Enhanced field emission properties of graphene-based cathodes fabricated by ultrasonic atomization spray

Two types of graphene cathodes were constructed by doctor blade and ultrasonic atomization spray respectively. The effects of cathodic film morphology and thickness on graphene cathodes' field emission performance were investigated. Ultrasonic atomization spray coated graphene cathodes possess a much lower turn-on and threshold field but much higher emission current density than graphene cathodes coated by doctor blade. The enhanced field emission properties can be ascribed to the suppression of field-screening effect by roughened surface geometry rendered by ultrasonic atomization spray. For ultrasonic atomization sprayed graphene cathodes at a film thickness of 116 μm, an emission current density as large as 29.6 mA cm^-2 was achieved at 5 V μm^-1, along with a turn-on field and threshold field as low as 1.52 V μm^-1 and 2.65 V μm^-1, respectively. Emission stability examination shows no visible emission current density fluctuation or decline over a 10 hour operation at ∼3.72 mA cm^-2, demonstrating excellent field emission stability for ultrasonic atomization sprayed graphene cathodes. The luminance test also indicates good uniformity of electron emission from ultrasonic atomization sprayed graphene cathodes. The above experiment results indicate that the ultrasonic atomization spray method is suitable for large-area fabrication of high-performance graphene field emitters and holds great potential for applications in field emission displays.