Performance
The most useful species that can be selected by the mass filter are as follows:
| SPECIES | % OF BEAM CURRENT |
|---|---|
| Au | 58.9 |
| Au | 16.2 |
| Au2 | 6.4 |
| Au3 | 4.3 |
| Au3 | 1.4 |
The use of a gold cluster ion beam gives a significant improvement in ion yields compared with lower mass primary ions. The figure below shows that the gold and gold cluster beams show a progressive increase in yield, all being superior to a gallium primary beam. In the 1000-2500 mass range, Au3 shows 75 times the yield from gallium.
Absolute ion yields from a thin film of PS2000, a low molecular weight polystrene
The next figure illustrates the imaging capabilities of the IOG 25AU, with the four prevalent gold cluster ions. The Au shows particularly high spatial resolution of the 12.5 micron mesh.
Secondary electron images of a 12.5 micron repeat copper grid.
Ion Optics
The ion gun consists of a gold-alloy liquid metal ion source and a high precision two-lens optics assembly. This assembly includes:
- stigmation and alignment units
- aperture selection
- deflection plates for blanking the beam
- pulse bunching units
- raster plates
The IOG 25AU can be set up for minimum motion blanking for TOF-SIMS by placing an intermediate field image is between the pulsing plates. This crossover mode can also be used in d.c. operation as a variable probe current mode – controlling the beam current by moving the intermediate image along the optical axis.
Electronics & Control
The ion gun is driven by a 6U, 19 inch high-voltage power supply unit. Control is via a PC user interface, with communication between computer and power supply via a serial interface. The control software is available as an installable package or ready installed on a PC. The software comes with a range of useful features including the option of running either voltage or current control, wobble function, panel lock and saving settings.
The high voltage unit provides the following supplies:
- Source Voltage
- Extractor Voltage
- Lens 1 Voltage
- Lens 2 Voltage
- Stigmation (amplitude and angle)
- Alignment
- Heater Current
Installation
The IOG 25AU has a compact design, to facilitate its installation as an instrument upgrade. The envelope of the gun can be varied to meet individual user needs, and the following versions are available:
- Standard version: NW63CF with 170mm long nose
- Extended version (length to customer specification)
- NW100CF, or NW150CF flanged versions
- Differentially pumped versions
Optional Equipment
The following items are also available from Ionoptika, for use with the IOG 25AU:
The gun can be connected to alternative scanning or pulsing electronics if desired.
| Beam Energy: | 5 to 25 keV |
| Max Current: | 10 nA |
| Minimum spot size: | < 50 nm |
| Computer Interface: | RS232 |
| Power requirements: | 110 / 220 Vac (50 / 60 Hz) |
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