Ion Beam Analysis of Materials (IBeAM)
Arizona State University
Ion beam analysis (IBA), using MeV ion beams for compositional and
structural determination of materials, combines the advantages of
non-destructive and standardless analysis of the surface and near
surface regions (0-2 microns) of solids. IBA is most advantageously
applied to analysis problems where elemental composition and depth or
thickness information are needed.
Rutherford backscattering (RBS) is a surface analysis technique which
uses the recoil energies of accelerated ions (e.g., He or H) to
determine the species and depth profiles of atoms in a given
sample. RBS is extremely useful when quantitative results are required
in the absence of standards. A variation of RBS is ion channeling, in
which a single crystal sample is aligned on a goniometer in situ so
that one of its major symmetry axes is parallel to the incident MeV
ion beam. In this arrangement the backscattered yield is reduced in
proportion to the crystalline quality of the sample. Studies can be
made of lattice locations of impurities or dopants (substitutional vs.
interstitial lattice sites). Ion beams can also be used for X-ray
analysis (Proton Induced X-ray Emission: PIXE) with the advantage of
a much improved signal/noise ratio when compared to electron induced
X-rays. PIXE is sensitive to impurities in the ppm range and requires
no sample preparation. Another unique application is hydrogen content
analysis. H atoms are scattered from the sample (by the incident
accelerated ions) and energy analyzed for concentration and depth
distribution. All of the above processes are virtually non-destructive
to the sample. It is important to note that these techniques yield
elemental composition, independent of the type of chemical bonding
present.
IBeAM Lab Facilities
The IBeAM facility consists of a 1.7 MeV tandem accelerator with a
beamline and analysis chamber. The Tandetron accelerator is a
Cockroft-Walton, gas-insulated high frequency device which can use
either a gas source for ions (H, He, N, O, etc.) or a sputter source
for heavy ions (MeV implantation). Ion energies of several MeV can be
created since the tandem accelerator operates by producing negative
ions at ground potential and then uses a gas stripper at the high
voltage terminal, thereby creating multiply charged states of positive
ions which are accelerated to ground and selected by the bending
magnet on the beamline where the sample chamber is located.
IBA measurements are done in a high vacuum environment requiring
samples to be clean and vacuum compatible. The ion beam is typically
1-2 sq. mm in area. An additional beamline allows the ion beam to pass
from the vacuum through a polymer window into the room
atmosphere. Samples placed at the beamline exit window can be X-ray
analyzed in air. This allows chemical composition analysis of samples
which are large or liquid or in some way not vacuum compatible. A
variety of materials ranging from objects of art and archeological
specimens to environmental (air and water samples) and
geological (meteorites and rocks) samples can be analyzed.
Online Tutorial
For further information on the IBeAM theory and instrumentation, please check out this web page that provides online tutorial.
www.cea.com/tutorial.htm
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