Non-equilibrium Thermal Resistance of Interfaces Between III-V Compounds

Interfacial thermal resistance has been often estimated and understood using the Landauer formalism that assumes incident phonons with equilibrium distribution. However, previous studies suggest that phonons are out-of-equilibrium near the interface because of the heat flow through the leads and the scattering of phonons by the interface. In this paper, we report a systematic study on how vibrational spectra mismatch affects the degree of phonon non-equilibrium near an interface, how fast it is relaxed as the phonons diffuse into a lead, and the overall interfacial thermal resistance from the non-equilibrium phonons. Our discussion is based on the solution of the Peierls-Boltzmann transport equation with ab initio inputs for 36 interfaces between semi-infinite group-III (Al, Ga, In) and group-V (P, As, Sb) compound semiconductor leads. The simulation reveals that the non-equilibrium phonons cause significant interfacial thermal resistance for all 36 interfaces, making the overall interfacial thermal resistance two to three times larger than that predicted by the Landauer formalism. We observe a clear trend that the degree of phonon non-equilibrium near an interface and the interfacial thermal resistance from the non-equilibrium phonons increase as the mismatch of the Debye temperature of two lead materials increases. This contrasts with Landauer formalism's predictions, which show no correlation with the Debye temperature mismatch. The relaxation length of the phonon non-equilibrium varies significantly from 50nm to 1.5um depending on the combination of the lead materials. The relaxation length is proportional to the phonon mean free path of the corresponding lead material but also largely depends on the material in the opposite lead. This suggests the relaxation length cannot be considered an intrinsic property of the corresponding lead material

Thermal resistance from non-equilibrium phonons at Si-Ge interface

As nanostructured devices become prevalent, interfaces often play an important role in thermal transport phenomena. However, interfacial thermal transport remains poorly understood due to complex physics across a wide range of length scales from atomistic to microscale. Past studies on interfacial thermal resistance have focused on interface-phonon scattering at the atomistic scale but overlooked the complex interplay of phonon-interface and phonon-phonon scattering at microscale. Here, we use the Peierls-Boltzmann transport equation to show that the resistance from the phonon-phonon scattering of non-equilibrium phonons near a Si-Ge interface is much larger than that directly caused by the interface scattering. We report that non-equilibrium in phonon distribution leads to significant entropy generation and thermal resistance upon three-phonon scattering by the Boltzmann's H-theorem. The physical origin of non-equilibrium phonons in Ge is explained with the mismatch of phonon dispersion, density-of-states, and group velocity, which serve as general guidance for estimating the non-equilibrium effect on interfacial thermal resistance. Our study bridges a gap between atomistic scale and less studied microscale phenomena, providing comprehensive understanding of overall interfacial thermal transport and the significant role of phonon-phonon scattering

Effects of medium range order on propagon thermal conductivity in amorphous silicon

We discuss the dependence of the propagon contribution to thermal conductivity on the medium range order (MRO) in amorphous silicon. Three different amorphous structures with the same size of 3.28 nm were studied. Among these three structures, two structures were constructed with experimentally observed MRO [Treacy and Borisenko, Science. 335, 6071 (2012)] and the other structure is from continuous random network (CRN), which lacks MRO and thus represents a randomized amorphous structure [Barkema and Mousseau, Physical Review B, 62, 8 (2000)]. Using the simulated fluctuation electron microscopy and dihedral angle distribution, we confirm that the first two structures contain MRO in the length scale of 10-20 Å while the CRN structure does not. The transport of propagons in the MRO and CRN structures are compared using the dynamic structural factor calculation and normal mode decomposition of the molecular dynamics simulation data, showing noticeably longer lifetime of propagons in the MRO structures than in the CRN structure. The propagon thermal conductivity in the MRO structures is estimated 50% larger than that in the CRN structure

Critical role of next-nearest-neighbor interlayer interaction in magnetic behavior of magnetic/nonmagnetic multilayers

We report magnetoresistance data in magnetic semiconductor multilayers, which exhibit a clear step-wise behavior as a function of external field. We attribute this highly non-trivial step-wise behavior to next-nearest-neighbor interlayer exchange coupling. Our microscopic calculation suggests that this next-nearest-neighbor coupling can be as large as 24% of the nearest-neighbor coupling. It is argued that such unusually long-range interaction is made possible by the quasi-one-dimensional nature of the system and by the long Fermi wavelength characteristic of magnetic semiconductors

Enhancement of thermoelectric figure-of-merit by resonant states of aluminium doping in lead selenide

By adding aluminium (Al) into lead selenide (PbSe), we successfully prepared n-type PbSe thermoelectric materials with a figure-of-merit (ZT) of 1.3 at 850 K. Such a high ZT is achieved by a combination of high Seebeck coefficient caused by very possibly the resonant states in the conduction band created by Al dopant and low thermal conductivity from nanosized phonon scattering centers.United States. Dept. of Energy. Office of Basic Energy Sciences (Solid-State Solar-Thermal Energy Conversion Center Award DE-SC0001299/DE-FG02-09ER46577

Ion-selective and chemical-protective elastic block copolymer interphase for durable zinc metal anode

Aqueous rechargeable batteries based on zinc anodes are among the most promising systems to replace conventional lithium-ion batteries owing to their intrinsic safety, high ionic conductivity, and economic benefits. However, inferior reversibility of zinc anode resulting from zinc dendrites and surface side reactions limits the practical realization of zinc-ion batteries. Herein, we develop a thin but robust polymeric artificial interphase to enhance reversibility of zinc anode. The grafted maleic anhydride groups in the polymer structure restrain the detrimental reactions through selective zinc-ion penetration and homogenize ion distribution, leading to a smooth electrode surface after plating-stripping processes. Consequently, the coated zinc anode shows excellent stability with a long-term symmetric cell lifespan (>3,000 h at 3 mA??cm???2) and maintains capacity retention of 80% after 2,500 cycles, paired with a manganese oxide cathode. This study provides a facile fabrication process and accessible analysis methods to rationalize the development of high-performance zinc-ion batteries