Images are produced by scanning a focused electron beam across the surface of a specimen. In the most common mode, the low energy secondary electrons emitted are detected and used to modulate the brightness of a synchronously scanned CRT. Other signals can also be detected. X-rays, characteristic of that part of the specimen probed by the electron beam, allow both a qualitative and quantitative determination of the elements present in the selected region. High energy backscattered electrons can be separated and used for image formation. Since the backscattering efficiency is a function of atomic weight, this image reveals compositional variations due to average atomic number.

Information Obtained
° Surface topography if low energy secondary electrons are collected
° Atomic number or orientation information if higher energy backscattered
   electrons are used for imaging
° Differentiation between surface roughness, porosity, granular deposits,
   stress-related gross microcracks (often used in conjunction with microsectioning)
° Observation of grain boundaries in unetched samples
° Critical dimension measurements

Sensitivity and Resolution
° Lateral resolution for SEM: 1.2 nm
° Lateral Resolution for EDX: 1 µm
° Detection limits for EDX: 0.5 - 1% atomic

Instrumentation
° JEOL JSM-6320F Field Emission Microscope with Digital Imaging
° JEOL 820i Scanning Electron Microscope with Kevex light element
  Quantum Energy Dispersive X-Ray Analyzer, Digital Elemental
  Imaging, Backscattered Electron Detection
° Cambridge Stereoscan 360 Scanning Electron Microscope with 40kV LaB6
   Emitter

Advantages
° Depth of field is better than optical microscopy or transmission
   electron microscopy
° Fast, relatively inexpensive near-surface screening method