SEM/EDX

Scanning Electron Microscopy coupled with Energy Dispersive X-ray (SEM/EDX) Spectroscopy

Technique:
SEM Image Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX) is the best known and most widely-used of the surface analytical techniques. High resolution images of surface topography, with excellent depth of field, are produced using a highly-focused, scanning (primary) electron beam. The primary electrons enter a surface with an energy of 0.5 – 30 kV and generate many low energy secondary electrons. The intensity of these secondary electrons is largely governed by the surface topography of the sample. An image of the sample surface can thus be constructed by measuring secondary electron intensity as a function of the position of the scanning primary electron beam. High spatial resolution is possible because the primary electron beam can be focused to a very small spot (<10 nm). High sensitivity to topographic features on the outermost surface (< 5 nm) is achieved when using a primary electron beam with an energy of < 1 kV.

SEM NanotubesIn addition to low energy secondary electrons, backscattered electrons and X-rays are generated by primary electron bombardment. The intensity of backscattered electrons can be correlated to the atomic number of the element within the sampling volume. Hence, some qualitative elemental information can be obtained. The analysis of characteristic X-rays (EDX or EDS analysis) emitted from the sample gives more quantitative elemental information. Such X-ray analysis can be confined to analytical volumes as small as 1 cubic micron.

SEM, accompanied by X-ray analysis, is considered a relatively rapid, inexpensive, and basically non-destructive approach to surface analysis. It is often used to survey surface analytical problems before proceeding to techniques that are more surface-sensitive and specialized.

Instrument:

Hitachi SU8230 Regulus FESEM at Surface Science Western

Hitachi SU8230 Regulus FESEM at Surface Science Western


Hitachi SU8230 Regulus Ultra High-Resolution Field Emission SEM
Bruker X-Flash FQ5060 Annular Quad EDX detector
Bruker X-Flash 6160 EDX detector

System Capabilities:

  • Image Resolution: 0.6 nm at 15 kV, Image Resolution: 0.8 nm at 1 kV, Magnification Range: 20 X to 2,000,000 X
  • Imaging Detectors: 1) Lower secondary electron detector for topographic imaging, 2) Upper secondary electron detector for high resolution with E x B filter, 3) Top detector with energy filtration, 4) In-lens backscattered secondary electron detector (BSE), 5) Retractable backscattered secondary electron detector (PD-BSE), 6) BF-STEM and variable collection angle DF-STEM detector
  • Low voltage capability available from 10 V. The low voltage capability means that many samples that normally require a conductive coating to reduce charging problems can be examined directly.
  • Five axis eucentric motorised and automated stage with a 1 kg capacity
  • Large chamber can accommodate 200 mm diameter sample
  • Bruker QUANTAX FlatQUAD SDD detector with ESPRIT analytical software:

  • Ultra-fast spectroscopy with high 1.1 sr solid-angle
  • Annular four channel detector with 60 mm2 active area
  • 127 eV energy resolution at Mn K(alpha)
  • Light element detection from carbon to uranium
  • Fast mapping of rough surfaces with no shadowing
  • Low voltage analysis at high magnification
  • Quantitate mapping, particles analysis and phase analysis
  • Bruker Flat Quad SDD detector with ESPRIT analytical software:

  • 60 mm2 active area
  • 126 eV energy resolution at Mn K(alpha)
  • Light element detection from carbon to uranium
  • Quantitate mapping, particles analysis and phase analysis

Instrument:
Hitachi SU3500 Variable Pressure SEM combined with an Oxford AZtec X-Max50 SDD X-ray analyzer

System Capabilities:

  • Resolution: 3 nm at 30 kV in high vacuum mode
  • Resolution: 4 nm at 30 kV in low vacuum mode
  • Variable pressure from ~6 Pa up to 650 Pa
  • Useful images at 60 K X magnification
  • Low voltage capability available from 300 V beam voltage
  • Three imaging modes: secondary electron (SE) detector, multi-segment solid-state backscattered electron (BSE) detector and SE equivalent variable pressure (UVD) detector
  • Five axis asynchronous motorised and automated stage
  • Large sample chamber capable of holding an 8 kg specimen
  • X-Max 50mm2 Silicon Drift Detector with 127 eV resolution (Peltier cooling)
  • AZtecFeature Automated Analysis software for particle identification
  • Elemental analysis from carbon to uranium
  • Semi-quantitative analysis with detection limits of ~ 0.5 weight % for most elements
  • Linescans and elemental mapping

Conductive Coatings
Depending on the application it may be necessary to deposit a thin, conductive coating on a sample in order to minimize charging during SEM/EDX spectroscopy. For routine imaging and EDX analysis a thin coating of carbon or gold coating can be used, while chromium or iridium can be used for ultra-high resolution imaging.

Zone II Cleaner – Removing surface contamination
Surface contaminants from sample handling, cleaning residues and even exposure to air can reduce high resolution image quality by electron beam deposition of hydrocarbons. The Zone II cleaner uses a combination of ultraviolet (UV) and ozone to remove hydrocarbons from a sample surface, without any damage to the sample surface.

Selected Applications in Industry:

  • Imaging of a corroded copper surface
  • EDX analysis and mapping of dust from Beijing
  • Microstructure of a sputter-deposited silver film
  • Composition of a metallic brake pad
  • Pinhole in paint caused by cracks in the steel substrate