Density and sp 3 Content in Diamond-Like Carbon Films by X-ray Reflectivity and Electron Energy Loss Spectroscopy
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mass density can be deduced from the valence plasmon energy. Here, we show how grazing incidence x-ray Reflectivity (XRR) can be used to obtain information about density, roughness and cross-sectional layering for any amorphous carbon, without any sample preparation or damage [1-5]. Information about the possible layering within the films. This could be obtained by cross sectional EELS, but only with complex and careful sample preparation [6]. XRR gives information about the total electron density, which can be directly translated into mass density [5]. On the other hand, density determinations via EELS rely on an effective electron mass, for which different values can be found in literature [7-9]. We will show how a correct fit of the plasmon peak and an appropriate choice of the effective mass can give good agreement with the XRR mean densities, thus validating the use of the quasi-free electron model to analyse the low loss spectrum. Indeed an unique effective mass for all amorphous carbons and diamond is obtained. EXPERIMENTAL Samples We analysed tetrahedral amorphous carbon, ta-C, hydrogenated ta-C, ta-C:H, nitrogen containing ta-C:H, amorphous carbon (hydrogenated) a-C: (H), and nanostructured a-C, all deposited on Si. Two sets of ta-C films were analysed. The first was deposited using a single 293
Mat. Res. Soc. Symp. Proc. Vol. 593 © 2000 Materials Research Society
bend Filtered Cathodic Vacuum arc (FCVA) system [8] with different biases. The second series of ta-C films was deposited at different bias on a S-Bend FCVA [10]. Two series of taC:H samples were obtained using an Electron Cyclotron Wave Resonance source with an acetylene plasma and an ion energy from 80 to 170 eV [11]. Elastic Recoil Detection Analysis (ERDA) gave -30% at. H for all the films. One ta-C:H was deposited from methane with a Plasma Beam Source [12] with-40% at. H. Three ta-C:H:N were deposited by an ECWR source from N 2 /C 2H 2 , with known C/N and C/H ratios, by ERDA-XPS [11]. Three a-C:H were deposited from methane using a PECVD, two diamond like with an estimated H content -30-40% at. and one polymeric a-C:H with an estimated H-40-50%at. An a-C sample deposited by DC magnetron sputtering and a nanostructured a-C film was deposited by a pulsed microplasma cluster source [13]. XRR and EELS Specular reflectivity curves were acquired with a Bede Scientific GIXR reflectometer, with a Bede EDRa scintillation detector, using the Cu Kp radiation (X-1.3926 A). Specular and off-specular reflectivity curves were measured for each sample, with the incidence angle Oi in the range 0-8000 arcsecs, with a step of 20 arcsecs. Simulations were performed using the Bede REFS-MERCURY software package, which uses Parrat's recursive formalism of the Fresnel equations to calculate the reflected wave amplitude and, hence, the reflected intensity [5, 14-16]. XRR probes atomic scale surface roughness which results in x-rays being scattered out of the specular beam, causing a reduction in the specular reflected intensity. The intensity fall is faster than
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