nanocrystal deposition}, series = {2D Materials}, volume = {10}, journal = {2D Materials}, number = {3}, issn = {2053-1583}, doi = {10.1088/2053-1583/acd012}, pages = {1 -- 12}, abstract = {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.}, language = {en} } @misc{PutzeRitschelChekhoninetal., author = {Putze, Philipp and Ritschel, Tobias and Chekhonin, Paul and Geck, Jochen and Wolf, Daniel and Popov, Alexey and B{\"u}chner, Bernd and Schmidt, Peer and Hampel, Silke}, title = {Creating chirality in WSe₂ through screw dislocations by chemical vapor transport}, series = {Nanoscale horizons}, volume = {10}, journal = {Nanoscale horizons}, number = {5}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, doi = {10.1039/D4NH00567H}, pages = {944 -- 956}, abstract = {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.}, language = {en} } @misc{PutzeWolfChekhoninetal., author = {Putze, Philipp and Wolf, Daniel and Chekhonin, Paul and Popov, Alexey and Ritschel, Tobias and Lubk, Axel and Geck, Jochen and B{\"u}chner, Bernd and Schmidt, Peer and Hampel, Silke}, title = {Twisted and screw dislocation-driven growth of MoSe₂ nanostructures by chemical vapor transport}, series = {Nano research}, journal = {Nano research}, number = {18}, publisher = {Tsinghua University Press}, issn = {1998-0000}, doi = {10.26599/NR.2025.94908020}, pages = {1 -- 23}, abstract = {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 Moir{\´e} effects. The two-dimensional transition metal dichalcogenide MoSe₂ is a particular promising material for twisted multilayers, capable of sustaining Moir{\´e} 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.}, language = {en} }