Chap4MS学习摘要.pptVIP

热力学上表面（界面）的概念 * 表面切分原则 * 表面原子的坐标? * 表面坐标与体坐标相比，会有改变 * * Pt as example 立方密堆积与六方密堆积 * * 根据第一层原子坐标的Z值来确定面间距，再确定原子面密排次序。 分析表面的时候不是单一的最上层原子，而应考虑所有具有表面断键的原子层 * 1位上有下层原子，而另一间隙下没有下层原子，所以有两种不同的表面取法,一般的某种材料有fcc结构，往往会有hcp结构，如ZnO,纳米ZnO形状的多样性与它具有两种晶型相关 * 可以看剩下多少个键，来知道有多少断键 * The same thing happens at III-V semiconductor surfaces but with interesting added twists. As the figure indicates, the surface consists entirely of Group V atoms (or light B atoms, e.g., As), but it could just as easily consist of Group III atoms (or dark A atoms, e.g., Ga), These unique and distinct surfaces arise because cuts can only be made between planes AA and BB. The reasons for such cuts are: (a) only one bond between atoms needs to be disrupted and (b) the surface atoms remain triply bonded to the lattice. Other cuts such as those between AA and BB are not possible because three bonds must be severed and resultant surface atoms are singly bonded to the lattice. For the BB, so-called (111) surface, we note that only three of five valence electrons in each arsenic atom are attached or bonded, while on an AA (111) surface all three of borons valence electrons are bonded. As a consequence, the As surface is more electronically active than the Ga surface, and can, for example, be smoothed and polished more readily by etching. In contrast, Ga surfaces etch slowly and tend to be rougher. Such differences lead to varied epitaxial phenomena when films are deposited on these surfaces. * 前面讲的都是理想的低米勒指数面 * * 扭折处的原子的结合能可测，并且可用于估算体原子的结合能。 * 可用于得到任意面的表面能 * * 解释公式 分别用最近邻近似和第二近邻近似估算fcc结构金属(111)，(100)，(110)面的表面能比值，并与表中的比值进行比较。 * * 升华热（固体转变为气体），气化热（液体转变为气体在固体熔化状态，因为有约10％的少量键已经被打破（这时配位数约等于10或11），因此气化潜热比升华潜热约小10％。 Ns为表面断键密度 * * 离子键或共价键表面断键所产生的附加能量高。 Atomic positions of adatoms relative to substrate atoms arrayed on a (100) simple cubic plane * 表面增原子12个，第一层支撑原子42个，第二层原子48个(顶角缺位) * 12+42+4849*2 通过顶点凹陷的台阶上原子的总断键数少，在能连上有利 * Li et al., Phys. Rev. Lett. 88, 066101 (2002) Jia et al., Phys. Rev. B66, 165408 (2002) Jia e