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1、94ThinSolidFilms.206(I991)94IOIThinmetalfilmcharacterizationandchemicalsensors:monitoringelectronicconductivity,massloadingandmechanicalpropertieswithsurfaceacousticwavedevicesAntonioJ.RiccoandStephenJ.MartinMicrosensorDivision1315.SandiaNationalLaboratories,Albuquerque,
2、NewMexico87185(U.S.A.)AbstractAcoustoelectriccouplingbetweenchargecarriersinathinmetalfilmandtheevanescentelectricfieldassociatedwithasurfaceacousticwave(SAW)propagatingalongthesurfaceofapiezoelectricsubstrateprovidesauniqueinteractionmechanismwithwhichtostudythefilmsele
3、ctronicchargetransportproperties,aswellaschangesinthesepropertiesresultingfromchemisorptionfromthegasphase.Weutilized97MHzST-cutquartz-and32MHzY-cutLiNbO,-basedSAWdevicestofollow(I)theprocessofvacuumdepositionofthinmetalfilms(5-500A),(2)the(roomtemperature)relaxationofsu
4、chfilmsaftertheirdeposition,and(3)thechemisorption-inducedchangesinboththemassdensityandelectricalconductivityofsuchfilms.Changesinmassdensitywerefollowedwitharesolutionexceeding1%ofamonolayer.Sheetconductivitymeasurementsmadewiththe97MHzSAWdevicecorrelatedwellwithsimult
5、aneousmeasurementsmadewithad.c.electrometer.Inaddition.changesinthemechanicalpropertiesoffreshlydepositedthinfilmswereobservedduringrelaxationandwhengaseousspeciesinteractwiththem;webelievethisisaresultofadsorptionpredominantlyalonggrainboundaries.Thecombinationofrespons
6、estothreedifferentphysicalparameterscanbeutilizedinthedesignofchemicalsensors.1.Introductionwavenumber;m,p,q,0,E,p,andTrepresentmass,shearelasticmodulus,viscosity,electronicconductivity,Theapplicationofsurfaceacousticwave(SAW)permittivity,pressure,andtemperature,respecti
7、vely.devicestoproblemsinthefieldsofchemicalsensingTomonitorchangesinSAWpropagationcharacter-[1-121andcharacterizationofthinfilmmaterials[lo-istics,anoscillatorloopsuchasthatdepictedinFig.1201hasbeenexaminedbyanumberofresearchersisoftenutilized.Inthiscircuit,describedinSe
8、ction2,aroundtheworld.WhilethemajorityofthesestudiestheSAWdeviceservesasthefrequencycontrolele-havereli