Scanning Electron Microscopy |
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
|
