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Recent years have seen a rapid growth of interest by the scientific and engineering communities in the thermal properties of materials. Heat removal has become a crucial issue for continuing progress in the electronic industry, and thermal conduction in low-dimensional structures has revealed truly intriguing features. Carbon allotropes and their derivatives occupy a unique place in terms of their ability to conduct heat. The room-temperature thermal conductivity of carbon materials span an extraordinary large range--of over five orders of magnitude--from the lowest in amorphous carbons to the highest in graphene and carbon nanotubes. Here, I review the thermal properties of carbon materials focusing on recent results for graphene, carbon nanotubes and nanostructured carbon materials with different degrees of disorder. Special attention is given to the unusual size dependence of heat conduction in two-dimensional crystals and, specifically, in graphene. I also describe the prospects of applications of graphene and carbon materials for thermal management of electronics.

Thermal properties of graphene and nanostructured carbon materials

Li-ion battery materials: present and future

The lithium metal battery is strongly considered to be one of the most promising candidates for high-energy-density energy storage devices in our modern and technology-based society. However, uncontrollable lithium dendrite growth induces poor cycling efficiency and severe safety concerns, dragging lithium metal batteries out of practical applications. This review presents a comprehensive overview of the lithium metal anode and its dendritic lithium growth. First, the working principles and technical challenges of a lithium metal anode are underscored. Specific attention is paid to the mechanistic understandings and quantitative models for solid electrolyte interphase (SEI) formation, lithium dendrite nucleation, and growth. On the basis of previous theoretical understanding and analysis, recently proposed strategies to suppress dendrite growth of lithium metal anode and some other metal anodes are reviewed. A section dedicated to the potential of full-cell lithium metal batteries for practical applicatio...

Toward Safe Lithium Metal Anode in Rechargeable Batteries: A Review.

Recent years witnessed a rapid growth of interest of scientific and engineering communities to thermal properties of materials. Carbon allotropes and derivatives occupy a unique place in terms of their ability to conduct heat. The room-temperature thermal conductivity of carbon materials span an extraordinary large range – of over five orders of magnitude – from the lowest in amorphous carbons to the highest in graphene and carbon nanotubes. I review thermal and thermoelectric properties of carbon materials focusing on recent results for graphene, carbon nanotubes and nanostructured carbon materials with different degrees of disorder. A special attention is given to the unusual size dependence of heat conduction in two-dimensional crystals and, specifically, in graphene. I also describe prospects of applications of graphene and carbon materials for thermal management of electronics.

Thermal Properties of Graphene, Carbon Nanotubes and Nanostructured Carbon Materials

Interface delimitation is one of the major failure modes of diamond-coated carbide tools in machining. On the other hand, diamond coatings are prone of cracking easily due to its brittleness, which may affect interface delaminations. To study any influence between the two failure modes, micro-scratch testing on diamond-coated carbide tools was conducted and finite element (FE) modeling was developed to simulate the scratching process. In scratch testing, normal and tangential forces as well as acoustic emission signals were recorded to detect coating delaminations and crack initiations. Scratched samples were also observed by optical microscopy to determine the corresponding critical load of delaminations and cracking initiations. In the FE scratch simulation, a cohesive-zone interface and the extended finite element method (XFEM) were applied to investigate delamination and coating fracture behaviors, respectively. The cohesive elements were based on a bilinear traction separation model and XFEM was implemented to model cracking behavior in a diamond coating with a damage criterion of the maximum principal stress. The major findings are summarized as follows. The coating fracture energy has a negligible effect on the critical load for interface delaminations, and similarly, the interface fracture energy has no effect on the critical load for coating cracking, indicating that the two failure modes are mostly uncoupled for the testing range in this study. From the experiments and simulations, it is estimated that the coating fracture energy of the samples tested in this research is in the range of 120 to 140 J/m 2 , and the diamond-carbide interface fracture energy is from 77 to 192 J/m 2 . Moreover, increasing the coating Young's modulus will increase the critical load for coating delaminations, but decrease the critical load of coating cracking.

Interface delamination study of diamond-coated carbide tools considering coating fractures

In an example of a method for making an electrode active material, a sacrificial layer is formed on a nanomaterial. Carbon is coated on the sacrificial layer to form a carbon layer. Titanium dioxide is coated on the carbon layer to form a titanium dioxide layer. The sacrificial layer is removed to form a void between the nanomaterial and the carbon layer.

Forming electrode active materials

Synthesis and field emission properties of hybrid structures of ultrananocrystalline diamond and vertically aligned carbon nanofibers

First principles calculations were integrated with cohesive zone and growth chemistry models to demonstrate that adsorbed species can significantly alter stresses associated with grain boundary formation during polycrystalline film growth. Using diamond growth as an example, the results show that lower substrate temperatures increase the hydrogen content at the surface, which reduces tensile stress, widens the grain boundary separations, and permits additional atom insertions that can induce compressive stress. More generally, this work demonstrates that surface heteroatoms can lead to behavior which is not readily described by existing models of intrinsic stress evolution.

Impact of surface chemistry on grain boundary induced intrinsic stress evolution during polycrystalline thin film growth.

An analysis of size effects and doping on the strength of ultrananocrystalline diamond (UNCD) thin films is presented. The doping was achieved by the addition of nitrogen gas to the Ar/CH4 microwave plasma. The strength data, obtained by means of the membrane deflection experiment (MDE) were interpreted using Weibull statistics. The validity and predictive capability of the theory were examined in conjunction with detailed fractographic and transmission electron microscopy microstructural analysis. The Weibull parameters were estimated nonlinear regression based on 480 tests when the specimen volume varied from 500 to 16,000 μm3. Both undoped and doped UNCD films exhibited a decrease in strength with an increase in specimen size. A significant drop in strength was measured when the films were doped with nitrogen. Such a drop was almost independent of the percentage of doping. The results also showed that one can predict the fracture strength of a component possessing any arbitrary volume to within ±3%. Moreover, the failure mode of UNCD was found to be volume controlled. We also report changes in Young’s modulus as a function of doping for n-doped UNCD thin films.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0884291400093419

Xingcheng Xiao

Papers

Interface delamination study of diamond-coated carbide tools considering coating fractures

Forming electrode active materials

Synthesis and field emission properties of hybrid structures of ultrananocrystalline diamond and vertically aligned carbon nanofibers

Impact of surface chemistry on grain boundary induced intrinsic stress evolution during polycrystalline thin film growth.

Fracture size effect in ultrananocrystalline diamond : Applicability of weibull theory