12.2 Overall alignment procedure

The goal of this alignment is to set up the aperture positions and deflector values for desired primary current. In this chapter, all values are based on the high energy conditions: Source HV=15keV, Sample HV=5keV. These values can be extrapolated for other Sample HV, providing that all the lens voltages are modified in the same ratio as the source HV.

12.2.1 Starting conditions: Pre-alignment of Secondary optics

It is required that the secondary optics has been previously aligned so that it is possible to display a focused secondary sample image on the MCP (Micro Channel Plate).

- Detection mode: Image

- Transfer lens: 250 μm

- FA: #1 (1800μm)

- CA: #2 (150 μm)

In order to have a good grid image on the MCP, adjust fine controls of the Immersion lens, stigmators and Transfer lenses (LTR1, LTR2).

12.2.2 Starting conditions: Primary optics

It is required to have the following instrumental conditions.

- D0=3000 μm (no apertures)

- D4=750 μm (#1)

- All lenses and deflectors to 0, except:

○ L4: ~ 10200 V

- Beam Pos X: 1000~1200 digits

DefFC: 160 ~ 180 eV

which should be close to the typical values (for the source HV=15keV, Sample HV=5keV)

- Raster size: 100 μm × 100 μm

- DTOS: ON

Check that DTOS is correctly calibrated by comparing with Raster Off. Beam shape when turn on raster and DTOS should be the same as the beam shape when raster off. If not, DTOS values (X, Y) must be adjusted until both cases have the same beam shape.