Molecular beam epitaxy of organic films investigated by high resolution low energy electron diffraction (SPA-LEED): 3,4,9,10-perylenetetracarboxylicacid-dianhydride (PTCDA) on Ag(111)
Molecular beam epitaxy of organic films investigated by high resolution low energy electron diffraction (SPA-LEED): 3,4,9,10-perylenetetracarboxylicacid-dianhydride (PTCDA) on Ag(111)
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DOI：
10.1016/j.susc.2004.10.004
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发表时间：
2004-12-20
期刊：
影响因子：
1.9
通讯作者：
Sokolowski, M
中科院分区：
文献类型：
--
作者：
Kilian, L;Umbach, E;Sokolowski, M
报道了用高分辨LEED（SPA-LEED）技术在Ag（111）衬底上生长PTCDA多层膜的详细研究。前两个单层是封闭的，并表现出与下面的Ag（111）表面相当的结构。晶胞参数与PTCDA β体相（102）面的晶胞参数接近，偏差小于或等于2%。第二层相对于第一单层的垂直堆叠（在300 K下观察到）对应于PTCDA的β体相中的垂直堆叠。在高的生长温度（400 K），发生从第三单层向前的Stranski-Krastanov增长，和PTCDA集群，优先与几个明确的方面，增长。簇的结构是PTCDA的结晶更稳定的α体相的结构。相反，在较低的生长温度（200 K），在弗兰克货车der Merve模式，与几个开放层的增长收益。从斜坡选择有证据表明，一个埃利希-Schwoebel障碍。在低温下生长的PTCDA的横向包装对应于误差内的β体相。低温结构和形态是亚稳定的。在300 K的短时间退火使PTCDA薄膜发生形变，而在400 K的长时间退火使薄膜适应在400 K生长温度下直接获得的结构和形貌。据推测，在低温下形成具有β相样晶格的层是由于与α相晶格相比，β相更好地适合于下面的相称单层。然而，在高的生长温度下，晶体学上更稳定的α相生长，通过形成簇减少了与下面的相称的前两层晶格失配的面积。(C)2004 Elsevier B. V.保留所有权利。
A detailed investigation of the multilayer growth of PTCDA on Ag(111) by high resolution LEED (SPA-LEED) is reported. The first two monolayers are closed and exhibit a structure, which is commensurate with respect to the underlying Ag(111) surface. The lattice parameters are close to those of the (102) plane of the beta bulk phase of PTCDA, with deviations less than or equal to2%. The vertical stacking of the second layer with respect to the first monolayer (observed at 300K) corresponds to that in the beta bulk phase of PTCDA. At high growth temperatures (400K), Stranski-Krastanov growth occurs from the third monolayer onward, and PTCDA clusters, preferentially with few well defined facets, grow. The structure of the clusters is that of the thermodynamically more stable alpha bulk phase of PTCDA. Contrary, at low growth temperatures (200K), the growth proceeds in the Frank van der Merve mode, with several open layers. From slope selection there is evidence for an Ehrlich-Schwoebel barrier. The lateral packing of the PTCDA grown at low temperatures corresponds within error to that of the beta bulk phase. The low temperature structure and morphology is meta-stable. Short annealing at 300K flattens the PTCDA film, and prolonged annealing at 400K causes the film to adapt the structure and morphology obtained directly at 400K growth temperature. Presumably, the formation of layers with a beta-phase-like lattice at low temperature is due to the better fit of the beta phase, compared to the alpha phase lattice, to the underlying commensurate monolayer. However, at high growth temperatures, the thermodynamically more stable alpha phase grows, reducing the area of lattice misfit to the underlying commensurate first two layers by formation of clusters. (C) 2004 Elsevier B.V. All rights reserved.