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Atomic Force Microscopy Long Phan Nanotechnology Summer Series May 15, 2013 1
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AtomicForceMicroscopy

LongPhanNanotechnologySummerSeries

May15,2013

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World’sSmallestMovie

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Outline

•  WhatisAFM?•  HowdoesAFMWork?•  3Modes:–  Contactmode–  Non‐contactmode–  Tappingmode

•  Imaging•  AdvantagesofAFM

hNp://www.graphene‐info.com/files/graphene/images/atomic‐force‐microscope‐on‐graphene.jpg3

History•  ThefirstAtomicForceMicroscope(AFM)wasdevelopedbyG.Binnig,Ch.Gerber,andC.Quatein1985– Glueda[nyshardofdiamondontooneendofa[nystripofgoldfoil

– Smallhookatendofthe[ppressedagainstsamplesurface

hNps://en.wikipedia.org/wiki/File:Atomic_Force_Microscope_Science_Museum_London.jpghNp://img.direc[ndustry.com/images_di/photo‐g/atomic‐force‐microscope‐afm‐34990‐2834889.jpg

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WhatCanWeLookAt?•  AFMiscurrentlythemostwidelyusedscanningprobemicroscopytechnique

•  Materialsinves[gated:thinandthickfilmcoa[ngs,ceramics,composites,glasses,synthe[candbiologicalmembranes,metals,polymers,andsemiconductors

hNp://butler.cc.tut.fi/~foster/images/afmman.pnghNp://www.enm.bris.ac.uk/teaching/projects/2005_06/eb3990/pics/BlueDNA.jpg

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Applica[ons•  Toproduceatopographicalimageofasurfacewithatomicresolu[on

•  Determineroughnessofasample’ssurface

•  Measuretrenchestodeterminefilmthickness

•  Imagenon‐conduc[ngsurfaces•  Studythedynamicbehavioroflivingandfixedcells

hNp://phys.org/news/2012‐09‐world‐atomic‐microscope‐chemical‐bonds.htmlhNp://www.azonano.com/work/d47sB44Y9c5tWcR9EDKU_files/image005.jpg

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AFMEssen[alElements

hNp://stm2.nrl.navy.mil/how‐afm/how‐afm.html#imaging%20modeshNp://www.nanoscience.com/store/pc/catalog/03_oem‐probe‐series_tn_624_detail.jpg

•  1.Laser–deflectedoffcan[lever•  2.Mirror–reflectslaserbeamto

photodetector•  3.Photodetector–dualelement

photodiodethatmeasuresdifferencesinlightintensityandconvertstovoltage

•  4.Amplifier•  5.Register•  6.Sample•  7.Probe–[pthatscanssample

madeofSi•  8.Can:lever–movesasscanned

oversampleanddeflectslaserbeam

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AFMPrinciples–LeonardJonesPoten[al

hNp://engr.iupui.edu/bme/bbml/Figures/VDWPEcurve.jpg

Separa[ondistance

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AFMPrinciples

•  Duringscan,featuresaffectlaserdeflec[onoffcan[lever

•  Laserdetectorreadsdeflec[onandeither:– Translatesdeflec[onintotopographymap

– Movesstagetomaintainzerolaserdeflec[onandtranslatesstagemovementtotopography.

hNp://www.weizmann.ac.il/Chemical_Research_Support/surflab/peter/afmworks/9

3ModesofAFM

•  ContactMode–  Highresolu[on–  Damagetosample

•  Non‐ContactMode–  Lowerresolu[on–  Nodamagetosample

•  Tapping/IntermiNentMode–  Intermediateresolu[on– Minimaldamagetosample

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ContactMode•  Measuresrepulsionbetween[pandsample•  Commonly,forceof[pagainstsampleremainsconstant

•  Feedbackregula[onkeepscan[leverdeflec[onatzero

•  Voltagerequiredindicatesheightofsample•  Problems:Willdamagesoqersurfaces

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Non‐ContactMode•  Tipdoesn’ttouchsample•  MeasuresVanderWaalsforcesbetween[pandsampletoacquiretopographydata

•  Doesn’tdegradeorinterferewithsample‐beNerforsoqsamples

•  Problems:Can’tusewithsamplesinfluid

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Tapping/IntermiNentMode•  Tipver[callyoscillatesbetweencontac[ngsamplesurfaceandliqingoffat50‐500kHz.

•  Oscilla[onamplitudereducedasprobenearssurface

•  Advantages:overcomesproblemsassociatedwithfric[on,adhesion,electrosta[cforces

hNp://cdn.intechopen.com/pdfs/30111/InTech‐Tapping_mode_afm_imaging_for_func[onalized_surfaces.pdf13

Genera[nganImage

•  The[prastersbackandforthinastraightlineacrossthesample(thinkoldtypewriterorCRT)

•  Inthetypicalimagingmode,the[p‐sampleforceisheldconstantbyadjus[ngthever[calposi[onofthe[p(feedback).

•  Atopographicimageisbuiltupbythecomputerbyrecordingthever[calposi[onasthe[pisrasteredacrossthesample.

ScanningTip

RasterM

o[on

www.nanodevices.comwww.fz‐borstel.de/biophysik/de/methods/afm.html

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•  Radiusof[plimitstheaccuracyofanalysis/resolu[on

•  Widerproberadiileadtofeatureinaccuraciesandroundingofsteps

EffectofTipResolu[on

www.pacificnanotech.comhNp://jnm.snmjournals.org/content/48/7/1039/F1.large.jpg

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EffectofTipResolu[on

hNp://www.nilt.com/default.asp?Ac[on=Details&Item=51316

ImagingMaterials

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ImagingMaterials

Thakurdesai,M.;et.al.Vacuum2008,82,639–644hNp://ej.iop.org/images/0960‐1317/22/4/045012/Full/jmm399735f1_online.jpg

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ImagingMaterials

Biro,L.;Lambin,P.NewJ.Phys.,2013,15,035024.19

ImagingBiologicalSamples

hNp://www.parkafm.com/AFM_guide/true_non_contact_mode_4.php

Single‐strandedG4DNA

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OtherCapabili[es•  Electrosta[cForceMicroscopy(EFM)

•  Dis[nguishingdifferencesinsamplecomposi[on(crystalorienta[on,chemicalcomposi[on)

•  Measuringconduc[vity(CAFM)

•  Micro/nanoindenta[on

•  PiezoresponseForceMicroscopy(PFM)

•  Magne[cForceMicroscopy(MFM)

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Electrosta[cForceMicroscopy(EFM)

•  Non‐contactmode– Constantheightorconstantdeflec[on

•  Trackchangesin[poscilla[onsduetoelectrosta[cforcegradientsbetween[pandsample(atlargesepara[on).

hNp://www.nanowerk.com/nanobusiness/showroom/Park_Systems/downloads/Electrosta[c_Force_Microscopy.pdf 22

hNp://www.nanoandmore.com/uploads/gallery/Veeco‐Electrosta[c‐Force‐Microscopy‐EFM‐test‐sample‐20120828090801.png23

hNp://www.nanoandmore.com/uploads/gallery/Veeco‐Electrosta[c‐Force‐Microscopy‐EFM‐test‐sample‐20120828090801.pnghNp://www.sciencedaily.com/releases/2011/05/110524094507.htm

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hNp://www.nanoandmore.com/uploads/gallery/Veeco‐Electrosta[c‐Force‐Microscopy‐EFM‐test‐sample‐20120828090801.pnghNp://www.sciencedaily.com/releases/2011/05/110524094507.htm

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MoreEFMImages

26hNp://www.asylumresearch.com/Gallery/Materials/Materials.shtml#conduc[ve

CarbonNanotubeFerrite(bright)andAustenite(dark)

AFMPhaseMapping

hNp://www.intechopen.com/source/html/16843/media/image12.png

•  InTapping/IntermiNentmode,changesinmaterialleadtochangesinphaseangleof[poscilla[on

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PhaseImages

hNp://www.surfacesciencewestern.com/research/publica[ons/28

Conduc[veAFM

•  OperatesinContactmodetomapvaria[oninelectricalconduc[vityofsample

•  Alsoabletocollectcurrent‐voltage(IV)spectraatspecificpointsonsample

hNp://www.azom.com/ar[cle.aspx?Ar[cleID=328529

CAFMImages

30hNp://www.asylumresearch.com/Gallery/Materials/Materials.shtml#conduc[ve

GaAsQuantumDots DVDRecording

Micro/Nanoindenta[on

•  Testmechanicalproper[esofmaterials:– Hardness(maxloaddividedbyindentarea)– Young’sModulus(elas[city)

31hNp://www.engineering.unl.edu/research/bm3/graphics/nanoindenter_cube_corner_[p_01.jpghNp://www.asylumresearch.com/Gallery/Materials/Materials.shtml#conduc[ve

Load‐Displacement

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Young’sModulus

PiezoresponseForceMicroscopy

•  Measuresthemechanicalresponsewhenanelectricalvoltageisappliedtothesamplesurfacewithaconduc[ve[p

33hNp://www.asylumresearch.com/Applica[ons/PFMAppNote/PFMAppNote.shtml

PFMImages

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Magne[cForceMicroscopy(MFM)

•  Asthe[pmovesoveranmagne[cfieldgradient,itiseitherpulledtowardorrepulsedawayfromthesample.

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MFMImages

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AdvantagesofAFM

•  AFMvs.STM(scanningtunnelingmicroscope):Imagesbothconductorsandinsulators

•  AFMvs.SEM(scanningelectronmicroscope):Greatertopographiccontrast

•  AFMvs.TEM(transmissionelectronmicroscope):Noexpensiveand[me‐intensivesampleprep

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Summary

•  AFMimagessurfacetopography•  3Modes– Contact–  IntermiNent/Tapping– Non‐Contact

•  Manydifferentimagingabili[es!– EFM,Phase,CAFM,Indenta[on,PFM,MFM

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