Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Energy of electron and its effective mass

  1. May 19, 2009 #1
    Could somebody tell what is connection
    between effective mass of electron and
    its energy?
    As I know rest energy of electron is about
    500 KeV what is pretty big.
    In some materials effective mass of electron
    is one thousand of its rest mass.
    Could we create some energy storage device
    which would play on difference of effective
    mass of electron in different materials?
  2. jcsd
  3. May 30, 2009 #2
    Having different effective masses in different materials does not change the TOTAL energy of an electron supposing that the electron passes through these materials.

    It's the still the same total energy, but the electron will simply change its kinetic energy, thus speed.

    This is like climbing an incline --- I don't see how you can use that energy for storage??

    Am I missing what you imply here?
    Last edited: May 30, 2009
  4. May 31, 2009 #3

    Dr Transport

    User Avatar
    Science Advisor
    Gold Member

    The effective mass in a crystal is related to the band structure and the energy bands curvature at the center of the Brillouin zone.
  5. May 31, 2009 #4
    It's the still the same total energy, but the electron will simply change its kinetic energy, thus speed.

    I just thought that we have different Fermi energy in different materials and this is also connected to speed of
    electrons,if I no make mistake,and we could create energy
    storage which uses difference between those energies.
    This is usual electrochem. batteries.So I thought that we
    may try to use the same principle related to different
    effective mass of electron.If effective mass doesn't really
    related to energy then things are different.
    Also in graphene electrons seems to slow down if they
    gain energy.Could we influence those electrons so they
    will gain more energy and slow down and thus store energy?
  6. May 31, 2009 #5
    No, the energy storage is not possible in your sense. But you probably know of chemistry where the energy can be stored in complex molecules. Gun powder, dynamite, etc., all are the energy stores.

    With different electron mass in different materials you can make contact phenomena - thermoelectric current, diodes, lots of electronic devices, etc.

  7. May 31, 2009 #6
    I wander if there is some possibility to create an energy
    storage which would be more dense than chemical but
    will not be nuclear?Or there is some serious theoretical
    limits which make such storage impossible?
    Is difference in Fermi energies between different atoms
    maximum that we could attain?And thus Boron is the ultimate energy storage (per volume) which isn't nuclear?
  8. Jun 1, 2009 #7
    Okay, you are right in the sense that the potential energy of a moving electron changes when it passes through different media. So there's at least energy conversion (potential to kinetic)

    But, it has to be a tangible storage, how will you transform that potential energy into something useful?

    Every storage mechanism has a well-defined read-out operation. IN batteries, you transform the stored energy into electric current, in capacitors stored electric charge is read-out by current flow, in spin RAMs, magnets store the information and they interact with current flow via GMR, etc...

    So, propose a device-like structure where you can actually sense (read-out) the potential energy change of a moving electron. It doesn't make sense right?
  9. Jun 1, 2009 #8
    So, propose a device-like structure where you can actually sense (read-out) the potential energy change of a moving electron.

    I would just patent it.
    But fist of all I'm trying to understand how much energy
    would be able to yield such device.
    It would be interesting to create something more energy dense than chemical processes to make it competitive.
    Could there be solids in which electron has very different
    TOTAL energy?
    Last edited: Jun 1, 2009
  10. Jun 1, 2009 #9
    I remember that a mix of two different metal powders compressed to a solid tablet can contain a huge energy. When you ignite a piece of it, the chemical reaction starts and the whole tablet gets very hot. Kind of melting and dissolving two metals. Something similar is possible with ceramics.

    I do not have any references, it is an old recollection from my studentship.

    Last edited: Jun 1, 2009
  11. Jun 1, 2009 #10

    Well, for that you need INELASTIC processes, which involve energy exchange, and of course, this goes to batteries, diodes, solar cells, etc...

    But simply putting two different materials and assuming no other interactions won't cut it. Remember it's still the same electron, but swimming in a different water, that change may not even be measurable, experimentally speaking.

    Maybe if f5toli sees this he could comment on this, he might give a different input.

    But to me, it doesn't make sense. You have a pretty general idea, try narrowing it down.
  12. Jun 2, 2009 #11
    So as I've understood we need to have system which changes its own energy in WHOLE.
    In this case we probably will need to have two different
    materials where electron have different TOTAL energy.
    Or one material in which electron could have different
    energy values.
    Unfortunately, electrons are not vehicles themself,otherwise
    we would be able to gain from conversion of their potential
    energy into kinetic. :smile:
    I read that some company promises to create electronically pumped Betavoltaic batteries which would not be
    radioactive by itself.Although I don't believe in possibility of it.
    Last edited: Jun 3, 2009
  13. Jun 6, 2009 #12
    There is something interesting about graphene yet:
    If I no make mistake Fermi energy have some relation
    to energy capacity of batteries.Could we use graphene as
    one of the components of battery?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook