0485-晶体生长基础-郭学锋[hejizhancom].pptVIP

1.4 材料科学研究与发展方向 （1）材料复合化 （2）纳米材料 （3）智能材料 （4）生物医学材料 （5）C60系列材料 非平衡材料 C－CARBON Carbon is an element that exists in various polymorphic forms, as well as in the amorphous state. This group of materials does not really fall within any one of the traditional metal, ceramic, polymer classification schemes. 1. DIAMOND Diamond is a metastable carbon polymorph at room temperature and atmospheric pressure. Its crystal structure is a variant of the zinc blende, in which carbon atoms occupy all positions (both Zn and S), as indicated in the unit cell shown in Figure 3.4. Figure A unit cell for the diamond cubic crystal structure. 2. GRAPHITE Graphite has a crystal structure distinctly different from that of diamond and is also more stable than diamond at ambient temperature and pressure. The graphite structure is composed of layers of hexagonally arranged carbon atoms; within the layers, each carbon atom is bonded to three coplanar neighbor atoms by strong covalent bonds. The fourth bonding electron participates in a weak van der Waals type of bond between the layers. Figure The structure of graphite. covalent bond Weak van der Waals type 3. FULLERENES Another polymorphic form of carbon was discovered in 1985. It exists in discrete molecular form, and consists of a hollow spherical cluster of sixty carbon atoms. A single molecule is denoted by C60 . Each molecule is composed of groups of carbon atoms that are bonded to one another to form both hexagon (six-carbon atom) and pentagon (five-carbon atom) geometrical configurations. One such molecule is found to consist of 20 hexagons and 12 pentagons, which are arrayed such that no two pentagons share a common side; the molecular surface thus exhibits the symmetry of a soccer ball. The material composed of C60 molecules is known as buckminsterfullerene, named in honor of R. Buckminster Fuller, who invented the geodesic dome. C60 is often referred to as ‘‘buckyball’’ for short. The term fuller