Chapter 7.1, Problem 5MI

Summary Introduction

To determine:

Information about electron microscope.

Introduction:

A microscope is an instrument that can be utilized to watch little articles, even cells. The picture of an article is amplified through in any event one focal point in the magnifying instrument. This focal point twists light toward the eye and causes an item to seem bigger than it really is.

Explanation of Solution

The limitations of the light microscope, with respect to resolution succeeded by using electron beams instead of light beams. The microscope which uses electron beams instead of light beams is known as electron microscope. The high resolution images obtained by EM can be used to identify viruses and even to visualize individual biomolecules.

Electron microscope features:

1. Electron beam and electromagnetic lens used for the magnification of the sample.
2. Durcopan, araldite glass/diamond, 10-100 nm used for embedding the sample.
3. Perforated metal disc used for mounting the sliced tissues.
4. Heavy metal salts- osmium tetroxide, lead acetate, uranium acetate dyes used for staining the sample.
5. The sample is magnified between the condensing lens and the objective lens and the image is viewed in an ocular lens.
6. STM and TEM are the subtypes of electron microscope.

Electron microscope are of two type:

1. Transmission electron microscope (TEM)
2. Scanning tunneling electron microscope (SEM)

Transmission electron microscope (TEM) produces an enlarged image of the object using a trajectory for the electron beam that is similar to the trajectory of light beam in an optical microscope. Visual detection is not possible, therefore, a photographic film or a charge coupled device has to be used for image detection. The electron beam is collimated and bent using a set of electrostatic and magnetic lenses. The resolution of the electron microscope is much higher than that of the light microscope.

Scanning tunneling electron microscope has a resolution higher than that of the transmission electron microscope. Image of single atoms have been detected by using the STM. The basis of the STM is the tunneling current, a current that passes between two objects that are in very close proximity. The amplitude of the current depends on the overlap of the wave functions of the two objects, which in turn depends upon the distance between the two objects. As a result, the tunneling current is extremely sensitive to distance.