S.R.J. Pearce

XPS and laser Raman analysis of hydrogenated amorphous carbon films

Abstract Hydrogenated amorphous carbon films were deposited in an RF parallel plate plasma reactor using various values of process pressure (10–50 mTorr) and DC self-bias (0–300 V). The films were then analysed by laser Raman spectroscopy (LRS) at 514.5 nm and X-ray photoelectron spectroscopy (XPS). Values for the ratio of sp 2 :sp 3 bonded carbon in the various films were obtained by suitable fitting of the XPS carbon 1s energy peaks, using a three-curve fitting procedure, which recognises a portion of the peak attributable to CO surface bonding. The sp 3 content was found to depend upon the DC self bias (and hence the ion impact energy) during deposition, peaking at a value of 81% at approximately 150 V. The softer films grown at lower DC bias values still had an sp 3 content of approximately 70%. Microcombustion analysis showed that films deposited with low DC bias contained 7 at.% H compared to less than 2 at.% for films deposited at biases greater than 100 V. This high sp 3 content can be explained by H-termination of dangling bonds, suggesting that sp 3 content alone is not a reliable indication of film properties. Curve-fittings of LRS spectra of the films showed that the Breit–Wigner–Fano lineshape is inappropriate for use with hydrogen containing films. Fitting using a Gaussian profile gave precise values for the FWHM, intensity, and Stokes’ shift of the G and D-peaks. A linear relationship between the intensity ratio of the D to G peaks and the width of the G peak was found for films deposited at high DC bias (with low H content), but not for films deposited at low DC bias. This is consistent with the increased H content of the films causing a change in the elastic constants and/or affecting the stress levels within the films.

Low temperature diamond growth using CO2/CH4 plasmas: Molecular beam mass spectrometry and computer simulation investigations

Microwave plasma enhanced chemical vapor deposition has been used to grow diamond films at substrate temperatures down to 435 °C using CO2/CH4 gas mixtures. An Arrhenius plot of growth rate as a function of substrate temperature yields a value for the activation energy for the growth step of 28 kJ mol−1. This is lower than that measured previously for CH4/H2 systems and hints at a different gas-surface chemistry when using CH4/CO2 plasmas. Molecular beam mass spectrometry has been used to measure simultaneously the concentrations of the dominant gas phase species present during growth, for a wide range of plasma gas mixtures (0%–80% CH4, balance CO2). The CHEMKIN computer package has also been used to simulate the experimental results in order to gain insight into the major reactions occurring within the microwave plasma. The calculated trends for all species agree well with the experimental observations. Using these data, the model for the gas phase chemistry can be reduced to only four overall reactions...

Deposition and properties of amorphous carbon phosphide films

a Abstract Radio frequency plasma deposition has been used to deposit phosphorus doped diamond-like carbon (DLC) films on Si and quartz substrates, using a gas mixture consisting of CH with additions of 0-90% PH . XPS studies reveal that the films contain 43

Structural characterisation of CNx thin films deposited by pulsed laser ablation

Abstract Carbon nitride (CN x ) film growth by 193 nm pulsed laser ablation of graphite in a low pressure of N 2 has been investigated both by studying optical emission from the plume and by analyses of the composition, structure and bonding of material deposited at a range of substrate temperatures. Spectral analysis of the emission reveals the presence of C + ions, C atoms, C 2 and CN radicals and N 2 + molecular ions within the ablation plume travelling towards the substrate. Films deposited at low substrate temperature ( T sub ) are amorphous, with an N/C ratio of ∼20 at.%. Raman analysis shows CN x films grown at higher T sub to be increasingly nanocrystalline, but thinner, and suggests that N inclusion encourages nanocrystallite formation. X-ray photoelectron spectroscopy reveals that CN x films grown at higher T sub also have a reduced overall N content. The observations have been rationalised by assuming an increased propensity for sputtering or desorption of more labile CN species from the growing film surface at higher T sub , resulting in a higher fraction of CC bonding—most probably in the form of graphitic nanocrystallites embedded in an amorphous matrix.

Molecular beam mass spectrometry investigations of low temperature diamond growth using CO2/CH4 plasmas

Diamond films have been successfully deposited at substrate temperatures as low as 435C using CO CH gas mixtures in a 24 Ž. microwave plasma chemical vapour deposition CVD reactor. In order to understand why it is possible to grow diamond at these low temperatures using these gases, we have performed the first in situ molecular beam mass spectrometry studies to measure, simultaneously, the concentrations of the dominant gas phase species present during growth over a wide range of plasma gas Ž. mixtures 080% CH , balance CO . Optical emission spectroscopy has also been used to investigate gas phase species present 42 in the microwave plasma. These experimental measurements give further evidence that CH radicals may be the key growth 3 species and suggest that CO may be of greater importance to the plasma chemistry of CO CH gas mixtures than previously 24 thought. 2001 Elsevier Science B.V. All rights reserved.

The effect of ion energy on the deposition of amorphous carbon phosphide films

Abstract A detailed study has been performed of diamond-like carbon films containing high concentrations of phosphorus deposited onto a variety of substrates. These ‘amorphous carbon phosphide’ films have been grown using RF plasma CVD at varying ion impact energies by changing the DC self bias on the powered electrode. X-ray photoelectron spectroscopy (XPS), and secondary ion mass spectrometry (SIMS) have been used to determine changes in the chemical composition and chemical bonding structure of these films. UV/visible absorption spectroscopy employing the Tauc-plot method has determined the band gap change with varying ion energies. Results show the enhancement of CP bonding ratios with deposition under high average ion energies, and also with the dramatic reduction in contaminant elements (O, H).