Scanning Probe Microscopy Introduction and Atomic Force Microscopy

SPM (Scanning Probe Microscopy) SPM: Consists of a family of microscopy forms where a sharp probe is scanned across a surface and probe/sample interaction is monitored. Two primary forms of SPM: Scanning Tunneling Microscopy Atomic Force Microscopy (AFM): contact mode non-contact mode tapping mode

Atomic Force Microscopy - Introduction In simple terms, the atomic force microscope works by scanning a sharp probe over the surface of a sample in a raster pattern. By monitoring the movement of the probe, a 3-D image of the surface can be constructed. The schematic is shown to the right Figure 4. Three common types of AFM tip. (a) normal tip (3 µm tall); (b) supertip; (c) Ultralever (also 3 µm tall). Electron micrographs by Jean-Paul Revel, Caltech. Tips from Park Scientific Instruments; supertip made by Jean-Paul Revel. http://stm2.nrl.navy.mil/how-afm/how-afm.html#imaging%20modes

Atomic Force Microscopy -Tip – Surface Interaction The combination of these interactions results in a force-distance curve similar to that below When the tip is brought close to the sample, a number of forces may operate. Typically the forces contributing most to the movement of an AFM cantilever are the coulombic and van der Waals interactions. Coulombic Interaction: This strong, short range repulsive force arises from electrostatic repulsion by the electron clouds of the tip and sample. This repulsion increases as the separation decreases. Van der Waals interactions: These are longer range attractive forces, which may be felt at separations of up to 10 nm or more. They arise due to temporary fluctuating dipoles.

Atomic Force Microscopy - Topography Contact Mode High resolution Damage to sample Can measure frictional forces Non-Contact Mode Lower resolution No damage to sample Tapping Mode Better resolution Minimal damage to sample 2.5 x 2.5 nm simultaneous topographic and friction image of highly oriented pyrolytic graphic (HOPG). The bumps represent the topographic atomic corrugation, while the coloring reflects the lateral forces on the tip. The scan direction was right to left http://stm2.nrl.navy.mil/how-afm/how-afm.html#imaging%20modes