Transmission electron microscopy-TEM, principle and working.pptx

It describes how TEM works, what is the basic principle, what are the components of the TEM instrument, and how the results will be.

1. TRANSMISSION ELECTRON MICROSCOPY (TEM) AISWARYA GOWRI V S RESEARCH SCHOLAR SRMIST KTR

2. CONTENT INTRODUCTION PRINCIPLE COMPONENTS WORKING TRANSMISSION ELECTRON MICROSCOPY VS SCANNING ELECTRON MICROSCOPY ADVANTAGE AND DISADVANTAGE OF TRANSMISSION ELECTRON MICROSCOPY

3. INTRODUCTION Transmission electron microscopy was the first electron microscopy that used a high-energy electron beam to generate morphology , composition , and crystallographic information of a given sample. * Resolution Magnification Light microscope 200nm 1000X Transmission electron microscope 0.2 nm 20,00,000X

4. PRINCIPLE Once the electron beam interacts with the specimen , they are either scattered or are transmitted based on the mass and density ratio. The transmitted electron beam will strike the fluorescent screen or a charge-coupled device (CCD) camera , which will generate an image with varying contrast based on the intensity of the electron beam.

5. COMPONENTS Electron gun: Tungsten and Lanthanum- Hexaboride. Condenser system: Focus the electron beam to sample. Image producing system: consists of the objective lens, aperture lens, and projection lens- (for magnification). Image recording system: Fluorescent screen, or charge-coupled device (CCD) camera.

6. TEM can operate on two modes, Diffraction mode and image mode 1 . Diffraction mode The objective lens forms a diffraction pattern in the back focal plane with electrons scattered and diffracted by the sample and combines them to generate an image in the image plane . Difraction mode can say whether the sample is single crystalline, poly crystalline, or amorphous by taking Selective Area Diffraction (SAD). Single crystal : Produces diffraction pattern consist with a centre spot associated with transmitted beam and other diffracted spot. Poly crystal :Produces diffraction pattern on the rings of different radius. Amorphus sample : Follows a halo ring pattern. single crystall Poly crystall Amorphous

7. 2. Image mode Image of the sample is focused and projected onto the screen, Which is of two types Darkfield image and Bright field image. Bright field images: It is obtained by passing transmitted waves to the objective aperture. Dark field images: It is obtained by allowing the diffracted beam to the objective aperture. Bright field image Dark field image

8. SEM Vs TEM SEM TEM  SEM shows only the morphology of samples. SEM can resolve objects as close as 20 nm . The magnifying power of SEM is up to 50,000X . SEM allows for a large amount of sample to be analyzed at a time. Secondary or backscattered electrons arising from the interaction of electron beam and metal-coated specimen are collected and the resulting image is displayed on a computer screen. TEM can show many characteristics of the sample, such as internal composition, morphology, and crystallization. TEM has a much higher resolution than SEM.  It can resolve objects as close as 1 nm  i.e. down to near-atomic levels. The magnifying power of TEM is up to 2 million times. With TEM only a small amount of samples can be analyzed at a time. Transmitted electrons hit a  fluorescent screen  giving rise to a “shadow image” of the specimen with its different parts displayed in varied darkness according to their density. The image can be studied directly by the operator and photographed with a camera.

9. ADVANTAGE Less sample is required. TEMs provide information on element and compound structure . TEMs are able to yield information of surface features, shape, size and structure. DISADVANTAGE High vacuum is required. TEMs are large and very expensive. Laborious sample preparation.

10. Thank you……