RHEED原理及说明ppt课件.ppt

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1、RHEED(reflectionhigh-energyelectrondiffraction)YiLiBackgroundThefirstRHEEDexperimentwasconductedbyNishikawaandKikuchiin1928.Theoriginofpatterns,especiallythestreaks,wereexplainedindetailbyusingkinematicsdiffractiontheory(KirchnerandRaether,1932;Raether,1932).ArthurandLePoreincorporatedaRHEEDme

2、asurementintoanapparatusdevelopedbyArthurforthemolecularbeamepitaxial(MBE)growthofGaAs.Harrisetal.(1981),Wood(1981),Neaveetal.(1984),VanHoveetal.(1983b)andSakamotoetal.(1986)sawintensityoscillations,RHEEDbecameessentialformeasuringgrowthrate.ElectronDiffractionTechniquesLowEnergyElectronDiffracti

3、on(LEED)(E:10~500eV)Electronwavelength:0.5~4ÅPenetrationlength:5~10Å2ReflectionHigh-EnergyElectronDiffraction(RHEED)(E:5~100keV)Electronwavelength:0.02~0.2ÅPenetrationlength:20~100ÅAhighenergyelectrongunAfluorescentscreenRHEEDInstrumentsPrinciplesofRHEEDBriefoftheDiffractionTheory(1)EwaldSpherean

4、dLaueequation(Laueequation)Weknow(2)BraggdiffractionThefigureshowstheEwaldsphereoftheincomingelectronwavesandthereciprocalspacemapofaperiodicstructure.WheretheLaueequationismet,theEwaldsphereoftheincomingelectronwaveswillintersectthereciprocallatticerodsofthesurfaceofthesample.Thiswillresultinstr

5、eaksofspacingsontheflorescentscreen.AstheradiusoftheEwaldsphereisabouttwoordersofmagnitudegreaterthanthemodulusofthereciprocallatticevector,wefindthattheanglebetweenpointsintersectingthespherewillbealmostthesamek=50Å-1for10keVelectronsa*=2Å-1fora=3ÅtheEwaldsphereisverylargecomparedtoreciprocalve

6、ctor,soitcutsthereciprocalrodsalmostalongitslength.RHEEDpatternFlat-streaks:IncidentanglewidthEnergywidthThermalvibrationRough-spots:manyelectronswillbetransmittedthroughsurfaceasperitiesandscatteredindifferentdirections,resultinginaRHEEDpatternconstitutedbymanyspottyfeatures.Amorphous:-nopattern

7、itisevidentthatdiffractionfromAnamorphoussurface(suchasanoxideontopofasemiconductor)givesnodiffractionpatternatall,andonlyadiffusebackgroundRHEEDTechniqueChangingChangingChangingIncreasemeansmorespots,butlesssurfac