Kimball Physics specializes in the design and manufacturing of precision high-tech scientific instruments with over 55 years of experience in ultra-high-vacuum electron and ion optics. Our expertise is in high stability electron emitters, precision electrostatic and magnetostatic optics, along with state-of-the-art vacuum chambers and fittings.

Our goal with the  “Learning Center” is to provide an informal resource base for fundamental understanding of the basic terminology, principles and parameters, and specifications of electron and ion beam systems.

With this information resource, our intent is to help you move more quickly towards your solution and to choose the system and components that would work best for your application.

Learning Center Topics and Resources will include tutorials and overviews for :  Electron Gun (Beam) Systems, Cathodes /Electron Emitters, Multi-CF Vacuum Chambers and Hardware Accessories, Detectors (Faraday Cups and Phosphor Screens), and eV Parts ( a prototyping and mounting system toolkit).

We also include additional documents and white papers that discuss and cover relevant and more advanced topics.

A Quick References roadmap is provided below to help you quickly find content.

A glossary of terms frequently used is also provided for user convenience.

This section will always be a work in progress with continued updates and the addition of new and relevant topics. Please reach out to Kimball Physics for any additional topic suggestions. 

Quick References

eV Parts

  • ev Parts: General Information (PDF)
  • ev Parts: Information and Construction Techniques (PDF)
  • Internal Mounting Concepts and Examples




A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z 


AEI Base

An industry standard base for cathode emitters. Typically, the ceramic disk dimensions are approximately 12.0 mm in diameter with a thickness of 2 mm. The spacing between the center of the pins on the socket side is about 6.45 mm, with 1.0 mm pin diameters and 4.7 mm pin lengths.


1)  Positioning of the physical elements of the electron/ion gun so that the charged particles travel in  the optimal path through the gun.

2) Mechanical beam alignment: A mechanical adjustment of the gun that changes the orientation of elements of the gun with respect to other elements or with respect to the target; use of a device to line up gun with the target, for example, using a Port Aligner which consists of two rotating angled disks.

3) Magnetic compensation alignment: Displacement of the electron/ion beam in a plane (X-Y) perpendicular to the line of travel (Z) of the beam, by means of the magnetic    fields    produced    by    electric    coils (X+,X- and Y+,Y-) arranged around the beam; used to position the beam on the target and improve beam current and beam uniformity.

Analog Meter:

A meter with a dial and pointer which displays current or voltage.

Amperes, Amps; A:

A measure of current (electron flow).

1 Ampere = 1 Coulomb/sec = 6.242 x 1018 electrons/sec

Anode: (also G-2)

Often referred to the more positively charged electrode.

The second electrostatic lens element in an electron gun, which usually provides the more positive potential difference with respect to the cathode electron source that accelerates the electrons.

The third element of the triode (cathode, grid and anode); usually a tube with an aperture (hole); often grounded.


A small hole that the electron/ion beam passes through, which can limit the divergent trajectory of the beam path and also control the diameter of the beam.


Most electron guns in SEM and TEM use auto-bias operation, whereby the only electrical variable other than the cathode heating is the value of the auto-bias resistor.


Barium Oxide (BaO):

A coating applied to a cathode electron source that reduces the work function enabling electron emission at lower temperatures, thus also reducing light output.

Barium Oxide (BaO) Cathode:

A Kimball Physics thermionic low light and low temperature electron emitter, with these characteristics related to its lower work function.

Bake out:

Heating the electron/ion gun while in vacuum to remove and pump away contaminants.

Beam Blanking:

Deflecting the electron/ion beam to one side of the gun tube to interrupt the flow of particles to the target without actually turning off the beam; can be used to pulse the final beam current repeatedly on and off, controlled by a TTL signal input.

Beam Current:

The electron/ion current exiting the gun, usually, measured by a Faraday cup at the end of the gun (in mA, µA, or nA); not identical to emission current.

Beam Current Density:

The beam current per unit area reaching the target (typically in µA/cm2).

Beam Divergence:

The angular spread of the electron/ion beam as it exits the gun (in degrees º).

Beam Uniformity:

A qualitative statement about the beam current distribution, usually Gaussian-like.

Beam Spot Size:

The spot size is the diameter of the electron/ion beam at a given distance from the gun (working distance). Typically range from 10 µm to several hundred mm, depending on the gun. The spot is measured either visually on a phosphor screen, or by a Faraday cup array; as the edge of the circle may not be clear cut, the full-width- half-max measurement (FWHM) is defined as the width that includes all beam current densities greater than half the maximum density. In a flood gun, which does not have focusing lenses, the size of the spot is mainly dependent on the working distance, on how far away the target is from the end of the gun.

Bias Resistor, controllable:

A resistor used to control emitter heating current more accurately.

Brightness: β:

Brightness or source brightness; electron density or number of electrons per unit area or (spherical sector).  High brightness applications (which require small spot, high resolution) include scanning electron microscopes, transmission microscopes, electron probes, scanning Auger systems and electron lithography systems.

β = σ /πkT

σ = work function= eV

k = Boltzmann constant = 8.617 x10-5 eV/K

T= absolute temperature = K

Units=Current/unit area/unit solid angle

Brightness Limited:

Brightness-limited electron optical systems: SEM’s, TEM’s, probes, electron lithography systems, etc.



 (1) Firing unit cartridge:  For  electron  Guns: An assembly containing cathode and grid which is part of a larger firing unit of some guns and can be replaced separately.

(2) Ion source cartridge or alkali metal cartridge: For Ion Guns: A cup containing a solid that is heated to produce alkali metal ions directly by a solid-solid chemical reaction, part of the ion source firing unit.


The structure in the electron gun that emits electrons, also known as emitter, electron source; the first element of the triode (cathode, grid and anode); simple configuration may consist of a sharply bent wire (hairpin) or a heated wire and an emitting disc; several other types of materials and configurations to optimize performance and live-time parameters.

Cathode Loading:

A/cm2;  Typical ranges of 3.8 to 80

Cathode Poisoning:

Usually refers to an unintended chemical process involving the surface of the cathode that unfavorable alters its emission characteristics.

CB-104 base: 

A compact Kimball Physics ceramic cathode base

CB-105 base:

A compact Kimball Physics ceramic cathode base.

CF, ConFlat:

A type of vacuum flange with a knife edge on the sealing surface; sized by the approximate outside diameter: 1.33 CF ~1.33 inch ~34 mm,

2.75” CF ~2.75 inch ~70 mm, 4.5” CF ~4.5 inch ~114 mm.

(The ConFlat flange was invented by Bill Wheeler at Varian; ConFlat is a registered trademark of Varian Associates.)

Current Density: J (emitted current density)

Derived for thermionic emission with Richardson-Dushman equation (related to work function and temperature). Amperes per meter2, A/m2

Cut off (also Grid cut off):

 (1) Shutting off the flow of electrons/ions to the target; for electrons, by making the grid voltage sufficiently negative that the electrons from the cathode are repelled and do not go through the grid, or similarly for positive ions, by making the grid sufficiently positive that the ions in the source region are repelled.

(2) The minimum grid voltage that reduces the beam current to zero.



Data acquisition

(1) Communication between a computer program, such as a LabVIEWTM executable program, and a physical system, such as an electron or ion gun power supply

(2) Also refers to computer boards and cables used to transfer data and control signals to and from the equipment

Deflection, X and Y Deflection:

(1) Electrostatic or electromagnetic displacement of the electron/ion beam in a plane (X-Y) perpendicular to the line of travel (Z) of the beam; a) Electrostatic by means of voltages applied to two pairs of plates (X+,X- and Y+,Y-) , or b) Magnetostatic by currents applied to deflection coils, arranged around the beam; used to position the beam on the target, generally without affecting the focus and energy of the beam. Also sometimes called centering or X-Y centering.

(2) The two power supplies that apply voltage to the deflection plates. Also the manual control on the power supply panel that control the deflection power supplies.

Differential Pumping:

 Maintaining a different vacuum pressure in the electron or ion gun and the main vacuum chamber by connecting separate vacuum pumps to the two areas, usually using a Compact Tee differential pumping connector on the gun.



(1) Emission Current Control for Electron Guns: Feedback circuitry that regulates the source power supply that heats the filament; used to maintain a constant emission current from the cathode.

(2) Emission Current Control For Alkali metal Ion Guns: Feedback circuitry that regulates the source power supply that heats the alkali metal cartridge; used to maintain a constant ion emission current from the ion source.

(3) Electron Current Control for Gas Ion Guns: Feedback circuitry that regulates the source power supply that heats the filament in the ion source, so that a constant flow of electrons is given off; only indirectly controls the production of ions by the ion source.

(4) Also the power supply panel controls and switch that control the ECC circuitry.

Electric Field, E:

Typically, a field around an electric charge that exerts a force on other charges, with attraction between dis-similar charges, and repulsion between like charges. Electric fields are created by electric charges (Gauss’s law) or by time varying magnetic fields (Faraday’s law of induction). For example, an electric field is present between the conduction plates of capacitor while maintain a voltage (potential difference) between the plates. With an electron gun, an electric field is created between the source cathode and the anode to accelerate the thermionic emitted electrons into an electron beam. An electric field is also typically created between the Wehnelt and the cathode source to modify or temporarily suppress emission.

-on an atomic scale, an electric field is responsible for the attractive force between the electrons and the atomic nucleus.

-SI units, Newtons per Coulomb, N/C

-Volts/meter, V/m


An electrode is typically an electrical conductor used to contact a non-metallic part of a circuit. In an electron gun system, the negative electrode is the cathode, the positive electrode is the anode, and the non-metallic medium is the partial vacuum space. In an EKG system to measure electrical cardiac activity, electrodes are placed opposing sides of the chest to analyze the cardiac rhythm.

electron Volt (eV):

  • a unit of energy equivalent to 1.6 x 10-19joules. It is amount of energy gained or lost by the charge of a single electron moving across an electric potential difference of 1 volt.
  • 1 eV is equivalent to the energy obtained by a particle with unit electronic charge of (1.6021 x10-19coulombs) accelerated by a 1-volt potential difference and is equal to 1.6021×10-19joules.
  • eV = kg m2/sec2
  • eV = 1.602 x 10-19joules
  • 1 eV = E(eV) = V(V)x Q(e) = (1 V) x (1.6 x 10-19 C) per electron   = 1.6 x 10-19 J
  • 1 eV = V x e (volt x elementary charge (1))
  • For example what is energy in eV in a circuit with a 20 volt electric field potential and the charge flow of 40 electron charges;  E = 20V x 40e = 800 eV
  • E(eV)= V(V) x Q(C) / 1.602176565 x 10-19 (Volts to eV calculation with coulombs)
  • To convert from eV to V with e an elementary charge  of 1;  V = eV / e: for example      100 eV / 1 = 100 V
  • To convert from eV to V with coulombs, V(V)= 1.602176565 x 10-19 x E(eV) /Q(C)

Electron Charge e :

  • charge carried by a single electron
  • e- = electron charge = -1.602176565 x 10-19C/electron
  • 1 coulomb (C)= 6.242 x 1018electrons

Electron Gun:

Also known as an electron emitter source, a typically system produces a collimated electron beam that has a precise kinetic energy. A typical thermionic system is comprised of a heated cathode, electrodes to generate an electric field, including a Wehnelt electrode to initially focus the beam and an anode, with a large potential difference with the cathode to accelerate and further focus the electrons. The system typically needs to function in a moderate to high vacuum and requires several power supplies for various components of the systems.

Electron mass:

  • 9.11 x 10-31kg/electron

Emission Current:

(1) For Electron Guns: The total electron current that leaves the cathode and  goes  to  ground  (in mA or µA); equivalent to all the current that exits the gun (beam current) plus all the current that lands on grounded elements within the gun.

(2) For Ion Guns: The total ion current produced by the ion source that goes to ground (in mA or µA), directly measured in only some gun; not identical to the electron emission current which causes gas ionization or to the ion beam current which exits from the gun; equivalent to all the current that exits the gun (beam current) plus all the current that lands on grounded elements within the gun.

Encoder Wheel:

 A disc-shaped rotary switch (thumb wheel) on early power supplies with FlexPanel control that adjusts the programming signal of a selected supply or menu item. The rate of increase/ decrease varies with the speed of rotation.


A device for emitting charged particles, i.e. a cathode to emit electrons, or an anode to emit charged ions.


(1) Kinetic energy  of a charged particle  emitted  from the gun; equal to ½mv2, where m is the particle mass and v is the particle velocity; this energy is achieved by applying accelerating voltages to elements of the gun. 1 eV is equivalent to the energy obtained by a particle    with unit electronic charge (1.6021×10-19 coulombs) accelerated by a 1 volt potential difference and is equal to 1.6021×10-19 joules.

(2) The energy power supply that provides the electron/ion accelerating voltage; other power supplies can be referenced to this power supply. Also, the potentiometer and switch that control the energy power supply.

(3) For Ion Guns: also called Ion Energy.

Extract (also G-2):

 (1) The second electrostatic lens element in the ion gun, which provides the potential difference that extracts the ions from the ion source region and accelerates them; usually a tube with an aperture (hole); often grounded, but may be referenced to Energy and have a variable voltage.

(2) The power supply that applies voltage to the extract element in some ion guns. Also, the potentiometer that controls this power supply.

(3) For Ion Guns: also called Ion Energy


Faraday cup:

A particle-collecting device consisting of a shielded cup and output wire; usually used with an ammeter in series to ground to measure beam current.


Electrical, gas, mechanical and other connections (wires, tubing, insulators etc.), usually from vacuum to non-vacuum parts of a system.

Filament, Fil+, Fil-:

 (1) The wire heating part of the standard cathode or ion source.

(2) Also the positive and negative leads to the cathode or ion source.

Firing Unit:

 (1). For Electron Guns: The part of the gun that emits the electrons; the assembly that can be replaced as a unit, usually consisting of the complete triode (cathode, grid and anode) or just the cathode and grid; in some guns, only a part of the firing unit called the firing unit cartridge needs to be replaced.

(2) For Ion Guns: The part of the gun that produces the ions; the assembly that can be replaced as a unit, usually consisting of the gas ion source or alkali metal ion cartridge, the grid and sometimes extract elements.

Flange Multiplexer:

A vacuum component with one flange surface (usually 2.75” CF) to connect to a vacuum port and five smaller flanges (usually 1.33” CF) for various feedthrough and cable connections; used as the mounting system on many electron/ion guns.


(1) A Kimball Physics power supply control panel design featuring a digital screen, selector buttons and a single variable control (up/down arrows).

(2) More specifically, the set of digital interface controller boards designed by Kimball Physics, used in power supplies for programmed control of supplies, metering, and display on a digital vacuum fluorescent screen. Power supplies with this controller are considered FlexPanel units even if they are “black box” style with no manual controls or display screen.

Focus (also Lens):

(1) One or more electrostatic or magnetic lens elements in the electron/ion gun that control the beam spread; usually controls spot size at the target; in some guns, may control beam divergence at points internal to the gun.

(2) The power supply that applies voltage or current to the focus/lens element(s). Also, the potentiometer that controls this power supply.


Gasket to Gasket Nominal Thickness:

Gasket Crushing Allowances:  In general, with copper gasket use, the copper gasket is not fully “crushed” to enable surface to surface mating of the CF flange surfaces with a zero gap (of course there are always exceptions).  A typical remaining gap between the CF flange surfaces is roughly 0.20 inches.  Multi-CF Fittings have been designed to provided assembled center-to-center spacings which are multiples of 0.700 inch.  To maintain this 0.700 inch spatial periodicity, each CF flange face has been set back by a gasket crushing allowance of 0.010” (0.25 mm),  to provide a “gasket to gasket” nominal thickness that is used for system planning and layout.

For example, a MCF450-ThnFlg-E2-400 Thin Flange fitting,  with a nominal thickness of 0.400 inch between opposite gasket center planes, the actual thickness is 0.380 inch (=0.400 – (2 x 0.010)).


 A normal distribution curve: even if a beam current distribution is not strictly Gaussian, this term is used to describe distributions that are brightest in the center of the spot and fade off at the edges.

G-1, G-2, G-3, G-4:

 The series of apertures and electrostatic lens elements in the electron/ion gun labeled by their position (first, second, third, fourth) instead of by common names.

Grid (also G-1 or Wehnelt):

The first electrostatic lens element in the electron/ion gun; the second element of the triode in electron guns; provides the first control and usually focuses the beam to a crossover; usually a tube with an aperture (hole), but may be a mesh (like a screen); can be used to cut-off the beam in most guns.

-The power supply applies voltage to the grid element. Also, the potentiometer that controls the grid power supply.

-This is all commonly referred to as the Wehnelt or grid cap.

Gun Bias Voltage:

This is the voltage between the filament and Wehnelt cap or grid that shapes the e- beam at its origin and keeps the filament current (feedback) at saturation.


High Brightness:

In an electron gun system, typically a cathode emitter that enables emission of electrons into a beam with a high current density.


 High Voltage, sometimes used as a label on the Energy switch or to refer to an additional Power Supply unit needed for a high current electron gun.


Insertion Length:

 The length of the gun that is in vacuum, from the vacuum sealing surface to the beam-exit end of the gun.

Ion Cage:

 The part of the ion source where the gas is ionized in some ion guns, consisting of a wire coil that accelerates the ionizing electrons.

Ion Emission Current:

 The total ion current produced by the ion source (in mA or A); not identical to the electron emission current which causes ionization or to the ion beam current which exits from the gun.


 (1). The production of a charged particle (ion) from a neutral atom or molecule by either the loss of one or more electrons (positive ion), or gain of one or more electrons (negative ion).

(2) Electron impact ionization- Ionization by bombarding a gas with electrons, which collide with and remove electrons from the neutral gas molecules producing positive ions.

(3) Surface ionization- Ionization by heating a solid alkali metal compound so that ions are produced in a solid-solid chemical reaction.

Ion Source:

 (1) The structure in the ion gun that produces ions; for gas ions, usually consists of an electron-emitting filament, shields and an ion cage; for alkali metal ions, consists of a chemical cartridge and its heating filament.

(2) Another term for a complete ion gun; the entire unit made up of the ion source which creates the ions, and the electrostatic lens system that controls and focuses the ions to produce the final ion beam.


A conductive material used to mount or support materials used as electron emitters (Yttrium)



Kelvin (K):

  • absolute temperature
  • 0 Kelvin = absolute zero
  • 0 Celsius (C) = 273.16 degrees (K) = triple point of water


Lanthanum Hexaboride (LaB6):

A cathode material with low work function and long lifetime; a single crystal structure cut and mounted on a heating rod; used as a cathode in some electron guns to produce electrons that can be focused to a small spot.

LaB6 Cathodes:

Kimball Physics manufactures several cathodes based on LaB6, including single-crystal, guard ring, and planner disc.


National Instruments Inc. software used by Kimball Physics to develop programs to control the electron or ion gun power supply; allows the system to  be operated remotely via a virtual instrument panel on a computer screen; also allows automated collection of data.

Lens (also Focus):

(1) One or more electrostatic or magnetic lens elements in the electron/ion gun that control the beam spread; usually controls spot size at the target; in some guns, may control beam divergence at points internal to the gun.

(2) The power supply that applies voltage or current to the focus/lens element(s). Also, the potentiometer that controls this power supply.




Nominal Distance:

In engineering, a nominal value is a typical or specified value of a physical quantity that is close to, but not the same as, the actual value. It is also known as the “design” or “expected” value.  For example with Kimball Physics Thin Flanges, the ”gasket to gasket” nominal thickness is not the actual thickness of the flange if measured with a caliper or micrometer.  The actual thicknesses are 0.155” for the nominal 0.175” flange, and 0.380” for the nominal 0.400” flange. The nominal distance is an estimated thickness to account for the crushing of the copper gasket in the CF flange, and to provide spacing guidance for designing and planning the system.

For example, a MCF450-ThnFlg-E2-400 Thin Flange fitting,  with a nominal thickness of 0.400 inch between opposite gasket center planes, the actual thickness is 0.380 inch (=0.400 – (2 x 0.010)).




A quantitative term used in the description of charged particle beams that indicates how significant the space charge effect influences the beam’s motion.


 A state of matter in which outer electrons are not held to the rest of the atoms or molecules, so there are free electrons and free ions in a gas-like cloud; used as a source for ions in some guns.

Power Supply:

 (1) The complete unit containing electronic circuitry, meters, and controls, that takes power input from the outside line and converts it to voltages and currents required to run the electron/ion gun.

(2)  An individual group of electronic circuits, contained in the larger unit, that produces voltage/current applied to a specific element in the electron/ion gun.

Pulsing (also Beam Pulsing):

 Rapidly stopping and starting the flow of electrons/ions, with a variable width (time on/off) and variable repetition rate; usually accomplished by rapidly switching the grid voltage to the cut-off potential; can be controlled in one of several ways: manual control with the grid potentiometer, remote computer control, dual grid power supplies with a TTL switching signal, capacitive pulsing with a pulse junction box and an external pulse generator.

Pulse Junction Box:

A capacitor-containing device that combines input from an external pulse generator and the voltage from the grid power supply to vary the voltage applied to the grid; used to turn the beam current on and off rapidly; can be a separate box or part of a Grid Pulsing Cable.




Movement of the electron/ion beam in a synchronized   pattern   sweeping    back    and    forth  (X direction) while simultaneously moving down more slowly (Y direction), then returning to the start position without sweeping back and forth (retrace); used to cover an area of the target region fairly uniformly over time; produced by two synchronized cyclical voltages or currents applied to the X and Y deflection plates or deflection coils in the gun. Rastering may also be non-synchronized, in which case there is no retrace segment

Refractory Metal Cathode:

A cathode based on a class of metals that are extraordinarily resistant to heat and wear. Elements such as niobium, molybdenum, tantalum, tungsten and rhenium, with their melting points above 2000C, their high hardness and density, and relative chemical inertness are typically included in this group.

Richardson Constant AR:

  • AR= A/m2K2
  • AR(LaB6) = 29
  • AR(CeB6) = 3.6

Richardson-Dushman Equation:

Equation used to estimate the current density (emission) from thermionic heated cathode electron source.

  • σ = j = A/m2
  • σ= j  = ART2exp(-eΦ/kT)
  • = ART2 e(-eΦ/kT)
  • AR= Richardson constant
  • T = temperature K
  • Φ = work function eV
  • k= Boltzmann’s Constant
  • -e = electron charge = -1.60 x 10-19 C/electron

Rocking (also Beam rocking):

Movement of the electron/ion beam in an unsynchronized pattern sweeping back and forth (X direction), while simultaneously moving up and down more slowly (Y direction), with no retrace; used to cover an area of the target region uniformly over time; produced by magnetic fields from varying currents in electrical coils around the beam in the gun.


Schottky Effect:

The effect where a strong electric field (E) at the cathode surface enhances cathode emission current density and lowers the barrier to thermionic emission.

Secondary emission: a phenomenon whereby a primary incident particle of sufficient energy, hitting or passing through a surface, induces the emission of secondary particles.


Scanning electron microscopy


 (1) For Electron Guns: The power supply that produces the voltage and current that heats the cathode causing it to emit electrons. Also the potentiometer and switch that control the source power supply.

(2) For Ion Guns: The power supply that produces the voltage and current that heats the filament of the ion source, either causing the filament to emit electrons for gas ionization, or heating the alkali metal cartridge for solid ionization, depending on gun. The potentiometer and switch that control the source power supply.

(3) The cable and power supply connector that include the source (filament), grid and other leads, depending on the electron/ion gun; the H.V. Multiconductor Source Cable.

(4) Ion source See Ion Source above.

Space Charge:

The electric field resulting from the presence of several charged particles (electrons and ions) in a region of space; can limit the emission of more electrons from a cathode or limit the ions extracted from an ion source; can also affect the path of charged particles through a region.


The electron/ion beam at the target area; can be seen as a (usually circular) light area on a phosphor screen.

Spot Size:

The diameter (in mm or μm) of a circle that contains most of the electron/ion beam at a given distance from the gun (working distance); measured either visually on a phosphor screen, or electrically by sampling beam current density across the spot with a Faraday cup; FWHM (full-width-half-max) measurement is the width that includes all beam current densities greater than half the maximum density.

Sterad: Steradian:

the SI unit of solid angle, equal to the angle at the center of a sphere subtended b a part of the surface equal in area to the square of the radius.



A refractory metal commonly used as the electron emitting material in a cathode.

Tantalum Disk Cathode:

A Kimball Physics cathode electron emitter

  • Kimball Physics resource:
  • ES-042 Tantalum Disc Cathode
  • ES-042 Tantalum Disc Cathode Tech Doc


The place (a plane) at which the electron/ion beam is aimed.


Transmission electron microscope: a form of microscope where the image is derived from electrons passing through a sample, and where there is variable passage of electrons through the various spatial regions (x, y) of the specimen with the variable attenuation used to create an image. At lower magnifications TEM image contrast is due to differential absorption of electrons related to differences in material due in composition or thickness. For higher magnifications, more complex wave interactions occur and modulate the intensity of the image, requiring more advanced methods of images analysis.


An electron extraction and acceleration unit used in some electron guns, consisting of four elements: cathode, grid, a variable first anode, and a grounded second anode.

Thermionic Emission:

Emission of electrons or ions from a metal or other coating material by heating the emitter in order to impart enough energy to overcome the work function of the emitting material.


The basic electron extraction and acceleration unit of most electron guns, similar to a vacuum tube, consisting of three elements: cathode, grid (Wehnelt), and anode.


A refractory metal commonly used in cathodes, because of its high melting point, either as the electron emission surface or as the heater leg.


Typically measured in torr (760 torr = 1 atmosphere).  Several types of pumping systems are used to lower pressure to create vacuum- roughing pumps, ion pumps and getter pumps.

  • Low vacuum ~ 10-4torr
  • High vacuum ~10-7torr
  • Note that a high vacuum means lower pressure and less gas molecules.

Vapor pressure:

The pressure exerted by a vapor in equilibrium with its condensed phases (liquid or solid) in a closed space at a given temperature. Vapor pressure increases with temperature.

Equilibrium vapor pressure can be defined as the pressure reached when a condensed phase is in equilibrium with its own vapor. In the case of an equilibrium solid, such as a crystal, this can be defined as the pressure when the rate of sublimation (solid directly to gas) of a solid matches the rate of deposition of its vapor phase. For most solids this pressure is very low. However, with cathodes functioning at elevated temperature with small physical dimensions, the magnitude of physical structure loss secondary to sublimation is significant and limits the lifetime of the cathodes.





-Another term for grid, G1 or cap, from the physicist, A. Wehnelt.

-Creates a secondary electric field in the vicinity of the cathode to influence /control electron emission

Work function: Φ, W:

A material-dependent measure of the work per unit charge needed to emit a charged particle (usually an electron) from the emitting material into the vacuum just adjacent to the material surface.

  • Φ (LaB6) = 2.70 eV
  • Φ (CeB6) = 2.65 eV
  • Φ (Tungsten ) = 4.5 eV


 X axis, Y axis:

Arbitrarily-defined horizontal and  vertical lines used as reference for motion of the beam in the target area for deflection, rastering, or alignment; correspond to the position of four deflection plates in the gun.



Material with atomic number of 39 that is a transition metal used for fabrication of electron sources.  At Kimball Physics, the oxide of Yttrium, Y2O3, is used as a coating on the surface of Iridium and used as an electron emission source.

Yttria-Coated Iridium Cathodes:

A Kimball Physics thermionic cathode that is designed for more rugged applications and is more resistant to oxidation in less favorable vacuum conditions.


Z axis:

A reference line through the exact center of the electron or ion gun, in the direction of electron or ion travel; the approximate beam line.

Zoom Lens:

 A series of electrostatic lens elements in the electron/ion gun (including anode or G-2, focus, and sometimes other lenses) that both focuses and accelerates / decelerates the beam; allows spot size and beam current to remain roughly constant as energy is varied.