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I N T R O D U C T I O N
The EQP mass spectrometer combines anelectrostatic sector energy analyser with a highperformance quadrupole mass filter in an instrumentdesigned for plasma diagnostics. The EQP canacquire the mass spectra and energy distributions ofneutrals, radicals and ions (positive and negative).Trends in intensity can be plotted against time. Fastacquisition modes mean that transients andafterglows can be studied.
C O N F I G U R AT I O N
The EQP mass spectrometer is a PC controlledinstrument for plasma analysis and diagnostics.Spectra can be easily acquired, stored andmanipulated using Windows™ based MASsoftsoftware. The EQP uses an electrostatic sector fieldenergy analyser for ion energy analysis, thetransmission and resolution of this device making itthe instrument of choice for plasma diagnostics.
The energy analyser is followed by a triple sectionquadrupole mass filter. A pulse counting electronmultiplier, which can be configured for positive ornegative ion operation is used for ion detection. Thisdetector provides high sensitivity, fast response andhigh dynamic range (>1010) for plasma ions andneutrals. Mass range options are 300 amu, 510 amu,1000 amu and 2500 amu. An energy range of 100 eVis standard and 1000 eV optional to provide the userwith analysis of positive and negative ions andappearance potential spectra for radicals analysis.Signal gating by direct TTL input is also available withgating resolution to 1 µs for afterglow studies.
EQPM A S S A N D E N E R G Y A N A L Y S E R F O R P L A S M A D I A G N O S T I C S
EQP
A P P L I C AT I O N
The EQP operates in one of two modes:
PI Mode: Ions can be directly extracted from theplasma. These plasma ions (PI) are formed in theplasma, extracted from it and focussed into theenergy filter.
EI Mode: Neutrals and radicals are sampled from theplasma and then ionised at low pressure (10-5 torr)inside an electron impact (EI) ion source. The energyof the ionising electrons may be controlled to enablethe detection of radicals. Ions from the electron beamsource are first transferred and then focussed directlyinto the energy filter.
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Typical IEDs are shown in the figures. The spectrashow the energy distributions for mass resolved ionsas indicated. The energy range of the instrument is100 eV with an option for 1000 eV operation. Theenergy spectrum can be used to determine theplasma potential, tailing on the energy spectra is anindication of collisions taking place in the plasmasheath.
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quadrupoles for advanced science
Hiden Analytical Ltd.420 Europa BoulevardWarringtonWA5 7UNEngland
Tel: +44 (0) 1925 445225Fax: +44(0) 1925 416518Email: [email protected]: www.HidenAnalytical.com
The main constituents of the EQP Plasma DiagnosticSystem are as follows:
Sampling Orifice: The sampling orifice is removable and ismounted at the probe tip. This can be configured in various wayswhich include grounded, dc biased, heated, RF driven andelectrically floating.
Electron Impact (EI) Ion Source: The electron impact ion sourceis not used in plasma ion mode. In EI mode the dual filamentelectron impact ion source is used to create ions from the neutralspecies which diffuse into the ion source. The selected filamentemits electrons with an energy defined by the variable electronenergy. The electron emission current is the current collected bythe ion source cage, this current is measured and used to stabilisethe filament current. The electron emission current can be usercontrolled to enable the user to find the ionisation potential ofradicals and neutrals. The electron energy is scanned with otherparameters fixed and intensity is plotted against electron energy.
Transfer Ion Optics: A drift space and lens are usedto transfer the EI or PI ions to the input of the energyfilter. In this drift space ions are accelerated to ahigher kinetic energy. A lens is used to match the ion(EI or PI) into the energy filter.
Quadrupole Lens: To focus ions in both x and ydirections into the energy filter.
Energy Filter: The energy filter is a 45° sector fieldelectrostatic energy analyser fitted with fringe fieldcorrection apertures. The analyser radius is 75 mmproviding high resolution and transmission. Energypass band is 0.5 eV with 100% transmission withinpass band.
Decelerating Lens: A decelerating lens reduces thekinetic energy of the ion beam before injection intothe quadrupole mass filter.
Quadrupole Mass Filter: The quadrupole mass filter is constructedin three sections, prefilter (RF only), main filter (RF and dc) and postfilter (RF only). The mass filter resolution is electronically controlledand is software adjustable to allow the user to easily optimise allparameters according to the requirements of the experiment.
Detector: The detector is an off axis mounted continuous dynodeelectron multiplier which operates in the pulse counting mode. Thethree variables which control the detector are: (i) the first dynodevoltage - this is the voltage on the front of the detector; (ii) themultiplier HT - this is the voltage across the detector; and (iii) adiscriminator which is used to set a counting threshold on the pulseoutput from the multiplier. The pulses from the detector can beelectronically gated so that only pulses detected during the gatetime are included in the energy or mass spectra. This feature can beused to study afterglows and transient phenomena.
Differential Pump Port: High conductance ConFlat® port for turbopump mounting.
O P E R AT I O N
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