Depth profiling methods that provide information complementary to neutron reflectivity

Abstract

Neutron reflectometry (NR) has the potential to revolutionize our knowledge of the structure of polymers and other organic materials near surfaces and interfaces. The hydrogens of a polymeric species can be selectively replaced by deuterium so that the concentration versus depth profile of the deuterated species will result in a profile of neutron scattering length density of high contrast which, in turn, will strongly change the neutron reflectivity. Despite the excellent sensitivity of NR to rapid changes in the profile with depth, more gradual gradients in the depth profile can be almost invisible, and thus it is advantageous to pair NR with other experimental methods for depth profiling deuterium. Such methods allow one to place severe constraints on possible models of the scattering length density that can be refined to fit the reflectivity data. This paper reviews three such methods which recently have been developed for depth profiling hydrogen and deuterium in polymers, namely, forward recoil spectrometry, nuclear reaction analysis and dynamic secondary ion mass spectrometry. These methods have depth resolutions which range from 10 to 800 nm and can provide details of the profile not readily “visible” in reflectometry.