ES-423GR Guard Ring LaB6 CathodeUser Information

Kimball Physics recommends that the LaB6-7
cathode be operated only in a vacuum of 10 torror better and at currents less than 2.2 A.
Poor vacuum or excessive current will reduce
cathode lifetime.

OPERATING VACUUM
A vacuum of 1x10-6 torr or better is required for proper
operation of the cathode, but is not considered satisfactory forlong life operation. A pressure of less than 5x10-7 torr-7(preferably 1x10 torr) is required for longer lifetimes.
Cathode lifetime will increase as the vacuum is reduced to-8
the 10 torr range. (Reference Kimball Physics Technical
Bulletin #LaB6-02, “The Relationship Between LaB6 and GunVacuum” for additional information.)Fig. 1 ES-423GR Guard Ring LaB6 Single Crystal
Cathode on AEI BaseINTRODUCTION
The Kimball Physics ES-423GR Guard Ring Lanthanum
Hexaboride LaB6 Cathode is a high performance, resistivelyheated, thermionic electron source. It is currently employedin electron sources such as SEMs, electron lithographysystems, x-ray systems, etc. The emitter is a 10 m to250 mdiameter(userspecified)singlecrystal,<100> orientation mounted on the end of a single-piece,
stress-free carbon heater rod, held in place by a carbonferrule.

INITIAL RUN-UP
Follow the initial start–up procedure recommended by
the manufacturer of the system receiving the cathode. This
serves the purpose of outgassing water vapor from inside theWehnelt cap (water vapor forms oxides on the LaB6 surface)and removes any oxides that have already formed on theLaB6 surface. Alternatively, for outgassing, run the cathode at
reduced power (about 1.8 V or about 1.6 A) for 15 to 20
minutes. During this initial run-up, the pressure in the gun will
-6
increase and should not be allowed to exceed 1x10 torr.
The temperature should be adjusted up to the normal
operating temperature gradually so that pressures do not
exceed 1x10-6 torr in the process. For operation, pressures-7
better than 10 torr are recommended. The ES-423GR
cathode is designed to resist thermal shock: after the initial
run-up and outgassing of the Wehnelt, the cathode can beturned off and on to maximum current instantly.

The model ES-423GR is available with the LaB6 crystal
cut at a cone angle of 60º or 90º and a microflat size from10 m to 250 m. These dimensions are included in the partnumber, e.g the ES-423GR style 90-50, having a 90º conewith a 50 m microflat. The LaB6 cathode is available
mounted on a standard AEI base, a Kimball Physics CB-104
ceramic base, or on a variety of custom bases for particularsystems.
HANDLINGOPERATING POWER

Cathodes are fragile and caution must be used inhandling. Do not touch the cathode structure itself, only
the cathode base. The cathodes are shipped vacuum clean
and ready to install. The use of clean room gloves isrecommended to keep parts free of fingerprints and othercontaminants.

During typical operation, the temperature of the LaB6
crystal is in the range of 1700 K (~1.8 A) to the maximum
high brightness temperature of 1900 K (~2.1 A) (1425ºC to1625ºC).
Increasing the power gradually, in smallincrements, will enable the operator to determine best
operating power. The cathode power will depend on othersettings of the system, particularly bias voltage. (ReferenceKimball Physics Technical Bulletin #LaB6-01, “GeneralGuidelines for Operating ES-423E LaB6 Cathodes,” for furtherdetails.) Always run the cathode at the minimum power
necessary for adequate emission. As with all cathodes, there
is a compromise between operating lifetime and total
emission current. See graphs for typical operating parametersof the cathode.
CAUTION: Operating the cathode above 2.1 A will limit
the lifetime of the cathode to a few hundred hours.

To remove the cathode assembly from the purple shippingcontainer:a) Place the purple base on a level surface.
b) Holding onto the lower part (purple) of the shippingcontainer, unscrew the upper cover (plexiglass) andremove it vertically to avoid hitting the cathode.
c) Grasp the edges of the cathode base and depress thepush button or loosen the screw on the side of thecontainer (shipping containers differ slightly dependingon base style) to release the cathode base (and wholeassembly).
d) Carefully lift off the cathode assembly.

311 KIMBALL HILL ROAD, WILTON, NH 03086-9742 USA
Tel: (603) 878-1616 1-888-546-7497 Fax: (603) 878-3700
e-mail: info@kimphys.com Web: www.kimballphysics.com

1

EMISSION INSTABILITY

In case of breakage, handle the cathode assembly withtweezers, being careful to touch only the carbon mount or thebase of the cathode (never the cone or the flat). If broken offprior to usage, place the cathode in a capsule or in tissue or
secure with double-sided adhesive, and return to Kimball
Physics along with the cathode base in the original shippingtube.

The <100> surface of the emitter can be sensitive to gas
evolution from downstream elements of the system,
particularly during the initial stages of use. Gas pulses, due
to electron desorption or heating, can result in emission
current variations. The persistence of possible effects likethese depends on outgassing within the system. Once thesystem is fully outgassed, cathode operation should bestable. Even though source current values are often given as
operational benchmarks here, it is still assumed that the cathodeis being driven by a voltage source.
The operating procedure of the ES-423GR cathoderequires careful attention to the cathode heating current,
cathode emission current, and chamber pressure, but should
be driven by a voltage source rather than a current source.
A current source will cause an unstable increase in cathodetemperature, resistance and voltage which results inpremature heater burnout. When driven by a voltage
source, heater current decreases over time as the cathodetemperature and resistance rise, resulting in stablepower
conditions.

FURTHER INFORMATION
Additional details are available in the following Kimball
Physics
Technical
Bulletinsonthewebsite
atwww. kimballphysics. com.

SERVICE
If a problem arises during initial installation, call Kimball
Physics Customer Service at (603) 878-1616. Cathodes may
be returned to Kimball Physics for evaluation with a return
authorization number.

2.5

LaB6-01

LaB6-02

LaB6-03
LaB6-04



LaB6-05



LaB6-06



LaB6-07

General Guidelines for Operating ES-423E
LaB6 Cathodes
The Relationship Between LaB6 and
Gun Vacuum
Emission Drift - LaB6 Gun Stability
Oxygen Activation of LaB6 Cathodes – The
Double Saturation EffectKimball Physics ES-423E LaB6 Cathode
Style 60-06 (60º Included Cone Angle,
6 m Diameter Flat)
Kimball Physics ES-423E LaB6 Cathode
Operating Instructions for Leica/ Cambridge
Stereoscan Series SEM’s
Recovery of Emission from ES-423E LaB6
Cathodes Following a Vacuum Dump

2000

V-I CHARACTERISTIC
ES-423GR on AEI Base

1900

2.0

TEMPERATURE vs SOURCE CURRENT
ES-423GR on AEI Base

1800

C7269
C7377

True Temperature (K)Source Current (A)



1.5

1.0

0.5

1700
1600
1500
1400
1300

C7269
C7377

1200
1100

0.0
0.0

0.5

1.0

1.5

2.0

2.5

3.0

1000
0.9

Source Voltage (V)

1.0

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2.0

2.1Source Current (A)Fig. 2 Typical Operating Parameters of the ES-423GR LaB6 Cathode2000

TEMPERATURE vs SOURCE POWER
AT FEEDTHROUGH

1900

ES-423GR on AEI Base

True Temperature (K)

1800
1700
1600
1500
1400
1300

C7269
C7377

1200
1100
1000
123456311 KIMBALL HILL ROAD, WILTON, NH 03086-9742 USA
Tel: (603) 878-1616 1-888-546-7497 Fax: (603) 878-3700
e-mail: info@kimphys.com Web: www.kimballphysics.com

Source Power at Feedthrough (W)22.2