Thus the low materials possessing quantum size effects
have significantly changed their electronic properties and deeply modified their photonic and optoelectronic performances when compared with their bulk form.
Herron, "Nanometer-sized semiconductor clusters: materials synthesis, quantum size effects, and photophysical properties," The Journal of Physical Chemistry, vol.
The blue shift phenomenon is caused by the quantum size effect changes of the electronic transition; due to the decrease of the nanoparticle size, the energy gap becomes wider, which leads to the optical absorption band shift to the short wave direction.
"I was reading the physics literature about 'quantum size effects
,'" he recalls.
"This is called Quantum Size Effects
, or QSE, and a consequence of this relationship is that certain film thicknesses are more stable than others," explains Tringides.
Researchers Phaedon Avouris and In-Whan Lyo report in the May 13 SCIENCE that tiny, naturally formed terraces on metal surfaces trap electrons and that these electrons exhibit quantum size effects. The researchers used a scanning tunneling microscope to map the surfaces of both gold and silver sheets on an atomic scale and simultaneously to observe the distribution and energy levels of electrons.
To see quantum size effects, says Avouris, scientists must look at materials on approximately the same scale as the electron wavelengths.
If the terraces are small enough -- as they are on these metal surfaces -- the energy levels of the trapped electrons are so far apart that even the jiggling effects of thermal radiation can't prevent the quantum size effects from being detected at room temperature.
When the sizes of such QDs become close to or smaller than the bulk exciton Bohr radius, the electronic and optical properties of these nanomaterials show a significant change from their corresponding bulk properties, which are called quantum size effects
. One such effect is the quantization of the bulk valence band and conduction band, resulting in discrete atomic-like transitions that shift to higher energies as the size of nanocrystals decreases.
Varonides, "Quantum size effects
in amorphous Si superlattice solar cells," Renewable Energy, vol.