br The corresponding number of

The corresponding number of trajectories is ten at h=3d= 1.2mm, and the ‘useful’ area increases:
After choosing relative position of the emitter and lens end, calculations were done of how to transport and focus the beam by the lens. It was again implemented with the use of the program ‘Simion7’. The following values were taken as the initial calculation parameters: three potentials of focusing electrodes UL1, UL2 and UL3, and the retarding coefficient Kdec, the last being defined actually by the ratio of to . It was accepted in the calculations that =–10V, and that the electrons leave the emitter surface normally to it with the initial energy = 20meV. Before describing the calculation results, we note that the signal was detected at the analyzer exit by the method of single E64 recording with the use of a VEU-6 secondary-electron multiplier (SEM). In the multiplier, each incoming electron produces at the exit an electron avalanche which is recorded as an electric pulse. This means that each particular electron is recorded rather than an integral electric current. The unit of signal level is ‘electrons per second’ (el/s). Using the SEM allows, on the one hand, not to worry too much about the signal intensity because an emission peak can easily be recorded even if the top intensity does not exceed 300–500el/s. But on the other hand, the SEM of the model mentioned above cannot work stably if the intensity exceeds 105el/s. That is why, while choosing the best focusing modes, the emphasis was made not only on the output intensity but more on minimizing the beam divergence angle at the analyzer entrance (that is at the lens exit) equal to 2Δα. It was accepted that Δα should not exceed 2°. Evaluations showed that in this case the aberration blurring in the analyzer could be neglected as the ξ value in Eq. (1) was negligible. Fig. 4 demonstrates typical deformations of the beam axial section inside the lens and near its exit when the potentials UL1, UL2 and UL3 vary. Because of the beam axial symmetry, calculations were only made for a half of its section. The source data for the results presented in the figure are as follows: =+ 300V, which means, in accordance with Eq. (4), that Kdec= 31; d=h= 0.4mm; the diameter of the round output lens diaphragm, which at the same time is the analyzer input one, is = 0.6mm. The initial electron radial coordinates are = 2(i–1) μm, where i is the ‘number’ of an electron (i= 1, 2, …, N). So, the starting point coordinate step Δr= 2μm, and opposite the upper half of the lens input diaphragm start their flights, the first one moving along the axis. Fig. 4c shows ‘strong’ focusing when about 50% of the electrons whose starting points are opposite the entrance diaphragm (it means all the particles with 0 <e of the beam after passing the exit diaphragm is very small, and anyway 2Δα< 4°. The intensity of the recorded beam makes approximately 4% of the full emission current of the electrons passing the entrance diaphragm of the lens. was calculated as some part of the electrons passing through the lens. It is supposed meanwhile that the whole emissive area is equal to that of the entrance diaphragm. This would not be correct in the case of geometry in Fig. 3a or c. But as d is approximately equal to h, which geometry corresponds to Fig. 3b, the emitted electrons are accelerated at the early stage of their way by strong and practically plane field. This means that almost all the electrons emitted opposite the entrance diaphragm will pass it, and that almost no electrons emitted from out of this area will pass the entrance diaphragm. Thus, the relative intensity of the recorded electron flow can be evaluated as /=4/π d2.