Raman Spectroscopy of Thin FilmsVincent Lewis ’20, Frank
Peiris
Kenyon College Summer Science 2017
AbstractRamanSpectroscopyisapowerfulexperimentaltechniquetoanalyzethevibrationalmodesofthinfilms.UsingRamanSpectroscopy,wehaveinvestigatedzirconiainordertodeciphertheirvibrationalmodesandtoexplorethequalityofsample.Thezirconiawasdepositedonsiliconsubstrates,treatedwitheitherOleicAcidorTrioctylphosphine
oxide(TOPO),andthencalcinedatspecifictemperatures.Usingacombinationofresultsfrom632nmand532nmlaserspectroscopy,wefoundthatthezirconiaunderwentcrystalphasetransformationaround700to900degreesCelsius.ThespectraofthezirconiatreatedwithTOPOshowedstrongsignsofbothmonoclinicandtetragonalcrystalstructure,resultswhichwereverifiedbyX-raydiffractionaswell.
WealsousedAtomicForceMicroscopytoexplorethetopographyofthezirconiasamples.Fromtheseimageswewereabletocalculatetherootmeansquare,whichistheaverageroughnessofthesurface.
Raman Spectroscopy
Background
Zirconia Samples
Raman Spectra AFM
Conclusions
References1.
https://images.nature.com/full/nature-assets/nprot/journal/v11/n4/images_article/nprot.2016.036-F1.jpg2.
https://pharm.virginia.edu/files/2014/01/AFM2.jpg3. A. Muñoz
Tabares, José & J. Anglada, Marc. (2010). Quantitative Analysis
of Monoclinic Phase in 3Y-TZP by Raman Spectroscopy. Journal of the
American Ceramic Society. 93. 1790 -1795
AcknowledgmentsThis work was funded by NIH R15 ES011130 to WHP
and by the Kenyon College Summer Science Scholars program.
•
TheRamanEffect,otherwiseknownasRamanScattering,istheinelasticscatteringofaphotonduetoexcitedvibrationalmodesofamaterial.
•
Byshootingalaseratathinfilm,wecanexcitenewvibrationalmodesofamaterial.Sincetheexcitinglaserisinfluencedbythevibrationalmodes,thephotonscanloseorgainenergy.
•
WhiletheRayleighScatteringisbyfarthedominantphenomena,RamanScatteringstilloccurs.Thisshiftonlyoccurswithinonepermillionsofthereflectedphotons,andisthusunobservabletothenakedeye.
•
ARamanSpectrometerisabletofilteroutalotofthosereflectedphotons,andgraphaspectrumoftheshifts.Thisisonlypossiblethroughexcitationwithasinglewavelength,asnotchfilterscanbeoptimized.
TOPOZirconia• FromourdatawefoundthatTOPOzirconiabeganto
undergoaphasetransformationaround700C.•
At900C,theTOPOzirconiahasbothmonoclinicand
tetragonalstructure.•
ThisresultswereconfirmedbyX-raydiffraction.OAZirconia•
TheOleicAcidzirconiaonlyshowedatetragonal
crystalstructureathighertemperatures.•
Theseresultswerealsoconfirmedbyx-raydiffraction.
Analyzing Spectra
•
ZirconiumDioxide(zirconia)isacompoundwithmanyemergingusesinindustry
•
ZirconiawasspincoatedonSiliconsubstrates,andthentreatedwitheithertrioctylphosphine
oxide(TOPO)oroleicacid(OA).
•
Thesechemicalsaffectthecrystalphasesofthezirconia.Zirconiacanforminamorphous,monoclinic,tetragonal,andcubicstructures.Thesephasesarereachedthroughexposuretotemperature.Oursampleswereannealedfor168hoursatdifferenttemperaturesrangingfrom300Cto900C.
300COA
AtomicForceMicroscopy• AtomicForceMicroscopy(AFM)usesa
cantilevertomeasureforceonthesurfaceofamaterial.
•
Asthecantileverrunsacrossthetopofthematerial,fluctuationsinthesurfaceheightwillapplydifferentforces.
• Piezoelectronics
areabletomovethesampleatfinelytunedincrements,whilealaserisreflectedoffofthecantilever.Thepositionofthethelaserisrecordedbyaphotodiode.
•
Bycomparingthedisplacementofthelaserwiththedisplacementofthesamplebythepiezoelectronics,weareabletocreateatopographyofthesample.
TOPO
OleicAcid
Vibrationmodesofmonoclinicandtetragonalzirconia[3]
Astheannealingtemperatureincreases,shownintheAFMimages,theindividualcrystallinesizesdecrease.Athightemperatures,thecrystallinesizescorrespondedtotheexpectedzirconiananoparticlesizes
600COA
700COA
TOPO OleicAcid
300CTOPO
900COA
400CTOPO
600CTOPO 800CTOPO
•
PicturedaboveareportionsoftheRamanspectraforbothTOPOandOleicAcid
•
PicturedtotheupperrightisagraphofgeneralRamanspectraforzirconia,bothmonoclinic,zirconia,andmixedcrystalstructures
•
Colorcodedarespecificpeaksatwavenumberscorrespondingtovibrationalenergylevelsofspecificcrystallinestructures
• At146and260𝑐𝑚#$, tetragonalpeaksexist.
• Ataround180and190𝑐𝑚#$,adoublemonoclinicpeakexists.
•
Theremainingpeaksinthespectra(suchastheonearound300)arefromthesiliconsubstrate.
•
PicturedinthelowerrightisaspectrumofSiliconobtainedinourlab.Thesepeaksalsoappearintheabovespectrabecauseofthesubstrate.
DiagramofAFM[2]
DiagramofRaman[1]
AFM• Thecrystalsizesinimagesweobtained
correspondedtothenanocrystalsizesofzirconia.
300℃ 400℃ 600℃ 700℃ 800℃ 900℃
RamanSpectrumofSiliconin𝑐𝑚#$
