Surface Structure, Adsorption, and Thermal Desorption Behaviors of Methaneselenolate Monolayers on Au(111) from Dimethyl Diselenides

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• 作者：Sang Yun Lee ; Eisuke Ito ; Hungu Kang ; Masahiko Hara ; Haiwon Lee ; Jaegeun Noh
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：April 24, 2014
• 年：2014
• 卷：118
• 期：16
• 页码：8322-8330
• 全文大小：461K
• 年卷期：v.118,no.16(April 24, 2014)
• ISSN：1932-7455

文摘

To understand the effect of headgroups (i.e., sulfur and selenium) on surface structure, adsorption states, and thermal desorption behaviors of self-assembled monolayers (SAMs) on Au(111), we examined methanethiolate (CH₃鈥揝, MS) and metheneselenolate (CH₃鈥揝e, MSe) monolayers formed from dimethyl disulfide (DMDS) and dimethyl diselenide (DMDSe) molecules by ambient vapor-phase deposition. Scanning tunneling microscopy imaging revealed that DMDS molecules on Au(111) after a 1 h deposition form MS monolayers containing a disordered phase and an ordered row phase with an inter-row spacing of 1.51 nm, whereas DMDSe molecules form long-range-ordered MSe monolayers with a (鈭? 脳 3鈭?)R30掳 structure. X-ray photoelectron spectroscopy measurements showed that MS or MSe monolayers chemisorbed on Au(111) were formed via S鈥揝 bond cleavage of DMDS or Se鈥揝e bond cleavage of DMDSe. On the other hand, we monitored three main desorption fragments for MS and MSe monolayers using TDS monomers (CH₃S⁺, CH₃Se⁺), parent mass species (CH₃SH⁺, CH₃SeH⁺), and dimers (CH₃S鈥揝CH₃⁺, CH₃Se鈥揝eCH₃⁺). Interestingly, we found that thermal desorption behaviors of MSe monolayers were markedly different from those of MS monolayers. All desorption peaks for MSe monolayers were observed at a higher temperature compared with MS monolayers, suggesting that the adsorption affinity of selenium atoms for the Au(111) surface is stronger than that of sulfur atoms. In addition, the desorption intensity of dimer fragments for MSe monolayers was much lower than for MS monolayers, indicating that selenolate SAMs on Au(111) did not undergo their dimerization efficiently during thermal heating compared with thiolate SAMs. Our results provide new insight into understanding the surface structure and thermal desorption behavior of MSe monolayers on Au(111) surface by comparing those of MS monolayers.