Chemical Imaging of Buried Interfaces in Organic–Inorganic Devices Using Focused Ion Beam-Time-of-Flight-Secondary-Ion Mass Spectrometry

Abstract

Organic-inorganic hybrid materials enable the design and fabrication of new materials with enhanced properties. The interface between the organic and inorganic materials is often critical to the device's performance and therefore chemical characterization is of significant interest. Since the interfaces are often buried, milling by focused ion beams (FIB) to expose the interface is becoming increasingly popular. Chemical imaging can subsequently be obtained using secondary ion mass spectrometry.However, the FIB milling process damages the organic material. In this study, we make an organicinorganic test structure to develop a detailed understanding of the processes involved in FIB milling and SIMS imaging. We provide an analysis methodology that involves a "clean-up" process using sputtering with an Argon gas cluster ion source to remove the FIB induced damage. The methodology is evaluated for an additive manufactured encapsulated strain sensor containing silver tracks embedded in a polymeric material. We show a polymer-silver interface with a resolution of 440 nm and that the polymer contains a low level of silver particulates.

Argon cluster cleaning of Ga+ FIB‐milled sections of organic and hybrid materials

“…The sample for this study is made using a glass multichannel plate (MCP) electron multiplier with 10‐μm diameter tube diameters which are filled with either poly(styrene) (PS) or poly(methyl methacrylate) (PMMA). This composite sample sections very nicely, but, of course, the final surface has been heavily exposed to the Ga + milling ions. The surface layer of the polymers is highly damaged and implanted with Ga + .…”

“…Thus, direct depth profiling of these structures using Ar + GCIBs is difficult and liable to poor depth resolution even if the inorganic layers are thin. Structures with uneven overlayers but smooth interfaces, like membrane electrode assemblies used in fuel and other cells, become impossible by the direct approach but are more easily tackled by FIB‐sectioning.…”

“…To overcome this problem, we have studied Ga + FIB sectioning of samples involving both inorganic and organic materials . The sample for this study is made using a glass multichannel plate (MCP) electron multiplier with 10‐μm diameter tube diameters which are filled with either poly(styrene) (PS) or poly(methyl methacrylate) (PMMA).…”

“…The surface layer of the polymers is highly damaged and implanted with Ga + . Using the Ar + GCIB to remove this layer requires quite a high dose, which may be caused by needle cones similar to the microtopography that can be observed in the crater base of FIB‐milled sections of some inorganic materials. If so, the development of such microtopography would require study to minimize it.…”

“…In our previous study, it was shown that the angular dependence of the sputtering yield of the polymer by the Ga + ion beam, combined with the focused spot size, the raster array pitch, and the sputtering dose, would lead to the final section wall surface being not parallel to the Ga + ion beam direction but at some 5 to 10° inclined to that direction. This was confirmed by atomic force microscope measurements.…”