Experimental Condensed Matter Physics in the Nanoscale

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Experimental Condensed Matter Physics in the
Nanoscale

• Leigh M. Smith
• Howard Jackson
• Nathalie Mukolobwiecz Sebastian Mackowski
• Kapila Hewaparakrama Nguyen Tuan
• Tak Gurung Suvranta Tripathy

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The year(s) of the nano
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Reduced Dimensionality
Confining the electron motion in at least one
spatial dimension affects
the energy levels and the density of states
Based on Bimberg (1999)
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Photoluminescence Spectroscopy

• A laser excites electrons from the valence band
  into the conduction band, creating electron-hole
  pairs.
• These electrons and holes recombine and emit a
  photon.
• We measure the number of emitted photons
  (intensity) as a function of energy.

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Strain Driven Quantum Dot Growth

• Expect states with strong binding (confinement)
  to CdSe dots.
• Strain, alloying, and dot-layer morphology very
  important.

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Characterization of CdSe SAQDs
Atomic-Force Microscopy
Scanning Tunneling Electron Microscopy
1.5 ML
2.6 ML
Phys. Rev. Lett. 85, 1124 (2000).

• Observations
• Hemispherical in shape
• Quite uniform in size
• height 10 nm, diameter 20 nm
• Distinguishable from surface variations
• Number density is about 2025 ?m-2

• Observations
• Even at 1.5 ML, CdSe layer not uniform
• Variation in size both laterally and vertically
• Co-existence of 2-D platelets and 3-D islands
• Dots extend above and below the interface

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Looking for single dots
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From thousands to tens
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Some dots are different than others.
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Different in other ways too..
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Resonant PL as a Function of Laser Focus
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Exciton relaxation dynamics
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Future Work Controlling the Electromagnetic
Field
Exciton-Polaritons in 0D Strong coupling
between the EM Field and excitons in QDs.
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Future Work Ferromagnetic Semiconductors
What is the origin of Ferromagnetism in
GaMnAs? Clearly hole-driven, but can The
magnetism be driven optically?