Experimental methods in chemical engineering: Atomic force microscopy - AFM

Atomic force microscopy (AFM), part of the scanning probe microscopy family, exploits the local interaction forces between the sharp tip of a scanning mechanical probe and a material sample to profile its surface topography or map mechanical and tribological properties over nanometre to micron length scales. AFM images the topography at a sub-angstrom resolution in height and sub-nanometre to nanometre lateral resolution for diverse materials spanning extremely soft biological samples to hard metals in air, fluid, or vacuum. The accuracy of dimensional metrology measurements depends on the probe tip radius and geometry, calibration of the piezoelectric scanner movement, and applied force. A number of experimental aspects must be considered to ensure imaging reproducibility and maximize imaging resolution. These considerations include sample preparation, imaging environment, choice of AFM mode and probe, and imaging parameters. AFM offers specialized modes to characterize materials properties such as surface potential, electrochemical reactivity, and electrical and magnetic properties. Recent advances combine AFM and infrared spectroscopy to simultaneously map the surface topography and distribution of chemical species. High-speed or fast-scanning AFM captures dynamic structural changes and (bio)molecular processes occurring on the millisecond time scale. Every year, Web of Science indexes over 3200 articles that appear when adding AFM and microscopy in the search field topic. A bibliometric analysis grouped AFM research into five clusters: (1) mechanical properties, membranes, and adhesion, (2) morphology, microstructure, and roughness, (3) spectroscopy, nanocomposite, and oxide, (4) adsorption and steel, and (5) polymer and wettability.