Overview
The IOG 25GA delivers a focused beam with beam energy of up to 25 keV. The wide current range enables the system to be used in a variety of applications from high precision direct write to large area quadrupole SIMS. In the lower current range, spatial resolution down to 50nm is achievable, subject to platform stability.
The assembly is configured for ease of installation as an instrument upgrade, with feedthroughs clustered together to allow minimum mechanical interference. A range of versions is available to accommodate different flange sizes or port lengths, and the column can be conventionally pumped or differentially pumped.
Ion Optics
The assembly consists of a gallium liquid metal ion source and a high precision two-lens optics assembly, illustrated in figure 1. There are manual and motorised options for aperture selection.
The IOG 25GA can be operated in collimated mode or in crossover mode, in which an intermediate field image is produced between the lenses. In this mode it can be set up for minimum motion blanking for TOF-SIMS.
The crossover mode can also be used in DC operation as a variable probe current mode, controlling the beam current by moving the intermediate image along the optical axis.
Electronics
The IOG 25GA power supply unit is a 6U rack-mountable 19 inch box. This provides all the high voltage and static deflector voltages required by the system. A sophisticated control software package is included; this can be installed on a PC running Windows 7 or higher.
Schematic of IOG25GA Ion Optics
Performance
The IOG 25 gives excellent spatial resolution throughout its current range, from micron performance at over 10 nA of beam current to below 50 nm in low current mode. It should be noted that the small spot performance requires a stable instrument platform with suitable isolation from vibration.
Figure 2 is a secondary electron image of a 12.5 micron copper grid, showing features below 50 nm across at a 25 mm working distance. A larger scan field can be achieved with a ± 200 V scan at greater working distances, as shown in Figure 3.
Secondary electron image of 12.5 micron repeat grid
A chamber vacuum of < 1x10-8 mbar is required. If the system does not achieve this, a differentially pumped version should be considered.
Field of view of IOG 25GA is > 2.5 x 2.5 mm
Installation
The IOG 25GA has a compact design, to facilitate its installation on a range of instruments. The envelope of the gun can be varied to meet individual user needs, and the following versions are available:
- Standard version (see figure).
- Extended nose length, to customer specification.
- NW100CF, and other flanged versions.
- Differentially pumped version.
- Version with bellows for adjusting the length and angle of the gun.
Key dimensions of the IOG 25GA
Optional Equipment
The following items are also available from Ionoptika, for use with the IOG 25GA:
- Raster & Imaging Equipment
- Fast Beam Pulsing Electronics
- Motorised Aperture Drive
- Differential Pumping
- Mono-isotopic Ga Source
- Wien Filter
| Beam Energy: | 10 to 25 keV |
| Current Range: | 20 pA to 20 nA. Option for 50 nA. |
| Resolving Power: | <: 50 nm (subject to suitable vibration isolation) |
| Source Lifetime: | >: 500 μA hrs |
| Computer Interface | RS232 |
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