Scanning Electron Microscope (SEM)

(From IOWA U. web site)

Danny Porath 2002

Scanning Electron Microscope (SEM)

Radiolarian (in Plankton) x 750

(From IOWA U. web site)

With the help of…….1. Bruce Kahn - RIT2. Yossi Rosenwacks3. Yosi Shacam – TAU4. JEOL guide for SEM5. “Electron Microscpy and Analysis”,

P.J. Goodhew and F.J. Humphreys.6. IOWA state U., Dept. of Material Science &

Engineering site 7. …

Internet Siteshttp://www.rit.edu/~bekpph/

http://www.rit.edu/~bekpph/sem/ARS/sem.htmhttp://www.unl.edu/CMRAcfem/em.htmhttp://www.jeol.com/sem_gde/tbcontd.htmlhttp://mse.iastate.edu/microscopy/home.html

http://laser.phys.ualberta.ca/~egerton/SEM/sem.htmhttp://acept.la.asu.edu/PiN/rdg/elmicr/elmicr.shtml

http://www.mos.org/sln/sem/seminfo.htmlhttp://www.mih.unibas.ch/Booklet/Lecture/Chapter1/Chapter1.html....

Homework 21. Find on the web, in a paper or in a book the 3 most impressive

SEM and TEM images:a. 1 - Technicallyb. 1 - Scientificallyc. 1 - Aesthetically

Explain your choice. If needed compare with additional images.

2. Explain the differences between SEM and TEM. Elaborate more on the TEM.

3. Which types of analysis can be done by SEM/TEM beyond imaging. Explain shortly.

4. Be prepared to present each one of them to the class in 5 minutes.

Outline SEM/TEM:

1. Links and examples2. Optics

a. Ray diagramsb. Resolutionc. Magnification

3. SEM/TEM structure4. Electrons-surface interactions and

signals5. Types of disturbances

SEM Image (Leo 1530)

High resolution image of a frozen, hydrated yeast uncoated chromite

SEM Images (Leo 1530 and JEOL Guide to SEM)

Toner x2,500 Gold particles x36,000 Integrated Circuit x720

Eye of a fly x100 Kosher Salt x75 Toilet Paper x500

SEM Images (Leo 1530 and JEOL Guide to SEM)

Black widow spider x500 Cucumber skin x350 Staple in paper x35

Big Radiolarian x500 and x2,000 Ceropia moth x350 and 15,000

SEM Imaging

~4 nm gap

Before Au55trapping

After Au55trapping

2 nm

Some History….1611 Kepler suggested a way of making a compound microscope.

1655 Hooke used a compound microscope to describe small pores in sections of cork that he called "cells".

1674 Leeuwenhoek reported his discovery of protozoa. He saw bacteria for the first time 9 years later.

1833 Brown published his microscopic observations of orchids, clearly describing the cell nucleus.

1838 Schleiden and Schwann proposed the cell theory, stating that the nucleated cell is the unit of structure and function in plants and animals.

1857 Kolliker described the mitochondria in muscle cells.

1876 Abbé analyzed the effects of diffraction on image formation in the microscope and showed how to optimize microscope design.

1879 Flemming described with great clarity chromosome behavior during mitosisin animal cells.

1881 Retzius described many animal tissues with a detail that has not been surpassed by any other light microscopist. In the next two decades he, Cajal, and other histologists developed staining methods and laid the foundations of microscopic anatomy.

Some (more) History….1882 Koch used aniline dyes to stain microorganisms and identified the bacteria

that cause tuberculosis and cholera. In the following two decades, other bacteriologists, such as Klebs ans Pasteur, identified the causative agents of many other diseases by examining stained preparations under the microscope.

1886 Zeiss made a series of lenses, to the design of Abbé, that enabled microscopists to resolve structures at the theoretical limits of visible light.

1898 Golgi first saw and described the Golgi apparatus by staining cells with silver nitrate.

1924 Lacassagne and collaborators developed the first autoradiographic method to localize radioactive polonium in biological specimens.

1930 Lebedeff designed and built the first interference microscope.

1932 Zernike invented the phase-contrast microscope. These two developments allowed unstained living cells to be seen in detail for the first time.

1941 Coons used antibodies coupled to fluorescent dyes to detect cellular antigens.

1952 Nomarski devised and patented the system of differential interference contrast for the light microscope that still bears his name.

1981 Allen and Inoué perfected video-enhanced contrast light microscopy.

Image Through a Thin Lens

Various Optical Ray Diagrams

M=(v1-f1)(v2-f2)/f1f2M=f/(u-f)=(v-f)/f1/f=1/u+1/v

Two lens System and Magnification

Objective Projector

M1=(v1-f1)/f1 M2=(v2-f2)/f2

M=(v1-f1)(v2-f2)/f1f2

Light Sources

Transmission illumination

TEM

Reflected illumination

SEM

Spectral range

ResolutionThe resolution depends on the lens ability to collect light (~1/f#) and inverse to the aperture number (NA)

f/#=f/D

NA=n sin(α)

NA = 1/(2 f/#)

NAksolution λ1Re =

Resolution … Airy Discs

Laser beam Diffraction through a pinhole

75 µm 100 µm

~84 %

d1~1/aperture-diameter

Rayleigh Resolution Criterion

R1= d1/2=0.61λ/µsin(α)= 0.61λ/NA

Diffraction limited Resolution

UnresolvedPartially resolved

Resolved

Thus the smallest separation is determined by the N.A. (1/2f#)

Typically the best objective has N.A ≈1.6 ⇒ resolution ≈170 nm

For λ~400 nm (green light)

⇒ Decrease λ

Electron Microscopy - Decreasing The Wavelength

eVmpE ==⇒2

2

Energy Conservation

meVp 2=⇒

P h=

λ

λ = = =⋅

⋅ ⋅ ⋅ ⋅ ⋅≈

−

− −

hp

hmeV

A2

66 102 91 10 16 10 50000

00534

31 19

.. .

.o

Resolution (50 kV): R1= 0.61λ/NA~(0.6.0.05)/1.6~0.2 Å

The Evolution of Resolution

Magnifications

Optical

SEMx70

x300

x1400

x2800

Depth of Field

h=0.61λ/[µsin(α)tg(α)]