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A facile approach is developed to easily fabricate field emission (FE) cathodes based on TiO 2 nanotubes with different geometrical structures at low temperature. Planar TiO 2 nanotubes (P-TNTs) are first synthesized using the electrochemical anodization process with applied voltages of 20–50 V for 1 h at room temperature followed by thermal oxidation at 280 °C for 2 h under atmosphere ambient. P-TNTs can be transformed into aggregated TiO 2 nanotubes (A-TNTs) after H 2 O 2 post-treatment for 1 h at room temperature. FESEM, XRD, and Raman spectroscopy were used to analyze the surface morphology, crystallinity, and chemical binding, respectively. The A-TNTs fabricated with the applied voltages of 30–50 V cathodes possess higher levels of FE properties (lower turn-on electric field and higher current density) than the other cathodes due to their greater number of emission sites and decrement of the screening effect. The A-TNT with an applied voltage of 40 V cathode exhibits the lowest turn-on electric field (4.87 V/μm, 1 μA/cm 2 ) and the highest enhancement factor β (1486). These superior properties indicate that the A-TNTs are promising field cathodes for future FE applications.

A hybrid structure of graphene sheets (GSs)/ZnO nanorods (ZNRs) is developed on glass substrates for applications in field emission (FE) cathodes. ZNRs are grown on glass substrates by a combination of sputtering and hydrothermal processes. Graphene films are synthesized on the Cu foils by the thermal chemical vapor deposition technique, and are transferred onto the ZNRs with various cycles (one, two, and three times) to form GS/ZNR hybrids with different morphology. FESEM, XRD, and Raman spectroscopy are used to analyze the surface morphology, crystallinity, and chemical composition, respectively. It is found that the FE properties of all GS/ZNR cathodes possess a lower turn-on electric field and higher current density than pristine ZNR cathode owing to the presence of the GS. The GSs/ZNRs with two transferred cycle exhibit the lowest turn-on electric field (3.7 V/μm, 1 μA/cm 2 ) and highest enhancement factor β (8723). These superior properties indicate that the GS/ZNR hybrids are promising field cathodes in FE applications.