Environmental Scanning Electron Microscope –ESEM

The invention of Environmental SEM (ESEM) during 1980s allowed samples to be observed in low-pressure gaseous environments of 1-50 Torr and high relative humidity. This was made possible by the development of a secondary-electron detector capable of operating in the presence of water vapour and by the use of pressure-limiting apertures with differential pumping in the path of the electron beam to separate the vacuum regions around the gun and lenses from the sample chamber.The first commercial ESEMs were produced by the ElectroScan Corporation in USA in 1988

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Photodiode Design

Photodiode is a type of light detector capable of converting light energy into either current or voltage, depending upon the mode of operation. Photodiodes are similar to typical semiconductor diodes except that they may be either exposed or packaged with a window to allow light to reach the sensitive part of the device.

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