Plasma chamber

A third possibility of converting nonfluorescent substances to fluorescent derivatives, without the use of additional reagents apart from the stationary phase on which the separation has been carried out, is to place the plate in a plasma chamber for some time. 

A twin torch plasma furnace, where DC anode and cathode arcs were coupled together above an aluminum melt, was developed for synthesis of AIN UFPs in order to control the aluminum evaporation rate and the concentration of nitrogen atoms in the plasma column independently (19). A two-stage transferred-arc plasma reactor was built for AIN synthesis, where aluminum is evaporated in a transferred-arc plasma chamber and then reacted in a separate tubular reactor, allowing a better control of the reaction conditions (20). Arc plasma technique has been modified and... 

The use of a plasma chamber that creates a diffuse light reaching all parts of painted vehicle ... 

Prior to application of the aqueous solution of 3-APTHS, the samples were subjected to a water plasma treatment for 1-3 h. The pressure of water vapor in the plasma chamber was 26 Pa. The plasma was fired by an RF power supply. 

FIGURE 7.15 Schematic of a plasma emission chip consisting of the top and bottom plates. Features of the bottom plate (20 x 30 x 0.5 mm) are 1, gas inlet 2, gas outlet 3, pressure sensor connection 4, electrodes 5, electrode connection pads. Etched in the top plate (14 x 30 x 0.5 mm) are 6, plasma chamber 7, inlet channel 8, outlet channel [718). Reprinted with permission from the Royal Society of Chemistry. 

The electrons are extracted through a slit in the chamber wall, the anode, that simultaneously acts as electron optic and a pressure stage between the 100 Pa in the plasma chamber and <1 Pa outside, to which the mass spectrometer chip is evacuated in an appropriate housing. 

The electrons are accelerated across this low pressure region between the plasma chamber and the adjoining ionization chamber to typically 100 eV, the optimum for the ionization of most gases. They are focused to the input slit into ionization chamber, into which the sample gas is introduced via another capillary, alternatively via a microchannel chip, which reduces the pressure from atmospheric again to about 15 Pa, the pressure for maximum ionization efficiency for the chamber diameter of also 150 pm. Analyte ions are extracted from the ionization chamber through a second slit on the opposite side into an ion optic and are then accelerated into the mass separator to an energy of typically 100 eV. 

The PIMMS-elements can be divided in the fields of fluidic, plasma physics, electrostatic, and high frequency technology. The fluidic part covers the supply with plasma and sample gas, their distribution inside, and their evacuation out of the system. By means of plasma physics both the ionization of the plasma gas by the microwave field and the ionization of the sample gas by impact ionization are described. Electrostatic theory governs to design the elements for acceleration, focusing, and deflection of the plasma electrons and the sample gas ions. Electromagnetic wave theory describes the creation of a microwave-field inside the plasma chamber. 

The electron source of the PIMMS is an argon plasma. Inside the plasma chamber the gas is ionized by a 2.45 GHz microwave field, ignited by an electric spark. In the plasma chamber free electrons are created, that are accelerated by a static electric field for impact ionization of the sample gas atoms. The layout of the plasma chamber has to incorporate both the fluidic and the electrostatic requirements. On the one hand the gas apertures of the chamber must have the appropriate dimensions to assure that the gas flow out of the chamber is low. On the other hand the geometry must be such that most of the electrons are generated close to the outlet of the chamber and can be extracted through this small aperture. Electrons should be generated close to the acceleration field, which intrudes the chamber only to a small depth. 

The layout of the plasma chamber is optimized for a high electron yield at a low gas flow. Special attention was paid to obtain a low reflected power under fluctuating pressure conditions. This is important to protect the RF-generator and to ensure a stable plasma, which is crucial for a reliable ionization rate of the sample gas. 

Figure 3 shows the resulting plasma chamber. Its diameter is 600 pm and its outlet aperture is 40 pm wide. 

Fig. 3 Optimized plasma chamber design with reduced side gaps, optimized electrode surface ratio and without bottom metallization...

For this layout of the plasma chamber the trajectories of the electrons as well as the ions in an applied electrical field were simulated with the SIMION 8.0 software [18], Figure 4 depicts the extraction of electrons out of the plasma chamber for a potential difference of 100 V between the plasma and the ionization chamber [19] at vacuum conditions, i.e., without electron-gas interaction. The corresponding electron energy... 

The ionization chamber is of similar design as the plasma chamber. As there is no electric field inside the chamber, its geometry matters only with respect to ionization yield and gas flow. 

As already mentioned the plasma is ignited by a high voltage discharge in the plasma chamber at a relatively high pressure. In continuous operation, a stable RF plasma will bum at much lower chamber pressures [13]. This requires switching between two different flow resistances, i.e., capillary lengths, which is accomplished by a four-way valve operated as shown in Fig. 14. 

Fig. 17 This figure depicts the computed and measured throughput of the plasma chamber vs. the inlet capillary pressure extrapolated to low flows...

Fig. 18 Pressure drop diagram for the plasma chamber in operation mode. The inlet capillary pressure is 2e4 Pa...

The current gas supply consists of two capillaries of different diameters that satisfy the previously mentioned pressure values (30 and 180 pm). Thus, a rapid pressure drop across a short length is accomplished with a short delay time, which is about 350 ms in this arrangement. The pressure drop of the sample gas for the plasma chamber in operation mode is shown in Fig. 18. 

To ignite the microplasma the pressure of the inert gas in the plasma chamber is temporally increased to allow a controlled arc discharge according to the Paschen law. With the RF-power applied between the center electrode and the chamber walls... 

Fig. 23 Plasma chamber (a) before ignition (b) at ignition pressure after arc discharge (c) at operation pressure...

Figure 30 displays a spectrum of lab air, neon, and argon. The Ar peak represents the leakage from the plasma chamber and thus can be used for mass calibration. The measured resolution ml Am at full width at half maximum (FWHM) is 10.8, and 4.3... 

Organic conductive films, e.g. polyaniline or polythiophene, have an interesting potential application due to their easy processability combined with a low weight. A plasma deposition process is even more interesting from a technical point of view, because it is, as opposed to wet chemistry, much more compatible with production processes in vacuum. The sample used was polymerized by Kruse et al. [454] on a silicon wafer over 20 min in a microwave plasma chamber at 2.45 GHz using 2-iodothiophene (at... 

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