Strain Tunable Thermoelectric Material: Janus ZrSSe Monolayer.

Thermoelectric (TE) performance of the Janus ZrSSe monolayer under biaxial strain is systematically explored by the first-principles approach and Boltzmann transport theory. Our results show that the Janus ZrSSe monolayer has excellent chemical, dynamical, thermal, and mechanical stabilities, which provide a reliable platform for strain tuning. The electronic structure and TE transport parameters of the Janus ZrSSe monolayer can be obviously tuned by biaxial strain. Under 2% tensile strain, the optimal power factor PF of the n-type-doped Janus ZrSSe monolayer reaches 46.36 m W m-1 K-2 at 300 K. This value is higher than that of the most classical TE materials. Under 6% tensile strain, the maximum ZT values for the p-type- and n-type-doped Janus ZrSSe monolayers are 4.41 and 4.88, respectively, which are about 3.83 and 1.49 times the results of no strain, respectively. Such high TE performance can be attributed to high band degeneracy and short phonon relaxation time under strain, causing simultaneous increase of the Seebeck coefficient and suppression of the phonon thermal transport. Present work demonstrates that the Janus ZrSSe monolayer is a promising candidate as a strain-tunable TE material and stimulates further experimental synthesis.

First-principle study of neutron irradiation induced performance degradation of amorphous porous silica.

Neutron irradiation induced degradation of porous silica film is studied by Molecular Dynamics and Density-Functional theory-based methods. The degradation of microscopic structure, thermal property, and optical property of porous silica film are systematically investigated. Low-energy recoil is used to simulate the neutron irradiation effect. The pair and bond angle distributions, and coordination number distributions reveal that, under neutron irradiation, the microscopic structure of porous silica film is obviously modified, and the coordination defects are induced. We find that the higher recoil energy, the more coordination defects are formed in the film. The increased defects lead to a decrease in thermal conductivity. In addition, neutron irradiation induces additional optical absorption peaks in UV region and increasement in refractive index, resulting in a noticeable reduction in light transmittance. The detailed calculation of density of states reveals that these optical absorption peaks originate from the irradiation induced defect states in band gap. Our work shows that low-energy neutron irradiation can induce obvious defect density and degrade thermal and optical properties of porous silica film, which are responsible for subsequent laser-induced damage.

Strong UV laser absorption source near 355 nm in fused silica and its origination.

As a high-performance optical material, fused silica is widely applied in high-power laser and photoelectric systems. However, laser induced damage (LID) of fused silica severely limits the output power and performance of these systems. Due to the values in strong field physics and improving the load capacity and performance of high power systems at UV laser, LID at 355 nm of fused silica has attracted much attention. It has been found that, even be treated by advanced processing technologies, the actual damage threshold of fused silica at 355 nm is far below the intrinsic threshold. It means that there is an absorption source near 355 nm in fused silica. However, to date, the absorption source is still unknown. In this paper, a absorption source near 355 nm is found by first-principles calculations. We find that the absorption source near 355 nm is neutral oxygen-vacancy defect (NOV, ≡Si-Si≡) and this defect originates from the oxygen deficiency of fused silica. Our results indicate that NOV defect can be taken as a damage precursor for 355 nm UV laser, and this precursor can be obviously reduced by increasing the ratio of oxygen to silicon. Present work is valuable for exploring damage mechanisms and methods to improve the damage threshold of fused silica at UV laser.

Boosting thermoelectric performance of HfSe2 monolayer by selectivity chemical adsorption.

In this work, a strategy to boosting thermoelectric (TE) performance of 2D materials is explored. We find that, appropriate chemical adsorption of atoms can effectively increase the TE performance of HfSe2 monolayer. Our results show that the adsorption of Ni atom on HfSe2 monolayer (Ni-HfSe2) can improve the optimal power factor PF and ZT at 300 K, increased by more than ∼67% and ∼340%, respectively. The PF and ZT of Ni-HfSe2 at 300 K can reach 85.06 mW m-1 K-2 and 3.09, respectively. The detailed study reveal that the adsorption of Ni atom can induce additional conductional channels of electrons, enhance the coupling of acoustic-optical phonons and the phonon anharmonicity, resulting in an obvious increment of electrical conductivity (increased by more than ∼89%) in n-type doped system and an ultralow phonon thermal conductivity (1.17 W/mK at 300 K). The high electrical conductivity and ultralow phonon thermal conductivity results in the significant increments of PF and ZT. Our study also shows that, Ni-HfSe2 is a thermal, dynamic and mechanical stable structure, which can be employed in TE application. Our research indicates that selectivity chemical adsorption is a promising way to increase TE performance of 2D materials.