Utilization of Stern-Gerlach Effect to achieve direct write deposition of Cu films

Dr. Clinton B. LeeAssociate Professor

ECE DepartmentNorth Carolina A&T State University

Experimental Set-up

Space quantization of atomic angular momenta• A magnet (atom) tends to move so as to

increase the magnetic flux through it in the direction of its magnetic axis

• In a uniform field, the only result is that the magnet experiences a torque tending to line it up with an applied field

t = m X B• In a non-uniform field, the magnet experiences

a translatory force as well F= -grad(m.B)

A particle in a magnetic dipole performs three motions: 1. Larmor rotation. 2. Motion along the force lines

with reflection in the polar zones. The reflection is given in the dense parts of the magnetic field by the influence of the force grad B (magnetic mirror effect).

3. Drift transversal to the force lines by effect of the centrifugal force generated from motion 2. The velocity of this drift is perpendicular to both the magnetic field and this centrifugal force.

Atomic Magnetic Moment

• An electron moving in an orbit is equivalent to a circular current, which possesses a magnetic moment: m= IA

• An applied magnetic field acts on the orbital magnetic moment by trying to align the magnetic moment, angular momentum, and the applied field

Magnetic field applied to fermions (precession)

Additional factors in applying magnetic field • The magnetic moment associated with

the orbital angular momentum is quantized due to its wave nature

• The electrons individually precess about the direction of the field

• There is also a potential energy of E = –m.B

Effects of quantized spin• If the particles are classical, "spinning"

particles, then the distribution of their spin angular momentum vectors is taken to be truly random and each particle would be deflected up or down by a different amount, producing an even distribution on the screen of a detector.

• Instead, the particles passing through the device are deflected either up or down by a specific amount.

Actual result of Stern Gerlach experiment wo/field on left, w/field on right

Tools for utilizing Stern Gerlach Effect for focusing of thermally evaporated Cu atoms

Thickness profiles with and without magnetic field

0

5

10

15

20

25

30

35

40

1 2 3 4 5 6 7 8 9 10

Position

Thickness

(

KÅ

)

S

SM 5

Longitudinal Stern Gerlach Effect• Magnetic gradients may be applied with

radial symmetry that bends the trajectory of a specific spin orientation towards the center of the beam’s target

• This process may be increased by applying a gradient closer to the source of the beam

A magnetic dipole creates a magnetic gradient with rotational symmetry

Magnetic annealing - Annealing and cooling in a strong magnetic field • Results show that the magnetic field can considerably

increase the driving force for the transformation from austenite to ferrite by enhancing the Gibbs free energy difference between the two phases

• As compared with annealing without magnetic field, the high magnetic field annealing increases the volume fraction of crystal grains with c-axis aligned along the annealing magnetic field direction. A corresponding uniaxial magnetic anisotropy was also observed in the magnetically annealed FePd alloy.

Thermal evaporation as means of depositing Cu• Sputtering in a magnetic field

gradient makes things a lot more complicated, since there are charged particles and electric field gradients.

• A thermal evaporation source is as simple as a strip heater and an aperture

Field Pattern from cone pole piece

Magnetic Bottles are formed through creating appropriate magnetic gradients

Magnetic lenses for electrons are formed with dipoles

Rotation accompanies the focusing of electrons

Initial magnetic field placement model