The Blind men and the ElephantIntroduction to SPMs

By Dr. WhyX (Yu Xi)

Email: WhyX@cambolt.com 2005.9

The Blind men and the Elephant

Wall?

Spear?

Snake?

Fan?

Tree?

Rope?

John Godfrey Saxe (1816 -1887)

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.

When we are blind…?

• Microscope: Helping people to see since 1604

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)

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

Tunneling Effect

2 modes

Questions HERE:

• What’s the difference between those 2 modes?

• What are they used for?

• Advantages? Disadvantages?

STM Images

Flat Gold Surface (Oops, tip crashed!!)

What else we have?

• SFM (AFM) – Atomic Force

• MFM – Magnetic Force

• SCM – Capacitance

• …

Commercial AFM/MFM

Force Distance Curve

AFM/MFM Images

IBM’s 20G Hard disc (can u read the bits?)

What the Hell is Capacitance?

: Dielectric Permittivity

AFM/SCM(dC/dV) Images

SCM test Sample by DI’s Dimension 3000 at room temperature

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

Summary 1

• When we can’t see, we have to feel.• SPM = Scanning + Probe + PC• Different probes = Different SPMs

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

A Sharp Tip

A Typical Tungsten (W) Tip

A Force Sensor: Tuning Fork

Tuning fork with tungsten tip

An AFM/MFM/SCM Probe

A Real One…

A Scanning Tube

PTZ: PbZrO3 and PbTiO3 mixture

Secret equation here:

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

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?

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

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

Low-T AFM Image

Gold thin film acquired in superfluid helium at 1.7k and magnetic filed of 10T

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.

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

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.

Low-T SCM data analysis

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

Thank u 4 ur attention!Questions Please!

whyx@cambolt.com

Lift-mode explained