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Abstract
111 pta ma i the quasi-neutral gas of charged and neutral particle which exhibits collective behavior. (eIJen, 1974) The coil’ rive behavior is
the behavior of a neutral gas, which is de cribed b. the kinetic theory of ga
In pIa ’111ft, the motion of the particles can cau e I cal concentration of
po itive and negative electric charges. These charge concentrations create
long-ranged coulornoic fields that affect the motion of charged particle tar
away from the charge concentrations. TIlUS elements of the plasma affect each
other. e en at bilge separations gi ing the plasma its characteristic collective
behavior: A charged particle in a pla 1113 moves along a patlt which all average
follow the electric field. In some conditions, at low pre sure. tlte effect of the
long-rang electromagnetic force. on th motion of the panicl s can be much
tronger than the effect of the collisions between dIe particles. In uch ca es
the pia rna is called a collisionles pla ma (Gl’il’, 1993).
There are two kinds of pla mao the irst one i called pltitlally low
ionized plasma, or cold plasma. For exampl neon lamp i cold pia rna at
which lectron temperature lower than W e and ion’ Are at room
temperature. Til second tale 1 called totally Ionized pia ma Or hot pla ma at
whi h the plR Ina exi I at temperatures more than 10 eV and it could rea h up
to 10 KeV (Mao’(wl’ 1964). It is well known over lumdred year that pia una
was first used in technology. Examples of the early applications. are gas-filled
valve . switch gear and lighting. Since the early seventies. grO\ ing nttention
ha been focus d on plasma 11 a medium for materials processing (ProlUuf et
at., 1991 ami at/glum 1991). The use of plasma for environmental
applications u h as the processing of industrial W::I res i becoming impcrtanr.Plasma is all enabling technology allowing new products 10 be conceived
which would be impo ible to make with traditional manufacturing proces e .
PIli nID i accepted a suitable environmentally friendly process technology
producing extremely lov levels of industrial wa re especially when compared
with the more traditional liquid chemical treatments. A critical parameter,
which oft n determines th boice of pIa rna source for particular materials
proce sing application, is tl, ion energy distribution function (IEDF) (Dendy
1993J- Electronic’ fire a good example of an industry in which clean plasma
technology ha enabled rapid progre to be made (e.g, plasma reactors .. and
increasing the componeur density, e, pecially for large and faster computer
memory). However, pia mas are in increasing use in a number of important
applications uch a pia rna etching, welding, CUlling of metals, hardening of
reel by nitriding. coating cursing tools with titanium nitride optical coatings,
polymer. irface treatment and coating or hardening of hip knee (shoulder
implants).
1.2 Plasma Gene.’atioll
A pia mil can be easily generated by ga breakdown using either
electron beams or through lin application of au electric field (as de. ac, rf
microwave and optical frequenci ). A breakdown is usually initiated by a few
free electrons that exist in the gas at room temperature due to cosmic my
irradiated (sometimes it is required 10 1.1 e U\ radiation to liberat more free
electrons from the electrode’ . urfac .. These free electrons are accelerated by
rhe applied electric field which impart energy to them, and thi energy i
converted to thermal energy a a result of lasric colli ions with ga atoms or
m Ie n] . When the electron energy exceeds the ionization energy of the ga .
inela: tic coni iOlLS take place and result ill the gas being e. cited and ionized.
This leads 10 more free electrons. and these electron multiplication processe
still take place ,intil a steady tate is reached.therefore electrons play animportant role in plasma ’. Thi is especially 50 lit high electric field
frequencies where only the electrons respond to the time varying field
(because of it small mas compared with ionma ). TIlUS the diagno ti s of
plasma such as electron temperature T.r’ electron density n, and electron
en rgy disrribnrion function (EEDF) are crucial for und rsranding the physical
and chemical processes which takes place in the pia mao Som plasma typ s
art’ shown ill figur (I-I), on ele tron den ity versus electron temperature
diagram (Lif!benlllIl/1 J994).
1.2.1 Plasma generation by beams
A beam-pro due d plasma discharge is usrained, e.g. by the interaction
of an electron beam with a ga eous medium (. clI11I.iflt et (II.; 1982). ollecrive
effects pro ince turbulent plasma 0 illations with high amplitude The
heating of the pIa 1JJ.aelectron in this turbulent field is sufficient to usraiu the
beam-produced discharge plasma. Th I:nergy transf r i very effectiv as up
to 70 % of the beam energ call be rransferred to rhe pla: mao It i po ’sible to
create pla mas with high degree of ionization in low-pre ure environment .
The pla rna properties may be controlled by the electron beam current, the
acceleration voltage, the ga pressure. and by the shape of the beam. Electronbeam
generated plasma are being used for large area material processing
(.leger et at., 1999).
The intera non of If! ier beams of sufficient energy with matter is
connected with the formation of plasmas, It i U I’d, e.g., tor fusion re eareh,
for material Ult.IDg, and f r chemical analysi f evaporated solid ’tate
materials by optical pecrroscopy or mass re rrometry.
1.2.2 Plasma generation bv electric field
Technical plasmas are gel) rated mostly by the electrical breakdown of
a neutral ga in the pre ence of an external electric field. Discharge type.