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Al-doped ZnO (AZO) is a promising candidate as a transparent conducting electrode. However, the electrical properties of AZO deteriorate greatly after exposing it to excessive heat. This limits the applications of AZO in devices that experience a demanding operation environment. It has been shown that a ZnO cap layer with proper morphology is capable to dramatically improve the thermal stability of AZO. However, the detailed mechanism is not yet clear. A comparison study of the electrical properties of AZO with a ZnO cap layer prepared by magnetron sputtering (MS) at low substrate temperature (70 °C) and chemical vapor deposition (CVD) at high substrate temperature (600 °C) indicates that MS-prepared ZnO is much less effective in protecting AZO from an oxidizing environment under elevated temperature than the CVD-prepared ZnO. The morphology and crystal structures of two types of ZnO/AZO, investigated by a scanning electron microscope and x-ray diffraction, are relatively similar, whereas the atomic structures (e.g., defects) revealed by Raman spectroscopy are rather different. The results suggest that it is difficult to improve the thermal stability of electrical properties of AZO without a proper restructuring process and a ZnO cap layer that could sacrifice its own structural order. The discoveries offer a novel approach to improve the performance of other transparent conducting oxides. [ABSTRACT FROM AUTHOR]

Efficient thermal interface materials (TIMs) are urgently needed for heat dissipation of high-power density electronics. In this study, vinyl polydimethylsiloxane (PDMS) composites with the spatial alignment of carbon fibers (CFs) bridged by Al 2 O 3 particles were fabricated by the flow field. The through-plane thermal conductivity (TPTC) of the composites with 24 vol% CFs and 47 vol% Al 2 O 3 loading reached 38.0 W m−1 K−1. The oriented CFs bridged by Al 2 O 3 acted as the efficient through-plane thermal conductive network. Furthermore, the effects of shape factor (b/a), spatial angle (γ) of CFs, and CF loading (V f) on the TPTC were quantitatively discussed by steady-state finite element simulation combined with micro-computed tomography and machine learning. The positive contribution of the increased V f to TPTC was in competition with the negative contribution of b/a and γ , both of which increased with the increase of V f. Moreover, b/a exerted more negative effects than γ. The PDMS composites demonstrated excellent thermal stability (T d = 407.5 °C, CTE = −55.3 × 10−6 K−1), low compress modulus (1.71 MPa), and hardness (47 (Shore C)), which made them potential candidates for TIMs. This work offers a feasible method to prepare TIMs on large scale and refreshes the thermal conduction mechanism of TIMs by introducing the influencing factors (b/a and γ). [Display omitted] • Efficient heat conduction paths were constructed by spatial alignment of CFs bridged by Al 2 O 3. • The through-plane thermal conductivity of PDMS composites reached 38 W m−1 K−1. • The effect of spatial orientation angle of CFs on the thermal conduction property was revealed. • The PDMS composites with excellent comprehensive properties can be used as TIMs. [ABSTRACT FROM AUTHOR]

Currently, epoxy-based composites are widely used in thermal management. However, with the development of complex and high power-density electronic devices, the thermal properties of the composites need to be improved. Inspired by the unique galls-leaf structure of Distylium chinense, a graphene-diamond framework (GRDF) is developed by a simple filtration method. A through-plane and in-plane thermal conductivity of 22.7 and 21.8 Wm−1 K−1, respectively, have been achieved by forming epoxy-based composites with the GRDF annealed at 3000 °C. The result is 70% higher than the best-reported value for epoxy-based composites prepared by vacuum filtration under a filler content of 43 wt%. Such high thermal conductivity remains unchanged (within 2%) in a temperature range from 25 to 100 °C. Based on various microscopic characterizations, the diamond particles evenly distribute in a framework formed by graphene sheets, which bridge the gaps in the framework and improve its structural integrity. High-temperature annealing converts most diamond particles to graphite, which further enhances the thermal properties of the composite. The observations provide a feasible way for developing polymer-based composite with high thermal conductivity, which could meet the ever-increasing demands for heat dissipation in high-power electronics. [Display omitted] • The epoxy composite with a through-plane thermal conductivity of 22.7 Wm−1K−1 is achieved under 43.2 wt.% filler filling. • The composites show a high degree of isotropic thermal properties, and a good thermal stability. • The high thermal conductivity of the composite is due to diamond filling and high-temperature graphitization. [ABSTRACT FROM AUTHOR]