Laser-induced modifications in a-C:H thin films

doi:10.1016/0169-4332(93)90511-9

Applied Surface Science

Volume 69, Issues 1–4, 2 May 1993, Pages 242-248

https://doi.org/10.1016/0169-4332(93)90511-9 Get rights and content

Abstract

We have studied the transformations of amorphous hydrogenated carbon films (a-C:H) induced by pulsed laser irradiations. By the complementary use of isotopic (hydrogen/deuterium) tracing experiments and nuclear microanalysis, the changes induced by the laser treatments in the elemental composition of the films were evidenced. The loss of deuterium atoms was accompanied by a graphitization of the films. In addition, even at laser intensities much lower than the ablation threshold, a large exchange phenomenon was evidenced between the deuterium atoms initially incorporated in the amorphous carbon layers, and hydrogen atoms coming from the ambient water vapour. These findings are certainly related to the thermal effects induced in the a-C:H films by the laser pulses.

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Cited by (10)

Kinetic modeling of laser annealing processes in a-C:H films
2011, Vacuum
Citation Excerpt :
The highest temperatures are just below the surface, and there is a continuous decrease in temperature when going deeper in the film. Pulsed nanosecond and femtosecond laser irradiation in the visible light and UV domain was shown to induce the loss of hydrogen from the film, graphitization, and ablation [11–14,17–22]. The growth of Si and SiC crystallites was also reported [16].
In this research work, a nanosecond-pulsed YAG:Nd laser was used to modify the properties of an amorphous hydrogenated carbon film, which was deposited on c–Si substrate. Experimental examination has revealed that the primary effect of irradiation is diamond-to-graphite transformation or, more specifically, carbon sp³-to-sp² hybridization transition. These findings were qualitatively verified by numerical simulation of kinetic processes that proceed in the film under laser irradiation.
Effect of annealing on the structural and electrical properties of d.c. multipolar plasma deposited a-C:H films
2000, Thin Solid Films
The changes upon annealing in CH and CC bonding in relation to the structural and electronic properties have been investigated in two different series of a-C:H samples prepared in a direct current (d.c.) multipolar plasma system from pure methane at quite different substrate bias (−40 and −600 V). Using a combination of infrared absorption, elastic recoil detection analysis, high resolution transmission electron microscopy and electrical resistance measurements, we fully characterize the samples in their as-deposited state as well as after successive annealing cycles at increasing temperatures up to 700°C. The results show clearly that the two types of series exhibit quite different microstructures and hydrogen incorporation in their as-deposited state. The low bias (−40 V) series exhibits a highly disordered structure, while the high bias (−600 V) one already contains well ordered regions. They also have a completely different behavior upon annealing up to high temperature. A microstructure conversion such as from hydrogenated as well as non-hydrogenated sp³ C sites to sp² C ones occurs in the temperature range 400–500°C in all cases. However, a more efficient graphitization is observed in the high bias series (−600 V) for annealing temperatures as high as 700°C. Quite surprising results are obtained for the low bias series (−40 V): contrarily to what is usually observed for this type of sample, this series is found to be more thermally stable for high annealing temperature (>400°C) than the high bias one (−600 V). These results are discussed and explained in terms of the relaxation process in the local microstructure.
Carbon sputtering of polymer-like amorphous carbon by swift heavy ions
1999, Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms
Thin films of “polymer-like” deuterated amorphous carbon have been irradiated at GANIL (Caen, France) by several swift heavy ion beams : S, Ar, Nb, Sn, Pb and U in the energy range between 2 and 10 MeV/amu, covering the electronic stopping power (S_e) range between 1 and 13 keV/nm. Using Rutherford backscattering spectrometry, the carbon content remaining in the film has been determined versus fluence for several values of S_e. The deduced yield of carbon sputtering increases significantly above a S_e threshold value of 2.5 ± 1.0 keV nm⁻¹, which is larger than the S_e threshold value of deuterium effusion (0.75 ± 0.35 keV nm⁻¹). Using the thermal spike model, an effective temperature around 2800 K is defined for carbon sputtering in polymer-like amorphous carbon in the S_e regime.
The effect of hydrogen evolution on the mechanical properties of hydrogenated amorphous carbon
1998, Diamond and Related Materials
The nature of hydrogen bonding and its influence on mechanical properties and atomic structure were investigated in two types of a-C:H films, prepared in a DC multipolar plasma system from pure methane at different substrate bias, by performing H evolution and annealing experiments. The results clearly indicate that these two types of samples have different H bonding and microstructures in their as-deposited state. They behave differently upon annealing up to high annealing temperatures. These results show that a decrease of the hydrogen concentration reduces the internal stress from compressive to slightly tensile values, increases the sp² bonded carbon cluster sizes and reduces the magnitude of the stresses.
Hydrogen pumping in amorphous deutered carbon films irradiated by swift heavy ions
1997, Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms
Deutered amorphous carbon films have been irradiated at GANIL using 5 to 10 MeV/u sulfur beam with an electronic stopping power from 1 to 1.4 keV/nm. Such films have been deposited on silicon substrates by decomposition of CD₄ gas containing 10% of CH₄ in a dc multipolar plasma. After irradiation, they were analyzed firstly using absorption infrared spectroscopy to determine the number of CD and CH bonds. Secondly, deuterium, hydroge and carbon areal density were determined by ERDA and RBS. The results analysis shows a decrease of the atomic ratio ( $D C$ ) as well as CD bonds down to a minimum value versus the fluence without a threshold fluence and in the same time an increase of the atomic ratio ( $H C$ ) as well as CH bonds to a maximum value. So we may conclude that the hydrogen pumped after the irradiation is stabilized on broken (or unpaired) bonds.
Influence of the hydrogen evolution on the structural and electronic properties of a-C:H films
1996, Diamond and Related Materials
The nature of hydrogen bonding and its influence on the electronic properties and the atomic structure was investigated in two types of a-C:H films prepared in a d.c. multipolar plasma system from pure methane at different substrate bias, by performing H evolution and annealing experiments. The results indicate clearly that these two types of samples have different morphologies in their as-deposited state, and that they behave differently upon annealing up to high temperature.

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Laser-induced modifications in a-C:H thin films

Abstract

Mater. Sci. Eng. B

Nucl. Instr. Meth. B

Appl. Surf. Sci.

J. Non-Cryst. Solids

Appl. Surf. Sci.