Modification of alkanethiolate monolayers on Au-substrate by low energy electron irradiation: Alkyl chains and the S/Au interface
Modification of alkanethiolate monolayers on Au-substrate by low energy electron irradiation: Alkyl chains and the S/Au interface
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通过低能电子辐照对金基底上链烷硫醇单分子层进行改性：烷基链和 S/Au 界面
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发表时间：
1999
期刊：
影响因子：
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通讯作者：
M. Grunze
中科院分区：
文献类型：
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作者：
M. Zharnikov;W. Geyer;A. Gölzhäuser;S. Frey;M. Grunze
以金基底上的十六硫醇[HDT：CH_3-（CH_2）_（15）-S_-]膜为模型体系，研究了低能电子辐照对烷基乙醇（AT）自组装膜（SAM）的损伤.通过原位光电子能谱和角分辨近边X射线吸收精细结构谱监测诱导的变化。AT SAM被发现是非常敏感的低能电子辐照。烷基链和S/Au界面通过C-H、C-C、C-S和Au-硫醇键的电子诱导解离同时受到影响。最引人注目的过程是取向和构象顺序的损失，部分脱氢和脱附的膜，和新的硫物种的出现。后一个过程可以与在S/Au界面处形成二硫化物或通过与相邻脂肪链中的辐照诱导的碳自由基键合将硫醇盐（或相应的自由基）并入烷基基质中有关。AT膜中最本质的损伤发生在辐照的早期阶段。在50 eV的初级电子能量下，以1000 µC cm-2（每个HDT链约13个电子）的剂量辐照，导致最初有序的HDT膜中的取向顺序几乎完全崩溃，厚度减少约25%，原始Au-硫醇盐键破坏约40%。膜变成包括饱和烃和不饱和烃的无序结构。进一步照射残留膜伴随着连续的C-C键断裂和剩余氢的解吸，这仅仅导致增加交联和饱和烃通过C2C双键的形成转化为不饱和烃。
Low-energy electron irradiation damage in alkanethiol (AT) self-assembled monolayers (SAM) has been studied by using hexadecanethiolate [HDT: CH3–(CH2)15–S-] film on Au-substrate as a model system. The induced changes were monitored by insitu photoelectron spectroscopy and angle resolved near edge X-ray absorption fine structure spectroscopy. AT SAMs are found to be very sensitive to low-energy electron irradiation. Both the alkyl chains and the S/Au interface are affected simultaneously through the electron-induced dissociation of C–H, C–C, C–S, and Au–thiolate bonds. The most noticeable processes are the loss of the orientational and conformational order, partial dehydrogenation and desorption of the film, and the appearance of new sulfur species. The latter process can be related to the formation of disulfide at the S/Au interface or an incorporation of the thiolate (or the corresponding radical) into the alkyl matrix via bonding to irradiation-induced carbon radicals in the adjacent aliphatic chains. The most essential damage in the AT films occurs in the early stages of irradiation. Irradiation with a dose of 1000 µC cm-2 (about 13 electrons per HDT chain) at the primary electron energy of 50 eV results in almost complete breakdown of the orientational order in the initially well-ordered HDT film, a decrease of its thickness by about 25%, and a destruction of ≈40% of the original Au–thiolate bonds. The film becomes a disordered structure comprising both saturated and unsaturated hydrocarbons. Further irradiation of the residual film is accompanied by a continuous C–C bond cleavage and the desorption of the remaining hydrogen, which merely leads to increasing cross-linking and the transformation of saturated hydrocarbons into unsaturated ones through C2C double bond formation.