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Applied Physics 298r

Scanning Electron Microscopy (SEM)

Techniques for Nanostructures

David C. Bell

Center for Imaging and Mesoscale

Structures

David C. Bell Scanning Electron Microscopy (SEM)Techniques for Nanostructures

Basic Methods of Materials Analysis •

Look at the Material (Shiny or Dull?)

Hold Material (Heavy of Light?)

Taste Material (Surface Chemistry?)

Bite Material (Ductile ?)

Drop Test (Brittle ?)

• Put it in a Scanning Electron

Microscope (SEM)!

Other Methods

David C. Bell Scanning Electron Microscopy (SEM)Techniques for Nanostructures

Scanning Electron Microscope (SEM)

Applied Physics 298r David C. Bell Scanning Electron Microscopy (SEM)Techniques for Nanostructures

What is an SEM? Detector Amp Scan Generator

Electron Gun Scan Coils

VacuumSystem

Magnification Control

Electron lensApertures

Sample ona Stage

Display

David C. Bell Scanning Electron Microscopy (SEM)Techniques for Nanostructures

Anode Plate

• o+

0

d

0

ie

Filament

Wehnelt

Optic axis

Gun(Wehnelt )Bias

Applied kV

GunCrossover

Equipotentiallines

FilamentHeatingsupply

Emissioncurrent

Into

illumination

system

The Electron Gun Thermal Emission Field Emission

David C. Bell Scanning Electron Microscopy (SEM)Techniques for Nanostructures

Light bulb

Underfocus

but centered

Underfocus

& off center

Centered &

focussed

Hairpin Tungsten Filament

Applied Physics 298r David C. Bell Scanning Electron Microscopy (SEM)Techniques for Nanostructures

Power Coppercoils Water Soft ironPole pieces Water-cooled surface Electron ray pathsGap Bore Out In

Concentrate fluxField varies

Zero force on axial electrons

Magnetic lens

David C. Bell Scanning Electron Microscopy (SEM)Techniques for Nanostructures

Secondary Electron Detector

Note: error in handout

David C. Bell Scanning Electron Microscopy (SEM)Techniques for Nanostructures

SEM: Electron Detectors Backscattered Electron Image Secondary Electron Image

David C. Bell Scanning Electron Microscopy (SEM)Techniques for Nanostructures

Brief History of SEM

• 1935 Knoll Scanning TEM• 1942 RCA Labs, Zworykin• 1948 Cambridge University C. W. Oatley• 1963 Pease, SEM V became Cambridge Scientific Instruments Mark 1 Stereoscan - 1960 Everhart and Thornley : development of the SE Detector

David C. Bell Scanning Electron Microscopy (SEM)Techniques for Nanostructures

SEM Flavors ScanningElectron Microscopy

Environmental

Scanning Electron

Microscopy (ESEM)

Low Vacuum SEM Conventional SEM

David C. Bell Scanning Electron Microscopy (SEM)Techniques for Nanostructures

Environmental Scanning Electron Microscope (ESEM)

Turbomolecular

Pump

W Electron

Gun

Pressure

(Torr)

Vacuum

Pump

Vacuum

Pump

H

Auxilary Gas(CO

, N 2

, Ar) 2

SpecimenChamber

Sample

PLA #2PLA

Electron

Beam

EnvironmentalBacking Valve

David C. Bell Scanning Electron Microscopy (SEM)Techniques for Nanostructures

ESEM Example: Salt Water Diatom

David C. Bell Scanning Electron Microscopy (SEM)Techniques for Nanostructures

ESEM Example: Silicon Nanowires