Table Of ContentNOVELSPECTROSCOPICTECHNIQUESUSING
THEPULSEDGLOWDISCHARGE
By
WILLIAMOTISWALDEN
ADISSERTATIONPRESENTEDTOTHEGRADUATESCHOOL
OFTHEUNIVERSITYOFFLORIDAINPARTIALFULFILLMENT
OFTHEREQUIREMENTSFORTHEDEGREEOF
DOCTOROFPHILOSOPHY
UNIVERSITYOFFLORIDA
1995
ToEndeavor
ACKNOWLEDGEMENTS
Asmymentors,IhavethehighestregardforDr.WillardW.HarrisonandDr.
J.D.Winefordner. Specifically,IwouldliketothankDr.Winefordnerforstressing
tomethebasicsofscientificresearch. I'mindebtedtoDr.Harrisonforhissupport
andstrengtheningmyartisticability.
IwillremembereveryoneinDr.Harrison'sandDr.Winefordner'sgroupsas
good friends. They were always there to lend a hand or to offer a helpful
suggestion. Theclosenessandcooperationbetweenthesharedgroupshasmade
mygraduateyearsmuchmorebearable. Dr.BenSmithhasofferedmeinvaluable
experienceininstrumentationandtheoryandIappreciatetheremarkablepatience
heshowed.
Finally, thisworkwouldnothavebeenpossiblewithouttheappreciated
supportbytheUnitedStatesDepartmentofEnergy,DivisionofChemicalSciences.
TABLEOFCONTENTS
Page
ACKNOWLEDGEMENTS m
LISTOFFIGURES vi
ABSTRACT x
CHAPTERS
1 THEGLOWDISCHARGEASA SPECTROSCOPIC
SOURCE
1
Historical Background 1
ElectricDischarges 5
GlowDischarges 8
PlasmaInitiation 12
Sputtering 14
Excitation 19
ModesofOperation 25
Directcurrentdischarges 25
Radiofrequencydischarges 26
PulsedGlowDischarges 26
History 26
PulseCharacteristics 27
Theprepeak 28
Theplateau 28
Theafterpeak 29
2 ATOMICFLUORESCENCESPECTROSCOPY 32
History 32
Theory 34
AtomicReservoirs 46
iv
3 MULTIELEMENTGLOWDISCHARGEATOMIC
FLUORESCENCE 46
Introduction 46
Experimental 50
XenonArcLamp 56
XenonFlashlamp 60
Diagnostics 70
AnalyticalUsefulness 76
4 THEMICROSECONDPULSEGLOWDISCHARGE 83
Introduction 83
Experimental 85
MPGDEmission 88
PlasmaDiagnostics 105
MassSpectrometry 108
TemperatureMeasurements 112
AtomicAbsorption 117
DiffusionStudies 120
Nonconductors 126
5 CONCLUSIONS 129
REFERENCES 134
BIOGRAPHICALSKETCH 143
v
01
LISTOFFIGURES
Figure Page
1 Representationofasimpleglowdischarge 2
2 Relationshipbetweenvoltageandcurrentingaseousdischarges 6
3 Luminouszoneswithinaglowdischargetube 1
4 Potentialdropacrossaglowdischargetube 1
5 Processbywhichincidentionssputtersurfaceatoms 16
6 Sputteryieldsforvariouselements 22
7 Gasphasereactionsinthenegativeglow 23
8 Profilesforthemillisecond-pulsedglowdischarge 30
9 Atwolevelsystemforfluorescence 36
10 Pathwaysforexcitationandde-excitationinatwolevelsystem 37
11 Fluorescencecurvesforcontinuumandlinesources 39
12 SchematicoftheGO-LEAFSexperimentalsystem 45
13 Xenonflashlampemissionspectrum 48
14 Explodedviewofthedirectinsertionprobecathodeassembly 52
15 SchematicformultielementGDAFSusingxenonlamps 54
16 Glowdischarge 58
17 SignalandS/Bforthecopper324.7nmlineversuspressure 61
18 Spatialprofileofemissionandfluorescencesignals 62
VI
19 Copper249.2nmfluorescenceprofileandS/BforthepulsedGO 65
20 Fluorescencespectraattheinitiationofthedischarge 66
21 Temporalprofilesobservedafterdischargetermination 67
22 Copperemissionspectrumusingthexenonflashlamp 69
23 Copper324.7nmfluorescencedecayinNIST#602 73
24 Aluminum309.1 nmfluorescencedecayinNIST#602 74
25 Magnesium285.2nmfluorescencedecayinNIST#602 75
26 AluminumNIST#602fluorescencespectrum 77
27 Calibrationcurveformagnesiuminaluminumstandards 78
28 Tantalumemissionandfluorescencespectra 80
29 SteelNIST#462emissionandfluorescencespectra 81
30 ManganesefluorescenceinSteelNIST#462 82
31 SchematicdiagramforopticalspectroscopywithMPGD 86
32 Currentandvoltageprofilesforatenmicrosecondpulse 91
33 Current,voltageandsignalafterinitiation 92
34 ProfilesofvariousMPGDemissionlines 94
35 MPGDtemporalemissionprofiles 95
36 CopperMPGDemissionspectraforgateddelaytimes 96
37 Spatialintensityprofilesforthecopper324.7nmline 98
38 MPGDemissionprofileacrossacopperpin 99
39 MPGDcopper249.2nmemissionversuspressure 100
vii
40 MPGDcopper249.2nmemissionversusfrequency 102
41 MPGDcopper249.2nmemissionversuspulsewidth 103
42 MPGDBrassNIST#1109fluorescenceandemissionspectra... 106
43 Calibrationcurvesforzincincopper 107
44 CopperMPGDionprofilesversusextractiondistance 109
45 MPGD/MSspectraforiron,NIST#661 111
46 MPGDN2+emission,10%N2inargon,0.9torr,100mWpower. 114
47 BoltzmannplotfortheMPGDrotationaltemperature 115
48 MPGDabsorptionprofilesfora10microsecondpulses 117
49 Peakabsorbanceplotsatvariouspowersupplypulsewidths.., 118
50 SputterratecomparisonsfortheDCandMPmodes 119
51 (A)MPGDabsorptionandemissionprofiles.(B)Profilefor
absorptionaftersubtractingoutemission 121
52 Copperfluorescenceprofilesatvariousboxcardelays 122
53 Copper324.7absorptionprofileversusdistancefromcathode. 123
54 Uncorrectedandcalculatedpeakabsorbancetimes 127
55 MPGDspectrumforMACOR 128
viii
AbstractofDissertationPresentedtotheGraduateSchool
oftheUniversityofFloridainPartialFulfillmentofthe
RequirementsfortheDegreeofDoctorofPhilosophy
NOVELSPECTROSCOPICTECHNIQUESUSING
THEPULSEDGLOWDISCHARGE
By
WilliamOtisWalden
DECEMBER1995
Co-Chairs:WillardW.HarrisonandJamesD.Winefordner
MajorDepartment:Chemistry
Theglowdischargeisaversatileatomsourcefortheanalyticalchemist.
Thisplasmaproducesatoms,ions,andexcitedspecies,allowingittobeusedas
asourceformosttraditionalspectroscopicmethods. Themostattractiveaspectof
thissourceisthatitcandirectlyatomizealmostanytypeofsolidsample.
Analyticalchemistscontinuallysearchfortheperfectmethodofanalysis.
Thismethodwouldaccommodateallsampletypes,havemultielementcapability
requirelittleornosamplepreparation,beinexpensive,havelowmaintenance,and
obtain low detection limits. Glow discharge atomic emission spectroscopy
possessesthefirstfivecharacteristicsofaperfectmethodbutfallsshortwithits
limitsofdetection.
IX
Thisdissertationreportsontwopulsedglowdischargemethodsdesigned
toincreasesignal-to-backgroundratiosoverthosefoundwithdirectcurrent(DC)
glowdischargeemission. Thefirstmethodinvolvestheuseofspectralcontinuum
sourcestopromotemultielementfluorescence. Boththexenonarclampandxenon
flashlampwereusedassources. The lampswerefoundto induceselectively
atomic fluorescence without exciting argon or molecular species. The best
analyticalspectrawereobtainedbysamplingtheatomicpopulationwiththexenon
flashlamp,firedattheterminationofamillisecondpulsedglowdischarge.
Thesecondmethodtoimprovethesignal-to-noisewasprovidedbyahigh
powered,microsecondpulsedglowdischarge. Withthismethod,anincreaseof
50to500timesintheemissionsignalwasobservedcomparedwithaDCglow
discharge. The very short on-times of the microsecond discharge permitted
diagnosticstudiesofdiffusionandtheevolutionofcertainplasmaspecies.
x
