Improving Secondary Ion Mass Spectrometry C₆₀ⁿ⁺ Sputter Depth Profiling of Challenging Polymers with Nitric Oxide Gas Dosing

Abstract

Organic depth profiling using secondary ion mass spectrometry (SIMS) provides valuable information about the three-dimensional distribution of organic molecules. However, for a range of materials, commonly used cluster ion beams such as C60(n+) do not yield useful depth profiles. A promising solution to this problem is offered by the use of nitric oxide (NO) gas dosing during sputtering to reduce molecular cross-linking. In this study a C60(2+) ion beam is used to depth profile a polystyrene film. By systematically varying NO pressure and sample temperature, we evaluate their combined effect on organic depth profiling. Profiles are also acquired from a multilayered polystyrene and polyvinylpyrrolidone film and from a polystyrene/polymethylmethacrylate bilayer, in the former case by using an optimized set of conditions for C60(2+) and, for comparison, an Ar2000(+) ion beam. Our results show a dramatic improvement for depth profiling with C60(2+) using NO at pressures above 10(-6) mbar and sample temperatures below -75 °C. For the multilayered polymer film, the depth profile acquired using C60(2+) exhibits high signal stability with the exception of an initial signal loss transient and thus allows for successful chemical identification of each of the six layers. The results demonstrate that NO dosing can significantly improve SIMS depth profiling analysis for certain organic materials that are difficult to analyze with C60(n+) sputtering using conventional approaches/conditions. While the analytical capability is not as good as large gas cluster ion beams, NO dosing comprises a useful low-cost alternative for instruments equipped with C60(n+) sputtering.

A wavelet‐PCA method saves high mass resolution information in data treatment of SIMS molecular depth profiles

“…The inspection of the loadings plot shows that the outer region is mostly characterized by the presence of the typical fragments of PSS molecules (negative loadings), while the positive loadings region (corresponding to the inner part of the organic film) mostly contains C x N clusters, and a few C x H y O z peaks. The presence of C x N is reasonably diagnostic of ion beam‐induced damage accumulation along the sample depth, causing NO uptake, not surprising for a system in which some components (namely, PSS) are known to undergo extensive damage under C 60 bombardment in the absence of NO dosing . Notably, the damage‐related peaks are present in a depth region where the intensity of peaks diagnostic of the undamaged polymer is rather low (Fig.…”

“…Nitric oxide (Praxair) was used for gas dosing. NO was introduced into the main chamber until a total pressure of 1.5 °10 −5 mbar (this pressure value can be regarded as the partial pressure of NO, considering that the base pressure in the analysis chamber is in the range 10 −8 –10 −9 mbar) …”

“…The presence of C x N is reasonably diagnostic of ion beam-induced damage accumulation along the sample depth, causing NO uptake, not surprising for a system in which some components (namely, PSS) are known to undergo extensive damage under C 60 bombardment in the absence of NO dosing. [34,35] Notably, the damage-related peaks are present in a depth region where the intensity of peaks diagnostic of the undamaged polymer is rather low (Fig. 2).…”

“…NO was introduced into the main chamber until a total pressure of 1.5°1 0 À5 mbar (this pressure value can be regarded as the partial pressure of NO, considering that the base pressure in the analysis chamber is in the range 10 À8 -10 À9 mbar). [34] Data structure During ToF-SIMS dual-beam experiments, depth profiling is performed by alternating sputtering cycles (obtained by a high-current density fullerene beam) with analysis cycles (via the low-current Bi 3 + beam) each of them providing a ToF mass spectrum representative of the current surface of the sputtering crater. Each spectrum is collected by splitting the ToF in 50 ps long intervals (channels), and storing the counts/channel in a raw data file with a proprietary format that can be exported to a readable format file.…”

Development of a Primary Ion Column for Mass Spectrometry-Based Surface Analysis

“…Dynamics SIMS is common for 3D-SIMS as the higher dosage allows for the necessary yields over time to generate voxels, consequently providing better limits of detection (LOD) over Static SIMS (2D imaging) 22 . A voxel considers both lateral (XY) and depth (Z) resolution in order to define the effective resolution 21 .…”