Comprehensive Compositional Imaging of Heterogeneous Materials with Atomic Force Microscopy

Distinguishing of individual constituents in complex materials is one of the primary tasks of microscopy that is achieved by visualization of specific shapes and features of components. Electron microscopy and atomic force microscopy (AFM) [1] extend visualization of objects down to the atomic scale thus enhancing compositional imaging. The situation becomes less trivial when the constituents lack definite structures either being amorphous by nature or covered by contamination or oxide layers. In such cases one can use mechanical, electromagnetic, thermal, or spectroscopic responses of components for their identification. Probing of these properties can be performed using AFM-related techniques with high sensitivity and nanometer-scale spatial resolution. The latter is important as functional structures are continuously shrinking in dimensions. Since the introduction of AFM its capabilities have substantially expanded beyond high-resolution visualization of surface structures. Probing of the tipsample mechanical [2] and electrostatic [3] interactions was first demonstrated at single surface locations, and later extended to mapping of the elastic modulus, work of adhesion, surface potential, dielectric response, etc., simultaneously with topography imaging. The current arsenal of AFM modes helps a practitioner to optimize compositional imaging by selecting the most suitable techniques. Below, we will overview probing different sample properties with AFM methods and will provide examples of compositional imaging of polymer blends and complex natural compound – bitumen. Comprehensive Compositional Imaging of Heterogeneous Materials with Atomic Force Microscopy