Present Erfan Zaker EsfahaniEmail aref_z_e@yahoo.comCourse NanotechnologyNumber 09131299216Lecturer Dr. Monajati

Local density of states (LDOS) is a physical space-resolved quantity that describes the number of states at each energy level that are available to be occupied. According to crystal's structure, this quantity can be predicted by computational methods, as for example with density functional theory

Artifact is any perceived distortion or

other data error caused by the instrument of observation

..Terms DefinitionTerms Definition

.Motivation.Motivation

.Historical Overview.Historical Overview

.SPM Overview.SPM Overview

.AFM Overview

.SPM Software.SPM Software

.Summary.Summary

..Terms DefinitionTerms Definition

.Motivation.Motivation

.Historical Overview.Historical Overview

.SPM Overview.SPM Overview

.AFM Overview

.SPM Software.SPM Software

.Summary.Summary

.Surface is the shell of a macroscopic object (the inside) in contact with its environment (the outside world). An interface is the boundary between two phases. Object inside is called bulk

.In large objects with small surface area A to volume V ratio (A/V) the physical and chemical properties are primarily defined by the bulk

.In small objects with a large A/V-ratio the properties are strongly influenced by the surface

Hydrophobic effectHydrophobic effect

WaterWater

Hydrophobic materialHydrophobic materialSurface structureSurface structure(20-100μm)(20-100μm)

Bulk

Source DrainGate

Current flow near the surfaceCurrent flow near the surface

In modern semiconductor devices surface is In modern semiconductor devices surface is dominantdominant

LayerLayer byby layer …layer …

Surface Surface byby surfacesurface ……

surface topography valley,

planes, hills

• physical materials behavior (conducting / insulating)

• polarity (hydrophilic / hydrophobic)• tribological behavior (friction on "rough" or

"smooth" surface)• physical surface behavior (reflectivity)

• understanding and inhibition of corrosion• chip manufacturing / microelectronics• hard disks (anti-friction, ultra-smooth,...)• biological surfaces (patterned cell growth)• sensors (chemical, biological, electrical)• modification of anti-reflection (displays)• modification of wetting (inkjet printing)

• According to all the mentioned before our motivation as electrical engineers for surface research is clear. The modern physical materials properties, in general, affected by surface.

• Moreover, we want not only passively receive information about the surface, but actively affect on it topology, moving the atoms

Microscopy small, – see

Scanning Probe Microscopy (SPM) is a branch of microscopy that forms images of surfaces using a physical probe that scans the specimen. SPM able to receive 3D surface topography

Local density of states (LDOS) is a physical space-resolved quantity that describes the number of states at each energy level that are available to be occupied. According to crystal's structure, this quantity can be predicted by computational methods, as for example with density functional theory

Artifact is any perceived distortion or other data error caused

by the instrument of observation

Input transducer or sensorConvert nonelectrical signal to electrical one

Output transducer or actuatorConvert electrical signal to nonelectrical one

PiezoceramicCeramic that convert electrical field to mechanical deformation and vice versaPiezoelectric properties

are time-depended

SPM Scanning Probe MicroscopeSTM Scanning Tunneling MicroscopeAFM Atomic Force MicroscopeSFM Scanning Force MicroscopeFFM Force-Modulated AFMLFM Lateral Force Microscope MFM Magnetic Force Microscope SThM Scanning Thermal MicroscopeEFM Electrical Force Microscope

ActuatorActuator

SensorSensor

ComputerComputer

ProbeProbe

SampleSample

The blind mouse can’t see the object (sample), but using the stick (probe), he can scan it.Arm skin (sensor) send the received from the probe information to the brain (computer), the computer “see” the picture, if it need receive additional information about the sample (decision done using feedback), it send requirement to arm muscle (actuator), arm carefully moves the probe to required coordinate and vice versa

All of the SPM techniques are based upon scanning a probe (typically called the tip, since it literally is a sharp metallic tip) just above a surface whilst between scanned surface and probe exist interactionThe nature of this chosen interaction defines a device accessory to this or that type within the family of Scanning Probe MicroscopeThe information on a surface is taken by fixing (by means of feedback system) or monitoring of interaction of a probe and the sample

Surface divided to matrix of N rows by M columns

Scanning performed row by row, as result we receive per each couple of coordinates {x i,yj}, vector with measurement results that described surface at this point

Control SystemScanning System

We will present scanning probe microscopes based on two kind of iteration1.Iteration is electrical current STM2.Iteration is atomic force AFM/SFMIn general, as mentioned, SPM have two modes, defined by tip movement over the surface1.Fixed probe Z coordinate, iteration or parameter depended on iteration monitoring 2.Fixed iteration, height change monitoring

Cantilever

LaserPhoto

detector

Control Electronics

Computerconnection

Sample

Control voltage signal

Piezoelectric tubeswith electrodes

Cantilever

Laser

Photodetector

Cantilever is a beam supported on only one end

t

w

L

Force

Tip to sample distance

repulsive force

attractive force

contact

non-contact

tapping

phase

1. Contact Mode2. Friction mode3. Tapping Mode4. Phase mode

Contact (repulsive) mode: tip makes soft "physical contact" with the

sample, the contact force causes the cantilever to bend to accommodate

changes in topography

Stoney's formula

2

2

L

E

v1σ3δ

m

kω

L4

ωEt

δ

Fk o3

3

σ is applied stress

E, v are known physical parameters

t

w

L

δ

L

F

Lateral force / friction mode: AFM cantilever incontact mode is laterally deflected in the sampleplane due to scanning motion perpendicular to cantilever axes, lateral deflection is measuredand gives information on surface material apart from topography

Intermittent contact: AFM cantilever is vibrated near the surface of a sample with spacing on the order of tens to hundreds of angstromsIn this case the oscillator is non linear, mathematical calculation is pretty complicated, it is out of scope of this presentation

Phase mode: AFM cantilever is vibrated near the surface of a sample with known amplitude frequency equal to resonance cantilever one . Compare phase of driving signal and cantilever response

F

x

z

ωtcosAF

x

z

ωtcosA

QF

karctg

ωtcosZz

FωtcosAzωzβ2z

ω

20

0

Image of a Si surface imaged with a force sensor. In the left half of the image, the cantilever does not oscillate, in the right half it oscillates with an amplitude of 0.09 nm, yielding a double image of every atom

Image size 3.3 nm x 3.3 nm.

AFM contact scanning

Scan Scan

after scanningbefore scanning

• Repeat the scan to ensure that it looks the same.

• Change the scan direction and take a new image.

• Change the scan size and take an image to ensure that the features scale properly.

• Rotate the sample and take an image to identify tip imaging

• Change the scan speed and take another image

• User-friendly interface, basic Windows tools• Offline simulation tool• Calibration tool, ability to see results• Variety of supported formats• Control unit monitoring• Filtering control• Mathematical tools• Programming tools• 3D studio – capture and editing images and

videos in real time

SPM standardization has only recently begun

as part of an effort by the

International Organization for Standardization (ISO) !!!

25 years of scanning probe microscopy www.nanowerk.com , 2007

Today, Jan 2008, 25 years of STM, UNDER DEVELOPMENT