The only commercially available TlInS2 vdW crystals have been synthesized at our facilities through float zone technique. TlInS2 semiconductors belong to the thallium chalcogenides family with the chemical formula TlBX2 (where B=In or Ga, X=S, Se or Te). Members of this family have both layered (TlGaSe2, TlGaS2, TlInS2) and chain (TlInSe2, TlInTe2, TlGaTe2) structures. Stacking of the atoms in TlGaSe2, TlGaS2 and TlInS2 layered crystals is arranged in the form of two twisted anionic layers with the weak bonded Tl(+1) cations located in the trigonal cavities between them. As a result, these crystals exhibit layered structure with weak vdW coupling between the adjacent layers. In particular, TlInS2 is a direct gap semiconductor with optical band gap of 3.5 eV, it exhibits rather novel ferroelectric, ferroelastic behavior. Owing to its crystal structure it is also known to be second harmonic generation (SHG) semiconductor.
Properties of TlInS2 crystals
Raman spectrum of TlInS2 crystals