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

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)

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

•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)

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

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

Thanks for listening.Questions?

(TEMs, courtesy of Prashanth Madras)