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Environmental Scanning Electron microscopy
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Esem
- 1. Environmental Scanning Electron Microscopy Dinara Zhussupova NANS 599
- 2. References • Philips Electron Optics Eindhoven, The Netherlands (1996). Environmental Scanning Electron Microscopy. An Introduction To ESEM® • Eric Doehne (2015). Esem Applications: From Cultural Heritage Conservation To Nano-beha Viour
- 3. Contents History of ESEM Why ESEM How it works Applications Limitations
- 6. Manfred von Ardenne (20 January 1907 – 26 May 1997)
- 7. Stewart A, Snelling M. (1965) A new scanning electron microscope, Proc. 3rd European Conference EM, Prague 55-56
- 8. Electron gun Anode Condenser Lens or Electromagnets Vacuum chamber 105 Torr Objective lens/ Electromagnet Secondary Detector Backscatter Detector High vacuum pump Mechanical pump
- 9. SEM Limitations High Vacuum Vacuum tolerancy of samples Sample conductivity Sample preparation Gas ionization
- 10. High vacuum pump Mechanical pump Vent Mechanical pump Gas inlet 10-1 Torr 10Torr 10-4 Torr 10-5 Torr 10-7 Torr
- 12. ESEM limitations Beam penetration Imaging depends on sample characteristics Higher noise
- 15. Applications
Editor's Notes
- Environmental scanning electron microscopy (ESEM) was developed about 15 years ago. Although it would likely be very expensive to modify a normal scanning electron microscope (SEM) to perform as an ESEM, a microscope designed from the beginning with a dual purpose (ESEM/SEM) can work quite well either way. ESEM allows the examination of practically any specimen under any gaseous conditions, unlike conventional SEM, which operates in vacuum. The ESEM allows the examination of any specimen, wet or dry, insulating or conducting in situ and close to its natural state, while the environmental gas medium produces completely novel possibilities of operation and imaging.
- The microscope has existed, in one form or another, for almost 1000 years. In the earliest days of the technology, light focused through lenses produced 6 to 10x magnifying power, an impressive feat in pre-Renaissance Europe. Currently, the finest optical microscopes which get their power from complex systems of mirrors and lenses, can reach between 500 and 1000x magnification. Optical microscopes are limited in their power by the properties of light. To surpass such primitive limits, scientists in the 1930s began working with electron microscopes. M. Knoll and Manfred von Ardenne were two of the pioneers in this field.
- M. Knoll and Manfred von Ardenne were two of the pioneers in this field starting 1930s. Although Max Knoll produced a photo with a 50 mm object-field-width showing channeling contrast by the use of an electron beam scanner,[3] it was Manfred von Ardenne who in 1937 invented[4] a true microscope with high magnification by scanning a very small raster with a demagnified and finely focused electron beam. Ardenne applied the scanning principle not only to achieve magnification but also to purposefully eliminate the chromatic aberration otherwise inherent in the electron microscope. Ardenne had performed early attempts on the examination of specimens inside "environmental" cells with water or atmospheric gas, in conjunction with conventional and scanning transmission types of electron microscopes (ESEM).
- In 1965, the first commercial Stereoscan SEM was built by Cambridge Instrument Company, a UK based predecessor company of Carl Zeiss Microscopy Ltd.
- The SEM uses a beam of electrons to scan the surface of a sample to build a three-dimensional image of the specimen. Scanning electron microscopy (SEM) has long played a central role in structural characterisation for material scientists. Bombarding the surface of a material with a beam of electrons and detecting those that are emitted or backscattered allows microscopists to see down to resolutions of 10 nanometres or so, giving them intricate details of the material’s structure. However, the requirements of SEM, such as a high vacuum and the need for a thin coating if an insulator is being analyzed, mean that certain types of materials have always proved difficult or impossible to image straightforwardly. For example, the coating can obscure the fine surface detail on some insulators - although SEMs equipped with field emission guns have made such samples easier to image. Another difficulty arises with wet and damp samples such as paints, inks, emulsions and biological tissue - these materials prove particularly challenging for SEM. The high vacuum requirements in the chamber mean lengthy specimen preparation techniques are required to remove or fix the water before imaging, raising the risk of artefacts being introduced.