Photoluminescence and Raman spectroscopy in hydrogenated carbon films

Marchon, B.; Gui, Jing; Grannen, K.; Rauch, G.C.; Ager, Joel W.; Silva, S. Ravi P.; Robertson, John

doi:10.1109/20.617873

Cited by 187 publications

(104 citation statements)

References 11 publications

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“…%͒ 20 and rather high sp 3 bond content. The structure of these samples can be characterized by the presence of polymeric bonding type due to saturation of CϭC bonds by H as ϵCH x groups, rather than by increasing the fraction of C-C bonds.…”

Section: A Raman Spectra Behaviormentioning

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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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: A Raman Spectra Behaviormentioning

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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“…The optical properties of carbon films are largely governed by the sp 2 phase, with the tribological properties determined by the sp 3 phase. However, in these nanocomposite materials, some care must be exercised in extracting and interpretation of the Tauc band gap and the Urbach energy.Photoluminescence (PL) in amorphous carbon, is thought to occur due to the radiative recombination of electrons and holes in the band-tail states created by sp 2 rich clusters.4,5 PL has been extensively studied for polymeric a-C:H films, 4,6,7 where an increase in the PL intensity has been observed for increasing H content.7 In this letter we investigate the PL properties of hydrogen-free a-C films deposited by PLA of graphite in background pressures of argon. Unlike in vacuum, these conditions have been shown to produce low density nanostructured amorphous carbon (NAC) films.…”

mentioning

confidence: 99%

“…4,5 PL has been extensively studied for polymeric a-C:H films, 4,6,7 where an increase in the PL intensity has been observed for increasing H content.…”

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confidence: 99%

Room temperature photoluminescence from nanostructured amorphous carbon

Henley

Carey

Silva

2004

Applied Physics Letters

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Visible room-temperature photoluminescence (PL) was observed from hydrogen-free nanostructured amorphous carbon films deposited by pulsed laser ablation in different background pressures of argon ͑P Ar ͒. By varying P Ar from 5 to 340 mTorr, the film morphology changed from smooth to rough and at the highest pressures, low-density filamentary growth was observed. Over the same pressure regime an increase in the ordering of sp 2 bonded C content was observed using visible Raman spectroscopy. The pulsed laser ablation (PLA) of graphite, in vacuum, has typically been used to produce smooth, hard, high density amorphous carbon (a-C) films with high sp 3 content (up to 90%) 2,3 due to the local densification, on the impact of high energy C atoms/ions, favoring the formation of the sp 3 phase. The optical properties of carbon films are largely governed by the sp 2 phase, with the tribological properties determined by the sp 3 phase. However, in these nanocomposite materials, some care must be exercised in extracting and interpretation of the Tauc band gap and the Urbach energy.Photoluminescence (PL) in amorphous carbon, is thought to occur due to the radiative recombination of electrons and holes in the band-tail states created by sp 2 rich clusters.4,5 PL has been extensively studied for polymeric a-C:H films, 4,6,7 where an increase in the PL intensity has been observed for increasing H content.7 In this letter we investigate the PL properties of hydrogen-free a-C films deposited by PLA of graphite in background pressures of argon. Unlike in vacuum, these conditions have been shown to produce low density nanostructured amorphous carbon (NAC) films. 8,9 Such films have been shown to have useful properties including low thresholds for electron emission 10 and high porosities. Films were deposited by PLA of a 99.999% pure pyrolytic graphite target (Kurt J. Lesker) using a Lambda-Physik LPX 210i excimer laser operating at 248 nm. The laser pulse was focused onto the rotating target, producing a fluence of ϳ6 J/cm 2 . The growth chamber was evacuated using a turbomolecular pump to 9 ϫ 10 −8 Torr, then backfilled with argon to the required pressure. Films were deposited onto Si substrates at a range of different background pressures of argon ͑P Ar ͒ from 5 to 340 mTorr. The target to substrate distance was fixed at 6 cm. Between 2000 and 5000 laser shots were used, depending on the background pressure in order to keep the film thickness constant as it was affected by P Ar .The morphology of the films was investigated in a Hitachi S4000 field emission gun scanning electron microscope (SEM). The structure and bonding configuration in the films was investigated by visible Raman spectroscopy (Renishaw Ramanscope) using two different laser wavelengths 488 and 514 nm. The PL measurements were also performed using the system with the 488 nm laser, which was also equipped with a cryostat (Oxford Instruments) that allowed measurements at substrate temperatures down to 6 K.After deposition the surface morphology of the films was ex...

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“…Figure 4 shows gravimetric density of electrochemically hydrogenated graphene vs. hydrogen cluster density, where gravimetric density, from Table I, is extrapolated from hydrogen content (%) which is calculated from normalized slope, 33 and hydrogen cluster density extracted from I(D)/I(G), 33,36 of the ten (10) samples after hydrogenation. In this analysis, we assume that each cluster is small enough (much smaller than the Raman probe wavelength) that it registers as a single Raman active D-peak site during the Raman measurement.…”

Section: Resultsmentioning

confidence: 99%

Metal Catalyzed Electrochemical Synthesis of Hydrocarbons from Epitaxial Graphene

Daniels

Obe

Daas

et al. 2016

J. Electrochem. Soc.

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Pt/Au transition metal catalysts are shown to significantly improve the electrochemical hydrogenation of low defect density epitaxial graphene (EG) layers ∼2ML thick on Si-face 6H-SiC Initial experiments using Pt nanoparticles deposited from aqueous solution showed large increases in hydrogenation, however, this method demonstrated large variability, attributed to the aqueous nature of the catalyst deposition, known to change the conductivity and reactivity of graphene, as well as clustering of Pt nanoparticles. To reduce process variability, 20 nm thick evaporated metals were used. From Raman, the average observed hydrogen cluster density ∼10 11 cm −2 was similar to the average densities of intrinsic defects (10 10,11 cm −2 ) and charge impurities (10 11 cm −2 ) consistent with recent reports that these sites play a crucial role in the hydrogenation of EG. Au catalysts (3.23 ± 0.22%wt) showed slightly better H-incorporation than Pt (2.81 ± 0.03%wt), an observation we attribute to the fact that H 2 dissociation is no longer the rate-limiting step, as H + is readily available in the aqueous state. The electrochemical enablement of these hydrogenation pathways using catalysts offers new routes to carbon chemistries for hydrogen storage, bandgap engineered hydrocarbons as well as EG-based battery electrodes.

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Photoluminescence and Raman spectroscopy in hydrogenated carbon films

Cited by 187 publications

References 11 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

Room temperature photoluminescence from nanostructured amorphous carbon

Metal Catalyzed Electrochemical Synthesis of Hydrocarbons from Epitaxial Graphene

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