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Ion Microscope Imaging Low Energy Mass Spectrum











Low Energy Ion Mass Spectrometry

The ion microscope functionality of the IMS-6f is retained by the ion optical systems of the recombinator and projection system. The image shows the AlO- signal from a test sample consisting of a 25 µm pitch copper grid pressed into an aluminum substrate. Based on this image, we estimate the spatial resolution of the system to be better than 2 µm. Ion microscope imaging is important for identifying and avoiding potential micron-sized dust contaminants on the Genesis collector surfaces.

Recombination images

Recombination

The recombinator band-pass filters the beam in mass and then recombines the separated masses into a single beam for injection into the accelerator. This unique method for accelerator injection filters out interferences in the high energy mass spectrum from multiply-charged ions while still allowing MegaSIMS to simultaneously detect all isotopes of a single element. This series of images shows the beam detected by the Colutron microchannel plate located in the beamline at the entrance of the accelerator. All magnets and electrostatic elements were adjusted to achieve recombination except for the second Einzel lens (EL2) between the magnets. The four images show the output of the recombinator for EL2 values of 10, 11, 12 and 12.5 kV. At 12.5 kV (bottom) refocussing of all isotope beams to the same image point is achieved providing a well-defined object for the accelerator.

Transmission and distribution of charge states

Transmission and Charge State Distribution

High transmission is key for high sensitivity. Preliminary data indicate transmission of Si into the Si+ and Si2+ states can exceed 33%. Further optimization, particularly at terminal voltages > 250 kV, may be possible by tuning of ion optics (einzel lens, acceleration gradient, and the accelerator-exit quadrupole triplet).

High Energy Mass Spectrum

High Energy Mass Spectrum

A mass spectrum was obtained by scanning the AMS magnet to pass a 1.01 MeV 28Si+ beam over one of the Faraday cups (FC) on the mass focal plane.The peak width is set by the opening aperture of the FC. An artifact appears on the baseline of the low field side of the peak due to the beam striking the electron suppressor in front of the FC. A high resolution scan of the high-field peak edge demonstrates a width of ΔB = 3 Gauss, corresponding to a mass resolution (M/ΔM) of ~1000. The bottom panel shows the deconvolved beam profile (width ~0.03 amu) in the mass dispersion plane.

Paper

Please see Mao et al. for more about our instrument.

bottomleftshadow Last Modified: November 8, 2012, 12:54 pm | megasims [at] ess.ucla.edu bottomrightshadow