Desorption of butanethiol from Au(111) during storage in ultrahigh vacuum: Effects on surface coverage and stability toward displacement by solution-phase thiols
Desorption of butanethiol from Au(111) during storage in ultrahigh vacuum: Effects on surface coverage and stability toward displacement by solution-phase thiols
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DOI：
10.1021/la961014e
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发表时间：
1997-05-28
期刊：
影响因子：
3.9
通讯作者：
Leggett, GJ
中科院分区：
文献类型：
--
作者：
Hutt, DA;Leggett, GJ
近年来，通过扫描隧道显微镜(STM)的应用，我们对自组装单分子膜(SAM)结构的理解取得了重大进展。对于长链甲基端基分子(CH3(CH2)n-1SH，其中ng8)的1-6个自组元模型，基于相对于Au(111)衬底的(3Ũ3)R30晶格的衍射研究预测的模型已被证实，并随后被修正为包括Ac(4Ũ2)超晶格。1-3 Poirier和同事7-9进行了许多优雅的研究，在这些研究中，他们研究了丁硫醇在Au上的单分子膜的行为。它们显示了一系列与长链自组装膜非常不同的结构。当从溶液中沉积时，首先在整个表面上观察到2D类液体相，没有可分解的结构。然而，在真空中储存时，这在几天的时间内转化为归因于pŨ3(P)8-10)单位目数的有序相。这似乎由沿着Au(111)衬底的次最近邻方向(即，〈112h〉)排列的几排硫醇分子组成，由几行(由p确定的)暴露的Au行隔开。用超高真空(UHV)条件下沉积的长链分子的He原子衍射法，观察到了其他基团10、11的类似结构。此外，p-Ũ-3结构也被注意到在扫描隧道显微镜研究长链分子非常迅速地暴露在稀溶液中沉积。6因此，这种布置似乎是在(3Ũ3)R30层完成之前形成的稳定的低覆盖结构。这一点的支持来自研究7，10最初具有(3Ũ3)R30结构的单层，其在真空中热处理后，在足够的时间和温度升高后转化为pŨ3层，表明一些单层解吸。对于较长的链分子，p值与亚甲基链的长度密切相关，这导致了pŨ3结构可能由附着在表面的二硫键分子组成，亚甲基链平行于金衬底。11.
In recent years, significant advances have been realized in our understanding of the structures of self-assembled monolayers (SAMs) through the application of scanning tunneling microscopy (STM). 1-6 For SAMs of long chain methyl-terminated molecules (CH3 (CH2) n-1SH, where n g 8), the model predicted by diffraction studies, based on a (3Ũ3) R30 lattice relative to the Au (111) substrate, has been confirmed and subsequently refined to include ac (4Ũ2) superlattice. 1-3 Poirier and co-workers7-9 have performed a number of elegant studies in which they have examined the behavior of butanethiol monolayers on Au. These have shown a very different series of structures to those formed by long chain SAMs. Upon deposition from solution, a 2D liquid-like phase is first observed over the whole surface, with no resolvable structure. On storage in vacuum, however, this converts, over a period of several days, to an ordered phase ascribed to a pŨ3 (p) 8-10) unit mesh. 7 This appears to consist of rows of thiol molecules aligned along the next-nearest neighbor direction (ie,〈 112h〉) of the Au (111) substrate, separated by several (determined by p) exposed Au rows. Similar structures have been observed by other groups10, 11 using He atom diffraction for long chain molecules deposited under ultrahigh vacuum (UHV) conditions. In addition, pŨ3 structures have also been noted in STM studies of long chain molecules deposited by very rapid exposure to dilute solution. 6 It therefore appears that this arrangement is a stable low coverage structure formed before completion of the (3Ũ3) R30 layer. Support for this comes from studies7, 10 of monolayers originally possessing the (3Ũ3) R30 structure which, upon annealing in vacuum, convert after sufficient time and elevation of temperature to the pŨ3 layer, indicating desorption of some of the monolayer. For longer chain molecules, the value ofphas been found to correlate closely with the length of the methylene chain, leading to the suggestion that the pŨ3 structure may consist of a disulfide molecule attached to the surface with the methylene chains lying down parallel to the gold substrate. 11