Cathodic Arcs: From Fractal Spots to Energetic Condensation PDF
Preview Cathodic Arcs: From Fractal Spots to Energetic Condensation
Springer Series on atomic, optical, and plasma physics 50 Springer Series on atomic, optical, and plasma physics TheSpringerSeriesonAtomic,Optical,andPlasmaPhysicscoversinacomprehensive manner theory and experiment in the entire .eld of atoms and molecules and their interactionwithelectromagneticradiation.Booksintheseriesprovidearichsourceof newideasandtechniqueswithwideapplicationsin.eldssuchaschemistry,materials science,astrophysics,surfacescience,plasmatechnology,advancedoptics,aeronomy, andengineering.Laserphysicsisaparticularconnectingthemethathasprovidedmuch ofthecontinuingimpetusfornewdevelopmentsinthefield.Thepurposeoftheseriesis tocoverthegapbetweenstandardundergraduatetextbooksandtheresearchliterature withemphasisonthefundamentalideas,methods,techniques,andresultsinthefield. 47 SemiclassicalDynamicsandRelaxation By:D.S.F.Crothers 48 TheoreticalFemtosecondPhysics AtomsandMoleculesinStrongLaserFields ByF.Großmann 49 RelativisticCollisionsofStructuredAtomicParticles ByA.VoitkivandJ.Ullrich 50 CathodicArcs FromFractalSpotstoEnergeticCondensation ByA.Anders 51 ReferenceDataonAtomicPhysicsandAtomicProcess ByB.M.Smirnov Vols.20–46oftheformerSpringerSeriesonAtomsandPlasmasarelistedattheendofthebook Andre´ Anders Cathodic Arcs From Fractal Spots to Energetic Condensation With 262 Figures and 25 Tables 1 3 Andre´ Anders PlasmaApplicationsGroup LawrenceBerkeleyNationalLaboratory Berkeley,CA USA [email protected] ISSN:1615-5653 ISBN:978-0-387-79107-4 e-ISBN:978-0-387-79108-1 DOI:10.1007/978-0-387-79108-1 LibraryofCongressControlNumber:2008929568 #2008SpringerScienceþBusinessMedia,LLC Allrightsreserved.Thisworkmaynotbetranslatedorcopiedinwholeorinpartwithoutthewritten permissionofthepublisher(SpringerScience+BusinessMedia,LLC,233SpringStreet,NewYork, NY10013,USA),exceptforbriefexcerptsinconnectionwithreviewsorscholarlyanalysis.Usein connection with any form of information storage and retrieval, electronic adaptation, computer software,orbysimilarordissimilarmethodologynowknownorhereafterdevelopedisforbidden. Theuseinthispublicationoftradenames,trademarks,servicemarksandsimilarterms,evenifthey arenotidenti.edassuch,isnottobetakenasanexpressionofopinionastowhetherornottheyare subjecttoproprietaryrights. Printedonacid-freepaper springer.com InmemoriamIngmarKleberg(1971–2003). Ingmar wrote an excellent PhD thesis on cathode spot processes, a significant contributiontothephysicsofarcspotoperationandretrogrademotion.Hewas a good friend whose time ended abruptly in a tragic accident. He is fondly rememberedbyhismanyfriends. Preface Nottoolongago,afterwatchingDisney’sHerculesmovie,mythen-6-year-old daughtertestedmebyasking,‘‘Dad,didyouknowthattherearefourelements: Earth,Water,Air,andLightning?’’Becauseshedidnotusethecommonterms Earth, Water, Air, and Fire, it struck me that the Greeks may have had an appreciation for phases: just replace ‘‘element’’ by ‘‘phase,’’ and you will see theparalleltothemodernterminology:solid,liquid,gas,andplasma! Althoughtheplasmaphaseisbyfarthemostprevalentintheuniverse(well, set aside the mysterious dark matter), we have little experience with it in our daily life. Most plasmas we encounter are man-made, be it the plasma in fluorescent discharge lamps, plasma displays, or in a welder’s arc. In this book, a very special case of discharge plasma is explored, the plasma formed atelectrodes. Cathodicarcplasmadepositionisoneoftheoldestandatthesametimeone ofthemodern,emergingdepositiontechnologies.Thisisanapparentlycontra- dictorystatement.Iwillspanaviewfrommorethanacoupleofcenturiesagoto recentresearchinthehopetotranspireexcitement,providebackgroundknow- ledge,andreviewimportantprogress. Although cathodic arc plasma deposition belongs to the family of physical vapor deposition (PVD) techniques, I deliberately call it plasma deposition to emphasize an important feature: energetic condensation of plasma ions, as opposedtocondensationofatomsfromtheneutralvaporphase.Thesynthesis of films from ions, each carrying substantial kinetic and potential energy, can leadtofilmpropertiesthatareunique. As the name suggests, cathodic arcs are determined by cathode processes. Indeed,cathodeprocessesarequitedifferentthanprocessesinother,less‘‘vio- lent’’formsofdischarges.Thecurrentdensitiesandassociatedpowerdensitiesat cathodespotsareextremelyhigh,andthisistruedespitethecharacteristiclow cathode fall voltage of typically only 20V. The electron emission processes involve non-stationary stages and phase transitions, ultimately leading to the destructionoftheelectronemissioncenter.Thephasetransitionfromthesolid vii viii Preface cathode material to plasma is precisely what enables operation of the arc discharge and what makes cathodic arc plasmas and the films deposited so special. This book is written in the hope to be useful to the experts, practitioners, students, and newcomers alike. It is assumed that the reader is familiar with basic concepts of plasma physics and thin films. Thereare manyexcellenttext booksandreviewarticlesinthefield,andthereforethebasicsaredevelopedhere onlyastheydirectlyapplytocathodicarcsandthefilmsproduced.Eachchapter contains an extensive list of references for further reading, and a very brief introductiontoplasmasandsheathsisgiveninAppendixA. Writing this book had its challenges. For one, our understanding is still far fromcomplete,despitetheimpressiveprogressseeninexperimentaltechniques andtheoreticalmodeling.Yet,itturnedouttobedifficulttodeterminewhatis really secured knowledge based on accepted, self-consistent data and what are just hypotheses, even if plausible. The reasons for this difficulty are twofold. First,arcdatascatterappreciablyduetothenatureofthecathodespotphenom- ena, and second, some theories contradict each other, even when each is self- consistentandin‘‘good agreementwithexperimentalobservations,’’asusually claimed. The underlying problem in modeling is the choice of the simplifying assumptions,whicharenecessarytomakeduetothecomplexcharacterofthearc phenomena.Therefore,insomeinstances,Ifailedinmydesiretoproduceatext bookthatwouldbeacceptabletoallexpertsinthefield.SometimesIneededto diverttoreviewingwhathasbeendoneandleaveituptothereaderandfurther researchtoselectthemostappropriatedescriptionofthenatureofcathodicarcs andthefilmsproduced.AlthoughIbelievethatthereviewportionsarerelatively extensiveandinclusive,thereiscertainlyworkthathasbeenoverlookedorisnot sufficientlyappreciated.Iwillnotclaimtohaveproduceda‘‘balancedview.’’ There was the temptation to be as comprehensive and accurate as possible, whichmayhaveledtoahugebooknobodycouldreadandthatmayhavenever beenfinished.Perhapsallauthorsrealizeatsomepointthatitisimpossibletodo a perfect job. Periods of productive work flow were interrupted by times of distractionandprocrastination.Whywritinganotherarcbook?Therehasbeen a number of great books, and why could or should I add to this line of work? Havingaspecialinterestinhistory,Ilookwithadmirationataseriesofbooksby Joseph Priestley (1767), Vasilii Petrov (1803), Hertha Ayrton (1902), Clement Child(1913),IgorKesaev(1964,1968),VadimRakhovskii(1970),JamesLafferty (1980), Gennady Mesyats and Dmitry Proskurovsky (1989), and, last but not least, the edited Handbook by Raymond Boxman, David Sanders, and Phil Martin (1995). Each of them represented the state of knowledge and added substantially to the work of their predecessors. Not to count the numerous important publications that did not result in a book but became much cited classicsinthefield.Sincethefieldisvitalandmuchknowledgehasbeenaddedin recent years, there appeared to be a lack of systematic presentation, and so I hope toprovidea modern view on thefieldof cathode arcs andthe coatings madewithcathodicarcplasma. Preface ix A book like this one would not be possible without the input by many colleagues and friends. Here is the perfect opportunity to express my sincere gratitudefortheirgeneroushelpinfindingthenecessarysupplyofinformation, diagrams, illustrations, photographic material, raw data, etc. The list of the many dear colleagues is long, and if I listed them here, some may still be forgotten. So, I will only mention a few representative names of those who deservespecialrecognition.IwillstartwithIngmarKleberg,ayoungfriendof mine whose very untimely death in a mountaineering accident shocked us all. SomeresultsofhisthesiscanbefoundinChapter3.Idedicatethisbooktohim. Next,Ishouldstressthatthisworkwasgreatlyinfluencedbythethinkingofmy formermentors,BurkhardJu¨ttnerandErhardHantzsche,withwhomIspenta veryproductivetimeinthe1980sinEastBerlinbeforetheBerlinWallfell.From themIlearnedaboutexplosiveplasmaformationandthespecialroleofcathode surfaceconditionsthatleadtovariousarcmodesandspottypes.Specialthanks go to Ian Brown, Berkeley, who introduced me to the world of charge state analysisandapplicationofarcplasmastothinfilmsandmultilayers.Ianisalso one of the pioneers of combining arc plasmas and pulsed bias, enabling the synthesisofveryspecialsurfaces.Hisworkplantedaseedforthetechniqueof stress control via atomic scale annealing with high-energy ions. Othon Mon- teiro, former staff scientist of the Plasma Applications Group, contributed greatly, especially on the issues of energetic condensation and metallization of semiconductorstructures.MuchofthedataIwasabletocollectcamethrough thehelpofthetechnicalstaffofthePlasmaApplicationsGroup(thankstoyou, BobMacGill,MichaelDickinson,JoeWallig,TomMcVeigh)andthevisitorsof the Plasma Applications Group at Berkeley Lab; many of them have become distinguished researchers in the field. Just to name a few: Efim Oks (Russia), Gera Yushkov (Russia), Marcela Bilek (Australia), Jochen Schneider (Ger- many), Jochen Schein (Germany), Michael Keidar (USA), Johanna Rose´n (Sweden),SunnieLim(Australia),EungsunByon(Korea),andJoakimAnders- son(Sweden). Thelistofhelpfulcolleaguescouldgoonandon,buthereIwillconcludeby thanking my family for understanding that I was busy so many days and evenings...Loveyou,Christine,Mark,Mika,andGeorge! Berkeley,California Andre´Anders Contents 1 Introduction ............................................ 1 2 ABriefHistoryofCathodicArcCoating...................... 7 2.1 Introduction...................................... 7 2.2 CathodicArcsintheEighteenthCentury ............... 8 2.2.1 TheCapacitor:EnergyStorageforPulsed Discharges................................ 8 2.2.2 Priestley’sCathodicArcExperiments........... 10 2.2.3 ExperimentsLeadingtotheElectrochemical Battery................................... 15 2.3 CathodicArcsintheNineteenthCentury ............... 17 2.3.1 ImprovementstotheVoltaicPile .............. 17 2.3.2 Davy’sObservationofPulsed Discharges................................ 18 2.3.3 Petrov’sObservationofContinuousArc Discharges................................ 19 2.3.4 Davy’sWorkonContinuousArcDischarges..... 22 2.3.5 ElectromagneticInduction ................... 24 2.3.6 Ru¨hmkorffCoilandPulsedDischarges ......... 24 2.3.7 DischargeExperimentsinGasesand‘‘InVacuo’’.. 26 2.3.8 Faraday’sDeflagrator....................... 28 2.3.9 OpticalEmissionSpectroscopy................ 30 2.3.10 Maxwell.................................. 30 2.3.11 Wright’sExperiments:CoatingsbyPulsed GloworPulsedArc? ........................ 30 2.3.12 Lecher’sArcExperiments:DiscontinuousCurrent Transfer.................................. 31 2.3.13 Goldstein’sCanalRays...................... 33 2.3.14 Edison’sCoatingPatents..................... 33 xi xii Contents 2.3.15 CathodicArcIonVelocityMeasurements ....... 34 2.3.16 EarlyProbeExperimentsinArcPlasmas ........ 35 2.4 CathodicArcsintheTwentiethCentury ................ 36 2.4.1 AroundtheYear1905:Einstein,Weintraub, Stark,andChild............................ 36 2.4.2 TheDecadesUntilWWII .................... 45 2.4.3 SecretWorkDuringWWII................... 46 2.4.4 TheQuestforthe‘‘Correct’’CurrentDensity andCathodeModel......................... 47 2.4.5 IonVelocities:ValuesandAcceleration Mechanism................................ 49 2.4.6 CathodicArcDepositionIsEmerging asanIndustrialProcess...................... 50 2.4.7 Large-ScaleIndustrialUseinthe1980s and1990s................................. 55 2.4.8 MacroparticleFiltering:EnablingPrecision CoatingforHigh-TechApplications............ 56 2.5 CathodicArcsattheBeginningoftheTwenty-First Century.......................................... 59 2.5.1 AdvancesinDiagnosticsandModelingofArc PlasmaProcesses........................... 59 2.5.2 ImprovementsofCoatingQualityand Reproducibility,EnablingHigh-Tech Applications............................... 60 2.5.3 CathodicArcsforLarge-AreaCoatings......... 61 2.5.4 MultilayersandNanostructuresof Multi-componentMaterialsSystems............ 62 References............................................. 62 3 ThePhysicsofCathodeProcesses ........................... 75 3.1 Introduction...................................... 76 3.2 TheoryofCollectiveElectronEmissionProcesses: Steady-StateModels................................ 79 3.2.1 ThermionicEmission........................ 79 3.2.2 Field-EnhancedThermionicEmission .......... 82 3.2.3 FieldEmission............................. 84 3.2.4 Thermo-fieldEmission ...................... 86 3.3 RefinementstotheElectricPropertiesofMetalSurfaces ... 87 3.3.1 JelliumModelandWorkFunction............. 87 3.3.2 TheRoleofAdsorbates...................... 90 3.3.3 TheRoleofSurfaceRoughness ............... 94 3.4 TheoryofCollectiveElectronEmissionProcesses: Non-stationaryModels ............................. 95 3.4.1 Ion-EnhancedThermo-fieldEmission........... 95 3.4.2 TheExistenceofaCriticalCurrentDensity...... 98
Description:The list of books you might like
