Scanning Probe Microscopy

Front 1

Used to study the properties of surfaces at the atomic level
• Consists of scanning across a surface with an extremely sharp tip (3-50 nm radius curvature)
• Tip is usually mounted on a flexible cantilever – to follow surface profile
• Interactions between sharp tip and surface provide topographic information

Back 1

Scanning Probe Microscopy

Front 2

AFM (Atomic Force Microscopy), MFM (Magnetic Force Microscopy), and EFM (Electrostatic Force Microscopy) are examples of what?

Back 2

Scanning Force Microscopy (SFM)

Front 3

The probe is the _____ component of a SPM – Different probes can measure ______ properties of the sample. Probe determines the _______ applied to the sample and the ________ resolution of the system. Higher aspect ______ tips provide higher ______.

Back 3

critical, different, force, ultimate, ratio, resolutions

Front 4

The most common probes are ________. They are highly suited to measure the surface ________ of a sample. Using different ________ on the cantilevers different properties of the sample can be measure.

Back 4

cantilevers, topography, coating

Front 5

powerful technique for viewing surfaces at the atomic level
• invented in 1981 by Gerd Binnig and Heinrich Rohrer (at IBM Zürich)
• Nobel Prize in Physics in 1986
• good resolution is considered to be 0.1 nm lateral resolution and 0.01 nm depth resolution
• can be used not only in ultra high vacuum but also in air and various other liquid or gas ambients, and at temperatures ranging from near zero Kelvin to a few hundred degrees Celsius
• based on the concept of quantum tunneling

Back 5

Scanning Tunneling Microscopy (STM)

Front 6

When a conductive probe is brought ~_____ away from a sample and a ______ voltage is applied between the tip and the sample, then _________ current flows through the 10Å gap
• The tunneling current varies with the tip-to- sample __________, and the __________ properties of the surface and tip materials
• A few percent variation in tunneling current corresponds to a few ________ of an Angstrom change in separation (very high sensitivity)
• Because of ______ of tunneling current on the material, STM _________ is possible
• STMs can not image _______ materials.
• Can operate in two possible modes constant _____ or constant ________

Back 6

10Å,bias,tunneling,spacing, electronic, hundreths, dependence, spectroscopy, insulating, height, current

Front 7

Constant Height Mode

Back 7

In C-H mode, the magnitude of the Tunneling current is used to generate the surface topography map.

Front 8

Constant Current Mode

Back 8

In C-C mode, the position of the piezo scanner is used to generate the surface topography map.

Front 9

AFM has tip at end of _______ which _________ in response to force between tip & _________.

Back 9

cantilever, bends, surface

Front 10

Most AFMs use ________ technique to detect _______ of cantilever.

Back 10

optical, deflection

Front 11

Two primary modes for AFM are _______ and _______.

Back 11

Contact (measure repulsive forces), Non-contact (measure attractive forces)

Front 12

Cantilevers and probe tips are typically made of __________.

Back 12

SixNy

Front 13

Cantilevers and probe tips have spring ________ in the range of _________ N/m

Back 13

constants, 1-40

Front 14

Cantilevers and probe tips have forces from _________ to _________.

Back 14

1nN,20uN

Front 15

Tips range from a _________ to very sharp, high _______ ratio tips, to flat punches.

Back 15

pyramid, aspect

Front 16

The higher the aspect ratio the better the ___________.

Back 16

resolution

Front 17

Contact mode measures the _________ by sliding the probe tip across a surface.

Back 17

topography

Front 18

What are the different kinds of Non-contact modes?

Back 18

Tapping mode, Phase imaging, Lift Mode, Lateral Force Microscopy, Magnetic Force Microscopy

Front 19

measures topography by oscillating the probe tip over a surface to reduce sample damage.

Back 19

Tapping mode

Front 20

shows the contrast caused by differences in surface adhesion and viscoelasticity, uses Tapping mode.

Back 20

Phase imaging

Front 21

two pass technique that separately measures topography and another selected property (magnetic force).

Back 21

Lift mode

Front 22

measures frictional forces between the probe tip and the sample surface.

Back 22

Lateral Force Microscopy

Front 23

measures magnetic force gradient and distribution above the sample surface using amplitude, phase, or frequency shifts.

Back 23

Magnetic Force Microscopy

Front 24

In the absence of external fields the dominant forces are:

Back 24

Contact & short range repulsive interactions
– Van der Waals forces
– Adhesion
– Capillary forces

Front 25

In contact mode the AFM cantilever is held a few ________ away from the sample surface.

Back 25

Angsrtoms

Front 26

In contact mode the total force exerted by the tip on the sample is the sum of __________ and _______ forces and must be _________ by the repulsive forces.

Back 26

capillary, cantilever, balanced

Front 27

The _________ of the force exerted on the sample varies from _____ to ________ nN.

Back 27

magnitude, 100, 1000

Front 28

In contact mode the AFM can operate in ___________ or _______________.

Back 28

constant-height, constant-force

Front 29

What is a force distance curve?

Back 29

A Force-Distance curves is a plot of tip- sample force vs. tip-sample distance.

Front 30

In a ________, the cantilever remains __________ until it is close to the sample surface to experience the attractive ___________ force and snap to the surface.

Back 30

vacuum, undeflected, van der Waals

Front 31

In air, the cantilever _________ curve changes because of a water ________ on the surface. The water layer exerts strongly attractive _________ forces.

Back 31

retraction, monolayer, capillary

Front 32

If a ___________ layer is present, multiple _______ occur. The ________ and ________ of the snap-backs depend on the __________ and _______ of the contamination layer.

Back 32

contamination, snap-backs, position, amplitude, viscosity, thickness

Front 33

In Non-contact and Tapping mode the AFM cantilever is _________ near its _______ frequency (100-400 kHz) and at _______ near the surface.

Back 33

oscillated, resonant, 10-100 A

Front 34

In Non-contact and Tapping mode the AFM _______ detects changes in the ________ frequency or _______ of the ________ as the tip comes near the sample surface.

Back 34

scanner, resonance, amplitude, cantilever

Front 35

Most AFM cantilevers are made of _____, _______ and ______ and are coated in _______ or _______.

Back 35

silicon, silicon nitride, silicon dioxide, gold, aluminum

Front 36

__________ cantilevers provide good _________ stability under ________ and are preferred for ________ AFM

Back 36

V-shaped, mechanical, torsion, contact

Front 37

_________ cantilevers have low _________ stability under _________ and are used to measure _________ or ________ forces.

Back 37

I-beam, mechanical, torsion, frictional, torsional

Front 38

__________ cantilevers help increase the ____________ ratio in __________ AFM and avoid _________ of the tip to sample.

Back 38

Stiffer, signal-to-noise, non-contact, adhesion

Front 39

Cantilevers tips can be _________ or __________.

Back 39

conical, pyramidal

Front 40

Most tips have R ≈ __________, while sharpened tips have R ≈ __________.

Back 40

15-50 nm, 5-10 nm

Front 41

For a surface with roughness amplitude, ______, and wavelength, ________, the __________ of the tip should be _________ than the ________ slope of the surface.

Back 41

A, λ, slope, smaller, maximum

Front 42

Tip radius, R, must be _________ than the _______ radius of the _________ of the surface.

Back 42

smaller, local, curvature

Front 43

High-resolution AFM imaging can be achieved by using _________ CNTs mounted on common _______ and _______ AFM tips and used as _______ probes.

Back 43

multiwalled, conical, pyramidal, ultra-sharp

Front 44

CNT AFM tips have a __________ diameter and ____________ length.

Back 44

5-100 nm, 2000-5000 nm

Front 45

Sharp AFM tips can be manufactured via ____.

Back 45

FIB

Front 46

Hydrophobic diamond-like carbon tips with R= ______ have been grown at the end of ___ AFM tips and used to take images.

Back 46

1 nm, Si

Front 47

The AFM has the ability to show surface ________ with ________________ clarity.

Back 47

features, unprecedented

Front 48

The AFM can image any _________ surfaces in air or in _________.

Back 48

rigid, liquid

Front 49

The AFM can _________ very tiny features at __________ and _____________.

Back 49

resolve, atomic, molecular levels

Front 50

AFM's can image _______ field of view (125 microns).

Back 50

large

Front 51

AFM's can examine _________ surfaces (vertical range > 5 microns).

Back 51

rough

Front 52

The AFM can produce a ______ topography of the surface.

Back 52

3D

Front 53

The AFM does NOT require sample _______ or ________ preparation

Back 53

coating, expensive

Front 54

The highest resolution of an _______ microscope is about a ________ of a wavelength in diameter, which is about _______ nanometers (nm).

Back 54

optical, third, 200

Front 55

The _________ of SEMs is about _______ and it provides a large _______ of field.

Back 55

resolution, 1-5 nm, depth

Front 56

The resolution of ________ can approach _________ resolution (< 0.1 nm).

Back 56

TEMs (Transmission Electron Microscopes), atomic

Front 57

The _________ and ______ are used for surface imaging with atomic resolution. Disadvantages are ______ scanning speeds.

Back 57

STM, AFM, slow