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Abstract Group IV‐VI van der Waals crystals (MX, where M = Ge, Sn, and X = S, Se) are receiving increasing attention as semiconducting thermoelectric materials with nontoxic, earth‐abundant composition. Among them, SnSe is considered the most promising as it exhibits a remarkably high thermoelectric figure of merit (ZT), initially attributed to its low lattice thermal conductivity. However, it has been shown that the electronic band structure plays an equally important role in thermoelectric performance. A certain band shape, described as a “pudding mold” and characteristic for all MXs, has been predicted to significantly improveZTby combining good electrical conductivity with high Seebeck coefficient. This subtle feature is explored experimentally for GeS, SnS, and SnSe by means of angle‐resolved photoemission spectroscopy. The technique also allows for the determination of the effective mass and Fermi level position of as‐grown undoped crystals. The findings are supported by ab initio calculations of the electronic band structure. The results greatly contribute to the general understanding of the valence band dispersion of MXs and reinforce their potential as high‐performance thermoelectric materials, additionally giving prospects for designing systems consisting of van der Waals heterostructures.
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Electronic structure of designed [(SnSe)1+δ]m[TiSe2]2 heterostructure thin films with tunable layering sequence
A series of $${\left\hbox[ {{{\left\hbox( {{\rm{SnSe}}} \right\hbox)}_{1 \hbox+ \delta }}} \right\hbox]_m}{\left\hbox[ {{\rm{TiS}}{{\rm{e}}_2}} \right\hbox]_2}$$ heterostructure thin films built up from repeating units of m bilayers of SnSe and two layers of TiSe 2 were synthesized from designed precursors. The electronic structure of the films was investigated using X-ray photoelectron spectroscopy for samples with m = 1, 2, 3, and 7 and compared to binary samples of TiSe 2 and SnSe. The observed binding energies of core levels and valence bands of the heterostructures are largely independent of m . For the SnSe layers, we can observe a rigid band shift in the heterostructures compared to the binary, which can be explained by electron transfer from SnSe to TiSe 2 . The electronic structure of the TiSe 2 layers shows a more complicated behavior, as a small shift can be observed in the valence band and Se3 d spectra, but the Ti2 p core level remains at a constant energy. Complementary UV photoemission spectroscopy measurements confirm a charge transfer mechanism where the SnSe layers donate electrons into empty Ti3 d states at the Fermi energy.
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- Award ID(s):
- 1710214
- PAR ID:
- 10100873
- Date Published:
- Journal Name:
- Journal of Materials Research
- Volume:
- 34
- Issue:
- 12
- ISSN:
- 0884-2914
- Page Range / eLocation ID:
- 1965 to 1975
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1557/jmr.2019.128
