High-Resolution Molecular Secondary Ion Mass Spectrometry for Absolute Quantification of Materials in Low-Dimensional Structures: Foundation, Perception and Challenges

Material surfaces have unique structures and compositions that are strikingly different from the material itself. Atoms on the surface of a crystal are in an anisotropic condition markedly different from the situation experienced by the atoms in a bulk. The symmetry experienced by the individual surface atoms breaks down because of the fact that atoms at the surfaces are under-coordinated. The surface atoms have more energy compared to bulk atoms because the breaking of bonds occurs at the expense of energy. A surface as a natural interface between a material and its surroundings acts as a major counterpart in the interactions between them. Therefore, detailed characterizations of a surface are indispensable. Since the surface occupies a microscopic portion of a material, highly dedicated and specialized techniques are required to examine the surface region. Since the nanostructures hold the major fractions of surface atoms, physical and chemical properties of surfaces have important parts in describing the properties of nanomaterials. As the surface analysis provides a means to correlate the performance with surface composition and structure, it is used not only for the development of new surfaces with high functionality but also for helping materials exhibit their function properly. Amongst all existing analytical methods, “Secondary Ion Mass Spectrometry (SIMS)” provides an exclusive place in quantitative analyses of material surfaces and interfaces. Continuous development in the fundamental and technological aspects of SIMS has made this technique to be extremely sensitive and powerful. Secondary ion emission results predominantly from the sputtering of materials under ion bombardment and is a complex inelastic process of ion-surface interactions. Amongst existing models for explaining ionization probabilities for sputtered species, “electron tunnelling mechanism” has so far proven to have maximum acceptability for all materials. Intensity of secondary ions is directly coupled with “ionization efficiency”, which strongly depends on instantaneous local surface chemistry. This is the so-called “Matrix Effect”, that makes the SIMS technique challenging for quantitative analysis of materials despite the fact that the technique has the highest detection sensitivity (