Article Cite This: J. Phys. Chem. C XXXX, XXX, XXX−XXX
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Linear Alkane Polymerization on Au-Covered Ag(110) Surfaces Zeying Cai,† Rongsheng Pang,† Meizhuang Liu,† Helin Qin,† Shenwei Chen,† Jiuping Zhong,‡ and Dingyong Zhong*,† †
School of Physics and State Key Laboratory of Optoelectronic Materials and Technologies, Sun Yat-sen University, Xingang Xi Road 135, 510275 Guangzhou, China ‡ School of Materials, Sun Yat-sen University, Xingang Xi Road 135, 510275 Guangzhou, China
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ABSTRACT: Efficiently utilizing alkanes as the precursors to realize various chemical reaction processes is challenging due to the inertness of alkane C−H bonds. We report here the selective C−H activation and C−C coupling reaction of linear alkanes on Au-covered Ag(110) surfaces. Based on density functional theory calculations, thin gold films with a thickness of several atomic layers deposited on Ag(110) resemble the bulk Au(110) surface for alkane C−H bond activation. By using scanning tunneling microscopy (STM) we have observed that, instead of linear C−C coupling on unalloyed Au(110), alkane molecules desorb from Ag(110) surfaces at elevated temperatures. The featured missing-row (1 × 2) reconstruction of Au(110) surfaces has been obtained by deposition of ∼20 ML (200 °C). Next, we repeated the above experiments on the a 20 ML Au-covered Ag(110) surface. Figure 5a shows the highresolution STM image of the 20 ML Au-covered Ag(110) surface. Then C32H66 molecules were deposited on the surface at room temperature with a submonolayer coverage (Figure 5b). The blurred features (marked by the red dashed ellipses) also can be seen on the surface as mentioned above, indicating the existence of alkane molecules. After annealing to 200 °C, the substrate surface underwent a transition from (1 × 2) to (1 × 3) reconstruction, and the surface became more flat. At the same time, dehydrogenative end-to-end C−C coupling of the alkane monomers took place with the formation of polymeric chains located in the reconstruction grooves, as shown in Figure 5c,d, similar to our previous work on bulk Au(110).26,28
surface (see Figures S1−S4). After C32H66 molecules were deposited on the 16 ML Au-covered Ag(110) surface (Figure S1), they were adsorbed in the one-dimension grooves and diffused rapidly along the [1−10] direction so that only few blurred features were visible in the STM image (Figure S2).28 However, after annealing to 100 °C, the surface became more flat. Instead of linear C−C coupling, the alkane molecules climbed up on the uppermost gold rows from the grooves (Figure S3a). At the same time, the surface reconstruction grooves have vanished at some regions with the molecules desorption from the surfaces (Figure S3b). The result indicates that alloying of the Au layer with the Ag substrates took place at 100 °C. After the samples were annealed to 200 °C, the surface reconstructions completely vanished, and almost all the molecules had been desorbed from the surface (Figure S4). In other words, a coverage of 16 ML is not enough to form a D
DOI: 10.1021/acs.jpcc.8b09533 J. Phys. Chem. C XXXX, XXX, XXX−XXX
The Journal of Physical Chemistry C
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Article
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Zeying Cai: 0000-0002-0029-928X Meizhuang Liu: 0000-0002-0324-0478 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The work was financially supported by NSFC (No. 11574403 and No. 11374374) and Guangzhou Science and Technology Project (No. 201707020002). The computation part of the work was supported by the National Supercomputer Center in Guangzhou.
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Figure 5. STM images of n-dotriacontane (C32H66) on Au-covered Ag(110) surface before and after annealing. (a) High-resolution STM image of the 20 ML Au-covered Ag(110) surface. The (1 × 2) reconstruction grooves are clearly seen (−0.1 V, 0.5 nA, 30 by 30 nm2). (b) Submonolayer coverage of C32H66 deposited on the Aucovered Ag(110) surface at room temperature. The molecules were adsorbed in the grooves and diffused along the [1−10] direction (−1.0 V, 0.5 nA, 30 by 30 nm2). (c) After annealing at 200 °C, polymeric chains formed in the Au (110)-(1 × 3) reconstruction grooves. The surface morphology transformed from original rugged terrain to the flat topography (−0.5 V, 0.1 nA, 30 by 30 nm2). (d) High-resolution STM image of polymeric chains (0.05 V, 0.8 nA, 8 by 8 nm2).
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CONCLUSIONS With the combination of STM and DFT calculations, linear alkane polymerization on Au-covered Ag(110) surface has been investigated on the atomic scale. Although the Ag(110) surface exhibits a higher energy barrier than Au(110), the thin gold film with a thickness of several atomic layers can resemble the bulk Au(110) surface for alkyl C−H dissociation. The featured missing-row (1 × 2) reconstruction of the Au(110) surface has been obtained by deposition of ∼20 ML (
