Structural Changes as a Function of Thickness in [(SnSe)1+..delta..]mTiSe2 Heterostructures

Sage Bauers, Danielle Hamann, Alexander Lygo, Marco Esters, Devin Merrill, Jeffrey Ditto, Duncan Sutherland, David Johnson

Research output: Contribution to journalArticlepeer-review

11 Scopus Citations

Abstract

Single- and few-layer metal chalcogenide compounds are of significant interest due to structural changes and emergent electronic properties on reducing dimensionality from three to two dimensions. To explore dimensionality effects in SnSe, a series of [(SnSe)1+..delta..]mTiSe2 intergrowth structures with increasing SnSe layer thickness (m = 1-4) were prepared from designed thin-film precursors. In-plane diffraction patterns indicated that significant structural changes occurred in the basal plane of the SnSe constituent as m is increased. Scanning transmission electron microscopy cross-sectional images of the m = 1 compound indicate long-range coherence between layers, whereas the m >/= 2 compounds show extensive rotational disorder between the constituent layers. For m >/= 2, the images of the SnSe constituent contain a variety of stacking sequences of SnSe bilayers. Density functional theory calculations suggest that the formation energy is similar for several different SnSe stacking sequences. The compounds show unexpected transport properties as m is increased, including the first p-type behavior observed in (MSe)m(TiSe2)n compounds. The resistivity of the m >/- 2 compounds is larger than for m = 1, with m = 2 being the largest. At room temperature, the Hall coefficient is positive for m = 1 and negative for m = 2-4. The Hall coefficient of the m = 2 compound changes sign as temperature is decreased. The room-temperature Seebeck coefficient, however, switches from negative to positive at m = 3. These properties are incompatible with single band transport indicating that the compounds are not simple composites.
Original languageAmerican English
Pages (from-to)1285-1295
Number of pages11
JournalACS Nano
Volume12
Issue number2
DOIs
StatePublished - 2018

NREL Publication Number

  • NREL/JA-5K00-70991

Keywords

  • heterostructures
  • kinetic products
  • layered compound
  • low-dimensional materials
  • structural distortion
  • tin selenide

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