Neutron depth profiling

Neutron depth profiling

In NDP, a thermal or cold neutron beam passes through a material and interacts with isotopes that emit monoenergetic charged particles upon neutron absorption; either a proton or an alpha, and a recoil nucleus. Since the charged particles are equally likely to be emitted in any direction, reaction kinematics are straightforward. Because low-energy neutrons are used, there is no significant momentum transfer from the neutron beam to the substrate, and the analysis is practically non-destructive. As charged particles move towards the surface, they are rapidly slowed down, primarily by interacting with the electrons of the substrate. The amount of energy loss is directly related to the thickness penetrated by the particle. The depth of the reaction site can be found by stopping power correlations.

Profiling

Conventionally, the residual energies of charged particles and recoil nuclei have been measured by a silicon charged-particle detector; most commonly either a surface barrier detector (SBD) or a passivated implanted planar silicon (PIPS) detector. In this configuration, the semiconductor detector is placed opposite to the surface of the sample being analyzed, and an energy spectrum of charged particles emitted by the neutron-induced reaction is acquired.

References

• D. Fink, J.P. Biersack and H. Liebl, in Ion Implantation: Equipment and Techniques, (1983), H. Ryssel and H. Glawischnig, eds., Springer-Verlag, Berlin, pp. 318–326.