Synchrotron X-ray Scanning Tunneling Microscopy

Transcription

1 Synchrotron X-ray Scanning Tunneling Microscopy Volker'Rose' Advanced'Photon'Source'&'Center'for'Nanoscale'Materials' Argonne'Na<onal'Laboratory' Argonne,'Illinois,'USA'

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4 Synchrotron X-ray Scanning Tunneling Microscope 4'

5 Strength of X-rays and STM Photoemission*electron* microscopy*!elemental'and'magne<c'contrast' "Spa<al'resolu<on'10s'of'nm' SP1*Scanning*tunneling* microscopy*!high'spa<al'resolu<on'!qualita<ve'detec<on'of'single'spins' "No'quan<fica<on'of'moments'' "No'chemical'contrast' A P P L I E 24 DSEPTEMBER 2007 Volume 91 Number 13 P H Y S I C L E T T E R S 20nm Courtesy'of'SawPWai'Hla' V. Rose et. al, APL 91 (2007) D. Serrate et al., Nat. Nanotech. 5, (2010). 5'

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7 Synchrotron X-ray Scanning Tunneling Microscopy (SXSTM) The Physics of SXSTM 7'

8 The Scanning Tunneling Microscope Gerd'Binnig'and'Heinrich'Rohrer' Nobel'Price'1986'' Exponen<al'decaying'solu<on'for'electron'wave'func<on' in'barrier' ψ(d) = ψ(0) e κd 2m(Φ E) κ = Probability'of'finding'an'electron'behind'the'barrier' E F E n =E F ev W (d) = ψ(d) 2 I ψ n (0) 2 e κd 8'

9 The physics of synchrotron enhanced STM e - #excited tunneling electrons (because of X-ray absorption) X ray I tunnel X-ray E F Φ Sample ev Tip II tunnel topo #primary'photoelectrons' (from'the'photoabsorp<on'of'the'' incident'xprays)' Conventional STM ' #primary'auger'electrons'' I STM = I topo (from'the'depexcita<on'a\er'' photoioniza<on)' Synchrotron X-ray STM ' #secondary'photoelectrons'' (due'to'photoabsorp<on'of' fluorescent'' radia<on'in'the'sample)' ' #secondary'auger'electrons'' (from'the'relaxa<on'of'secondary'' excited'atoms).'' I SX STM = I topo + I X ray sample I pass V. Rose et al., New Capabilities at the Interface of X-rays and Scanning Tunneling Microscopy, in Scanning Probe Microscopy of Functional Materials: Nanoscale Imaging and Spectroscopy, S.V. Kalinin, A. Gruverman, (Eds.), Springer, New York (2011), pg '

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11 tip I SXSTM = I sample tip pass + I ejection I X ray tunnel I topo 11'

12 'Simula<ng'the'electron'trajectory' tip I SXSTM = I sample tip pass + I ejection I X ray tunnel I topo 12'

13 tip I SXSTM = I sample tip pass + I ejection I X ray tunnel I topo 13'

14 Synchrotron X-ray Scanning Tunneling Microscopy (SXSTM) Major Experimental Challenges 14'

15 Cu(111) Tip Smart tip X-rays Sample 15'

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17 Synchrotron X-ray Scanning Tunneling Microscopy (SXSTM) Simultaneous topographic and chemical contrast 17'

18 TopographyPfilter'' (U.S.'Patent'Pending)' Point'spectrum'taken'on'Cu(111)' Point spectra taken on Cu(111) 18'

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20 Synchrotron X-ray Scanning Tunneling Microscopy (SXSTM) Fabrication of smart tips 20'

21 Smart tips only see what you need Why'do'we'need'smart'<ps?' I SXSTM = I tunnel + I photo ejected Tunneling:' Highly'localized' Between'two'atoms' Ejec<on:' From'en<re'illuminated'area' Collec<on'at'apex'but'also' side'walls'of'<p' 21'

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23 Scanning electron microscopy Nanotomography 23'

24 Vol. 23 No. 20 May PtIr'apex' SiO 2' coa<ng' Lesker'PVD250'' epbeam'evaporator' Zeiss'1540XB'FIBPSEM' Materials Science on the Nanoscale: SPM at the Nanoscale Science Research Centers 24'

25 Coaxial'Smart'Tips'(U.S.'Patent'Pending,'13/791,157)' 25'

26 Synchrotron X-ray Scanning Tunneling Microscopy (SXSTM) Instrumentation and technical aspects 26'

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30 SXSTM beryllium window 70m Beamline Chopper 26-ID 30'

31 Controls LabVIEW TM Pbased'measurement'so\ware'allows'high'flexibility'and'simple' hardware'integra<on.' EPICS TM 'facilitates'communica<on'with'beamline'hardware.' MATLAB TM 'used'for'visualiza<on'and'realp<me'analysis.'' 31'

32 Synchrotron X-ray Scanning Tunneling Microscopy (SXSTM) Nanoscale chemical contrast: Current resolution record 32'

33 Chemical contrast of Ni/Cu(111) 190'x'110'nm 2 ','P1V,'1nA' Nozomi Shirato, Marvin Cummings, Heath Kersell, Yang Li, Benjamin Stripe, Daniel Rosenmann, Saw-Wai Hla & Volker Rose*, submitted 33'

34 Topography* NANOSCALE chemical contrast of Ni/Cu(111) Chemical' contrast'in' sample' current' 4'nm'Ni' cluster' Chemical' contrast'in' <p'current' Chemical'contrast'at'resolu<on'limit'of'smart'<p.' Here,'only''about'10'Ni'atoms'across.' Nozomi Shirato, Marvin Cummings, Heath Kersell, Yang Li, Benjamin Stripe, Daniel Rosenmann, Saw-Wai Hla & Volker Rose*, submitted 34'

35 World s first Low-temperature SXSTM Prep.'chamber' STM' chamber' Laboratory' UHV' suitcase' Beamline' Sample' Tip' LTPSXSTM' UHV' suitcase' 35'

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37 Takeaways!!Synchrotron!X+ray!Scanning!Tunneling!Microscopy!(SX+STM)! provides!high!spa:al!resolu:on!with!chemical!(and!magne:c)! contrast.!!nanoscale!resolu:on!enabled!by!topo+filter!and!smart!:ps.!!chemical!contrast!obtained!at!the!single!atomic!height!limit.!!growing!field!with!efforts!worldwide.!!!!!!!! Vol. 23 No. 20 May Materials Science on the Nanoscale: SPM at the Nanoscale Science Research Centers Scan me! Google!SXSPM!for!more!informa:on.! Funding'by'the'Office'of'Science'Early'Career'Research'Program'through'the'Division'of'Scien<fic'User' Facili<es,'Office'of'Basic'Energy'Sciences'of'the'U.S.'Department'of'Energy'through'Grant'SC70705.' 37'