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An N 2 discharge sustained by an electromagnetic surface wave is investigated in order to develop an efficient nitrogen atom source. We take advantage of the flexibility of surface-wave discharges (SWDs) in terms of operating frequency to examine the influence of the field frequency (f = 13.56, 40.68, 440 and 2450 MHz) on the nitrogen atom concentration in the discharge spatial afterglow. The effects of absorbed power P A (up to 200 W), pressure p (1 to 8 Torr) and discharge tube diameter φ (4.5 and 15 mm) are also considered. The N atom concentration is determined through emission spectroscopy from the afterglow following validation by NO titration. We find that: (i) the N atom concentration increases with P A but saturates past a certain power, the value of which decreases with increasing f , (ii) the N atom saturation concentration is 1.5 × 10 15 cm −3 at 2450 MHz but only 7 × 10 14 cm −3 at f = 13.56 MHz (p = 4 Torr); (iii) the vibrational 'temperature' of the N 2 (C 3 u ) state in the discharge varies in the same way as the N atom concentration with respect to f and P A ; (iv) whatever f , saturation of the N atom concentration occurs at a threshold value T r = 500-600 K (p = 4 Torr) of the N 2 molecule rotational 'temperature' in the discharge, suggesting that too high a gas temperature is the limiting factor of the N atom yield (v) the N atom concentration increases with increasing p and decreasing φ.

Spectroscopic analysis of a -C and a -CN x films prepared by ultrafast high repetition rate pulsed laser deposition J. Appl. Phys. 97, 073522 (2005); 10.1063/1.1874300 Effects of thermal annealing on the structural, mechanical, and tribological properties of hard fluorinated carbon films deposited by plasma enhanced chemical vapor deposition This paper consists of an investigation of the structural arrangement of the sp 2 phase in amorphous unhydrogenated carbon nitride ͑a-CN x ͒ films and its effect on their physical properties. The a-CN x films ͑0.16Ͻ x Ͻ 0.25͒ were synthesized using a hybrid deposition system combining laser ablation of graphite and a source of atomic nitrogen. The microstructure of the films was investigated by Raman spectroscopy and electron paramagnetic resonance ͑EPR͒, while their optical and mechanical properties were determined by spectroscopic ellipsometry and nanoindentation, respectively. It was found that deposition at high laser intensities leads to an increase in the spin density ͑Ͼ10 20 /cm 3 ͒ and the EPR linewidth ͑of a few gausses͒ along with a decrease in nitrogen content. Visible Raman measurements indicate that these effects are accompanied by an increase in the degree of disorder of the sp 2 phase, as inferred from the broadening and downshift of the G Raman band, and a reduction of the CN triple bond signal. The analysis of these results in terms of the structural configuration and bonding in the films, show that an enhancement of the connectivity of the sp 2 phase in the layers, takes place when deposition is performed at high laser intensities. These structural modifications are strongly correlated to a decrease in the optical gap from 0.61 to 0.21 eV as well as to an increase of the hardness value of the films from 12 to 24 GPa. The transition from a reduced to an enhanced connectivity of the sp 2 phase occurs when the nitrogen content decreases below 22 at. %, as a result of the detected reduction of the triply bonded CN species in the layers.

Diamond-like-carbon (DLC) thin films have been deposited at room temperature on Si substrates by ablation of a graphite target using a KrF excimer laser at intensities ranging from 0.9×108 W/cm2 to 6.0×109 W/cm2. The microstructure of the films was studied by x-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The macroscopic properties were evaluated by measurement of their optical constants using in-situ laser reflectometry and their hardness using the continuous stiffness measurement technique. Analysis of the XPS C 1s core level spectra of the DLC films shows that their sp3 hybridized carbon atom content increases with laser intensity up to a maximum value of about 60% obtained at 7.0×108 W/cm2. At higher laser intensities, the sp3 content appears to stabilize at about 53%. Such an evolution of the sp3 content can be understood in terms of the subsurface carbon ions implantation model which has been proposed for ion beam deposited films. On the other hand, Raman analysis indicates that an increase in laser intensity leads to the establishment of some long range order of the sp2 domains in the deposited layers. The extinction coefficient k of the deposited layers was found to be correlated to their sp3 content. Finally, it is shown that hardness values as high as 47 GPa can be obtained and that hardness is also correlated to the sp3 content of the films.

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Carbon nitride thin films have been deposited on silicon substrates, using a newly developed surface wave discharge/pulsed laser deposition system. Nitrogen incorporation in the films is examined by x-ray photoelectron spectroscopy (XPS). It shows that interaction between the laser ablated carbon species and nitrogen atoms from the surface-wave N2 plasma enhances the incorporation of N in the carbon nitride layers, for example, up to 19% at a deposition pressure of 2 mTorr. Increasing the deposition temperature decreases nitrogen incorporation and changes the local chemical environment of nitrogen atoms.

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Dense, vertically aligned multiwall carbon nanotubes were synthesized on TiN electrode layers for infrared sensing applications. Microwave plasma-enhanced chemical vapor deposition and Ni catalyst were used for the nanotubes synthesis. The resultant nanotubes were characterized by SEM, AFM, and TEM. Since the length of the nanotubes influences sensor characteristics, we study in details the effects of changing Ni and TiN thickness on the physical properties of the nanotubes. In this paper, we report the observation of a threshold Ni thickness of about 4 nm, when the average CNT growth rate switches from an increasing to a decreasing function of increasing Ni thickness, for a process temperature of 700°C. This behavior is likely related to a transition in the growth mode from a predominantly “base growth” to that of a “tip growth.” For Ni layer greater than 9 nm the growth rate, as well as the CNT diameter, variations become insignificant. We have also observed that a TiN barrier layer appears to favor the growth of thinner CNTs compared to a SiO2 layer.