R McCann

University of Ulster, Aontroim, N Ireland, United Kingdom

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Publications (14)19.05 Total impact

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    ABSTRACT: Surface and bulk properties of the Filtered Cathodic Vacuum Arc prepared nitrogenated tetrahedral amorphous carbon (ta-C:N) films were characterized by X-ray Photoelectron Spectroscopy (XPS), Time of Flight Secondary Ion Mass Spectroscopy (ToF-SIMS), Raman spectroscopy, Atomic Force microscopy and contact angle techniques. An increase in the Nitrogen (N) content of the films is accompanied by a reduction in the sp(3) fraction, confirmed via the deconvolution of the C 1 s XPS spectra. Critical Raman parameters such as peak position and peak width of the G band, defect ratio, I(D)/I(G) and skewness of the G line were analyzed as a function of N content. ToF-SIMS showed the variance of chemical composition with the increase in the sputtering depth. While some amount of incorporated oxygen and hydrogen were observed for all films; for high N content ta-C:N films signature of CN bonds was evident. Surface energies (both polar and dispersive components) for these ta-C:N films were analyzed in a geometric mean approach. Contact angle measurements using both deionized water and ethylene glycol reveal that upon the insertion of nitrogen into ta-C films, the initial change in the contact angle is sharp, followed by a gradual decrease with subsequent increase in N content. The variation of contact angle with increasing N content corresponds to an increase of the total surface energy with an increase of the polar component and a decrease of the dispersive component. (C) 2011 Elsevier B.V. All rights reserved.
    Thin Solid Films 01/2011; 520(1):294-301. · 1.87 Impact Factor
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    ABSTRACT: Tetrahedral amorphous carbon (ta-C) films were studied with and without applying fixed pulse bias and frequency at variable pulse widths in double bent Filtered Cathodic Vacuum Arc (FCVA) system. Both from Raman and X-ray photoelectron spectroscopy (XPS) analyses it has been observed that the ratio of sp(3)/sp(2) is maximal at pulse width of 15 mu s with fixed pulse bias 3 kV and frequency 200 Hz. Increasing or decreasing pulse width from this threshold value accompanies the decreasing sp(3) content in the film. It is also observed that with applying pulse bias width at said frequency and bias voltage G peak position was shifted to lower values and after reaching a minimum at 15 ps G peak position shifted to higher wave numbers. At the 15 ps pulse width, 3 kV bias voltage and 200 Hz frequency we have formed ta-C films with maximum sp(3) content. This study clearly suggests that it is possible to tune the ta-C film's most important properties such as percentage of sp(3) content, internal stress, and hardness by applying pulse width at particular frequency and bias voltage. (C) 2009 Elsevier B.V. All rights reserved.
    Diamond and Related Materials 11/2009; 18(11):1343-1347. · 1.71 Impact Factor
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    ABSTRACT: Polarization dependent studies of near edge x-ray absorption fine structure (NEXAFS) show evidence for the presence of aligned pi-bonded carbon structures and the formation of a nonplanar CN phase in tetrahedral amorphous nitrogenated carbon (ta-CN) films deposited at room temperature. Moreover, the analysis of NEXAFS data as a function of nitrogen concentration and annealing temperature leads to a comprehensive assignment of the local CN bonding configurations in these ta-CN films and suggests an unusual and almost thermally stable nitrogenated carbon structure.
    Journal of Applied Physics 03/2006; 99(4):43511. · 2.21 Impact Factor
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    ABSTRACT: The nature of bonding in tetrahedral amorphous carbon nitride (ta-C:N) films deposited by filtered cathodic vacuum arc (FCVA) technique was studied with near edge X-ray absorption fine structure (NEXAFS), X-ray photoelectron and Raman spectroscopies. The interpretation and interrelation of these spectra are discussed. The changes in the local structure were systematically studied as a function of nitrogen content. Deconvolution of the C 1s and N 1s XPS spectra shows that the sp(3)-C fraction decreases with an increase in nitrogen content. The pi* peak at the C K (carbon K) and at the N K (nitrogen K) edges were systematically studied. Comparison of intensities of the pi* peak confirms the formation of CN bond at the expense of CC bond. Analysis of NEXAFS spectra at N K edge revealed as the nitrogen concentration in the films increases, the pi*/sigma* intensity ratio increases, indicating that there is an increase of the amount of C=N bond relative to the C-N bonds. Raman parameters, such as G peak width, I(D)/I(G) ratio, skewness of the G line (Q), were critically analysed in terms of N content and sp(2) content of the films. We demonstrate that the combined study of normalised Raman, XPS and NEXAFS spectra is very useful in determining the role of nitrogen incorporation in the structure of ta-C films. The hardness values, measured by nanoindentation technique reduced at higher (> 7 at.%) N content films. (c) 2004 Elsevier B.V. All rights reserved.
    Thin Solid Films 06/2005; 482(1-2):145-150. · 1.87 Impact Factor
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    ABSTRACT: Tetrahedral amorphous carbon nitride (ta-C:N) films obtained by filtered cathodic vacuum arc deposition have been investigated by Near edge X-ray absorption fine structure (NEXAFS) spectroscopy. The C K (carbon K) edge NEXAFS spectra clearly revealed the increase of CN bonds with the increase of nitrogen concentration. The C K edge NEXAFS analysis further showed that the content of the surface defect (mainly C–H bonds) decreased with the increase of nitrogen in the films. As the nitrogen concentration increased a pronounced change in the π* features were observed at the N K (nitrogen K) edge. The origin of the N K edge π* peaks are mainly due to the formation of CN bonds and nitrogen substitution in the graphite network. Polarization dependent NEXAFS measurements showed an angular distribution of CN bonds. The electrical resistivity of the ta-C:N films decreased at higher nitrogen concentration and this may be from the development of graphite-like structures in these films. The electrical measurements were confirmed further with electrochemical measurements.
    Diamond and Related Materials. 01/2005; 14:1057-1061.
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    ABSTRACT: Two sets of experiments were carried out for both ta-C and ta-C:N films prepared by filtered cathodic vacuum arc deposition (FCVA). For the first experiment films were prepared as a function of arc current ranging from 30 to 100 A with a film thickness of approximately 70 nm. In the second experiment a series of films was prepared as a function of thickness ranging from 30 to 100 run at 80 A arc current. Raman studies showed that for ta-C and ta-C:N films, an arc current of 100 A produced films with the lowest sp(2) configurations as well as the highest density values. The effect of thickness on ta-C and ta-C:N films revealed different trends. Raman and XRR analysis identified a decrease in sp(2) content and an increase in density as film thickness was increased for ta-C films. However ta-C:N films exceeding 70 nm showed an increasing trend in sp(2) content whilst a significant drop in density was observed. (c) 2005 Published by Elsevier B.V.
    Diamond and Related Materials 01/2005; 14(3-7, SI):983-988. · 1.71 Impact Factor
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    ABSTRACT: The electronic properties of amorphous carbon nitride were studied by x-ray-absorption near-edge structure (XANES) and valence-band photoelectron spectroscopy (PES). The nitrogen incorporation was found to induce graphitization, as evidenced by an increase of the sp(2) cluster in C and N K-edge XANES spectra. The structure is found to be similar to pyridine. Hybridized C-N bond lengths were determined from the position of the sigma(*) resonance of XANES spectra and the obtained results suggest sp(2) hybridization. A valence-band PES spectrum showed that the p-pi band became more intense than the p-sigma band upon higher at. % nitrogen addition, which confirmed the role played by the pi bonds in controlling the electronic structure of a-CNx films. (c) 2005 American Institute of Physics.
    Journal of Applied Physics 01/2005; 98(3). · 2.21 Impact Factor
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    ABSTRACT: The effect of nitrogen partial pressure on amorphous carbon nitride (a-CNx) (0.0 <= x <= 0.17) and laser fluence on amorphous carbon (a-C) films prepared by ultrafast high repetition rate pulsed laser deposition has been studied. The chemical bonding structure of the films was investigated by x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and Fourier transform infrared (FTIR) analysis. XPS studies of films revealed an increase in the CN sites at the expense of CC bonded carbon sites as nitrogen content in the films increased. Films (a-C) prepared as a function of laser fluence showed an increase in sp(3)-bonded carbon as laser fluence was increased from 0.36 to 1.7 J/cm(2). The I-D/I-G ratio and G peak position increased as a function of nitrogen whereas the full width at half maximum (FWHM) of the G peak decreased. This is indicative of either an increase in the size or number of the sp(2) sites. Films prepared as a function of laser fluence revealed a decrease of the I-D/I-G ratio and an increase in the FWHM of the G peak. The use of two visible excitation wavelengths when analyzing the samples indicated a resonant process. FTIR analysis revealed an increase in the peaks attributed to C=N bonds as well as indicated a tiny amount of C=N bonds within the nitrogen-doped films. Additionally, surface morphology analysis showed a greater particle density on films prepared at the highest laser energy in comparison to those prepared at lower fluences. Film hardness characterized by nanoindentation revealed that films became softer as a function of nitrogen content. (C) 2005 American Institute of Physics.
    Journal of Applied Physics 01/2005; 97(7). · 2.21 Impact Factor
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    ABSTRACT: Tetrahedral amorphous carbon (ta-C) and nitrogenated tetrahedral amorphous carbon films (ta-CN(x)), deposited by double bend off plane Filtered Vacuum Cathodic Arc were annealed up to 1000 degrees C in flowing argon for 2 min. Modifications on the chemical bonding structure of the rapidly annealed films, as a function of temperature, were investigated by NEXAFS, X-ray photoelectron and Raman spectroscopies. The interpretation of these spectra is discussed. The results demonstrate that the structure of undoped ta-C films prepared at floating potential with an arc current of 80 A remains stable up to 900 degrees C, whereas that of ta-CN(x) containing 12 at.% nitrogen is stable up to 700 degrees C. At higher temperatures, all the spectra indicated the predominant formation of graphitic carbon. Through NEXAFS studies, we clearly observed three pi* resonance peaks at the N K edge structure. The origin of these three peaks is not well established in the literature. However our temperature-dependant study ascertained that the first peak originates from C=N bonds and the third peak originates from the incorporation of nitrogen into the graphite like domains. (c) 2004 Elsevier B.V. All rights reserved.
    Thin Solid Films 01/2005; 482(1-2):34-40. · 1.87 Impact Factor
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    Journal of Applied Physics. 01/2005; 98(3):033708-033708.
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    ABSTRACT: The effect of nitrogen addition and laser fluence on the atomic structure of amorphous carbon films (a-C) synthesized by femtosecond pulsed laser deposition has been studied. The chemical bonding in the films was investigated by means of X-ray photoelectron (XPS) and Raman spectroscopies. XPS studies revealed a decrease in the sp3 bonded carbon sites and an associated increase in the N-sp2C bonding sites with increasing nitrogen content in the CNx films. An increase in laser fluence from 0.36 to 1.7J/cm2 led to a rise in sp3C sites. These results were further confirmed by Raman spectroscopy. The ID/IG ratio increased monotonically and G line-width decreased with the increase of nitrogen content in the films indicating a rise in either the number or the size of the sp2 clusters. Furthermore a visible excitation wavelength dependence study established the resonant Raman process in a-C and CNx films.
    Applied Physics A 08/2004; 79(4):1009-1014. · 1.69 Impact Factor
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    ABSTRACT: Nitrogenated tetrahedral amorphous carbon (ta-C:N) films having nitrogen content from 0 to 10.3 at.%, have been produced by a double bend off-plane filtered cathodic vacuum arc system. X-ray photoelectron and Raman spectroscopies have been applied to study the effect of nitrogen in the bonding structure in the films. Deconvolution of the XPS spectra revealed a decrease in the amount of sp3-bonded carbon in the ta-C:N films. A comparative study between the Raman parameters at 514 and at 633 nm excitation wavelength was presented. Nitrogen (N) incorporation led to a lower G peak position and higher ID/IG ratios, indicating the development of larger sp2 domains. Q (−ve) parameter (which measures the skewness of G line) increased sharply with the increased of N content in the films. The hardness of the films was evaluated by nanoindentation.
    Diamond and Related Materials 04/2004; · 1.71 Impact Factor
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    ABSTRACT: A double bend off-plane filtered cathodic vacuum arc system was used to produce tetrahedral amorphous carbon (ta-C) and tetrahedral amorphous carbon nitride (ta-C:N) films on silicon substrates at room temperature. The magnetic filter employed in this method was mainly to guide the ionized plasma as well as to prevent the macro-particles reaching the substrates. An investigation has been carried out to optimize the film structure under different arc current, which directly control the plasma efficiency. Two sets of experiments were carried out to investigate the structural changes that take place within the films. The first experiment investigated the structural changes that took place within ta-C and ta-CN films as the film thickness was increased from 10nm to 100nm. In the second experiment the arc current varied over the range of 30A to 100A. XPS, Raman and XRR spectroscopies were utilised to establish the relationship between film thickness, deposition arc current, chemical bonding structure and density. The effect of thickness on ta-C and ta-C:N films were totally different. With the increase of arc currents, the films became more and more disordered due to the energy enhancement of species in the plasma. For films prepared as a function of arc current the Raman D-peak to G-peak intensity ratio (ID/IG) exhibited a decreasing trend. The G peak positions and the FWHM for both films showed similar trends as they all shifted to higher wavenumbers as a function of arc current. The ta-C films deposited at arc current 80 A displayed the lowest level of sp2 configurations and the highest density.
    APS Meeting Abstracts. 01/2004; 1:1055.
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    ABSTRACT: The tetrahedral amorphous carbon (ta-C) films with thickness 1-10 nm were obtained by filtered cathodic vacuum arc deposition and investigated by near edge X-ray absorption fine structure (NEXAFS) and Raman spectroscopies. The C K (carbon K) edge NEXAFS spectra clearly revealed that the C=C bonds are more or less same for the film above 2 nm thickness. The evidence of surface defect was clearly visible for films with 1 nm thickness. The C K edge NEXAFS analysis further showed that the content of the surface defect (mainly C–H bonds) decreased with the increase thickness in the films. The intensity of the Raman G peak increased with the increase of thickness. The X ray reflectivity measurements revealed the increased of film density with thickness.