12.3 Alignment Procedure with Oxygen source:

STEP A: Alignment of the primary beam in D4 aperture

1. Reset to 0 all Stigmators: Stig 45, Stig 90 and D5-S1.

2. Apply the starting conditions described above, if not yet done.

3. Set L1 to 65% of the source HV (ex: L1=8.25 keV for source HV=15 keV)

4. Turn ON the primary beam, center it in the FA plane using Beam pos (X, Y) deflectors.

5. With Beam On, wobble L4. The beam should focus and defocus at the same place. If not, correct the alignment with D4 aperture positions (X, Y).

6. Re-center the beam on the secondary optical axis; at the center of the field aperture plane using Beam pos (X, Y).

7. Validate D4_750 μm (#1) position by clicking the [VAL] button on the ‘Mass & Apertures’ panel.

■ Note: The positioning for other D4 apertures will be covered in the following procedure STEP C.

■ Note: Remove Wien before alignment.

STEP B: Alignment of the primary beam in Lens 2

1. Keep the beam focused in a small probe with L4, as set previously. With beam On, increase L2 slowly then wobble it. When wobble L2, the beam should focus and defocus at the same place. If not, use DP1 (X, Y) to center it.

■ Note: It is probably necessary to adjust the height of Z-electrode of Duoplasmatron in order to center the plasma position physically. When the beam is well aligned in L2, we can see a halo image which is passing through the D4 aperture.

2. Set L2 value at your desired primary current and focus the beam on the sample surface with L4 lens.

3. Final adjustment to improve the beam shape using stigmators (Stig_45, Stig_90), quadrupole (D5-S1) and L4 focusing.

STEP C: Adjust/Validate the position of the D4 apertures

1. Until now, we have been working with D4=750 μm (#1) while keeping D0=3000 μm. To be able to change the primary current freely, all D4 aperture should be correctly aligned and be validated. Set D4=500 μm (#2) while keeping D0=3000 μm.

■ Note: It is recommended to write down the position (X, Y) of D4=750 μ m before change to another D4 aperture.

2. With Beam On, wobble L4. The beam should focus and defocus at the same place. If not, correct the alignment with D4 aperture positions (X, Y).

3. Re-center the beam on the secondary optical axis; at the center of the field aperture plane using Beam pos (X, Y).

4. Validate D4=500 μm (#2) position by clicking the [VAL] button on the ‘Mass & Apertures’ panel.

5. Change D4 aperture to the next one and repeat 2~4 for each D4 aperture.

■ Note: The X-position of D4 aperture is usually similar for all 6 apertures (< 1000 digits). Whereas the Y-position of D4 is different. Consecutive apertures have a difference about 1800 digits in y-axis.

6. Set D4=750 μ m (#1) again after all validation.

STEP D: Centering/Validating the position of the D0 apertures

1. Until now, we have been working with D0=3000 μ m which means no aperture. To be able to change the primary current freely, all D0 aperture should be correctly aligned and be validated. Set D0=2000 μ m (#1) while keeping D4=750 μ m (#1) as set previously.

2. With Beam Off, adjust the position (X, Y) of D0 aperture to maximize the primary current.

3. Validate D0=750 μm (#2) position by clicking the [VAL] button on the ‘Mass & Apertures’ panel.

4. Change D0 aperture to the next one and repeat 2 & 3 for each aperture.

■ Note: The X-position of D0 aperture is usually similar for all 6 apertures (< 1000 digits). Whereas the Y-position of D0 is different. Consecutive apertures have a difference about 1800 digits in y-axis.

STEP E: Using the Wien filter

1. Open ‘Synoptic panel’ and select the corresponding menu as it is shown hereunder picture: 2. Primary → 1. L1+L2+L3 → 4) WIEN COIL, WIEN LENS, WIEN DY.

2. Set WIEN COIL = 2 Amp. When you increase the Wien coil value, the primary beam will move continuously along Y-axis.

3. In order to keep the beam inside of the FA plane, in other words; in order not to lose completely the beam on the MCP plate; use WIEN DY deflector for bring it back to the center of the image gradually. The final value of WIEN DY should be close to the typical value – 250 digits.

STEP F: Using the Accel-Decel electrode

1. For lower impact energy conditions so Duo Source HV < 2keV, the Accel-Decel electrode (DUO ACL parameter) must be used in order to increase the primary current.

2. Increase DUO_ACL up to 200 eV (note that it is negative for O₂⁺ primary ions). Maximize the primary beam intensity first by re-center the beam with DP1 (X, Y) and then by tuning L1 lens. Go back and forth between deflector and lenses to maximize the beam intensity.

■ Note: It might worth reducing the Duo_coil value to increase the beam intensity. When the Duo_coil decreases, L1_HV must be also decreased in order to maximize the beam intensity.

3. Increase DUO_ACL by steps of 50 digits, maximize the beam intensity as just aforementioned, as long as a beam density improvement can be observed.

4. Adjust the primary beam size at the desired value by adjusting L4. It is recommended to keep L1 at the value giving the maximum beam intensity.

STEP G: Using L3 lens for higher primary current

1. Increase L3 HV slowly. As the L3 value increases, it is possible that the beam shape is deformed, and the beam position moves. The primary current also could be decreased.

2. Maximize the current using DP_3a (X, Y).

3. Repeat 1~2 until the desired current is reached.

■ Note: In general, the L3 HV is optimized about 30~40 % of source HV.

4. Bring the beam back to the center of the FA plane using Beam pos (X, Y).

5. Focus the beam as small as possible using L4 lens.

■ Note: No need to center the beam in D4 aperture while wobbling L4 mentioned in STEP A. As it is actually very difficult to align the primary optics with all four lenses (L1, L2, L3 and L4). Therefore, after L3 lens is applied, it is strongly recommended to keep all other parameters except L4 to focus the beam as small as possible.