Thin Metal Films and Surface Plasmons

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Thin Metal Filmsand Surface Plasmons
By Joel Rovner and Will Bagienski
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Our Goal Was

• Create thin films of metals
• Compare thickness measurements made by different
  methods deposition monitor, resistance, and
  surface plasmon resonance.

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Thickness Measurement

• Deposition monitor
• Uses a vibrating quartz crystal
• Sensitive to added mass on crystal
• Gives rate and total thickness
• Resistance resistivity of silver
• p 1.59 x 10-8 ohm meters
• Area of film about 2.5 x 2.5 cm
• Surface Plasmons
• Laser table, measure reflected intensities,
• Look for resonance

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Surface Plasmons

• Surface Plasmons are oscillations of the free
  electron gas at the surface of a metal.
• In this lab we tried to detect them by shining a
  laser on the films.
• If we could detect them we could have used our
  results to estimate the films thickness.
• The dispersion relation for surface plasmons is
  ?ckxsqrt(1(1/1-(?p/?)2)).

Glass
Surface Plasmon
Metal
Air
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Experimental Apparatus

• The apparatus consisted of a digital light
  intensity meter, a red laser, an angle table, a
  power supply, and the thin film.
• The angle of incidence of the laser was held
  constant and the detector arm was turned until
  the reflected light was detected.
• Some of the problems that developed were that it
  was very difficult to make small changes to the
  angle of incidence and detect it without
  accidentally changing it.

Laser
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Results

• Indium 1 forgot to open shutter (oops)
• Indium 2 meter thickness 500 angstroms, but
  didnt conduct, couldnt use other methods.
• Silver 1 750 angstroms on meter, about 400
  angstroms by resistance, couldnt find SP
  resonance.
• Silver 2 333 angstroms on meter, about 150 by
  resistance, still couldnt find SP resonance ?
• Made nice mirrors though!!!

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What went wrong?

• Each time we evaporated, vacuum got a little
  worse, despite resealing.
• Too much air in chamber, some reaction?
• Uniformity of the film?
• Tarnished?
• Laser table and measurement procedure?
• Resonance too small to see?
• Something else?
• The true thickness remains a mystery