Thermally Strain-Induced Band Gap Opening on Platinum
Diselenide-Layered Films: A Promising Two-Dimensional Material with
Excellent Thermoelectric Performance
posted on 2021-05-05, 13:03authored byTeng-Yu Su, Te-Hsien Wang, Deniz P. Wong, Yi-Chung Wang, Angus Huang, Ying-Chun Sheng, Shin-Yi Tang, Tsu-Chin Chou, Ta-Lei Chou, Horng-Tay Jeng, Li-Chyong Chen, Kuei-Hsien Chen, Yu-Lun Chueh
In this work, we, for the first time, observed the remarkable thermoelectric
properties of a few high-quality PtSe2 layered films fabricated
by a post selenization of Pt thin films. An excellent power factor
of ≳200 μW/mK2 with a Seebeck coefficient
of >100 μV/K in the PtSe2 layered film of 10 layers
can be experimentally demonstrated over a wide temperature range,
which is much better than those of most of the two-dimensional materials
reported in the literature. Optical absorption spectra and DFT (density
functional theory) calculations indicate a semiconductor–metal
transition at a critical thickness once the thickness increases from
7.7 (15 layers) to 14.3 nm (30 Layers). The results are consistent
with the experimental results of the dramatic reduction in the power
factor, the magnitude of the Seebeck coefficient, and the resistivity
when the thickness increases from 7.7 (15 layers) to 14.3 nm (30 Layers).
Nevertheless, the semiconductor–metal transition would occur
when the thickness increases from 1.5 nm (3 layers) to 2 nm (4 layers).
To figure out this unusual performance, a detailed material examination
has been conducted. After the transmission electron microscopy examination,
∼7% biaxial compressive strain built in the polycrystalline
PtSe2 thin film can be observed. The strain, as revealed
by our DFT calculations, plays an important role in opening the electronic
energy gap and hence significantly improves the thermoelectric performance.
Boltzmann transport calculation results suggested that both the strain
and the hole concentration in the p-type specimens are well optimized.
We further propose that an even better power factor can be achieved
with n-type-doped PtSe2.