Machine learning assisted understanding of the layer-thickness dependent thermal conductivity in fluorinated graphene.

Manipulating thermal conductivity () plays vital role in high-performance thermoelectric conversion, thermal insulation and thermal management devices. In this work, we using the machine learning-based interatomic potential and the phonon Boltzmann transport equation to systematically investigate layer thickness dependentof fluorinated graphene (FG). We show that the latticeof FG can be significantly decreased with Bernal bilayer stacking.

Anisotropic thermoelectric properties in hydrogenated nitrogen-doped porous graphene nanosheets.

By using density functional theory calculations combined with the nonequilibrium Green's function method and machine learning, we systematically studied the thermoelectric properties of four kinds of porous graphene nanosheets (PGNS) before and after nitrogen doping. The results show that the thermoelectric performance of porous graphene nanosheets along the armchair or zigzag chiral direction is improved due to the dramatically enhanced power factor caused by nitrogen doping. The calculated values of nitrogen-doped porous graphene nanosheets are boosted by about one order of magnitude compared with those of undoped porous graphene nanosheets at room temperature.

Nano-phononic metamaterials enable an anomalous enhancement in the interfacial thermal conductance of the GaN/AlN heterojunction.

Improving the interfacial thermal conductance (ITC) is very important for heat dissipation in microelectronic and optoelectronic devices. In this work, taking GaN-AlN contact as an example, we demonstrated a new mechanism to enhance the interfacial thermal conductance using nano-phononic metamaterials. First, how a superlattice affects the ITC is investigated, and it is found that with decreasing superlattice periodic length, the ITC first decreases and then increases, because of the coherent phonon interference effect.

Tuning interfacial thermal conductance of GaN/AlN heterostructure nanowires by constructing core/shell structure.

The ability to tune the interfacial thermal conductance of GaN/AlN heterojunction nanowires (NWs) with a core/shell structure is shown using molecular dynamics and non-equilibrium Green's functions method. In particular, an increase in the shell thickness leads to a significant improvement of interfacial thermal conductance of GaN/AlN core/shell NWs. At room temperature (300 K), the interfacial thermal conductance of NWs with specific core/shell ratio can reach 0.

Excellent Medium-Temperature Thermoelectric Performance of Monolayer BiOCl.

Recently, a ternary-layered material BiOCl has elicited intense interest in photocatalysis, environmental remediation, and ultraviolet light detection because of its unique band gap of around 3.6 eV, low toxicity, and earth abundance. In particular, Gibson et al.

Enhancement of thermoelectric performance in graphenylene nanoribbons by suppressing phonon thermal conductance: the role of phonon local resonance.

Based on the method of non-equilibrium Green's function, we investigate the thermal transport and thermoelectric properties of graphenylene nanoribbons (GRNRs) with different width and chirality. The results show that the thermoelectric (TE) performance of GRNRs significantly increases with decreasing ribbon width, which stems from the reduction of thermal conductance. In addition, by changing the ribbon width and chirality, the figure of merit (ZT) can be controllably manipulated and maximized up to 0.

Magnetic order-dependent phonon properties in 2D magnet CrI.

We carried out a systematic theoretical study on how spin affects the phononic properties of CrI3 monolayers. We find that the frequencies of two infrared-active (IR) modes are significantly influenced by the magnetic configuration. Thus an IR spectrum may be applied to identify the magnetic order by utilizing the spin-lattice correlation.

KAgX (X = S, Se): High-Performance Layered Thermoelectric Materials for Medium-Temperature Applications.

Monolayer KAgX are a class of novel two-dimensional (2D) layered materials with efficient optical absorption and superior carrier mobility, signifying their potential application prospect in photovoltaic (PV) and thermoelectric (TE) fields. Motivated by the recent theoretical studies on the KAgX monolayer, we carried out systematic investigations on the TE performance of KAgS and KAgSe monolayers, employing density functional theory (DFT) and semiclassical Boltzmann transport equation (BTE). For both KAgSe and KAgS monolayers, large Grüneisen parameters, low group velocities, and short phonon scattering time greatly hinder their heat transport and result in an ultralow thermal conductivity, 0.

α-AgS: A Ductile Thermoelectric Material with High .

Using first-principles calculation and Boltzmann electron/phonon transport theory, we present an accurate theoretical prediction of thermoelectric properties of the α-AgS crystal, a ductile inorganic semiconductor reported experimentally [. 421]. The semiconductor α-AgS has ultralow thermal conductivity associated with high anisotropy, which can be attributed to the complex crystalline structure and weak bonding.

Thermal transport properties in monolayer group-IV binary compounds.

New classes of two-dimensional (2D) materials beyond graphene are now attracting intense interest owing to their unique properties and functions. By combining first-principle calculation and the Boltzmann transport equation, we investigated the thermal transport properties of monolayer honeycomb structures of group-IV (C, Si, Ge, Sn) binary compounds. It is found that the thermal conductivity (κ) of these compounds span an enormously large range from 0.

Probing thermal transport across amorphous region embedded in a single crystalline silicon nanowire.

While numerous studies have been carried out to characterize heat transport behaviours in various crystalline silicon nanostructures, the corresponding characteristics of amorphous one-dimension system have not been well understood. In this study, we amorphize crystalline silicon by means of helium-ion irradiation, enabling the formation of a completely amorphous region of well-defined length along a single silicon nanowire. Heat conduction across both amorphous region and its crystalline/amorphous interface is characterized by an electron beam heating technique with high measurement spatial resolution.

Excellent thermoelectric performance induced by interface effect in MoS/MoSe van der Waals heterostructure.

Herein, thermoelectric properties of MoS/MoSe lateral and van der Waals heterostructure are investigated by using density functional theory calculations and non-equilibrium Green's function method. Compared with pure MoS, the thermoelectric performance of MoS/MoSe lateral heterostructure is significantly improved due to the sharply decreased thermal conductance and slightly reduced power factor. Moreover, the thermoelectric performance can be further improved by constructing MoS/MoSe van der Waals heterostructure.

Monolayer SnP: an excellent p-type thermoelectric material.

Monolayer SnP is a novel two-dimensional (2D) semiconductor material with high carrier mobility and large optical absorption coefficient, implying its potential applications in the photovoltaic and thermoelectric (TE) fields. Herein, we report on the TE properties of monolayer SnP utilizing first principles density functional theory (DFT) together with semiclassical Boltzmann transport theory. Results indicate that it exhibits a low lattice thermal conductivity of ∼4.

Phonon transport in periodically and quasi-periodically modulated cylindrical nanowires.

Phonon transport in periodically modulated cylindrical nanowire (PMCN) and quasi-periodically modulated cylindrical nanowire (QPMCN) is comparatively studied. It is shown that the transmission coefficient and thermal conductance for PMCN is greater than the corresponding values for QPMCN. At low frequencies, a wide stop-frequency gap due to the destructive interference between the incoming and back waves can be clearly observed here.

Effect of electrophilic substitution and destructive quantum interference on the thermoelectric performance in molecular devices.

Using density function theory combined with the non-equilibrium Green's function method, the thermoelectric properties of para-Xylene-based molecular devices are investigated. It is found that destructive quantum interference can be triggered in n-type of para-connected para-Xylene-based molecular device and can obviously enhance the thermoelectric performance of the devices. Moreover, bridge atom electrophilic substitution can significantly improve the thermoelectric properties of p-type monolayer molecular device.

Thermoelectric Properties of Hexagonal M₂C₃ (M = As, Sb, and Bi) Monolayers from First-Principles Calculations.

Hexagonal M₂C₃ compound is a new predicted functional material with desirable band gaps, a large optical absorption coefficient, and ultrahigh carrier mobility, implying its potential applications in photoelectricity and thermoelectric (TE) devices. Based on density-functional theory and Boltzmann transport equation, we systematically research the TE properties of M₂C₃. Results indicate that the Bi₂C₃ possesses low phonon group velocity (~2.

Ab initio study of the moisture stability of lead iodine perovskites.

The stability of hybrid lead iodine perovskite in a humid environment has been a major obstacle to developing long-term photovoltaic devices. However, understanding the detailed degradation mechanism of lead iodine perovskite in moisture is still challenging. Herein, using first-principles calculations, we show that embedded water molecules will facilitate the decomposition of lead iodine perovskite.

Excellent thermoelectric properties induced by different contact geometries in phenalenyl-based single-molecule devices.

We investigated the thermoelectric properties of phenalenyl-based molecular devices by using the non-equilibrium Green's function method combined with density function theory. The results show that the thermoelectric performance of molecular device can be significantly improved by different contact geometries. The ZT value of the device can reach 1.

Excellent Thermoelectric Properties in monolayer WSe Nanoribbons due to Ultralow Phonon Thermal Conductivity.

By using first-principles calculations combined with the nonequilibrium Green's function method and phonon Boltzmann transport equation, we systematically investigate the influence of chirality, temperature and size on the thermoelectric properties of monolayer WSe nanoribbons. The results show that the armchair WSe nanoribbons have much higher ZT values than zigzag WSe nanoribbons. The ZT values of armchair WSe nanoribbons can reach 1.

Conjunction of standing wave and resonance in asymmetric nanowires: a mechanism for thermal rectification and remote energy accumulation.

As an important way to control and manage heat transport, thermal rectification has become an elementary issue in the field of phononics and plays a key role in the designing of thermal devices. Here we investigate systematically the standing wave and the accompanying resonance process in asymmetric nanowires to understand the standing wave itself and its great effect on thermal rectification. Results show that the standing wave is sensitive to both the structural and thermal properties of the material, and its great effect on enhancing the thermal rectification is realized not only by the energy-localization nature of the standing wave, but also by the resonance-caused large amplitude and high energy of the standing wave.

First-Principles Determination of Ultralow Thermal Conductivity of monolayer WSe2.

By using first-principles calculations combined with the phonon Boltzmann transport equation, we systematically investigate the phonon transport of monolayer WSe2. Compared with other 2D materials, the monolayer WSe2 is found to have an ultralow thermal conductivity due to the ultralow Debye frequency and heavy atom mass. The room temperature thermal conductivity for a typical sample size of 1 μm is 3.

Enhancement of thermoelectric performance by reducing phonon thermal conductance in multiple core-shell nanowires.

The thermoelectric properties of multiple core-shell nanowires are investigated by using nonequilibrium Green's function method and molecular dynamics simulations. The results show that the thermoelectric performance of multiple core-shell NWs can be improved observably with the increase of shell number compared with the single component NWs due to the significant reduction of phonon thermal conductance. The ZT value of multiple core-shell NWs can reach three times greater than that of the single component GaSb NWs at room temperature.

[RNAi-mediated knockdown of cyclooxygenase 2 inhibits the growth and migration of SaOS2 human osteosarcoma cells].

Objective: To explore the effects of a knockdown of cyclooxygenase 2 upon the growth and migration of SaOS2 cells.

Methods: We employed lentivirus mediated-RNA interference technology to knockdown the endogenous expression of gene COX-2 in human osteosarcoma cells (SaOS2) and analyzed their phenotypical changes. The effects of COX-2 silencing on the proliferation, cell cycle and migration of SaOS2 cells were assessed by thiazolyl blue tetrazolium bromide, flow cytometry and migration assays respectively.