94 research outputs found
Thermal conductivity of monolayer MoS2, MoSe2, and WS2: Interplay of mass effect, interatomic bonding and anharmonicity
Phonons are essential for understanding the thermal properties in monolayer
transition metal dichalcogenides, which limit their thermal performance for
potential applications. We investigate the lattice dynamics and thermodynamic
properties of MoS2, MoSe2, and WS2 by first principles calculations. The
obtained phonon frequencies and thermal conductivities agree well with the
measurements. Our results show that the thermal conductivity of MoS2 is highest
among the three materials due to its much lower average atomic mass. We also
discuss the competition between mass effect, interatomic bonding and anharmonic
vibrations in determining the thermal conductivity of WS2. Strong covalent W-S
bonding and low anharmonicity in WS2 are found to be crucial in understanding
its much higher thermal conductivity compared to MoSe2.Comment: 19 pages, 7 figure
Possible atomic structures for the sub-bandgap absorption of chalcogen hyperdoped silicon
Single-crystal silicon wafers were hyperdoped respectively by sulfur,
selenium, and tellurium element using ion implantation and nanosecond laser
melting. The hyperdoping of such chalcogen elements endowed the treated silicon
with a strong and wide sub-bandgap light absorptance. When these hyperdoped
silicons were thermally annealed even at low temperatures (such as 200~400 oC),
however, this extra sub-bandgap absorptance began to attenuate. In order to
explain this attenuation of absorptance, alternatively, we consider it
corresponding to a chemical decomposition reaction from optically absorbing
structure to non-absorbing structure, and obtain a very good fitting to the
attenuated absorptances by using Arrhenius equation. Further, we extract the
reaction activation energies from the fittings and they are 0.343(+/- 0.031) eV
for S-, 0.426(+/-0.042) eV for Se-, and 0.317(+/-0.033) eV for Te-hyperdoped
silicon, respectively. We discuss these activation energies in term of the bond
energies of chalcogen-Si metastable bonds, and finally suggest that several
high-energy interstitial sites instead of the substitutional site, are very
possibly the atomic structures that are responsible for the sub-bandgap
absorptance of chalcogen hyperdoped silicon.Comment: 18 pages, 3 figures, 1 tabl
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