Denka M-3 LaB6 cathodes, FEI/Philips

The use of an electron beam enables not only observation of the submicron world (TEM’s SEM’s and X-ray microanalysers) but also processing with submicron precision (electron beam lithography systems). The optimum cathode material for use in these instruments would possess the following properties:

• Low potential barrier (work function)
• High melting point and stability at high temperatures
• Low vapour pressure so as to reduce evaporation loss
• Chemical stability

The relative drawbacks of tungsten cathodes are a work function of 4.7eV, insufficient beam current, and a short service life. LaB₆ has a work function of 2.66eV – thus more easily emitting electrons – and is a relatively stable material, so it has been increasingly used as a material for cathodes instead of tungsten. Using LaB₆ cathodes with TEMs and SEMs, even with the electron beam narrowed down, it is possible to obtain enough beam current to achieve better resolution and clear micrographs with less noise. The principle advantage, however, is that LaB₆ can be used in a stable condition for a much longer time. Denka manufactures the purest, highest quality LaB₆ crystals for use in their cathode tips.

Applications:

• SEM
• TEM
• X-ray Beam Analysis (EPMA)
• Electron Beam Lithography

Benefits:

• High Brightness: A LaB₆ beam is 10 times brighter than tungsten, has superior resolution, and features a wide range of acceleration voltages. It provides sharp, clear pictures, down to the smallest detail. The initial brightness of a Denka Model 3 cathode (1 x 10⁶A/cm².Str) is substantially better than that of competing, mini-vogel type cathodes (typically 5 x 10⁵A/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 expected.
• Stability: Thanks to its simple and durable construction, every Denka Model 3 LaB₆ Cathode offers a stability of better than 3% per hour at 1550°C.
• Interchangeability: Denka Model 3 LaB₆ cathodes are designed as direct replacements for tungsten filaments when a vacuum in the 10^-7 range is provided.

Technical Data

Specifications: 

Denka M-3 LaB₆ Cathode for FEI, Philips Instruments (Except XL-30). Denka M-3 LaB6, Filament, PH2/90-15, standard tip.

Kimball Physics have extensive information on the use, optimisation and vacuum dump recovery of these cathodes. 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