Topical lecture: Quantum Size Effects in Nanostructures
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Topical lecture:
Quantum Size Effects in Nanostructures
A. Tavkhelidze
Ilia State University
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Contents
• Quantum mechanical tunneling and applications• Quantum wells and super lattices• Quantum wires and quantum dots (applications)• Carbon nanotubes• Graphene
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Quantum mechanical tunneling
)(22
exp)( EUmd
ED
Where hbar is the Plank’s constant, d is barrier width, m is the electron mass, and U is the height of the potential barrier.
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Tunnel diode
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I-V characteristic of forward based tunnel diode
Applications for tunnel diodes included local oscillators for UHF television tuners, trigger circuits in oscilloscopes, high speed counter circuits, and very fast-rise time pulse generator circuits.
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Josephson juction
Main applications: SQUIDsMillimeter wave detectors and mixersVoltage standards
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Scanning tunneling microscope (STM)
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Coulomb blockade
T<1 K
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Single electron transistor
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Single electron transistor
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Problem 1
Why samples are cooled down in the scanning tunneling microscope?
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Quantum wells and super lattices
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Super lattice
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Quantum well applications
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Quantum wires and dots
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Electron inside the quantum dot
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Quantum dot solar cell
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Problem 2
• Why electron wave function should equal to zero at the object boundary?
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Carbon nanotubes
Armchar Zigzag
Triple-walled armchair
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Carbon nanotube propertyes
• Carbon nanotubes are the strongest and stiffest materials yet discovered in terms of tensile strength and elastic modulus respectively
• Standard single-walled carbon nanotubes can withstand a pressure up to 24GPa without deformation.
• All nanotubes are expected to be very good thermal conductors along the tube, exhibiting a property known as "ballistic conduction", but good insulators laterally to the tube axis.
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Graphene
Carbon carbon bond length 0.142 nm
Interplanar spacing 0335 nm
The Nobel Prize in Physics for 2010 was awarded to Andre Geim and Konstantin Novoselov at the University of Manchester "for groundbreaking experiments regarding the two-dimensional material graphene
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Band structure of for arm-chair orientation
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Band structure of for zig-zag orientation
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Problem 3
• Why such hard material as graphite in your pencil easily transfers to the paper when you write?
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Thank you for attention!