The graphene double-walled carbon nanotube (DWCNT) hybrid films were prepared by vacuum filtration and screen printing. Their electron field emission properties have been studied systematically. The electron emission properties of the hybrid films are much better than those of pure DWCNT films and pure graphene films. Comparing with the screen printed films, the vacuum filtered films have many advantages, such as lower turn-on field, higher emission current density, better uniformity, better long-term stability, and stronger adhesive strength with conductive substrates. The optimized hybrid films with 20% weight ratio of graphene, which were fabricated by vacuum filtration, show the best electron emission performances with a low turn-on field of 0.50？V m？1 (at 1？ Acm？2) and a high field enhancement factor of 27000. 1. Introduction Field emission relies on the electron extraction from the material surface by quantum mechanical tunneling [1]. This simple principle has been widely used in field emission displays (FED) [2], electron guns [3, 4], back-light devices [5], and so on. Due to their high aspect ratio, nanometer-sized tip radii, low work function, and high electrical conductivity, carbon nanotubes (CNTs) are considered one of the most promising materials for electron field emission [6–12]. However, the integration of CNT field emission into device remains a challenge which stems from the method of preparing field emission films and the contact between CNT films and the electrical substrates. Lots of methods for fabricating CNT field emission films are developed. CNT films prepared by the chemical vapor deposition (CVD) method [13–15] have high conductivity. But this method is very complex and expensive. Screen printing [16] is widely used to fabricate CNT field emission films, due to its low cost, easy control, and scalable preparation; however, the simple screen printing technique also brings some drawbacks, such as the poor adhesive strength to the substrate, residual organic binders, and high annealing temperature. The electrophoresis method [17] for fabricating CNT films owes some disadvantages, like the bad uniformity of films and the poor adhesive strength to the substrate. Vacuum filtration [18] is also widely used to prepare CNT films, owing to its low cost, being scalable, and low temperature preparation. Films prepared by vacuum filtration have the advantages of no organic binders and strange adhesive strength to the substrate. On the other hand, graphene a two-dimensional (2D) carbon material owns the highest electron mobility of
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