Photooxidation of self-assembled monolayers by exposure to light of wavelength 254 nm: A static SIMS study

被引:65
作者
Brewer, NJ
Janusz, S
Critchley, K
Evans, SD
Leggett, GJ
机构
[1] Univ Sheffield, Dept Chem, Sheffield S3 7HF, S Yorkshire, England
[2] Univ Manchester, Dept Chem, Manchester M60 1QD, Lancs, England
[3] Univ Leeds, Sch Phys & Astron, Leeds LS2 9JT, W Yorkshire, England
关键词
D O I
10.1021/jp0443299
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
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.
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收藏
页码:11247 / 11256
页数:10
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