Edit by :- Ala’a Ali Qudah.

ID :- 20053092012.

Advicor :- Dr. Hasan Al-Khateeb.

Research Of Spin Polarized Electron (Phys 791).

Jordan University of Science and Technology

Spin Polarized Electron Spin polarized electron (SPE) beams have wide applications 1) Condensed matter2) 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 target2) Photoemission from polarized atoms3) Fano effect4) The most suitable source photoemission from GaAs.

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)/(8+2)

=0.6

NN

NNP

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:-

1) Photoexcitation.2) Transport.3) Escape.

Optical Spin Orientation

Transport and Escape

The electron affinity χ 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.

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

Important of polarized electrons

1) it is important to know the spin state of incident electron as it is important to know it is energy and momentum .

2) 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.

3) 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.

)()()( photonselectronAtomAtomelectron

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 ).

The intensity of the transmitted light of the incident light beam which has Stokes parameters , and

+

+

To measure the linear polarization of light and

cossin)(2sin2cos)(2cos1

2),,( 1

I

PII

cos2cos)(2sin2sin)(2cos2 I

P

I

P3sin)(2sin

)90()0(

)90()0(1

PP

PP

II

IIP

And the circular polarization

Then it possible to express the intergrated Stokes parameters in terms of state

multipoles

)135()45(

)135()45(2

PP

PP

II

IIP

)90,135,0()90,45,0(

)90,135,0()90,45,0(3

II

IIP

/)(2 1 1

2/3 201 JTJJJ

Pf

/)(Re2 1 1

2/3 212 JTJJJ

Pf

/)(Im2 1 1

2/3 213 JTJJJ

Pf

Where

)(2 1 1

6

1)(

123

)1(22000 JT

JJJJT

JI

f

JJ f

JMJMQMM

KJTM

MJ

KQ

K J J)12()1()(

JKJ KQK

and

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.