VAMAS interlaboratory study on organic depth profiling. Part I: Preliminary report

Abstract

We present preliminary results of a VAMAS interlaboratory study on organic depth profiling, TWA2, sub-project A3 (d). A layered organic system was used to assess the repeatability and comparability of organic depth profiling. Nineteen respondents have provided sufficient data to demonstrate that the coefficients of variation for depth resolution, sputtering yield and relative secondary ion intensities are typically 5-10%. This can be as good as 2-3% with modern instruments, when using a stable sputtering ion current and careful procedures, which approaches the limits set by the samples themselves. The respondents have also demonstrated three methods to improve the quality of depth profiling for this system, namely, sample rotation, cooling to at least −80• C and grazing incidence angles for the sputtering ion.

Molecular Depth Profiling with Cluster Ion Beams

“…is observed. 39,11,23,25,28,33,81,85 Furthermore, increased fragmentation and beam damage effects (initial signal decay/damage cross sections) are observed in the mass spectral data at higher beam energies. 39,23,26,28,33,95 -97 Finally, XPS results are also consistent with increased structural damage at higher beam energies.…”

“…The authors concluded that polymeric depth profiling was more of an exception than a rule. 8 However, starting with the discovery of certain well-behaved polymers, 9,10 and followed by the determination and optimization of important experimental parameters, 5,11 including temperature, 5,11 -17 beam chemistry, size and type, 5,11,18 -21 beam angle, 5,11,22 -24 beam energy, 5,11,25 -28 and sample rotation, 11,17 it is now understood that this is not the case, and that even polymers that were originally thought of as "impossible to depth profile" (e.g., PS), 5 can be depth profiled using cluster beams, thus opening the door for 3D molecular characterization in more complex systems, such as biological tissue and complex organic devices.…”

“…11,17,20,27,28,81 Much of the following section refers to the results from this very important series of studies by Shard et al, and therefore, a brief introduction of the sample structure and typical results observed during depth profiling of this sample is warranted.…”

“…As an example, Figure 5.24c plots the FWHM measured from each of the four peaks under different experimental conditions. 11 The curve on the top (•) shows the control values acquired using 20 keV C 60 + at 45 • incidence and 25 • C. The depth resolution of the peaks (FWHM) clearly decays with depth. The corresponding sputter rates are also nonlinear with increasing depth.…”

“…SIMS is also extremely useful for the study of highly ordered and/or multilayer molecular films. 11,17,20,27,28,33,34 Figure 5.5 shows an excellent example of this, displaying molecular information as a function of depth for perfectly alternating Langmuir-Blodgett (LB) layers of arachidic acid (AA) and dimyristoyl phosphatidate (DMPA). 32 The profile shown in Figure 5.5a was acquired using a 40 keV C 60 + source, operated at glancing incidence angles of 73 • with respect to the surface normal, and the sample was maintained at liquid nitrogen temperature for the duration of the experiment.…”