Investigation of micropores in amorphous hydrogenated carbon by a pulsed positron beam

Kögel, G.; Schödlbauer, D.; Triftshäuser, W.; Winter, J.

doi:10.1103/physrevlett.60.1550

Cited by 69 publications

(9 citation statements)

References 20 publications

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“…These lifetimes are shorter than those obtained as an intermediate lifetime component in the present work, which suggests that the defects in hydrogen-doped alkali-metal fullerides are not monovacancy, but higher-order one. The lifetime of positrons in the surface state has been reported to be 0.400 ns for a hydrogenated carbon film [15], 0.45 ns for graphite [16] and longer than 0.520 ns for a 6-vacancy cluster in Si [17]. From these results, it is concluded that hydrogen-doping to alkalimetal fullerides increases the concentration of higher-order vacancy-type defects, through which more than 50% injected positrons annihilate.…”

Section: Resultsmentioning

confidence: 82%

Positron annihilation in hydrogen-doped alkali-metal fullerides

Murakami¹,

Ohtsu²,

Ichikawa³

et al. 2001

Radiochimica Acta

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Positron-annihilation / Alkali-metal-fulleride / Thermal-desorption / Raman-shiftSummary. Hydrogen-doped alkali-metal fullerides were studied by means of mass-analyzed thermal desorption and positron annihilation. The hydrogen desorption spectra reveal the inclusion of hydrogen in the fullerides as two types of components; one weakly adsorbed and the other strongly bound, probably as hydride ion. The positron lifetime spectra demonstrate that hydrogen-doping to alkali-metal fullerides increases a concentration of higher-order vacancy-type defects, through which more than 50% injected positrons decay with a lifetime of 0.42-0.71 ns.

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Section: Resultsmentioning

confidence: 82%

Positron annihilation in hydrogen-doped alkali-metal fullerides

Murakami¹,

Ohtsu²,

Ichikawa³

et al. 2001

Radiochimica Acta

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“…Until now only a few SPA studies on disordered carbon films have been done. [43][44][45] For ta-C, as yet, no reported data is available. As most of SPA studies, the shape parameter S is used to characterize the Doppler-broadened 511-keV annihilation gamma line.…”

Section: Resultsmentioning

confidence: 99%

Sandwich atomic structure in tetrahedral amorphous carbon: Evidence of subplantation model for film growth from hyperthermal species

Zhao

2001

Phys. Rev. B

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High-resolution transmission electron microscopy ͑HRTEM͒ was used to characterize the cross-sectional and planar atomic structures and bonding states of highly tetrahedrally bonded amorphous carbon ͑ta-C͒ films, particularly concentrating on the surface layer and interface between substrate and pure ta-C film. A ''sandwich'' cross-sectional structure was found to be existing in ta-C grown from hyperthermal carbon species, and can be expressed as A/B/A layer-by-layer stacks. The interface ͑A͒ was shown to be very thick ͑ϳ40 nm͒, and consisted of sp 2 -bonded carbon domains and quasicontinuous two-dimensional layers. The initial pure carbon layer on silicon substrate exhibits relatively ordered atomic configuration, which can be attributed to the presence of graphitelike structure. The surface layer ͑A͒ was investigated in detail by using both cross-sectional and planar HRTEM observations. Results indicated a large number of ordered structure existed in the surface, in the manner of entangled ribbons that were identified to be sp 2 -bonded glassy carbon. The ordered sp 2 -bonded surface layer is proposed to form immediately while stopping deposition, i.e., the final stage of film growth, due to thermal spike-induced stress relaxation on surface. The interior film ͑B͒ is predicted to possess higher sp 3 -bond content than that measured by electron-energy-loss spectrum. In addition, slow positron annihilation, as well as a classical-trajectory calculation concerning the projected range R p and range straggling ⌬R p of carbon species implantation into silicon substrate, were conducted for further investigating and interpreting the observed atomic structures in surface, interior film, and interface. The fact that sp 2 -bonded surface and interface are present in a primarily sp 3 -bonded film gives a direct corroboration of subplantation model and compressive stress mechanism for sp 3 -bonded film growth from hyperthermal species.

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“…where Lf is the mean diffusion length of positron for a defect-free sample, and L, for the as-grown CZ-crystal [10]. The value of L, is determined to be the largest value of L, obtained from this experiment.…”

Section: S•(e)=sf(e)+sb[1-_f(e)]mentioning

confidence: 99%