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Glossary terms about Electron

Electron

Electrons are elementary particles, found in all atoms, that are grouped in shells around the nuclei of the atoms.

▼17 more terms contain Electron

Electron

Electrons are elementary particles, found in all atoms, that are grouped in shells around the nuclei of the atoms.

Electron beam

A stream of electrons (cathode rays).

Electron volt (eV)

A unit of energy equal to the amount of kinetic energy an electron gains when it is accelerated through an electric potential difference of one volt

Auger electrons

Secondary electrons emitted from atoms in the sample as a result of inner shell ionisations due to bombardment by the primary electron beam.

Electron scattering

The process in which a travelling electron is deflected from its original trajectory.

Secondary Electrons

Produced through inelastic scattering that results in the ejection of loosely bound electrons from the specimen. Secondary electrons have energies from ~2-50eV.

Electron beam voltage

The voltage of the electron beam. A scanning electron microscope usually has the capacity to operate in a range from from 0 to 30 kilovolts (kV), and sometimes up to 40 kV.

Backscattered Electrons (BSE)

Produced through an elastic scattering interaction with the atoms in the sample that results in the primary electron being re-emitted from the specimen. The electron is said to have backscattered (or reflected back) from the sample. In backscattering, the electron trajectory is changed by more than 90 deg from the forward direction of motion. This results in the scattered electron propagating back in the general direction of the original beam. Note that between the multiple elastic events (that form Backscattered electrons), the beam electrons may also be involved in inelastic events, and thus reduce the electron's energy. Backscattered electrons usually have energy in the kV range.

Secondary Electron Image (SEI)

The image that is obtained from secondary electrons that are reflected from a specimen. The image contrast depends on surface roughness, profile of sample and sample composition.

Electron-beam lithography (E-bea)

The beam of electrons is scanned across the sample in a patterned fashion in order to remove material, not image it.

Backscattered Electron Image (BEI)

The image that is obtained from backscattered electrons that are reflected from a specimen. The BEI image is dependent on surface topography and average atomic number of specimen.

Scanning Electron Micrograph

An image, normally a digital image, achieved by using a scanning electron microscope. Note that use of the acronym, SEM, for Scanning Electron Micrograph is strictly speaking, incorrect.

Scanning Electron Microscope (SEM)

An instrument which scans or rasters a fine electron probe over a material, and using a variety of detectors reconstructs an image from the signals generated within the sample.

Scanning Electron Microscopy

A technique: the use of a scanning electron microscope.

Cryo-scanning electron microscope (Cryo-SEM)

A conventional SEM that has been fitted with specific equipment that allows samples to be viewed in the frozen state.

Electron Backscatter Diffraction (EBSD )

An electron microscope technique used for viewing crystallographic information based on backscattered electrons whose scattering efficiency depends on the crystallographic orientaiton of the specimen. See http://www.ebsd.com/

Low Vacuum Scanning Electron Microscope (LV-SE)

A scanning electron microscope in which pressure can be adjusted in the sample chamber.

Environmental scanning electron microscope (ESEM)

A scanning electron microscope in which relative humidity, pressure and temperature can be controlled in the sample chamber.

41 pages mention Electron

Additional material

Links Physics behind electron Microscopy  

Alignment

The beam travels from the electron gun at the top through the sample and down to the viewing screen. 

Applications and practical uses - what the TEM can do

The transmission electron microscope (TEM) is used to examine the structure, composition, and properties of specimens in submicron detail. 

Astigmatism

This occurs when the electrons sense a non-uniform magnetic field as they spiral around the optic axis. 

Background information - What is transmission electron microscopy?

A transmission electron microscope (TEM) is an analytical tool allowing visualisation and analysis of specimens in the realms of microspace (1 micron/1μm = 10-6m) to nanospace (1 nanometer/nm = 10-9m). 

Camera length

Once an accurately calibrated diffraction pattern is achieved, the information in the pattern is used to determine lattice planes and in the indexation of diffraction patterns [see useful links for information on how to index diffraction patterns]. The images are convergent beam electron diffraction patterns (CBED) from a ZnO crystal. 

Chromatic aberration

The term chromatic aberration is related to the energy of the electrons. 

Combining images

 

Concepts - introduction

The fundamental basis of electron microscopy is the use of an electron beam. 

Detectors

One of the most common detectors seen on a transmission electron microscope is the x-ray energy dispersive spectroscopy (EDS or EDX) system. 

Diffraction basics

This is because a crystal lattice acts as a diffraction grating: interference patterns are produced in the electron beam as it travels out from the lattice and these can be projected as an image of regular dots or rings. 

Diffraction patterns

When the electron beam interacts with the sample when the sample is oriented with a zone axis pattern parallel to the electron beam, then the diffraction pattern form in the back focal plane of the objective lens is a regular array of reflections. 

Electron column

The electron column is made up of the gun assembly at the top, a column filled with a set of electromagnetic lenses, the sample port and airlock, and a set of apertures that can be moved in and out of the path of the beam. 

Electron gun

The electron gun generates the electron beam. 

Frequently asked questions

 

Image appearance

This can occur for one of two reasons: Strongly diffracting regions of crystals can appear darker because there are fewer electrons transmitted along the primary beam. 

Image formation basics

The TEM images are formed in two stages: Stage A is the scattering of an incident electron beam by a specimen. 

Image types

Some areas of the sample scatter or absorb electrons and therefore appear darker. 

Images from electrons

electron images from the TEM can be used to achieve different information, for example for morphological, crystallographic or compositional studies. 

Imaging mode setup

There are a number of concepts that need to be mastered when setting up the electron column for suitable imaging modalities. 

Inorganic sample/physical science specimen preparation for TEM

 

Introduction - aims and learning outcomes

Welcome to the online learning module for transmission electron microscopy. 

Kikuchi Patterns

Bragg scattering, that is diffraction of inelastically scattered electrons, can lead to the formation of pairs of parallel lines in the diffraction pattern called Kikuchi lines. 

Lenses: electromagnetic lenses

 

Machine operating procedures

The following provide examples of the actual steps used in one electron microscope laboratory for some TEMs. 

Magnetic lens system

Within the column the electromagnetic lenses shape the electron beam, which travels in a spiral trajectory. 

Organic sample/physical science specimen preparation for TEM

 

Parts of the machine

The typical transmission electron microscope laboratory contains a machine with these components:  

Pole-pieces and Coils

a pole-piece: a cylindrically symmetrical core of soft iron with a hole drilled through it (bore) a coil of copper wire which surrounds each pole-piece. 

Problems with lenses: aberrations

Spherical and chromatic aberrations limit the resolution of conventional electron microscopes. 

Resolution

 

Specimen/sample chamber

The cable is plugged into the column to enable electronically-controlled tilting of the holder and therefore the sample. 

Spherical aberration

The further off-axis the electron is, the more strongly it is bent back toward the axis. 

The diffracted beam

When the electron beam passes through the thin crystalline sample, it is diffracted by the atomic planes in the sample when the Bragg condition is satisfied. 

The electron wavelength

 

The Eucentric Position

 

Tilting

The appearance of a diffraction pattern will depend on the orientation of the specimen to the electron beam. 

Transmission electron microscopy in practice

Virtual transmission electron microscopy  

Using the JEM-1010 Transmission Electron Microscope for physical science material

 

Using the JEM-1010 Transmission Electron Microscope for thin resin sections of biological material

 

What the TEM can't do

electrons cannot readily penetrate sections much thicker than 200nm.