XAFS and Its Applications

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1、XAFSandItsapplicationsInMaterialResearchRuanKunming2009301020045XAFSspectroscopyisapowerfultechniquefordeterminingelementspeciation.Itshowsasteepriseatthecore-levelbindingenergyofX-ray-absorbingatomandattenuatesgraduallywiththeX-rayenergy.Anditisapowerfultoolinmaterialresearch.Inthi

2、spaper,Iwillgivebriefintroductiontosomeofitsapplication.Keywords:X-rayabsorptionfinestructure(XAFS)radionuclidesinterfaceinteraction,EXAFS,semiconductorIntroduction1.ThedevelopmentofXAFS.TheXAFSistheabbreviationofTheX-rayabsorptionspectra.TheXASspectraareusuallydividedinthreeenergyr

3、egions:1)theedgeregion,2)theX-rayAbsorptionNearEdgeStructure(XANES);3)theextendedX-rayabsorptionfinestructure(EXAFS).XAFSofZnS(Sphalertite)Theabsorptionpeaksattheabsorptionedgesinarangeofabout5eVwerefirstexplainedbyWaltherKosselasduetoelectronictransitionstofirstunoccupiedmolecularl

4、evelsabovethechemicalpotential,andformanyyearswasreferredtoasthe“Kosselstructure”nowitisknownasabsorptionedgeregion.Theoscillatorystructureextendingforhundredsofelectronvoltspasttheedgeswascalledthe“Kronigstructure”afterthescientist,RalphKronig,whoassignedthisstructuretothesinglesca

5、tteringoftheexcitedphotoelectronbyneighbouringatoms.ThisisnowcalledEXAFS.TheenergyregionofXANES(extendingoverarangeofabout100eV)betweentheedgeregionandtheEXAFSregionhasbeenassignedtomultiplescatteringresonances.Inthecaseoforganicmoleculesthisenergyregionhasbeenlatercallednear-edgeX-

6、rayabsorptionfinestructure(NEXAFS),butNEXAFSissynonymouswithXANES.2.TheoreticAnalysistheX-Rayabsorptioncoefficient:μWhenX-Raygothroughthematerial,partoftheraywasabsorbedbyit.Andbasedonthedifferenceofthestructureandatommass,theabsorptiondifferfromeachother.Howcanwestudythedegreetheab

7、sorbtheray?Itisnecessarytointroduceaphysicquantitytodescribetheability.Letmeshowyouthecoefficientofsomematerialinthepicturebelow.Theintensityofanx-raybeamasitpassesthroughamaterialofthicknesstisgivenbytheabsorptioncoefficientµ:whereI0isthex-rayintensityhittingthematerial,andIisthein

8、tensitytransmittedt