ELECTRON GUNSLaB6 CATHODESSINGLE-CRYSTAL LANTHANUM HEXABORIDEES-423E (Extended Life) LaB6 Crystal
FOR USE IN:PRECISION MICROFLATON LaB6 CRYSTALSCANNING ELECTRON MICROSCOPES
TRANSMISSION ELECTRON MICROSCOPES
ELECTRON LITHOGRAPHY SYSTEMSELECTRON ACCELERATORS
X-RAY SOURCES
FREE ELECTRON LASERSCUSTOM APPLICATIONSCARBON FERRULE
CARBON HEATER ROD
CERAMICSUB-BASE

FEATURES / OPTIONS:BASE

BASE PIN

LaB6 single crystal cathode mounting (10 X)
The Kimball Physics ES-423E (Extended Life) Lanthanum Hexaboride Heating current path through precision-machined, single-piece carbon rod
Cathode is a high performance, resistively heated, thermionic electron and mounting strips; sub-base provides rigidity and easier mounting.
source. It is currently employed in many brightness-limited electron
optical systems: SEM’s, TEM’s, probes, electron lithography systems,
etc. It is based on a well-proven heater structure, which has recently
With electron-gun oxidizing-gas partial pressures kept below 10-7 torr,
been further refined with features that include improved reliability of themany instruments can achieve thousands of hours of stable cathodeheater circuit, improved stability of the LaB6 crystal, and less exposure
operation. In SEM type instruments, lifetimes up to 3000 to 4000 hours
of LaB6 to reduce Wehnelt aperture contamination. Lifetimes in excess
may be achieved at operating temperatures of 1850 K (correspondingof 6 months of continuous operation are regularly achieved into material surface loss rates in the 0.025 micron/hour range), with fullcommercial SEM’s and TEM’s with suitable gun vacuum. Continuousbrightness and excellent stability.
With somewhat reducedoperation at the full operating temperature improves the thermalbrightnesses, as required by typical TEM instruments, lifetimes can bestability of the gun and hence beam current stability. It is no longer
even longer. The ES-423E mounting structure will last more thannecessary to wait hours for stable beam conditions in order to perform
10,000 hours. Moreover, neither the electrical heating circuit drive
quantitative EEL or EDX measurements.
impedance nor the thermal properties will drift perceptibly over thatToll Free: 1 888 KIM-PHYS (1 888 546-7497) e-mail: info@kimphys.com
Tel. 1 603 878-1616 Fax: 1 603 878-3700

period. Chemical reactivity and mechanical drift problems have beeneliminated.

COMPONENTS

The emitter is a 15 µm-diameter (standard), <100> oriented-singlecrystal, surface (standard), mounted on the end of a single-piece,
stress-free, carbon heater rod, held in place by a carbon ferrule. Therod has been precision machined with a 100 µm slot cut along the axis,
such that the heating current goes up one side and down the other.
The small area of the heating current loop keeps the unwanted heatercurrent magnetic field low. Because the rod is one single piece, noheating current passes through the crystal; there are no hightemperature current-carrying joints. A high degree of axial symmetry
keeps mechanical motions small. The small physical size fits mostWehnelts with ease. In the ES-423E, the crystal can be completely
evaporated away without affecting the heating circuit. The very tighttolerances, and the enclosed structure prevent the loss of LaB6 in themounting region throughout the entire crystal life. Reduced materialloss also means less Wehnelt contamination. Emitter dimensions aremachined to a 2 µm tolerance, (standard, 2 µm to 16 µm for microflats
up to 320 µm) with a tilt tolerance of 0.5o. Microflat alignment to the
instrument base can be provided to a tolerance of 13 µm for x, y and76 µm for z, the height above the base (less than 70 µm on request).
A high angular tolerance is maintained on the perpendicularity of theoriented single-crystal emission plane to the electron optical axis. All
cathodes receive a stabilizing run-up prior to shipment.

DETECTORSHEATING CURRENT FLOWEMITTERSMOUNTINGSTRIPLaB6 crystal mounted on carbon heater rod, and heldin place by precision carbon ferrule; note roundnessand smoothness of microflat.

3-2

INDEX / INFORMATIONEXTENDED LIFETIMEGUARANTEED LIFETIME
THOUSANDS of HOURS IN CLEAN VACUUM(MEASURED IN SURFACE LOSS)GUARANTEED AGAINST MOUNTINGSTRUCTURE FAILURE
EXCEPTIONAL STABILITY
THERMAL / CHEMICAL / MECHANICAL / ELECTRICALPRECISION MACHINED CARBON MOUNTINGHIGH OVER-TEMPERATURE TOLERANCEHIGH BRIGHTNESS / LOW ENERGY SPREAD<100> ORIENTED SINGLE-CRYSTALBEST QUALITY / HIGH PURITY MATERIALACCURATE MICROFLATSSUPERIOR OPTICS / CONTROLLED SOURCE SIZESTANDARD DIAMETERS AVAILABLE

ION GUNSLaB6 SINGLE CRYSTALLaB6 CATHODES
The real figure of merit of a thermionic electron emitter is the numberof coulombs of electrons which may be boiled off per kilogram ofcathode surface evaporated away. LaB6 is an order of magnitude
superior to the refractory metals in this key parameter. Any failure of acathode mounting structure, before the LaB6 cathode itself has beenused up, represents a waste of cathode life. The ES-423E single-piecestress-free ultra-stable carbon mount is unique. Unlike other designs
which operate near the temperatures where chemical instabilities will
set in, the ES-423E carbon mount is almost impossible to destroy byaccidental over-temperature. The melting point of Lanthanum
Hexaboride itself is somewhat over 2800 K; there have been examplesof crystals being melted (extreme over-temperature), in which theES-423E carbon mount survived. The Kimball Physics mount isguaranteed.

The ability to run over-temperature may also be utilized to clean acontaminated crystal, and reduces the risks associated with lessexperienced operating personnel.
This small source size fits most Wehnelts with ease. In excellent
vacuum with low material loss rates, the size of the cathode does not
limit lifetimes. The Kimball Physics ES-423E Long Life Lanthanum
Hexaboride Cathode is the most recent improved version of the IR 100
Award Winning design which has been used in many instruments types
for many years. Kimball Physics invented the Directly Replaceable
Lanthanum Hexaboride Cathode. Take advantage of the mostexperience in the business.

2.0 X

ES-423 LaB6 Cathode(single cone-shaped crystal with microflat emitting surface)mounted on standard AEI base (4 X)

ES-423E Single cone-shaped crystal LaB6 cathodemounted on an AEI Base

2.0 X

ES-423E Single cone-shaped crystal LaB6 cathodemounted on a CB-104 ceramic baseES-423 LaB6 Cathode(single cone-shaped crystal with microflat emitting surface)mounted on a Kimball Physics CB-104 ceramic base (4 X)

ALL DIMENSIONS ARE IN INCHES(MILLIMETERS IN PARENTHESES)

Heater Voltage and Current vs Temperature; Electrical
Characteristics vary only a few percent from Cathodeto Cathode, thus insuring predictable operation.

3-3

It is not necessarily possible to achieve all maximum specifications
simultaneously. Specifications Subject to Change Without Notice.

ELECTRON GUNSLaB6 CATHODES
3.5

HEATEREMISSION AREAHEATING CURRENTCATHODE LOADINGWORK FUNCTION
OPERATING TEMPENERGY SPREAD
LIFETIMEVACUUM LEVEL
POWER SUPPLYCAPABILITY

Lanthanum Hexaboride (LaB6) single crystal
Cone with 90o sides and microflat tip
Standard: 0.015 mm dia., larger or smaller
available
Single piece carbon rod
1.7x10-6 cm2 standard microflat, excluding sides
1.7A to 2.1A
20-30A/cm2 recommended
High loadings result in reduced lifetime
2.69 eVapprox. 1700-1900K
approx. 0.4 eVThousand plus hours with medium currents, goodvacuum
10-7 torr or better, recommended
Voltage regulated power supply
recommended, 4 V, 3 A

V-I CHARACTERISTIC (AVERAGE)

3.0

LANTHANUM HEXABORIDE CATHODE
MODEL# ES-423E

2.502/20/01
BASE STYLE: AEIo
LaB6 CRYSTAL SHAPE: 90 CONE
(AVERAGE OF 15 CATHODES)

2.0
1.5
1.00.5
ES423_V-I_00.eps
ES_423_catalog_J12300124graphs.jnb
Using Equations for Fit

0.0
0.00.51.0

1.5

ION GUNSCATHODE MATERIALCATHODE SHAPE
MICROFLAT SIZEHEATING VOLTAGE (V)ES-423E

2.0

HEATING CURRENT (A)Standard microscopy styles include: 90-15, 90-20, 60-06

1400
1200

0.0

0.5

1.0

1.5

2.0

HEATING CURRENT (A)Instrument Conditions for LaB6 Cathodes
While the cathodes can be fitted to virtually any instrument,
there are several requirements needed for achieving
quality results. The most important requirement is forclean vacuum, with partial pressures of oxidizing gases
being kept below 10-7 torr in the electron gun. Many
instruments achieve adequate vacuums as a matter ofcourse; however many others do not. A major problem is
instruments in which the pressure measurement takes
place outside the gun itself (as in the measurement of anion pump current). The actual pressure inside the gun,where outgassing is frequently high, may be much worse
than the operator is led to believe. The condition of thecathode itself, along with that of the Wehnelt aperture, may
often be used to verify the partial pressures in the gun. It
is a waste of money to put good cathodes into poorvacuum.

EMITTERS

02/20/01
BASE STYLE: AEIo
LaB6 CRYSTAL SHAPE: 90 CONE

10-5
10-6
10-7

CALCULATED EMISSION CURRENTFOUR SIZES OF MICROFLATON LaB6 CRYSTAL:
0.200 mm DIA.

10-8

0.100 mm DIA.

10-90.015 mm DIA.

0.040 mm DIA

ES423_Emis-I_00.eps
ES_423_catalog_J12300124graphs.jnb
Using Equations for Fit

10-10ES423_Temp-I_00.eps
ES_423_catalog_J12300124graphs.jnb
Using Equations for Fit

1000

10-40.0
Typical performance;data for guidance only.

0.5

1.0

1.5

2.0

HEATING CURRENT (A)A second requirement is that it must be possible toaccurately and correctly position the cathode behind theWehnelt. Some guns do not have adequate adjustment
systems. Another requirement is for controllable bias
resistors, which can reach adequately high values; some
instruments are limited by values which are too low. While
not a requirement, it is desirable to have the capability forindependent bias. It is also desirable to have accurate
heater circuit voltage and current meters. Most of these
problems can be solved in most instruments, however
significant efforts may be required. Note that the higher thebrightness level desired, the lower the tolerance to tiprecession. The electron optically allowed tip recession,and the acceptable contamination on the Wehnelt (before
gun instabilities set in), are in fact the life-limiting
parameters for current state-of-the-art cathodes. Moreinformation on all these topics may be found in the Kimball
Physics Technical Bulletins.

For more information on LaB6 operation in TEM’s and SEM’s you may download detailed technical bulletins from the website cathode support page.
# LaB6-01 General Guidelines for Operating LaB6 Cathodes.
# LaB6-02 The Relationship Between LaB6 and Cathode Life and Gun Vacuum# LaB6-03 Emission Drift—LaB6 and Gun Stability.
# LaB6-04 Oxygen Activation of LaB6 Cathodes—The Double Saturation Effect# LaB6-05 Kimball Physics ES-423E LaB6 Cathode Style 60-06 (60° Included Cone Angle, 6µm Diameter Flat)# LaB6-06 Kimball Physics ES-423E LaB6 Cathode Operating Instructions for LEICA/Cambridge Stereoscan Series SEM’s# LaB6-07 Recovery of Emission From ES-423E LaB6 Cathodes Following a Vacuum Dump
Toll Free: 1 888 KIM-PHYS (1 888 546-7497) e-mail: info@kimphys.com
Tel. 1 603 878-1616 Fax: 1 603 878-3700

3-4

DETECTORS

02/20/01
BASE STYLE: AEIo
LaB 6 CRYSTAL SHAPE: 90 CONE
(AVERAGE OF 15 CATHODES)

10-3

EMISSION CURRENT vs HEATING CURRENTLANTHANUM HEXABORIDE CATHODE
MODEL# ES-423E

COMPONENTS

1600

LANTHANUM HEXABORIDE CATHODE
MODEL# ES-423E10-2INDEX / INFORMATION

1800

TRUE TEMPERATURE vs HEATING CURRENT(AVERAGE)EMISSION CURRENT (A)TRUE TEMPERATURE (K)2000