ABSTRACT
The preceding chapters have provided the necessary ingredients to finally address the question about the limits of Schottky source performance. It has been shown in Chapter 4 that the performance of a system in terms of probe size-probe current, or probe current and coherence, is limited by the brightness and energy spread of the beam and the aberration coefficients of the column. And it has also been shown that the brightness and energy spread of the beam are interrelated. Which combination of brightness and energy spread will give the best performance depends on the specific application. And which operating conditions are associated with that optimum performance depends on the emitter geometry. Chapter 5 has shown that the possible range of operating conditions is limited by the geometrical stability of the tip. Section 6.1 brings this together and discusses the maximum possible performance for different applications. To be able to set the right operating conditions that translate to the desired optimal brightness-energy spread combination, it is required that it be known how the applied voltages and heating current translate to a temperature and field strength for the center of the end facet of the emitter. The voltage-field relation is a strong function of the emitter geometry (Chapter 3), and in Chapter 5 it has been shown that the emitter shape evolves in operation. To maintain optimum emission properties one should thus adjust the operating
conditions during the emitter lifetime. Section 6.2 addresses possible source-monitoring tools to keep track of the changes. Finally, Section 6.3 gives some practical considerations.
