Electronic properties of amorphous carbon (a-C:H)

Schütte, Susanne; Will, Stephan; Mell, H.; Fuhs, W.

doi:10.1016/0925-9635(93)90185-5

Cited by 72 publications

(24 citation statements)

References 11 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Variation in the a-C:H absolute photoluminescence quantum yield η with the a-C:H optical gap E 04 . Relative quantum yields result from other photoluminescence studies (Schütte et al 1993;Xu et al 1993;Silva et al 1996;Rusli et al 1996;Bourée et al 1998) are converted into absolute quantum yields using our absolute results (filled red circles) and added to this figure. The solid line is an exponential fit to all these efficiency data (see text for details) and each of the dotted lines corresponds to a 3σ variation in the fit parameters.…”

Section: Resultsmentioning

confidence: 99%

Photoluminescence of hydrogenated amorphous carbons

Godard

Dartois

2010

A&A

View full text Add to dashboard Cite

Context. Hydrogenated amorphous carbons (a-C:H or HAC) have proved to be excellent analogs of interstellar dust observed in galaxies diffuse interstellar medium (DISM) through infrared vibrational absorption bands (3.4 μm, 6.8 μm, and 7.2 μm bands). They exhibit photoluminescence (PL) after excitation by UV-visible photons, and are possible carriers for the extended red emission (ERE), a broad red emission band observed in various interstellar environments. Aims. As many candidate materials/molecules can photoluminesce in the visible, along with the carrier abundance, the PL efficiency represents one of the strongest constraints set by such ERE observations. We wish to precisely characterize the PL behavior of a-C:H as a family of materials. Methods. The a-C:H samples are produced in the form of films deposited on substrates by plasma-enhanced chemical vapor deposition. The produced films were analyzed in transmission by UV-visible and IR spectroscopy, and the wavelength dependent PL spectra were recorded. The intrinsic absolute quantum yield η was then rigorously calculated taking self-absorption of the PL by the film and interfaces effects into account. Results. A wide range of different laboratory synthesized a-C:H were analyzed. Their PL properties are dependent on the optical gap E 04 : when E 04 decreases from 4.3 eV to 2.8 eV, the a-C:H vary from highly (η ∼ 1%) yellow photoluminescent soft materials to hard materials that emit a wider PL band in the red spectral range, with a lower efficiency (η ∼ 0.01−0.1%). For any given a-C:H, the PL characteristics (central wavelength, band width and efficiency) are found to be essentially constant over the explored excitation range (λ exc > ∼ 250 nm). We compared the characteristics of the produced interstellar dust analog to the constraints imposed by the ERE observations. Conclusions. As for ERE observations, PL efficiencies and band widths of a-C:H are both correlated to the PL central wavelengths. The excitation responsible for the a-C:H emission is efficient over a wide spectral range that matches the ERE excitation. The present a-C:H encounter difficulties for the diffuse ISM ERE observations (η ≥ 10%) in simultaneously satisfying the high quantum yield criteria and PL spectral characteristics. We still need to investigate the role of a small number of residual oxygen atoms in the laboratory-produced a-C:H network in quenching the PL yield, as well as to consider the interstellar temperature effect for our analogs.

show abstract

Section: Resultsmentioning

confidence: 99%

Photoluminescence of hydrogenated amorphous carbons

Godard

Dartois

2010

A&A

View full text Add to dashboard Cite

show abstract

“…One explanation proposed for this is that the spins are less able to tunnel to neighboring graphitic clusters as the energy is initially increased. 8 At higher ion energies the linewidth decreases as the ion energy is further increased. [8][9][10][11][12][13] In this latter region the line is usually reported [8][9][10]12,13 as having a Lorentzian shape although it has also been assumed to be Gaussian.…”

Section: Introductionmentioning

confidence: 99%

“…8 At higher ion energies the linewidth decreases as the ion energy is further increased. [8][9][10][11][12][13] In this latter region the line is usually reported [8][9][10]12,13 as having a Lorentzian shape although it has also been assumed to be Gaussian. 11 In the latter case the change in width was attributed to a change in unresolved hydrogen hyperfine lines brought about by a change in the local H/C ratio 11 and it has been shown 14 that changing the hydrogen content can affect the linewidth.…”

Section: Introductionmentioning

confidence: 99%

“…In most cases a single resonance is reported which has a g value of about 2.0028. [6][7][8] However, it is still uncertain what these defects are and they could, for example, be either sp 2 clusters with an odd number of sites or single dangling bonds.…”

Section: Introductionmentioning

confidence: 99%

“…[8][9][10][11][12][13] Several authors [8][9][10] have reported that when the ion energy is increased from very low values there is an initial increase in the linewidth. One explanation proposed for this is that the spins are less able to tunnel to neighboring graphitic clusters as the energy is initially increased.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

EPR linewidth variation, spin relaxation times, and exchange in amorphous hydrogenated carbon

2000

View full text Add to dashboard Cite

Electron paramagnetic resonance ͑EPR͒ measurements have been made of amorphous hydrogenated carbon ͑a-C:H͒ films grown by plasma enhanced chemical vapor deposition ͑PECVD͒ with negative self-bias voltages V b in the approximate range 10-540 V. For V b Ͻ100 V, as the film changes from polymerlike to diamondlike, the changes in linewidth and shape are interpreted in terms of changes to two contributions-one due to dipolar interactions between the unpaired spins and one due to unresolved lines arising from hyperfine interactions with H 1 . The former yields a Lorentzian line, the latter a Gaussian, and the resultant spectrum has the Voigt shape. The empirical relation ⌬B pp G ͑in Gauss͒ϭ͑0.18Ϯ0.05͒ϫ͑at. % H) between the peak-to-peak Gaussian contribution ͑in Gauss͒ ⌬B pp G and the hydrogen content in atomic percentage is obtained. For V b Ͼ100 V the linewidth is shown to be dominated by the dipolar interactions and exchange and it decreases as V b increases; the change is shown to arise primarily from a change in the exchange interaction. Evidence for this comes from measurements which show that the spin-lattice relaxation time appreciably shortens and the spin-spin relaxation time lengthens as the bias voltage is increased. The magnitude and variation with bias of the linewidth are consistent with the EPR signal originating from the -type radicals.

show abstract

Defects in Diamond-Like Carbon

Robertson

2001

phys. stat. sol. (a)

View full text Add to dashboard Cite

The nature and role of electronic defects in amorphous diamond-like carbons (DLC) is described. The defect has recently been shown by electron spin resonance to be an unpaired spin on a small sp 2 -bonded cluster. The defect density is large in DLC so defect states form continuous distribution of states with tail states. Defects and tail states can act as non-radiative recombination centres to quench photoluminescence, depending on the position of the demarcation levels.

show abstract

Electronic properties of amorphous carbon (a-C:H)

Cited by 72 publications

References 11 publications

Photoluminescence of hydrogenated amorphous carbons

Photoluminescence of hydrogenated amorphous carbons

EPR linewidth variation, spin relaxation times, and exchange in amorphous hydrogenated carbon

Defects in Diamond-Like Carbon

Contact Info

Product

Resources

About