Atomic force microscopy for nanoscale mechanical property characterization
Gheorghe Stan, Sean King
Over the past several decades, atomic force microscopy (AFM) has advanced from a technique used primarily for surface topography imaging to one capable of characterizing a range of chemical, mechanical, electrical, and magnetic material properties with sub-nanometer resolution. In this review, we focus on AFM as a nanoscale mechanical property characterization tool and examine various AFM contact and intermittent contact modes that add mechanical contrast to an imaged surface. Through detailed analysis of the tip-sample contact mechanics, this contrast can be converted into quantitative measurements of various nanomechanical properties including elastic modulus, shear modulus, wear rate, adhesion, and viscoelasticity. Different AFM modes that provide such measurements are compared and contrasted in this work on a wide range of materials including ceramics, metals, semiconductors, polymers, and biomaterials. In the last few years, considerable improvements have been made in terms of fast imaging capabilities, tip preservation, and quantitative mechanics for multifrequency measurements as well as well-known AFM modes like amplitude-modulation and peak force tapping. In line with these developments, a major highlight of this review is the discussion of the operation and capabilities of one such mode, namely intermittent contact resonance AFM (ICR- AFM). The applications of ICR-AFM to nanoscale surface and subsurface quantitative mechanical characterizations are reviewed with specific examples provided for thin polymeric films and patterned nanostructures of organosilicate dielectric materials. The combination of AFM-based mechanical characterization with AFM-based chemical spectroscopy (AFM-IR) to allow nanoscale structure-property characterization is also discussed and demonstrated for the analysis of low-k dielectric/copper nanoelectronic interconnect structures and further highlights synergistic advances in the AFM field.