Scanning Probe Microscopy Introduction

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Scanning Probe MicroscopyIntroduction
Brook Hamilton Application Scientist
www.pacificnanotech.com
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Outline

• History
• Instrumentation
• Applications

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Mechanical Profilers
Mechanically Scan A Probe Over A Surface
Z Height
X Distance
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Past Profilers
In 1929, Smaltz described a tracer instrument
using a tilting mirror and a long light arm to
obtain the necessary magnification.
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Past - Profilers
- 1955 - Vibrating tip profiler - From null point
to surface - Piezo activated Motion - Piezo
detection of surface
Becker U.S. 2,728,222
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Past TopoGraphiner
- 1972 - Non-contact profiler - X,Y,Z Piezo -
Constant current feedback
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Past Scanning Tunnelling Microscope
- 1982 - Needle Close to Surface - Reduce
Vibrations - x,y,z Piezoelectrics/Feedback
Pictures of Atoms !!!
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Atomic Force Microscope

• Piezoelectric Ceramics
• Sensor/Probe/Cantilever
• Modes

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Piezoelectric Ceramics

• Electrical Mechanical Transducer - Nanometers

Configured to Generate 3-D motion Tubes,
Tripods, Flexures
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Piezoelectric Ceramics
Hysteresis
Displacement, m
Ideal Actual
Voltage, V
Creep
Displacement, m
Time, s
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Piezoelectric Problems
Zoom to Feature
First Scan
Zoomed image
Second Scan
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Motion Control

• Piezoelectric Ceramic Calibration Sensor

Piezo
Motion Sensor
PID
Sensor Electronics
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Measurements
Step Height Standards - gt 18 nm Pitch Standards -
gt ½ Micron
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Accurate, Fast

• Zoom on feature, 5?mx5?m image
• 87?mx87?m image
• of polipeptide film

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Atomic Force Microscope - Sensor
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Cantilever/Probe
F - k D (hooks law)
F Force k Force Constant D Displacement E
Youngs modulus W Cant. Width T Cant.
Thickness L Cant. Length D Density
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Force Constant k EW T
4 L
Resonance Frequency f .162 E T
D L

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Probes - Resolution
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Probes
Si Probe
Nanotube Probe
Diameter lt 20 nm
Diameter 2 nm
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Probes Artifacts
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Imaging Modes
Continuous Mode Contact Mode Repulsive Region
Vibrating Mode Non-Contact Intermittent
Contact "Tap"
Material Sensing Modes Lateral Force Vibrating
Phase
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Continuous - Contact
Probe
Contact Point
Surface
Potential
Distance
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Potential Diagram
Repulsive Cantilever pushed up
Distance
Potential
AttractiveCantilever pulled down
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Continuous - Contact
Cantilever(Si) Force constant .2 N/m
Resonance 13 kHz
W/T/L 50/2/450 (µ)
Applications Hard Samples Learning to use
AFM Lower Resolution (gt50 nm)
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Vibrating Mode
Probe
Potential
Surface
Distance

• The tip is vibrated in and out of the potential
  associated with the surface.- Large or small
  amplitudes- Advantages are low forces, reduced
  lateral forces

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Vibrating Modes
Feedback set-point is selected to keep the
vibration amplitude constant while scanning.
Vibration Amplitude
Frequency
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Vibrating Modes
Cantilever Force Constant 42 N/M Resonant
Frequency 330 KHz W/T/L 30/4/12
5 (µ) Applications Sharp Probes Soft
Samples Features loosely held to a surface
It is best not to Tap the probe because this can
cause probe/sample damage.
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Vibrating Phase

• The probe is vibrated as it is scanned across the
  surface
• Monitor phase changes between the driving and
  senor signal

Driving Signal
AFM Sensor Signal
White Region
Yellow Region
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Vibrating Mode - Example
Topography
Vibrating Phase
Triblock co-polymer styrene butadyene
styrene(SBS) Scan range 1.5 X 1.5 µ
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Lateral Force (Frictional force)
Torsional motion of Cantilever
Scan Direction
Topography profile Friction profile
High friction Low Friction
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Example
Topography
Lateral Force
6 X 6 µ scan of composite sample with coating
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AFM Applications
High Technology - Semiconductor - Data
Storage - Life Sciences Physical Sciences -
Physics - Polymers - Chemistry -
Materials Life Sciences - Bio-molecules -
Bio-materials - Cells
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Conclusion

• AFM is derived from profiler techniques
• Instrumentation Scanners(piezoelectric) Probes
  Scanning modes
• Applications in all areas