Dual beam depth profiling of organic materials: assessment of capabilities and limitations

With the advent of large argon cluster beams, organic materials can be sputtered without the accumulation of radiation damage. The dual beam mode with a Bi cluster analysis beam is successfully applied to depth profiling and 3D analysis of organic materials providing both high-depth resolution and high-lateral resolution. For the analysis of very small sample volumes, it is desirable that a rather large fraction of the material is consumed by the analysis beam and contributes to the analytical signal. However, at higher analysis beam sputter rates, the radiation damage by the Bi clusters can become quite severe leading to a molecular ion signal decay with depth. In this paper, we investigate the conditions for the optimum use of the sample material in the dual beam mode using the Irganox delta layer structure introduced by NPL (National Physical Laboratory (UK)). A model that describes the dual beam mode and allows calculating the intact area fraction in the steady state is presented. Yield volumes and damage volumes are determined for Bi-3(+) and Bi-5(++) as well as the useful sample fraction that contributes to the molecular ion signal. We will compare the results to the depth profiling with C-60 and Ar clusters in a single DC beam mode. Copyright (c) 2014 John Wiley & Sons, Ltd.