Principle Of A F S


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Principle Of A F S

  1. 1. Chapter 5. Energetic particles-surface interactions Energetic particles: electron, ion, photon, atoms 1. Scanning Probe Microscopies STM, AFM, MFM, EFM, etc. 2. Electron spectroscopy and microscopies AES, XPS, UPS, PEEM, LEEM, SEM, TEM 3. Vibrational spectroscopies RAIRS, MIR, HREELS 4. Ion spectroscopies ISS, RBS, SIMS 5. Others TPD or TDS
  2. 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, ion tip e, hv, ion
  3. 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 electronics Local probes with nm spatial resolution for characterization
  4. 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. 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, 11. ThermoMicroscope, 12. Digital Instrument, 13. H.-Y. Nie,
  6. 6. Interactions used for Imaging in SPM (a) Tunneling I~exp(kd) (d) Capacitance C(d) ~ 1/d (b) Forces (e) Thermal gradient F(d) ~ various (f) Ion flow f(d) ? (c) Optical near fields E ~1/d4 Resolution limits •The property probed •The probe size
  7. 7. Comparision of Microscopes 106 SEM OM Vertical scale (A) TEM 104 102 1 STM 1 102 104 106 Lateral scale (A)
  8. 8. Characteristics of Microscopies OM SEM/TEM SPM Operation air,liquid vacuum air,liquid,UHV Depth of field small large medium Lateral resolution 1 µm 1-5nm:SEM 2-10nm: AFM 0.1nm:TEM 0.1nm: STM Vertical resolution N/A N/A 0.1nm: AFM 0.01nm: STM Magnification 1X-2x103X 10X-106X 5x102X- 108X Sample not completely un-chargeable surface height transparent vacuum <10 mm compatible thin film: TEM Contrast absorption scattering tunneling reflection diffraction
  9. 9. Limits of Resolution • HM (High Resolution Optical Microscope) diffraction limit ~ 150 nm • PCM (Phase Contrast Microscope) subwave length 배율 가능 • X-ray Microscope λ ∼1Α; Synchrotron radiation and X-ray optics • SEM (Scanning Electron Microscopy) Focused e-beam size > 3nm • TEM (Transmission Electron Microscopy) ~1 A; 얇은 박막시료 • LEEM (Low Electron Emission Microscopy) low energy e-beam; 20nm • PEEM (Photoemission electron Microscopy) lateral resolution~100nm; chemical analysis • FIM (Field Ion Microscopy) tip 형태 시료
  10. 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 µm • X-ray ~ 5 µm • Penetrated electron: 5 µm Atomic Number Interaction Accelerating voltage Volume Incidence angle
  11. 11. Principle: Scanning Electron Microscopy (SEM) •Beam size: a few – 30 A •Beam Voltage: 20-40kV •Resolution: 10-100 A •Magnification: 20x-650,000x •Imaging radiations: Secondary electrons, backscattering electrons •Topographic contrast: Inclination effect, shadowing, edge contrast, E-gun •Composition contrast: backscattering yield ~ bulk composition Lens Detectors •Detections: Secondary - Secondary electrons: topography electron - Backsactering electrons: atomic # and topography Sample - X-ray fluorescence: composition
  12. 12. Instrumentation: SEM
  13. 13. Principle: Transmission Electron Microscopy (TEM) •Beam size: a few – 30 A •Beam Voltage: 40kV- 1MV E-gun •Resolution: 1-2A Condenser •Imaging radiations: transmitted electrons, lens •Imaging contrast: Scattering effect Thin •Magnification: 60x-15,000,000x sample •Image Contrast: Objective 1) Amplitude (scattering) contrast lens - transmitted beam only (bright field image) - diffraction beam only (dark field image) Projector lens 2) Phase (interference) contrast - combination of transmitted and diffraction Screen beam - multi-beam lattice image: atomic resolution (HRTEM)
  14. 14. Example: TEM images of Co-nanoparticles 60 nm Self-assembled Self-assembled 2D-monolayer 2D-monolayer Surface Modification A A Co nanoparticles B 평균 지름 = 7.8 ±1 nm B Self-assembled Self-assembled 3D-multilayer 3D-multilayer From J.I. Park and J. Cheon
  15. 15. Scanning Tunneling Microscope Coarse positioning device Scanning Modes: Piezo tube scanner 1. Constant current X,Y,Z 2. Constant height Tip Current Feedback Computer Sample amplifier controller Sample bias voltage Real space imaging with atomic resolution
  16. 16. Theory of STM J. Tersoff and D.R. Hamann, Phys. Rev. lett. 50, 1988 (1983) Figure From J. Wintterlin - + ψsample ψtip Ef eVbias Ef d It ~ ∑ |ψtip|2 |ψsample|2 e-2κd ~ ∑ |ψsample|2 δ(E-Ef) for low voltage limit; a point tip Constant current STM image corresponds to a surface of constant state density.
  17. 17. Tunneling probability and tunneling current From Y. Kuk, W-tip Au(100)-5x20
  18. 18. Charge density and Potential energy contour of Tip facing the surface S. Ciriaci, Phys. Rev. B 42, 7618 (1990)
  19. 19. Bias polarity : probing filled and empty states - + ψsample ψtip Occupied state (HOMO) Ef Ef d Unoccupied state (LUMO) Ef Ef d J.J.Boland, Adv. Phys. 42, 129(1993) + -
  20. 20. Tunneling Spectroscopy d: fixed It ~ ∑ ρ tip (E) ρ sample (E-eV)T(E,V) dE A (Z)IV- x,y : Topography di/dV~ ρsample (E): LDOS d2i/dV2: local vibrational spectra Si(111)-2x1 Si Ni Theory I vs V (di/dV)/(I/V) vs V J. A. Stroscio et al. Phys. Rev. Lett. 57, 2579 (1986)
  21. 21. STS spectra: Si(111)-7x7 and NH3 /Si(111) Wolkow and Avouris, Phys. Rev. Lett, 60, 1049 (1988)
  22. 22. Current Imaging Tunneling Spectrscopy (CITS) -Take I/V curve at each pixel of a topographic image -Take dI/dV at the fixed bias voltage Vb = -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-bonds Empty(+2 V) filled ( -2V) Topographic images
  23. 23. Instrumentation C.J. Chen, Introduction to scanning tunneling spectroscpy (oxford, 1993) Tip -W tip : electrochemically etched -Pt-Ir tip: cutting Positioning -fine positioning piezoelectric ceramic (Pb(Zr,Ti)O3) eg: PZT5H d33=5.93A/V, d31 = -2.74 A/V From S.J. Garett δl = d31Vl/(OD-ID), δr = d33V x,y: 0.1A z: 0,01 A resolution -coarse positioning louse, step motor, inch worm Vibration isolation -spring, viton O-ring, air table -eddy current damping Thermal stability -smaller and simpler, better stability -symmetric component -matching the thermal coefficient
  24. 24. Tip preparation -Electrochemical etching in 2N NaOH solution -Ex situ : Vacuum annealing; Field emission; Ion sputtering -In situ: high field(>-7V) scanning, controlled collision From W. Ho group
  25. 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 = (ν/νn’)2/[(1- (ν/νn’)2)2+ (ν/Q’νn’)2]1/2 νn’ : the resonance frequency Q’: the quality factor of the tip-sample junction Rigid STM assembly Vib. amplitude>1A Add isolation table Vib. amplitude <0.01 A Internal spring and air table Vib. amplitude<0.001 A
  26. 26. Electronics -set the tip voltage (0-10V) and measure tunneling current (0.001~10nA) -tip-sample separation: 2-5 A, gap resistanace : 107~1010 Ω -scan x,y voltage: 1nm ~1000nm
  27. 27. UHV STM From Burleigh Instrument Inc.
  28. 28. Applications of STM • Surface geometry • Molecular structure • Local electronic structure • Local spin structure • Single molecular vibration • Electronic transport • Nano-fabrication • Atom manipulation • Nano-chemical reaction
  29. 29. Surface Structure Various Reconstructions of Ge(100)-2x1 p(2x2) Buckled 2x1 p(2x2) 2x1 c(4x2) c(4x2) J.Y. Maeng et al (2001)
  30. 30. Si(100) and Ge(100) 2x1 surface Si(001) at 80 K Clean Surface Structure Lattice Dimer Tilt π - π* Buckled- Constant Length Angle Symmetric Si(100) 5.43 Å 2.32 Å 70 0.66 eV 25 meV Ge(100 5.658 Å 2.41 Å 140 1.11 eV 60 meV )
  31. 31. Chemical identifications: bias polarity
  32. 32. Molecular Adsorption: 2+2 cycloaddition reaction Fabrication of molecularly ordered organic films Anisotropic optical and electrical properties A Possible way to orient molecular devices R.J. Hamers et al, J. Phys. Chem., 101, 1489 (1997)
  33. 33. Adsorption structure: Pyridine on Ge(100) tunneling through space and through bond bias dependence Vbias = -1.0 V Clean Ge Pyridine Dimer LUMO Image of π∗ bonds Substrate Ef Dimer HOMO Vbias = -1.8 V π bonds Image of It ~ ∑ |ψsample|2 δ(E-Ef) Substrate + Pyridine Ef Vbias = -2.4V Vbias = -2.4 V Ef Image of Py/Ge W-Tip Pyridine Organic molecules reduce DOS near EF, but increase DOS at lower energy.
  34. 34. Possible Adsorption States of Pyridine on Si(100) Lewis base-acid reaction Lewis base-acid reaction -δ +δ [4+2] cycloaddition [4+2] cycloaddition Lu et al. New. J. Chem. 26. 160 (2002)
  35. 35. Comparison of Theoretical STM Images with Experiment θ = 0.25 ML: experiment c(4x2) model theory θ = 0.5 ML: experiment p(2x2) model theory
  36. 36. Long chain molecules on surface Left A 3nm x 3nm image of docosanol taken at the liquid- solid interface on graphite. The black bar is superimposed over one molecular length, measured to be 3.0 + 0.2nm. The left-hand trough (marked in the image) signifies the alcohol group, which show up slightly darker relative to the rest of the hydrocarbon chain. The individual bright Leanna C. Giancarlo, Hongbin Fang, Luis (yellow) spots along the molecular axis depict individual Avila, Leonard W. Fine, hydrogen atoms. You can actually count them and get 22 and George W. Flynn, J. Chem. Ed., 77, hydrogens per molecule (only one hydrogen per carbon is 66-71 (2000) visible to the STM since the second hydrogen on each carbon is pointing down into the graphite and therefore not seen in the image).
  37. 37. STM of Metal phthalocyanines: Fe(II) d6 Ni(II) d8 Figure 3 Top view STM images of a 0.4 nm thick layer of NiPc and of 0.3 nm of FePc on Au(111) obtained with a W tip. Both samples Figure 2 Schematic orbital energy diagram for had MPc layers that had once been exposed to air. The gray scale several transition metal phthalocyanine extends over 0.3 nm. For NiPc the sample bias was +0.50 V and the complexes. In the case of iron(II), a single orbital tunneling current was 300 pA. For FePc the sample bias was +0.10 configuration cannot be used to describe the V and the tunneling current was 1.6 nA. The image was Fourier ground state, and at least two configurations are filtered to reduce noise. required. This situation is represented diagramatically by use of a broken × to indicate partial occupation of an orbital by an electron, while a full × represents near complete Xing Lu and K. W. Hipps, occupation by a single electron. This diagram is J. Phys. Chem. B, 101 (27), 5391 -5396, 1997 based on ref 1, 3, 30, and 31.
  38. 38. In-situ Monitoring of Self-assembly Self-directed growth of Nanostructures Wolkow et al, Nature, 406, 48 (2000)
  39. 39. Single Molecule Vibrational Spectroscopy Inelastic electron tunneling spectroscopy (IETS) hv/e I V dI/dV V dI2/dV2 V Vibration excitation of the molecule occurs when tunneling electrons have enough energy to excite a quantized vibrational level Inelastic tunneling channel B.C. Stipe. et. al., Science 280, 1732 (1998)
  40. 40. Atomic Manipulation by STM -high electric field: polarize the molecule and make it jump from the surface to the tip vice versa. Iron on Copper (111): -van der Waals force between the tip and the atom use to drag the atom - Circular corral (radius=71.3A) 48 Fe atoms - Quantum-mechanical interference patterns M.F. Crommie, C.P. Lutz, D.M. Eigler. Science 262, 218-220 (1993).
  41. 41. Single-Bond Formation by STM H.J. Lee and W. Ho, Science, 286, 1719(1999)
  42. 42. Real Space Imaging of Two-Dimensional Antiferromagnetism On the Atomic Scale Weisendanger et al, Science 288, 1805 (2000) Nonmagnetic W tip Magnetic W tip
  43. 43. Conductance : Landauer formula µ2 eVmol eV µ1 µ2 µ1 I = (2e/h)∫dE T(E,V) [f(E-µ1)-f(E- µ2)] •F(E): Fermi function •T(E,V): transmission function molecular energy levels and their coupling to the metallic contacts µ1, µ2 : electrochemical potentials µ1= Ef- eVmol µ2 =Ef+eV- eVmol W. Tian et al, J. Chem. Phys. 109, 2874(1998)
  44. 44. Conductance of molecular wire: STM •Tip bias voltage = 1V, •Tunnling current = 10 pA L. A. Bumm et al , Science 271, 1705 (1996).
  45. 45. Electronic Properties of Carbon Nanotubes Constant LDOS Metallic SWNT Semiconducting SWNT
  46. 46. STM Topograph of Quantum Dot Ge pyramid containing ~2000 Ge atoms on Si(100) Ge dome grown by PVD on a 600 C Si(100) R.S. Williams et al, Acc. Chem. Res. 32, 425 (1999)
  47. 47. STM Images of Ni Clusters at Different Sample Bias Voltages
  48. 48. STS and STM of Self-assembled Co-nanoparticles Tip on self-assembled monolayer Tip on a Co nanoparticle I vs V dI/dV vs V Pileni et al, Appl. Surf. Sci. 162/163, 519 (2000)
  49. 49. Tunneling Spectroscopy of InAs QD STM T=4.2K Optical d = 32A S-like P-like Ec=0.11 eV: single electron charging energy U. Banin et al, Nature, Eg=1.02 eV: nanocrystal band gap 400, 926 (2000)
  50. 50. Interactions between Sample and Tip in Force Microscopy vdW force magnetic or adhesion elastic and attractive electrostatic bonding plastic properties ionic repulsion forces friction forces f Contact van der Waals force Intermitant contact r f(r) ~ -1/r6 +1/r12 total force on sample ~ 10-7 ~10-11 N Noncontact
  51. 51. Force vs. Distance f r Vacuum touching untouch Air Capillary Pull off force Slope: elastic modulus of soft Contamnated sample or force constant k of in air cantilever
  52. 52. Atomic Force Microscope (AFM) •Sample: conductor, nonconductor, etc •Force sensor: cantilever •Deflection detection - photodiode interferometry (10-4A) - STM
  53. 53. Mode of Operation Force of interaction Contact strong (repulsive): constant force or constant distance Noncontact weak(attractive): vibrating probe Intermittent contact strong(repulsive): vibrating probe Lateral force frictional forces exert a torque on the scanning cantilever Magnetic force the magnetic field of the surface Thermal scanning the distribution of thermal conductivity
  54. 54. Force Sensor: Cantilever •Material: Si , Si3N4 •Shape: pyramidal, conical tip •Typical Dimension: 100-200 µm 1-4 µm 10 µm •Stiffness - soft: contact mode ∼20nm - stiff: vibrating (dynamic force) mode •Spring constant (k): 0.1-10N/m (atom-atom k ~10N/m) •Resonance frequency: 10~100kHz eg: f = (/2π)(k/m)1/2 From DI m=1µg, k=0.1 N/m, f=100kHZ
  55. 55. Nanotube tip Review: - attaching with glue - in situ CVD grwoth (a) AFM image of 2 nm tall, 10 mm wide, and 100 nm spaced silicon-oxide H.Dai et al, Nature 384, 174 (1996) (light) lines fabricated by a nanotube tip. Bias voltage = – 9 V; speed = 10 APL 73, 1508 (1998) m/s; cantilever amplitude during lithography = 0.55 nm; cantilever amplitude = 9.6 nm. (b) Silicon oxide ``words'' written by the nanotube tip.
  56. 56. Image Artifacts •Tip imaging •Feedback artifacts •Convolution with other physics •Imaging processing How to check ? •Repeat the scan •Change the direction •Change the scan size •Rotate the sample •Change the scan speed AFM image of random noise. Left image is raw data. Right image is a false image, produced by applying a narrow bandpass filter to the raw data
  57. 57. Scanning Modes of AFM Contact Noncontact Vibrating (tapping) •Cantilever soft hard hard •Force 1-10nN 0.1-0.01nN •Friction large small small •Distance <0.2nm ~ 1nm >10nm •Damage large small small •Surface hard surface soft or elastic surface Polymer latex particle on mica From Digital Instrument
  58. 58. Vibrating Cantilever (tapping) Mode •Vibration of cantilever around its resonance frequency •Change of frequency (fo) due to interaction between sample and cantilever Resonance Frequency keff = k0 - dF/dz feff = 2π(keff /m)1/2 •Amplitude imaging •Phase imaging •Removal of lateral force contribution
  59. 59. H.-Y. Nie,
  60. 60. Applications of SPM • Surface morphology, especially for insulators • Lateral, adhesion, molecular and magnetic forces • Temperature, capacitance, and surface potential mapping • Nano-lithography • Surface modification and manipulation • Imaging of biomolecules, and polymers
  61. 61. Atomic resolution AFM AFM (contact mode): AFM (non-contact mode): Au(111) polycrystalline film Atomic resolution on Si(111)7x7 on a glass substrate From Omicron Inc.
  62. 62. STM and AFM Images of Co-Nanoparticles STM: on H/Si(111) AFM: on HOPG TEM: on Carbon grid Co-nanoparticle stripes prepared By Mirco Contact Printing AFM image UHV-STM image (200 nm x 200 nm) after annealing under 500 °C S.S.Bae et al (2001)
  63. 63. Applications to biological system DNA and RNA analysis; Protein-nucleic acid complexes; Chromosomes; Cellular membranes; Proteins and peptides; Molecular crystals; Polymers and biomaterials; Ligand- receptor binding. Bio-samples have been investigated on lysine-coated glass and mica substrate, and in buffer solution. By using phase imaging technique one can distinguish the different components of the cell membranes.
  64. 64. Force Measurement of DNA strands Baselt et al, J. Vac. Sci. Tech. B14, 789 (1996)
  65. 65. Manipulation of Nanoparticles by AFM Ref 15 in G.S. McCarth and P.S.Weiss, Chem. Rev. 99, 1983 (1999)
  66. 66. Dip pen nanolithography using AFM C. Mirkin et al, Science 283, 661 Read Prof I. Choi, lecture note (spring 2002) (1999); 295, 1702 (2002) Figure 1. AFM images and height profiles of lysozyme nanoarrays. (A) Lateral force image of an 8 µm by 8 µm square lattice of MHA dots deposited onto an Au substrate. The array was imaged with an uncoated tip at 42% relative humidity (scan rate = 4 Hz). (B) Topography image (contact mode) and height profile of the nanoarray after lysozyme adsorption. A tip-substrate contact force of 0.2 nN was used to avoid damaging the protein patterns with the tip. (C) A tapping mode image (silicon cantilever, spring contant = ~40 N/m) and height profile of a hexagonal lysozyme nanoarray. The image was taken at a scan rate of 0.5 Hz to obtain high resolution. (D) Three-dimensional topographic image of a lysozyme nanoarray, consisting of a line grid and dots with intentionally varied feature dimensions. Imaging was done in contact mode as described in (B).
  67. 67. Conductive AFM Conductive AFM is used for collecting simultaneous topography imaging and current imaging. Specifically, standard conductive AFM operates in contact AFM mode. Variations in surface conductivity can be distinguished using this mode. Conductive AFM operates in contact AFM mode by using a conductive AFM tip. The contact tip is scanned in contact with the sample surface. Just like contact AFM, the Z feedback loop uses the DC cantilever deflection signal to maintain a constant force between the tip and the sample to generate the topography image. At the same time, a DC bias is applied to the tip. The sample is held at ground potential. The built-in pre- amplifier in the scanner head measures the current passing through the tip and sample.
  68. 68. AFM/STM lithography resist의 표면 topography에도 매우 민감합니다. 대부분 E- beam resist는 주입된 전자 수에 민감하므로 전압에 의하여 제어보다 전류를 집적 제어하는 것이 보다 재현성 있는 패턴 을 얻을 수 있습니다. 따라서 AFM과 STM를 결합하여 resist 표면을 일정한 거리와 힘를 유지하도록 하면서resist 막의 두 께가 변화더라도 전류를 일정하게 유지시키도록 ( 20 pA ~ 1 nA ) 탐침의 전압을 (10~100 V) 변화 시키는 독립적인 feedback loop를 도입하였습니다.(STM mode). 두 제어 방 법을 결합하여 패턴 전체에 걸쳐 전자의 주입양(electron dose) 일정하게 유지하여 수십 nm 수준의 패튼의 재현성을 얻었을 뿐만 아니라 기존 E-beam lithography에서 발생하는 depth of focal length 문제를 해결하였습니다. From
  69. 69. AFM-tip-induced Local Oxidation on Si Ph. Avouris et al, App. Phys. A 66, S659 (1998)
  70. 70. Lateral Force Microscopy •Contact mode •Detect vertical and lateral twisting due to friction •Simultaneous AFM & LFM imaging •Information about friction High resolution topography (top) and Lateral Force mode (bottom) images of a commercially avail-able PET film. The silicate fillers show increased friction in the lateral force image.
  71. 71. Force Modulation Microscopy •Contact AFM mode •Periodic signal is applied to either to tip or sample •Simultaneous imaging of topography and material properties •Amplitude change due to elastic properties of the sample PSIA,
  72. 72. Phase Detection Microscopy Phase imaging is useful for differentiating between component phases of composite materials. The bulk of the wood pulp shown in this figure consists of cellulose microfibrils that are highlighted by phase imaging. In addition, a lignin component -- not apparent in From Digital Instrument the topography -- appears as areas of light contrast atop the cellulose component •Intermittant-contact AFM mode •Monitoring of phase lag between the cantilever oscillation (solid wave) relative to the piezo drive (dashed wave). •Simultaneous imaging of topography and material properties •Change in mechanical properties of sample surface
  73. 73. Chemical Force Microscopy CH3 COOH (A) topography (B) friction force using a tip modified with a COOH-terminated SAM, (C) frinction force using a tip modified with a methyl-terminated SAM. Light regions in (B) and (C) indicate high friction; dark regions indicate low frinction. A. Noy et al, Ann. Rev. Mater. Sci. 27, 381 (1997)
  74. 74. Magnetic Force Microscopy Glass Hard Disk Sample dF/dz =dFm/dz + dFvdw/dz, •Ferromagnetic tip: Co, Cr •Noncontact mode (>100A) AFM •vdW force: short range force image •Magnetic force: long range force small force gradient •Close imaging: topography •Distant imaging: magnetic properties MFM image
  75. 75. Scanning Hall Probe Microscopy z H y ++++++ RH= Ey/jxH i x -------- = -1/ne Ey F= -evxH The spots correspond to individual magnetic lines or vortices that are formed in a superconducting film of LaSrCaCuO This probe allows one to measure microscopic magnetic patterns by using a submicron Hall probe to sense local magnetic fields. Fields as low as 0.1 gauss with 0.3um spatial resolution can be achieved. It competes with magnetic force microscopy which might have superior resolution but is not calibrated and with scanning SQUID microscopy which has higher magnetic field sensitivity but poorer spatial resolution. Hans Hallen and Albert Chang. (Bell lab), Applied Physics Letters, 61, pg 1974 (1992).
  76. 76. Electrostatic Force Microscopy(EFM) Scanning Kelvin Probe Microscopy (SKPM) Scanning Tunneling Potentiometry (STP) Scanning Maxwell Microscopy (SMM) Metallic tip Bias Voltage • Ferroelectric materials • Charge distribution on surfaces • Failure analysis on the device
  77. 77. Theory of EFM Electrostatic force between the sample and the tip (Fcapacitance = dEc /dz , Ec = CV2/2) F = Fcapacitance + F coulomb = (1/2)V2(dC/dz) + (1/4πε z2)QsQt = (1/2) (dC/dz) (Vdc+Vac cos ωt)2 - (1/4πε z2)Qs (Qs+CVdc+CVaccos ωt) = (1/2) (dC/dV) (V 2dc+ (1/2) V2ac) - (1/4πε z2)Qs (Qs+CVdc) + (2Vdc dC/dz - QsC /4πε z)Vaccos ωt + (1/4)dC/dzV2ac cos 2ωt •Ist harmonic term - Surface potential (Vdc ) - surface charge (Qs) •2nd harmonic term - dC/dz : doping concentration
  78. 78. Scanning Capacitance Microscopy (SCM) Transistor Oxide Thickness Metallic tip Contact Topograph SCM • LC capacitance circuit • Doping concentration • Local dielectric constant
  79. 79. Scanning Thermal Microscopy • Subsurface defect review • Semiconductor failure analysis • Measure conductivity differences in copolymers, surface coatings etc
  80. 80. Hybrid Tools: AFM inside SEM M.F. Yu et al, Nanotechnology 10, 244 (1999)
  81. 81. Nearfield Scanning Optical Microscopy Topography and Optical properties Glass hv Detector Al φ=60-200nm d Fluorescence image of •Near field: d<<λ a single DiIC molecule. •Resolution ~ d and φ Image courtesy of P. •Approach: shear force Barabara/Dan Higgins
  82. 82. Scanning Electrochemical Microscopy From Prof. J. Kwak Electrochemistry Surface structure Electrochemical deposition Corrosion
  83. 83. Photon Emission STM Photon detector A A FEEDBACK Local chemical environment G.S. McCarty and P.S. Weiss, Chem. Rev. 99, 1983 (1999)
  84. 84. BEEM (Ballistic Electron Emission Microscopy) A Ballistic Electron A Ef gap FEEDBACK Tip Base Collector(Si) STP (Scanning Tunneling Potentiometry) A .. . . FEEDBACK
  85. 85. Summary STM • real space imaging • high lateral and vertical resolution • STS probe electronic properties • sensitive to noise • image quality depends on tip conditions • not true topographic imaging • only for conductive materials AFM and others •apply to nonconducting materials : biomolecules, ceramic • real topographic imaging • probe various physical properties: magnetic, electrostatic, hydrophobicity, friction, elastic modulus, etc. • can manipulate molecules and fabricate nanostructures • low lateral resolution ~50A • contact mode can damage the sample • image distortion due to the presence of water • difficulties in chemical identification
  86. 86. Future Directions for Characterization of Nanosystems • Instrument for analysis of biomolecules, and polymers • 3-D structure determination • Nanostructure chemical determination • Functional parallel probe arrays • Standardization and metrology • New nano-manipulator • Non-SPM probes that use ions or electrons • In-situ nondestructive monitoring techniques