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Title: Structural Changes as a Function of Thickness in [(SnSe) 1+δ ] m TiSe 2 Heterostructures

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+δ] mTiSe 2 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(TiSe 2) 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 negativemore » 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.« less
Authors:
ORCiD logo [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [2] ; ORCiD logo [1]
  1. Univ. of Oregon, Eugene, OR (United States)
  2. National Renewable Energy Lab. (NREL), Golden, CO (United States); Univ. of Oregon, Eugene, OR (United States)
Publication Date:
Report Number(s):
NREL/JA-5K00-70991
Journal ID: ISSN 1936-0851
Grant/Contract Number:
AC36-08GO28308
Type:
Accepted Manuscript
Journal Name:
ACS Nano
Additional Journal Information:
Journal Volume: 12; Journal Issue: 2; Journal ID: ISSN 1936-0851
Publisher:
American Chemical Society (ACS)
Research Org:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; heterostructures; kinetic products; layered compound; low-dimensional materials; structural distortion; tin selenide
OSTI Identifier:
1422879