Since the mid-20th century, electron-beam technology has provided the basis for a variety of novel and specialized applications in

semiconductor A semiconductor is a material with electrical conductivity between that of a conductor and an insulator. Its conductivity can be modified by adding impurities (" doping") to its crystal structure. When two regions with different doping level ...

manufacturing,

microelectromechanical systems MEMS (micro-electromechanical systems) is the technology of microscopic devices incorporating both electronic and moving parts. MEMS are made up of components between 1 and 100 micrometres in size (i.e., 0.001 to 0.1 mm), and MEMS devices ...

nanoelectromechanical systems Nanoelectromechanical systems (NEMS) are a class of devices integrating electrical and mechanical functionality on the nanoscale. NEMS form the next logical miniaturization step from so-called microelectromechanical systems, or MEMS devices. NE ...

, and

microscopy Microscopy is the technical field of using microscopes to view subjects too small to be seen with the naked eye (objects that are not within the resolution range of the normal eye). There are three well-known branches of microscopy: optical mic ...

Mechanism

Free

electron The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...

s in a

vacuum A vacuum (: vacuums or vacua) is space devoid of matter. The word is derived from the Latin adjective (neuter ) meaning "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressur ...

can be manipulated by

electric Electricity is the set of physical phenomena associated with the presence and motion of matter possessing an electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by Maxwel ...

and

magnetic field A magnetic field (sometimes called B-field) is a physical field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular ...

s to form a fine beam. Where the beam collides with solid-state matter, electrons are converted into

heat In thermodynamics, heat is energy in transfer between a thermodynamic system and its surroundings by such mechanisms as thermal conduction, electromagnetic radiation, and friction, which are microscopic in nature, involving sub-atomic, ato ...

kinetic energy In physics, the kinetic energy of an object is the form of energy that it possesses due to its motion. In classical mechanics, the kinetic energy of a non-rotating object of mass ''m'' traveling at a speed ''v'' is \fracmv^2.Resnick, Rober ...

. This concentration of energy in a small volume of matter can be precisely controlled by the fields, which brings many advantages.

Applications

Electron beam techniques include

electron probe microanalysis An electron microprobe (EMP), also known as an electron probe microanalyzer (EPMA) or electron micro probe analyzer (EMPA), is an analytical tool used to non-destructively determine the chemical composition of small volumes of solid materials. I ...

transmission electron microscopy Transmission electron microscopy (TEM) is a microscopy technique in which a beam of electrons is transmitted through a specimen to form an image. The specimen is most often an ultrathin section less than 100 nm thick or a suspension on a g ...

, auger spectroscopy, and

scanning electron microscopy A scanning electron microscope (SEM) is a type of electron microscope that produces images of a sample by scanning the surface with a focused beam of electrons. The electrons interact with atoms in the sample, producing various signals that ...

. The rapid increase of temperature at the location of impact can quickly melt a target material. In extreme working conditions, the rapid temperature increase can lead to evaporation, making an electron beam an excellent tool in heating applications, such as welding or electron beam evaporation.Harsha, K. S. S, "Principles of Physical Vapor Deposition of Thin Films", Elsevier, Great Britain (2006), p. 400. Electron beam technology is used in cable-isolation treatment, in electron lithography of sub-micrometer and nano-dimensional images, in

microelectronics Microelectronics is a subfield of electronics. As the name suggests, microelectronics relates to the study and manufacture (or microfabrication) of very small electronic designs and components. Usually, but not always, this means micrometre ...

for electron-beam curing of color printing and for the fabrication and modification of polymers, including liquid-crystal films, among many other applications.

Furnaces

In a

, the electron beam provides a source of heat that can melt or modify any material. This source of heat or phase transformation is absolutely sterile due to the vacuum and scull of solidified metal around the cold copper crucible walls. This ensures that the purest materials can be produced and refined in electron-beam vacuum furnaces. Rare and

refractory metals Refractory metals are a class of metals that are extraordinarily resistant to heat and wear. The expression is mostly used in the context of materials science, metallurgy and engineering. The definitions of which elements belong to this group di ...

can be produced or refined in small-volume vacuum furnaces. For mass production of steels, large furnaces with capacity measured in

metric tons The tonne ( or ; symbol: t) is a unit of mass equal to 1,000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton in the United States to distinguish it from the non-metric units of the sh ...

and electron-beam power in megawatts exist in industrialized countries.

Welding

Since the beginning of electron-beam welding on an industrial scale at the end of the 1950s, countless electron-beam welders have been designed and are being used worldwide. These welders feature working vacuum chambers ranging from a few liters up to hundreds of cubic meters, with electron guns carrying power of up to 100 kW.

Surface treatments

Modern electron-beam welders are usually designed with a computer-controlled deflection system that can traverse the beam rapidly and accurately over a selected area of the work piece. Thanks to the rapid heating, only a thin surface layer of the material is heated. Applications include hardening, annealing, tempering, texturing, and polishing (with argon gas present). If the electron beam is used to cut a shallow trough in the surface, repeatedly moving it horizontally along the trough at high speeds creates a small pile of ejected melted metal. With repetition, spike structures of up to a millimeter in height can be created. These structures can aid bonding between different materials and modify the surface roughness of the metal.

Additive manufacturing

Additive manufacturing 3D printing, or additive manufacturing, is the construction of a three-dimensional object from a CAD model or a digital 3D model. It can be done in a variety of processes in which material is deposited, joined or solidified under computer ...

is the process of joining materials to make objects from 3D model data, usually by melting powder material layer upon layer. Melting in a vacuum by using a computer-controlled scanning electron beam is highly precise. Electron-beam direct manufacturing (DM) is the first commercially available, large-scale, fully programmable means of achieving

near net shape Near-net-shape is an industrial manufacturing technique. As the name implies, the initial production of the item is very close to the final, or ''net'', shape. This reduces the need for surface finishing. By minimizing the use of finishing methods ...

parts.

Metal powder production

The source billet metal is melted by an electron beam while being spun vigorously. Powder is produced as the metal cools when flying off the metal bar.

Machining

Electron-beam machining is a process in which high-velocity electrons are concentrated into a narrow beam with a very high planar power density. The beam cross-section is then focused and directed toward the work piece, creating heat and vaporizing the material. Electron-beam machining can be used to accurately cut or bore a wide variety of metals. The resulting surface finish is better and kerf width is narrower than what can be produced by other thermal cutting processes. However, due to high equipment costs, the use of this technology is limited to high-value products.

Lithography

An electron lithograph is produced by a very finely focused electron beam, which creates micro-structures in the resist that can subsequently be transferred to the

substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached ** Substrate (aquatic environment), the earthy material that exi ...

material, often by etching. It was originally developed for manufacturing integrated circuits and is also used for creating

nanotechnology Nanotechnology is the manipulation of matter with at least one dimension sized from 1 to 100 nanometers (nm). At this scale, commonly known as the nanoscale, surface area and quantum mechanical effects become important in describing propertie ...

architectures. Electron lithographs uses electron beams with diameters ranging from two nanometers up to hundreds of nanometers. The electron lithograph is also used to produce computer-generated holograms (CGH). Maskless electron lithography has found wide usage in photomask making for

photolithography Photolithography (also known as optical lithography) is a process used in the manufacturing of integrated circuits. It involves using light to transfer a pattern onto a substrate, typically a silicon wafer. The process begins with a photosensiti ...

, low-volume production of

components, and research and development activities.

Physical-vapor-deposition solar-cell production

Physical vapor deposition Physical vapor deposition (PVD), sometimes called physical vapor transport (PVT), describes a variety of vacuum deposition methods which can be used to produce thin films and coatings on substrates including metals, ceramics, glass, and polym ...

takes place in a vacuum and produces a thin film of

solar cell A solar cell, also known as a photovoltaic cell (PV cell), is an electronic device that converts the energy of light directly into electricity by means of the photovoltaic effect.

s by depositing thin layers of metals onto a backing structure. Electron-beam evaporation uses thermionics emission to create a stream of electrons that are accelerated by a high-voltage cathode and anode arrangement. Electrostatic and magnetic fields focus and direct the electrons to strike a target. The kinetic energy is transformed into thermal energy at or near the surface of the material. The resulting heating causes the material to melt and then evaporate. Temperatures in excess of 3500 degrees Celsius can be reached. The vapor from the source condenses onto a substrate, creating a thin film of high-purity material. Film thicknesses from a single atomic layer to many micrometers can be achieved. This technique is used in

, optics, and material research, and to produce solar cells and many other products.

Curing and sterilization

Electron-beam curing is a method of curing

paint Paint is a material or mixture that, when applied to a solid material and allowed to dry, adds a film-like layer. As art, this is used to create an image or images known as a painting. Paint can be made in many colors and types. Most paints are ...

s and inks without the need for traditional solvent. Electron-beam curing produces a finish similar to that of traditional solvent-evaporation processes, but achieves that finish through a polymerization process. E-beam processing is also used to cross-link polymers to make them more resistant to thermal, mechanical or chemical stresses. E-beam processing has been used for the sterilization of medical products and aseptic packaging materials for foods, as well as disinfestation, the elimination of live insects from grain, tobacco, and other unprocessed bulk crops.

Electron microscopes

An electron microscope uses a controlled beam of electrons to illuminate a specimen and produce a magnified image. Two common types are the

scanning electron microscope A scanning electron microscope (SEM) is a type of electron microscope that produces images of a sample by scanning the surface with a focused beam of electrons. The electrons interact with atoms in the sample, producing various signals that ...

(SEM) and the

transmission electron microscope Transmission electron microscopy (TEM) is a microscopy technique in which a beam of electrons is transmitted through a specimen to form an image. The specimen is most often an ultrathin section less than 100 nm thick or a suspension on a gr ...

(TEM).

Medical radiation therapy

Electron beams impinging on metal produce X-rays. The X-rays may be diagnostic, e.g., dental or limb images. Often in these X-ray tubes the metal is a spinning disk so that it doesn't melt; the disk is spun in vacuum via a magnetic motor. The X-rays may also be used to kill cancerous tissue. The Therac-25 machine is an infamous example of this.

History

Electron beam technology ultimately derives from work that lead to the discovery of the electron at a time when electron beams were called

cathode rays Cathode rays are streams of electrons observed in vacuum tube, discharge tubes. If an evacuated glass tube is equipped with two electrodes and a voltage is applied, glass behind the positive electrode is observed to glow, due to electrons emitte ...

. Key advances in technology to control electron beams lead resulted in the first useful scanning electron microscope in 1952 by McMullan in

Charles Oatley Sir Charles William Oatley (14 February 1904 – 11 March 1996) was Professor of Electrical Engineering, University of Cambridge, 1960–1971, and developer of one of the first commercial scanning electron microscopes. He was also a founder mem ...

's lab at

Cambridge University The University of Cambridge is a Public university, public collegiate university, collegiate research university in Cambridge, England. Founded in 1209, the University of Cambridge is the List of oldest universities in continuous operation, wo ...

. A series of PhD students in that lab continued to improved the technique. Thomas Eugene Everhart, working mostly on semiconductor surfaces, developed the voltage contrast technique and the Everhart-Thornley detector.

References

Bibliography

* Schultz, H.: Electron beam welding, Abington Publishing * Von Dobeneck, D.: Electron Beam Welding – Examples of 30 Years of Job-Shop Experience * elfik.isibrno.cz/en : Electron beam welding (in Czech and/or English) * Visser, A.: Werkstoffabtrag durch Elektronen-und Photonenstrahlen; Verlag <Technische Rundschau>, Blaue Reihe, Heft 104 * Klein, J., Ed., Welding: Processes, Quality and Applications, Nova Science Publishers, Inc., N.Y., Chapters 1 and 2, pp. 1–166 * Nemtanu, M. R., Brasoveanu, M., Ed., Practical Aspects and applications of Electron Beam Irradiation, Transworld Research Network, 37/661(2), Fort P.O., Trivandrum-695 023, Kerala, India {{Electron microscopy Electron beam