Electrical conduction in undoped ultrananocrystalline diamond thin films and its dependence on chemical composition and crystalline structure

Abstract

Ultrananocrystalline diamond film deposition by direct-current plasma assisted chemical vapor deposition using hydrogen-rich precursor gas in the absence of the positive columnInteresting trends in direct current electrical conductivity of chemical vapor deposited diamond sheetsThe electrical conduction behavior of undoped ultrananocrystalline diamond ͑UNCD͒ and its dependence on deposition temperature and chemical structure are presented. UNCD films were grown using a microwave plasma-enhanced chemical vapor deposition technique at deposition temperatures of 400°C and 800°C. The chemical structure of the UNCD films is characterized with several tools including: Elastic recoil detection analysis, Fourier transform infrared spectroscopy, electron energy loss spectroscopy, Raman spectroscopy, and environmental scanning electron microscope. The results show a higher content of sp 2 -bonded carbon for the 800°C deposition samples ͑ϳ65%͒ in comparison with the 400°C samples ͑ϳ38%͒. In both kinds of films, the hydrocarbon bonds have the saturated sp 3 structures, while there is lower hydrogen content in the 800°C samples ͑ϳ8%͒ than in the 400°C samples ͑ϳ10%͒. For conduction properties, experiments are conducted using a probe station and conductive-atomic force microscopy. Experimental data show that the samples deposited at 800°C are several orders of magnitude more conductive than the 400°C samples. The conduction occurs primarily along the grain boundary for both types of samples. The conductivity of both types of films also shows field dependent nonlinear behavior. Both the Poole-Frenkel models and single and overlapping Coulombic potential models show that the conduction is directly correlated with the sp 2 bond carbon density, and the role of the hydrocarbon bonds in the conduction path is formed by the network of the sp 2 bonded carbon.

Structural and electronic properties of nitrogen ion implanted ultra nanocrystalline diamond surfaces

“…Overall the implanted nitrogen enhances the field emission properties of UNCD even after post-implantation annealing as reported by Joseph et al 10 Several mechanisms have been proposed to explain the observed field enhancement behavior, while no single mechanism alone could give a complete picture. 10,[13][14][15][16][17][18][19] To understand the enhancement of field emission in nitrogen implanted UNCD samples further, Raman, XPS, TEM, STM, and STS measurements have been carried out in more detail. STS in CITS mode is used to confirm the emission sites in the nitrogen implanted UNCD samples.…”

“…Our results support the possibility of a grain-boundary electron transport mechanism (conductivitychannel process). [13][14][15] Even though CITS observations show that grain boundaries are the prominent electron emission sites at the nitrogen fluence of 5 Â 10 15 ions=cm 2 , I-V curves show that emission is also coming from the grains but at a higher turn-on field. If the nitrogen ion fluence is increased further, sp 2 content and the density of states at the grains are expected to increase proportionally, and band structure will show metallic behavior like that of grain boundaries, and the grains may not remain purely as diamond.…”

Effect of gigaelectron volt Au-ion irradiation on the characteristics of ultrananocrystalline diamond films

“…3 During the growth of diamond films, hydrogen is usually incorporated into the materials and is presumed to reside at the grain boundaries. 4 Studies have been conducted on the correlation of hydrogen retention with the bonding, 4-6 conductivity, 7 and field emission 8,9 of diamond films. However, the control of hydrogen content in the diamond films is complicated.…”

“…On the other hand, the sp 2 -bonded carbon within chemical vapor deposited ͑CVD͒ diamond films can be thought of as a conduction promoter, particularly if the sp 2 -bonds form interconnected networks along which electrons are free to move. 4 Control of the proportion of sp 2 -bonds can be achieved by the irradiation of energetic heavy ions into the diamond thin films. Many reports have discussed the effects of ion beam irradiation on the characteristics of type IIa diamond, 10 diamondlike carbon films, 11 taC, 12 , graphite, 13 and polycrystalline CVD diamond films.…”

Microstructure evolution and the modification of the electron field emission properties of diamond films by gigaelectron volt Au-ion irradiation

“…Much work has been carried out to improve the field emission of microcrystalline and nanocrystalline diamond by the ion implantation process. 10,11 Moreover, many reports have discussed the effects of ion beam irradiation on the characteristics of carbon based materials such as type IIa diamond, 12 diamond-like carbon films, 13 taC, 14 graphite 15 and polycrystalline CVD diamond films. [16][17][18] Furthermore, Pandey et al 19 and Koinkar et al 20 have studied the field emission enhancement by swift heavy ion irradiation in CVD diamonds; nevertheless, the mechanism for the modification of these characteristics remains unclear.…”