Introduction to the Ion Beam Analysis
V. Havránek
Nuclear
Physics Institute of the ASCR, v.v.i., Řež 130, 250 68 Řež, Czech
Republic
havranek@ujf.cas.cz
Introduction
The Ion Beam Analysis (IBA) is a group of analytical
techniques which use a beam of accelerated MeV ions to study the composition
and structure of investigated samples. The (IBA) methods are usually multi-elemental,
non-destructive and relatively fast. They require only little or no sample
preparation prior to the analysis. The analysis can be performed, both in the
vacuum, or using the external beam (in air). Thus a variety of different
samples from a single cell to historical art paintings can be analysed. The IBA
methods are interdisciplinary and they find its place in many scientific
disciplines as, aerosol research, solid state physics, thin layer analysis,
biology, medicine, archaeology and art and in many others. However the main principles of IBA methods
are now known roughly one hundred years, they start to be widely used as late
as in seventies, when sophisticated semiconductor detectors and appropriate
computing technology became available.
Methods
The IBA methods are based on principles of interaction
of energetic MeV ions with the matter. They can be characterized and divided
according to the main interaction process which is utilized by the particular
method. Brief description of some common IBA methods follows.
RBS - Rutherford Backscattering Spectroscopy. It is
based on nuclear elastic scattering of the incident ion and the nucleus of the
target atom. The backscattered ions and their energy are detected. The RBS
method can be used for quantitative determination of the amount of target atoms
(with moderate mass resolution) and also for their depth distribution. The
typical depth resolution for He ions is about
10nm.
PIXE - Particle Induced X-ray Analysis. The method is based on the detection of
characteristic X-rays produced by the energetic ion beam. It has a favourable
detection limits (in ppm range) and provide a good
quantitative results of atom concentration in measured samples with relative
uncertainty below 5%. Usually elements from Na and above are detected. When the
thin window or windowless detector is used, the elements down to the Boron can
be detected.
PIGE - Particle Induced Gamma-ray Analysis. It is
based on inelastic ion scattering or on nuclear reaction, in which gamma rays
from exited target nuclei are emitted. It is well suited for the determination
of the light elements, mainly for Li,F,Al,Na
and B.
NRA - Nuclear Reaction Analysis. The term describes a group of analytical techniques
based on nuclear reactions in which charged particles or gamma rays are
producing. They are isotopically specific and are
usually used only in a special cases. For instance the
NRA based on the 18O(p,alfa)15N
reaction can be used for the fine depth
profiling of the 18O. The
PIGE method is sometimes consider as a special case of NRA techniques.
ERDA - Elastic Recoil Detection Analysis. The ERDA method is based on the detection of forward recoiled
particles. Contrary to the RBS, all nuclei (ions) which are in the sample, and
also the primary particle, can be scattered (kick off) to the forward
directions. Thus we have to discriminate them. One way is to measure both velocity
and the energy of each particle and calculate the particle mass. This method is
called TOF-ERDA (time of flight ERDA).
There are several other options to discriminate the recoils, to use
electric or magnetic field analyzer, measure the ion stopping power or use thin
foil to stop all highly ionizing ions (high Z ones).
RBS-Channelling refers a special use of the RBS
method, when it is applied on crystalline materials. If one of the crystal axis
is aligned with the ion beam direction a number of backscattered particles are
significantly reduced. The position of the lattice host atoms or the number and
depth distribution of defects can be studied by this method.
Ion microbeam. The beam of the accelerated ions can be focused and
scan over the sample. This way, two or three dimensional information
about the distribution of atoms in the sample cam be obtained. A beam spot of
1um or smaller can be produced, using the set of slits and focusing quadrupoles.
There are several tents of such systems worldwide. Above mentioned IBA methods
(and lot of others) can be used in the combination with the ion microbeam. As the MeV protons are most common in such
systems, an alternative name "proton microprobe" is often used.
Laboratory
of IBA in Řež
General
references to the IBA methods (further study)
1. Handbook
of Modern Ion Beam Materials Analysis, Second Edition, Y. Wang and M. Nastasi, Materiále Research
Society, Warendale, Pensylvania
2009.
2. S. A. E.
Johansson and J. L. Campbell , PIXE: A Novel Technique for Elemental Analysis , John Wiley &
Sons, New York (1988), 347 p.
3. L.C.Feldman, J.W.Mayer, Fundamentals of Surface and Thin Film Analysis, Elsevier
Science Publishing Co., Inc. , New York (1986), 352 p.
4. Luděk Frank, Jaroslav Král, Metody analýzy povrchů
iontové - iontové, sondové a speciální metody, Academia, Praha (2002)
6. Mark
B. H. Breese, David N. Jamieson, Philip J. C. King, Materials Analysis Using a Nuclear Microprobe, Wiley-Interscience
, (1996), 464 p.
7. Zeev B. Alfassi, Max Peisach,
Elemental Analysis by Particle Accelerators, CRC Press, 1.edition (1991), 480 p.