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A blog on the repair, operation and calibration of surface analysis systems and components including electron spectrometers, sputter ion guns and vacuum related hardware. Print PDFUsing Ta2O5 or SiO2 works well for aligning an ion beam to the focal point of an X-ray photoelectron or scanning Auger electron spectrometer. Because the current measured into the Faraday cup is in the low nA range, a picoammeter (such as the RBD Instruments Inc. Another benefit of using a Faraday cup is that you can also determine the electric current density using a multiplication factor.
While observing the picoammeter, adjust the focus (objective) and condenser on the ion gun control and the mechanical offsets (thumbscrews) on the ion gun for maximum current into the Faraday cup. This entry was posted in Ion Sources and tagged faraday cup, ion beam alignment, picoammeter by Randy. But, in order to optimize the ion beam focus at larger beam sizes, a Faraday cup is required. For Auger electron spectrometers, acquire an elastic peak just to the side of the Faraday cup hole and then move the Faraday cup hole to the center of the TV image.

This will ground the target and apply +90V to the ion lead on the specimen stage (which in turn makes the electrical contact to the Faraday cup). By optimizing a few ranges of current and using those parameters to acquire depth profiles on a standard such as SiO2 or TaO5 (both available from RBD) you can create a matrix of reproducible sputter rates. When the bias box is set to the ion input, the target is grounded and the output of the bias box is routed from the ion lead (Faraday cup) on the specimen stage to the input of the picoammeter. For X-ray photoelectron spectroscopy systems, move the Faraday cup hole to the center of the system microscope’s image at the highest possible magnification setting. Once the mechanical offsets on the ion gun have been adjusted to where no further increase in current is noted, lock them down securely and also make sure that the ion gun housing is tight. When an ion beam is larger than the 250um Faraday cup aperture, only the portion of the beam that is 250um or smaller is measured. Do not adjust the mechanical offsets for subsequent focus adjustments at different condenser (COND) or beam voltage settings. By adjusting the ion beam focus and position for maximum current into the Faraday cup, the ion beam can be aligned and the current density can be optimized for any ion beam condition.

In those cases, short out the target and and connect the picoammeter to the ion lead on the specimen stage. Instead, you can optimize the position of the ion beam into the Faraday cup by using the offset adjustments on the ion gun control if necessary. Typically, though, the 04-303 ion source is operated at 3-to-4kV with 15MPa of argon pressure.
Therefore, the maximum ion current passing into a Faraday cup under those conditions is more in the range of 150 to 200nA.

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