afm technique

8/6/2019 Afm Technique

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Non Linearity

Nonlinearity is the behavior of a circuit, particularly

an amplifier, in which the output signal strength

does not vary in direct proportion to the input signal

strength.

In a nonlinear device, the output-to-input amplituderatio (also called the gain) depends on the strength

of the input signal.

Non Linearity

Suppose the applied voltages start from zero andgradually increase to some finite value.

If the extension of the piezoelectric material is

plotted as a function of the applied voltage, theplot is not a straight line, but an s-shaped curve.

The straight line in the graph is a linear fit to thedata.

Non Linearity

Hysteresis

It refers to the system that exhibit pathdependence or rate independent memory.

Hysteresis means lagging of an effect behind itscause. It occurs in magnetic, ferromagneticmaterials as well as in elastic, electric behavior of materials in which a lag occur in application and

removal of force or field.

Hysteresis Graph

Hysteresis

FIB (Focused Ion Beam)

It is a technique used particularly in the

semiconductor materials.

An FIB setup uses a focused beam of ions.

The ion beam allows the milling of small holes inthe sample at well localized sites, so that cross-

sectional images of the structure can be obtained

or that modifications in the structures can be

Focused Ion Beam

Focused Ion Beam Technology for

Local material removal down to sub-100 nm

Local deposition of conducting and insulating

layers in direct writing mode Process control by high resolution secondary

electron imaging.

Used in semiconductor and material science field

site specific analysis.

deposition and ablation of material.

Applications of FIB

Cross-sectional imaging through semiconductor devices (or any layered structure)

Modification of the electrical routing on

semiconductor devices Preparation for physico-chemical analysis

Preparation of specimens for transmissionelectron microscopy (TEM)

Preparation of samples for Atom Probe analysis

Non-semiconductor applications

Scanning Capacitance Microscopy

Scanning capacitance Microscopy is a techniquefor imaging of surface capacitance distribution.

Measures capacitance variations between aconductive probe and semiconductor sample

while scanning in contact mode Produces a 2D image.

Sample prep is critical due to sensitivity of thetechnique.

Surface must be able to withstand contact mode

imaging.

Scanning Capacitance

Microscopy - Implementation

� SCM can function even through an insulatinglayer, a finite conductivity is not required tomeasure electrical properties

Use Contact Mode AFM System.

Use Metal Coated (Conducting) Tip

Add Capacitance Resonator Circuit

Measure Capacitance of Tip/Sample System atFrequency of Applied Bias.

Resolution of SCM is about 2 nm. SCM require careful preparation of analyzed

surface which is supposed to be almost flat.

Scanning Spreading Resistance

Microscopy (SSRM)

Scanning spreading resistance microscope isused for material characterization in terms of localresistance.

In SSRM, conductive probe is used and a bias

voltage is applied to the tip and resulting current

through the sample is measured. R(x,y)= V/ I

Where,

R (x,y)= Resistance of sample at point (x,y)V = applied voltage

I= Current

Scanning Thermal Microscopy

(SThM)

Scanning Thermal Microscopy (SThM) is anadvanced SPM mode intended for simultaneousobtaining nanoscale thermal and topography

images. The cantilever used in SThM is made up of two

different materials which respond differentlyagainst changes in thermal conductivity of thesample and cause the cantilever to deflect.

This gives the SThM image. Operates in contact mode AFM using specially

modified silicon nitride cantilevers.

SThM«.

SThM allows thermal measurements at thenanoscale.

These measurements can include:-

1. Temperature.

2. Thermal properties of materials.3. Thermal conductivity.

4. Heat capacity.

5. Glass transition temperature.

6. Latent Heat.

7. Enthalpy.

SThM..

NT-MDT¶s thermal probes provide better than 100

nm lateral resolution for both topography and

thermal images.

At NT-MDT system, we have the possibility to scan

a sample at a wide temp range of -30°c to +300°c

A type of SPM.

The probe is a sharp tip of optical fiber put to thesurface close enough to provide near field effects.

Fiber conduct light which is passing through a subwave aperture, forms an image free of far fieldoptics limitation.

Allows nano-scale object optical investigationovercoming the optics diffraction limits.

Modes of SNOM

Luminescence Mode

Reflection Mode

Transmission Mode

Transmission Mode SNOM

Reflection Mode SNOM

Luminescence Mode SNOM

Limitation of SNOM

Very low working distance and extremely shallow

depth of field.

Limited to study of surfaces.

Not conducive for studying soft materials,especially under shear force mode.

Long scan times for large sample areas or high

resolution imaging.

R AM AN EFFECT

Raman scattering or the Raman effect is

the inelastic scattering of a photon.

It was discovered by Sir Chandrasekhar Venkata

Raman. He received the NOBEL Prize in 1930 for his work

on scattering of light.

Two Type of Raman scattering:-

Stokes scatteringAnti Stoke scattering

R AM AN SC ATTERING

Highly Ordered Pyrolytic Graphite.

HOPG is a pyrolytic graphite with an angular spread of the c-axes of the crystallites of less

than 1 degree. HOPG, is a relatively new form of high purity

carbon and provides microscopists with arenewable and smooth surface.

Unlike mica, HOPG is completely non-polar, andfor samples where elemental analysis will also bedone, it provides a background with only carbon inthe elemental signature.

The modern-day material known as HOPG can be

traced back to what at one time was called "Kish

graphite"

Atomic-level images of HOPG can be used tocalibrate the STM for high-resolution imaging.

The extreme smoothness of HOPG gives results in

a featureless background, except at atomic levels

of resolution.

Can also serve as a substrate for other materials

that can be image by STM.

Force Modulation

Based on contact mode AFM.

The probe is scanned over the surface in x-y raster

scan rate.

The feedback loop maintains a constantcantilever deflection, and consequently a,

substantial constant force on the sample.

Force Modulation

On the stiff areas of the sample surface depth of

indentation will be smaller, and on the compliant

areas larger.

Tracing of the sample surface relief height isconducted by the usage of the averaged cantilever

deflection in the feedback circuit.

s = · (Dz/D - 1) .

By finding elasticity of sample surface one can

also find modulus of elasticity.

Phase Imagining

A powerful extension of tapping Mode AFM.

Provides nanometer scale about surface structure.

Phase imaging is a powerful tools for mappingvariation in sample properties at very highresolution.

Oscillate the cantilever at its resonant frequency.

The amplitude is used as a feedback signal.

Phase Imagining

The phase lag is dependent on several things,including composition, adhesion, friction andviscoelastic properties

Identify two-phase structure of polymer blends

Identify surface contaminants that are not seen inheight images

Less damaging to soft samples than lateral forcemicroscopy

Phase Imagining

Magnetic Force Microscopy

A two pass Technique.

Used for analysis of magnetic properties of sample.

Special probes are used for MFM. These aremagnetically sensitized by sputter coating with aferromagnetic material.

The cantilever is oscillated near its resonantfrequency (around 100 kHz).

The tip is oscillated 10¶s to 100¶s of nm above thesurface

Gradients in the magnetic forces on the tip shiftthe resonant frequency of the cantilever .

Monitoring this shift, or related changes inoscillation amplitude or phase, produces amagnetic force image.

Many applications for data storage technology.

Two passes are made over the sample. The firstmeasures topography while the second measuresa material property (magnetic, electric, etc.)

Eliminates ³cross-contamination´ of the images.

C- AFM

� C-AFM uses the probe of an AFM to contact thesample surface, and measures the current througha sample for a given applied potential.

� Provides current images simultaneously withtopographic images.

� Provides I-V curves.� Specially suitable to find micro shunting in solar

cells.

� Main advantage: High spatial resolution (down to

10 nm, but highly dependent on the sample).

C- AFM

Piezo Force Microscopy

Piezo response microscopy is a SPM technique

based on reverse piezo electric effect.

where a material expands (if parallel) or contracts

(if anti-parallel) upon applying an electric field.

PFM measures the mechanical response when an

electrical voltage is applied to the sample surface

with a conductive tip of an AFM.

In response to the electrical stimulus, the sample

then locally expands or contracts.

Multi Pass Technique

In multi pass technique; there are two or morethan two passes of scanning.

During first pass surface topography is measuredusing either semi-contact or contact mode and

subsequent passes (usually done in non contactmode) gives the additional information e.g.electrical, magnetic and other samplecharacteristics.

EFM and MFM both are two pass Technique.

MFM is a technique for imaging of magnetic fieldspatial distribution on the sample surface.

EFM is a technique for imaging of electric fieldsand electric charge distribution on the sample

surface

Q-Control

Q-control is a hardware, used to improve theresolution of the system by improving the Q-factor of cantilever.

The Q-Control is an add-on module for atomic

force microscopes. The electronic system adds an additional feedback

circuit to AFM, giving control over the qualityfactor (Q) of dynamic force mode AFM.

This control enables to improve the resolution of system or increase the maximum scan speed byvarying the AFM cantilever's Q factor.

Q- Control

By reducing the damping of the cantilever in adynamic force mode AFM, the Q control increasesthe effective quality factor of the system.

The result is minimized forces exerted by the tip

and improved resolution on sensitive surfacestructures.

This has been shown to resolve features that werenot possible with standard tapping mode AFM.

Q-Control Application

Minimizing the force exerted by the probing tip on

the surface.

Improving the overall sensitivity in MFM or EFM.

Increases the signal to noise ratio. Increase the maximum scan speed by reducing

quality factor.

Reducing the time constant of oscillating probe.

M AC Mode ( Magnetic AC Mode)

Agilant Technology has patented MAC Mode of

A gentle , non destructive technique for AFM.

Designed for imaging extremely delicate samples.

With MAC Mode, a magnetically coated

cantilever called a MAC Lever is driven

by an oscillating magnetic field.

The magnetic field is applied directly to the MAC

Lever from either above (Top-MAC) or below (MAC

Stage) the cantilever.

Features and Benefits of M AC

Patented technique optimized or high resolution

AFM imaging in fluids.

Intelligent design facilitate simple operation in air

or fluid.

DSP lock in from 200-1MHz ensure true phase and

amplitude.

Easy tuning provides a simple resonance peak.

M AC«..

Wide range of operating frequency afford greater

versatility.

Operates simultaneously with

Environment control.Temperature control.

Electrochemical control.

Control fluid exchange.

Deoxyribonucleic Acid

Contain the genetic instruction used in

development.

DNA sizeradius- 1 nanometer

pitch- 3.4 nanometer

Millimeter

Represented by mm. 1mm= (10)^(-3)

Micro meter

Represented by um

1 um= (10)^(-6)

Nano meter.

Represented by nm.

1 nm= (10)^(-9).

A degree= (10)^-10

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