Adaptive genetic algorithm-based design of gamma-graphyne nanoribbon incorporating diamond-shaped segment with high thermoelectric conversion efficiency

The gamma-graphyne nanoribbons(γ-GYNRs) incorporating diamond-shaped segment(DSSs) with excellent thermoelectric properties are systematically investigated by combining nonequilibrium Green’s functions with adaptive genetic algorithm. Our calculations show that the adaptive genetic algorithm is efficient and accurate in the process of identifying structures with excellent thermoelectric performance. In multiple rounds, an average of 476 candidates(only 2.88% of all16512 candidate structures) are calculated to obtain the structures with extremely high thermoelectric conversion efficiency.The room temperature thermoelectric figure of merit(ZT) of the optimal γ-GYNR incorporating DSSs is 1.622, which is about 5.4 times higher than that of pristine γ-GYNR(length 23.693 nm and width 2.660 nm). The significant improvement of thermoelectric performance of the optimal γ-GYNR is mainly attributed to the maximum balance of inhibition of thermal conductance(proactive effect) and reduction of thermal power factor(side effect). Moreover, through exploration of the main variables affecting the genetic algorithm, it is revealed that the efficiency of the genetic algorithm can be improved by optimizing the initial population gene pool, selecting a higher individual retention rate and a lower mutation rate. The results presented in this paper validate the effectiveness of genetic algorithm in accelerating the exploration of γ-GYNRs with high thermoelectric conversion efficiency, and could provide a new development solution for carbon-based thermoelectric materials.

Excellent thermoelectric performance predicted in Sb_(2)Te with natural superlattice structure

Using first-principles calculations combined with the Boltzmann transport theory,we explore the thermoelectric properties of natural superlattice(SL)structure Sb_(2)Te.The results show that n-type Sb_(2)Te possesses larger Seebeck coefficient of 249.59(318.87)μV/K than p-type Sb_(2)Te of 219.85(210.38)μV/K and low lattice thermal conductivity of 1.25(0.21)W/mK along the in-plane(out-of-plane)direction at 300 K.The excellent electron transport performance is mainly attributed to steeper density of state around the bottom of conduction band.The ultralow lattice thermal conductivity of Sb_(2)Te is mainly caused by low phonon group velocity and strong anharmonicity.Further analysis shows that the decrease of group velocity comes from flatter dispersion curves which are contributed by the Brillouin-zone folding.The strong anharmonicity is mainly due to the presence of lone-pair electrons in Sb_(2)Te.Combining such a high Seebeck coefficient with the low lattice thermal conductivity,maximum n-type thermoelectric figure of merit(ZT)of 1.46 and 1.38 could be achieved along the in-plane and out-of-plane directions at room temperature,which is higher than the reported values of Sb_(2)Te_(3).The findings presented here provide insight into the transport property of Sb_(2)Te and highlight potential applications of thermoelectric materials at room temperature.

Coexistence of giant Rashba spin splitting and quantum spin Hall effect in H–Pb–F

Rashba spin splitting(RSS)and quantum spin Hall effect(QSHE)have attracted enormous interest due to their great significance in the application of spintronics.In this work,we theoretically proposed a new two-dimensional(2D)material H–Pb–F with coexistence of giant RSS and quantum spin Hall effec by using the ab initio calculations.Our results show that H–Pb–F possesses giant RSS(1.21 eV·A)and the RSS can be tuned up to 4.16 e V·A by in-plane biaxial strain,which is a huge value among 2D materials.Furthermore,we also noticed that H–Pb–F is a 2D topological insulator(TI)duo to the strong spin–orbit coupling(SOC)interaction,and the large topological gap is up to 1.35 e V,which is large enough for for the observation of topological edge states at room temperature.The coexistence of giant RSS and quantum spin Hall effect greatly broadens the potential application of H–Pb–F in the field of spintronic devices.

Design of Multichannel Adaptive Filter by Constructing Multidimensional Wiener-Hopf Equation

In the satellite-to-ground high-speed data transmission link,there are signal self-interference problems of symbols in the co-channel,as well as between orthogonal and polarized channels.A multichannel adaptive filter is designed by constructing a multichannel Wiener-Hopf equation,and the influence of five channel nonideal factors is suppressed to improve the BER performance.Experiments show that this method is effective to suppress the signal selfinterference,and the BER floor is optimized from 1E3 to 1E-7.

Space-confined and substrate-directed synthesis of transition-metal dichalcogenide nanostructures with tunable dimensionality

Atomically thin transition-metal dichalcogenide(TMDC) nanostructures are predicted to exhibit novel physical properties that make them attractive candidates for the fabrication of electronic and optoelectronic devices. However, TMDCs tend to grow in the form of two-dimensional nanoplates(NPs) rather than one-dimensional nanoribbons(NRs) due to their native layered structure. Herein, we have developed a space-confined and substrate-directed chemical vapor deposition strategy for the controllable synthesis of WS2, WSe2, MoSe2, MoS2, WS2(1-x)Se2x NPs and NRs. TMDC NRs with lengths ranging from several micrometers to 100 μm have been obtained and the widths of TMDC NRs can be effectively tuned.Moreover, we found that TMDC NRs show different growth behaviors on van der Waals(vdW) and nonvd W substrates. The micro-nano structures, optical and electronic properties of synthesized TMDC NRs have been systematically investigated. This approach provides a general strategy for controllable synthesis of TMDC NRs, which makes these materials easily accessible as functional building blocks for novel optoelectronic devices.

Robust transport of charge carriers in in-plane 1T′-2H MoTe_(2) homojunctions with ohmic contact

Metal-semiconductor ohmic contacts are required to reduce the energy dissipation for two-dimensional (2D) electronic devices, and phase engineering of 2D transition-metal dichalcogenides (TMDCs) is a promising approach for building ohmic contacts. Here, 2D in-plane 1T′-2H MoTe2 homojunctions were prepared by direct epitaxy via vapor deposition. The interface properties of in-plane 1T′-2H MoTe2 homojunction were investigated in detail by combining experiments, calculations and theories. The ohmic contact properties of 1T′-2H MoTe2 homojunction were proved according to Kelvin force probe microscopy and density functional theory calculations. The charge carriers robust transport in in-plane 1T′-2H MoTe2 homojunction without Fermi-level pinning can be well described by Poisson equation and band alignment. These results indicate that phase engineering of 2D TMDCs is promising to construct ohmic contacts for device applications.