Chalcogenoether complexes of Nb(v) thio- and seleno-halides as single source precursors for low pressure chemical vapour deposition of NbS₂ and NbSe₂ thin films

Abstract

. The thin films were characterised by grazing incidence and in-plane XRD, pole figure analysis, scanning electron microscopy and energy dispersive X-ray analysis.

Chalcogenoether complexes of tantalum(V) sulfide trichloride – Synthesis, properties and structures

“…equivalent of the dithioethers PhSCH2CH2SPh, MeSCH2CH2SMe, 17, Cl2−Ta1−S3 = 167.641 (17), S3−Ta1−S2 = 78.929 (14), S1−Ta1−Cl1 = 98.236 (17), S1−Ta1−Cl3 = 97.905 (18), S1−Ta1−Cl2 = 103.941 (19), S1−Ta1−S2 = 165.867 (16), S1−Ta1−S3 = 87.635 (17). The spectroscopic data are similar to those reported for the corresponding niobium systems [8].…”

“…The solid complexes also darken and become sticky over time in the glove box. Similar colour variation has been observed in the NbSCl3 systems[7,8,21] and was attributed to the presence of small amounts of disulfide([S2]2-) ligands in some samples, formed by a redox-disproportionation reaction, and formation of complexes such as [Nb2Cl4S3(tht)4] (tht = tetrahydrothiophene) [7]. Similar disulfide species have not been identified thus far in the tantalum thiochloride systems, but this appears a likely explanation for the colour variation in the complexes reported here.…”

“…Introducing tantalum in place of niobium has the obvious consequence of increasing the molecular weight of the corresponding complex by 88 a.m.u.. However, this is unlikely to be the major cause of the failure of the Ta(V) complexes to function as CVD reagents for TaS2, since, based upon the coordination chemistry, the TaOCl3 and TaSCl3 complexes generally appear to be significantly less stable than the niobium analogues, reflecting the harder Lewis acidity of Ta(V) [4,6,7,8,10].…”

“…Thus, [NbCl5(E n Bu2)] produced thin films of the 3R-polytype (R3mh) of NbS2 and NbSe2; the butyl-substituents provide a β-hydride decomposition route facilitating cleavage of the ligands in an accessible temperature range. Similar LPCVD experiments using the niobium sulfide trichloride complexes, [NbSCl3(S n Bu2) and [NbSCl3{ n BuS(CH2)3S n Bu}], produced 3R-NbS2, whilst [NbSe2Cl3(Se n Bu2)] produced 2H-NbSe2 thin films [8]. On the other hand, none of the corresponding tantalum complexes were found to be suitable LPCVD reagents, and single source precursors to TaE2 remain to be developed.…”

“…The early 4d and 5d metals in their higher oxidation states form sulfide and selenide halides which are modest Lewis acids, forming complexes with neutral ligands from groups 15 and 16, although they have received much less study than the corresponding oxide halides [1,2,3]. The TaECl3 (E = S, Se) were first obtained some 50 years ago by reaction of TaCl5 with Sb2E3 or Bi2E3 in CS2 [3,4] but in marked contrast to the NbECl3 [5,6,7,8], have been little studied, and the structures of the TaECl3 species appear to be unknown. A very small number of complexes of TaECl3 have inorganic analogues of graphene and their band gaps and other properties for various applications can be tuned by varying the chalcogen or the metal [11], [12].…”