the blind men and the elephant introduction to spms by dr. whyx (yu xi) email: [email protected]...
TRANSCRIPT
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The Blind men and the ElephantIntroduction to SPMs
By Dr. WhyX (Yu Xi)
Email: [email protected] 2005.9
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The Blind men and the Elephant
Wall?
Spear?
Snake?
Fan?
Tree?
Rope?
John Godfrey Saxe (1816 -1887)
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What does this Allegory tells?
• When we can’t see, we have to feel.
• Something is better than nothing.
• Different VALID visions maybe only a part of the COMPLETE picture.
• Put them together at RIGHT place, we may have the picture.
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When we are blind…?
• Microscope: Helping people to see since 1604
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Helping people to see since 1604
• 1604-1st optical microscope: Hans Janssen (Holland)
• 1938-1st TEM(Transmission Electron Microscope): Max Knoll, Ernst Ruska (German)
• 1952-1st SEM(Scanning Electron Microscope): Charles Oatley (England)
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When we can’t see, we have to feel.
• 1981- 1st STM (Scanning Tunneling Microscope) Gerd Binning and Heinrich Rohrer (IBM Zurich). Won Nobel Prize in 1986.
• SPM=Scanning Probe Microscope.• SPM=Scanning + Probe + PC• SPM=Feel the sample and display in the
PC
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Tunneling Effect
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2 modes
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Questions HERE:
• What’s the difference between those 2 modes?
• What are they used for?
• Advantages? Disadvantages?
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STM Images
Flat Gold Surface (Oops, tip crashed!!)
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What else we have?
• SFM (AFM) – Atomic Force
• MFM – Magnetic Force
• SCM – Capacitance
• …
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Commercial AFM/MFM
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Force Distance Curve
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AFM/MFM Images
IBM’s 20G Hard disc (can u read the bits?)
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What the Hell is Capacitance?
: Dielectric Permittivity
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AFM/SCM(dC/dV) Images
SCM test Sample by DI’s Dimension 3000 at room temperature
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Which are which?
1. substrate (Si)
2. implanted areas
3. gate (poly-Si)
4. a lower n-type concentration
5. p-n junction
6. p-type
7. n-type source/drain implants
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Summary 1
• When we can’t see, we have to feel.• SPM = Scanning + Probe + PC• Different probes = Different SPMs
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SPM DIY
List of components:1. A Sharp Tip
2. A Force Sensor
3. A Scanning Tube
4. A Feed-back Loop
5. A PC
6. Some Wires
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A Sharp Tip
A Typical Tungsten (W) Tip
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A Force Sensor: Tuning Fork
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Tuning fork with tungsten tip
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An AFM/MFM/SCM Probe
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A Real One…
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A Scanning Tube
PTZ: PbZrO3 and PbTiO3 mixture
Secret equation here:
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Feed-back Control
FunctionGenerator
Preamplifier Lock-inAmplifier
PLLControl
Scanning,Image Acquisition,
Height Control
Scan Tube
Sample
f
f
z
f0, APhase-locked
loop
Height controlloop
PLL noise level ~ 10mHz
A
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Questions HERE:
• Why moving the sample?
• Why we need SHARP tip? How sharp?
• Why tuning fork?• Why 1 tine of the
tuning fork is immobilized?
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Tuning Fork Advantages
• Low power dissipation (~ pW)• Cheap and readily available• No need for optics inside cryostat -
eliminates misalignment problems on cooldown
• No laser light - important for semiconductors at low temperatures
• Low amplitude, self-sensing motion• High Q
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Going Deep Deep Cold
Difficulties at Low Temperature:•Sample and probe alignment•Distance between the sample and the probe•Temperature/pressure changes introduces noise•High voltage discharge in helium gas
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Low-T AFM Image
Gold thin film acquired in superfluid helium at 1.7k and magnetic filed of 10T
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Low-T AFM/MFM Images
Comparison of topography and magnetic force images with and without Q control at 140K in vacuum, Sample is a piece of commercial Zip disc.
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MFM images(10µm square) of multi-layer Co/Pd thin film sample for external magnetic fields of (1)-0.5T, (2)-0.4T, (3)-0.3T, (4)-0.2T, (5)-0.1T, (6)0T at 113K
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Low-T SCM images
upper row: (left)Topographic (middle)capacitance and (right) corrected capacitance images at 1.7K in superfluid helium.(1.2µm by 0.75µm area) lower row: line profile of line 80 in corresponding images.
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Low-T SCM data analysis
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Future work
• Plenty: blah blah blah…
• Profiling of quantum Hall edge states
• Study dopant distributions in GaN
• Magnetic force microscopy of (Ga,Mn)As (Tc ~ 100K)
• Numerous other applications
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Lift-mode explained