TRANSMISSION ELECTRON MICROSCOPE STUDY OF INTERNAL STRESSES AT RECONSTRUCTED CLEAN AND METAL ADSORBED SURFACES

在超高真空条件下，透射电子显微镜（TEM）可以揭示表面结构和表面动态过程。该技术的特点之一是它可以表征由于表面重建而产生的表面内部应力。大多数表面重构和吸附结构，如果没有衬底，并不总是具有与衬底晶格相同的晶格周期。这就是内表面应力的来源。这会导致晶体薄膜的弯曲。相反，在弯曲晶体上，表面结构或表面结构域有利于这种应变提名。在前一种情况下，即使在强内应力的情况下，多畴形成也不会引起弯曲。透射电镜可观察到由内表面应力引起的晶格应变。我们的观察总结如下。(1) Si (111) 4 × 1- in结构无内应力。(2) Si (001) 2x1表面是各向异性的。(3) Si (111) 7x7结构处于弱应力状态，7x7和1x1结构之间的相界具有较强的晶格应变。(4) Si (111) 5x2-Au表面具有各向异性晶格应力。在TEM图像中，5x2结构的畴边界具有较强的应变对比度。(5) Si（111）上的台阶具有平行于表面的晶格应变。这可能部分是由于表面重建。在本研究项目中，我们设计并制造了一个电子显微镜样品架，通过它我们可以对表面施加应变。结果表明，Si试样可以在显微镜下原位加热至1200℃，表面应变约为0.1%。使用该支架，我们可以观察到Si (001) 2x1畴在压缩应变下在表面上畴化，而1x2畴在拉伸应变下占主导地位。先前有报道称，电流升高会导致Si（001）表面出现2x1的主要畴。但发现电流效应弱于应变效应。少

Transmission electron microscopy (TEM) in an ultra-high vaccuum condition can reveal structures of surfaces and surface dynamic processes. One of the characteristics of the technique is in that it can characterize internal surface stresses at surfaces which are due to surface reconstruction. Most of the surface recon-structions and adosrbate structures, if it is free from the substrates are not always have the same lattice period with that of the substrate lattice underneath. This is the origin of the interna lsurface stresses. This causes bending of thin crystal films. Inversely, on the bend crystals surface structures or surface structure domians which favor such strain nominates. In the former cases, multi-domain formation does not cause bending even in cases of strong internal tress. TEM can see lattice strain caused by internal surface stress.Our observations were summarized as follows.(1) Si (111) 4x1-In structure does not have internal stress.(2) Si (001) 2x1 surface is anisotro … More pically stressed.(3) Si (111) 7x7 structure is under a delatational stress and phase boundaies between 7x7 and 1x1 structure have strong lattice strain.(4) Si (111) 5x2-Au surface has anisotropic lattice stress. Domain boundaies of the 5x2 structure have strong strain contrast in TEM images.(5) Steps on Si (111) have lattice strain parallel to the surface. This may be partly due to surface reconstruction.In the present reseach project we designed and constructed a electron microscope specimen holder by which we can apply strain on surfaces. It was found that Si specimen can be heated in-situ in the microsocpe up-to 1200ﾟC and surface strain of about 0.1% can be applied.With use of this holder, we could observe that Si (001) 2x1 domains domainate on the surface under a compressive strain and 1x2 domains dominate under a delatational strain. It was previously reported that a step up current causes major domains of 2x1 on Si (001) surface. However, it was found that current effect is weaker than the strain effect. Less