Erosion rate variations during XPS sputter depth profiling of nanoporous films

Abstract

Sputter depth profiling is commonly used to obtain valuable information regarding the three dimensional distribution of elements within a sample, and is one of the best ways to measure the composition of a buried interface or the uniformity of a thin film. X-ray photoelectron spectroscopy (XPS) is one of the analysis tools often used in conjunction with ion beam erosion to obtain sputter depth profiles. However, to obtain accurate depth information it is often necessary to understand better the sputtering process for a specific materials system. Artifacts such as differential sputtering, varying sputter rates and ion beam-induced chemistry are well known. Here, however, we present evidence from experiments on a porous thin film deposited on an Si wafer that relatively small chemical and/or structural changes in a nanoporous film can affect the rate of erosion measured during sputter depth profiling. Reproducible variations in sputter rate are found with chemical modification leading to compositional changes of the nanoporous thin film. The origin of the sputter rate changes is discussed with the aid of results obtained using Fourier transform infrared spectroscopy, profilometry, nuclear reaction analysis, electron microscopy and XPS-based depth profiling.

Application of surface chemical analysis tools for characterization of nanoparticles

“…The deliberate application of coatings has been used to control particle shape during growth [78], and the use of coatings on nanoparticles can be used to control particle spacing and the resulting properties of nanoparticle composites [79]. Because of capillary and sorption effects, the high surface area present in collections of nanoparticles may retain solvent in circumstances that can surprise researchers [21, 80]. Even using surface tools, it can sometimes be difficult to characterize the nature of the actual nanoparticle surfaces.…”

Characterization challenges for nanomaterials

“…[47] The impact of ions on nanostructured objects will be influenced by object size, [36] shape (due to angle of impact effects), [48,49] as well as other physical characteristic effects such as how the objects are supported [51] or if they are porous. [50] The two latter characteristics may lead to environmental effects as objects suspended in space respond differently to an ion beam than when they are supported on a substrate, and a porous structure may adsorb and retain ambient gases or solvents for considerable time in vacuum.…”

XPS depth profiling of functional materials: applications of ion beam etching techniques

“…With the etching cycles increasing, the N1s peak was found to enhance in intensity, while the Ti–O peak disappeared gradually, indicating the chemisorption of oxygen from the air to replace the nitrogen position on the surface layer. Similarly, the CdS thin film 51 and a porous organosilane film 52 were etched by Ar + MAIB beam to explore the uniform distribution of species in the bulk. Besides, the polymetallic compound thin film, such as Ba(Zr x Ti 1− x )O 3 thin films, 53 perovskite, 54 barium strontium titanate thin films, 55 barium strontium titanate film, 55 and silver-implanted diamond complex film 56 were also analyzed using an XPS technique combined with Ar + MAIB sputtering method.…”