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How do quantum mechanical effects change materials at the nanoscale?
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Examples from biological and mechanical realms illustrate various “orders of magnitude” (powers of 10), from 10−2 meter down to 10−7 meter.
At the nanoscale, materials exhibit unique properties because their dimensions become comparable to the characteristic wavelengths of fundamental excitations, such as electrons, photons, and phonons. These quantum mechanical effects fundamentally alter material behavior in several ways:1
- Quantization of Energy: When structures are small enough to be comparable to these fundamental quanta, excitations are restricted to discrete energy states. This phenomenon is central to the function of quantum dots, where particle size dictates specific electronic and optical properties.123
- Confinement and Selection Rules: Small structures can limit the flow of charges or photons, creating wave interference effects and imposing new selection rules that do not exist at larger scales. For example, quantum wells confine electrons to specific regions, while superlattices use periodic structures to control charge flow.14
- Tunneling: The wavelike nature of electrons allows them to pass through potential barriers that would be impassable under classical physics. This tunneling effect is the operational basis for the scanning tunneling microscope, which can image and manipulate individual atoms.5
- Photonic Control: When material periodicity approaches the wavelength of light, quantum rules define how photons propagate, allowing for the creation of photonic crystals that can steer or separate light.4