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ICP Plasma
Josh Mandich
DC Plasma
 Plasma: partially ionized gas
 DC plasma relies on the gas between the two
electrodes to have a potential high enough to be
ionized.
Inductively Coupled Plasma
 Energy supplied by electric currents
 Time varying electric current
passes through coil
 Creates time-varying mag. field
 Induces oscillating electric currents in gas
 Ionizes atoms
Inductively Coupled Plasma
 Mag. field increases distance electron travels
(thus ionization rate)
 At rate of excitation > 10KHz, ions cannot follow
voltage change
 ICP uses RF range of 10 MHz-14MHz
Inductively Coupled Plasma
 If Magnetic field is added to plasma:
 Lorentz force deflects motion of electron perpendicular
to velocity and mag. field
 If velocity is constant, field induces circular motion
AC vs. DC Plasma
Which is better?
DC problems
 Electrons move in only one direction
 Insulating materials will not sustain a plasma (SiO2)
Plasma Temperatures
 Range between 6000-10000 K
 (comparable to the surface of the sun)
Applications
 ICP-MS: mass spectrometry
 ICP-AES: atomic emission spectroscopy
 ICP-RIE: reactive ion etching
ICP Mass Spectrometry
 Measures the mass-to-charge ratio of ionized atoms
 ICP ionizes molecules
 Magnetic field separates them on basis of m/z ratio
 Recorder detects graph of Abundance vs. m/z ratio
Atomic Emission Spectroscopy
 excited electrons emit certain wavelengths when they
return to ground state
 Each element emits a specific wavelength particular to its
chemical make-up
 Intensity of wavelength is proportional to concentration of
element in analyzed sample
 Used to determine elemental composition
Reactive Ion Etching
 Plasma removes material deposited on wafers
(sputtering)