Structural analysis of clean LaB6(100), (111), and (110) surfaces via quantitative low-energy electron diffraction
Structural analysis of clean LaB6(100), (111), and (110) surfaces via quantitative low-energy electron diffraction
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DOI：
10.1016/j.susc.2020.121686
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发表时间：
2020-11-01
期刊：
影响因子：
1.9
通讯作者：
Mizuno, Seigi
中科院分区：
文献类型：
--
作者：
Noguchi, Akio;Takamura, Yu;Mizuno, Seigi
LaB6具有非常重要的电子发射特性，但其所提出的基面表面结构与功函数的取值相矛盾。在本研究中，我们通过定量的低能电子衍射分析确定了LaB6单晶的表面结构。在(100)面上，La原子在(100)面上被一个La原子终止，La原子向块体晶体一侧驰豫。在(111)和(110)面上，表面由一个La原子和一个B原子团终止，但该原子团的B原子数少于B-6八面体。因为B-6八面体很稳定，所以表面很可能是由B-6八面体终止的。相反，我们的结构分析显示，(111)面的表面被一个B-3三角形终止。(110)面具有c(2×2)周期，根据我们的分析得到了三种可能的模型。我们不知道这些模型中的哪一个存在于表面上，它们可以共存于表面上。这三个模型具有相似的结构；然而，模型1具有B-4终止，模型2具有B(4)和B(3)混合终止，而模型3具有B-3终止。所确定的(111)和(110)面的结构与先前提出的模型有很大的不同。基于我们的表面分析，可以合理地解释LaB6单晶上述表面的功函数值。
LaB6 has very important features for electron emission, but its proposed surface structures of the fundamental planes contradict the work function values. In this study, we determined the surface structures of the LaB6 single crystal via quantitative low-energy electron diffraction analysis. On the (100) plane, the surface was terminated by a La atom, which relaxed toward the bulk crystal side. On the (111) and (110) planes, the surfaces were terminated by a La atom and a cluster of B, but the cluster had smaller number of B atoms than the B-6 octahedron. Because the B-6 octahedron is quite stable, it is likely that the surfaces are terminated by a B-6 octahedron. In contrast, our structural analysis revealed that the surface of the (111) plane was terminated by a B-3 triangle. The surface of the (110) plane has a c(2 x 2) periodicity, and we obtained three possible models according to our analysis. We cannot tell which of these models exists on the surface, and they can coexist on the surface. These three models have similar structures; however, model 1 has B-4 termination, model 2 has B(4 )and B(3 )mixed termination, and model 3 has B-3 termination. The determined structures for the (111) and (110) planes are very different from previously suggested models. Based on our surface analysis, the work function values of the above surface planes of the LaB6 single crystal can be reasonably explained.