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Nanowires and HeterostructuresMichael Christiansen
Mentor: Dr. Jeff DruckerStatewide Space Grant Symposium
17 April 2010
Special thanks to: Jeff Drucker, Nick Jungwirth, Sutharsan Ketharanathan, Prashanth Madras, and Eric Dailey
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Nanowires
•Made of the Group IV elements silicon and germanium
•Length is generally about 1 m and 𝜇diameter is 10 to 100 nm
500nm
•“One dimensional” nanostructures, approximately cylindrical
•May contribute to applications such as photovoltaics, thermoelectrics, and nanoelectronics
(SEM, courtesy of Jeff Drucker)
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Vapor-Liquid-Solid Growth Process•Thermal deposition of metal catalyst (e.g. gold), forming droplets that are a liquid mixture of silicon and gold
•Addition of silicon or germanium to the droplet (via reaction of Si2H6 or Ge2H6) results in crystal growth outward from the substrate
(Diagram courtesy of Jeff Drucker)
(Graph from Scientific Thermodata Group Europe, www.sgte.org)
Au - Si
1700
1500
1300
1100
900
700
500
3000.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10
mole Si/(Au+Si)
Tem
pe
ratu
re(K
)
FCC_A1 + Si(diamond-A4)
LIQUID
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•Grown by switching between adding silicon and adding germanium, resulting in alternating segments
•Two main challenges:1. An atomically abrupt transition between silicon and germanium
is desirable.2. Sidewall deposition needs to be minimized.
•Our project: to investigate thermal deposition of alternative metal catalysts
Axial Heterostructures: Our Project
(TEM, courtesy of Jeff Drucker)
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Gold vs. Indium
(Graphs from Scientific Thermodata Group Europe, www.sgte.org)
1850
1650
1450
1250
1050
850
650
450Te
mp
era
ture
(K)
2500.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10
mole Si/(In+Si)
In - Si
Si(diamond-A4) + In(tetragonal-A6)
Liquid + Si(diamond-A4)
LIQUID
Au - Si
1700
1500
1300
1100
900
700
500
3000.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10
mole Si/(Au+Si)
Tem
pe
ratu
re(K
)
FCC_A1 + Si(diamond-A4)
LIQUID
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Progress•Construction of ultrahigh vacuum chamber (target pressure 10-9 Torr, or 1/1012 atm)•Transfer mechanism for samples
•Calibration of In evaporation source•Characterization of substrate heating
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Thanks for listening.Questions?
(TEMs, courtesy of Prashanth Madras)