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Chemical vapor transport (CVT)

Chemical vapor transport represents the standard technique to grow crystalline bulk transition metal dichalcogenides (TMDC's). The starting materials for the crystal growth (high purity transition metal T and chalcogen X) are filled with stoichiometric composition using a slight chalcogen excess into a quartz ampoule together with a transport agent (here iodine J). The ampoule is introduced into a furnace with a temparature gradient T and T-DT (see Fig. 1).


 

Figure 1: Schematic plot of chemical vapor transport.

In the hotter region of the ampoule with temperature T, the starting materials form the gases TJ4 and X which react in the cooler part with temperature T-DT growing crystalline bulk TMDC's via the following equation

TJ4 + 2X <-> TX2 + 2J2 .

Figure 2 shows the TMDC crystal TiS2 grown by CVT.

Figure 2: TiSe2 crystal grown by CVT (scale in cm).

Giving an additional material M into the ampoule such as Pb or Sn, chemical vapor transport also allows to grow bulk misfit layer compounds MX[TX2]m (m = 1,2,3).


 

Figure 3: A CVT grown misfit layer compound (PbSNbS2 ).


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