Potential well
A
potential well is the region surrounding a
local minimum of
potential energy. Energy captured in a potential well is unable to convert to another type of energy (
kinetic energy in the case of a
gravitational potential well) because it is captured in the local minimum of a potential well. Therefore, a body may not proceed to the global minimum of potential energy, as it would naturally tend to due to
entropy.
Energy may be released from a potential well if sufficient energy is added to the system such that the local minimum is surmounted. In
quantum physics, potential energy may escape a potential well without added energy due to the
probabilistic characteristics of
quantum particles; in these cases a particle may be imagined to
tunnel through the walls of a potential well.
The graph of a 2D potential energy function is a
potential energy surface that can be imagined as the Earth's surface in a landscape of hills and valleys. Then a
potential well would be a valley surrounded on all sides with higher terrain, which thus could be filled with water (i.e., be a
lake) without any water flowing away toward another, lower minimum (i.e.
sea level).
In the case of
gravity, the region around a mass is a gravitional potential well, unless the density of the mass is so low that
tidal forces from other masses are greater than the gravity of the body itself.
A
potential hill is the opposite of a
potential well, the region surrounding a
local maximum.
Quantum confinement is when electrons and holes in a
semiconductor are restricted in one or more dimensions. A (
quantum dot) is confined in all three dimensions, a (
quantum wire) is confined in two dimensions ,and a (
quantum well) is confined in one dimension. That is, quantum confinement occurs when one or more of the dimensions of a nanocrystal is made very small so that it approaches the size of an
exciton in bulk crystal, called the Bohr exciton radius. A quantum well is a structure where the height is approximately the Bohr exciton radius while the length and breadth can be large. A quantum wire is a structure where the height and breadth is made small while the length can be long. A quantum dot is a structure where all dimensions are near the Bohr exciton radius, typically a small sphere.
*a
Graphical representation of a potential well
* W. E. Buhro and V. L. Colvin,
Semiconductor nanocrystals: Shape matters, Nat. Mater., 2003, 2, 138 139.
