材料表面与界面1分析课件

材料的表面与界面

SurfacesandInterfaces

inMaterials任课教师：耿林教授哈尔滨工业大学材料科学与工程学院材料的表面与界面

SurfacesandInterfac第1章前言主要参考文献：(1)李恒德，肖纪美，材料表面与界面，清华大学出版社。(2)叶恒强，材料界面结构与特性,科学出版社,1999。(3)胡福增，陈国荣，杜永娟，材料表界面，华东理工大学出版社，2007。(4)JamesM.Howe,InterfacesinMaterials,AWiley-intersciencePublication,1997.(5)HansLuth,SurfacesandInterfacesofSolidMaterials,Springer,1995.(6)D.WolfandS.Yip,MaterialsInterfaces,Chapman&Hall,1992.固态界面的定义:Asolidinterfaceisdefinedasasmallnumberofatomiclayersthatseparatetwosolidsinintimatecontactwithoneanother,wherethepropertiesdiffersignificantlyformthoseofthebulkmaterialsitseparates.1.1序第1章前言主要参考文献：1.1序固态界面的特点:

●Someofthemostimportantpropertiesofmaterialsinhigh-technologyapplicationsarestronglyinfluencedorevencontrolledbythepresenceofsolidinterfaces.

●Itiswidelyappreciatedthatahighlyinterdisciplinaryapproachholdsthegreatestpromiseforprovidingnovelinsightsintothefundamentalphysical,chemical,electronic,andmechanicalprocessesatsolidinterfaces.

●Theimportanceofinterfacematerialsisbasedprimarilyontheirinherentinhomogeneity,i.e.thefactthatphysicalpropertiesatornearaninterfacecandifferdramaticallyfromthoseofthenearbybulkmaterial.●Anapproachutilizingthecomplementarycapabilitiesofcomputersimulationandexperimentseemstobeparticularlypromisingintheinvestigationofstructure-propertycorrelations.固态界面的特点:固态界面的分类:

Onecanimaginemanywaysofclassifyinginterfacialsystems,forexample,bydistinguishingcommensuratefromincommensuratesystem,coherentfromincoherentinterfaces,homophase(grainboundary)materialsfromheterophase(dissimilar-material)interfaces,orinternalinterfacesfromthin-film-typesystems.Thelatterdistinctionbetweenburiedinterfacesandsystemscomposedofthin-film-typeinterfacesappearstobeparticularlymeaningfulfortworeasons:first,becauseofthefundamentallydifferentexperimentaltechniquesrequiredfortheirinvestigationandsecond,becausethelatticeparameter(s),andhencethephysicalpropertiesintheinterfacialregion,dependstronglyonwhetherornottheinterfaceisembeddedbetweenbulkmaterial.

固态界面的分类:Fig.1-1Distinctionofthreetypesofinterfacialsystems.Dependingonwhetherthesystemisembeddedinbulkmaterialonbothsidesoftheinterface,ononlyonesideornotatall,wedistinguish“bulk”,“epitaxial”,and“thin-film”interfaces.AandBaregenerallydifferentmaterials.BulkperfectCrystal2BulkperfectCrystal1Interfaceregion2Interfaceregion1InterfaceplaneMaterialBXYZMaterialAFig.1-1Distinctionofthreet固态界面的研究内容:

●Relationshipamonginterfaceenergy,interfacestructureandinterfaceproperties.

●Formationandstabilityoftheinterfaces:Energyofthesystem,thermodynamicandkineticsoftheinterfaces.固态界面的研究内容:固态界面的研究方法:●Theexperimentalproblemsliemainlyintheextremelyhighspatialresolution,coupledwithhighdetectionsensitivity,whicharerequiredtoidentityminuteamountsofchemicalspecies,chargestatesofatomsandpointdefects,anddifferentphaseswhichmaybepresentinthenarrowinterfaceregion.●Becausethepropertiesintheinterfacialregionarecontrolledbyrelativelyfewatoms,electronicandatomic-levelcomputersimulationscanprovideaclose-upviewofthemostcriticalpartofthematerial.Thelocalnatureofatomicbonding,thepositionsandmovementsofatoms,localstresses,etc.,canbeinvestigatedbycomputersimulations.材料表面与界面(1)分析ppt课件1.2Atomicstructureandinteratomicbonding●Thebindingenergyisdefinedastheenergyneededtotransformonemoleofsolidorliquidintoagasatzerotemperatureandpressure.Itisapproximatelythesamemagnitudeastheenergyofsublimation△Hswhentransformingasolidtoagasortheenergyofvaporization△Hvwhentransformingaliquidtoagas,exceptthattheseareusuallymeasuredat1atmpressure.Thesequantitiesareoftenobtainedatfinitetemperaturessuchas298Korattheboilingpoint,butthisdoesnotalterthebindingenergyorbondenthalpy,whichisassumedtobeindependentoftemperature.Theseenergiesarerelatedtoafundamentalenergyinmaterials,theinteratomicpotentialenergybetweenatoms.1.2.1Interatomicpotentialandbindingenergy

1.2Atomicstructureandinter1.2.2Interatomicpotentialandbindingenergy

Iftheatomsaredisplacedtowardoneanother,arepulsiveforceactstoincreasetheinteratomicdistance.Thisrepulsiveforceispositive.Theoppositeoccurswhentheatomsarestretchedapart.

Hooke’slaw

Theminimumpotentialenergycorrespondstotheequilibriuminteratomicseparationre.Insolids,recanreadilybemeasuredbyX-raydiffraction.Thedepthofthewellisclearlyproportionaltothestrengthoftheinter-atomic

bond.

Lennard-Jonespotential:1.2.2Interatomicpotentiala1.2.2Interatomicpotentialandbindingenergy

Inmetals,attractiveinteractionbetweenatomsisshort-rangewithanr-6

dependence.Hence,thenearest-neighborapproximationworkswellforestimatingthebindingenergyformetals.

Inionicsolids,theattractionbetweenthepositiveandnegativeionsiscoulombicandmuchlongerinrange.Theattractivecoulombicpotentialisproportionalto

r-1,whichdecaysslowlywithincreasingr.Therepulsivepotentialmaydisplayanr-12

dependence,aswithmetals,sotheresultingprofilelookslikethatshowninFig.1-3

Fig.1-3Thebrokencurveshowstheinteratomicpotentialenergywhentheattractiveinteractionislong-rangewithanr-1

dependence

1.2.2Interatomicpotentiala1.2.2Interatomicpotentialandbindingenergy

刚性球模型：Clearlytherepulsiveinteractionisveryshort-range,whereastheattractiveinteractionissomewhatlonger.Thisstrongrepulsiveinteractionmakesitoftenrealistictorepresentatomsas“hardspheres”.最近邻假设：Whentheinteratomicdistanceistwicetheequilibriumdistance(i.e.,),thepotentialenergydecreasesbyafactorof32.Thus,onecanlargelyignoretheinteractionenergybeyondthenearestneighborsandapproximatethebindingenergybyconsideringonlythenearest-neighborbonds.

1.2.2Interatomicpotentiala1.2.3Correlationofbindingenergyandinteratomicpotentialwithphysicalandmechanicalproperties

●BindingEnergyandEnthalpyofSublimationIfwedefinez

asthecoordinationnumber(thenumberofnearestneighbors)ofanatominasolidorliquid,thenthebindingenergyof1moleofatomsisgivenby:WhereNAisAvogadro'snumberandthefactorof1/2arisesbecausewehavecountedeachbondtwiceintheproducezNA

ifoneassumesthatthebindingenergypermoleofsolidisequaltotheenthalpyofSublimationpermoleatlowpressure,thenEb

=1/2zNAeb1.2.3Correlationofbinding1.2.3Correlationofbindingenergyandinteratomicpotentialwithphysicalandmechanicalproperties

●BindingEnergyandEnthalpyofSublimationTable1-1.Comparisonoftheinteratomicpotentialenergiesofcopper,silverandgoldcalculatedfromtheheatsofsublimationandvaporizationusingEq.(1.4)ElenentCuAgAu3362843680.580.490.64300.5250.6324.40.570.470.61*Heatsofvaporizationareusuallyspecifiedattheboilingpoint,notat0K.1.2.3Correlationofbinding1.2.3Correlationofbindingenergyandinteratomicpotentialwithphysicalandmechanicalproperties

●InteratomicPotentialandTheoreticalStrength

Ifweapplyanexternaltensileforcetoasolid,theexternalforceisdefinedas:Fex=+dΦ/drwhereapositivesignisusedtoreflectthefactthatanexternaltensileforce(orstress)tendstolengthenthesolidandincreasetheinteratomicdistance.OnthebasisofthesignconventionestablishedinFig.1-2c,theforcethatincreasestheinteratomicdistanceispositiveandhencethetensileforce(orstress)ispositive.Anexternalcompressiveforce(orstress)whichtendstoshortenthesolidisnegative.Therelationshipamongtheinteratomicpotential,theexternalforceandthesignoftheforce,areshownschematicallyinFig.1-4.Fig.1-4.(a)Interatomicpotentialfunctionplottedversusinteratomicdistance.(b)Appliedforceplottedversusatomicdisplacement.(c)Thedirectionandsignoftheappliedforceac-cordingtotheestablishedconvention.

1.2.3Correlationofbinding1.2.3Correlationofbindingenergyandinteratomicpotentialwithphysicalandmechanicalproperties

●InteratomicPotentialandTheoreticalStrengthWecandefineapointFmaxasthemaximumforcethatcorrespondstothedissociativedistancerdofthematerial.FmaxisthusthemaximumtensileforceneededtopullthesolidapartbecausetheforceneededtoincreasetheinteratomicdistancebeyondrdislessthanFmax.WecanregardFmaxasthetheoreticalstrengthofthesolid.TocalculateFmax,werequirethat

atr=rd.IfweassumethatthesolidobeystheLennard-JonespotentialandthatthefunctionΦ

isgivenby:weobtain

atr=rd

1.2.3Correlationofbinding1.2.3Correlationofbindingenergyandinteratomicpotentialwithphysicalandmechanicalproperties

●InteratomicPotentialandTheoreticalStrengthTheoretically,thesolidcanbestrainedapproximately11%beforeitbreaks.Furthermore,ifstretchedjustbelowthatstrain,itwouldreturntoitsoriginalcondition.Weknowthatexperimentallytheseconditionsarenotfound.Mostpolycrystallinemetals,whethertheyobeytheLennard-Jonespotentialornot,haveanelasticlimitofonly0.2%.Afterthat,plasticdeformationsetsin.Itisinterestingtoestimatethemagnitudeoftheenergyinvolvedinelasticstrain.Considerthecaseatthelimit.Theelasticenergyisgivenbywhereσisthestress,eisthestrainandYisYoung’smodulus.Toestimatetheelasticenergy,let’sselectoneofthestiffestmaterials,steel,withY=2.0×1011Paanduse8.4×1022atoms/cm3toconverttoelectronvoltsperatom.Ifwetakee=0.2%,then1.2.3Correlationofbinding1.2.3Correlationofbindingenergyandinteratomicpotentialwithphysicalandmechanicalproperties

●InteratomicPotentialandTheoreticalStrengthThisvalueoftheelasticenergyperatomisseveralordersofmagn