Raman ‘‘fingerprinting’’ of amorphous carbon films

Tamor, M. A.; Vassell, W. C.

doi:10.1063/1.357385

Cited by 947 publications

(414 citation statements)

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“…A correlation exists between the fraction of carbons in the sp 2 configuration and the optical gap. Figure 3 presents results from different workers who measured these two parameters for a-C:H samples (Jarman et al 1986;Kleber 1991;Tamor & Vassell 1994;Robertson 1996;Kassavetis et al 2007). The Dartois et al (2005) a-C:H sample is represented by the colored area: the sample optical gap is evaluated from its high degree of hydrogenation and low refractive index.…”

Section: Sp 2 /Sp 3 Ratio Determinationmentioning

confidence: 99%

“…The external medium during this measurement, designed by the subscript 1, is the air. The quasi-monochromatic excitation (excitation FWHM < 10 nm) of the samples occurs at UV-visible wavelengths greater than 200 nm but quantitative measurements are Jarman et al 1986;Kleber 1991;Tamor & Vassell 1994;Robertson 1996;and Kassavetis et al 2007). The colored area corresponds to the Dartois et al (2005) a-C:H sample (see text for details).…”

Section: Photoluminescence Measurementsmentioning

confidence: 99%

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Photoluminescence of hydrogenated amorphous carbons

Godard

Dartois

2010

A&A

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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.

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Section: Sp 2 /Sp 3 Ratio Determinationmentioning

confidence: 99%

Section: Photoluminescence Measurementsmentioning

confidence: 99%

Photoluminescence of hydrogenated amorphous carbons

Godard

Dartois

2010

A&A

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“…The well-defined Raman peaks differentiate our thin films from amorphous C (a-C). 21 In fact, atomically thin a-C films have never been realized by CVD. 22 The G band centered at 1600 cm −1 and the 2D band at 2695 cm −1 are well resolved, which are signatures of sp 2 graphitic materials.…”

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confidence: 99%

Noncatalytic chemical vapor deposition of graphene on high-temperature substrates for transparent electrodes

Sun

Cole

Lindvall

et al. 2012

Applied Physics Letters

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A noncatalytic chemical vapor deposition mechanism is proposed, where high precursor concentration, long deposition time, high temperature, and flat substrate are needed to grow large-area nanocrystalline graphene using hydrocarbon pyrolysis. The graphene is scalable, uniform, and with controlled thickness. It can be deposited on virtually any nonmetallic substrate that withstands ∼1000 o C. For typical examples, graphene grown directly on quartz and sapphire shows transmittance and conductivity similar to exfoliated or metalcatalyzed graphene, as evidenced by transmission spectroscopy and transport measurements. Raman spectroscopy confirms the sp 2 -C structure. The model and results demonstrate a promising transfer-free technique for transparent electrode production.Graphene, a monolayer of sp 2 carbon atoms, has received much attention. The use of graphene in transparent electronics is one of its most promising applications. 1 Apart from its high transparency/conductivity, the flexibility and ease of integration on a variety of substrates are obvious advantages. 30-inch graphene has been demonstrated by virtue of the recent advances in chemical vapor deposition (CVD), 2 which is compatible with the existing semiconductor technology. 3 Nevertheless, the necessity of etching the metal catalyst and transfer of graphene to foreign substrates hampers wide industrialization. Thus, efforts are put into the metal-free growth of graphene on materials including SiO 2 , 4-6 Al 2 O 3 , 7 MgO, 8 etc. To date, however, the graphitization process on dielectrics is poorly understood while the experiments are largely experience based. Recently, we have shown that large-area uniform graphene can be grown on virtually any hightemperature substrates, on Si 3 N 4 or HfO 2 , for instance. 9 In this letter, we provide a broader and deeper insight, discussing in detail the growth mechanism of graphene directly on insulators. As an example, we show our results on graphene on quartz and sapphire, hinting at the future prospects of the transfer-free graphene for transparent electrodes.Bulk graphite is usually made at >3000 o C and catalysis is needed to lower the temperature. 10 However, nanoscale graphene flakes form without any catalysts at merely ∼1000 o C. For example, carbon black which is produced massively by natural gas pyrolysis 11-14 is nothing else but chaotically connected graphene flakes. 11 Although widely used in industry, this process has so far been overlooked for making large-area graphene. Here, we show that macroscopically amorphous carbon black can be turned into textured graphene thin films when a) Electronic mail: jiesu@chalmers.se. the carbon precursor concentration and growth temperature are high, also requiring a relatively long deposition time and flat substrate. Fig. 1(a) illustrates the CVD reactor used in this work. The middle region is heated to 1000 o C while the left and right sides are <600 o C. There is no material deposition in the right zone because of the reduced CH 4 decomposition efficiency at lo...

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“…In the spectrum taken from samples grown under condition II (Figure 4b, spectrum B) a strong luminescence is also noted. The presence of the luminescence band is likely due to small amounts of hydrogenated amorphous carbon [23] and has also been detected in other experiments of C deposition carried out employing high self-bias induced by RF [24]. Under such conditions the electrical field related to the negative self-bias is expected to interact with the hydrogen ions of the plasma, giving them a sufficient energy to induce an effective hydrogenation of the amorphous carbon produced during the CVD process.…”

Section: Resultsmentioning

confidence: 83%