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Vilma Buršíková, Pavel Rehulka, Josef Chmelik, Milan Alberti, Z Spalt, Jan Janča, Josef Havel

Laser ablation time-of-flight mass spectrometry (LA-TOF-MS) of "nitrogen doped diamond-like carbon (DLN) nano-layers"

Journal of Physics and Chemistry of Solids 68 (2007) 701-706

Nitrogen-doped diamond-like carbon (DLC) layers (a-C:H:N, N-DLC or DLN) were prepared by the plasma-enhanced chemical vapor deposition (PECVD) technique, using a RF capacitive discharge (13.56 MHz), at low pressures (20 Pa), produced from a mixture of methane, nitrogen and hexamethyldisiloxane (HMDSO), deposited on single-crystalline silicon wafers placed on steel samples. The films, of differing deposition times, were subjected to laser ablation time-of-flight (LA-TOF) mass spectrometric measurements, using different commercial instrumentation to characterize their structures. The analysis of mass spectra was made and the following positively singly charged species were detected and identified: C-n(+) (n = 4-30), Si-n(+) (n = 2, 3), SinH (+)(n = 2, 3), SiOK (+), Si3H4+, Si2N+, Si2NH2+ 2 and Si3C+. The later three species could reflect the presence of nitrogen-silica and carbon-silica chemical bonds in the structure of the DLN layer. The stoichiometry of all species was confirmed by isotopic pattern simulation. In the negative detection mode, the C-n(-) (n = 2-12) clusters were observed. The findings are discussed in the light of the current research concerning analysis of the DLN thin layers and it is concluded that namely Si2N+, Si2NH2+ and Si3C+ species are reflecting the chemical structure of the DLN layer. LA-TOF-MS was found useful supplementary method for the characterization of DLN nano-layers. (c) 2007 Elsevier Ltd. All rights reserved.

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