Construction and working of electron microscope, Other Engineering

Electron Microscope

The development of the electron microscope was based on theoretical work done by Louis De Broglie, who found that wavelength is inversely proportional to momentum. A few years later to De Broglie, the first modern prototype electron microscope is introduced by Max Knoll and Ernst Ruska.

An electron microscope is type of microscope that uses a beam of electrons, rather than electromagnetic radiation, to "illuminate" the specimen and create an image of a specimen. It has much higher magnification and resolving power than a light microscope, with magnifications up to two million times, allowing it to see smaller objects and greater detail in these objects. Unlike a light microscope, which uses glass lenses to focus light, the electron microscope uses electrostatic and electromagnetic lens to control the illumination and imaging of the specimen. A schematic diagram of electron microscope is given in fig.

Where d is the smallest distance between two parts of an object, l the wavelength of light used for illumination of the object space and µ sin a is the numerical aperture of the objective, µ being the refractive index of the object space and a is the semi vertical angle of the cone of rays entering the objective. The reciprocal of the limit of resolution gives the resolving power (R. P.). As the wavelength decrease the resolving power increases. Thus using ultra - vilolet light we get greater resolving power than with the ordinary visible light. As shown by De Broglie the wavelength associated with an electron accelerated through V volts is given by

Electrons of energy will have for instance a wavelength of 0.0122 À, a wavelength 50000 times smaller than the wavelength of the visible light. Hence if we use a beam of fast electrons instead of ordinary light we shall obtain much higher resolving power. As such electron microscopes have been constructed and used to reveal still finer details ordinarily impossible to be revealed by optical microscopes.

The two most common kinds of electron microscope are -

(1)  Transmission electron microscope (TEM)

(2)  Scanning electron microscope (SEM)

A transmission electron microscope (TEM) works like a light microscope, transmitting a beam of electrons through a thin specimen and then focusing the electrons to form an image on a screen or on film. This is the most common form of electron microscope (SEM) scans a fine beam of electron onto a specimen and collects the electrons scattered by the surface. This has poorer resolution, by gives excellent 3-dimensional images of surface.

Posted Date: 7/11/2012 2:36:06 AM | Location : United States

Related Discussions:- Construction and working of electron microscope, Assignment Help, Ask Question on Construction and working of electron microscope, Get Answer, Expert's Help, Construction and working of electron microscope Discussions

Write discussion on Construction and working of electron microscope
Your posts are moderated
Related Questions
Suppose you borrow $10,000 at 10% and you are going to make monthly payments of $2,500. How long until you pay off the loan?

Re-heat Ignition The atomised fuel spray is fed into the re-heat jet pipe and ignited by one of three methods:- • Spark Ignition • Hot Streak Ignition • Catalytic Ignition a

Re-Heat Nozzles : If re-heat was fitted to an engine with a standard sized fixed area propelling nozzle, the expansion of gases caused by the use of re-heat would increase the

Evacuation of a high rise building - means of escape: Evacuation of a high rise building is likely to be split into two or more phases.  Initially, when the alarm activates (f

x(t)=integration((Vx(t)+Vy(t))/2*cos(theta)dt) where Vx, Vy and theta is a function of t I am getting problem with how to write it down in matlab in order to get the position x.

how to use mean and standard deviation with matlab?

Let C(K) denote a European vanilla Call option with strike price K. Assume that all options are identical except for strike price, and strike prices satisfy (K1) What are the no-

when same music is played in veena and violin , we shall hear the sound of

Propeller control : CONSTANT SPEED UNIT: In the normal flight range, the main control of the propeller is exercised by the propeller control unit (PCU). MANUAL AND AU

Need to understand the method for calculating the maximum deflection and maximum stresses on a rigidly supported circular plate. The plate has a 500 mm radius and is 12mm thick.