Stem

scanning transmission electron microscope

1. SCANNING TRANSMISSION ELECTRON MICROSCOPE(STEM)

2. FACULTY OF TECHNOLOGY &ENGINNERING MATERIAL TECHNOLOGY SCANNING TRANSMISSION ELECTRON MICROSCOPE(STEM ) PRESANTED BY.... AKSHAY SAVANI PRN NO-2017033800128346 NIKUNJ MANGUKIYA PRN NO-2017033800128242 STEM

3. Principle Construction Working Application Advantage Disadvantage Refrences CONTENT

4. The scanning transmission electron microscope (STEM) is a very powerful and highly versatile instrument capable of atomic resolution imaging and nano scale analysis. The basic principle of image formation fundamentally different from static beam TEM. the STEM technique scans a very finely focused beam of electrons across the sample in a raster pattern.  PRINCIPLE

5. Types of insterument used EELS spectrometer Bright-field detector Annular dark field detector Objective lens Scan coils Condenser lens Gun lens CONSTRUCTION

6. EELS spectrometer-As the electron beam passes through the sample, some electrons in the beam loss energy via inelastic scattering interactions with electrons in the sample. In  electron energy loss spectroscopy  (EELS), the energy lost by the electrons in the beam is measured using an electron spectrometer. In STEM, EELS can be used to spectroscopically map a sample at atomic resolution CONSTRUCTION

7. Bright-field detector-In STEM, bright-field detectors are located in the path of the transmitted electron beam. Axial bright-field detectors are located in the centre of the cone of illumination of the transmitted beam, and are often used to provide complementary images. Annular bright-field detectors, located within the cone of illumination of the transmitted beam, have been used to obtain atomic resolution images in which the atomic columns of light elements such as oxygen are visible CONSTRUCTION

8. Annular dark field detector-In annular dark-field mode, images are formed by fore-scattered electrons incident on an annular detector, which lies outside of the path of the directly transmitted beam. By using a high-angle ADF detector Scan coil-it is used for scanning the electron beam across the specimen surface in a raster pattern. CONSTRUCTION

9. Scan coils consist of to solenoids oriented in a such a way to create two magnetic fields perpendicular to each other. Condenser lens-if we want to focus the beam to a size<10nm on the specimen surface the magnification should be 1/5000 which is not easily attained with one lens objective lens only at that time condenser lens added to demagnify the cross over point CONSTRUCTION

10. In many ways, the STEM is similar to the more widely known scanning electron microscope(SEM). An electron gun generates a beam of electrons that is focused by a series of lenses to form an image of the electron source at a specimen. The electron spot, or probe, can be scanned over the sample in a raster pattern by exciting scanning deflection coils, and scattered electrons are detected and their intensity plotted as a function of probe position to form an image WORKING

11. Scanning transmission electron microscopes are used to characterize the nanoscale , and atomic scale structure of specimens, providing important insights into the properties and behaviour of materials and biological cells. Materials science - Scanning transmission electron microscopy has been applied to characterize the structure of a wide range of material specimens, including  semiconductor  devices, complex oxides, batteries,  fuel cells ,  catalysts , and  2D materials . APPLICATION

12. Biology - The first application of STEM to the imaging of biological molecules was demonstrated in 1971 STEM has been widely used to solve a number of structural problems in molecular biology. which can allow imaging of biological samples without the need for staining APPLICATION

13. Easy to operate with the proper training Advance in computer technology Insrument work fast It gives detailed in 3d and topografical imaging and the versatile information generated from different ditector It allows for the generation of data in digital form Most sample require minimum preparation action ADVANTAGE

14. STEM are expensive and large. Special training require to operate STEM The preparation of samples can result in artifacts Its limited to solid samples DISADVANTAGE

15. https://en.wikipedia.org/wiki/Scanning_transmission_electron_microscopy https://www.slideshare.net/e_gulfam/scanning-transmission-electron-microscope REFRENCES

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