Powerpoint presentation on electron microscopy
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Electron microscopy is a technique that uses beams of electrons instead of light to view objects. There are two main types: transmission electron microscopy (TEM) and scanning electron microscopy (SEM). TEM uses electrons transmitted through an ultra-thin sample to form magnified images, allowing visualization of structures as small as single atoms. SEM scans a focused beam of electrons across a sample to produce high-resolution 3D images of surface topology and composition. Newer techniques like scanning tunneling microscopy can achieve even higher resolution down to fractions of a nanometer. Electron microscopy has enabled significant advances in fields like materials science, biology, and nanotechnology.
Powerpoint presentation on electron microscopy
- 1. Electron Microscopy Submitted by:- Decoy B.Tech(B.T.)-4th sem Pt nanoparticles
- 2. The Central player - (e) • The electron “e” is an elementary particle • Also called corpuscle • carries a negative charge. • the electron was discovered by J. J. Thompson in 1897 • e is a constituent of the atom • 1000 times smaller than a hydrogen atom. • the mass of the electron 1/1836 of that of a proton.
- 4. The Wave Properties • In 1924, the wave-particle dualism was postulated by de Broglie (Nobel Prize 1929). • All moving matter has wave properties with the wavelength λ being inversely related to the momentum p by λ = h / p = h / mv (h : Planck constant; m : mass; v : velocity)
- 5. The Wavelength • Resolving power of EM is from Wave properties of electrons • Limit of resolution is indirectly proportional to the wavelength of the illuminating light • ie, longer the wavelength, lesser is the resolution • λ = √150 / V, where • λ – wavelength in Angstroms, V – accelerating voltage in volts
- 6. The electron wave • The generation of a monochromatic and coherent electron beam is important • Design of modern electron microscopes is based on this concept
- 7. Scheme of electron-matter interactions arising from the impact of an electron beam onto a specimen. A signal below the specimen is observable if the thickness is small enough to allow some electrons to pass through
- 8. Elastic Electron Interactions • no energy is transferred from the electron to the sample. • These signals are mainly exploited in - Transmission Electron Microscopy and - Electron diffraction methods.
- 9. Inelastic Electron Interactions - Energy is transferred from the electrons to the specimen - The energy transferred can cause different signals such as - X-rays, - Auger electrons - secondary electrons, - plasmons, - phonons, - UV quanta or cathodoluminescence. • Used in Analytical Electron Microscopy … SEM
- 10. What is Electron Microscopy? • Electron microscopy is a diagnostic tool with diversified combination of techniques …… • that offer unique possibilities to gain insights into - structure, - topology, - morphology, and - composition of a material.
- 11. What is an Electron Microscope ? • A special type of microscope having a high resolution of images, able to magnify objects in nanometers, which are formed by controlled use of electrons in vacuum captured on a phosphorescent screen
- 12. Why were the EMs ad vented? • To study objects of < 0.2 micrometer • For analysis of sub cellular structures • Intra cellular pathogens - viruses • Cell metabolism • Study of minute structures in the nature Greater resolving power of the EMs than light microscope • An EM can magnify structures from 100 – 250000 times than light microscopy
- 14. The novelty of EMs from others • Beam of Electrons …… instead of a beam of light • Electro-magnetic lens ………..instead of Ground glass lenses • Cylindrical Vacuum column - Electrons should travel in vacuum to avoid collisions with air molecules that cause scattering of electrons distorting the image
- 15. Comparison of lens system of Light & Electron Microscope
- 16. Commonly used EMs in biology • Transmission Electron Microscope • Scanning Electron Microscope “ mainly for various life forms and microbes” • Scanning tunneling microscope • Atomic Force Microscope “ Actual visualization of molecules and individual atoms, also in motion”
- 17. Transmission Electron Microscopy The first TEM was built by Max Knoll and Ernst Ruska in 1931, with this group developing the first TEM with resolving power greater than that of light in 1933 and the first commercial TEM in 1939.
- 18. TEM - Definition TEM is a microscopy technique whereby a beam of electrons is transmitted through an ultra thin specimen, interacting with the specimen as it passes through. An image is formed from the interaction of the electrons transmitted through the specimen; the image is magnified and focused onto an imaging device, such as a fluorescent screen, on a layer of photographic film, or to be detected by a sensor such as a CCD camera.
- 19. Applications • TEMs are capable of imaging at a significantly higher resolution than light microscopes, owing to the small de Broglie wavelength of electrons. • To examine fine detail—even as small as a single column of atoms, which is tens of thousands times smaller than the smallest resolvable object in a light microscope. • Application in Biological sciences like cancer research, virology, materials science as well as pollution, nanotechnology, and semiconductor research. • Application in chemical & physical sciences like in chemical identity, crystal orientation, electronic structure and sample induced electron phase shift as well as the regular absorption based imaging.
- 20. High resolution TEM - HRTEM • Crystal structure can also be investigated by high- resolution transmission electron microscopy (HRTEM), • HRTEM is also known as phase contrast. • In a specimen of uniform thickness, the images are formed due to differences in phase of electron waves, which is caused by specimen interaction. • Image formation is given by the complex modulus of the incoming electron beams. • The image is dependent on the number of electrons hitting the screen, • it can be manipulated to provide more information about the sample as in complex phase retrieval techniques.
- 21. • By taking multiple images of a single TEM sample at differing angles, • typically in 1° increments, • a set of images known as a "tilt series" can be collected. • This methodology was proposed in the 1970s by Walter Hoppe. • Under absorption contrast conditions, this set of images can be used to construct a three-dimensional representation of the sample. Gold particles on E. coli appear as bright white dots due to the higher percentage of backscattered electrons compared to the low atomic weight elements in the specimen
- 22. Scanning TEM (STEM) • Modified type of TEM • by the addition of a system that raster the beam across the sample to form the image, combined with suitable detectors. • The STEM uses magnetic lenses to focus a beam of electrons • The image is formed not by secondary electrons as in SEM but by primary electrons coming through the specimen
- 23. Limitations of TEM • Many materials require extensive sample preparation • Difficult to produce a very thin sample • relatively time consuming process with a low throughput of samples. • The structure of the sample may change during the preparation process. • Small field of view may not give conclusive result of the whole sample.
- 24. Definition of SEM • An electron microscope that produces images of a sample by scanning over it with a focused beam of electrons. • The incident electrons interact with electrons in the sample, producing various signals that can be detected and • contain information about the sample's surface topography and composition.
- 25. The electron beams • The types of signals produced by a SEM include - secondary electrons, - back-scattered electrons (BSE), - X-rays, - light rays (cathodoluminescence), - A standard SEM uses Secondary electrons & Back scattered electrons
- 26. Salient features • Electrons are used to create images of the surface of specimen - topology • Resolution of objects of nearly 1 nm • Magnification up to 500000 x (250 times > light microscopes) • secondary electrons (SE), backscattered electrons (BSE) are utilized for imaging • specimens can be observed in high vacuum, low vacuum and • In Environmental SEM specimens can be observed in wet condition. • Gives 3D views of the exteriors of the objects like cells, microbes or surfaces
- 27. Scanning tunneling microscopy • 1980 – Gerd Bennig and Heinrich Rohrer invented STM • Also called Scanning Probe microscopes • Object resolution 0.1-0.01 nm • Thin wire probe made of platinum - iridium is used to trace the surface of the object • Electrons from the probe overlap with electron from the surface - tunnel into one another’s clouds - tunnels create a current as the probe moves on the uneven surface of the specimen
- 28. The applications • The STM can be used in ultra high vacuum, air, water, and various other liquid or gaseous environments • and at temperatures ranging from near zero to a few hundred degrees Celsius • First movie made using STM – “individual fibrin molecule forming a clot” • Live specimen examination – as in “Virus infected cells exploding and releasing new viruses” • Visualization of intra cellular changes
- 29. Recent advances The effect of metallic nanoparticles on cells was probed by treating two cell lines with C-coated Cu nanoparticles. The up-take of these nanoparticles was shown by HAADF-STEM that reveal them as bright patches inside the cells (s. image). Nanoparticle Cytotoxicity Depends on Intracellular Solubility: Comparison of Stabilized Copper Metal and Degradable Copper Oxide Nanoparticles
- 30. References:- • A. M. Studer, L. K. Limbach, L. Van Duc, F. Krumeich, E. K. Athanassiou, L. C. Gerber, H. Moch, and W. J. Stark Toxicology Lett. 197 (2010) 169-174 DOI • www.Wikipedia.en.us/electron microscopy • www.slideshare.com