The utility of molecular precursors to create thin-film
components
for constructing van der Waals heterostructures was explored by studying
the layered Tm(II) compound [(THF)Cs(μ-η5:η5-Cp′)3TmII]
n
(Cp′ = C5H4SiMe3).
This compound, synthesized by the reduction of Cp′3TmIII with metallic cesium, crystallizes as layers of
hexagonal nets composed of Tm(II) ions and Cs(I) ions at alternating
vertices, bridged by Cp′ ligands. Full characterization of
the compound, including SQUID magnetometry, was consistent with 4f13 Tm(II). Though the triangular orientation of S = 1/2 Tm(II) ions in the layered structure indicated a potential
environment for spin frustration, the SQUID data suggest these metal
centers lack enough interaction to enforce such behavior. Successful
exfoliation of the air- and moisture-sensitive single crystals was
achieved in a glovebox at low temperatures to yield thin films. These
could be stacked under hexagonal boron nitride to create an air-stable
van der Waals heterostructure, which allowed analysis by AFM to determine
a thickness of approximately 50 layers for the covered Tm-containing
structure.