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Characterizationtechniques: (A)XPS(X-rayphotoelectronspectroscopy): HydrothermallydepositedepitaxialthinfilmsarecharacterizedbyXPStoretrieveusefulinformationlikecomposition,chemicalstructureandlocalarrangementofatomsthatmakeupfewlayersofsurfaceoffilmandalsotheinterfaciallayerbetweenthefilmandsubstrate. X-rayphotoelectronspectroscopy(XPS)wasdevelopedinthemid–1960sbyKaiSiegnahmandhisresearchgroupattheUniversityofUppsala,Sweden. SurfaceanalysisbyXPSinvolvesirradiatingasolidinvacuumwithmonoenergeticsoftx-raysandanalyzingtheemittedelectronsbyenergy.Thespectrumisobtainedasaplotofthenumberofdetectedelectronsperenergyintervalversustheirkineticenergy.TheprincipleonwhichtheXPStechniqueisbasedcanexplainedwiththehelpoffigure1asshownbelow.[27] Figure1.AnenergyleveldiagramshowingthephysicalbasisofXPStechnique. TheenergycarriedbyanincomingX-rayphotonisabsorbedbythetargetatom,raisingitintoexcitedstatefromwhichitrelaxesbytheemissionofaphotoelectron.MgK(1253.6eV)orAlK(1486.6eV)x-raysaregenerallyusedasasourceofmonoenergeticsoftx-rays.Thesephotonshavelimitedpenetratingpowerinasolidontheorderof1-10micrometers.Theyinteractwithatomsinthesurfaceregion,causingelectronstobeemittedbythephotoelectriceffect.Theemittedelectronshavemeasuredkineticenergiesgivenby: KE=h-BE-s Wherehistheenergyofthephoton,BEisthebindingenergyoftheatomicorbitalfromwhichtheelectronoriginatesandsisthespectrometerworkfunction.Thebindingenergymayberegardedastheenergydifferencebetweentheinitialandfinalstatesafterthephotoelectronhaslefttheatom.Becausethereareavarietyofpossiblefinalstatesoftheionsfromeachtypeofatom,thereiscorrespondingvarietyofkineticenergiesoftheemittedelectrons.PhotoelectronsareemittedfromallenergylevelsofthetargetatomandhencetheelectronenergyspectrumischaracteristicoftheemittingatomtypeandmaybethoughtasitsXPSfingerprint.Eachelementhasuniquespectrum.Thespectrumfromamixtureofelementsisapproximatelythesumofpeaksoftheindividualconstituents.Becausethemeanfreepathofelectronsinthesolidsisverysmall,thede