Topic 5 - The electron microscope

Question 1

What happened in 1920?

Answer 1

it waws discovered that accelerated electrons behavein vacuum just like light.

• they travel in a straight line.
• wavelenght 100.000 times smaller than light
• can be manipultaed with electronmagnetic field just like the light with glass lens

Question 2

Who bult the first electron microscope and when?

Answer 2

Ernst Ruska, 1931

Question 3

Two types of electron microscope

Answer 3

Transmission electron microscope

Scanning electron microscope

Question 4

TEM
Electron source
MAgnification
Imageformation
Specimen

Answer 4

-Lightsource: Electron gun
-Electomagnetic lenses
-Immage appears on Fluorescent screen
UNDER VACUM –> No live subjects
E- forms a superheated filament accelerated by the anode and then mad into a parallel beam thorough a wenhelt cylinder.
-Specimen:
- Thin! 60-90 nanometre
- Contrasted with heavy metals
(dark spot duringscattering)

Question 5

SEM

Answer 5

For observating surface structures (thicker than TEM)
Large vacum chamber - no limit on specimen size
Short column : only 3 focusing lenses
Electrons deflected by the specimen - turned into a electric signal.
Turned into light and produce img on fluorescent screen

Question 6

RESOLUTION VALUES

Answer 6

Human eye: 0.2mm
Best light microscope: 0.2mm(x1000) useful magnification
EM:
SEM: 1.0 nm (x400.000 useful magnification)
TEM: 0.1 nm (x1.000.000 useful magnification)