Secondary Electron Yield Measurements of TiN Coating and TiZ(2)

In the beam pipe of the positron Main Damping Ring (MDR) of the Next Linear Collider (NLC), ionization of residual gases and secondary electron emission give rise to an electron cloud which can cause the loss of the circulating beam. One path to avoid the

Figure1:SEYofbakedtechnicalsurfaces.350 Cfor24hr[10]2ExperimentDescription

ThesystemusedtomeasureSEYiscomposedoftwocoupledstainlesssteel(S/S)UHVchamberswherethepressureisinthelow10 10Torrscaleinthemeasurementchamberandhigh10 9Torrscaleinthe”loadlock”chamber,Fig.2.Samplesindividuallyscrewedtoacarrierplate,areloaded rstontoanaluminiumtransferplateintheloadlockchamber,evacuatedtoalow10 8Torrscale,andthentransferredtothemeasurementchamber.

Themeasurementchamberhastwoelectrongunsandasoft(1.49keV)x-raysource.Oneelectrongun(energy,1-20keV)isusedforAugerelectronspectroscopy(AES)lightelementsurfacecontaminationanalysis.Thex-raysourceisusedtoexcitephotoelectronsforsurfacechemicalvalenceanalysis,calledESCA(ElectronSpectroscopyforChemicalAnalysis).TiNstoichiometryismeasuredbyESCAtechniquewhichisalsocalledXPS(X-rayPhotoelectronSpectroscopy).

TheprincipleofXPSistocollectphotoelectronsejectedbyx-raysofknownenergynearthesurface(1-5nminformationdepth).TheemittedelectronshaveanenergyEkwhichisgivenbyequation1

Ek=hν Eb Φ(1)

wherehνistheenergyoftheincidentphoton,EbthebindingenergyoftheelectronrelativetotheFermilevelofthematerialandΦthespectrometerworkfunction.Thespectrumofthemeasuredkineticenergygivesthespectrumofthebindingenergyofthephotoelectrons.

Thex-raysourceisalsousedforexcitingsecondaryX-rayFluorescence(XRF)forthicknessmeasurementofthedepositedTiNoverlayers.Thesecondelectrongun(0-3keV)isusedmeasuretheSEY,andcanalsobeusedtoelectronconditionthesurface.