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제  목 : Interfacial interactions in surface chemistry

연  사 : Dr.JUNG, Jaehoon(RIKEN Advanced Science Institute, Hirosawa)
 

일  시 : 2014년 6월 20일 (금) 오후 4시 30분

장  소 : 화학관 세미나실 (330226호실)

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Interfacial interactions in surface chemistry

JUNG, Jaehoon

RIKEN Advanced Science Institute, Hirosawa 2-1, Wako-shi, Saitama 351-0198, Japan

e-mail: jjung@riken.jp

Interfacial interaction has long served as a key element to get fundamental insights into surface science and related chemical phenomena. Understanding interfacial interaction is, therefore, of great importance to achieve robust predictability and high controllability in a variety of applications. Herein, we discuss the role of interfacial interaction in (i) fabricating a well-ordered molecular superstructure on metal surface, (ii) controlling chemical reactivity of ultrathin oxide film grown metal substrate, and (iii) introducing a novel functional group to the basal plane of graphene grown on metal substrate. Computational study based on density functional theory (DFT), in close conjunction with scanning tunneling microscopy (STM) experiment at atomic spatial resolution, has been mainly performed to unveil the influence of a broad range of interfacial interactions on geometric and electronic features of various surface species.

Firstly, we successfully achieved a two-dimensional molecular superstructure of a fluorinated fullerene (C₆₀F₃₆) on Au(111) in a highly ordered manner.^[1] In STM experiment, we observed that the molecules in the well-ordered region are composed of only theC₃ isomer, despite the existence of three isomers (C₃,C₁, and T). The DFT results revealed that the adsorption and lateral orientations of individual C₆₀F₃₆molecules in the superstructure are determined by the localized distribution of LUMO and by intermolecular electrostatic interactions, respectively. We expect that such well-ordered molecular film with high electron affinity might be useful to achieve a uniformn-type semiconducting molecular component in organic electronic device.

Secondly, we demonstrated that the chemical reactivity for water dissociation on an ultrathin MgO film grown on Ag(100) substrate depends greatly on film thickness and is enhanced as compared to that achieved with their bulk counterpart.^[2] The change in the chemical reactivity of ultrathin MgO film depending on the film thickness can be explained by the interaction strength between the oxide and metal interface layers. Therefore, the manipulation of the local structure at the oxide-metal interface plays a pivotal role in controlling the chemical reactivity of ultrathin oxide film.^[3a] We have recently presented that the chemical reactivity of MgO/Ag(100) for the dissociation of individual water molecules can be systematically controlled by interface dopants over the film thickness.^[3b]We introduced the 3d transition metal dopants (Sc ~ Zn) into the oxide-metal interface due to the high tunability with a number of d electrons. DFT calculations revealed that the adhesion at the oxide-metal interface can be addressed by the interaction between a dopant and the oxide layer with aid of ligand field theory and is linearly correlated with the chemical reactivity of the oxide film. Our study provides not only profound insight into the chemical reactivity control of ultrathin oxide film but also an impetus for investigating ultrathin oxide films for a wider range of applications.

Lastly, we suggest, for the first time, that the atomic oxidation of graphene grown on a metal substrate results in the formation of graphene enolate, i.e., negatively charged oxygen adsorbed at ontop position on its basal plane,^[4] which is strikingly different from the formation of epoxy groups, i.e., adsorption of atomic oxygen at bridge position, on free-standing graphene and on graphite. Whereas the enolate is the transition state between two nearest epoxides both on graphene and on graphite, we revealed that improved interfacial interaction between graphene and metal substrate during atomic oxidation plays a crucial role not only in the formation of graphene enolate as a local minimum but also in stabilizing it over the graphene epoxide.

To conclude, our studies open up a new vista for the design of novel materials of new potentials with desired functions based on the deep insight into the a wide range of interfacial interactions and its fine control.  

1. T. K. Shimizu^§, J. Jung^§, T. Otani, Y.-K. Han, M. Kawai, and Y. Kim, ACS Nano 6, 2679 (2012). [^§equally contributed].

2. (a) H.-J. Shin, J. Jung, K. Motobayashi, S. Yanagisawa, Y. Morikawa, Y. Kim, and M. Kawai, Nat. Mater. 9, 442 (2010); (b) J. Jung, H.-J. Shin, Y. Kim, and M. Kawai, Phys. Rev. B 82, 085413 (2010).

3. (a) J. Jung, H.-J. Shin, Y. Kim, and M. Kawai, J. Am. Chem. Soc. 133, 6142 (2011); (b) J. Jung, H.-J. Shin, Y. Kim, and M. Kawai,J. Am. Chem. Soc. 134, 10554 (2012).

4. J. Jung, H. Lim, J. Oh, and Y. Kim, J. Am. Chem. Soc.submitted (2014).