High-pressure<i>in situ</i>x-ray-diffraction study of the phase transformation from graphite to hexagonal diamond at room temperature

Yagi, T.; Utsumi, Wataru; Yamakata, Masaaki; Kikegawa, Takumi; Shimomura, Osamu

doi:10.1103/physrevb.46.6031

Cited by 250 publications

(253 citation statements)

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“…Figure 4 also indicates that for the formation of dense amorphous carbon films by MS/IP high flux ratios are required. The stress threshold of 13 GPa can be compared to the pressure values found by Erskine et al, 22 Yagi et al, 23 Takano et al, 24 and Endo et al 25 for transitions from graphite to a denser form of carbon. Below the stress transition value, the films have a density close to that of graphite and the other physical properties such as optical band gap are graphitelike.…”

Section: Resultsmentioning

confidence: 97%

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

Schwan

Ulrich

Theel

et al. 1997

Journal of Applied Physics

115

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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...

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Section: Resultsmentioning

confidence: 97%

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

Schwan

Ulrich

Theel

et al. 1997

Journal of Applied Physics

115

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“…2). Initially with a larger d-spacing than the graphite (002), the FSDP compresses rapidly, and becomes similar to the (002) d-spacing of cold-compressed superhard graphite at highest pressures [5,38] ( Fig. 3).…”

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confidence: 87%

Amorphous Diamond: A High-Pressure Superhard Carbon Allotrope

et al. 2011

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Compressing glassy carbon above 40 GPa, we have observed a new carbon allotrope with a fully sp 3 -bonded amorphous structure and diamond-like strength. Synchrotron x-ray Raman spectroscopy revealed a continuous pressure-induced sp 2 -to-sp 3 bonding change, while x-ray diffraction confirmed the perseverance of non-crystallinity. The transition was reversible upon releasing pressure. Used as an indenter, the glassy carbon ball demonstrated exceptional strength by reaching 130 GPa with a confining pressure of 60 GPa. Such an extremely large stress difference of >70 GPa has never been observed in any material besides diamond, indicating the high hardness of this high-pressure carbon allotrope.

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“…The phase transformation from graphite to diamond begins at this pressure. 31,32 To investigate more closely the differences observed with the three pressure media, we have carried out ab initio calculations. Figure 4 plots the electronic density at a distance of the average van der Waals radius for the three molecules of the pressure medium and DWCNT.…”

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confidence: 99%