Jie Zhu

As main states of matter, crystal, glass, and liquid manifest themselves in distinct transverse collective atomic vibrations. In contrast to crystals where transverse phonons are well-defined throughout Brillouin zones, glasses and liquids process such motions in long and/or short wavelength limits, respectively. Considerable efforts have been made to experimentally probe transverse phonon behavior in these highly anharmonic and disordered materials in pursuit of a universal framework for thermal transport. In this work, inelastic neutron scattering on AgCrSe2 single crystals reveals liquid-, glassy-, and crystal-like phonon features along different crystallographic directions. In particular, the liquid-like behavior is attributed to the significant softening and scattering arising from the nesting effect and dynamical atomic disorder while the glassy-like behavior is due to the selective disorder effect. Our findings challenge conventional boundaries between states of matter at the level of atomic dynamics and establish a materials platform for unifying the thermal transport theories across different states.

Thermoreflectance techniques are widely used to extract interfacial thermal conductance (ITC) and thermal conductivity from time-domain thermoreflectance (TDTR) signals. However, when multiple parameters are coupled, the extent to which their physical values can be uniquely recovered from experimental data remains unclear. In this work, we investigate this issue for an Al/GaN system using Bayesian and machine-learning approaches. Sensitivity analysis and root-mean-square error (RMSE) landscape mapping show that ITC and substrate thermal conductivity ksub affect the TDTR response differently but are not fully separable. Consequently, multiple correlated parameter combinations can produce similar thermal responses. Joint Bayesian parameter estimation (BPE) further quantifies this behavior by revealing a finite, strongly correlated posterior region in the ITC-–ksub parameter space rather than an isolated solution. To enable rapid probabilistic inference, we further develop a physics-informed multivariate Gaussian regression network (PMGRN) that directly predicts the means, standard deviations, and correlation coefficient of ITC and ksub. A physics-based loss coupled to the TDTR forward solver constrains the predicted parameter combinations to remain consistent with the measured thermal response. After training, PMGRN reduces the inference time from hours for the present full-grid BPE implementation to approximately 1 s for a new in-domain measurement. These results show that, although the underlying thermal properties have definite physical values, the experimentally accessible inverse result can remain distributed over a correlated, probability-weighted region because of parameter coupling and limited identifiability. Thermoreflectance inversion should, therefore, report not only a representative parameter estimate but also the uncertainty and correlation structure supported by the measurement.

Due to the lack of effective methods to decouple the individual contributions of atomic defects and the resulting lattice strain to phonon transmission during film growth, elucidating that atomic defects synergistically regulate cross-plane thermal transport with lattice strain during columnar-grained films growth remains challenging. In this study, based on the three-stage film growth theory and a thermal analysis model refined by incorporating a phonon mean free path (MFP) term that accounts for the influence of atomic defects, the synergistic effects of atomic defects and the resulting lattice strain on cross-plane thermal transport during the growth of columnar-grained TiSiN films are investigated. The results indicate that the phonon scattering rate induced by atomic defects first increases and then decreases during film growth. In the competitive growth stage, in addition to the intrinsic scattering effect, atomic defects enhance compressive lattice strain, which reduces the phonon relaxation time and MFP by altering interatomic force constants and the scattering phase space. Upon entering the columnar growth stage, due to the increased probability of Umklapp scattering, the presence of electron–phonon interactions, and the relaxation of strain energy, the scattering rates of both atomic defects and lattice strain decrease simultaneously.

硫化亚锡（SnS）作为一种环境友好、成本低廉且储量丰富的窄带隙半导体材料，在中温热电转换领域展现出巨大的应用潜力。然而，其块体材料固有的点缺陷（如空位）和特定的能带结构，在一定程度上限制了其热电性能的进一步提升。低维化已被证明是改善材料热电性能的有效策略之一。本工作通过时域热反射法（TDTR）和薄膜热电参数测量系统（ZEM-3），系统研究了不同厚度（82 nm、199 nm、616 nm和813 nm）的SnS纳米薄膜在300–600 K温度范围内的热电性能。结果表明，薄膜厚度对SnS的热电性能具有显著影响。本工作不仅为优化SnS纳米薄膜的热电性能提供了实验依据和理论参考，而且为开发高效、环保的中温热电材料奠定了基础，具有重要的科学指导意义和实际应用价值。