Continuous wave plasmas

A considerable decrease both in the deposition rate and in powder formation was found when the 13.56-MHz excitation was modulated with a square wave of 2 Hz [510, 511]. In the y -regime, Biebericher et al. [512] have observed a decrease in deposition rate from 1.0 nm/s in a continuous-wave (cw) 50-MHz SiH4-H2 plasma, to 0.2 nm/s in a similar (i.e. with the same average power of 10 W) plasma, modulated by a frequency of 100 kHz. 

In a typical procedure, a continuous wave laser (50 mW) excites ICG at 780 nm and the fluorescence signal is captured at 830 nm. Subsequent to a bolus injection in the tail vein of the rat, the time-dependent clearance of ICG from plasma can be monitored in real-time as shown in Eig. 9 for three rat data sets. 

It should be remembered that the aim of this work was to produce defined layers with monosort functional groups, which can be used for grafting. Now, in contrast to the irregularly structured continuous-wave plasma polymers, the structure of pulsed plasma polymers was so much improved that partial or complete solubility was observed. Therefore, the further chemical processing in solvents and water led to dissolving the layer. Here, also chemically crosslinking copolymers as butadiene, di-vinylbenzene and trivinylcyclohexane were necessary as schematically shown in Fig. 9. 

Table 7.1 are continuous wave (CW), not pulsed. Second, frequency stability to < 1 cm" is important to assure Raman shift precision and avoid line broadening. Although the Raman shift axis is usually calibrated periodically, the laser frequency must remain stable between calibrations. Third, lasers vary significantly in output linewidth, from hundreds of reciprocal centimeters to much less than 1 cm". For the majority of samples of analytical interest, a laser linewidth below 1 cm" is sufficient. Laser linewidths are often quoted in terms of frequency rather than wavenumber, in which case 1 cm" equals 30 GHz. Lasers are available with < 1 MHz linewidths (< 10 em ), but such lasers would be unnecessarily narrow for most analytical Raman applications. Fourth, lasers differ in their output of light at wavelengths other than the laser line itself. Gas lasers (Ar+, Kr+, He-Ne) emit atomic lines (plasma lines), and solid-state lasers luminesce, both of which can interfere with Raman scattering. Essentially all lasers require a bandpass filter or monochromator to reduce these extraneous emissions. 

Most studies of plasma polymerization have been conducted in continuous wave rf plasmas. The effects of pulsed mode operation have received only limited attention. In a recent study, Yasuda et al. (1 ) found that while the polymerization rate of most monomers decreased when polymerization was carried out in a pulsed versus continuous plasma, the polymerization rate of a few monomers was enhanced. The present study was undertaken to determine the effects of pulsed operation on the plasma polymerization of ethylene and ethane. These monomers were selected because their behavior in continuous wave plasmas had been examined extensively in previous investigations (2 - ). ... 

One can argue that aliphatic plasma polymers from ethylene or propylene produced in the continuous-wave mode have significant structural anomalies in comparison with the respective classical products [24] and therefore they should increase the adhesion strength rather than keeping it at a constant (low) level. As seen in this work, the structural anomalies of aliphatic layers were minimized by the use of the pulsed plasma technique. This is demonstrated by the... 

The laser-based methods make use of different types of laser sources. Many of them, such as the solid-state laser or the semiconductor laser, are under continuous development because of the discovery of new lasing materials or the optimization of frequency conversion techniques. The type of the analytical application and the nature of the required information determine the choice of a special laser source, particularly pulsed or continuous-wave (CW) operating mode. Pulsed laser sources with fixed wavelength are usually used for LA, whereas both tunable pulsed and CW laser sources are preferred for element-specific detection or plasma diagnostics. 

The authors of this chapter conducted a recent study, which evaluated the efficacy of plasma treatment on a model wood substrate. In order to imderstand the effect of plasma treatment on wood-based fibers, clear pine wood veneers with an identical chemical composition was used as a model substrate. Plasma treatment was conducted using a custom built 13.56MHz inductively coupled plasma chamber in continuous wave mode (CW) and continuous wave mode plus pulse plasma mode [60]. During continuous wave mode the plasma is always on , so the formation of functional groups is accompanied by their destruction due to the continuous ion bombardment or surface ablation. During the pulse mode, the plasma source is on for a specific period and the plasma generated is similar to the continuous wave mode, where the plasma reactive species interact with the surface of the wood substrate. During the period when the... 

Li, L. Dai, X. J. Xu, H. S. Zhao, J. H. Yang, P. Maurdev, G. Plessis, J. d. Lamb, P. R. Fox, B. L. Michalski, W. R, Combined continuous wave and pulsed plasma modes For more stable interfaces with higher functionahty on metal and semiconductor surfaces. Plasma Process. Polym 2009,6 (10), 615-619. 

Nakajima et al. carried out plasma polymerization in continuous-wave and pulsed radio-frequency discharges to establish the effects of reaction conditions on the kinetics of polymer deposition as well as on the polymer structure. Under conditions favoring low deposition rates, the dominant functional group is -CF2. At higher deposition rates the of -Cp2 group concentration is reduced and a cross-linked polymer was obtained [738]. 

A CO2 laser operates on the emission bands between vibrational combination states generating emission on discrete rovibrational transitions in the i>i and 2 2 3 bands, centred around 10.6 and 9.6 pm, respectively. Population inversion is achieved by collisional energy transfer from plasma-excited N2 to CO2, usually in a mixture with He. A particular rovibrational emission line can be selected using a rotatable diffraction grating incorporated in the laser cavity. CO2 lasers can achieve very high continuous-wave (cw) power levels of up to 100 W from commercially available systems. In addition, CO2 lasers are robust, narrow-bandwidth and low-cost systems well able to induce IRMPD, but a disadvantage is clearly its limited tunability. It should be noted that fixed-frequency CO2 lasers are used routinely in commercial MS platforms to induce dissociation as an alternative to CID. 

Plasma techniques are employed for the deposition of thin polymer films on solid substrates, for the chemical modification of polymer surfaces, and for the etching of polymer coatings. These processes are usually performed with the aid of low-pressure, low-temperature continuous plasmas, so-called continuous wave (CW) plasmas. Some typical laboratory-scale set-ups for these plasma processes are shown in Figure 1.6 [45]. 

Guo, T., Nikolaev, P., Thess, A., Colbert, D. T., SmaUey, R. E. - Catalytic growth of single walled nanotubes by laser ablation , Chem. Phys. Lett. 243 (1995) 49—54 Zhang, H., Ding, Y., Wu, C., Chen, Y., Zhu, Y, He, Y, Zhong, S. - The effect of laser power on the formation of carbon nanotubes prepared in CO2 continuous wave laser ablation at room temperature , Physica B 325 (2003) 224—229 Burakov, V. S., Bokhonov, A. F., Nerdel ko, M. I., Savastenko, N. A., Tarasenko, N. V. — Optical Emission Characteristics of Carbon Plasma Produced by Single and Double Pulse Laser Ablation, Institute of Molecular and Atomic Physics National Academy of Science of Belarus... 

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