Mechanisms Governing the Growth, Reactivity and Stability of Iron Sulfides Francis William Herbert

140 Pages·2014·10.43 MB·English

Mechanisms Governing the Growth, Reactivity and
Stability of Iron Sulfides
by
Francis William Herbert
M.Eng, Materials Science, University of Oxford, UK
Submitted to the Department of Materials Science and Engineering
in partial fulfillment of the requirements for the degree of
Doctor of Philosophy in Materials Science and Engineering
at the
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
February 2015
(cid:13)c Massachusetts Institute of Technology 2015. All rights reserved.
Author................................................................
Department of Materials Science and Engineering
November 20, 2014
Certified by...........................................................
Bilge Yildiz
Associate Professor of Nuclear Science and Engineering
Thesis Supervisor
Certified by...........................................................
Krystyn J. Van Vliet
Associate Professor of Materials Science and Engineering
Thesis Supervisor
Accepted by...........................................................
Donald Sadoway
John F. Elliott Professor of Materials Chemistry
Chair, Departmental Committee on Graduate Students
2
Mechanisms Governing the Growth, Reactivity and Stability of Iron
Sulfides
by
Francis William Herbert
SubmittedtotheDepartmentofMaterialsScienceandEngineering
onNovember20,2014,inpartialfulfillmentofthe
requirementsforthedegreeof
DoctorofPhilosophyinMaterialsScienceandEngineering
Abstract
Thekineticsofelectrochemicalprocessesinionicmaterialsarefundamentallygoverned
bydynamiceventsattheatomicscale,includingpointdefectformationandmigration,
andmolecularinteractionsatthesurface.Acorrosionsystemcomprisinganironsulfide
film(passivelayer)formedonironorsteelincontactwithanhydrogensulfide(H S)-
2
richfluidcanthus,inprinciple,bemodeledbyaseriesofunitreactionstepsthatcontrol
therateofdegradationundergiventhermodynamicconditions.Thisoverarchingthesis
goal necessitates a concerted experimental and computational approach to determine
the relevant kinetic parameters such as activation barriers E and rate constants ν
a o
forthehomogeneousandheterogeneousreactionsofinterest.Thesefundamentalval-
uescanbeobtainedexperimentallyviatemperature-dependentmeasurementsonpure,
model iron sulfide samples. This thesis therefore consists of three case studies on the
stableFe-Sphasespyrrhotite(Fe S)andpyrite(FeS )toidentifytheelementarycor-
1-x 2
rosion mechanisms and their kinetic parameters. Pyrrhotite is of interest because the
off-stoichiometryofthisphaseleadstorelativelyrapidbulkprocessessuchasdiffusion;
pyritehasacomparitivelyinertbulkbutthisworkshowedthatithasachemicallylabile
surface.
Thefirststudyfocusesontwobasic,rate-controllingstepsinthegrowthofpyrrhotite:
cationdiffusionandsulfurexchangeatthesurface.First,ironself-diffusivity*D isde-
Fe
terminedacrossthetemperaturerange170-400oCthroughmagnetokineticstudiesof
thediffusion-driven"λ"magnetictransformation,aswellasdirecttracerdiffusionmea-
surementsinFe Scrystalsusingsecondaryionmassspectrometry(SIMS).Thisrange
1-x
encompasses the sponteneousmagnetic and structural order-disordertemperature T
N
=315oCinpyrrhotite.TheeffectofspontaneousmagnetizationbelowT istoincrease
N
the Fe vacancy migration energy by a combined 40% increasing E for diffusion from
a
0.83eVinparamagneticFe Sto∼1.20eVinthefullymagnetizedstate.Anextrapola-
1-x
tionoftheArrheniuslawfromtheparamagneticregimewouldthereforeoverestimate
actualdiffusivitiesbyupto102timesat150oC.Second,thesurfaceexchangeofsulfur
from H S into the solid state in Fe S is measured using electrical conductivity relax-
2 1-x
ation, yielding E = 1.1 eV for sulfur incorporation into pyrrhotite. With their similar
a
thermaldependence,thereisnocleartemperaturecrossoverfromcationdiffusion-to
surfaceexchange-limitingregimes,orviceversa.Instead,surfaceexchangeisexpected
toconstrainpyrrhotitegrowthforfilmsunder∼100µmthickness,beyondwhichdif-
fusion becomes the rate limiting mechanism, independent of external driving factors
suchastemperature.
Thesecondstudyexplorestheroleofsurfaceelectronicstatesontheelectrochemi-
calreactivityofpyrite.Chargetransferbetweenasolidsurfaceandanadsorbatesuch
asH Srequiresthemutualavailabilityoffilled/emptyelectronicstatesatthesameen-
2
ergylevel.ThesemiconductingFeS (100)surfaceispredictedtohaveintrinsicsurface
2
states (SS’s) from Fe and S dangling bonds, as well as extrinsic SS’s related to delo-
calized defects at the surface, both of which would affect charge transfer character-
istics. A novel, broadly-applicable methodology is developed in this thesis to quantify
3
the energy and density of these SS’s, based on experimental scanning tunneling mi-
croscopy/spectroscopy (STM/STS) in conjunction with first principles tunneling cur-
rentmodeling.Asaresult,adecreasedsurfacebandgapE of0.4eV,comparedto0.95
g
eVinbulkpyrite,ismeasured.Thefindingshighlighttheneedtodifferentiatebetween
bulkandsurfaceelectronicstructurewhenassessingheterogeneousreactivity,andhave
implicationsfortheuseofFeS inpotentialtechnologicalapplications,forexampleas
2
aphotovoltaicadsorber.
Finally,thedynamicsofpointdefectformationandclusteringonFeS (100)under
2
high-temperature, reducing conditions are investigated to understand the stability of
the surface under extreme conditions. Synchrotron x-ray photoelectron spectroscopy
(XPS)isusedtomeasureaformationenergy∆H forsulfurvacanciesinthetopmost
f
atomic layerof 0.1 eVup to approximately 240oC. Abovethis temperature, however,
pointdefectsareshowntocondenseintosurfacepitsasmeasuredbyscnaningtunneling
microscopy (STM). The combined, experimental XPS and STM results are replicated
withhighprecisionbyakineticMonteCarlo(kMC)simulation,developedbyAravind
Krishnamoorthytowardshisdoctoralthesis,ofsurfacedegradationonrealisticlength-
and timescales of 10−10−10−7 m and up to several hours, respectively. The findings
have implications for the initiation of surface breakdown via pitting in ionic passive
films, as well as providing a broader understanding of the non-stoichiometry of the
pyritesurface.
Thecommonthreadisafocusoneventsattheatomicandelectronicscale,withan
emphasisonpointdefects.Theresultstherebyfacilitateabottom-upapproachtomod-
elingelectrochemicalprocessessuchascorrosioninFe-Sphases,inwhichtheunitsteps
arecastintoprobabilisticsimulationtools.Whilethethreestudiesherecompriseonly
apartialexaminationoftheatomic-scaleeventsregulatingthebehaviorofFe-Spassive
layers, this approach makes inroads towards more accurate component lifetime pre-
dictionandthedesignofrobustmaterialsforaggressiveenvironments.Moreover,the
fundamentalsurfaceandbulkphysicalchemistryofironsulfidesexploredinthiswork
hasimplicationsbeyondcorrosiontootherusesofthesematerials,includingpotential
magnetic devices (Fe S) and earth-abundant photovoltaic and photoelectrochemical
1-x
adsorbers(FeS ).
2
ThesisSupervisor:BilgeYildiz
Title:AssociateProfessorofNuclearScienceandEngineering
ThesisSupervisor:KrystynJ.VanVliet
Title:AssociateProfessorofMaterialsScienceandEngineering
4
Acknowledgments
Iamdeeplygratefultomyco-advisors,ProfessorBilgeYildizandProfessorKrystynvan
Vliet,fortheirencouragement,guidanceandsupport.Ithasbeenanimmensepleasure
to witness both Bilge and Krystyn establish themselves with tenure at MIT during my
time here and be part of two flourishing laboratories. Meanwhile, Bilge’s passion for
solid state chemistry and keen eye for important details, and Krystyn’s diligent and
organized approach to high-quality scientific inquiry have greatly inspired me. I also
thankKrystynforteachingmehowtospell"properly":thewordsulphideseemsasalien
tomenowassulfidedidfiveyearsago.
Thisworkwouldnothavebeenpossiblewithoutmyever-dependablecollaboratorand
friendAravindKrishnamoorthy.Heisgiftednotonlywithabrilliantscientificintellect,
butanimmenselyhumbleandgenerouspersonalitythathasmadeworkingtogetheron
thisprojectaricherexperience.Hiseffortstrulyallowedourcombinedcomputational
andexperimentalapproachtobecomemorethanthesumofitsparts.
I am also thankful to my collaborators on this project and others, including: Wen Ma,
YanChenandQiyangLufromtheLaboratoryforElectrochemicalInterfacesatMIT;Pe-
ter Albrecht at Brookhaven National Laboratory; Predrag Lasic and Rickard Armiento
(Cedergroup,MIT);RupakChakrabortyandKatyHartman(Buonassissigroup,MIT).
Thank you to Prof. Randall Feenstra at Carnegie Mellon University for his help deci-
pheringtheSEMITIPcodefortunnelingspectroscopysimulations.
I would like to thank all members, past and present, from my two fantastic reasearch
groups:theLaboratoryforElectrochemicalInterfaces(LEI)andtheLaboratoryforMa-
terial Chemomechanics who have taught me so much, from defect chemistry in ionic
solids to the mechanics of living cells. In particular, I am very grateful to Roza Mah-
moodianforhersupportandforputtingupwithmyincessantcomplainingoverfailed
experiments.AlsotoBalMukundDharforhisinfectiousenthusiasmandhelpwithCVD,
andtoLucyRandsforherhelpandeagernessasasummerintern.
Iamindebtedtomythesiscommittee-Prof.CarlThompsonandProf.HarryTuller-for
theirusefulcommentsandconstructivecriticism.Inaddition,IgreatlythankProf.Chris
Schuhforprovidinginvaluablefeedback,despitenotsittingonmyfinalcommittee.
BPPlc.hadalreadysupportedmyeducationforover20yearswhentheyarrivedatMIT
toproposethisproject,soIamdelightedtheyextendedtheircommitmenttomygrad-
uatestudies.Inparticular,IwouldliketothankSaiVenkatesweran,RichardWoolam,
SteveShademanandtheircolleaguesfortheirhelpandadvice.
Myparents,RichardandKate,haveinspiredandguidedmemywholelife;Iwouldnot
be here without the opportunities and unwavering support they have provided. And I
cannotomittheotherfourfifthsofmybandofbrotherswhoaremyframeofreference
foreverythingandneverstopinjectinghumourandhappinessintomylife.
Finally,thankyoutoallthosewhohavemademytimeatMITsospecialoutsideofthe
lab.Myfamilyawayfromhome;theeclecticanddynamiccommunityat"Martha"(216
Norfolk St): Sam, Katy, Georgie, Jake, Benji, Ines, Chris, Nina, Alex, Federico, Elison,
Andre,James,Andre,Stephanie,Rob,Balthazar,Simon,Sebastian,Nico,Melissa,Ser-
jumbi,Aron,allofourotherguests,andlastbutnotleastTeresafornotlosingfaithin
meafteralltheseyears.
5
6
Contents
1 Introduction 13
1.1 Context . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
1.2 Passivity:abriefintroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
1.3 Ironsulfidephasesandcorrosionproducts . . . . . . . . . . . . . . . . . . 14
1.3.1 Sourcorrosionmechanism:labandfieldexperience . . . . . . . . 17
1.3.2 Modelphases:Pyrrhotite(Fe S)andPyrite(FeS ) . . . . . . . . 19
1-x 2
1.4 Towardsapredictive,multiscalecorrosionmodel . . . . . . . . . . . . . . 20
1.4.1 Existingpassivefilmmodels . . . . . . . . . . . . . . . . . . . . . . . 20
1.4.2 UnitprocessescontrollingFe-Spassivelayerbehavior . . . . . . . 23
1.4.3 Theneedforexperimentally-derivedparameters . . . . . . . . . . 24
1.5 Thesisgoalsandorganization . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2 Growth:cationdiffusionandsurfaceexchangeasrate-limitingmechanisms
inpyrrhotite,Fe S 27
1-x
2.1 BackgroundandMotivation. . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.2 Pyrrhotite:polytypesandtransitions . . . . . . . . . . . . . . . . . . . . . . 29
2.2.1 Structuralandmagneticproperties. . . . . . . . . . . . . . . . . . . 30
2.2.2 Theλ-transitioninNCpyrrhotites . . . . . . . . . . . . . . . . . . . 34
2.3 Diffusion-limitedλtransition . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
2.3.1 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
2.3.2 Resultsanddiscussion . . . . . . . . . . . . . . . . . . . . . . . . . . 37
2.3.3 Continuousre-orderingofferrimagneticsuperlattice . . . . . . . 40
2.3.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
2.4 Isotopetracerdiffusionmeasurements . . . . . . . . . . . . . . . . . . . . . 45
2.4.1 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
2.4.2 ResultsandDiscussion . . . . . . . . . . . . . . . . . . . . . . . . . . 48
2.4.3 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
2.5 SulfurexchangekineticsattheFe Ssurface . . . . . . . . . . . . . . . . . 54
1-x
2.5.1 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
2.5.2 ResultsandDiscussion . . . . . . . . . . . . . . . . . . . . . . . . . . 57
2.5.3 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
2.6 Outcomes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
2.6.1 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
2.6.2 Futurework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
7
3 Reactivity:quantificationofelectronicbandgapandsurfacestatesonFeS (100) 69
2
3.1 Backgroundandmotivation. . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
3.1.1 Electrochemicalchargetransferinsemiconductor-absorbatesys-
tems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
3.1.2 Surfacestates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
3.1.3 ScanningtunnelingspectroscopyandTIBB . . . . . . . . . . . . . . 74
3.1.4 TheFeS (100)surface . . . . . . . . . . . . . . . . . . . . . . . . . . 76
2
3.2 Methods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
3.2.1 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
3.2.2 Computational . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
3.3 ResultsandDiscussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
3.3.1 Current-separationandcurrent-voltagetunnelingspectroscopy . 80
3.3.2 SimulatedtunnelingspectrabasedonDFT-calculatedDOS . . . . 82
3.4 Outcomes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
3.4.1 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
3.4.2 ImplicationsforotherapplicationsofFeS ,e.g.PV . . . . . . . . . 89
2
3.4.3 Futurework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
4 Stability: dynamics of point defect formation, clustering and pit initiation
onthepyritesurface 91
4.1 Backgroundandmotivation. . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
4.1.1 Chaptergoals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
4.1.2 Passivitybreakdownbypitting . . . . . . . . . . . . . . . . . . . . . 92
4.1.3 FeS surfacechemistryandnon-stoichiometry . . . . . . . . . . . . 94
2
4.2 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
4.2.1 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
4.2.2 Computational . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
4.3 ResultsandDiscussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
4.3.1 Evolutionofpyritesurfacestructureandchemistry . . . . . . . . . 97
4.3.2 Mechanismofvacancyformationandcoalescence . . . . . . . . . 103
4.4 Outcomes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
4.4.1 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
4.4.2 Futurework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
5 Conclusions 109
5.1 Summaryofactivationbarriers. . . . . . . . . . . . . . . . . . . . . . . . . . 109
5.2 Contributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
5.3 Outlookandperspectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
A PourbaixdiagramsfortheFe-H S-H Osystem 113
2 2
B ChemicalVaporDepositionofFe-S 119
B.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
B.2 Methods:CVDsetupandapparatus . . . . . . . . . . . . . . . . . . . . . . . 119
B.3 Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
C Diffusivitymeasurementsusingthinfilmsamples 129
8
List of Figures
1-1 PotentialEvs.currenti(polarization)curveforagenericmetal. . . . . . 14
1-2 Globalsouroilandgasstatistics.. . . . . . . . . . . . . . . . . . . . . . . . . 15
1-3 Thermodynamicpredictionsofcorrosionproducts. . . . . . . . . . . . . . 17
1-4 MechanismofironsulfideformationonsteelsinH S-bearingelectrolytes. 18
2
1-5 Ironsulfidestabilityphasediagram.. . . . . . . . . . . . . . . . . . . . . . . 20
1-6 Sulfidecorrosionof4130carbonsteelat220oC.. . . . . . . . . . . . . . . 22
1-7 SchematicofunitprocessesinFe-Spassivelayers. . . . . . . . . . . . . . . 24
1-8 Overviewofstrategytoconstructanon-empiricalpassivefilmmodel.. . 25
2-1 CollectedliteraturevaluesofFeself-diffusivity. . . . . . . . . . . . . . . . . 28
2-2 Structuralunitcellsofpyrrhotite. . . . . . . . . . . . . . . . . . . . . . . . . 30
2-3 Pyrrhotitestructuralandmagneticphasediagrams. . . . . . . . . . . . . . 32
2-4 IdealizedFe Ssuperstructures. . . . . . . . . . . . . . . . . . . . . . . . . . 33
1-x
2-5 Distributionsofvacanciesin4CandNCpyrrhotites.. . . . . . . . . . . . . 33
2-6 Thepeak-likeλ-transitioninNCFe S. . . . . . . . . . . . . . . . . . . . . 34
1-x
2-7 X-raydiffractionofsyntheticpyrrhotites.. . . . . . . . . . . . . . . . . . . . 35
2-8 SetupofcubickineticMonteCarlo(kMC)grid.. . . . . . . . . . . . . . . . 36
2-9 Temperature-dependentmagnetizationσ(T).. . . . . . . . . . . . . . . . . 38
2-10Magnetizationvs.appliedfield(σ-H). . . . . . . . . . . . . . . . . . . . . . 38
2-11Reversiblemagnetictransformationatshorttimescales. . . . . . . . . . . 40
2-12Bestfitstoexponentialequation. . . . . . . . . . . . . . . . . . . . . . . . . 41
2-13Long-timescaleisothermalmagnetization. . . . . . . . . . . . . . . . . . . . 42
2-14Differentialscanningcalorimetry(DSC)results. . . . . . . . . . . . . . . . 43
2-15Continuousre-orderingtowardsferrimagneticstate. . . . . . . . . . . . . 44
2-16Crosssectionofsulfidescale. . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
2-17Cu-kαpowderXRDpattern. . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
2-18Energy-dispersiveX-rayspectroscopy(EDS) . . . . . . . . . . . . . . . . . . 47
2-19Sourcesoferrorconsideredinstatisticalanalysisofdiffusiondata. . . . 49
2-20Secondaryionmassspectrometry(SIMS)profiles. . . . . . . . . . . . . . . 49
2-21Errorfunctionsolutiontodiffusionprofiles. . . . . . . . . . . . . . . . . . . 50
2-22Valuesforironself-diffusioncoefficient*D . . . . . . . . . . . . . . . . . . 52
Fe
2-23SputterdepositedthinfilmsforECRexperiments. . . . . . . . . . . . . . . 55
2-24Electricalconductivityrelaxationapparatussetup. . . . . . . . . . . . . . . 56
2-25Temperature-pressureequilibriumphasediagramforFe-S.. . . . . . . . . 57
2-26X-rayphotoelectronspectroscopy(XPS)fromaFe Sthinfilmsample. . 59
1-x
2-27Electricalresistancerelaxationat565oC. . . . . . . . . . . . . . . . . . . . 62
2-28Electricalconductivityrelaxationresults.. . . . . . . . . . . . . . . . . . . . 63
2-29Drift,stabilityandrepeatabilityofECRexperiments. . . . . . . . . . . . . 65
2-30Temperature-andfilmthicknessdependenceofratelimitingsteps. . . . 66
3-1 Chargetransferinelectrochemical(corrosion)systems. . . . . . . . . . . 72
3-2 BandbendingeffectsinSTSmeasurement. . . . . . . . . . . . . . . . . . . 75
3-3 FeS singlecrystalsamples. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
2
9
3-4 DistributionsofsurfacestatesasdefinedintheSEMITIPprogram. . . . . 80
3-5 Scanningtunnelingspectroscopy(STM)imagesoftheas-grownFeS (100)
2
surface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
3-6 Current-separationspectroscopy.. . . . . . . . . . . . . . . . . . . . . . . . . 82
3-7 Current-voltagespectroscopy.. . . . . . . . . . . . . . . . . . . . . . . . . . . 83
3-8 Pyritevalenceband. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
3-9 Modelingtunnelingspectroscopywithsurfacestates . . . . . . . . . . . . 85
3-10Densityfunctionaltheory(DFT)-computedbandstructures. . . . . . . . . 86
3-11FittingtoexperimentalsurfaceE .. . . . . . . . . . . . . . . . . . . . . . . . 87
g
3-12VisualizationofFeS (100)surfacechargeq . . . . . . . . . . . . . . . . . . 88
2
3-13LowsurfacebandgapimplicationsforPV. . . . . . . . . . . . . . . . . . . . 89
3-14Preliminaryinvestigationsonbulkand2-dimensionalMoS . . . . . . . . 90
2
4-1 Proposedmechanismsofpassivitybreakdownandpitting. . . . . . . . . . 93
4-2 Nanopitsformedbyvacancyagglomeration. . . . . . . . . . . . . . . . . . 94
4-3 XPSsampleclampforFeS crystals. . . . . . . . . . . . . . . . . . . . . . . . 96
2
4-4 S2pphotoelectronspectraofFeS (100). . . . . . . . . . . . . . . . . . . . 98
2
4-5 AtomicmodeloftheFeS (100)surfaceasviewedside-on. . . . . . . . . . 99
2
4-6 Sulfurmonomervacancyconcentration. . . . . . . . . . . . . . . . . . . . . 101
4-7 ProportionoftheMandScomponentsoftheS2pphotoelectronspectra. 101
4-8 Scanningtunnelingmicroscopy(STM)imagesofsinglecrystalFeS (100)
2
surfaces.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
4-9 Pitsareonehalf-oronelatticeparameterdeep. . . . . . . . . . . . . . . . 104
4-10Illustrationofatomicprocessesinvolvedintheproposedmechanismof
pitformationandgrowthonpyrite(100). . . . . . . . . . . . . . . . . . . . 105
4-11kineticMonteCarlosimulationresults. . . . . . . . . . . . . . . . . . . . . . 105
B-1 Home-madeChemicalVaporDeposition(CVD)system. . . . . . . . . . . . 121
B-2 DescriptionandsafetyinformationforFeandSprecursors. . . . . . . . . 122
B-3 IronsulfidefilmsdepositedfromFe(acac) andTBDS. . . . . . . . . . . . 124
3
B-4 CarboncontaminationinFe-SfilmsfromFe(acac) . . . . . . . . . . . . . . 125
3
B-5 IronsulfidefilmsdepositedfromFe(CO) andTBMS. . . . . . . . . . . . . 125
5
B-6 IronsulfidefilmsdepositedfromFe(CO) andH S. . . . . . . . . . . . . . 126
5 2
B-7 Templatestrippingforultrasmoothsulfidesurfaces. . . . . . . . . . . . . . 127
C-1 Ironself-diffusivity*D measurements. . . . . . . . . . . . . . . . . . . . . 130
Fe
C-2 X-raydiffractionofthiinfilmsforECRexperiments. . . . . . . . . . . . . . 131
C-3 Representativediffusionprofiles. . . . . . . . . . . . . . . . . . . . . . . . . 132
C-4 Oxidationofsamplesannealedinquartzvials. . . . . . . . . . . . . . . . . 133
10