Enhanced electron field emission of two-dimensional boron-doped ZnO nanoflakes on nanocrystal diamond films

B doping into ZnO to improve the electrical property is one of the hot topics to push forward its application in field-emission devices. Besides, compared with the conventional Si substrates, nanocrystalline diamond (NCD) films have been considered as more promising substrates for use in extreme environments, due to their wide band gap, high thermal conductivity breakdown voltage, and large Baliga's figures of merit (~43,938). In this work, boron-doped ZnO (BZO) nanoflakes have been grown on NCD films by hydrothermal method. The morphologies, crystallographic structure, and electrical conductivity of the BZO nanoflakes on NCD films with different growth time have been investigated. Besides, the electron field emission (EFE) properties of the specimens were compared with those on the Si substrates. The results illustrate that the ZnO growth along the c-axis direction was inhibited by B doping and formed two-dimensional nanoflakes. New flaky assembly units would be generated and grown by the surface adsorption of HMTA molecules and Zn2+ ions with prolonged growth time, causing the transformation from single-layer nanoflakes to multi-layer ones. Meanwhile, the formation of oxygen vacancies was effectively inhibited by B doping, increasing the ZnO crystal quality. The BZO nanoflakes grown for 8 h possessed multilayer structure and the highest crystal quality which provided more efficient electron emission sites, leading to better EFE properties than that of other specimens. In addition, the NCD-based emitters obtained a longer lifetime and better stability due to their higher electrical conductivity and steady electron transport, compared with Si-based emitters. These can prove that the BZO nanoflakes/NCD films own notable EFE performances, which can make them achieve promising applications for different field-emission devices.