Carbon Nitride (Cn x ) Films Formed by Ion Implantation into Thin Carbon Films
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were applied to the substrate in order to extract the nitrogen ions from the plasma. Nitrogen ions also diffuse into the films between the high voltage pulses via thermal diffusion [ 15]. Voltages of 1-2 kV were used with a pulse length of 4-8 [is and a repetition frequency of 6-14 kHz. In the ion beam implantation method, nitrogen implantation was performed with fluences ranging from lxlO17 to lx 101 8 ions/cm2 at energies between 16-18 keV. No external heating was used, and the maximum sample temperature during exposure was less than 130 TC. The ion beam was directed at 90' or 450 with respect to the surface. Table I summarizes the processing conditions and N/C ratios as obtained by XPS analysis. Table I. Ion beam implantion into a-C films proces ing conditions and N/C ratios. Sample ID Beam angle Dose (ions/cm 2) Energy (KeV) N/C ratio IB-I 450 1 x loll 18 0.084 IB-2
IB-3 IB-4 IB-5
450
900 900 450
1 x lol
8
17
3 x 10 1 X 101 7 1 X 1017
16
0.083
16 16 16
0.16 0.1 0.075
The composition and the carbon-nitrogen bonding nature of the films were investigated by XPS. XPS measurements were obtained on a Leybold MAX 200 x-ray photoelectron spectrometer with both a monochromatised Al Kox x-ray (1486.6 eV) source and a nonmonochromatised Mg Kct x-ray (1253.6 eV) source. The monochromatised Al Kot source was used to obtain C Is high resolution spectra, while the nonmonochromatised Mg Kct source was used to collect the survey spectra and the N ls high resolution spectra. The spectra were fitted using the Gaussian-Lorentzian mix (75% Gaussian). Raman spectroscopy was conducted using a Dilor Omars 89 Raman spectrometer in microscope mode. The excitation laser wavelength was 514.5 nm using a power of 100 mW as measured at the laser. A slit width of 130 u.tm was used in conjunction with an integration time of 30 seconds. The interfacial tension was obtained from the advancing contact angle measurements of three testing liquids on a-C and CNx films. Deionized water having surface tension of 72.8 dyne/cm, ethylene glycol with 48.2 dyne/cm, and diiodmethylene with surface tension of 50.8 dyne/cm were used. The sessile drop technique [ 17] was employed with droplets volumes of 2-3 [d. RESULTS AND DISCUSSION Nitrogen to carbon (N/C) ratios between 0.135-0.25 were found in the PIll films and between 0.075-0.16 in the IB films. Typical XPS high resolution C Is and N Is lines are shown in Figure 1 and Figure 2 for a Pill and an EB implanted films respectively. Pill and IB implanted films with similar nitrogen contents have similar C Is and N Is lines. In the C ls spectra, the carbon peaks at the binding energies 284.3 eV and 284.9 eV indicate the formation of -C-C-Cgroups [18]. The peaks at 288.3 eV and 289.5 eV can be attributed to some C(O) type groups on the surface. Two peaks of interest are identified at the binding energies 285.6 eV and 286.6 eV. The intensity of these peaks and the ratio to the main peak for an a-C film and some IB and PIll films are summarized in Table IL. Analysis of the changes in the intensity rat
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