Plasma source

Various functions of the instrument and data acquisition are carried out by a micro computer. For example, in a scanning spectrometer the analyses are carried out automatically according to a preset program, which permits the rapid successive determination of each analyte element with optimum operating conditions. 

An ideal excitation source for AES should have the following features (i) high specificity (ii) high selectivity (iii) high sensitivity (iv) high accuracy (v) high precision (vi) capacity for multi-element determinations (vii) ease of operation (viii) free of matrix interferences. 

Classical excitation sources in atomic emission spectroscopy do not meet these requirements. Flame, arc, and spark all suffer from poor stability, low reproducibility, and substantial matrix effects. However, the modem plasma excitation sources, especially ICPs, come very close to the specification of an ideal AES source. 

The analytical plasmas are classified according to the method of power transmission to the working gas. There are three dominant types of plasma source in use today (i) Inductively coupled plasmas, ICPs (ii) Direct current plasmas, DCPs (current carrying DC plasmas and current-free DC plasmas) (iii) Microwave plasmas (microwave induced plasmas, MIPs, and capacitively coupled microwave plasmas, CMPs). 

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Microwave discharges at pressures below 1 Pa witli low collision frequencies can be generated in tlie presence of a magnetic field B where tlie electrons rotate witli tlie electron cyclotron frequency. In a magnetic field of 875 G tlie rotational motion of tlie electrons is in resonance witli tlie microwaves of 2.45 GHz. In such low-pressure electron cyclotron resonance plasma sources collisions between tlie atoms, molecules and ions are reduced and the fonnation of unwanted particles in tlie plasma volume ( dusty plasma ) is largely avoided. 

Flopwood J 1992 Review of inductiveiy coupied piasmas for piasma processing Plasma Sources Sol. Technol. 1 109-16... 

Chen F F 1995 Fleiicon piasma sources High Density Plasma Sources ed O Popov (Park Ridge, MD Noyes)... 

Korzec D, Werner F, Winter R and Engemann J 1996 Scaiing of microwave siot antenna (SLAN) a concept for efficient piasma generation Plasma Sources Sol. Technol. 5 216-34... 

Rutscher A and Wagner H - E 1993 Chemical quasi-equilibria a new concept in the description of reactive plasmas Plasma Sources Sc/. Technol 2 279-88... 

Preparing the Sample Flame and plasma sources are best suited for the analysis of samples in solution and liquid form. Although solids can be analyzed by direct insertion into the flame or plasma, they usually are first brought into solution by digestion or extraction. 

Accuracy When spectral and chemical interferences are insignificant, atomic emission is capable of producing quantitative results with accuracies of 1-5%. Accuracy in flame emission frequently is limited by chemical interferences. Because the higher temperature of a plasma source gives rise to more emission lines, accuracy when using plasma emission often is limited by stray radiation from overlapping emission lines. 

Holland, J.G. and Eaton, A., Applications of Plasma Source Mass Spectrometry, The Royal Society of Chemistry, Cambridge, 1991. 

Plasma sources are also being iatroduced to produce plasmas at lower pressures and process temperatures. Inductively coupled plasma (ICP) and transformer-coupled plasma (TCP) are among the more commonly used sources, operating below 2.6 Pa (20 mTorr) (42). Low temperature RIE processiag operates between 26—67 Pa (200—500 mTorr). 

The plasma source implantation system does not use the extraction and acceleration scheme found in traditional mass-analy2ing implanters, but rather the sample to be implanted is placed inside a plasma (Fig. 4). This ion implantation scheme evolved from work on controlled fusion devices. The sample is repetitively pulsed at high negative voltages (around 100 kV) to envelope the surface with a flux of energetic plasma ions. Because the plasma surrounds the sample, and because the ions are accelerated normal to the sample surface, plasma-source implantation occurs over the entire surface, thereby eliminating the need to manipulate nonplanar samples in front of the ion beam. In this article, ion implantation systems that implant all surfaces simultaneously are referred to as omnidirectional systems. 

Fig. 4. A schematic of the plasma source ion implantation system, a plasma source chamber linked to a high voltage pulser. The plasma can be created from...

These limitations can be addressed in a number of ways. First, plasma source implantation techniques have the ability to treat compHcated geometries and are presently being evaluated for commercial appHcations. Where the estimated cost for beam-line implantation is estimated to be as high as 0.64/cm (2) or as low as 0.01 /cm for coming generation machines (3), industrial-scale plasma source implantation techniques have also been estimated to cost around 0.01/cm (4). 

The development of mote intense sources (eg, plasma sources, soft x-ray lasers, and synchrotron sources) has made possible highly effective instmments both for x-ray microscopy and x-ray diffraction on a few cubic nanometer sample. The optical problem of focusing x-rays is accompHshed by the use of zone plates or by improved grazing incidence or multilayer reflectors. 

Spectroscopic methods for the deterrnination of impurities in niobium include the older arc and spark emission procedures (53) along with newer inductively coupled plasma source optical emission methods (54). Some work has been done using inductively coupled mass spectroscopy to determine impurities in niobium (55,56). X-ray fluorescence analysis, a widely used method for niobium analysis, is used for routine work by niobium concentrates producers (57,58). Paying careful attention to matrix effects, precision and accuracy of x-ray fluorescence analyses are at least equal to those of the gravimetric and ion-exchange methods. 

Sources of matter and energy are necessary for the production of gaseous plasmas, and such plasmas serve as sources of matter and energy in their appheations ie, gaseous laboratory plasmas can be viewed as transducers of matter and energy. The initial and final forms of the material that enters a plasma and the requisite energy vary widely, depending on the particular plasma source and its utilization. 

Use of glow-discharge and the related, but geometrically distinct, hoUow-cathode sources involves plasma-induced sputtering and excitation (93). Such sources are commonly employed as sources of resonance-line emission in atomic absorption spectroscopy. The analyte is vaporized in a flame at 2000—3400 K. Absorption of the plasma source light in the flame indicates the presence and amount of specific elements (86). 

V. Loon, Plasma Source Mass Spectroscopy, CRC Press Inc., Boca Raton, Fla., 1994. 

Two colorimetric methods are recommended for boron analysis. One is the curcumin method, where the sample is acidified and evaporated after addition of curcumin reagent. A red product called rosocyanine remains it is dissolved in 95 wt % ethanol and measured photometrically. Nitrate concentrations >20 mg/L interfere with this method. Another colorimetric method is based upon the reaction between boron and carminic acid in concentrated sulfuric acid to form a bluish-red or blue product. Boron concentrations can also be deterrnined by atomic absorption spectroscopy with a nitrous oxide—acetjiene flame or graphite furnace. Atomic emission with an argon plasma source can also be used for boron measurement. 

High-frequency plasma source having no consumable electrodes ... 

This chapter describes the basic principles and practice of emission spectroscopy using non-flame atomisation sources. [Details on flame emission spectroscopy (FES) are to be found in Chapter 21.] The first part of this chapter (Sections 20.2-20.6) is devoted to emission spectroscopy based on electric arc and electric spark sources and is often described as emission spectrography. The final part of the chapter (Sections 20.7-20.11) deals with emission spectroscopy based on plasma sources. 

The inductively coupled plasma source (Fig. 20.11) comprises three concentric silica quartz tubes, each of which is open at the top. The argon stream that carries the sample, in the form of an aerosol, passes through the central tube. The excitation is provided by two or three turns of a metal induction tube through which flows a radio-frequency current (frequency 27 MHz). The second gas flow of argon of rate between 10 and 15 L min-1 maintains the plasma. It is this gas stream that is excited by the radio-frequency power. The plasma gas flows in a helical pattern which provides stability and helps to isolate thermally the outside quartz tube. 

HIGH DENSITY PLASMA SOURCES edited by Oleg A. Popov... 

As a plasma source, we used commeicially avaiUbk argon gas. Us iysicBl properties of Uonass arc shown in Table 1. As base conpounds fin lnamass, ( used ceUukise (Indian... 

Etching- metal and oxide etch equipment are used to remove excess parts of the deposited film. High density plasma sources... 

Inductively coupled plasma Plasmas generated by application of radiofrequency power to a nonresonant inductive coil and maintained by an inductive electromagnetic field. Low-pressure ICP is a high-density plasma source. 

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