This glossary provides definitions for electron microscopy techniques, terms and acronyms - as well as links to further information on our site. The terms are listed alphabetically, and are quick-linked to their definitions so you can easily find the information you are looking for.

Low-angle shadowing

This is a transmission electron microscopy (TEM) specimen coating technique designed to improve contrast of small, flat specimens, such as RNA, DNA, virus particles and protein spread preparations. Typically, the specimen is dried onto a TEM support grid and transferred into a high vacuum coater fitted with sources for the thermal evaporation of metals and carbon (C).

First, a metal coating - normally platinum (Pt) - is evaporated at a low angle of incidence to the specimen surface (typically 5-10°). This creates an electron-dense ‘shadow’ of the specimen surface. A layer of carbon is then thermally evaporated from an angle of 90° to give electron density to the rest of the specimen.

Further information: Bench-Top Vacuum Evaporators

Low vacuum (‘Rough’ vacuum)

Defined as a vacuum with a pressure of between just above atmosphere and around 10^-2mbar.

Magnetron sputtering

Magnetron sputtering using a crossed-field electromagnetic configuration keeps the ejected secondary electrons near the cathode (target) surface and in a closed path on the surface. This allows a dense plasma to be established near the sputter target surface. The ions that are accelerated from the plasma do not sustain energy loss by collision before they bombard the sputter target.

For electron microscopy (EM) specimen coating, the magnetron sputtering head design ensures that minimal heat energy (electrons) reach the specimen surface. This is important as it reduces heat damage to specimen and is a significant factor in ensuring the grain size within the sputtered film is optimally small – essential for high resolution field emission scanning electron microscopy (FE-SEM).

Further information: Sputter coating technical brief (PDF) on Sputter Coating Techniques and Advantages

Micrometer (µm)

A metric unit of length measurement equal to 1x10^-6metre (0.000001m). For reference, a human hair is around 20 micrometers in diameter.

Micro-electromechanical systems (MEMs)

Micro-electromechanical systems (MEMs) are often defined as the technology of the very small, but not within the realm of molecular nanotechnology. MEMs are mechanical components on the micrometer scale and are typically manufactured using semiconductor processes such as surface micromachining.

Examples of common applications include piezoelectric motors (eg in inkjet printers), pressure sensors (eg on car tyres) and accelerometers in car safety airbags. Devices generally range in size from a micrometer (1µm) to a millimetre (1mm). At these size scales, due to MEMs’ large surface area to volume ratio, surface effects such as electrostatics and ‘wetting’ (surface tension) come into play.

Critical point drying (‘supercritical drying’) is widely used to overcome the detrimental surface tension effects associated with air drying. We manufacture a range of small critical point dryers, of which the K850WM is suitable for small scale and R&D MEMs drying applications.

Further information: Critical Point Dryers

Nanometer (nm)

A metric unit of length measurement equal to 1x10^-9metre (0.000000001m).

Pirani vacuum gauge

A gauge for measuring vacuum that uses a heated sensor wire. Pressure is determined by measuring the current needed to keep the wire at a constant temperature. A Pirani gauge will only measure vacuum levels in the lower range (down to 10^-3mbar) and is typically used in low vacuum systems, such as rotary-pumped sputter coaters.

A Pirani gauge is sometimes used in conjunction with a high vacuum gauge, such as Penning, to measure vacuum in the low pressure range. Most of our high vacuum products now use full-range gauges - a single gauge which measures vacuum from atmosphere to high vacuum.

Plasma asher

An instrument used for plasma ashing.

Also see: Plasma ashing
Further information: RF Plasma Techniques and Advantages

Plasma ashing

Plasma ashing, using a radio frequency (RF) plasma barrel reactor, is the total removal of organic matter by oxygen plasma. The resulting carbon oxides and water vapour are volatile and pumped away by the vacuum system. If specimens are a mixture of organic and inorganic material, the end product is an ‘ash’ residue. Plasma ashing takes place at relatively low temperatures and will retain many volatile components that may be lost using alternative, high-temperature methods. Applications include removing photoresist from semi-conductor wafers and ashing polyacetate filters as part of the process for detecting asbestos fibre using light and electron microscopy (EM).

Also see: Plasma etching
Further information: RF Plasma Techniques and Advantages

Plasma etcher

An instrument used for plasma etching.

Also see: Plasma etching
Further information: RF Plasma Techniques and Advantages

Plasma etching

Radio frequency (RF) plasma etching is used in the semi-conductor industry to fabricate integrated circuits. Plasma etching uses an RF plasma and appropriate reactive gas, such as CF₄, or gas mixture.

Also see: Plasma ashing
Further information: RF Plasma Techniques and Advantages

Rotary pump

A type of vacuum pump where pumping is produced by moving air from one side of a rotating cylinder to another by means of an eccentric drum. Rotary pumps are used with all of our coaters, either to evacuate instruments directly, or to ‘rough pump’ and ‘back’ high-vacuum sputter coaters and vacuum evaporators.