Photooxidation of self-assembled monolayers by exposure to light of wavelength 254 nm: A static SIMS study
Photooxidation of self-assembled monolayers by exposure to light of wavelength 254 nm: A static SIMS study
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DOI：
10.1021/jp0443299
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发表时间：
2005-06-09
影响因子：
3.3
通讯作者：
Leggett, GJ
中科院分区：
文献类型：
--
作者：
Brewer, NJ;Janusz, S;Leggett, GJ
烷硫醇的自组装单分子层（SAMs）通过暴露于来自发射具有254 nm波长的光的灯的光而被光氧化。数据证实，SAM氧化暴露于紫外线光源发生在臭氧的情况下，但也表明，该机制是从以前的研究中观察到的使用广谱弧光灯不同。特别是，对于金和银上的单层，羧酸封端的自组装膜氧化速度显着快于甲基封端的自组装膜，与早期的观察单层暴露于汞弧灯的光。两类单层的光氧化速率的差异在银上显著大于在金上。这些数据支持我们最近的建议，虽然甲基封端的自组装膜能够更紧密地包装在银上比在金上，羧酸封端的硫醇不能采用相同的紧密堆积结构，和它们的光氧化率银是相似的，或略大于，那些测量的相同的吸附物在金上。表面电位测量羧酸和甲基封端的自组装膜使用开尔文探针装置。有人发现，羧酸封端的自组装膜的功函数显着大于甲基封端的单分子膜。它的结论是，这些数据是一致的氧化反应被发起的“热”电子产生的光子与金属基板的相互作用。
Self-assembled monolayers (SAMs) of alkanethiols have been photooxidized by exposure to light from a lamp emitting light with a wavelength of 254 nm. The, data confirm that SAM oxidation on exposure to UV light sources occurs in the absence of ozone, but also suggest that the mechanism is different from that observed in previous studies using broad-spectrum arc lamps. In particular, for monolayers on both gold and silver, carboxylic acid-terminated SAMs oxidize significantly faster than methyl-terminated SAMs, in contrast to earlier observations for monolayers exposed to light from a mercury arc lamp. The difference in rates of photooxidation for the two classes of monolayer is significantly greater on silver than on gold. These data support our recent suggestion that while methyl-terminated SAMs are able to pack much more closely on silver than on gold, carboxylic acid-terminated thiols are not able to adopt the same close-packed structures, and their rates of photooxidation on silver are similar to, or slightly greater than, those measured for the same adsorbates on gold. Surface potential measurements were made for carboxylic acid- and methyl-terminated SAMs using a Kelvin probe apparatus. It was found that the work functions of carboxylic acid-terminated SAMs are significantly greater than those of methyl-terminated monolayers. It is concluded that these data are consistent with the oxidation reaction being initiated by "hot" electrons generated following the interaction of photons with the metallic substrate.