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Glossary terms about Detector

A device that can collect and process signals produced by interactions between the primary electron beam and the sample. Different signals are processed by different detectors.

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16 pages mention Detector

Acceleration voltage vs. specimen type
For secondary electron (SE) imaging at typical voltages (say 15 keV), BSEs can enter the secondary electron detector and degrade resolution because they come from deeper in the sample. 
Background information - What is scanning electron microscopy?
The SEM uses an electron beam instead of a torch, an electron detector instead of eyes, and a viewing screen and camera as memory. 
Concepts - introduction
Electron wavelengths are much smaller than the visible light we see with our eyes, but the main reason SEM images are not coloured is that they are formed by electrons hitting a detector (see below). 
Due to the low energies of secondary electrons (SE) (~2 to 50 eV) they are ejected only from near-surface layers. 
Electron-matter interactions
Generating an image
This is achieved by placing a positively biased grill on the front of the SE detector, which is  
High vacuum mode and pump system
Therefore the detectors can be used (but only semi-qualitavely) in the so-called 'low vacuum' operational mode. 
Images from electrons
There are a range of imaging techniques available. Image from secondary electrons (below lens SE detector) Zincite (ZnO) powder and tabular crytals of shigate (Mn7AL4(SO4)2(OH)228H2O) showing crystal shape and size. 
Signals generated from the specimen are collected by an electron detector, converted to photons via a scintillator, amplified in a photomultiplier, and converted to electrical signals and used to modulate the intensity of the image on the viewing screen. 
Perfecting an image - signal processing
Natural contrast can be considered as the contrast contained in the signal that comes immediately from the specimen+ detector system. 
Risk assessment example: transport and analysis of a SEM sample
Sample size must also be considered (care must be taken with sample insertion and height adjustment to avoid detector/microscope damage). 
Risk assessment example: using a SEM
cryo-SEM, anticontaminant traps, EDS detector dewars. 
Sample preparation
Scan rate and signal to noise ratios
Noise pulses are derived from such sources as beam brightness, condenser lens settings (spot size), and SE detector ‘gain’, and may impart a salt-and-pepper (grainy) appearance to the image. 
Troubleshooting: edge effect, charging, sample damage
They are caused by the effects of topography on the generation of secondary electrons and are what gives form and outline to the images produced by the Secondary Electron detector
What the SEM can't do
Note: Some SEMs can collect true colour images via a wavelength selective cathodolumenence (CL) detector