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Edit by :- Ala

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Jordan University of Science and Technology Edit by :- Ala a Ali Qudah . ID :- 20053092012. Advicor :- Dr. Hasan Al-Khateeb. Research Of Spin Polarized Electron ... – PowerPoint PPT presentation

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Title: Edit by :- Ala


1
Jordan University of Science and Technology
  • Edit by - Alaa Ali Qudah .
  • ID - 20053092012.
  • Advicor - Dr. Hasan Al-Khateeb.
  • Research Of Spin Polarized Electron (Phys 791).

2
Spin Polarized Electron
  • Spin polarized electron (SPE) beams have wide
    applications
  • 1) Condensed matter
  • 2) Atomic and molecular
  • 3) High energy physics
  • Historically, the development of a suitable SPE
    source and have been tried in attempts to
    produce beams of spin polarized electrons
  • 1) Scattering from unpolarized target
  • 2) Photoemission from polarized atoms
  • 3) Fano effect
  • 4) The most suitable source photoemission from
    GaAs.

3
  • polarized electron -
  • If the electron spins have a preferential
    orientation so that there exists a direction for
    which the two possible spin states are not
    equally populated .
  • Polarization is defined -
  • For example -
  • 10 electrons ,8 electrons spin up and 2 electrons
    spin down
  • P (8-2)/(82)
  • 0.6

4
  • In the mid-1970s Pierce, Meier, and Zurcher
    developed an intense source of polarized
    electrons based on photoemission from p-type
    GaAs, because have many advantages.
  • Advantages of GaAs source-
  • 1) Narrow energy width.
  • 2) Quantum efficiency.
  • 3) Good degree of polarization .
  • 4) High brightness.
  • Photoemission from GaAs can be described
    particular three step model-
  • Photoexcitation.
  • Transport.
  • Escape.

5
Optical Spin Orientation
6
  • Transport and Escape
  • The electron affinity ? of p-type GaAs is large
    (about 4eV). It represents the
  • difference in energy between the vacuum level and
    the conducting band
  • prevents electrons from leaving the crystal
    surface. adding layers of cesium to
  • the crystal will reduce the electron affinity to
    values close to zero.
  • Furthermore, adding layers of cesium and oxygen
    will reduce the electron
  • affinity to negative values (negative electron
    affinity (NEA)).
  • NEA GaAs is able to extract photoelectrons with
    high quantum efficiency.

7
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8
  • Increase the efficiency of current
  • Then Adding several layers of cesium and oxygen
    (is called activating the crystal) is able to
    increase the photocurrent of electrons to many
    orders of magnitude

9
  • Important of polarized electrons
  • it is important to know the spin state of
    incident electron as it is important to know it
    is energy and momentum .
  • studying spin-dependent electron-atom scattering
    processes such as spin-orbit interaction between
    the incident electron and the atom as well as the
    exchanges between them.
  • the polarized-electron atom collisions can
    provide valuable information about collision
    mechanisms and electron correlation.
  • The polarization of the light emitted from
    excited state provides us with a lot of
    information about the processes during the
    collision between the electron and atom.

10
  • To determine the polarization properties of the
    light completely, we must measure the Stokes
    parameters and To determine these parameters, we
    have to measure the intensity of the light after
    passing through rotatable retarder and linear
    polarizer (optical polarimeter ).

11
  • The intensity of the transmitted light of the
    incident light beam which has Stokes parameters
    , and
  • To measure the linear polarization of light
    and

12
  • And the circular polarization
  • Then it possible to express the intergrated
    Stokes parameters in terms of state multipoles

13
  • Where


and

14
Summary
  • Electron beam is said to be polarized if there
    exists a direction for which the two possible
    spin states are not equally populated.
  • it is important to know the initial and final
    states of the system and to know the spin states
    of the incident electron and can provide
    valuables information about collision mechanisms.
  • The most suitable source photoemission from GaAs
    , because have many advantages .and can be
    described this source in three steps
    photoemission, transport and escape.

15
Thanks
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