Jacobus E. Crombeen

Properties and manufacture of top-layer scandate cathodes

Abstract The life and/or the staying power against ion bombardment of scandate cathodes can be improved by using a top layer of W + Sc2O3 or W + W/ScH2 on a tungsten matrix. The latter is impregnated with the usual 4-1-1 impregnant. Even at high voltage pulses the current densities are so high that the deviation from space charge limitation is small. The manufacture is discussed and the cathode life at the operating temperature of 1220 K is shown to be very long. Moreover, the relationship between processing parameters and emission recovery after ion bombardment is examined with the aid of combined sputter- and scanning-Auger measurements. It is shown that thin-layer coverage of tungsten by scandia is important to the high emission. This coverage is related to the impregnation process. After extended sputtering it cannot be completely recovered by reactivation. Consequently, the top layer cathodes cannot withstand sufficiently the usual processing and operation of television display tubes. On the other hand, they can improve the life and performance of electron devices with good vacuum and/or relatively low accelerating potentials. Moreover, activated top-layer scandate cathodes are relatively insensitive to exposure to (moist) air.

Epitaxial CoSi2 formation on (001)Si by reactive deposition

The formation of epitaxial CoSi2 thin films by reactive deposition of cobalt onto silicon (001) substrates at temperatures around 600 degrees C is described. When the deposition rate is below a certain critical value for a particular substrate temperature (for example below 0.02 nm s-1 at 600 degrees C), epitaxial disilicide formation can be achieved. Deposition rates above this critical value lead to the production of polycrystalline disilicide. A mechanism is described to explain the influence of the deposition rate on the formation of epitaxial material.

Comment on progress in scandate cathodes

Emission capability and emission recovery after ion bombardment are discussed. Impregnated top-layer scandate cathodes show better performance than cathodes with a mixed matrix of tungsten and scandia and impregnated cathodes with a sputtered layer consisting of tungsten and scandia. The recovery of scandate cathodes has been considerably improved, and it has been shown that fast emission recovery after ion bombardment is most probably feasible at a cathode operating temperature of 950 degrees C/sub b/. >

The formation of epitaxial CoSi2 thin films on (001) Si from amorphous Co-W alloys

Abstract A novel way of forming predominantly epitaxial CoSi 2 on (001) Si from an amorphous Co-W alloy layer on Si is explained Auger electron spectroscopy depth profiling, Rutherford backscattering spectrometry and X-ray diffraction have been used to investigate the interaction between the amorphous alloy and Si. An alloy composition of Co 60 W 40 was chosen which has a crystallization temperature of about 850°C. By employing anneals below 600°C, Co diffuses out of the alloy into the substrate to form CoSi 2 . After the anneal, the remaining amorphous alloy could be selectively removed from the underlying CoSi 2 film by wet-chemical etching. X-ray diffraction measurements indicated that about 75% of the disilicide film has an epitaxial relationship with the Si substrate while the other 25% has a simple twin relation with the majority of the material. The formation mechanism of CoSi 2 from an amorphous alloy on Si is discussed.

CoSi2 formation on Si(100) using an amorphous Co-Ti alloy

The formation of CoSi2 from an amorphous Co70Ti30 alloy film on Si(100) has been studied by Auger depth profiling, Rutherford backscattering spectrometry, cross-section transmission electron spectroscopy and X-ray diffraction. The solid-state reaction starts around 400 degrees C with the diffusion of Co out of the alloy into the substrate, forming an interface layer consisting of CoSi and CoSi2. The simultaneous diffusion of Si into the Co-depleted region of the film is limited for annealing temperatures below 600 degrees C. After removing the remaining top layer by selective etching, an extra heat treatment is performed to transform the mixed silicide layer completely into CoSi2. The latter is found to be partially aligned with the substrate. The amount of epitaxial CoSi2 increases with the use of higher post-anneal temperatures.

Comment on "Investigation of scandate cathodes: emission, fabrication, and activation processes" by J.W. Gibson et al

Critical comments are made on the experimental results for zero field current density j/sub 0/ and work function obtained by J.W. Gibson et al. (ibid., vol.36, no.1, p.209-14, 1989) on top-layer scandate cathodes and on an emission model proposed for them. It is shown, for example, that the determination of j/sub 0/ gives rise to erroneous results. >