Electron-beam irradiation of photopolymerized C60 film studied using in situ scanning tunneling microscope, in situ Fourier-transform infrared spectroscopy, and first-principles calculations

Jun Onoe,Masato Nakaya,Kaoru Ohno,Tomonobu Nakayama,Yusuke Noda,Shinta Watanabe

doi:10.1063/5.0018985

Abstract

We have examined the formation of a two-dimensional (2D) new carbon network by inducing the general Stone–Wales transformation between adjacent C60 molecules in a 2D dumbbell-type C60 polymer film. Structural changes in pristine C60 films after ultraviolet-visible (UV-vis) light and electron-beam (EB) irradiations were studied using in situ scanning tunneling microscope (STM) and in situ Fourier-transformed infrared (IR) spectroscopy, in combination with first-principles calculations based on density functional theory. Analyses of STM images and depth profiles found that three types of photopolymerized dumbbell-shaped dimers and trimers are formed on the surface layers of pristine C60 films: (i) [2+2] C60 dimers formed in a lateral direction, (ii) [2+2] dimerization of C60 between the first and second layers, and (iii) a triangular [2+2] C60 trimer along a lateral direction. As UV-vis light irradiation time increases, a comparison between experimental and theoretical IR spectra indicated that 2D dumbbell-shaped C60 polymers are formed within a few surface layers of the C60 film (in a similar manner, a 1D dumbbell-shaped polymer is also formed in a shallow space of the C60 film), whereas a [2+2] dumbbell-shaped dimer is formed in any bulk space of the film. Thereafter, when the EB was irradiated to the photopolymerized C60 film, the evolution of IR spectra with respect to EB irradiation time suggested that the 2D dumbbell-type C60 polymer is not decomposed but structurally changed to form a new network polymer.

Highlights

S is introduced to the planar sheet [Fig. 1(b)], it was theoretically predicted that the Dirac cone is rotated by 90○, and this causes an intense and narrow density of states (DOS) at the Fermi level (EF),[5] which is similar to that of platinum metal
Structural changes in pristine C60 films after ultraviolet-visible (UV-vis) light and electron-beam (EB) irradiations were studied using in situ scanning tunneling microscope (STM) and in situ Fouriertransformed infrared (IR) spectroscopy, in combination with first-principles calculations based on density functional theory
As UV-vis light irradiation time increases, a comparison between experimental and theoretical IR spectra indicated that 2D dumbbell-shaped C60 polymers are formed within a few surface layers of the C60 film, whereas a [2+2] dumbbell-shaped dimer is formed in any bulk space of the film

Summary

Introduction

S is introduced to the planar sheet [Fig. 1(b)], it was theoretically predicted that the Dirac cone is rotated by 90○, and this causes an intense and narrow density of states (DOS) at the Fermi level (EF),[5] which is similar to that of platinum metal. There have been no reports on synthesis of the 2D uneven sheet so far The aim of the present study is to form a new 2D carbon network sheet with the combination of photo-induced and EB-induced polymerization processes applied to a pristine C60 film. We examined the structural characteristics of the photo/EB-polymerized C60 film formed under ultrahigh vacuum (UHV) conditions, using in situ scanning tunneling microscope (STM) and in situ Fourier-transformed infrared (FT-IR) spectroscopy, in combination with first-principles calculations based on density functional theory

Objectives

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Results

Conclusion