Optical Phonon Branches Research Articles

Composition-Dependent Phonon and Thermodynamic Characteristics of C-Based XxY1−xC (X, Y ≡ Si, Ge, Sn) Alloys

Novel zinc-blende (zb) group-IV binary XC and ternary XxY1−xC alloys (X, Y ≡ Si, Ge, and Sn) have recently gained scientific and technological interest as promising alternatives to silicon for high-temperature, high-power optoelectronics, gas sensing and photovoltaic applications. Despite numerous efforts made to simulate the structural, electronic, and dynamical properties of binary materials, no vibrational and/or thermodynamic studies exist for the ternary alloys. By adopting a realistic rigid-ion-model (RIM), we have reported methodical calculations to comprehend the lattice dynamics and thermodynamic traits of both binary and ternary compounds. With appropriate interatomic force constants (IFCs) of XC at ambient pressure, the study of phonon dispersions ωjq→ offered positive values of acoustic modes in the entire Brillouin zone (BZ)—implying their structural stability. For XxY1−xC, we have used Green’s function (GF) theory in the virtual crystal approximation to calculate composition x, dependent ωjq→ and one phonon density of states gω. With no additional IFCs, the RIM GF approach has provided complete ωjq→ in the crystallographic directions for both optical and acoustical phonon branches. In quasi-harmonic approximation, the theory predicted thermodynamic characteristics (e.g., Debye temperature ΘD(T) and specific heat Cv(T)) for XxY1−xC alloys. Unlike SiC, the GeC, SnC and GexSn1−xC materials have exhibited weak IFCs with low [high] values of ΘD(T) [Cv(T)]. We feel that the latter materials may not be suitable as fuel-cladding layers in nuclear reactors and high-temperature applications. However, the XC and XxY1−xC can still be used to design multi-quantum well or superlattice-based micro-/nano devices for different strategic and civilian application needs.

Realizing High Thermoelectric Performance in GeTe‐Based Supersaturated Solid Solutions

AbstractAs a highly promising thermoelectric material in the mid‐temperature region, pristine GeTe shows deteriorated thermoelectric properties due to the low Seebeck coefficient and the intrinsic high thermal conductivity. Herein, it is discovered that the introduction of strongly correlated d, f electrons by alloying rare‐earth atoms at Ge sites will increase the band effective mass and promote band convergency, which can largely improve the electric transport property. Moreover, the heavy atoms (Pb, Bi) doping induces optical phonon softening and the avoided crossing between acoustic and optical phonon branches, decelerating both optical and acoustic phonon velocities. The modulated composition wave from the fluctuated multi‐component distribution introduces a complicated hierarchical structure including point defects and nanoprecipitates, which provides all‐scale scattering sources for heat‐carrying phonons and results in low lattice thermal conductivity. Consequently, a high zT of 2.4 at 800 K can be obtained in the Ge0.86Pb0.09Bi0.03Ce0.005Te sample due to the combination of strong correlation for d, f electrons and the full‐spectrum scattering for phonons. This work provides an effective strategy to increase the thermoelectric performance of IV–VI compounds by combining the modulated band structure and the softening phonon dispersion.

The effect of optical-acoustic phonon coupling on the thermal conductivity of 2D MgI2.

2D MgI2 has a large phonon band gap and strong coupling of optical and acoustic phonons, and it is difficult to accurately predict thermal conductivity by considering only three-phonon scattering. Thus, in this study, the effect of four-phonon scattering on the thermal conductivity of a 2D MgI2 lattice was investigated using first-principles calculations combined with Boltzmann transport theory. The results show that with increasing temperature, four-phonon scattering induces an increase in the scattering of phonons at the optical and acoustic phonon coupling (2 THz), as well as in the vicinity of the optical phonon branch (4.5 THz), which leads to the enhancement of the anharmonicity of phonon transport and results in a decrease in the thermal conductivity of the 2D material. At 700 K, the thermal conductivity of MgI2 decreases by over half, from 0.47 W m-1 K-1 to 0.23 W m-1 K-1, when considering both three- and four-phonon scattering, compared to considering only three-phonon scattering. This study confirms the need to consider the role of four-phonon scattering to enhance optical and acoustic phonon coupling to accurately predict the thermal conductivity of 2D materials with larger phonon band gaps.

Intrinsic ultralow lattice thermal conductivity in lead-free halide perovskites Cs3Bi2X9 (X = Br, I).

Lead-free halide perovskites have recently garnered significant attention due to their rich structural diversity and exceptionally ultralow lattice thermal conductivity (κL). Here, we employ first-principles calculations in conjunction with self-consistent phonon theory and Boltzmann transport equations to investigate the crystal structure, electronic structure, mechanical properties, and κLs of two typical vacancy-ordered halide perovskites, denoted with the general formula Cs3Bi2X9 (X = Br, I). Ultralow κLs of 0.401 and 0.262 W mK-1 at 300 K are predicted for Cs3Bi2Br9 and Cs3Bi2I9, respectively. Our findings reveal that the ultralow κLs are mainly associated with the Cs rattling-like motion, vibrations of halide polyhedral frameworks, and strong scattering in the acoustic and low-frequency optical phonon branches. The structural analysis indicates that these phonon dynamic properties are closely relevant to the bonding hierarchy. The presence of the extended Bi-X antibonding states at the valence band maximum contributes to the soft elastic lattice and low phonon group velocities. Compared to Cs3Bi2Br9, the face-sharing feature and weaker bond strength in Cs3Bi2I9 lead to a softer elasticity modulus and stronger anharmonicity. Additionally, we demonstrate the presence of wave-like κC in Cs3Bi2X9 by evaluating the coherent contribution. Our work provides the physical microscopic mechanisms of the wave-like κC in two typical lead-free halide perovskites, which are beneficial to designing intrinsic materials with the feature of ultralow κL.

Raman fingerprint of the graphene buffer layer grown on the Si‐terminated face of 4H‐SiC(0001): Experiment and theory

AbstractIn this work, we present the results of measurements of the Raman spectrum of the √3x√3R30° reconstruction of graphene grown on 4H‐SiC(0001), the so‐called buffer layer. The extracted Raman spectrum of the buffer layer shows bands, different from those of graphene, which can be attributed to the interaction of the buffer layer with the SiC substrate. In particular, in the high‐wavenumber region, at least three bands are observed in the wavenumber regions 1,350–1,420, 1,470–1,490 and 1,520–1,570 cm−1. The assignment of the buffer layer bands is supported here by tight‐binding simulations of the one‐phonon density of states for structures with a sufficiently large number of Si‐C bilayers for reaching convergence. The converged phonon density of states is found to be in semi‐quantitative agreement with the latter two bands, and therefore, the tight‐binding predictions of the lattice dynamics of the structure can be used for their assignment to buffer layer vibrations. Namely, the Raman band at about 1,550 cm−1 can be assigned to modified in‐plane optical phonon branches of graphene, while the Raman band at about 1,490 cm−1 can be assigned to modified folded parts of these branches inside the Brillouin zone of the buffer layer and can be considered as a Raman fingerprint of the buffer layer.

Break of thermal equilibrium between optical and acoustic phonon branches of CsPbI3 under continuous-wave light excitation and cryogenic temperature

The kinetic of low-temperature carrier and lattice of lead-halide perovskite is yet to be fully understood. In this work, we investigate the steady-state photoluminescences (PLs) of CsPbI3 at the environmental temperature (Te) ranging from 20 K to 300 K, and observed anomalous behaviors at cryogenic temperatures: The carrier temperature (Tc) of pure CsPbI3 exhibits a negative correlation with Te, accompanied by an expansion in Urbach tails of absorption spectra (Abs.) and excessive red-shifts at peak energy of PLs. These phenomena are also observed in those samples containing a certain amount of Cs4PbI6, but to a lesser extent and occurs at lower temperatures. It is attributed to the intensified hot phonon bottleneck effect (HPB) in CsPbI3 at cryogenic Te, which hinders the energy transfer from hot carriers, via longitudinal optics (LO) phonons to longitudinal acoustic (LA) phonons, to the ambient. For samples under continuous-wave laser excitation, in specific, the barrier induced by the enhanced HPB at low Te prevents the effective thermalization among carriers, LO and LA phonons, which, therefore, form thermally isolated ensembles with different temperatures. At cryogenic Te range, the elevated temperatures of carrier and LO phonon expand the high-energy side of PLs and the low-energy tail of Abs., respectively. For those samples in which the CsPbI3 is mixed with Cs4PbI6, the interfacial LO-LO interaction across them provides a bypass for heat dissipation, mitigating the heat accumulation in LO-phonons of CsPbI3. The results suggest that a strong HPB effect may break the thermal equilibrium among different branches of phonons in the lattice under certain extreme conditions.

Modulation of localized phonon thermal transport at GaN/AlxGa1-xN heterointerface: Polar surface, doping, and compressive Strain

The phonon transport processes within a few atomic layers near heterointerfaces play a crucial role in thermoelectric applications such as nitride-based high electron mobility transistors (HEMTs) and light-emitting diodes (LEDs). However, a systematic investigation of their localized transport characteristics remains unexplored. This article employs the Interfacial Phonons method based on first-principles calculations to extract interface phonon information for GaN/AlxGa1-xN heterostructures. Molecular dynamics simulations are utilized to compare the phonon behaviors between Ga-face and N-face GaN-based heterointerfaces. The research extensively investigates the dependence of interfacial thermal transport on the concentration of Al atoms under ordered substitutional doping and the strength of uniaxial compressive strain. The research revealed that both Ga-face and N-face GaN/AlxGa1-xN heterointerfaces exhibit phonon branch drift. The differences in charge distribution at the polar surfaces lead to varying degrees of Brillouin zone distortion. The vibrational modes of the atoms at the N-face GaN interface are more compact and localized than those of Ga-face GaN, resulting in a stronger degree of localization for the optical phonon branches. When varying the doping concentration of Al atoms, some phonon branches at the GaN interface appear outside the band structure of the intrinsic bulk and surface states, exhibiting strong localized characteristics. The introduction of Al atoms at the heterointerface induces additional phonon scattering, and the lattice vibration mismatch between Al and Ga atoms results in a non-uniform residual stress field at the interface, further enhancing phonon-interface scattering. Moderate compressive strain-induced lattice distortion promotes the overlapping of phonon modes at the interface, allowing some localized phonons to serve as interface transport modes. This optimization enhances phonon transport at the heterointerface. This research provides valuable insights into a comprehensive understanding of interfacial thermal transport in GaN-based semiconductors. Moreover, it offers useful theoretical guidance for thermal management through the manipulation of phonon wave properties.

Electronic and optical properties of two-dimensional III2-VI3 materials with the FE-WZ′ structure

Based on the first-principles calculations, we have investigated the mechanical, phonon, electronic and optical properties of two-dimensional (2D) In2Te3 (FE-WZ′ phase) family. The Y(θ) value for all M2X3 materials exceeds 67 N/m, with Al2S3 exhibiting the best mechanical strength, surpassing to that of MoS2 (∼124.3 N/m in the x and y directions). Phonon calculations reveal that the acoustic branch with the lowest frequency is mainly dominated by out-of-plane vibrations of the metal atoms and non-metallic atoms. Ga2Te3 exhibits dynamic instability due to the softening of the optical phonon branch. Incorporating spin–orbit coupling (SOC) in In2Se3 and In2Te3 converts them into direct semiconductors. These materials possess an electrostatic potential difference ranging from 0.73 to 2.11 eV, which effectively reduces the band gap required for water splitting in the infrared region. Moreover, the M2X3 monolayers with intrinsic electric fields are great coveted photocatalysts for overall water splitting. Remarkably, In2Se3 displays a solar-to-hydrogen efficiency of 28.6%, which is significant for commercial applications.

Topological phonons and low lattice thermal conductivity of Li[formula omitted]CaX (X = Sn and Pb) type Heusler compounds

The topological phonons, electronic structure, and transport properties of Li2CaX (X = Sn and Pb) have been investigated using first-principles. Topological phononic states are facilitated by Dirac-like band crossings observed in optical phonon branches, which are ensured by calculated surface states in the (001) plane. Li2CaPb has very low lattice thermal conductivity(κl), as evidenced by shorter phonon lifetime, acoustic phonon mode dispersion, and low Debye temperature. The value of κl is low at high temperatures due to Dirac-like crossings in optical phonon branches exhibiting non-trivial topological properties. The inclusion of hybrid functional transits Li2CaPb into an indirect bandgap semiconductor. Li2CaPb has a figure of merit of 0.15 for holes and 0.2 for electrons at 500 K. Topological phonons combined with promising transport features in Li2CaX (X = Sn and Pb) may be desirable for future device applications.

The effect of spin–orbit coupling on the physical and superconducting properties of the Ir-rich cubic Laves superconductors AIr[formula omitted] (A = Y, Lu, and Th)

We have examined the impact of spin–orbit coupling (SOC) in cubic Laves superconductors AIr2 (A = Y, Lu, and Th) by realizing ab initio pseudopotential calculations of their physical and electron–phonon interaction properties. The inclusion of SOC removes the degeneracy of the electronic states and moderately influences the elastic and mechanical properties of all the compounds investigated. A critical examination of the elastic and mechanical properties reveals that all the compounds studied are soft (ductile) because of significant metallic bonding. The SOC effect on the phonon and electron–phonon interaction properties depends on the type of A element. This coupling has little influence on the phonon properties of YIr2. However, differently from YIr2, three optical phonon branches of LuIr2 and ThIr2 originating from the triply degenerate zone-center T2u mode are significantly affected by the inclusion of SOC. Although the effect of SOC on the electron–phonon interaction properties changes with the type of A atom, the presence of this coupling improves the agreement with experiment for the superconducting transition temperatures of all the cubic Laves superconductors investigated.

The electronic structure, elastic properties, dynamical stability and thermoelectric properties of rock-salt and orthorhombic phases of CdS: First-principles calculations

Combined with first-principles calculation and Boltzmann transport theory, we investigated the electronic structure, dynamic stability, mechanical and thermoelectric properties of rock-salt (rs-CdS) and orthorhombic CdS (orth-CdS). Both phases are mechanical and dynamical stable, showing semiconductor characteristics with an indirect band gap of ∼0.2 eV and excellent resistance to deformation and external pressure. Due to the strong coupling of optical and acoustic phonon branches, the predicted lattice thermal conductivities of these phases are quite low. The electron transport properties including Seebeck coefficient and power factor of p-type doping are excellent. From 300 K to 800 K, the maximum ZT values are in the range of 0.56 to 0.71 for p-type doping, hinting that the rs-CdS and orth-CdS are superior thermoelectric materials.

Physical properties and superconductivity in the cubic A15-type Ta[formula omitted]Ge compound: A first principles study

In this theoretical study, we have targeted to present the characteristic features of the superconductivity in the cubic A15-type compound Ta3Ge by investigating its structural, electronic, elastic, mechanical, phonon, and electron–phonon interaction properties in detail. A critical examination of elastic moduli of Ta3Ge reveals that it is soft (ductile) due to significant metallic bonding. A critical surveying of electronic density of states reveals that Ge electronic states make negligible additive to the main valence band region of Ta3Ge while its transition metal d states dominate this region. An examination of our phonon results indicate that the low-frequency optical phonon branches and three acoustic phonon branches of Ta3Ge are mainly dominated by the vibrations of Ta atoms. Thereby, their d states and their vibrations become the main actors of the transition from the normal state to the superconducting state for Ta3Ge. From the integration of the Eliashberg spectral function of Ta3Ge, the values of average electron–phonon coupling parameter and logarithmically averaged phonon frequency are found to be 1.08 and 123.05 K, respectively, producing its superconducting temperature Tc = 8.3 K, being in good accordance with the experimental value of 8.0 K.

Integrating band engineering with point defect scattering for high thermoelectric performance in Bi2Si2Te6

A layer-structure compound Bi2Si2Te6 is introduced as a promising thermoelectric material. The intrinsic low lattice thermal conductivity of Bi2Si2Te6 is because of the low phonon group velocities near the Γ point and the overlap of optical and acoustic phonon branches. A further decreased thermal conductivity is obtained by alloying Sb at the Bi site for the additional point-defect scattering of phonons. This Sb alloying also enhances the density-of-states near the valence band maximum for a larger carrier effective mass, and suppresses the bipolar effect by increasing the carrier concentration and widening the band gap. Benefitting from both the enhancement of power factor and the decrease of lattice thermal conductivity, the peak zT value is improved from ∼ 0.45 at 573 K for Bi2Si2Te6 to ∼ 1.2 at 773 K for BiSbSi2Te6.

Observation of photo-induced plasmon-phonon coupling in PbTe via ultrafast x-ray scattering.

We report the observation of photo-induced plasmon–phonon coupled modes in the group IV–VI semiconductor PbTe using ultrafast x-ray diffuse scattering at the Linac Coherent Light Source. We measure the near-zone-center excited-state dispersion of the heavily screened longitudinal optical (LO) phonon branch as extracted from differential changes in x-ray diffuse scattering intensity following above bandgap photoexcitation. We suggest that upon photoexcitation, the LO phonon-plasmon coupled (LOPC) modes themselves become coupled to longitudinal acoustic modes that drive electron band shifts via acoustic deformation potentials and possibly to low-energy single-particle excitations within the plasma and that these couplings give rise to displacement-correlations that oscillate in time with a period given effectively by the heavily screened LOPC frequency.

Magnon-phonon interaction and the underlying role of the Pauli exclusion principle

The magnon-phonon interaction is receiving growing attention due to its key role in spin caloritronics and the emerging field of acoustic spintronics. At resonance, this magnetoelastic interaction forms magnon polarons, which underpin exotic phenomena such as magnonic heat currents and phononic spin, but is mostly investigated using mesoscopic spin-lattice models. Motivated to integrate the magnon-phonon interaction into first-principles many-body electronic structure theory, we set out to derive the exchange contribution, which is subtler than the spin-orbit contribution, using Schwinger functional derivatives. To avoid having to solve the famous Hedin-Baym equations self-consistently, the phonons are treated as perturbations to the electronic structure. A formalism based on imposing a crossing-symmetric electron-electron interaction is developed in order to treat charge and spin on equal footing to respect the Pauli exclusion principle. Due to spin conservation, the magnon-phonon interaction first enters to second order through the magnon-magnon interaction, which renormalizes the magnons. We show by iteration that the magnon-magnon interaction contains a ``screened $T$ matrix'' term and an arguably more important term which, in the local-spin limit, enables first-principles phonon emission and absorption amplitudes, predicted by phenomenological magnetoelastic models. These terms are, respectively, of first and second order in the screened collective four-point interaction $\mathcal{W}$---a crossing-symmetric analog of Hedin's $W$. Proof-of-principle results are presented at varying temperatures for an isotropic magnon spectrum in three dimensions in the presence of a flat optical phonon branch.

Spin excitations coupled with lattice and charge dynamics in La2−xSrxCuO4

Spin excitations of layered copper oxide show various characteristic features, depending on the carrier concentration. In this study, we conducted inelastic neutron scattering (INS) measurements on La$_{2-x}$Sr$_{x}$CuO$_4$ (LSCO), with $x$ = 0, 0.075, 0.18, and 0.30 and La$_{2-x}$Sr$_{x}$NiO$_4$ (LSNO) with 1/3, to clarify the origin of the intensity enhancement in the excitation spectrum of LSCO at the energy ($\omega$) of 16--19 meV [Phys. Rev. B {\bf 91}, 224404 (2015), {\it ibid}. {\bf 93}, 094416 (2016)]. We confirmed the presence of a peak-structure in the $\omega$-dependence of the local spin susceptibility $\chi''(\omega)$ of superconducting (SC) LSCO with a peak energy of 16--19 meV, where the spin excitations intersect optical phonon branches. A comparable peak-structure is not observed in the insulating La$_2$CuO$_4$, LSNO, and heavily overdoped LSCO with $x$ = 0.30. A dome-shaped $x$-dependence of the integrated intensity around the peak energies is revealed for SC phase by summarizing the present and previously reported results. Furthermore, our phonon calculation on LCO shows the existence of two optical branches at $\sim$19 meV that could stabilize stripe-alignment of carriers due to out-of-plane vibrations of Cu or O of the CuO$_2$ planes. These results indicate the interplay among spin, charge, and lattice dynamics and suggest that the intensity enhancement is associated with their composite excitations.

Pressure-driven thermoelectric properties of defect chalcopyrite structured ZnGa2Te4: ab initio study.

The pressure induced structural, electronic, transport, and lattice dynamical properties of ZnGa2Te4 were investigated with the combination of density functional theory, Boltzmann transport theory and a modified Debye–Callaway model. The structural transition from I4̄ to I4̄2m occurs at 12.09 GPa. From the basic observations, ZnGa2Te4 is found to be mechanically as well as thermodynamically stable and ductile up to 12 GPa. The direct band gap of 1.01 eV is inferred from the electronic band structure. The quantitative analysis of electron transport properties shows that ZnGa2Te4 has moderate Seebeck coefficient and electrical conductivity under high pressure, which resulted in a large power factor of 0.63 mW m−1 K−2 (750 K). The ultralow lattice thermal conductivity (∼1 W m−1 K−1 at 12 GPa) is attributed to the overlapping of acoustic and optical phonon branches. As a result, the optimal figure of merit of 0.77 (750 K) is achieved by applying a pressure of 12 GPa. These findings support that ZnGa2Te4 can be a potential p-type thermoelectric material under high pressure and thus open the door for its experimental exploration.

Coupling to zone-center optical phonons in VSe2 enhanced by charge density waves

We investigate electron-phonon coupling (EPC) in the charge density wave (CDW) phase of $\mathrm{V}{\mathrm{Se}}_{2}$ by Raman spectroscopy, angle-resolved photoemission spectroscopy (ARPES), and ab initio calculations. Zone folding induced by the $4\ifmmode\times\else\texttimes\fi{}4$ in-plane CDW phase promotes the appearance of a Raman peak at $\ensuremath{\sim}170\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$. The suppression of ARPES intensity in parts of the Fermi surface is also a result of CDW-induced zone folding and anticrossing of the electron energy bands. The appearance of the new Raman peak is in line with the ARPES observation of a kink feature in the spectral function at the same energy. A self-energy analysis yields an EPC constant of $\ensuremath{\lambda}=0.3$. Our calculations of the EPC are in excellent agreement and reveal that the kink is caused by several optical phonon branches close in energy. Our paper highlights the CDW phase as a means of inducing EPC pathways to optical phonons that directly affect its Raman spectrum.

Non-monotonic thickness dependent and anisotropic in-plane thermal transport in layered titanium trisulphide

Due to the potential applications in many fields such as thermoelectric, transistor, and electrode materials, a novel two-dimensional layered material TiS3 has attracted tremendous attention recently. In this article, the thickness dependent and anisotropic in-plane thermal transport behavior is explored by first-principles calculation with Boltzmann transport equation. The calculation results show that when the thickness is smaller than phonon confinement size (PCS), the phonon confinement effect is dominant and the in-plane thermal conductivity has a negative dependence on thickness due to the increase of phonon–phonon scattering; when the thickness is larger than PCS, the confinement effect is weak and the dependence becomes positive due to the decrease of phonon–boundary scattering. Through further analysis, we find this non-monotonic dependence or phonon confinement phenomenon is mainly caused by the low-frequency phonons. The calculation results also show strong thermal anisotropy within the basal plane. The coupling strength, bond length, phonon group velocity, dispersiveness of optical phonon branches, iso-energy surface and iso-surface of electron density distribution are analyzed to explain the anisotropy. Based on the 1D diatomic chain model, a unit cell having similar atomic mass and strong intracell bond can enhance the dispersiveness of optical phonon branches. Those findings here can give physical insights into the thickness dependent and anisotropic in-plane thermal transport in layered materials.

Interfacial thermal resistance between nm-thick MoS2 and quartz substrate: A critical revisit under phonon mode-wide thermal non-equilibrium

2D materials experience a cascading energy transfer under intense laser irradiation, which leads to a strong thermal non-equilibrium between energy carriers, especially between optical (OP) and acoustic (AP) phonon branches. In previously reported Raman optothermal techniques, this non-equilibrium effect is neglected that leads to very large physics errors in interface thermal resistance characterization. Here, the optical phonon temperature rises of both in-plane and out-of-plane modes of nm-thick MoS 2 films supported on quartz substrate are determined using a steady-state Raman, and the non-equilibrium between OP-AP and their energy coupling factor are characterized by controlling the heating domain and precise calculation of Raman signal and subsequently absorbed laser power by using a transfer matrix method. It is concluded that the OP-AP temperature difference under laser heating area could be as high as ~45% of the total OP temperature rise probed by Raman. The interfacial thermal resistance ( R ″ tc ) between MoS 2 and quartz is reevaluated by considering this non-equilibrium effect, and it is observed that neglecting it could lead to R ″ tc over-prediction by ~100%. By determining R ″ tc using both Raman modes of MoS 2 , it is observed that due to the ballistic and diffusive phonon transport and difference of interface thermal resistance among phonon modes, the flexural optical mode has a higher temperature rise than the longitudinal/transverse optical modes. This agrees well with atomistic modeling results of other 2D materials, e.g. graphene on BN. • First time distinguishing of LO/TO and ZO phonon temperatures of supported MoS 2 . • First time determination of OP-AP energy coupling factor of supported MoS 2 . • Intrinsic interfacial thermal resistance measurement under phonon non-equilibrium. • ZO mode has a much higher temperature rise than the LO/TO modes.