Carbon Forms Structured by Energetic Species: Amorphous, Nanotubes, and Crystalline
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Modern materials science aims at the development of controlled ways of structuring novel materials. High-pressure, high-temperature (HPHT) methods (initiated by the legendary pioneering work of Bridgman ) indeed provide numerous exotic phases for thousands of materials. Among the most important ones that find a billion-size market are diamond and cubic boron nitride. The massive nature of HPHT systems inhibits their use for modern (thin film) technology. An alternative emerging technique (in the past 30 years) for the structuring of materials is the application of energetic species for deposition and surface and bulk modification. It is now very well established that the use of energetic species either by direct ion beam deposition or by bombardment of materials (ion beam-assisted methods) provides a way to structure materials (metals, semiconductors, ceramic, and polymers) controlling a variety of physical properties (including hardness, density, wear resistance, resistivity, optical transparency, surface morphology, and oriented/epitaxial growth). Surprisingly, utilization of energetic species sometimes produced metastable phases previously reported only from HPHT experiments. It is most important to note that ion beam techniques currently provide the most controlled technique known to the semiconductor industry for material modification (e.g., doping) and is extensively used.
In the last decade many efforts were dedicated to the emerging field of nanostructuring of materials, which is the topic of this encyclopedia. Top-down and bottom-up techniques have been developed to structure nanosized materials. A crucial issue in most of the approaches utilized, which have successfully produced a host of novel nanosized materials, is the controlled growth, i.e., processes that yield materials with a narrow distribution of size, structure, and composition thus possessing well-defined properties.
The purpose of this entry is to describe how ion beams can be used in a controlled way to nanostructure a wide spectrum of materials: amorphous, medium-range (multiwall tubes and fullerenelike), and crystalline. Ion beams use the idea of HPHT in a very localized region (nano-HPHT) taking advantage of the control offered by ion beam techniques. Carbon, with its wealth of configurations that will be highlighted in the next section, offers the best study case to demonstrate the idea of ion beam structuring of materials. This entry shortly discusses the experimental systems used for ion beam structuring of carbon and for characterization of the products. It presents the basic physical processes leading to the formation of the nanostructured materials and then describes how amorphous, medium-range, and crystalline forms can be structured and their properties can be tuned accordingly. For additional reading the reader is referred to recent reviews covering structuring of carbon forms by energetic species, structuring by energetic species in general, and superhard materials in general.