Materials Research Laboratory

Background

Techniques in this category measure the interaction between medium to high energy ions (0.5 - 2.5 MeV) in order to gain insight as to a materials composition as a function of depth, crystallinity, and degree of disorder. For the ion scattering techniques, different information is obtained depending on the primary ion energy and the scattered ion which is detected.

Instrumentation. The Van de Graaff operates at energies up to 2.3 MeV for H, He, Ar, Kr , Xe and Ne with 1-2-3 mm beam-size apertures. There is a beam line for Rutherford backscattering spectroscopy (RBS) and elastic recoil detection of hydrogen. There is a goniometer for channeling studies as well as sample rotation to prevent channeling.

The tandetron offers energies up to 4.6 MeV for He with a 3 mm beam. Sample rotation is available.

Features. There is a vacuum RBS beam line with provision to heat or cool samples during analysis. For the end stations on this and the general purpose beam line, there are high angular resolution goniometers suitable for channeling studies. The elastic recoil method for the detection of H is also available.

Applications. RBS is used for nondestructive compositional depth profiling and thickness measurements on thin films. Computer simulation programs are available for analysis. Applications include thin-film compositional analysis and diffusion studies. Channeling of the incident and scattered beams has been used to identify crystal structures and estimate the number of defects and degree of disorder in crystalline specimens, and it has also been for lattice location of impurity atoms.