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37. Polyethylene glycol with dual three-dimensional porous carbon nanotube/diamond: a high thermal conductivity of composite PCM.

Author

Feng, Xurui, Zhang, Yuanying, Yang, Zhiliang, Zhao, Zihao, Zhu, Fen, Wei, Xinyi, Chen, Liangxian, Liu, Jinlong, Feng, Yanhui, Li, Chengming, Feng, Daili, and Wei, Junjun

Subjects
POLYETHYLENE glycol, HEAT storage, CARBON nanotubes, LATENT heat, MICROWAVE plasmas, PHASE change materials, THERMAL conductivity, CHEMICAL vapor deposition
Abstract

Polyethylene glycol (PEG) is widely used as a phase change material (PCM) in thermal energy storage systems due to its high latent heat and chemical stability. However, practical application has been hindered by its low thermal conductivity and leakage issues. Therefore, developing shape-stable high thermal conductivity PCM is of great importance. In this study, new shape-stable composite PCM with high thermal conductivity and leak-prevention capabilities were designed. The porous carbon skeleton of diamond foam (DF) and dual-3D carbon nanotube-diamond foam (CDF) were prepared using the microwave plasma chemical vapor deposition method. The composite materials (DF/PEG and CDF/PEG) were produced by vacuum impregnation with PEG and skeletons. The results showed that CDF/PEG had the highest thermal conductivity, measuring 2.30 W·m−1·K−1, which is 707% higher than that of pure PEG. The employing of 3D networks of CNTs, which can improve the phonon mean free path in DF/PEG (1.79 W·m−1·K−1) while reducing phonon dispersion.The phonon vibration of dual-3D CDF plays an important role in heat transfer. PEG was physically absorbed and well-distributed in CDF, alleviating leakage of liquid PEG. The weight loss of CDF/PEG was only 25% at 70 °C for 120 s. Using CDF is an attractive and efficient strategy to increase the heat transfer of PEG and improve heat storage efficiency, alleviate the problem of poor shape-stability. [ABSTRACT FROM AUTHOR]

Published
2024
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48. Preparation and Characterization of Single Crystal Diamond with High Purity and Low Dislocation Density.

Author

HU Tingting, MU Lianxi, WANG Peng, TU Juping, LIU Jinlong, CHEN Liangxian, ZHANG Jianjun, OUYANG Xiaoping, and LI Chengming

Subjects
SINGLE crystals, DIAMOND crystals, CRYSTAL growth, DISLOCATION density, CHEMICAL vapor deposition, MICROWAVE plasmas, EPITAXIAL layers
Abstract

With its excellent properties such as high thermal conductivity, strong radiation resistance and high electron mobility, diamond has become one of the most suitable materials for radiation detectors. Detector-grade diamond requires low impurity content, low dislocation density and other defects. However, it is very difficult to keep low impurities and low dislocations simultaneously in the actual crystal growth process. In this study, microwave plasma chemical vapor deposition (MPCVD) method was used to grow diamond layer on two high-quality HPHT diamond substrates with the previously optimized process conditions. The nitrogen impurity content and structure of the HPHT substrate and growth layer were characterized and analyzed. The results show that, the content of nitrogen impurity on two HPHT substrates are 7. 1 x 10-6% and 4. 04 x 10-8%, respectively, whereas in their epitaxial diamond layers, the nitrogen impurity content are 2. 1 x 10-7% and 5 x 10-8%, respectively. The full width at half-maximum of the rocking curve shows that the dislocation density of the MPCVD growth layer is comparable to the HPHT substrate, though some dislocations were introduced into the MPCVD growth layer, which increases the stress. Overall, the dislocations in the HPHT substrate and epitaxial layer of single crystal diamond are in the same order of magnitude. The high-purity single crystal diamond prepared in this work may be used in nuclear radiation detection and semiconductor fields. [ABSTRACT FROM AUTHOR]

Published
2023

50. High Performance of Normally‐On and Normally‐Off Devices with Highly Boron‐Doped Source and Drain on H‐Terminated Polycrystalline Diamond.

Author

Zhu, Xiaohua, Shao, Siwu, Chan, Siyi, Tu, Juping, Ota, Kosuke, Huang, Yabo, An, Kang, Chen, Liangxian, Wei, Junjun, Liu, Jinlong, Li, Chengming, and Kawarada, Hiroshi

Subjects
DOPING agents (Chemistry), DIAMOND crystals, FIELD-effect transistors, DIAMONDS, ELECTRIC conductivity, DIAMOND films, POWER electronics
Abstract

Diamond exhibits large application potential in the field of power electronics, owing to its excellent and desirable electronic properties. However, the main obstacles to its development originate from the small‐sized single‐crystal wafers and the instability of the electrical conductivity. This work presents a metal‐oxide‐semiconductor field‐effect transistor (MOSFET) on a diamond substrate derived from a five‐inch (110) highly preferred polycrystalline diamond film. The MOSFETs with excellent performance are fabricated by combining an H‐terminated channel and an epitaxially grown boron‐doped layer as the source/drain contacts of the diamond devices. According to the electrical statistical results of ≈110 devices on the polycrystalline diamond substrate, 44% of devices show normally‐off operation with a maximum current density of 400 mA mm−1, while 56% of devices demonstrate normally‐on operation with a maximum current density of 525 mA mm−1. The normally‐off characteristics are more related to the higher amounts of nitrogen concentration than the grain boundaries. The stable boron‐doped source and drain provide a high concentration of holes, which facilitate transport in the surface p‐type channel induced by the H‐termination. The characteristics of the MOSFETs are inspiring for the fabrication of complementary inverter circuits on large diamond wafers. [ABSTRACT FROM AUTHOR]

Published
2023
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