27 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
Engineering vacancy and hydrophobicity of two-dimensional TaTe2 for efficient and stable electrocatalytic N2 reduction
Demand for ammonia continues to increase to sustain the growing global population. The direct electrochemical N2 reduction reaction (NRR) powered by renewable electricity offers a promising carbon-neutral and sustainable strategy for manufacturing NH3, yet achieving this remains a grand challenge. Here, we report a synergistic strategy to promote ambient NRR for ammonia production by tuning the Te vacancies (VTe) and surface hydrophobicity of two-dimensional TaTe2 nanosheets. Remarkable NH3 faradic efficiency of up to 32.2% is attained at a mild overpotential, which is largely maintained even after 100 h of consecutive electrolysis. Isotopic labeling validates that the N atoms of formed NH4+ originate from N2. In situ X-ray diffraction indicates preservation of the crystalline structure of TaTe2 during NRR. Further density functional theory calculations reveal that the potential-determining step (PDS) is ∗NH2 + (H+ + e–) → NH3 on VTe-TaTe2 compared with that of ∗ + N2 + (H+ + e–) → ∗N–NH on TaTe2. We identify that the edge plane of TaTe2 and VTe serve as the main active sites for NRR. The free energy change at PDS on VTe-TaTe2 is comparable with the values at the top of the NRR volcano plots on various transition metal surfaces
Accurate reconstruction in digital holographic microscopy using antialiasing shift-invariant contourlet transform
Modeling and analysis of sub-aperture tool influence functions for polishing curved surfaces
Low lattice thermal conductivity of stanene
A fundamental understanding of phonon transport in stanene is crucial to predict the thermal performance in potential stanene-based devices. By combining first-principle calculation and phonon Boltzmann transport equation, we obtain the lattice thermal conductivity of stanene. A much lower thermal conductivity (11.6 W/mK) is observed in stanene, which indicates higher thermoelectric efficiency over other 2D materials. The contributions of acoustic and optical phonons to the lattice thermal conductivity are evaluated. Detailed analysis of phase space for three-phonon processes shows that phonon scattering channels LA + LA/TA/ZA TA/ZA are restricted, leading to the dominant contributions of high-group-velocity LA phonons to the thermal conductivity. The size dependence of thermal conductivity is investigated as well for the purpose of the design of thermoelectric nanostructures