Temperature and interlayer coupling induced thermal transport across graphene/2D-SiC van der Waals heterostructure

Graphene based two-dimensional (2D) van der Waals (vdW) materials have attracted enormous attention because of their extraordinary physical properties. In this study, we explore the temperature and interlayer coupling induced thermal transport across the graphene/2D-SiC vdW interface using non-equilibrium molecular dynamics and transient pump probe methods. We find that the in-plane thermal conductivity κ deviates slightly from the 1/T law at high temperatures. A tunable κ is found with the variation of the interlayer coupling strength χ. The interlayer thermal resistance R across graphene/2D-SiC interface reaches 2.71 $$\times$$ × 10–7$${\text{Km}}^{2} /{\text{W}}$$ Km 2 / W at room temperature and χ = 1, and it reduces steadily with the elevation of system temperature and χ, demonstrating around 41% and 56% reduction with increasing temperature to 700 K and a χ of 25, respectively. We also elucidate the heat transport mechanism by estimating the in-plane and out-of-plane phonon modes. Higher phonon propagation possibility and Umklapp scattering across the interface at high temperatures and increased χ lead to the significant reduction of R. This work unveils the mechanism of heat transfer and interface thermal conductance engineering across the graphene/2D-SiC vdW heterostructure.

Vibrational Dynamics in crystalline 4-(dimethylamino) benzaldehyde: Inelastic Neutron Scattering and Periodic DFT Study

The structure and dynamics of crystalline 4-(dimethylamino) benzaldehyde, 4DMAB, are assessed through INS spectroscopy combined with periodic DFT calculations. The excellent agreement between experimental and calculated spectra is the basis for a reliable assignment of INS bands. The external phonon modes of crystalline 4DMAB are quite well described by the simulated spectrum, as well as the modes involving low-frequency molecular vibrations. Crystal field splitting is predicted and observed for the modes assigned to the dimethylamino group. Concerning the torsional motion of methyl groups, four individual bands are identified and assigned to specific methyl groups in the asymmetric unit. The torsional frequencies of the four methyl groups in the asymmetric unit fall in a region of ca. 190 ± 20 cm−1, close to the range of values observed for methyl groups bonding to unsaturated carbon atoms. The hybridization state of the X atom in X-CH3 seems to play a key role in determining the methyl torsional frequency.

Многократное изменение электрон-фононного взаимодействия в квантовых ямах с диэлектрически различными барьерами

The specific features of the interaction of charged particles with polar optical phonons have been studied theoretically for quantum wells with the barriers that are asymmetric in their dielectric properties. It is shown that the interaction with interface phonon modes makes the greatest contribution in narrow quantum wells. The parameters of the electron-phonon interaction were found for the cases of different values of the phonon frequencies in the barrier materials. It turned out that a significant (by almost an order of magnitude) change in the parameters of the electron-phonon interaction can occur in such structures. This makes it possible, in principle, to trace the transition from weak to strong interactions in quantum wells of the same type but with different compositions of barrier materials. The conditions are found under which an enhancement of the electron-phonon interaction is possible in an asymmetric structure in comparison with a symmetric one with the barriers of the same composition.

Anharmonicity Induced Faster Decay of Hot Phonons in Rutile TiO2 Nanorods: A Raman Spectromicroscopic study

Temperature dependent Raman spectromicroscopy from rutile TiO2 nanorods has been studied here to understand the effect of thermal perturbations on different Raman active phonon modes. The TiO2 nanorods, characterized using...

Спектроскопическое исследование структурных и магнитных свойств TbCr-=SUB=-3-=/SUB=-(BO-=SUB=-3-=/SUB=-)-=SUB=-4-=/SUB=-

The paper presents a flux crystal growth technique, studies of the structural peculiarities and the optical absorption spectra of double orthoborate TbCr3(BO3)4 with a huntite structure. The intensities of the phonon modes were used to determine the ratios of the rhombohedral and monoclinic polytypes for this compound, depending on the growth conditions. The broadband absorption spectra of the Tb3+ ions in TbCr3(BO3)4 single crystals were studied in the temperature range from room temperature to 3.0 K. From them, the energies of the crystal-field levels of the Tb3+ ion were determined. The temperature dependence of the absorption spectra of the Er3+ probe ion in TbCr3(BO3)4:Er(1%) shows that there are two phase transitions and agrees with their previously proposed interpretation: at 8.8 K, the chromium subsystem antiferromagnetically orders, and at 5 K, a reorientation of chromium magnetic moments occurs.

Insight into Structural and Optical Properties of Pristine and Sr2+ Doped La2NiMnO6

Double perovskites oxide (DPO) multiferroics La2-xSrxNiMnO6(x=0.0, 0.1, 0.2, 0.4, 0.6) are synthesized by sol-gel technique. The structural, optical and electrical (both DC and AC) properties of La2-xSrxNiMnO6 have been investigated by XRD and FTIR spectroscopy and two-probe resistivity and dielectric measurements as a function of temperature, respectively. The effect of doping of Strontium at A-site in double perovskites is discussed. XRD has revealed the formation of monoclinic structure of La2-xSrxNiMnO6 with space group P21 / n for x=0.0 and P21 for x=0.1, 0.2, 0.4, 0.6. The average crystallite size has been calculated to be in the range 31 to 46 nm as determined by Debye Scherrer equation. Infrared active optical phonons observed from reflectivity spectra have been analysed fitting the theoretical oscillators using Lorentz oscillator model. We have observed several well-resolved phonon modes in La2-xSrxNiMnO6 with increasing dopant concentration. Activation energy calculated using Arrhenius Plot is in the range of 0.31 to 0.18 eV, confirming the semiconducting nature of all samples. The dielectric constant and tangent loss as a function of temperature and frequency are also discussed for these multiferroics.

Phonon Localization in Boron Nitride Nanotubes: Mixing Effect of 10B Isotopes and Vacancies

We explored the mixing effect of 10B isotopes and boron (B) or nitrogen (N) vacancies on the atomic vibrational properties of (10, 0) single-wall boron nitride nanotubes (BNNT). The forced oscillation technique was employed to evaluate the phonon modes for the entire range (0-100%) of 10B isotopes and atomic vacancy densities ranging from 0 to 30%. With increasing isotope densities, we noticed a blue-shift of the Raman active A1 phonon peak, whereas an increased density of mixed or independent B and N vacancies resulted in the emergence of a new low-frequency peak and the annihilation of the A1 peak in the phonon density-of-states. High-energy optical phonons were localized as a result of both 10B isotopes and the presence of mixing defects. We generated typical mode patterns for different defects to show the phonon localization processes due to the defects. We found an asymmetrical nature of the localization length with increasing 10B isotope content, which corresponds well with the isotope inherited localization length of carbon nanotubes and mono-layer graphene. The localization length falls abruptly with the increase in concentration of both atomic vacancies (B or N) and mixing defects (10B isotope and vacancies). These findings are critical for understanding heat conduction and nanoscopic vibrational investigations like tip-enhanced Raman spectra in BNNT, which can map local phonon energies.

Guided waves in a functionally graded 1-D hexagonal quasi-crystal plate with piezoelectric effect

For the purpose of design and optimization for piezoelectric quasi-crystal transducers, guided waves in a functionally graded 1-D hexagonal piezoelectric quasi-crystal plate are investigated. In this paper, a model combined with the Bak’s and elastohydrodynamic models is utilized to derive governing equations of wave motion, and real, pure imaginary, and complex roots of governing equations are calculated by using the modified Legendre polynomial method. Subsequently, dispersion curves and displacements of phonon and phason modes are illustrated. Then, guided waves in functionally graded 1-D hexagonal piezoelectric quasi-crystal plates with different quasi-periodic directions are studied. And the phonon-phason coupling effect on Lamb and SH waves are analyzed. Accordingly, some interesting results are obtained: The phonon-phason coupling just affects Lamb waves in the x- and z-direction quasi-crystal plates, and SH waves in the y-direction quasi-crystal plate. Besides, frequencies of propagative phason modes decrease as phonon-phason coupling coefficients Ri increase. Furthermore, a variation in the polarization has a more significant influence on phonon modes, and a variation in the quasi-periodic direction has a more significant influence on phason modes.

Phonons transmission through atomic interface connecting two semi-infinite 2D lattices with different meshes

A calculation of the phonon contribution to the coherent transport between two-dimensional (2D) lattices is presented in this paper. The model structure is obtained by the juxtaposition of semi-infinites square ([Formula: see text] and triangular ([Formula: see text] leads, which thus define the nanojunction [Formula: see text]/[Formula: see text] and its inverse [Formula: see text]/[Formula: see text]. We determine, numerically and by simulation, the 2D interface observables for different values of masses and elastic coupling in the nanojunction zone. The local dynamics and atomic nanojunction response to the microscopic changes, in the interfacial domain, are subjects to our investigation. The theoretical formalism based on the matching technique is applied to describe the lattice dynamics and the evanescent phonon modes, in the two studied 2D interfaces. We mainly analyze the vibration spectra, the coherent phonon transmission/reflection and the phononic transmittance through the interface, as elements of a Landauer–Büttiker type scattering matrix. The obtained results show that the nanojunction domain is an effective phonon splitter and suggest that its characteristics may be controlled by varying its nanometric parameters. The observed fluctuations are due to the coherent coupling between continuum modes and the phonons’ discrete states induced by the connected atomic sites.