| AVS 58th Annual International Symposium and Exhibition | |
| Graphene and Related Materials Focus Topic | Wednesday Sessions |
| Session GR-WeA |
| Session: | Graphene Characterization including Microscopy and Spectroscopy |
| Presenter: | Elena Starodub, Sandia National Laboratories |
| Authors: | E. Starodub, Sandia National Laboratories N.C. Bartelt, Sandia National Laboratories K. McCarty, Sandia National Laboratories |
| Correspondent: | Click to Email |
We employ low-energy electron microscopy (LEEM) to study the thermionic emission of graphene on representative metals, Ru(0001) and Ir(111). In traditional LEEM, an image is produced using low-energy electrons reflected from a surface. The unique capabilities of LEEM allow us to image directly electrons thermionically emitted from graphene at high temperatures, above 1100K, using the same imaging optics. Due to the strong dependence of emission current on temperature, given by the Richardson-Dushman equation, we determine the work function of graphene-covered Ru(0001) and Ir(111) surfaces. The work function of graphene on Ru(0001) is determined to be 3.4 ± 0.1 eV, which is considerably smaller than work function of clean Ru (5.4 eV) and graphene (4.6eV). The obtained value is in good agreement with the result of first principles calculations, 3.6 eV [1], where strong graphene/metal interaction leads to significant film-to-substrate charge transfer and, as a result, reduced work function.
In contrast to the strong interaction with Ru, graphene bounds weakly to the Ir surface reducing the work function. The work functions of graphene on Ir(111) measured for two in-plane orientations on the Ir surface [2], R0 and R30, are 4.5 ± 0.1 eV and 4.7 ± 0.1 eV, respectively. Thus, the in-plane orientation noticeably changes the work function on Ir. It is consistent with our previous observation of the effect of electronic structure on orientation by electron reflectivity [3] and ARPES [4] .
Our finding shows that graphene has another application in addition to be a promising candidate for future electronics. One-monolayer graphene on metals such as Ru and Ir can be used as a chemically inert electron emitter with large surface area and low work function, comparable to lanthanum hexaboride, LaB6.
Acknowledgement: This work is supported by the Office of Basic Energy Science, Division of Materials Sciences and Engineering of the U.S. DOE under Contract No. DE-AC04-94AL85000.
[1] B. Wang, S. Günther, J. Wintterlin and M.–L. Bocquet, New Journal of Physics 12 (2010) 043041
[2] E. Loginova, S. Nie, K. Thürmer, N. C. Bartelt, and K. F. McCarty, PRB 80 (2009) 085430
[3] S. Nie S, A. L. Walter, N. C. Bartelt, E. Starodub, A. Bostwick, E. Rotenberg, K. F. McCarty, ACS NANO 5 (2011) 2298-2306
[4] E. Starodub, A. Bostwick, L. Moreschini, S. Nie, F. El Gabaly, K. F. McCarty, and E. Rotenberg, PRB 83 (2011) 125428