The effects of microstructures and surface states on the field emission, which are important to a good understanding of the field emission mechanism, are unclear. In this paper, the microstructures and surface states of graphene-Sn/SnO2 hybrids were analyzed, and the field emission mechanism was explored. Raman spectra and images revealed that SnO2/Sn droplets are strongly bound on graphene surface, and there exist oxygen vacancies at the surface of graphene-Sn/SnO2 hybrids. Among X-ray photoelectron spectroscopy spectra, the peak of 0 15 shifts 1.6 eV toward higher binding energies in the 5 min sample with the best field emission properties, which indicates that the field emission improvement in graphene-Sn/SnO2 hybrids arises from the band-bending effect and a lower work function. Crown Copyright (C) 2012 Published by Elsevier Inc. All rights reserved.