1. Chapter 5. Energetic particles-surfaceinteractions Energetic particles: electron, ion, photon, atoms 1. Scanning Probe MicroscopiesSTM, AFM, MFM, EFM, etc. 2. Electron spectroscopy and microscopiesAES, XPS, UPS, PEEM, LEEM, SEM, TEM 3. Vibrational spectroscopies RAIRS, MIR, HREELS 4. Ion spectroscopiesISS, RBS, SIMS 5. OthersTPD or TDS

2. Tools for Characterization Tools for Characterization Structural analysis: SEM, TEM, XRD, SAM, SPM, PEEM, LEEM, STXM, SXPEM Chemical analysis: AES, XPS, TPD, SIMS, EDX, SPM Electronic, optical analysis: UV/VIS, UPS, SPM Magnetic analysis: SQUID, SMOKE, SEMPA, SPM Vibrational analysis: IR, HREELS, Raman, SPM Local physico-chemical probe: SPM e, hv, iontipe, hv, ion 3. Scientific issues in nanotechnologies (Nanotech.Res. Directions: IWGN report,1999) Fundamental properties of isolated nanostructures Fundamental properties of ensemble of isolated nanostructures Assemblies of nanoscale building blocks Evaluation of concepts for devices and systems Nanomanufacturing Connecting nanoscience and biology Molecular electronicsLocal probes with nm spatial resolution for characterization 4. Scanning Probe Microcopy Scanning Tunneling Microscopy(STM): topography, local DOS Atomic Force Microscopy (AFM): topography, force measurement Lateral Force Microscopy (LFM): friction Magnetic Force Microscopy (MFM): magnetism Electrostatic Force Microscopy (EFM): charge distribution Nearfield Scanning Optical Microscopy (NSOM): optical properties Scanning Capacitance Microscopy (SCM): dielectric constant, doping Scanning Thermal Microscopy (SThM): temperature Ballistic Electron Emission Microscopy (BEEM): interface structure Spin-polarized STM (SP-STM): spin structure Scanning Electro-chemical Microscopy (SECM): electrochmistry Scanning Tunneling Potentiometry (SPM): potential surface Photon Emission STM (PESTM): chemical identification 5. References of SPM 1. P.Hansma, J. Tersoff, J. App. Phys. 61, R1 (1987) 2. Y. Kuk, P.J. Silvermann, Rev. Sci. Inst. 60, 165 (1989) 3. Scanning Tunneling Microscopy and related methods edited by R.J. Behm, N. Garcia, and H. Rohrer (1990) 4. C.J. Chen, Introduction to scanning tunneling spectroscpy (oxford, 1993) 5. H-J Gudtherodt and R. Wiesendanger(ed.), Scanning tunneling microscopy I,II,III (Springer,1991-1993) 6. J.A. Kuby and J.J. Boland, Surf. Sci. Rep. 26, 61 (1996) 7. R.J. Hamers, Scanning Probe Microscopy in Chemistry, J. Phys. Chem.100, 13013 (1996) 8. G.S. McCarty and P.S.Weiss, Scanning Probe Studies of Single Nanostructures, Chem. Rev. 99, 1983 (1999) 9. C. Bai, Scanning tunneling spectroscopy and its applications (Springer, 2000) 10. PSIA, www.psia.co.kr/appnotes/apps.htm 11. ThermoMicroscope, www.thermomicro.com/spmguide/contents. 12. Digital Instrument, www.di.com/app_notes/full_appnotes.htm 13. H.-Y. Nie, publish.uwo.ca/~hnie/mmo/all.html 6. Interactions used for Imaging in SPM (a) TunnelingI~exp(kd)(d) CapacitanceC(d) ~ 1/d (b) Forces(e) Thermal gradientF(d) ~ various (f) Ion flowf(d) ?(c) Optical near fields E ~1/d4Resolution limitsThe property probedThe probe size 7. Comparision of Microscopes 106SEMOM Vertical scale (A) TEM1041021 STM 1 102 104 106Lateral scale (A) 8. Characteristics of MicroscopiesOMSEM/TEM SPM Operationair,liquidvacuum air,liquid,UHV Depth of field small largemedium Lateral resolution1 m 1-5nm:SEM2-10nm: AFM 0.1nm:TEM0.1nm: STMVertical resolution N/AN/A0.1nm: AFM0.01nm: STMMagnification 1X-2x103X10X-106X 5x102X- 108X Sample not completely un-chargeablesurface height transparentvacuum 3nm TEM (Transmission Electron Microscopy) ~1 A; LEEM (Low Electron Emission Microscopy) low energy e-beam; 20nm PEEM (Photoemission electron Microscopy) lateral resolution~100nm; chemical analysis FIM (Field Ion Microscopy)tip 10. Interaction of Electrons with Sample When 20 KV e-beam is used for Ni(Z=28). Auger electron :10-30A Secondary electron: 100A Backscattering electron: 1-2 m X-ray ~ 5 m Penetrated electron: 5 mAtomic NumberInteractionAccelerating voltage VolumeIncidence angle 11. Principle: Scanning Electron Microscopy (SEM)Beam size: a few 30 ABeam Voltage: 20-40kVResolution: 10-100 AMagnification: 20x-650,000xImaging radiations: Secondary electrons,backscattering electronsTopographic contrast: Inclination effect,shadowing, edge contrast,E-gunComposition contrast: backscatteringyield ~ bulk composition LensDetectorsDetections: Secondary - Secondary electrons: topography electron - Backsactering electrons:atomic # and topography Sample- X-ray fluorescence: composition http://super.gsnu.ac.kr/lecture/microscopy/em.html 12. Instrumentation: SEM 13. Principle: Transmission Electron Microscopy (TEM) Beam size: a few 30 A Beam Voltage: 40kV- 1MV E-gun Resolution: 1-2ACondenser Imaging radiations: transmitted electrons, lensImaging contrast: Scattering effect Thin Magnification: 60x-15,000,000xsample Image Contrast: Objective 1) Amplitude (scattering) contrastlens- transmitted beam only (bright field image)- diffraction beam only (dark field image)Projectorlens2) Phase (interference) contrast- combination of transmitted and diffractionScreen beam- multi-beam lattice image: atomic resolution (HRTEM) 14. Example: TEM images of Co-nanoparticles 60 nm Self-assembled Self-assembled2D-monolayer 2D-monolayerSurface ModificationAA Co nanoparticles B = 7.8 1 nmBSelf-assembled Self-assembled 3D-multilayer3D-multilayer From J.I. Park and J. Cheon 15. Scanning Tunneling MicroscopeCoarse positioning deviceScanning Modes: Piezo tube scanner 1. Constant currentX,Y,Z 2. Constant height TipCurrent Feedback Computer Sampleamplifier controller Sample bias voltage Real space imaging with atomic resolution 16. Theory of STM J. Tersoff and D.R. Hamann, Phys. Rev. lett. 50, 1988 (1983) Figure From J. Wintterlin- + sampletip Ef eVbiasEf dIt ~ |tip|2 |sample|2 e-2d~ |sample|2 (E-Ef) for low voltage limit; a point tipConstant current STM image corresponds toa surface of constant state density. 17. Tunneling probability and tunneling current From Y. Kuk, W-tip Au(100)-5x20 18. Charge density and Potential energy contour of Tip facing the surface S. Ciriaci, Phys. Rev. B 42, 7618 (1990) 19. Bias polarity : probing filled and empty states - + sample tip Occupied state (HOMO)Ef Ef d Unoccupied state (LUMO) EfEf dJ.J.Boland, Adv. Phys. 42, 129(1993) +- 20. Tunneling Spectroscopyd: fixedIt ~ tip (E) sample (E-eV)T(E,V) dEA(Z)IV- x,y : Topographydi/dV~ sample (E): LDOSd2i/dV2: local vibrational spectra Si(111)-2x1 Si NiTheoryI vs V(di/dV)/(I/V) vs V J. A. Stroscio et al. Phys. Rev. Lett. 57, 2579 (1986) 21. STS spectra: Si(111)-7x7 and NH3 /Si(111)Wolkow and Avouris, Phys. Rev. Lett, 60, 1049 (1988) 22. Current Imaging Tunneling Spectrscopy (CITS) -Take I/V curve at each pixel of a topographic image -Take dI/dV at the fixed bias voltageVb = -0.15 ~ 0.6 V Dangling bonds in faulted half of unit cell (adatoms) Vb = -0.6 ~ -1.0 V Faulted unfaulted Dangling bonds in second layer of atoms (rest atoms)Vb = -1.6 ~ -2.0 V Si-Si back-bondsEmpty(+2 V) filled ( -2V) Topographic images 23. Instrumentation C.J. Chen, Introduction to scanning tunneling spectroscpy (oxford, 1993) Tip-W tip : electrochemically etched-Pt-Ir tip: cuttingPositioning-fine positioning piezoelectric ceramic (Pb(Zr,Ti)O3)eg: PZT5H d33=5.93A/V, d31 = -2.74 A/VFrom S.J. Garett l = d31Vl/(OD-ID), r = d33V x,y: 0.1A z: 0,01 A resolution-coarse positioning louse, step motor, inch wormVibration isolation-spring, viton O-ring, air table-eddy current dampingThermal stability-smaller and simpler, better stability-symmetric component-matching the thermal coefficient 24. Tip preparation-Electrochemical etching in 2N NaOH solution-Ex situ : Vacuum annealing; Field emission; Ion sputtering-In situ: high field(>-7V) scanning, controlled collisionFrom W. Ho group 25. Vibration isolation Y. Kuk, P.J. Silvermann, Rev. Sci. Inst. 60, 165 (1989) -needs ~0.01A or less(atomic corrugation ~0.1A) -Dapmed spring : fres =0.5 Hz -Vition stacks :fres = 10~100 Hz -Air tables Damping transfer function Ts Ts = (/n)2/[(1- (/n)2)2+ (/Qn)2]1/2 n : the resonance frequency Q: the quality factor of the tip-sample junction Rigid STM assemblyVib. amplitude>1A Add isolation table Vib. amplitude