Real-space composition–depth profiling in polymeric samples to 3 nm resolution using the 2H(3He, 1H)4He nuclear reaction

Abstract

Direct depth profiling techniques to date have largely lacked the necessary depth resolution to investigate interfacial phenomena of the order of the bulk correlation length (5—10 nm for a wide range of systems). Here we investigate the optimal spatial resolution and depth of probe that may be attained for composition — depth profiling of polymeric samples via nuclear reaction analysis (NRA) using the ²H(³He, ¹H)⁴He reaction. We find that the spatial resolution can be greatly improved by using a grazing incidence geometry of the incident ³He beam on the sample, and analyzing the emitted protons in a backwards direction. This results in spatial resolutions down to about 3 nm at the sample surface, compared to a value of some 7 nm or more previously reported in earlier studies when emitted α-particles were detected in the forward direction. At the same time the depth to which samples can be profiled via the backwards emitted protons may be considerably extended relative to the α-particle detection mode, when the ³He beam impinges on the sample surface at normal incidence (up to about 4 μm into the sample for incident energies of 1.2 MeV in the proton-detection mode compared to only 1 μm for the equivalent α-particle detection mode).