Development of an Effusive Molecular Beam Apparatus

118 Pages·2016·5.82 MB·English

by  Daniel Halwidl (auth.)

Daniel Halwidl
Development of an
Effusive Molecular
Beam Apparatus
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Daniel Halwidl
Development of an
Effusive Molecular
Beam Apparatus
Daniel Halwidl
Wien, Österreich
BestMasters
ISBN 978­3­658­13535­5 ISBN 978­3­658­13536­2 (eBook)
DOI 10.1007/978­3­658­13536­2
Library of Congress Control Number: 2016935968
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Acknowledgements
IwouldliketoexpressmygratitudeandappreciationtomysupervisorsProf. Ul-
rikeDieboldandJiriPavelec,whosupportedmeduringmydiplomathesis. Iwant
toespeciallythankJiriPavelecforthetechnicaldrawingsandencouragingmein
mywork. IalsofeelgratefultoProf. MichaelSchmid,whowasalwaysavailable
forfruitfuldiscussions.
IwanttothankHerbertSchmidtandRainerGärtner,whoshowedgreatskillsand
patience when it came to the production of the many parts the Molecular Beam
consistsof.
Many thanks I want to adress to Jan Hulva, Manfred Bickel, Florian Brunbauer
andJakubPiastekfortheirsupportinthelaboratory.
Finally,Iwanttothankmyfamilyforsupportingmeduringmystudy.
DanielHalwidl
Abstract
This thesis describes the development of an effusive molecular beam apparatus,
whichallowsthedosingofgases,liquidsandsolids. Theapparatuswasdesigned
toadsorbpreciseandreproducibledosestoadefinedareaonmetaloxidesamples,
whichisrequiredinThermalProgrammedDesorptionandothersurfacechemistry
experimentsinthe“MachineforReactivityStudies”. Thetheoreticalprofileofthe
molecular beam has a core diameter of 3.5mm and a standard core pressure of
4(cid:2)10−8mbar, while the background pressure of the beam is 4 orders of magni-
tude lower. The design and the construction of the apparatus is described. The
calculatedbeamprofilewasexperimentallyconfirmedandcorepressuresbetween
1.7(cid:2)10−8mbarand2.9(cid:2)10−6mbarweremeasured.
Kurzfassung
Diese Diplomarbeit beschreibt die Entwicklung einer effusiven Molekularstrahl-
apparaturfürdieAdsorptionvonGasen,FlüssigkeitenundFeststoffenaufMetall-
oxidprobeninder“MachineforReactivityStudies”.DieAdsorptioneinerpräzi-
sen,reproduzierbarenDosisaufeinemwohldefiniertenBereichderProbenoberflä-
cheistfürThermischeDesorptionsspektroskopieundandereMethodenderOber-
flächenchemienotwendig.DasberechneteProfildesMolekularstrahlsweisteinen
Kern mit Durchmesser 3.5mm und einen Standarddruck von 4(cid:2)10−8mbar auf,
währendderHintergrunddruckdesMolekularstrahlsum4Größenordnungenklei-
nerist.DerEntwurfunddieKonstruktiondesApparatssindbeschrieben.Dasbe-
rechneteProfilwurdeexperimentellbestätigtundeinDruckvon1.7(cid:2)10−8mbar
bis2.9(cid:2)10−6mbarimKerndesMolekularstrahlsgemessen.
Contents
Acknowledgements V
Abstract VII
Kurzfassung IX
ListofFigures XIII
ListofTables XVII
1 Introduction 1
1.1 MolecularBeams . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2 TemperatureProgrammedDesorption . . . . . . . . . . . . . . . 3
2 FlowofGases 5
2.1 FlowRegimes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2 Conductance . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2.1 Molecularflow . . . . . . . . . . . . . . . . . . . . . . . 7
2.2.2 Continuumflow . . . . . . . . . . . . . . . . . . . . . . 11
2.2.3 Transition flow and conductance over the whole pressure
range . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3 EffusiveMolecularBeamSources 19
3.1 Thin-walledOrifice . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.2 SingleTube . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.3 CapillaryArray . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
4 MolecularBeam 25
4.1 Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.2 Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
4.3 Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
XII Contents
4.3.1 CoreandPenumbra . . . . . . . . . . . . . . . . . . . . . 30
4.3.2 Equivalentpressure . . . . . . . . . . . . . . . . . . . . . 34
4.3.3 MolecularBeamintensitiesanddoses . . . . . . . . . . . 34
4.3.4 Geometry . . . . . . . . . . . . . . . . . . . . . . . . . . 37
4.3.5 MolecularBeamdimensions . . . . . . . . . . . . . . . . 42
4.3.6 Pressuresinthepumpingstagesandthechamber . . . . . 43
4.3.7 Effusinggasfromthepumpingstages . . . . . . . . . . . 46
4.3.8 MolecularBeamproperties . . . . . . . . . . . . . . . . . 47
4.3.9 Capillarypressure . . . . . . . . . . . . . . . . . . . . . 50
4.4 Construction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
4.4.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 53
4.4.2 MolecularBeamCorePart . . . . . . . . . . . . . . . . . 54
4.4.3 ShutterMotor . . . . . . . . . . . . . . . . . . . . . . . . 59
4.4.4 Pumpingstages . . . . . . . . . . . . . . . . . . . . . . . 62
4.4.5 Reservoir . . . . . . . . . . . . . . . . . . . . . . . . . . 67
4.4.6 Pumpingspeed . . . . . . . . . . . . . . . . . . . . . . . 68
4.4.7 ApertureandShutterconductances . . . . . . . . . . . . 72
5 Results 75
5.1 TestSetup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
5.1.1 Argoncorrectionfactor . . . . . . . . . . . . . . . . . . . 77
5.2 MolecularBeamProfile . . . . . . . . . . . . . . . . . . . . . . . 79
5.2.1 MolecularBeamlineprofile . . . . . . . . . . . . . . . . 79
5.2.2 MolecularBeam2Dprofile . . . . . . . . . . . . . . . . 84
5.2.3 PumpingStage1coreandpenumbra. . . . . . . . . . . . 84
5.2.4 MolecularBeamBackground . . . . . . . . . . . . . . . 85
5.3 Shutter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
6 SummaryandOutlook 89
A GasProperties 91
A.1 Maxwell-BoltzmannDistribution . . . . . . . . . . . . . . . . . . 91
B Conductance 93
B.1 MolecularFlowinanAnnularTube . . . . . . . . . . . . . . . . 93
B.2 OrificeinTransitionFlow. . . . . . . . . . . . . . . . . . . . . . 99
C PiraniGaugeArgonCorrectionFactor 101
References 103