1. Scanning Probe Microscopy – the Nanoscience Tool NanoScience & NanoTechnology Tools that operate in real space with Ångstrom to nanometer spatial resolution, in contrast to scattering techniques, such as for instance the SEM (scanning electron microscope), that operate in the reciprocal space. In principle, SPM systems consist of  probes that are nanosized (accomplished microlithographically),  scanning and feedback mechanisms that are accurate to the subnanometer level (achieved with piezoelectric material), and  highly sophisticated computer controls (obtained with fast DACs (digital analog converters, etc.). Field or Perturbation Sample Material SPM Probe Piezo Scanner Feedback Signal

2. SPM - Tree NanoScience & NanoTechnology

3. SPM – Basic Principles NanoScience & NanoTechnology Scanning Tunneling Microscope (STM) Scanning NearField Microsopye (SNOM) Scanning Force Microscope (SFM)

4. STM Background NanoScience & NanoTechnology In 1981, G. Binnig, H. Rohrer, Ch. Gerber and J. Weibel observed vacuum tunneling of electrons between a sharp tip and a platinum surface. The tunnel current is strongly distance,  z, dependent; i.e., A=4  (2m) 1/2 /h, with the tip-sample applied bias voltage, V bias, and the average potential barrier height . Tunneling occurs in the low bias voltage regime, i.e., ~0.1 V. At high bias voltage, i.e., V bias >  /e, the current flow is due to field emission (FE), i.e., (Fowler Nordheim Eq.)

5. STM Modes of Operation NanoScience & NanoTechnology  Constant height imaging or variable current mode (fast scan mode). The scan frequency is fast compared to the feedback response, which keeps the tip in an average (constant) distance from the sample surface. Scanning is possible in real-time video rates that allow, for instance, the study of surface diffusion processes.  Differential tunneling microscopy Tip is vibrated parallel to the surface, and the modulated current signal is recorded with lock-in technology.  Tracking tunneling microscopy Scanning direction is guided by modulated current signal (e.g., steepest slope).  Scanning noise microscopy Use current noise as feedback signal at zero bias.  Nonlinear alternating-current tunneling microscopy Conventionally, STM is restricted to non-conducting surfaces. A high frequency AC driving force causes a small number of electrons to tunnel onto and off the surface that can be measured during alternative half-cycles (third harmonics).

6. SAMPLE CANTILEVER PIEZO Scanning Force Microscopy (SFM) Photodiode LASER Topography NanoScience Tool AFM Friction Material Distinction A B Elasticity T g = 374K Glass Transition

7. Environmental chamber and heating /cooling stage for scanning probe microscope. SFM Environment NanoScience Tool

8. SFM Modes of Operation Lateral Force Microscopy Scanning Modulation Microscopy Force Approach Spectroscopy Contact Thermal Shear Modulation Analysis - Imaging (Material Distinction) - Rheological Analysis - Imaging (Material Distinction) - Rheological Analysis - Interaction Forces - Material Compliances - Rheological Boundary Layer - Thermally-Induced Transitions (e.g., glass transition) Modes of Operation: Provide: NanoScience Tool

9. SFM Modes of Operation Lateral Force Microscopy F 0 F static F dynamic x Scan Hysteresis FLFL Piezo Scanner/ Feedback SFM Tip Lateral Force: F L = k L *  x x scan directions kLkL xx Solid Interface Air or Liquid Environment Molecular Resolution Topography/Friction Molecular Stick Slip Rheological Analysis Material Distinction Lateral Force Rate and Thermal Analysis

10. SFM Modes of Operation Scanning Modulation Microscopy x resp x or z modulated piezo z resp Measured with two-phase lock-in technique Compares response signal to input signal Modulus and Contact Information Viscosity and Contact Information Shear Response and Thermal Analysis Molecular Resolution Topography Friction "Elasticity" - at constant applied load - with modulation frequencies exceeding feedback response PS Si 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 50.060.070.080.090.0100.0110.0120.0 Temperature (oC) Shear Response T g  95 o C 24 o C 94 o C 109 o C

11. linearly ramped z-Piezo x resp Probing Distance (D) x-modulation input Rheological Boundary Regime SFM Modes of Operation Force Approach Spectroscopy Normal Force Response F(D) R.M. Overney et al., Phys. Rev. Lett. 76, 1272-1275 (1996). F(D) 0 x resp (D) 0 Rheological Boundary Regime F D 0 x resp PS grafted Silicon in (a) water (poor solvent) (b) toluene (good solvent)

12. Entropic Structuring of Simple Liquids Principle Water  no boundary layer OMCTS  “monolayer" n-C 16 H 34  ~ 3 layers M. He et al., Phys. Rev. Lett. 88 p.154302/1-4 (2002). X - ray study: H. Kim et al., in Dynamics in Small Confining Systems V, edited by J.M. Drake et al., (Mat. Res. Soc. Symp. Proc. 2001) Vol 651, p T2.1 OMCS measurements are in agreement with x- ray reflectivity results (S. Sinha):

13.  x mod Shear Response Shear Displacement Sample Cantilever Tip  x L Heating/Cooling Stage  250350360370380400 0 TgTg  x L,  Contact Thermal Shear Modulation Analysis SFM Modes of Operation 7 27 87 67 47 127 107 MOLECULAR WEIGHT [Mn] 10 3 10 4 10 5 10 6 10 7 Tg ( O C ) C. Buenviaje, et al., ACS symposium series; 781 (2001): 76-92

14. NanoScience Tool SFM: Other Modes of Operation - Electrostatic Force Microscopy (EFM) Application:Study of the location and lifetime of surface charges on insulating surfaces. Procedure: Long-range electrostatic Coulombic forces are measured with a mechanically modulated conductive or clean silicon cantilever tip. An AC voltage is applied between the tip and the sample with a frequency w2 that is smaller than the mechanical modulation frequency w1 but larger than the gain of the feedback response. The AC voltage causes a charge and a mirror charge on the tip and the sample, respectively. The mechanically modulating tip is experiencing a Coulombic force gradient. For an uncharged surface the force gradient will oscillate at 2  2, whereas for a charged surface, the force gradient will be modulated at  2. A charge signal can be extracted by measuring the f and 2f signal with lock-in technique. The phase of that signal corresponds to the sign of the surface charge. - Magnetic Force Microscopy (MFM) Application: Measuring of surface magnetic structures Procedure: Using the non-contact mode with magnetically coated cantilever tips.

15. Environmental chamber and heating /cooling stage for scanning probe microscope (SFM). AFM/SFM Environment C

16. FORWARD SCAN REVERSE SCAN SAMPLE PHOTODIODE xx REFLECTED LASER BEAM CANTILEVER WITH LATERAL SPRING CONSTANT K L Friction Force Microscopy F 0 F static F dynam ic x FLFL FORWARD REVERSE Molecular Resolution Lateral Force Image (left) with Molecular Stick Slip behavior (below) Lateral force images on smooth surfaces may be used to distinguished materials displaying different coefficients of friction. FORWARD REVERSE SFM Modes

17. D linearly ramped z-Piezo x resp Probing Distance (D) x-modulation input Rheological Boundary Regime Normal Force Response F(D) R.M. Overney et al., Phys. Rev. Lett. 76, 1272-1275 (1996). F(D) 0 x resp (D) 0 Rheological Boundary Regime F D 0 x resp PS grafted Silicon in (a) water (poor solvent) (b) toluene (good solvent) SFM Modes Force Approach Spectroscopy

18. Tomlinson Model Molecular Stick- Slip Model (1920) R. M. Overney et al., Phys. Rev. Lett. 72, 3546 (1994) SFM/AFM on bilayer Lipid Film F ave =24 nN F ave =32 nN Molecular Stick-Slip NanoScience & Lubrication