Stress-induced formation of high-density amorphous carbon thin films

Abstract

Amorphous carbon films with high sp 3 content were deposited by magnetron sputtering and intense argon ion plating. Above a compressive stress of 13 GPa a strong increase of the density of the carbon films is observed. We explain the increase of density by a stress-induced phase transition of sp 2 configured carbon to sp 3 configured carbon. Preferential sputtering of the sp 2 component in the carbon films plays a minor role compared to the sp 2 ⇒sp 3 transition at high compressive stress formed during the deposition process. Transmission electron microscopy shows evidence of graphitic regions in the magnetron sputtered/Ar plated amorphous carbon thin films. Differences in the microstructure of the tetrahedral amorphous carbon ͑ta-C͒ films deposited by filtered arc and mass selected ion beam; and those films deposited using magnetron sputtering combined with intense ion plating can be used to explain the different electronic and optical properties of both kinds of ta-C films. © 1997 American Institute of Physics. ͓S0021-8979͑97͒09422-X͔ INTRODUCTIONCarbon films have been of considerable research interest since Aisenberg and Chabot 1 deposited the first hard, diamondlike amorphous carbon films. Amorphous carbon films with a high fraction of sp 3 hybridized carbons have been deposited by filtered cathodic vacuum arc ͑FCVA͒ 2-4 and mass selected ion beams. 5-8 C ϩ ions are used to deposit the amorphous carbon films by both techniques. Different mechanisms for the formation of the sp 3 rich phase have been proposed such as the shallow implantation process ͑subplantation͒ by Lifshitz et al.,5,6 selective sputtering processes by Reinke and Kuhr 9 ͑discussed for c-BN͒, and stressinduced phase transition processes by McKenzie et al. 3,10 Analytical expressions for the subplantation process describing the formation of stress and the densification have been proposed by Davis 11 and Robertson. 12 The basic idea of the models by Davis and Robertson is that a carbon ion needs at least the displacement energy to penetrate into the carbon film leading to a densification of subsurface layers of the evolving film. 6 But, not all the energy of the energetic carbon ion is used for penetration ͑displacement processes͒. Part of the ion energy is used by momentum transfer collisions which results in a thermal spike. Davis 11 and Robertson 12 modified calculations of Windischmann 13 by allowing implanted carbon atoms to relax to the film surface, due to the high localized temperature generated by the impinging C ϩ ions in the thermal spike. Yet, questions as to the validity of a thermal spike at ion energies of a few hundred electron volts in a low elemental mass material remains unanswered. Nevertheless, at such impact energies several thousand vibrations are involved for a time period of the order of 10 Ϫ12 s. 14 Dense and highly tetrahedral amorphous carbon films have also been deposited by the laser ablation technique, 15,16 by dual ion beam technique, 17 and recently by magnetron sputtering together with intense ion plating ͑MS/I...

Effects of applying stress on the electron field emission properties in amorphous carbon thin films

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Probing the band structure of hydrogen-free amorphous carbon and the effect of nitrogen incorporation

“…However, non-hydrogenated a-C deposited by sputtering can show small optical band gaps (less than 1eV) with a high sp 3 fraction as reported due to the stress induced sp 2 to sp 3 transitions [42]. However, the sp 3 fraction is still high, and stress induced localized states reduce the energy of the Tauc optical gap to less than 1eV.…”

Pulsed laser deposited tetrahedral amorphous carbon with high sp3 fractions and low optical bandgaps

“…[24][25][26][27] All the a-C films show similar Raman spectra consisting of only the G peak around 1580 cm −1 and almost no D peak around 1350 cm −1 . The second order TO peak of the Si substrate can be observed at around 960 cm −1 , as shown in Fig.…”