No abstract

Tungsten telluride WTe 2 is the sole candidate of a group of two-dimensional layered transition metal dichalcogenides (TMDCs) MX 2 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 WTe 2 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 ofAccording to modeling, crystal growth by short time vapor transport is reasonable under the addition of bromine or TeBr 4 in the temperature range between 650 and 750 °C. Experimental implementation of crystal growth of WTe 2 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.

The tellurides of bismuth and antimony (Bi 2 Te 3 and Sb 2 Te 3 ) are prominent members of the V 2 VI 3 material family that exhibit promising topological properties. We provide a method for the rational synthesis of mixed crystals of these materials ((Bi x Sb 1−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 °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 °C, T 1 = 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 R3̅ m crystal structure, high crystallinity, and overall quality of the synthesized (Bi x Sb 1−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.

No abstract

No abstract