Abstract
The effect of 2.245 GeV Au-ion irradiation and post-annealing processes on the microstructure and electron field emission (EFE) properties of diamond films was investigated. For the microcrystalline diamond (MCD) films, Au-ion irradiation with a fluence of approximately 8.4×1013 ions/cm2 almost completely suppressed the EFE properties of the films. Post-annealing the Au-ion irradiated MCD films at 1000°C for 1 h effectively restored these properties. In contrast, for ultra-nanocrystalline diamond (UNCD) films, the Au-ion irradiation induced a large improvement in the EFE properties, and the post-annealing process slightly degraded the EFE properties of the films. The resulting EFE behavior was still better than that of pristine UNCD films. TEM examination indicated that the difference in Au-ion irradiation/post-annealing effects on the EFE properties of the MCD and UNCD films is closely related to the different phase transformation process involved. This difference is dependent on the different granular structures of these films. The MCD films with large-grain microstructure contain very few grain boundaries of negligible thickness, whereas the UNCD films with ultra-small-grain granular structure contain abundant grain boundaries of considerable thickness. Au-ion irradiation disintegrated the large grains in the MCD films into small diamond clusters embedded in an amorphous carbon (a-C) matrix that suppressed the EFE properties of the MCD films. In contrast, the Au-ion irradiation insignificantly altered the crystallinity of the grains of the UNCD films but transformed the grain boundary phase into nano-graphite, enhancing the EFE properties. The post-annealing process recrystallized the residual a-C phase into nano-graphites for both films.
Highlights
Diamond films have been investigated extensively for their application as electron field emitters because of their negative electron affinity and low effective work function.[1,2] While the physical properties of these films depend on the crystallinity of the materials, their electrical and optical characteristics are more closely related to the microstructure of the samples.[3]
Contrary to the common understanding that diamond is a very strong material that is not damaged by heavy ion irradiation, the above observations indicate that the granular structure of microcrystalline diamond (MCD) films can be significantly modified if the Au ions have high energy and large fluence
transmission electron microscopy (TEM) examination revealed that Au-ion irradiation had disintegrated some of the diamond grains, resulting in nano-sized diamond particulates embedded in an amorphous matrix
Summary
Ion implantation (or irradiation) has long been used to modify the properties of materials through controlled doping with a variety of dopants.[8,9,10] Ion implantation (or irradiation) can break the C-C and hydrocarbon bonds to form sp[2] carbon. We report the improvement effect of heavy-ion (2.245 GeV Au) irradiation on the electron field emission properties of microcrystalline diamond (MCD) and ultra-nanocrystalline diamond (UNCD) films. Special attention is paid to the comparison of the difference in the Au-ion irradiation effects on MCD and UNCD films due to the different microstructures of these films
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