ABSTRACT
We report on the change in the shape, size and composition of spherical precipitates, found in an Fe-Cu and an Al-Ag alloy, as the base temperature, pulsing mode and parameters are adjusted. In the case of the Al-Ag alloy, the difference in the evaporation field between precipitates and matrix can be minimised at low temperature, while in the Fe-Cu alloy minimal changes are observed within the range of experimental conditions investigated. Comparison with transmission electron microscopy shows that some experimental conditions yield accurate precipitates size, while others enable reaching accurate composition measurements.
ABSTRACT
It is known that the distribution of the charge-states as well as the evaporation field shift to higher values as the specimen temperature is decreased at a constant rate of evaporation. This study has explored the effect of Mg or Ag addition on the evaporation field of Al in terms of the charge state distribution of the field evaporated Al ions. The fractional abundance of Al(2+) ions with respect to the total Al ions in Al-Mg alloy is lower than that in pure Al, whereas it shows higher level in the Al-Ag alloy at lower temperatures. The temperature dependence of the fractional abundance of Al(2+) ions has been also confirmed, suggesting that Al atoms in the Al-Mg alloy need lower evaporation field, while higher field is necessary to evaporate Al atoms in the Al-Ag alloy, compared with pure Al. This tendency is in agreement with that of the evaporation fields estimated theoretically by means of measurements of the work function and calculations of the binding energy of the pure Al, Al-Mg and Al-Ag alloys.
