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

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

Some of the challenges facing scientists in the area of the electronic structure and properties of solids are reviewed. At a time when computational advances have made possible high-quality calculations, not even conceivable 10 years ago, the article stresses the importance of going beyond the raw output of the calculation and understanding where the result originates. The areas selected for study include the Fermi surface and charge density waves, the stability of solids and the structures of solids under pressure, metal−insulator transitions, the method of moments, superconductivity, and the use of a relatively new technique for the study of chemical bonding, the electron localization function (ELF).

Electronic structure and properties of solids

A central challenge to modern materials science is the rational design and synthesis of new materials possessing exceptional properties. Recent advances in first-principles modeling methods and the availability of increasingly powerful computational resources make this goal increasingly achievable. The strength of these modeling methods lies in their predictive ability. They are able to reproduce the crystal structures and elastic properties of a large class of materials to within 2–3% of experimental values and have predicted a number of phase transitions that have been verified experimentally.Despite the power of these methods, the process of designing materials from first principles is not usually a straight-forward or simple one. It requires overcoming a number of obstacles, some of them quite formidable. First a calculable figure of merit that correlates well with the desired property must be identified. While this may be straightforward in some cases, in others—such as predicting the ability of a material to isolate radionuclides over million-year time scales—the process of reducing complex properties to a few calculable variables can be rather difficult. Next a promising chemical system and a realistic set of crystal structures must be selected. This is not trivial because predicting the structures that can crystallize in a given system can be exceedingly challenging. However a wide variety of methods are available to aid in the generation of promising structures — comparative crystallography, algorithms based upon the concepts of crystalline nets and close packing, modern alloy theory methods, and simulated annealing strategies being some examples.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0883769400031420

Computational Alchemy: The Search for New Superhard Materials

This invention provides novel nanofiber enhanced surface area substrates and structures comprising such substrates for use in various medical devices, as well as methods and uses for such substrates and medical devices. In one particular embodiment, methods for enhancing cellular functions on a surface of a medical device implant are disclosed which generally comprise providing a medical device implant comprising a plurality of nanofibers (e.g., nanowires) thereon and exposing the medical device implant to cells such as osteoblasts.

Medical device applications of nanostructured surfaces

The composition, growth mechanism, and phases of carbon nitride thin films obtained from the reaction of laser ablated carbon and atomic nitrogen have been investigated. The nitrogen composition was found to increase to a limiting value of 50% as the fluence was decreased for laser ablation at both 532 nm and 248 nm. Analysis of these data shows that the overall growth rate determines the nitrogen composition, and suggests that a surface reaction between carbon and nitrogen represents a key step in the growth mechanism. Infrared spectroscopy has also been used to assess the phases present in the carbon nitride thin films. The implications of these results to the stoichiometry of covalent carbon nitride are discussed.

http://cmliris.harvard.edu/assets/APL_66_3582.pdf

Growth and composition of covalent carbon nitride solids

A nitride material comprises C 2 N. A method of forming a covalent carbon material includes forming an atomic nitrogen source, forming an elemental reagent source and combining the atomic nitrogen, elemental reagent to form the covalent carbon material and annealing the covalent carbon material. The elemental reagent is reactive with the atomic nitrogen of the atomic nitrogen source to form the covalent carbon material. Annealing the covalent carbon material produces the C 2 N. In one embodiment, essentially all carbon nitride chemical bonds are single or double bonds.

Covalent carbon nitride material comprising C2 N and formation method

The intrinsic properties and bonding of single phase carbon nitride thin films of stoichiometry C2N have been studied. C2N exhibits high electrical resistivity and thermal conductivity that are similar to the properties shown by diamondlike carbon (DLC) films. Electron energy loss spectroscopy studies how, however, that the carbon in C2N is sp2‐hybridized rather than sp3‐bonded carbon as in DLC. This carbon bonding in C2N film leads to a high thermal stability that makes C2N distinct from DLC and nitrogen doped DLCs, and thus an attractive candidate for applications.

http://cml.harvard.edu/assets/APL_68_2639.pdf

Diamondlike properties in a single phase carbon nitride solid

Carbon nitride thin films were grown using an approach that combines pulsed laser deposition and atomic beam techniques. The composition and phases of the carbon nitride materials obtained from the reaction of laser ablated carbon and atomic nitrogen have been systematically investigated. The nitrogen composition was found to increase to a limiting value of 50% as the fluence was decreased for laser ablation at both 532 and 248 nm. Analysis of these experiments show that the growth rate determines the overall nitrogen composition, and thus suggests that a key step in the growth mechanism involves a surface reaction between carbon and nitrogen. Infrared spectroscopy has also been used to assess the phases present in the carbon nitride thin films. This spectroscopic measurement indicates that a cyanogen-like impurity occurs in films with nitrogen compositions greater than 30%. Investigations of the effects of thermal annealing have been carried out, and show that the impurity phase can be eliminated to yield a single phase material. In addition, systematic measurements of the electrical resistivity and thermal conductivity of the carbon nitride films were made as a function of nitrogen content. The implications of these results are discussed.

Z. John Zhang

Papers

Growth and composition of covalent carbon nitride solids

Covalent carbon nitride material comprising C2 N and formation method

Diamondlike properties in a single phase carbon nitride solid

Pulsed laser deposition and physical properties of carbon nitride thin films

Synthesis of covalent carbon—nitride solids: Alternatives to diamond?