Amorphous carbon films prepared by the “dip” technique: Deposition and film characterization

Ray, Sekhar C.; Fanchini, Giovanni; Tagliaferro, Alberto; Bose, Baishakhi; Dasgupta, D.

doi:10.1063/1.1578527

Cited by 18 publications

(12 citation statements)

References 36 publications

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“…Amorphous carbons, including our sputtered films, usually display broad asymmetric C(1s) lines; , the presence of a highly symmetric line therefore suggests that the sample undergoes graphitization during annealing. This is often observed after thermal treatment of amorphous carbons, which tends to increase the sp 2 /sp 3 carbon ratio. − The rapid annealing under H 2 /N 2 atmosphere has also the effect of reducing the oxygen content in the carbon film, as evidenced by the fact that the A O(1s) / A C(1s) ratio decreases from a typical value >0.09 to 0.04.…”

Section: Resultsmentioning

confidence: 99%

Influence of Surface Termination and Electronic Structure on the Photochemical Grafting of Alkenes to Carbon Surfaces

et al. 2008

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The ultraviolet-initiated photochemical grafting of n-alkenes to surfaces of amorphous carbon, diamond, and carbon nanofibers has recently emerged as a way to impart new surface properties to these materials. Recent studies have shown that grafting on these materials is initiated by a novel photoelectron ejection process, evidenced by a strong dependence of reaction efficiency on the electron affinity of the reactant molecules. Yet, the role of different surface functional groups and the resulting changes in valence band density of states and surface work function have not been determined previously. Understanding the influence of surface carbonyl groups is particularly significant because CdO groups increase the surface work function but are also known to catalyze certain electron-transfer processes at carbon surfaces. Here, we use infrared spectroscopy, X-ray photoelectron spectroscopy (XPS), and ultraviolet photoelectron spectroscopy (UPS) to investigate how changes in surface termination (H-termination vs O-termination) and surface annealing impact the valence electronic structure and work function of the samples, and how these changes influence the grafting of alkenes to the surfaces. Four different n-alkenes bearing terminal groups were used in order to identify the role of the molecular electron affinity, using alkenes terminated with -NHCOCF 3 , -NHCOO(tert-butyl), -COOMe, and -CH 3 groups. By using narrowly spaced interdigitated electrodes of amorphous carbon, we are able to directly detect the UV-induced photoemission. Our results show that O-termination of amorphous carbon surfaces enhances the photochemical grafting yield compared with H-termination of surfaces, contrary to what has been found on diamond surfaces. Surfaces annealed to increase the amount of sp 2 -hybridized carbon, and therefore being most metallic in character, have the highest reactivity. The changes in reactivity are explained in terms of the changes in valence electronic structure of the samples and the influence of oxygen on the photoelectron emission process that initiates the grafting reaction.

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Section: Resultsmentioning

confidence: 99%

Influence of Surface Termination and Electronic Structure on the Photochemical Grafting of Alkenes to Carbon Surfaces

et al. 2008

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“…Measurements, including the Raman and Fourier transform infra-red (FTIR) spectra [7], of the sp 2 and sp 3 (and/or sp 2 /sp 3 ratio) contents present in the films were often used to determine the carbon phases. In a previous report a range of a-C:H films were deposited at various baking temperatures and were studied by thickness (≈0.3-1.2 µm), Raman spectroscopy, FTIR, electron spin resonance and other methods [8]; the results showed that the carbon phase changed with the temperature during deposition. X-ray absorption near-edge structure (XANES) spectra are convenient and useful for accurately determining the sp 2 and sp 3 contents in the film's surface, because graphite and diamond phases yield very different spectra.…”

Section: Introductionmentioning

confidence: 98%

X-ray absorption spectroscopy (XAS) study of dip deposited a-C:H(OH) thin films

Ray

Tsai

Chiou

et al. 2004

J. Phys.: Condens. Matter

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This work measures the C and O K-edge x-ray absorption near-edge structure (XANES) spectra of hydrogenated amorphous carbon (a-C:H) films deposited at various baking temperatures Tb (Tb = 300–500 °C at 50 °C). The C–H σ* peak related to the content of the sp2 graphite-like bonding in the C K-edge spectra was found to yield to the C–H π* peak related to the sp3 diamond-like bonding at high temperature (500 °C). We find that the intensities of both the sp2 and sp3 features in the C K-edge XANES spectra decrease with increase of Tb, which suggests an increase of the defect concentration with Tb. The intensities of the O K-edge XANES spectra are found to decrease with increase of Tb, which suggests thermally induced decomposition of carbonyl contaminants on the surface. The elemental analysis C/O (or O/C) ratio was obtained from XPS spectra and indicates that films are not hydrogenated amorphous carbon but rather oxyhydrogenated amorphous carbon thin films.

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“…The glossy metallic appearance of this black coating on shells heated above 500°C can possibly be explained by structural modification of the layer due to release of O and H, previously reported to occur between 450°C and 500°C (Ray et al . ). Heating in an oxidizing atmosphere produced larger colour variation.…”

Section: Resultsmentioning

confidence: 97%

Assessing the Accidental Versus Deliberate Colour Modification of Shell Beads: a Case Study on PerforatedNassarius kraussianusfrom Blombos Cave Middle Stone Age levels

et al. 2013

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Colour plays an eminent role in beadwork. Colour modifications are reported on early shell beads from Middle Stone Age sites. However, identifying the colouring agent and demonstrating the intentional nature of the colouring process is not straightforward. Here, we provide analytical data on colour and structural modifications observed on Nassarius kraussianus (Nk) collected in modern thanatocoenoses and on shells of the same species experimentally heated in oxidizing and reductive atmospheres. Comparison with Nk shell beads from the 72 ka old Middle Stone Age levels of Blombos Cave, South Africa, and contextual analysis of other malacological remains from the same levels that were not used as ornaments identify the mechanisms responsible for the change of colour in modern Nk thanatocoenoses and heated shells, and show that although some Nk shell beads were heated, intentional heat treatment of shell beads is not demonstrated.

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Amorphous carbon films prepared by the “dip” technique: Deposition and film characterization

Cited by 18 publications

References 36 publications

Influence of Surface Termination and Electronic Structure on the Photochemical Grafting of Alkenes to Carbon Surfaces

Influence of Surface Termination and Electronic Structure on the Photochemical Grafting of Alkenes to Carbon Surfaces

X-ray absorption spectroscopy (XAS) study of dip deposited a-C:H(OH) thin films

Assessing the Accidental Versus Deliberate Colour Modification of Shell Beads: a Case Study on PerforatedNassarius kraussianusfrom Blombos Cave Middle Stone Age levels

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