Frequency magnetically enhanced

Figure 5. Deposition rate profile on the electrode and substrate for a glow discharge polymerization of ethylene activated at a frequency of 10 kHz with magnetic enhancement. The system pressure is 20 fim Hg. (O) 60 mA, (A) 200...

The characteristic feature of the so called cold plasmas employed in polymerization studies is that the typical temperature of the electrons in the plasma is some two orders of magnitude greater than the temperature of the ions and neutrals, which in turn approximate ambient. The important operator-controlled variables in a gas plasma are choice of monomer, choice of carrier gas (if any), power input and operating frequency, and gas pressure and flow rate. One may also include the effect of magnetic enhancement to increase locally the power density. Some of these factors are of course interdependent. 

The basic features of an epr spectrometer are shown in Figure 2.95. The microwave source is a Klystron tube that emits radiation of frequency determined by the voltage across the tube. Magnetic fields of 0.1 — 1 T can be routinely obtained without complicated equipment and are generated by an electromagnet. The field is usually modulated at a frequency of 100kHz and the corresponding in-phase component of the absorption monitored via a phase-sensitive lock-in detector. This minimises noise and enhances the sensitivity of the technique. It is responsible for the distinctive derivative nature of epr spectra. Thus, the spectrum is obtained as a plot of dA/dB vs. 

Electron-nuclear double resonance (ENDOR) spectroscopy A magnetic resonance spectroscopic technique for the determination of hyperfine interactions between electrons and nuclear spins. There are two principal techniques. In continuous-wave ENDOR the intensity of an electron paramagnetic resonance signal, partially saturated with microwave power, is measured as radio frequency is applied. In pulsed ENDOR the radio frequency is applied as pulses and the EPR signal is detected as a spin-echo. In each case an enhancement of the EPR signal is observed when the radiofrequency is in resonance with the coupled nuclei. 

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