Soft X-ray Exposure Promotes Na Intercalation in Graphene Grown on Si-Face SiC.

Somsakul Watcharinyanon,Chao Xia,Alexei Zakharov,Leif Johansson,Rositza Yakimova,Yuran Niu,Chariya Virojanadara

doi:10.3390/ma8084768

Somsakul Watcharinyanon, Chao Xia + Show 5 more

Open Access

https://doi.org/10.3390/ma8084768

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Journal: Materials	Publication Date: Jul 28, 2015
Citations: 12	License type: CC BY 4.0

Affiliation: Linköping University, Lund University, MAX IV Laboratory

Abstract

An investigation of how electron/photon beam exposures affect the intercalation rate of Na deposited on graphene prepared on Si-face SiC is presented. Focused radiation from a storage ring is used for soft X-ray exposures while the electron beam in a low energy electron microscope is utilized for electron exposures. The microscopy and core level spectroscopy data presented clearly show that the effect of soft X-ray exposure is significantly greater than of electron exposure, i.e., it produces a greater increase in the intercalation rate of Na. Heat transfer from the photoelectrons generated during soft X-ray exposure and by the electrons penetrating the sample during electron beam exposure is suggested to increase the local surface temperature and thus the intercalation rate. The estimated electron flux density is 50 times greater for soft X-ray exposure compared to electron exposure, which explains the larger increase in the intercalation rate from soft X-ray exposure. Effects occurring with time only at room temperature are found to be fairly slow, but detectable. The graphene quality, i.e., domain/grain size and homogeneity, was also observed to be an important factor since exposure-induced effects occurred more rapidly on a graphene sample prepared in situ compared to on a furnace grown sample.

Highlights

The effects induced by Na deposited on graphene samples grown on Si-face SiC and kept at room temperature and after subsequent heating have been investigated previously [1,2,3], using photoelectron spectroscopy (PES,ARPES), scanning tunneling microscopy (STM), and low-energy electron microscopy (LEEM)
This, we suggest, explains the difference in intercalation rates observed between the soft X-ray and electron beam exposures
Both electron and photon beam exposures are shown to affect the intercalation rate of Na deposited on graphene, prepared on Si-face SiC

Summary

Introduction

The effects induced by Na deposited on graphene samples grown on Si-face SiC and kept at room temperature and after subsequent heating have been investigated previously [1,2,3], using photoelectron spectroscopy (PES,ARPES), scanning tunneling microscopy (STM), and low-energy electron microscopy (LEEM). These investigations concluded that partial intercalation in between carbon layers and at the interface occurred directly after deposition, most of the Na initially remained on the sample surface and droplets of Na formed. It showed very similar though more pronounced effects, which we attributed to the considerably smaller graphene domain/grain sizes present on samples grown this way

Results and Discussion

Experimental Section

Conclusions