1. آشنایی با میکروسکوپ نیروی اتمی Dr. Janelle Gunther March 10, 1998 ACS Group and MENs, Beckman Institute adapted from the world wide web page at http://www.di.com Digital Instruments, Santa Barbara, CA

2. میکروسکوپ روبشی با پروب (SPM) A family of microscopy forms where a sharp probe is scanned across a surface and some tip/sample interactions are monitored Scanning tunneling Microscopy (STM) Atomic Force Microscopy (AFM) contact mode contact mode non-contact mode non-contact mode TappingMode TappingMode Other forms of SPM Lateral force Lateral force Force modulation Force modulation Magnetic or electric force Magnetic or electric force surface potential surface potential scanning thermal scanning thermal phase imaging phase imaging

3. SPMدستگاه چندکاره SPMدستگاه چندکاره

4. General AFM “Beam Deflection” Detection Used for Contact Mode, Non-contact and TappingMode AFM Laser light from a solid state diode is reflected off the back of the cantilever and collected by a position sensitive detector (PSD). This consists of two closely spaced photodiodes. The output is then collected by a differential amplifier Angular displacement of the cantilever results in one photodiode collecting more light than the other. The resulting output signal is proportional to the deflection of the cantilever. Detects cantilever deflection <1A Solid State Laser Diode Cantilever and Tip A B

5. روبشگر پیزوالکتریک SPM scanners are made from a piezoelectric material that expands and contracts proportionally to an applied voltage. Whether they expand or contract depends upon the polarity of the applied voltage. Digital Instruments scanners have AC voltage ranges of +220 to -220V. 0 V - V + V No applied voltage Extended Contracted l In some versions, the piezo tube moves the sample relative to the tip. In other models, the sample is stationary while the scanner moves the tip. l AC signals applied to conductive areas of the tube create piezo movement along the three major axes.

6. مدل تماسی AFM A tip is scanned across the sample while a feedback loop maintains a constant cantilever deflection (and force) The tip contacts the surface through the adsorbed fluid layer. Forces range from nano to micro N in ambient conditions and even lower (0.1 nN or less) in liquids.

7. Tapping Mode™ AFM A cantilever with attached tip is oscillated at its resonant frequency and scanned across the sample surface. A constant oscillation amplitude (and thus a constant tip-sample interaction) are maintained during scanning. Typical amplitudes are 20-100nm. Forces can be 200 pN or less The amplitude of the oscillations changes when the tip scans over bumps or depressions on a surface.

8. مدل غیرتماسی AFM مدل غیرتماسی AFM The cantilever is oscillated slightly above its resonant frequency. Oscillations <10nm The tip does not touch the sample. Instead, it oscillates above the adsorbed fluid layer. A constant oscillation amplitude is maintained. The resonant frequency of the cantilever is decreased by the van der Waals forces which extend from 1-10nm above the adsorbed fluid layer. This in turn changes the amplitude of oscillation.

9. AFMمزایا و معایب روشهای سه گانه AFMمزایا و معایب روشهای سه گانه Contact Mode Advantages: Advantages: High scan speeds The only mode that can obtain “atomic resolution” images Rough samples with extreme changes in topography can sometimes be scanned more easily Disadvantages : Disadvantages : Lateral (shear) forces can distort features in the image The forces normal to the tip-sample interaction can be high in air due to capillary forces from the adsorbed fluid layer on the sample surface. The combination of lateral forces and high normal forces can result in reduced spatial resolution and may damage soft samples (i.e. biological samples, polymers, silicon) due to scraping TappingMode AFM Advantages: Advantages: Higher lateral resolution on most samples (1 to 5nm) Lower forces and less damage to soft samples imaged in air Lateral forces are virtually eliminated so there is no scraping Disadvantages : Disadvantages : Slightly lower scan speed than contact mode AFM

10. Lateral Force Microscopy The probe is scanned sideways. The degree of torsion of the cantilever is used as a relative measure of surface friction caused by the lateral force exerted on the probe. Identify transitions between different components in a polymer blend, in composites or other mixtures This mode can also be used to reveal fine structural details in the sample.

11. Lateral Force Microscopy Magnetic recording head Al oxide grains and contamination 800nm scan Natural rubber/ EDPM blend 20 micron scan Polished poly- crystalle silicon carbide film. Grain structures 30 micron scan Images/photo taken with NanoScope® SPM, courtesy Digital Instruments, Santa Barbara,CA

12. آنالیز فازی Accessible via TappingMode Oscillate the cantilever at its resonant frequency. The amplitude is used as a feedback signal. The phase lag is dependent on several things, including composition, adhesion, friction and viscoelastic properties. l Identify two-phase structure of polymer blends l Identify surface contaminants that are not seen in height images l Less damaging to soft samples than lateral force microscopy

13. آنالیز فازی Compositepolymer imbedded in a matrix 1 micron scan Bond pad on an integrated circuit Contamination 1.5 micron scan MoO 3 crystallites on a MoS 2 substrate 6 micron scan Image/photo taken with NanoScope® SPM, courtesy Digital Instruments, Santa Barbara,CA

14. میکروسکوپ با نیروی مغناطیسی Special probes are used for MFM. These are magnetically sensitized by sputter coating with a ferromagnetic material. The cantilever is oscillated near its resonant frequency (around 100 kHz). The tip is oscillated 10’s to 100’s of nm above the surface Gradients in the magnetic forces on the tip shift the resonant frequency of the cantilever. Monitoring this shift, or related changes in oscillation amplitude or phase, produces a magnetic force image. Many applications for data storage technology

15. میکروسکوپ با نیروی مغناطیسی Overwritten tracks on a textured hard disk, 25 micron scan Domains in a 80 micron garnet film Image/photo taken with NanoScope® SPM, courtesy Digital Instruments, Santa Barbara,CA

16. Force Modulation Imaging Oscillate the cantilever vertically at a rate that is significantly faster than the scan rate. The amplitude of the oscillations changes in response to the sample stiffness. Used in conjunction with LiftMode to separate topography and elasticity data.

17. Force Modulation Imaging

18. روشهای دیگر Scanning capacitance microscopy Apply a constant amplitude sine wave voltage to the sample. The image is then reconstructed from the changes in the amplitude of the capacitance oscillations. Apply a constant amplitude sine wave voltage to the sample. The image is then reconstructed from the changes in the amplitude of the capacitance oscillations. Location of defects in wafers (pinning of electrical carriers) Location of defects in wafers (pinning of electrical carriers) Image carrier concentration Image carrier concentration Scanning thermal microscopy Uses a temperature sensitive probe with a special holder. Uses a temperature sensitive probe with a special holder. Location of “hot-spot” defects in semiconductor wafers Location of “hot-spot” defects in semiconductor wafers 90 micron scan size Image/photo taken with NanoScope® SPM, courtesy Digital Instruments, Santa Barbara,CA

19. روشهای دیگر Nanoindenting and scratching A diamond tip is mounted on a metal cantilever and scanned either with contact or TappingMode. A diamond tip is mounted on a metal cantilever and scanned either with contact or TappingMode. Indenting mode presses the tip into the sample Indenting mode presses the tip into the sample Scratch mode drags the tip across the sample at a specific rate and with a specified force. Scratch mode drags the tip across the sample at a specific rate and with a specified force. The use of TappingMode makes it possible to simultaneously image soft samples. The use of TappingMode makes it possible to simultaneously image soft samples. Imaging of biological samples cells, DNA (TappingMode in solution) cells, DNA (TappingMode in solution)