SEM EDX EBSD

Scanning Electron Microscopy or SEM is a technique of electronic microscopy  capable of producing high quality images of a sample surface.
SEM is generaly used to study morphology in 3D of a surface or item and also the chemical composition (microanalysis X). Today, that kind of electronic microscopy is used in areas going from biology to sciance of materials, and a huge number of constructors offer devices with captors of secondary electrons which resolution can go up to 1 nm.

Have a look into a gallery full of real applications.

 

Applications

  • Science of materials: microstructural caracterisation (morphology, distribution of components in mixtures or composites),  cristallographic information , chemical cartography, dimensional measurements
  • Microelectronic: technology of semiconductors and microfabrication
  • Biology: observation of micro-organisms

Using modes and specifications

  • 3D image: allows a visualisation of the sample topography by detection of secondary electrons.
  • Imaging in contrast of composition: gives images which contrast is function of the atomic number by detection of backscattered electrons.
  • Microanalysis X: allows elementary analysis (typically from carbon) of a sample part by detection of X-rays. X-rays come from a volume around µm3.  Elements in inferior quantity around 0.2 % in mass will not be detected.
  • Imaging X: allows repartition imaging of  one or several elements on the surface. Lateral resolution is around 1 micron
 

Operational principles

In SEM, electron beams incident of a few dozens of kilovolts sweep out the sample surface which emit back an all spectrum of particles and radiation : secondary electrons, backscattered electrons, Auger electrons and X-rays. Detection of these different particles or radiation allows to obtain an image of the sample surface, information brought by that image depending on detected emissions.

Secondary electrons

During an interaction between primary electrons and sample atoms, a primary electron can let a part of its energy to an other electron lightly linked of the band of conduction of the targeted atom, provoquing its ejection (called secondary electron). Secondary electrons have a low energy (under 50 eV) and are emitted in a huge number. As they come from superficial layers (under a few nanometers), secondary electrons are very sensitive to the sample topography, that’s why their detection gives an image with contrast linked to topography.

Backscattered electrons

Backscattered electrons are electrons resulting from diffusion almost elastic of electrons of primary beam with the atomic nuclei in surface of the sample. Those electrons are emitted back in a new direction similar to their original one, with a low loss of energy. Backscattered electrons have an energy similar to the primary beam energy and so have an escape depth of around 100 nm. The rate is directly linked to the atomic number of atoms making the sample, backscattered electrons detection gives an image with a contrast linked to chemical composition of sample. This particularity allows a qualitative analysis of chemical homogeneity of a sample.

Auger Electrons

During the collision between an atom of the sample and a primary electron, an electron of a depth layer of the target atom can be ejected (electron Auger). Auger electrons have a caracteristic energy of the atom which emitted it. It allows to obtain information on the chemical composition of the sample surface (see AES).

Microanalysis X

The bombing of the sample surface by primary electrons primaires of high energy leads also to X-rays emission, which wavelength is caracteristic of target atoms. The analisys of these rays allows to obtain information on the chemical nature of the atom.

 
SEM EDX EBSD
SEM image in secondary electrons of an eyelash