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 & eacute; effects. The two-dimensional transition metal dichalcogenide MoSe2 is a particularly promising material for twisted multilayers, capable of sustaining moir & eacute; 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 to 820 degrees C with a dwell time of 96 h. Hexagonally shaped 2H-MoSe2 flakes were grown from 710 to 685 degrees 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 and 2.9 nm on SiO2@Si(100) under the same conditions. Finally, twisted MoSe2 flakes exhibiting a twist angle of 19 degrees with respect to the [010] zone axis could be synthesized.

Creation of chirality through screw dislocation-driven growth for highly crystalline nano-WSe 2 by chemical vapor transport based on thermodynamic simulations.

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 degrees 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 degrees C -> 550 degrees 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.

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: RhBr x Cl 3− x and RhBr x I 3− 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 (RhCl 3 ) to 1.2 eV (RhI 3 ) 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 RhBr x Cl 3− 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 RhBr x I 3− 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.

Nanoscale phase separation was induced in the K‐doped RuCl 3 van der Waals material by annealing, and studied with the goal to find a natural design strategy for the formation of two‐dimensional architectures as an alternative to the costly and time‐consuming experimental artificial growth methods. Phase conversion was traced by means of thermogravimetric analysis combined with mass spectrometry. The local crystal structure of co‐existing K 3 Ru 2 Cl 9 domains with the sizes of about 100 nm was solved by 3D electron diffraction.

The two-dimensional(2D) chromium trihalides CrCl3,CrBr3, and CrI3 are most famous for their exoticmagnetic properties when their crystals get downscaled to nanometerdimensions. One way to tune the properties of such materials and tofurther increase their potential utility, e.g., in spintronics, isthe formation of solid solutions. Here, we present a detailed theoreticaland experimental study on the synthesis and nanoplatelet growth ofCrBr( x )Cl(3-x ) and CrBr x I3-x solid solutions. Phase pure powder was obtainedby tempering the respective parent compounds at 600 and 550 degrees C,using additional iodine in the case of CrBr x I3-x . The dominant stackingorder changes at x = 1.8 for CrBr x Cl3-x while remaining similarto CrI3 for the whole CrBr x I3-x series. A consecutive chemicalvapor transport from 575 -> 525 degrees C for 2 h (CrBr x Cl3-x ) or 600 -> 550 degrees C for 3 h with 0.1 mmol additional iodine (CrBr x I3-x )resulted in the deposition of high-quality nanoplatelets on a substratewith only several nanometers in height. The composition can be controlledby the choice of the starting material, since only small shifts inthe anion ratio occur during the transport. The deposited CrBr x Cl3-x nanoplateletscan then be easily delaminated by ultrasonication in ethanol to reducethe height even further to few-layer dimensions. These nanoplateletscould potentially be used to investigate the property changes (e.g.,in terms of magnetic response) for the downscaling of these solidsolutions. We further demonstrate the quality of the deposited materialby transmission electron microscopy, selected area electron diffraction,and X-ray photoelectron spectroscopy. Raman spectroscopy of the solidsolution series reveals a complex evolution of vibrational modes.Photoluminescence measurements on solid solution samples show emissionpeaks in the near-infrared energy range with the specific energy andintensity being composition and temperature dependent.

Integrating enzymes into thermoplastic polymers is challenging due to their lack of robustness with respect to temperature and shear fields during conventional melt processing. In the present study, blown films from lowdensity polyethylene (LDPE) were prepared containing a technical protease from Bacillus sp. First, LDPE/protease compounds were produced followed by blown film extrusion, both processes at melt mass temperatures of 130 degrees C or higher. Enzyme activity was proven, both for the LDPE/protease compound and the blown film. The highest enzyme activity in the compound was determined for processing at 132 degrees C and a screw speed of 75 rpm. The influence of melt temperature and shear fields was studied in detail. Enzyme activities were determined for melt temperatures up to 160 degrees C and for screw speeds ranging from 75 to 300 rpm during compounding by twinscrew extrusion. The process was also applied for biobased and biodegradable polyesters, where similar protease activity after compounding was verified. Electron microscopy, X-ray diffraction, nuclear magnetic resonance spectroscopy and differential scanning calorimetry served to analyze components and morphology of the enzyme formulation used here. It is proposed that the porous morphology of the protease particles is beneficial for the enzyme to remain active after processing. Additionally, the polymer matrix surrounding the particles protects the protease at elevated temperatures, which can be attributed to thermal insulation. Thus, the right combination of a suited technical enzyme formulation with appropriate mild melt compounding conditions allows enzymes to be incorporated into thermoplastics and retain their activity. This opens the way to use the abundant biological functions of enzymes in thermoplastic applications.

The cover picture shows an artistic representation of a nanoscale phase separation which can be naturally induced by rapid, out-of-equilibrium heating of K-doped RuCl3. Combining the pXRD, TGA-MS, HRTEM and 3D electron diffraction we step-by-step trace the phase conversion and unveil the crystal structure of a distinct K3Ru2Cl9 domain arising from the decomposition process, embedded into the KxRu2Cl6 matrix. Natural annealing can be beneficial for the formation of 2D architectures and serve as an alternative to the time- and energy-consuming artificial growth methods (DOI: 10.1002/zaac.202300141).

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.

DUT-8(Ni) metal-organic framework (MOF) belongs to the family of flexible pillared layer materials. The desolvated framework can be obtained in the open pore form (op) or in the closed pore form (cp), depending on the crystal size regime. In the present work, we report on the behaviour of desolvated DUT-8(Ni) at elevated temperatures. For both, op and cp variants, heating causes a structural transition, leading to a new, crystalline compound, containing two interpenetrated networks. The state of the framework before transition (op vs. cp) influences the transition temperature: the small particles of the op phase transform at significantly lower temperature in comparison to the macroparticles of the cp phase, transforming close to the decomposition temperature. The new compound, confined closed pore phase (ccp), was characterized by powder X-ray diffraction and spectroscopic techniques, such as IR, EXAFS, and positron annihilation lifetime spectroscopy (PALS). Thermal effects of structural transitions were studied using differential scanning calorimetry (DSC), showing an overall exothermic effect of the process, involving bond breaking and reformation. Theoretical calculations reveal the energetics, driving the observed temperature induced phase transition.

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)(2)Te-3 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 degrees 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 T-2 = 560 degrees C, T-1 = 390 degrees C with a reaction time of t = 36 h. Crystals with heights of down to 12 nm (12 quintuple layers) were syntheszed and analyzed by means of scanning electron microscopy, energy-dispersive X-ray spectrometry, and atomic force microscopy. High-resolution transmission electron microscopy confirmed the R (3) over barm crystal structure, high crystallinity, and overall quality of the synthesized (BixSb1-x)(2)Te-3 nanosheets. Magnetotransport measurements revealed that such ternary compounds can have a significantly reduced carrier density compared to the binary parent compounds.

The Cover Feature shows the correlation between the stability and reactivity of ionic liquids (ILs). Undercutting the maximum operating temperature (MOT) the IL initially is protected. Reaching the MOT, reactive species can be formed by thermal decomposition and functionality of the IL changes. Thus IL, actually used as a solvent, can become reactants. A current case study shows, that, exceeding the calculated MOT, reactive decomposition products of [C4C1im]BF4 lead to the reduction of the oxide precursor SeO2 and the formation of red amorphous selenium. Analyzing the gaseous species formed during the reaction, the reaction mechanism can be deduced similar to Riley oxidation. Thereby, but-1-ene, reacts with SeO2 to Se, H2O, and but-3-en-2-one. Concluding, the suitability of the single-source oxide precursor Bi2Se3O9 for the synthesis of Bi2Se3 is proven. More information can be found in the Full Paper by Monika Knorr et al.

The concept of maximum operation temperature is established for the prediction of the time dependent thermal stability of ionic liquids based on kinetic evaluation of thermogravimetric analysis. The influence of the furnace control parameters on the maximum operation temperature (MOT) is shown using the example of 1-methyl-3-propylimidazolium iodide ([C(3)C(1)im]I) with respect to three different parameter sets of a programmed proportional integral derivative (PID) controller of the TGA. Kinetics of thermal decomposition of [[C(3)C(1)im]I have been investigated with the implementation of an improved kinetic model. The activation energy obtained using the Kissinger-Akahira-Sunose equation showed variations apparently due to the decomposition degree. The model compound is decomposed by a one-step kinetics, which results from pseudo zero order relationship of the activation energy to the conversion rate. The activation energy, pre-exponential factor, and the activation energy are strongly dependent on the parameters of TGA furnace controller.

Germanium (Ge) nanowires (NWs) were grown in-plane on nano-structured Si(001)/SiO(2)substrates by molecular beam epitaxy using gold (Au) as the solvent. The site-selective NW growth was enabled by a rectangular array of gold droplets on silicon (Si) tips with an Au nuclei density below 0.25 mu m(-2)on the surrounding silicon oxide (SiO2). The initial growth of Ge NWs starting from Si-Au droplets with Si(x)Ge(1-x)nucleation from ternary alloy is discussed from a thermodynamic point of view. The in-plane NW elongation occurred within 110 directions on the substrate and NWs were mainly bounded by two 55 degrees inclined 111 facets and a less pronounced planar (001) top facet. Fully relaxed crystal lattices of Ge NWs were observed from two-dimensional reciprocal space maps of x-ray diffraction measurements.

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 degrees C, the values of Delta H-f(m)degrees(298 K) = -26.5 kJ.mol(-1) and S-m degrees(298 = 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 degrees C. Experimental implementation of crystal growth of WTe2 nanosheets succeeded in a temperature gradient from 725 to 675 degrees C on yttria-stabilized zirconia (YSZ) (111) substrates, observing the deposition of single crystal sheets of high crystallinity with thicknesses of 15-20 nm (similar to 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 (SHED), and atomic force microscopy as well as profound double-polarized Raman spectroscopy.

Germanium (Ge) nanowires (NWs) were grown in-plane on nano-structured Si(001)/SiO2 substrates by molecular beam epitaxy using gold (Au) as the solvent. The site-selective NW growth was enabled by a rectangular array of gold droplets on silicon (Si) tips with an Au nuclei density below 0.25 µm−2 on the surrounding silicon oxide (SiO2). The initial growth of Ge NWs starting from Si–Au droplets with SixGe1−x nucleation from ternary alloy is discussed from a thermodynamic point of view. The in-plane NW elongation occurred within 〈110〉 directions on the substrate and NWs were mainly bounded by two 55° inclined 111 facets and a less pronounced planar (001) top facet. Fully relaxed crystal lattices of Ge NWs were observed from two-dimensional reciprocal space maps of x-ray diffraction measurements.

The Ionic Liquid 1-butyl-3-methylimidazolium tetrafluoroborate [C(4)C(1)im]BF4 serves as a commonly solvent in inorganic material synthesis and analytics. Nevertheless, its application is frequently associated with trial and error approaches. Thereupon, detailed knowledge on the thermal behavior is the key information for understanding the reactivity of [C(4)C(1)im]BF4. 1-butyl-3-methylimidazolium tetrafluoroborate behaves as a glass in the cold, its glass transition temperature being theta(g) = -83 degrees C. During heating with 10 K.min(-1) [C(4)C(1)im]BF4 appears to be stable above 350 degrees C with onset temperatures theta(onset, DSC )= 375 degrees C, theta(onset), (DTG )= 422 degrees C, and (theta onset), (TG) = 437 degrees C. Thereby, thermal decomposition occurs in a single step reaction forming 1-methyl-1H-imidazole (CH3C3H3N2 or C4H6N2), but-l-ene (C4H8), fluoromethane (CH3F) and boron trifluoride (BF3) as main species, as determined by thermogravimetry coupled with mass spectrometry and FTIR spectroscopy. To be more specific in thermal behavior, the temperature and time dependent stability is evaluated here on the basis of the kinetic model of maximum operation temperature - MOT. Clearly, thermal stability rises with application time, thus being 193 degrees C for one hour, while reaching only 141 degrees C for one day, and 114 degrees C for one week. The incipient decomposition (<= 1 %) at the calculated time dependent maximum operation temperature finally is verified by optical analysis, infrared (IR), and nuclear magnetic resonance (NMR) spectroscopy.

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 nonequilibrium reactions in the system Ge-I, the experimental setup of high-temperature gasbalance (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 nonequilibrium 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 degrees C. Modeling shows that migration rates for germanium reaches a maximum at a mean temperature between 540 and 550 degrees C. Finally, vapor transport experiments were performed from 565 to 515 degrees C and from 690 to 590 degrees 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.