Re: quantum confinement

From: cosine (cosineREMOVE-THIS_at_gmail.com)
Date: 03/22/05

  • Next message: cosine: "Re: Nanoparticles and thermodynamics" 
    Date: Tue, 22 Mar 2005 16:31:47 -0000

    may abdelghani wrote:
    > dear all ...
    > -there is a quantum confinement phenomon in
    > molecules?( as the nanostructures, molecules have
    > discrete energy levels too).
    > - there is molecules have a nanometer size, but it
    > hasn't the size-depend properties'phenomena ... why?
    > i think that you can help me.

    The quantum confinement seen in nanostructures like semiconductor
    quantum dots, heterostructures, etc., depends on confining an electron
    (or a particle) in a potential well (or some form of potential).

    The potential that the electron/particle experiences, depends on the
    type of atoms that it interacts with and also the position and
    arrangement of those atoms. Confinement is dependent on size, but the
    correct way to look at it is by looking at the potential profiles, not
    just whether the molecule/structure is nanosized (potential profiles
    should automatically account for that).

    When the structure is made of atoms that have potential profiles
    different from one another, if other things permit, you will have
    confinement. For e.g., if you consider a heterostructure made of three
    layers, say, GaAs, AlAs and GaAs, the AlAs offers a different potential
    to the electrons compared to the GaAs part and the arrangement provides
    a potential well. To throw some numbers in, the band gap in AlAs is
    2.15eV, band gap is 1.42eV and you have a potential well of size (2.15eV
    -1.42eV) and this potential well provides confinement.

    However, not all molecules or heterostructures will provide confinement.
    In fact, the same atoms when arranged in a different way may or may not
    show confinement. The reason is simple - when you have a different
    arrangement of atoms, the potential profile changes. Since confinement
    is dependent on potential profile, even that changes.

    hope this helps,
    cosine!

  • Next message: cosine: "Re: Nanoparticles and thermodynamics"