Electron delocalization in amorphous carbon by ion implantation

Khan, R. U. A.; Carey, J. D.; Silva, S. Ravi P.; Jones, Benjamin; Barklie, R.C.

doi:10.1103/physrevb.63.121201

Cited by 39 publications

(24 citation statements)

References 26 publications

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“…This fact has a significant influence not only on the film structure but also on the film electronic properties such as the width of the band gap and the density of states in it 8 and consequently to the electric transport and optical properties. 9 As a rule, the spin density in the band gap is often more then 10 18 cm Ϫ3 in the a-C films 10 and results in pinning of the Fermi level thus making it difficult to change electronic properties by doping.…”

Section: Introductionmentioning

confidence: 99%

“…6,[9][10][11][12][13][14][15][16] It provides important information about the spin density and nature of unpaired electrons in the films, their spin-spin and spin-lattice interactions, and linking of these parameters with films microstructure. 9 In this article, we analyze the features of the ESR signal behavior in both nitrogenated and nitrogen-free W and Ni implanted a-C:H films. Visible Raman scattering measurements are also used to clarify the correlation between structure features and paramagnetic state properties.…”

Section: Introductionmentioning

confidence: 99%

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Effects of ion implantation on electron centers in hydrogenated amorphous carbon films

Konchits

Valakh

Shanina

et al. 2003

Journal of Applied Physics

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Electron spin resonance ͑ESR͒ and Raman spectra measurements are carried out on a-C:H and a-C:H:N films both as grown and implanted with W and Ni ions with doses ranged from 0.5 ϫ10 15 to 1.2ϫ10 16 cm Ϫ2 . The as-grown films have small concentration of paramagnetic centers with a spin density N s of 10 17 cm Ϫ3 . Upon implantation a significant increase in N s of (0.5-22) ϫ1019 cm Ϫ3 centers with g (Si) ϭ2.0055 and g (C) ϭ2.0025 was observed. These defects are ascribed to dangling bonds in the silicon substrate and in the carbon film, respectively. The correlation between variation of N s value with implantation dose and behavior of D and G band position and their intensity ratio in the visible Raman spectra is observed. The effects are attributed to changes in the sp 2 -sp 3 systems and hydrogen loss due to ion induced annealing of the carbon films at high ion doses. The temperature and concentration dependencies of the ESR line shape and linewidth are explained using the mechanism of motional narrowing over the temperature range 4.2-300 K. Low temperature anisotropy of the g value is found in the ESR spectra and is explained as arising from the dipole-dipole interaction in the infinitely thin films.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effects of ion implantation on electron centers in hydrogenated amorphous carbon films

Konchits

Valakh

Shanina

et al. 2003

Journal of Applied Physics

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“…Changes in the properties of DLC thin-films are related to changes in the film structure, such as sp 2 / sp 3 bonding ratio, hydrogen content, sp 2 clustering and defect concentration; alterations are facilitated by changing process parameters which may consist of bias voltage, type of precursor gases, surface treatment and post-deposition processing [3][4][5][6].…”

Section: Introductionmentioning

confidence: 99%

Energy efficiency improvements in dry drilling with optimised diamond-like carbon coatings

Zolgharni

Jones

Bulpett

et al. 2008

Diamond and Related Materials

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We demonstrate enhancements of performance and energy efficiency of cutting tools by deposition of diamond-like carbon (DLC) coatings on machine parts. DLC was deposited on steel drill bits, using plasma enhanced chemical vapour deposition (PECVD) with the acetylene precursor diluted with argon, to produce a surface with low friction and low wear rate. Drill bit performance in dry drilling of aluminium was quantified by analysis of power consumption and swarf flow. Optimised deposition conditions produced drill bits with greatly enhanced performance over uncoated drill bits, showing a 25% reduction in swarf clogging, a 36% reduction in power consumption and a greater than five-fold increase in lifetime. Surface analysis with scanning electron microscopy shows that DLC coated drills exhibit much lower aluminium build up on the trailing shank of the drill, enhancing the anti-adhering properties of the drill and reducing heat generation during operation, resulting in the observed improvements in efficiency. Variation of drilling efficiency with argon dilution of precursor is related to changes in the microstructure of the DLC coating.

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“…9 The use of the connectivity within closely spaced clusters on a three-dimensional scale has recently been explained by Khan et al which resulted in delocalized carriers transport in ion implanted a-C:H films. 15 The Tauc gap is a measure of the type of material and size of the clusters. 3 The low defect density PAC films possess a wide optical gap in which a high degree of field penetration occurs and the emission process is one that is largely controlled by the hetrojunction at the back a-C:H/Si interface.…”

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Origin of electric field enhancement in field emission from amorphous carbon thin films

Carey¹,

Forrest²,

Silva³

2001

Applied Physics Letters

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The observation of electron emission from amorphous carbon thin films at low applied electric fields is explained in terms of an enhancement of the field brought about by dielectric inhomogeneities within the film. These inhomogeneities originate from the differences between conductive, spatially localized sp 2 C clusters surrounded by a more insulating sp 3 matrix. By a more complete understanding of the concentration and distribution of the clusters, a generic model for field emission from amorphous carbon thin films can be developed. Extensions of this model to explain the emission properties of carbon nanotubes and carbon nanocomposite materials are also presented. The possible use of amorphous carbon (a-C) and hydrogenated amorphous carbon (a-C:H) based materials as cold cathodes has now been well documented.1,2 To date there have been numerous reports of field emission ͑FE͒ at low macroscopic electric fields from a range of a-C and a-C:H based materials. [1][2][3][4] In the case of emission from diamondlike carbon ͑DLC͒ films it has been reported that, the main barrier which controls emission may lie at the front film/ vacuum interface.3 By contrast, for low defect density polymeric-like carbon ͑PAC͒ a-C:H films the presence of a heterojunction at the a-C:H/Si rear contact, resulting in hot electron transport through the film has been proposed. 4 This model was used to explain the observed strong dependence of the threshold field (E th ) with film thickness. 5 Although the different types of film possess different physical properties and emission has been explained by different mechanisms, it has been observed that emission is often highly nonuniform across the film surface.3,4,6 One of the major problems hindering the development of thin film carbon cathodes is the lack of understanding of a definitive mechanism for emission at low applied fields, typically Ͻ20 V/m. [3][4][5][6][7] Emission from flat metal surfaces often requires fields in excess of 500 V/m, 2 whereas previous atomic force microscopy ͑AFM͒ studies of a-C and a-C:H films have indicated that the films possess rms roughnesses of less than 1 nm, [1][2][3][4] along with no evidence of surface protrusions which can act as a source of geometric field enhancement. Two recent studies by Ilie et al. 8 and Carey et al. 9 have proposed that it is the sp 2 C cluster size and concentration that play an important role in the FE process. In the study by Ilie, an optimum cluster size for emission of 1.5-2 nm was proposed. Carey showed that for a-C:H films deposited at different selfbiases, the FE could be explained in terms of the connectivity between sp 2 clusters. In this letter, we examine whether there is any dependence of E th with thickness for DLC films and compare these results to the behavior reported 5 for PAC films. Scanning tunneling microscope ͑STM͒ images of the DLC films, show that while the films may be atomically smooth they do exhibit variations in their conductivity, which are attributed to dielectric inhomogeneities within the film. ...

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Electron delocalization in amorphous carbon by ion implantation

Cited by 39 publications

References 26 publications

Effects of ion implantation on electron centers in hydrogenated amorphous carbon films

Effects of ion implantation on electron centers in hydrogenated amorphous carbon films

Energy efficiency improvements in dry drilling with optimised diamond-like carbon coatings

Origin of electric field enhancement in field emission from amorphous carbon thin films

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