Lanthanum hexaboride (LaB6) is one of the best thermionic emission materials, because of its low work function and high melting point. DENKA LaB6 Cathode has been highly reputed as an electron source for electron microscopes and electron beam lithograph apparatus.
Single crystal of high purity and quality, grown by floating zone technique, provides stable emission characteristics. Sophisticated machining covers various cone angles and dimensions. It is the only DENKA that can provide the hemispherical shape tip.
- Low potential barrier (work function)
- High melting point and stability at high temperatures
- Low vapour pressure ‐ reduces evaporation lost
- Chemical stability
- High brightness: LaB6 beam is ten times brighter than tungsten, has superior resolution ‐ wide range of acceleration voltages. It provides sharp and clear pictures even to the smallest details. The initial brightness of a Denka Model 3 cathode (1 x 106 A/cm².Str) is substantially better than that of competing mini‐vogel type cathodes (typically 5x105 A/cm².Str)
- Long life: Heat and vacuum are the final determinants of any cathode tip's life, but at 1550°C and a vacuum of 10‐7 Torr, a service life of about 500 hours can be achieved.
- Stability: Every Denka Model 3 cathode offers a stability of better than 3% per hour at 1550°C
- Interchangeability: Denka Model3 LaB6 cathodes are designed as direct replacement for tungsten filaments.
|Operating temperature||≤ 1600°C however operation ≤ 1550°C strongly recommended|
|Operating pressure||≤ 2.7x10‐4Pa (2x10‐6Torr) however operation ≤ 2.7x10‐5Pa (2x10‐7Torr) strongly recommended|
|Heating electrical power||Power consumption ≤ 8.0W at 1550°C|
|Typical life||500hr (depending on operating condition and circumstance)|
|LaB6 tip shape||90° 15µmR (standard type), 90° 20µmφ (long lifetime)|
The cathodes that are marked in stock can be dispatched immediately and are normally received within 1‐2 day/s of ordering (please advise at the time of ordering that you require expedited shipping). If out of stock, cathodes may take 4‐5 weeks to be delivered.
Please note that one base type suits LEO/ Zeiss/ CAMSCAN/ Cameca and TESCAN
SEM & STEM
Quartz lightpipes with P47P scintillator are available for most instruments. Email your requirements, stating make and model of instrument and, if possible, length and diameter of pipe; straight or angled. Inquire.
JEOL STEM detectors are recoated.
Tungsten filaments, new or rebuilt, are formed in high-precision fixtures using a special-alloy tungsten wire to minimise strain. Precise dimensions and microscopic inspection guarantee consistent quality and performance. All filaments are annealed to reduce movement during operation. For most instruments refurbished filaments are cheaper than new ones. There is no doubt about their quality: refurbished filaments' life expectancy and stability are identical to that of new ones.
Minimum order for refurbished filaments is six.
Filament rebuilding services include:
- reconditioning of the base
- cleaning and/or replacement of necessary parts
- instalment of new standard loop or special filament tip
- vacuum normalising
- microscopic inspection
Bases can be cleaned and rebuilt many times.
Below is the cost per filament, but minimum order for refurbished filaments is 6, sent to us in a suitable box.
The large gain in brightness and long operating life of Lanthanum Hexaboride cathodes are well known. Kimball Physics' LaB6 cathodes are at least equal in these respects to other cathodes and they also offer a price advantage.
Additionally, Kimball designed their cathodes with a much larger crystal and a one-piece base. The result is greater robustness and much improved life when the operating conditions are less than optimal, such as a vacuum of not quite the desirable 10-8 torr. Lesser vacua result in a contamination layer on the crystal. Overheating the cathode will remove this, but frequently leads to early failure of the Vogel mount design employed by other LaB6 cathode manufacturers. Accidental overheating of the cathode is much better tolerated by Kimball's design.
We recommend Kimball LaB6 cathodes for all electron beam instruments equipped with ion getter or turbo molecular pumps and nitrogen backfill of the column.
- Greater brightness that is available results in higher resolution, better EDS count rates in high power TEM and much greater uninterrupted operating life.
- For low power work where high brightness is less important, cathode life can be over 5000 hours. Even with less than ideal vacua, cathode life of more than 1000 hours is expected.
- Beam current stability is superb. This makes LaB6 cathodes suitable for quantitative microanalyses, provided the instrument has a suitable vacuum system.
In summary: Kimball's LaB6 cathodes are less risky to operate; their lower cost and long operating life yield savings in cathodes, instrument downtime and operator's time. If your instrument is suitable, then these better performing LaB6 cathodes are more economical to use for routine operation than standard tungsten filaments.
- The angle of the cone makes very little difference to LaB6 performance. All cathodes except for those with very small micro flats are supplied with a 90-degree cone. The top of the cone is machined to provide a micro flat.
- Micro Flats: Larger flats provide a larger illuminated area and greater longer-term beam stability, as is required for microprobes, but less brightness. Conversely, smaller micro flats result in greater brightness with a smaller illuminated area at given settings compared to larger micro flats. Cathodes with 15 or 20 square micrometer flats are most commonly sold to users who routinely need high magnifications. The 20 square micrometer flats are excellent for labs working mostly on sectioned specimens; they are a compromise that offers the LaB6 long cathode life and gives some additional brightness over W filaments. 40 square micrometer flats are available, but at considerably greater cost. At the other end of the scale we can provide a 60-6, which is especially suitable for constant very high-resolution work, these cost only ~AUD50 more than standard cathodes.
Please request a quotation for special cones/flats. Specials are generally on 5 weeks delivery.
Kimball Physics have extensive information on the use, optimisation and vacuum dump recovery of these cathodes. All of this available online at http://www.kimballphysics.com/
ProSciTech also supplies any other Kimball products, including tantalum disc and Thorium oxide emitters.
To order, indicate make and model of instrument. The size of the normally supplied microflat is 15 square micrometers
E.g.: LaB6 Cathode 90-15 for Cambridge S-410