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The best optical microscopes can see structures in the 200 – 400 nm range, at their limits of resolution.
The STM can “see” structures on the order of 0.1 nm [atoms!]—another SPM, the AFM—can distinguish things on the order of 100 nm [large molecules].
Optical microscopes are “diffraction limited”—the wavelength range of visible light (400-750 nm) sets the size of the smallest thing that can be imaged: ~ 400 nm.
Scanning Probe Microscopes don’t use visible light—they depend on measuring intermolecular forces or measuring quantum tunneling. The resolution limits are at the quantum scale (atoms & molecules
Using the STM in lab—
• Place the STM tip near the sample surface, by hand;
• Use the z-axis piezo electric motor to bring the tip close to the surface (within an atomic radius)—so that tunneling begins;
• Use the x-axis and y-axis piezo-electric motors to move the tip over a scan area.