Table 3.
Comparison of pertinent electron source characteristics
| Unit | Tungsten filament | LaB6 filament | CeB6 filament | Cold field emission filament | Schottky field emission filament | |
|---|---|---|---|---|---|---|
| Reference number | 99 | 14, 76 | 12 | 75,99,134 136, 143 | 75,99,125 126, 134 135, 136 139 | |
| Angular current intensity | mA/sr | n/a | n/a | n/a | <0.1 | 0.1 to 1.0 |
| Source brightness | A/(cm2·sr) | 106 | 107 | 107 | 109 | 108 to 109 |
| Emitting surface area | μm2 | >>1 | >1 | >1 | 0.02 | 0.2 |
| Crossover or virtual source diameter | nm | >104 | >103 | >103 | 3 to 5 | 15 to 25 |
| Energy spread | eV | 1 to 3 | 1 to 1.5 | 1 to 1.5 | 0.2 to 0.3 | 0.3 to 1.0 |
| Source temperature | K | 2500 to 2900 | 1800 | 1800 | 300 | 2.8 |
| Work function | eV | 4.5 | 2.6 | 2.4 | 4.5 | 2.8 |
| Operating vacuum | Pa | 10−4 | 10−6 | 10−6 | 10−9 to 10−11 | 10−6 to 10−9 |
| RMS short term beam current stability | % | <1 | <1 | <1 | 4 to 6 | <1 |
| Typical service life | h | 40 to 100 | 1000 | >1500 | >2000 | >2000 |