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Enhanced Cross-plane Thermoelectric Transport of Rotationally-disordered SnSe2 via Se Vapor Annealing.

A new interesting article has been published in Nano Lett. 2018 Oct 19. doi: 10.1021/acs.nanolett.8b02744. [Epub ahead of print] and titled:

Enhanced Cross-plane Thermoelectric Transport of Rotationally-disordered SnSe2 via Se Vapor Annealing.

Authors of this article are:

Chen J, Hamann DM, Choi DS, Poudel N, Shen L, Shi L, Johnson DC, Cronin SB.

A summary of the article is shown below:

We report cross-plane thermoelectric measurements of SnSe and SnSe2 films grown by the modulated element reactant (MER) approach. These materials exhibit ultra-low cross-plane thermal conductivities, which are advantageous for thermoelectric energy conversion. The initially grown SnSe films have relatively low Seebeck coefficients (-38.6 μV/K) due to significant unintentional doping that originates from Se vacancies when annealed in nitrogen, as a result of the relatively high vapor pressure of Se. By performing post-growth annealing at a fixed Se partial pressure (300°C for 30 minutes using SnSe2 as the Se source in a sealed tube), a transition from SnSe-to-SnSe2 is induced, which is evidenced by clear changes in the X-ray diffraction patterns of the films. This results in a 16-fold increase in the cross-plane Seebeck coefficient (from -38.6 to -631μV/K) after Se annealing due to the SnSe-to-SnSe2 transition and mitigation of unintentional doping by Se vacancies. We also observe a corresponding 6-fold drop in the electrical conductivity (from 3S/m to 0.5S/m) after Se annealing, which is consistent with both a drop in the carrier concentration and an increase in band gap. The power factor S2σ increased by 44X (from 4.5 nW/m·K2 to 0.2 μW/m·K2) after Se annealing. We believe that these results demonstrate a robust method for mitigating unintentional doping in a promising class of materials for thermoelectric applications. Keywords: tin diselenide, nanoscale, energy conversion, van der Waals, 2D materials.

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