Electron Microscopy Lecture 9

8/12/2019 Electron Microscopy Lecture 9

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FORTH / IESL / TCM@ V assilios B inas

Crete Center for Quantum Complexity andNanotechnology

Department of Physics, University of Crete

Transparent Conductive Materials (Head prof. G. Kiriakidis)Institute of Electronic Structure & Laser IESL

Foundation for Research and Technology - FORTH

Post Doc Researcher, Chemist

, Email: [email protected] Thl. 1269
mailto:[email protected]:[email protected]


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Scanning Electron Microscopy (S )


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( ~1930)

ntoni van Leeuwenhoek, 1673 :

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Robert Hooke, 1677: .

Ernst Abbe, 1870:

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Sir J.J. Thomson, 1897(Nobel Prize in Physics 1906):

( , .

Prince de Broglie, 1924 (Nobel Prize in Physics 1929):

.


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..

H. Busch, 1926:

: !!!!

Max Knoll Ernst Ruska, 1932 inHigh Voltage Laboratory at West Berlin(Nobel Prize in Physics 1089)

Bodo von Borries and Ruska, 1939:

SIEMENS Vladimir Zwoeykin, James Hillier andGerald Snyder, 1942 from radiocorporation of America: SEM


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.

http://nobelprize.org/educational_games/physics/microscopes/powerline/index.html


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Electromagnetic

lenses

Direct observation Video imaging (CRT)

Glass lenses


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SEM

Resolution

.. 4x 1400x 0,5mm 0,2mm

SEM 10x 500Kx 30mm 1,5nm


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SEM


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SEM



SEM


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SEM



(SEM) SEM



(2)

Condenses electrons into nearly parallel beam(controls spot size, and brightness or intensity)

Focuses beam that has passed through specimen

(primary and scattered) and forms a magnifiedintermediate image. Focusing accomplished byvarying current through lens

Allows higher mags, more compact, shortercolumn, no distortion

Magnifies a portion of the first image to form thefinal image

(SEM) SEM



Spray or Fixed

Provide contrast

Movable

Depending on the aperture, can control brightness, resolution (balance diffraction versusspherical aberration), contrast, depth of field

/Airlock

Fluorescent Screen

(SEM) SEM



(SEM) SEM



LaB6: W

Field Emission Guns:


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.

1. (Condenser)

2. (Objective)

3. (Projector)


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(SEM)


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.

,

, .


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S

- SEM

(secondary

electrons).

.


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S


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( condenser)

.

.


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(SEM)


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magnification: X 10 to X 300,000

30 ngstrom resolution

ZEISS DSM-960A Scanning Electron Microscope filament e - source


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SEM

magnification: X 10 to X 300,000

15 ngstrom resolution (LaB6 source)

backscattered electron detector,transmitted electron detector, electronchannelling imaging

$300,000 current value

JEOL JSM-880 high resolution SEM LaB 6 electron source


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SEM.EDS (Energy Dispersive Spectroscopy)


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SEM.EDS (Energy Dispersive Spectroscopy)


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SEM


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BIOLOGICAL SPECIMEN


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BIOLOGICAL SPECIMENPREPARATION

EMPHASIZING

ULTRAMICROTOMY


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Porter-Blum MT2B ultramicrotomeby Sorvall (ca. mid-1960s-1980)

Simple belt device drives themicrotome arm in MT2

MT2B has adjustable duration and

speed in the return stroke (much morecomplex)

Limited movement possible in thefluorescent bulb

Highly adjustable stage and specimenchuck, but all with spring locks ratherthan verniers making fine adj hard

Locks on microscope used rather thanscrews (also awkward)

Mechanical advance system

i h l l i


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All adjustments are onviernier set screwsfacilitating fine adj

Lighting with aboveand sub-stage lamps

Mechanical advancewith thick sectioningsettings

Water bath controls

Fine control of speedand duration of cut

and return cycle Future models had

innovations for serialsectioning

Reichert Ultracut Ultramicrotome

RMC MT 6000 Ultramicrotome


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RMC MT-6000 Ultramicrotome

RMC MT 6000 Ult i t ith FS 1000 C tt h t


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RMC MT-6000 Ultramicrotome with FS-1000 Cryo-attachment


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http://www.udel.edu/Biology/Wags/b617/micro/micro11.gif


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Glass Knife Boat



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http://www.emsdiasum.com/Diatome/knife/images/

Caring for diamond knives:http://www.emsdiasum.com/Diatome/diamond_knives/manual.htm

http://www.emsdiasum.com/Diatome/diamond_knives/manual.htmhttp://www.emsdiasum.com/Diatome/diamond_knives/manual.htm


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PHYSICAL SCIENCESSPECIMEN PREPARATION

- GENERAL TECHNIQUES FOR

MATERIALS SCIENCES

http://www.ph.qmw.ac.uk/images/molwires.jpgDirect lattice resolution in polydiacetylene single crystal showing(010)lattice planes spaced at 1.2 nm.


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PHYSICAL SCIENCESSPECIMEN PREPARATION

- GENERAL TECHNIQUES FOR

MATERIALS SCIENCES

http://www.ph.qmw.ac.uk/images/molwires.jpgDirect lattice resolution in polydiacetylene single crystal showing(010)lattice planes spaced at 1.2 nm.

TECHNOLOGY OF SPECIMEN PREPARATION


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TECHNOLOGY OF SPECIMEN PREPARATION

Coarse preparation of samples: Small objects (mounted on grids):

Strew Spray Cleave Crush

Disc cutter (optionally mounted on grids) Grinding device

Intermediate preparation: Dimple grinder

Fine preparation: Chemical polisher Electropolisher Ion thinning mill

PIMS: precision milling (using SEM on very small areas (1 X 1 m 2) PIPS: precision ion polishing (at 4 angle) removes surface roughness with

minimum surface damage Beam blockers may be needed to mask epoxy or easily etched areas

Each technique has its own disadvantages and potential artifacts


EPOXY MOUNTING


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EPOXY MOUNTING

Williams & Carter, 1996, Fig. 10-10

Epoxy mounting of sectioned specimens prepared by thinning: Sequence of steps for thinning particles and fibers. Materials are first embedding them in epoxy 3 mm outside diameter brass tube is filled with epoxy prior to curing Tube and epoxy are sectioned into disks with diamond saw Specimens are then dimple ground and ion milled to transparency


Critical point drying (CPD)


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Critical point drying (CPD)

Purpose: To completely dry specimen for mountingwhile maintaining morphological details.


M h d


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1) Water exchanged for ethanol.

2) Ethanol exchanged for liquid CO 2 (transitional fluid).

3) CO 2 brought to critical point (31.1 C and 1,073 psi),becomes dense vapor phase.

4) Gaseous CO 2 vented slowly to avoid condensation.

5) Dry sample ready for mounting.

Method



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Sample holders

-Keep samples separated

-Hold delicate or smallsamples

-Ease of sample retrieval



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Freeze Drying

-Sample is quick frozen in liquid nitrogen (LN2).

-Placed in vacuum evaporator on cold block(approx. -190 C).

-Left under vacuum for several days to sublimatewater.

-Mounted and coated.



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Conductivity of Samples

Charging results in:deflection of the beamdeflection of some secondary electronsperiodic bursts of secondary electronsincreased emission of secondary electronsfrom crevices


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Coating the Sample

-Using OsO4 as fixative (biological)

-Painting a grounding line with silver or carbon paste

-Coating with nonreactive metal or carbon

a) Increased conductivity

b) Reduction of thermal damage

c) Increased secondary and backscattered electron emission

d) Increased mechanical stability

Accomplished by:


Sputter coating


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Gold, gold palladium target-vacuum of approx. 2 millibar

-thickness 7.5 nm to 30nm

Sputter coating


Thermal evaporation


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Thermal evaporation

-Typically used for shadowing- 2 x10-7 torr-From coarse to fine:Carbon, gold, chromium,platinum, tungsten, tantalum



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Evaporation

Trough for powders/cleaning



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E-beam

Used for high melting pointmetals (e.g. tantalum)

Similar to create emission ofelectrons from filament inmicroscope

Provides highest resolution



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Carbon Coating

Good vacuum required

Carbon rod may need outgassing

Do not look directly at heated electrodes

For samples in SEM wherex-ray information is needed.

TEM grids needing extrasupport

Support for replicas


Carbon ribbon


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Rotary device to

ensure uniform coating

Carbon ribbon

Carbon Rods



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Backscattered Electron ..


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Backscattered Electron . .


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O.M. vs SEM


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(S )


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(SEM)

: c m

SEM:


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20 kV


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5 kV

kV and fine Structure


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Electron Microscopy Lecture 9

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Transcript of Electron Microscopy Lecture 9