XRD简介(英文)

OpticalrelatedtechnologyX-rayDiffractionAbstract:X-raydiffraction(XRD)technologyiswidelyusedinmaterialscharacterization.Identifychemistryconstituentsoftheproduct,analyzethespacegroup,latticeparameterandetc.Inthisarticle,IwillintroducetheprincipleofXRDincludingthediffractometerandsimpleapplicationwiththeXRDpattern.Introduction1.X-rayisakindofelectromagneticradiationgeneratedbytheinnerelectrontransition.Itswavelengthrangingfrom0.01to10nm.X-rayphotonswithashortwavelength(below0.2nm)havetheenergiesabove5keV.Thereforecomesthepenetratingability[1].Moreover,X-rayinteractwithmatterandprojectthematter’sinformationinX-raydiffractionpattern.Asresult,X-rayarewidelyusedtoimagetheinsideoftheobjectandisthoughthighlyinthefieldmedicalradiographyandmaterialcharacterization.2.X-raydiffractionisaninteractionbetweenX-rayandmatter.Considerthematerialaslatticeasshowatfigure1.Considerthesituationaswhatwehadlearned-theRayleighscattering.Insomedirection,wecandetecttheinterferenceoftwonarrowX-raybeams,andconstructiveinterferencemeettheopticalpathdifference:2dsinθ=nλ(n=0,1,2…).KwonastheBragg’slaw.disthedistancebetweentwoparticles,θistheanglebetweenincidentX-rayandlatticeplane,λisthewavelengthofX-ray.Wecanlearnfromtheequationthattheconstructiveinteronlyhappeninsomeparticularanglesincethewavelengthandthedistance(considerasthegratingconstant)arefixedforonematerial,andforthethreedimensionalworldwehavethreeconstantmarkedas(hkl)todescribethespacegroup.Nevertheless,ishardtodirectlydetectthe3Dpattern,instead,weintroducethesphericalprojectionpatternanddevelopsomemathematicaltranslationtorestructurethe3Dconditionshowsatfigure2.Wecanlearnthedirectionanddistancefromthesphericalcoordinate.Let’sgoovertheprocedureofXRD.FirstweshotaX-raytothesampleandgetitsdiffractionpatternandreadtheinformationfromthe2Dpattern[2].3.X-rayDiffractometerishighintegrationopticalapparatusshowsatfigure3.TheX-raysourceusuallychoosesCuastargetmaterialapplyinghotelectronswhichacceleratedbyhighvoltageandgenerateX-ray[3].Sampleplatformanddetectorlinktogetherandrotatealongthehorizontalsphericalcenteraxis.WecanalsohavethesampleplatformanddetectorfixedandrotatetheX-raygun.WeintroducetheconceptofresolutiontoevaluatethequalityoftheX-rayDiffractometer.AstrongandstableX-raygeneratorisnecessary.Theotherconditionistheminimumanglewhichthemachinecanstablerotate.TheresolutionusuallyplaysanimportantroleinquantifyinganalysissuchasdeterminethedopingratiobymeasuretheXRDpeakoffset.SimpleanalysiswithXRDpatternAssumewehavegotourXRDpatternfile,wecanimportthemintoXRDanalysissoftware“jade”showsatfigure4.AswealreadytalkaboutthatXRDcanidentifythespacegroupofthecrystalmaterial.IfwegetthestandardXRDpattern(verifiedbyothermethod).WecancompareourXRDpatterntothestandardpattern(PDF)andseewhetherthediffractionpeakmatch.Infigure4,ItaketheLeadsulfur(PbS)asanexample.ThemountainlikecurveistheXRDpatternwedetectfromtheX-rayDiffractometer,xaxisis2θ/degreeandtheyaxisrepresenttheintensity;VerticallineisPDF,itmarksthepositionandintensityofthestandarddiffractionpatternofPbS.SowecanreadthecrystalparameterfromthePDFinformation:spacegroupFm-3m(No.225),thesizeofthecellis5.9362*5.95362*5.936290*90*90wecanknowtheshapeofPbScellisalmostcube.ButwestillneedSEMandTEMtechnologytoprecisedetermine,recalltheXRDcharacterizationprocedure,weonlylearntheinformationfromPDF.IfyouhaveadeeperlookontheXRDpatterninfigure4,theXRDpatternpeakunitaryslightlyoffsettotheleftagainstthePDF’s.ItsuggeststhePbSsamplehasasmallersizethanthePDF’sstandardsize.WecancalculatetheexactsizebyapplyingmathematicsbutIwon’tgothatfurther.ConclusionandexpectationInthisarticle,wediscussedtheprincipleofX-ray,X-rayDiffraction,X-rayDiffractometerandX-raydiffractionpattern.ItturnsouttheXRDtechnologyissoconvenienttoimagetheinsideofthematter.Butwealsoseetheshortcomingofthistechnique:3Dto2Dprojectionlosesomeinformationandfailtodetecttheabsorptioninformation.IsuggesthavingmoredetectorindifferentpositiontoimprovetheaccuracyandtunableX-raysourcetodeterminetheabsorptionofthematerial.Reference[1][2]晶体学基础秦善[3]X衍射以及其应用简介—陶琨（清华大学）