▎ 摘　　要

This paper presents a study on electron field emission (FE) into ultrahigh vacuum (UHV) from a single, cleaned, graphene sheet where its single sheet nature has been carefully characterized and the emission zones are unambiguously the sheet edges. This definitive approach is in contrast to almost all other studies in the literature and can now guide theoretical work and applications. Our sample characterization starts with transmission electron microcopy imaging, Raman characterization, controlled mounting of individual flakes in a scanning electron microscope followed by in situ high temperature and high field treatments. Detailed FE characterization was carried out including current-voltage plots, FE microscopy, and electron energy spectroscopy during subsequent stages of sample cleaning, at room and liquid air temperatures. The full width at half maximum (FWHM) of the energy peak as well as its relative shift versus current and voltage were explored. A notable result is that the energy spectra are very narrow, ten times less than previously reported.