Microscopic structure of the discommensurate phases in Ge(111)/Ga. I. Atomic structure within domains.
Microscopic structure of the discommensurate phases in Ge(111)/Ga. I. Atomic structure within domains.
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DOI：
10.1103/physrevb.51.9952
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发表时间：
1995-04
期刊：
影响因子：
--
通讯作者：
Artacho;Molinàs-Mata;Boehringer;Zegenhagen;Franklin;Patel
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文献类型：
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作者：
Artacho;Molinàs-Mata;Boehringer;Zegenhagen;Franklin;Patel
本文用X射线驻波和第一性原理计算方法确定了Ge（111）/Ga中出现的三种不同非公度相畴内的原子结构。这些相的全局结构由被基本位错（畴壁）隔开的畴的超结构组成。畴的内部基本上保持了理想Ge（111）表面的对称性，除了晶格的膨胀应变。这些相的结构由畴的形状、尺寸和布置、畴内部每个晶胞中镓原子的数量、这些镓原子的吸附位点和化学键合以及畴内的应变决定。两个低覆盖度相γ和β在1× 1表面晶胞中含有一个Ga原子。在覆盖度最低的γ相，Ga原子取代了Ge（111）表面层的Ge原子，形成了等效畴的六方超结构。β相中的畴超结构显示了两种不同类型的畴，它们都是三角形的，平铺在表面上：Ga在两种畴类型中取代了表面Ge原子。它们的不同之处在于存在一个堆垛层错的Ga层相对于下面的大块锗在一种类型的域，而另一个显示正确的堆叠。在较高的覆盖率下，第二层Ga原子开始覆盖H3位的β相。这种称为β H3的结构可能是形成体Ga团簇的中间态。推测H3位的Ga原子对γ→ β相变有促进作用。
The atomic structure within domains of three different discommensurate phases that appear in Ge (111)/Ga is determined by means of x-ray standing waves together with first-principles total-energy calculations. The global structure of these phases consists of a superstructure of domains separated by elementary discommensurations (domain walls). The interior of the domains essentially preserves the symmetry of the ideal Ge (111) surface except for an expansive strain of the lattice. The structure of such phases is determined by shape, size, and disposition of the domains, by the number of gallium atoms per unit cell in the interior of the domains, and the adsorption site and chemical bonding of these gallium atoms, as well as strain within the domains. The two lower coverage phases γ and β have one single Ga atom per 1× 1 surface unit cell. In the lowest coverage phase γ, the Ga atom substitutes for the Ge atom of the ideal Ge (111) surface layer giving rise to a hexagonal superstructure of equivalent domains. The domain superstructure in the β phase shows two different types of domains, both of them triangular, that tile the surface: Ga substitutes for the surface Ge atom in both domain types. They differ by the presence of a stacking fault of the Ga layer with respect to the underlying bulk Ge in one type of domain, whereas the other one shows the correct stacking. At higher coverages a second layer of Ga atoms begins to cover the β phase in H 3 positions. This structure, called β H 3 is possibly an intermediate state towards the formation of bulk Ga clusters. It is speculated that Ga atoms at H 3 positions can facilitate the γ→ β phase transition.