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Notre Dame extended Research Community

From the Human Eye Down to Microscopes at the Nano-Scale

Michael CrockerValerie GossPat MooneyRebecca Quardokus

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Outline Discussion of Optics

History Ranges of Visual Resolution

Scanning Electron Microscopy (SEM) Fundamentals Operation Scheme

Atomic Force Microscopy (AFM) Scanning Tunneling Microscopy (STM)

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Scanning Bunny

A distant cousin of the energizer bunny who helps to explain nanoscience

concepts.WELCOME PENN HIGH SCHOOL

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target

sourceHow do we see an

object?

detector…and often you’ll need a lens

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Requirements of Vision The light that reaches the eye must have a color

between red (760nm) and blue (400nm) – or a mixture of these colors

The light that reaches the eye must be sufficiently bright – usually requires a sufficiently bright source

visible light

wavelength in nm400760 3000760290 320

www.uvabcs.com/uvlight-typical.php , August 31, 2009

infrared

UV UV UV

C B A

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Object and Source Matching

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Seeing Atomic Structure Light must be about 0.1nm in wavelength to see

atomic structure: x-rays But our eyes can’t detect x-rays - 0.1nm light -

(5000 times smaller wavelength than we can see) Options

• Use x-rays and detector (to replace the eye)• Use particles (e.g. electrons) and detector

Electrons of the appropriate wavelength are easier to produce and direct than light – Scanning Electron Microscope (SEM)

Alternate imaging techniques• Atomic Force Microscope (AFM)• Scanning Tunneling Microscope (STM)

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Scanning Electron Microscope

Michael Crocker

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Basic Idea?

Let’s bounce something else at the

surface!

Animal sight and traditional

microscopes collect deflected light

e-e-

e-

e-

e-

e-

e-

e-

e-

e-e-

Some are absorbed

Some are “reflected”

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Electron Beam Column

http://bioweb.usu.edu/emlab/TEM-SEM%20Teaching/How%20SEM%20works.html

Beam created from heated filament

Beam travels through a vacuum

Electro-magnetic fields act as lenses

Scattered and “secondary” electrons are detected

Electron beam hits the sample in a precise

location

Beam scans back and forth

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Electrons Hit Surface and Detection

http://www4.nau.edu/microanalysis/Microprobe-SEM/Signals.html

Primary electrons come from the beam

Some scatter back, others dislodge electrons

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Example Images

http://gsc.nrcan.gc.ca/labs/ebeam/sem_gallery_e.php

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Atomic Force Microscope

Valerie Goss

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What is the AFM?We can sense with

our hands by

touching. An analogue!

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AFM cantilever and AFM tips

www.veeco.com

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The powerful, versatile AFM

~30 um scan

www.nanotech-now.com/.../antonio-siber.htm Aug 27, 2009

Resolutions:

X and Y 2 -10 nm

Z 0.05 nm

Microstructure of solids:

CD, glass beads, circuits

Biological samples:

skin cross section, viruses, bacteria, blood, DNA and RNA

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Scanning Tunneling Microscope

Rebecca Quardokus

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Scanning Tunneling Microscopy (STM)

Electrons tunnel!

With a higher probability than cars

STM measures the current created by tunneling electrons

Images courtesy ofhttp://www.ieap.uni-kiel.de and www.renault.com

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Scanning Tunneling Microscopy (STM)

Image courtesy ofhttp://nano.tm.agilent.com

C60 “Bucky Balls”

Each C60 diameter is ~ 10Å1 Å = 1x 10-10 m

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Scanning Tunneling Microscopy (STM)

Xenon on Nickel

Iron on CopperImages courtesy of http://www.almaden.ibm.com

Individual atoms? That’s small!

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I’ll show you more in the microscope laboratory!