2012 Spring SEM Lecture 01

8/3/2019 2012 Spring SEM Lecture 01

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Basic Principles

Presented by Joven Calara Research Engineer, Metallurgy

Scanning ElectronMicroscopy


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Simple Magnifiers

Raindrop


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Simple Magnifiers

Raindrop

Simple lens

- hand magnifier

Magnification to ~10x


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Compound Magnifiers - Microscope

Maximum magnification ~1000x - WHY?


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Light Microscope limits of magnification

Green algae 400X magnification


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Light Microscope limits of magnification

Green algae 800X magnification


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Visible Light Spectrum

Wavelength () 400 700 nm


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Optical microscopes

Optical microscopes resolution limited bywavelength of light

Abbes Law;Maximum resolution = /2 = 200 nm


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Image of point light source the Airy disc


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Airy disk


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Airy disk

Airy disks and resolution


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Objects smaller than 500 nm

Viruses, as small as 5 nm


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Viruses, as small as 5 nm

Smoke or soot particles

Colloids (very fine particles) Milk !


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http://www.foodsci.uoguelph.ca


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Wavelengths shorter than 200nm needed


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Wavelengths shorter than 200nm needed

, nm Why not

Ultraviolet 100 200 Glass is opaque to UV

X-rays 0.1 100 Glass cant focus x-rays

Gamma rays < 0.1 Ionizes everything

By early 1900, new approaches to microscopy were desperately

needed.


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A Different Method of Magnification - Mapping

Mapping ; one-to-one correspondence betweenfinite number ofthe elements of two areas. Modern implementation is scanning.

Example; a small photograph mapped onto a building wall mural

scanning photo into picture elements (pixels) and enlarged

reproduction of the pixels. Each pixel a single color/brightness.


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20 cm x 20 cm

section of LCD

Subdivide this into pieces,

each to match a pixel on LCD


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A section of an LCD screen


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A section of an LCD screen


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Pixel count = 4 per mm


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20 cm x 20 cm

section of LCD

Subdivide this into pieces,

each to match a pixel on LCD

screen

800 pixels high and wide


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20 cm x 20 cm

section of LCD

Black and white picture, pixel attribute

is brightness only. Laser beam scan OK.


= laser spot diameter

d cm


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20 cm x 20 cm

section of LCD

Black and white picture, pixel attribute

is brightness only. Laser beam scan OK.


= laser spot diameter

d cm

d, cm magnification laser spot dia.

5 4x 0.063 mm

0.2 100x 0.0025 mm

0.02 1000x 250 nanometers

0.01 2000x 150 nm

Light beams at >>1000x


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Electron beams (electrical discharges)

Lightning electron beamin air

Lightning Globe toy

electron beams in partial

vacuum


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Early Electron Beam Device Crookes Tube

Cathode ray tube

Cathode ray deflection with

magnetic fields


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Early oscilloscope (1897)

First example of beam scanning, just on a

single line. Input signal appears as waveform.


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Cathode ray tube (CRT, 1907)

Raster scanning


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Modern Electron Beam Devices

Television - Computer monitors

CRT monitor ~1980

TV

Black and white TV - ~1950


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Technological skills in place by early 1900;

Generation of electron beam

Focusing of the beam

Scanning or rastering (scanninge.g. left to right, then down a bit,

repeat scan)


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Simplified sketch of electron scanning optics


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Simplified sketch of electron scanning optics

Laser scanning

detected signal = reflected light

E-beam scanning

detected signal = ? ? ? ?


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Electron beam solid interaction


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Secondary electrons,


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The Scanning Electron Microscope

T


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Electron Imaging Effect of Surface Topology

(Detector overhead sample)

T


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Electron Imaging Effect of Surface Topology

(Detector overhead sample)

T

Chrysanthemum pollens


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Small area on

specimen

Display device photo print or monitor

Magnification by the SEM

Effect of Probe (Beam Spot) Size


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Small area on

specimen

Display device photo print or monitor

Magnification with wide probe size (laser spot?)


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Wavelength of electron beams theDe Broglie Equation

Light can behave as waves (lightwaves), or as particles (photons).

De Broiglie proposed the converse is also true. Electrons have wave

properties.

De Broglie Equation adaptedto SEM

= h/sqrt(2meV)

= 1.23/sqrt(V) nanometers

At V = 10,000 volts, = 0.0123 nanometers

De Broglie Equation adaptedto SEM

= h/sqrt(2meV)

= 1.23/sqrt(V) nanometers

At V = 10,000 volts, = 0.0123 nanometers

h (Plancks constant) = 6.63x10-34 Js

m(electron mass) = 9.11x10-31 kg

e (electron charge) = 1.6x10-19 C


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SEM resolution

Theoretical 0.01 nm

Development lab grade 0.1 nm

High end 1.0 nm Typical 3 nm (ca. 300,000x)

Typical magnifications routine 200-8000x


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Depth of Field how deep is the field in sharp focus

Optical microscope SEM

Tungsten filament


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Characteristic X-rays;

Elements Chemical Analysis


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Characteristic X-rays;

Elements Chemical Analysis


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Ductile Iron


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JEOL JSF-6400 Scanning Electron Microscope of SLCC


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Hitachi TM3000 Scanning Electron Microscope

2012 Spring SEM Lecture 01

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