TYPES OF ELECTRON MICROSCOPE

Asad Rasheed

11-ARID-433

Type of Electron Microscope Transmission Electron Microscope Scanning Electron Microscope Reflection Electron Microscope Low-Voltage Electron Microscope

Transmission Electron Microscope The Original Form of EM that uses the

high voltage Beam of Electrons to create an image.

Its has Resolution power up to 0.5 angstrom (50 picometres).

Most Powerful for observing

minute objects

Components

Mechanism Electron Gun Produces Beam of 100 keV. Anode and Cathode accelerate Beam. Focusing occur by Electrostatic and

electromagnetic lenses Beam strikes the sample and pass through it. After emerging out it carries information about

Sample and magnify it by objective lens Information can be analyzed by Screen or

Film or CCD Cameras on LCD or monitor.

Advantages TEMs offer the most powerful magnification,

potentially over one million times or more TEMs provide information on element and

compound structure Images are high-quality and detailed TEMs are able to yield information of

surface features, shape, size and structure They are easy to operate with proper

training

Limits of TEM Spherical Aberration. High Voltage can damage Sample. Sample should be xtremely thin upto 100 nm. Bio Samples are Dehydrated , chemically

fixed, embedded in polymer resin to stabilize them.

Staining is required to highlight in order to achieve require image contrast.

Thinning of sample should be done upto 100 nm

Scanning Electron Microscope

SEM produces the image by scanning it with focus beam of electron.

Electrons interact with electrons in sample and convey information in form of signals to detectors. E.g. topography & sample surface.

SEM can achieve resolution better than 1 nanometer

Raster image focusing is used

Mechanism

When High energy Electrons strikes the surface, it lose energy by diff. mechanisms like heat, emission of low energy secondary electrons and high energy backscattered electrons.

X-ray or light emerges from sample that carries information on it.

Advantages

Its basically used for biological samples It can scan the processes occurring on

surface and tells about topography and composition.

Enable us to view without thinning dehydrating fixing the sample

Can scan bulk samples upto 2-3 cm which can not be examined by TEM.

View obtained is in 3D. ESEM produce image of Wet, gas &

Vacuumed Samples and biological samples.

Reflection Electron Mcroscope

Its is the fixation of Transmission and Scanning Electron Microscope.

Uses the Elastically Scattered Electrons for focusing the electron beam into a narrow spot which is scanned over the sample in a raster.

Raster is the rectangular pattern of image capture and reconstruction in television.

TEM Sample forming processes are involved like thinning.

Highly contrasted mage is produces with higher focusing

Difference Rastering of beam occurs by focusing on

rectangular area. In REM Focusing action occurs before the

beam strikes the sample but in TEM focusing action occurs after the striking

Also data is obtained in series image rather in parallel image form.

Low-Voltage Electron Mcroscope Microscope As the Name suggests that it uses low

voltage for scanning i.e. up to 5 KeV. Higher Contrasting focus and good quality

image are produces with good magnifying power better then TEM.

Pinpoint image are obtained on CCD Camera.

This type can be used as TEM, SEM, STEM.

No Staining Required

Comparison of LVEM & TEM of Rat Heart (Specific part)

LEVM @ 5 Kev TEM @ 80 Kev

Cont…

Present low voltage electron microscopes are capable of spatial resolutions of about 2.5 nm in TEM 2.0 nm in STEM and 3.0 nm in SEM.

Low voltage limits the maximum thickness of samples

It is about 100–200 nm in conventional TEM.

It decreases to around 20–65 nanometers for LVEM.

Thanks for being Patience

Any Question