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POP scattering is the dominant factor limiting the electron mobility for 2D Ga2O3, accompanied by a large ‘ion-clamped’ dielectric constant.

A deep learning potential distinct from the empirical potential is developed for the study of thermal transport across solid–liquid interfaces.

Increasing power density and miniaturization in 3D packaged power electronics demand innovative thermal management. Yet, the thermal performance of electrically insulated packages for power electronics is currently limited by the ultralow thermal conductivity of conventional thermal interface materials (TIMs) and their poor ability of directing heat to heat sink. Herein, we have prepared highly thermally conductive and electrically insulating TIMs composite based on boron nitride nanobars (BNNB). The polar characteristics of B-N bond in the BNNB outer tube wall-derived h-BN nanosheets facilitates the adsorption of magnetic particles. Modulating the arrangement of 3D-BNNB by an external magnetic field improves the thermal conductivity of composite up to 3.3 W m-1 K-1 at a concentration of 40 wt%, 17.8 times higher than the pure epoxy and also exhibiting significant anisotropy. Moreover, the composite shows a high stiffness of 510 MPa and a high resistivity of 27.2 MΩ·cm, demonstrating excellently mechanical and electrically insulating characteristics. Infrared thermography results show that the surface temperature of the composite depends on the orientation of BNNB and its interfacial interaction with the epoxy resin. The magnetic field-oriented modulation of 3D-BNNB can offer a promising solution to achieve the efficient thermal management of 3D integrated power packaging.

The hidden Rashba effect emerges in centrosymmetric rock-salt MTe and improves thermoelectric performance due to the local Te off-centering distortion.

In this paper, an ultra-high sensitivity MAPbBr3/NP GaN hybrid structure device was fabricated for the first time with a high current on/off ratio of about 5000 and fast response speeds of 0.21/0.44 s.

Most of the current predictions of the radiative properties of microalgae use the homogeneous sphere approximation based on the Mie scattering theory, and the refractive indices of the model were regarded as fixed values. Using the recently measured optical constants of various microalgae components, we propose a spherical heterogeneous model for spherical microalgae. The optical constants of the heterogeneous model were characterized by the measured optical constants of microalgae components for the first time. The radiative properties of the heterogeneous sphere were calculated using the T-matrix method and were well verified by measurements. It shows that the internal microstructure has a more significant effect on scattering cross-section and scattering phase function than absorption cross-section. Compared with the traditional homogeneous models selected with fixed values as refractive index, the calculation accuracy of scattering cross-section of the heterogeneous model improved by 15%-150%. The scattering phase function of the heterogeneous sphere approximation agreed better with measurements than the homogeneous models due to the more detailed description of the internal microstructure. It can be concluded that considering the internal microstructure of microalgae and characterizing the microstructure of the model by the optical constants of the microalgae components helps to reduce the error caused by the simplification of the actual cell.

Ferroelectric BaTiO3 with an electric-field-switchable spontaneous polarization has attracted wide attention in photovoltaic applications due to its efficient charge separation for photoexcitation. The evolution of its optical properties with rising temperature especially across the ferroelectric-paraelectric phase transition is critical to peer into the fundamental photoexcitation process. Herein, by combining spectroscopic ellipsometry measurements with first-principles calculations, we obtain the UV-Vis dielectric functions of perovskite BaTiO3 at temperatures varying from 300 to 873 K and provide the atomistic insights into the temperature-driven ferroelectric-paraelectric (tetragonal-cubic) structural evolution. The main adsorption peak in dielectric function of BaTiO3 is reduced by 20.6% in magnitude and redshifted as temperature increases. The Urbach tail shows an unconventional temperature-dependent behavior due to the microcrystalline disorder across the ferroelectric-paraelectric phase transition and the decreased surface roughness at around 405 K. From ab initio molecular dynamics simulations, the redshifted dielectric function of ferroelectric BaTiO3 coincidences with the reduction of the spontaneous polarization at elevated temperature. Moreover, a positive (negative) external electric field is applied which can modulate the dielectric function of ferroelectric BaTiO3 blueshift (redshift) with a larger (smaller) spontaneous polarization since it drives the ferroelectric further away from (closer to) the paraelectric structure. This work sheds light on the temperature-dependent optical properties of BaTiO3 and provides data support for advancing its ferroelectric photovoltaic applications.

GeTe has become a high-performance thermoelectric material with a figure of merit (ZT) over two through alloying and band engineering strategies. Yet, the question on how to effectively engineer the electronic band structure of GeTe toward achieving a better thermoelectric performance still cannot be clearly answered, and its underlying physics has not been well understood. Here, we manipulate the lattice structure of GeTe via modifying the lattice parameters, interaxial angles and reciprocal displacements, and investigate their influence on the electronic band structure and thermoelectric properties using first-principles calculations. The calculation results show that the reciprocal displacement directly manipulates the energy level of the L-band and the Z-band, resulting in an indirect–direct transition of the band gap and a strong Rashba effect. Modifications of lattice parameters and interaxial angles can affect band gaps, band convergence and density of states, which are crucial to determining thermoelectric performance. This work performs a systematic study on how the lattice structure manipulation influences the electronic band structure and thermoelectric properties of GeTe, and can provide a clear route to further enhance its ZT.

Acute radiation enteritis (ARE) is a common complication with radiotherapy for pelvic and abdominal malignancy. This research is designed to investigate the efficacy of Tong-Xie-Yao-Fang (TXYF) on ARE and to explore the underlying mechanisms by microarray analysis. The ARE rat model was established by a single abdominal irradiation with a gamma-ray dose of 10 Gy. Next, the ARE rats were treated with distilled water, TXYF, and glutamine by gavage for 7 consecutive days according to the scheduled groups. For each group, the jejunal tissue was taken at 6 h after gastric lavage. The morphology of intestinal tissue was observed by hematoxylin and eosin (H&E) stain under a light microscope. The height of the villus and the thickness of the whole layer of the TXYF-treated groups were significantly ameliorative than that of the model control group. The transcriptome analysis was produced using the Agilent SurePrint G3 Rat GE V2.0 microarray. A total of 90 differentially expressed genes (DEGs), including 48 upregulated genes and 42 downregulated genes, were identified by microarray and bioinformatics analysis. Protein–protein interaction (PPI), Gene Ontology (GO), and Kyoto Encyclopedia of Genes and Genomes (KEGG) were conducted to explore the possible mechanisms of DEGs taking part in the TXYF-mediated therapeutic process for ARE. In conclusion, we reveal that TXYF has a protective effect on the intestinal tissue of rats with ARE and summarize several DEGs, suggesting the possible mechanisms of TXYF-mediated efficacy for ARE.

The impact of increased shading stress on agronomic traits, photosynthetic performance and antioxidants activities in leaves of two soybeans cultivars (D16 and E93) was studied. Soybean seedlings were grown in pots and exposed to no shade (S0), slight shade (S1), moderate shade (S2), and heavy shade (S3). Our findings showed that under the S3 in both cultivars, leaf fresh weight (LFW), specific leaf area (SLA) and leaf thickness decreased significantly, accompanied by a reduction in photochemical parameters including the maximum quantum yield (Fv/Fm) and electron transport rate (ETR). Furthermore, compared to S0, S1 significantly increased the ETR, sucrose content and the activity of catalase (CAT) in both D16 and E93 cultivars while S2 and S3 decreased the activity. However, under all treatments of shading stress, the antioxidant activities of superoxide dismutase (SOD) and peroxidase (POD) were lowered in both cultivars. Such morphological and physiological plasticity to adapt S1 compensates for the decrease in biomass and leads to seed weight compared to that obtained with an amount of normal light. Through configuring the space in the intercropping systems, S1 could be helpful for optimum growth and yield. Redesigning photosynthesis through S1 for the intercropping systems could be a smart approach.

The prototype phonon-liquid electron-crystal β-Cu2Se has been ranked among the best thermoelectric material with its ultralow lattice thermal conductivity (κL). The atomic fluidity, harmonic approximation failure, and the existence of a large number of imaginary phonon modes hinder the atomistic analysis of phonon transport in β-Cu2Se. Thus, the atomistic origins of its ultralow κL remain elusive. In this study, we present a self-consistent phonon (SCPH) calculation of the lattice dynamical properties of β-Cu2Se by including quartic anharmonicity and stiffening imaginary phonon modes in the anharmonic phonon dispersion, aiming to unravel the atomistic origins of ultralow κL. Upon renormalizing harmonic phonon dispersion with quartic anharmonicity, those imaginary phonon modes arising from copper fluidity diminish as temperature increases and anharmonic phonon dispersions are obtained. By solving the Boltzmann transport equation within the relaxation time approximation (BTE-RTA), we predicted ultralow κL which demonstrated an overall agreement with previous experiments. After analyzing the harmonic as well as anharmonic phonon density of states, it was found that the inclusion of quartic anharmonicity induces the suppression of low-lying phonon modes, which coincides with the experimental observation of the selective breakdown of long-wave transverse acoustic phonons. However, for the propagative heat-carriers, the anharmonic scattering enhances and phonon relaxation lifetime decreases as temperature increases, leading to a further reduction of κL. This study provides an extra insight into the atomistic origins of ultralow κL in β-Cu2Se from first-principles anharmonic force constants and helps engineer the lattice dynamical properties for better thermoelectric performance.

The optical properties of biochemical compositions of microalgae are vital for the improvement of biosensor design, photobioreactor design, biofuel, and biophotonics techniques. A combination method using both the double optical pathlength transmission method (DOPTM) and the ellipsometry method (EM) is called DOPTM-EM, and it is used to acquire the optical constants of protein, lipid, and carbohydrate of Haematococcus pluvialis, Nannochloropsis sp., and Spirulina in both a solid state and a solution state within the visible and near-infrared spectral range. For different types of microalgae, the refractive indices of protein and carbohydrate in the solid state are similar to each other, but show an observed difference from lipid in the solid state. The refractive indices of protein and carbohydrate in the solution state presents a visible distinction in the researched spectral range. The absorption indices of protein, lipid, and carbohydrate in the solid state for these three types of microalgae are close to each other in the spectral range of 300–500 nm. However, an observed difference is shown in the spectral range of 500–1700 nm. For ease of application, the refractive index of biochemical composition of microalgae was fitted based on the Sellmeier equation. We believe this work can provide a reference to obtain the optical properties of biomaterial with high accuracy.

GeTe has become a high-performance thermoelectric material with a figure of merit (

The third-generation wide bandgap semiconductor GaN currently occupies a hot spot in the fields of high-power electronics and optoelectronics. Fully exploring its optical and optoelectronic characteristics is of great significance. Here, we provide a systematic study on the temperature-dependent dielectric functions of GaN grown by metal-organic chemical vapor deposition in the spectral range of 0.73–5.90 eV via spectroscopic ellipsometry experiments and first-principles calculations. Ellipsometric measurements identify two typical absorption peaks that originate from the excitonic and phonon-assisted indirect absorption process, respectively. To explore the underlying physics, we perform first-principles calculations using the independent-particle approximation, model Bethe–Salpeter equation (mBSE), and phonon-assisted indirect absorption process (Inabs). In comparison with ellipsometric measurements, the mBSE calculation determines the absorption peak contributed by the many-body excitonic effect, while the Inabs calculation successfully predicts the second absorption peak. When heating the crystal, it observes the redshift and weakening of absorption peaks, intrinsically due to the nontrivial electron–phonon interaction as lattice vibration strengthens. While doping GaN with Fe or Si elements, the introduced free carriers modify the electronic interband transition. As the temperature increases, more free carriers are excited, and the temperature influence on the absorption peak is more significant than that of the undoped one. This work fully explores the physical origins of the temperature and doping effect on UV–Vis dielectric functions of GaN, aiming to promote its application in the fields of high-power electronic devices.

Perovskite

LiCoO2 is the prototype cathode in lithium ion batteries. It adopts a crystal structure with alternating Li+ and CoO2- layers along the hexagonal axis. It is well established that ionic and electronic conduction is highly anisotropic; however, little is known regarding heat transport. We analyse the phonon dispersion and lifetimes of LiCoO2 using anharmonic lattice dynamics based on quantum chemical force constants. Around room temperature, the thermal conductivity in the hexagonal ab plane of the layered cathode is ≈ 6 times higher than that along the c axis based on the phonon Boltzmann transport. The low thermal conductivity (< 10Wm-1K-1) originates from a combination of short phonon lifetimes associated with anharmonic interactions between the octahedral face-sharing CoO2- networks, as well as grain boundary scattering. The impact on heat management and thermal processes in lithium ion batteries based on layered positive electrodes is discussed.

The accurate representation of optical and electrical properties of MAX phase ternary carbide Ti2AlC and its derivative two-dimensional MXenes at finite temperature is crucial to render their applications in electrodes and photocatalysis. With the assumption of empirical electron scattering rate, however, previous works fails to accurately predict their optical and electrical properties. In this work, we start from calculating the electron-phonon interactions to accurately obtain electron scattering rate and then use them to obtain optical and electrical properties of Ti2AlC and two-dimensional MXenes from fully first-principles without empirical parameters. By combining the electron-phonon interaction with semiclassical Boltzmann transport theory, the electronic resistivity at finite temperature was calculated. And the dielectric function was computed by superimposing the intraband and interband transition, with the electron scattering rate obtained from solving electron-phonon coupling. The calculated resistivity and dielectric function of Ti2AlC were compared with available experimental results in literature, and demonstrate an overall good agreement. The calculated electrical and optical properties of MXenes show strong dependence on the surface terminated groups. When terminated with F or OH, the 2D MXenes shows metallic properties with good conducting ability, while Ti2CO2 exhibits semiconducting property. The results obtained from this work help to advance 2D MXenes in the applications such as transparent electrodes and photocatalysis.

Alloying Ga2O3 with Al2O3 yields diverse structural phases with distinctive optoelectronic properties, making them promising candidates for ultrawide bandgap semiconductors in next-generation power electronics. Yet, there is a lack of sound knowledge of the carrier dynamics in the (AlxGa1−x)2O3 alloys due to their structural complexity. Herein, we focus on the ordered β-(AlxGa1−x)2O3 alloys, predict their carrier mobility, and determine the intrinsic electron mobility limit based on solving linearized Boltzmann transport equations from first principles. The predicted electron mobility for ordered β-(Al0.25Ga0.75)2O3 and β-(Al0.5Ga0.5)2O3 alloys at 300 K, respectively, is 103.6 and 80.60 cm2/V s, demonstrating excellent agreement with literature experiments. Such low electron mobility is limited by the intrinsically strong polar optical phonon (POP) scattering process. As the Al content further increases, the alloy's electron mobility further reduces mainly due to the enlarged Pauling ionicity, Fröhlich coupling constant, and POP scattering. This work provides physical insight into the carrier dynamics in ordered β-(AlxGa1−x)2O3 alloys and seeks to improve the electron mobility for potential applications in high-power electronics.

It contains details about computational details, the change of critical parameters describing the four Gaussian and one Psemi-Tri oscillators for the pristine SrTiO3 with increasing temperature, and temperature-dependent dielectric function of 0.5 %

The prototype phonon-liquid electron-crystal β-Cu2Se has been ranked among the best thermoelectric material with its ultralow lattice thermal conductivity (κL). The atomic fluidity, harmonic approximation failure, and the existence of a large number of imaginary phonon modes hinder the atomistic analysis of phonon transport in β-Cu2Se. Thus, the atomistic origins of its ultralow κL remain elusive. In this study, we present a self-consistent phonon (SCPH) calculation of the lattice dynamical properties of β-Cu2Se by including quartic anharmonicity and stiffening imaginary phonon modes in the anharmonic phonon dispersion, aiming to unravel the atomistic origins of ultralow κL. Upon renormalizing harmonic phonon dispersion with quartic anharmonicity, those imaginary phonon modes arising from copper fluidity diminish as temperature increases and anharmonic phonon dispersions are obtained. By solving the Boltzmann transport equation within the relaxation time approximation (BTE-RTA), we predicted ultralow κL which demonstrated an overall agreement with previous experiments. After analyzing the harmonic as well as anharmonic phonon density of states, it was found that the inclusion of quartic anharmonicity induces the suppression of low-lying phonon modes, which coincides with the experimental observation of the selective breakdown of long-wave transverse acoustic phonons. However, for the propagative heat-carriers, the anharmonic scattering enhances and phonon relaxation lifetime decreases as temperature increases, leading to a further reduction of κL. This study provides an extra insight into the atomistic origins of ultralow κL in β-Cu2Se from first-principles anharmonic force constants and helps engineer the lattice dynamical properties for better thermoelectric performance.

Polar wurtzite GaN can host surface phonon-polaritons (SPHPs) along its bulk surface and achieve sub-diffraction confinement with an ultralow optical loss and has emerged as a relevant technological material for infrared nanophotonics. Yet, few studies have reported on the temperature-dependent infrared dielectric functions, lattice vibration's influence on the hybrid phonon-polaritons, and the underlying physics that are largely unexplored. Herein, we perform the infrared spectroscopic ellipsometry (SE) measurements and multiscale simulations including first-principles and finite-difference time-domain (FDTD) to systematically study the infrared dielectric function at varying temperatures, phonon dynamics, and SPHPs in wurtzite GaN. SE experiments identify the reststrahlen band where the amplitude of ordinary dielectric function reduces significantly by a factor of 3.5 and the propagation length of SPHPs decreases by a factor of 4.18 as temperature increases from 250 to 800 K, suggesting the strong influence of lattice vibration on SPHPs. First-principles calculations confirm that the reststrahlen band for the ordinary dielectric function lies between the transverse and longitudinal E1 phonon modes, while that of extraordinary dielectric function lies between the transverse and longitudinal A1 phonon modes. FDTD simulations observe the localized surface phonon resonances in the nano-porous GaN thin films deposited on the sapphire substrate only for the transverse magnetic wave mode, which is consistent with the observation of extra dip in the measured pp-polarized reflection spectroscopy. This work provides a deep insight into lattice vibration influence on phonon dynamics and SPHPs in wurtzite GaN and helps engineer them in nanophotonic devices toward achieving better performance.

The thermal properties of β-Ga

Auxetic materials are characterized by a negative Poisson's ratio that they expand laterally in the directions perpendicular to the applied stretching stress and vice versa. Piezoelectrics will change their dimensions when exposed to an external electric field. Here we introduce the concept of the "electric auxetic effect": electric auxetic materials will contract or expand in all dimensions in response to an electric field. Such unusual piezoelectric response driven by an electric field is a close analogy to the auxetic effect driven by a stress field. A key feature of electric auxetic materials is that their longitudinal and transverse piezoelectric coefficients are of the same sign. We demonstrate using first-principles calculations that the Pca2_{1} orthorhombic phase of ferroelectric HfO_{2} exhibits both the negative longitudinal piezoelectric effect and the electric auxetic effect. The unusual negative longitudinal piezoelectric effect arises unexpectedly from the domination of the negative internal-strain contribution over the positive clamped-ion contribution, a character often found in van der Waals solids. We confirm a few more electric auxetic materials with finite electric field calculations by screening through a first-principles-based database of piezoelectrics.

Shade is widespread in agricultural production and affects lignin biosynthesis and lodging resistance of crops. We explored the effects of shade intensity on lignin biosynthesis and lodging resistance at the physiological and molecular levels in two soybean cultivars (Nandou12 and E93) with different shade tolerance under four progressively severe shade treatments, S0&ndash, S3 (S0: no shade, S1: slight shade, S2: moderate shade, S3: heavy shade). Our results showed no significant difference in breaking strength of the two cultivars under S1 and S0 treatments, with no prominent decrease in the lodging resistance index. The activity of lignin biosynthesis rate-limiting enzymes phenylalanine ammonia-lyase (PAL), peroxidase and cinnamyl alcohol dehydrogenase (CAD), which were considerably related to the two lodging resistance indexes above, was not significantly decreased by slight shade, while 4-coumaric acid ligase (4CL) activity was increased. Most genes involved in lignin biosynthesis were not significantly down-regulated by slight shade (S1) compared to S0, while p-coumarate 3-hydroxylase (C3H), 4-coumaric acid ligase (4CL) and laccase (LAC) genes were upregulated. Under heavy shade (S3), enzyme activity and gene expression associated with lignin synthesis in both soybean cultivars were strongly inhibited, moreover, stem mechanical strength and lodging resistance were remarkably decreased compared with those under S0. These physiological and molecular changes suggested that applicable shade levels do not significantly affect the mechanical strength and lodging resistance of soybean stem. Exploiting the lodging resistance potential of existing soybean cultivars was an effective and efficient way to address yield reduction caused by lodging in intercropped soybeans.

Demands for engineering thermal transport properties are ever increasing for a wide range of modern micro- and nanodevices and materials-based energy technologies. In particular, there is a severe situation due to the rapid progress in the synthesis and processing of materials and devices with structural characteristic length on the nanometer scales, which are comparable or even smaller than the intrinsic length scales (such as mean free path and wavelength) of basic energy carriers (such as phonons, electrons, and photons). Although advanced approaches for controlling the electronic and photonic transport have been proposed in the past decades, progress on controlling lattice vibrations (i.e., the phonons) is still far behind. Gaps between the fundamental understandings of the behavior of the basic energy carriers at small scales and the technological demands still remain, particularly from a computer modeling point of view. Herewith, we give a perspective of the computational approaches for predicting the thermal transport properties of low-dimensional materials and nanostructures, which are mainly sorted into three categories: empirical molecular dynamics, anharmonic lattice dynamics based Boltzmann transport equation, and Landauer theory. The advantage and disadvantage of each method are discussed and some possible solutions are suggested. The discussion is focused on fully and accurately characterizing the mode-level phonon behavior, possible all-order phonon scattering process, and incorporation of realistic nanostructures. Moreover, emerging challenges of phonon coupling effects, such as electron–phonon, phonon–photon, and phonon–magnon coupling, are also discussed. We expect that this perspective will stimulate future research in computer modeling of micro-/nanoscale heat transfer beyond traditional phonons.

Newly synthesized 3D graphene with large porosity and hollow structure holds great potential in many applications. However, there is still controversy over the stable structure of the observed 3D graphene and the relevant physical and chemical properties are still lacking. From first-principles lattice dynamics and ab initio molecular dynamics simulation, we found that the previously proposed model for experimentally synthesized 3D graphene is not stable due to the dangling bonds along the connection junctions. We show that reconstruction of equidistant carbon atoms along the junctions, i.e. dimerization, can make the structure more energetically favorable and thermodynamically stable. More intriguingly, an anomalous non-monotonic response of strain-engineered lattice thermal conductivity is observed for the new 3D graphene structure with the highest thermal conductivity achieved at 3% strain. Upon analyzing individual phonon modes, it is found that the anomalous change is dominated by an overwhelming increase of the phonon relaxation time and the governing physics is unraveled using root mean-square displacement, Grüneisen parameter and local potential well in forming the dimerization of the C-C linkage. The fundamental mechanism would be very beneficial for the relevant applications of 3D graphene, such as thermal management of high power density energy storage.