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Semiconductor Nanowires I: Growth, assembly, non-electronic applications
11/03/2005
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VLS growth of semiconductor nanowirs
Vapor-Liquid-Solid (VLS) growth process
cluster formation
nucleation and growth nanowire
Au Si
SiSiH4 Si+2H2
•Decomposition of precursors (vapor phase) via catalyst particles
•Liquid alloy droplet formation above the Eutectic temperature
•Supersaturation of the liquid droplet resulting in solid phase growth
•Diameter controlled by the catalyst particle size
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VLS growth of semiconductor nanowirs Y. Wu, Nano Lett. 4, 433 (2004)
20 nm
5 nm
5 nm
5 nm
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VLS growth of semiconductor nanowirs Y. Wu, Nano Lett. 4, 433 (2004)
d=3 to 10 nm
10 to 20 nm
20 to 30 nm
5 nm
5 nm Growth direction at different diameters
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Growth of compound nanowires with laser-assisted catalytic growth
Target: solid compound material + Au mixture
L+S phase above certain temperature
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Growth of compound nanowires via MOCVD
TMG+NH3
Tapering due to direct radial deposition
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Core/shell radial heterostructures Lauhon, Nature 420, 57 (2002)
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Core/shell radial heterostructuresGudiksen, Nature 415, 617-620 (2002).
GaP: indirect bandgapGaAs: direct bandgap
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Nanowire axial heterostructures Gudiksen, Nature 415, 617-620 (2002).
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Thermal evaporation and self-assembly formation of nanowires
Thermal evaporation of ZnONanowires and nanorings collected at cold fingerFormation of nanowires, nanoringsdue to self-assembly
Kong, Science, 303, 1348 (2004)
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Solution based nanowire growth
Solution phase decomposition of bimetallic precursors
Urban, Adv. Mater. 15, 423 (2003)
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Electroplating with polymer or anodized alumina membranes
Dobrev, Appl. Phys. A, 69, 233 (1999)
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Separation of growth and device fabrication processes
d ~ 10 nmL ~ 20 µm
GaNGaN CdSCdS InPInP SiSi
NW SolutionNW Solution
Single virus detection
By separating the high temperature synthesis from assembly and device fabricationa diverse set of materials can be integrated together on a common platform.
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Nanowire biosensorsF. Patolsky, PNAS 101, 14017 (2004).
•Wire surface functionalized by antibody (ab-A)
•Virus A specifically binds to ab-A
•Conductance of the nanowire changes due to the local gating effect.
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Nanowire biosensorF. Patolsky, PNAS 101, 14017 (2004).
Single virus binding signals
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Nanowire biosensorF. Patolsky, PNAS 101, 14017 (2004).
Multiplexing detectionselectivity
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Duan, Nature 421, 241 (2003)
•ZnS nanowire as optical waveguide
•Fabry-Perot interference due to reflection at the two ends, discrete cavity modes
•End emission vs. body emission
Nanowire optics
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Duan, Nature 421, 241 (2003)
•Amplified spontaneous emission in the ZnS nanowiremedium (superlinear vs. pump power)
•Lasing occurs soon above threshold
Lasing via optical carrier injection
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Lasing via electrical carrier injectionDuan, Nature 421, 241 (2003)
Electrically injection of n, p carriers
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Core/multishell nanowire LED
Band gap of the InGaN quantum well can be tuned by In/Ga ratio
Qian, Nano Lett. ASAP, (2005)
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Nanowire (nanoribbon) waveguideLaw, Science, 305, 1269, (2004)
mm long SnO2 nanoribbon waveguides
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Assembly of nanowires via flow alignment
Analogous to flowing logs of wood down the river
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Assembly of nanowires via flow alignment Y. Huang, Science 291, 630 (2001).
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Assembly of nanowires via Langmuir-Blodgett techniqueWhang, Nano Lett. 3, 1255 (2003).
•Nanowires forming a film at the air/liquid interface
•Squeezing the film by the two impedances causes the wires to align with the impedance
•Large scale assembly possible
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Whang, Nano Lett. 3, 1255 (2003). Assembly of nanowires via Langmuir-Blodgett technique
Control the spacing by controlling pressure between the impedances
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Assembly of nanowires via Langmuir-Blodgett techniqueWhang, Nano Lett. 3, 1255 (2003).
Pattern formation by selectively removing excess wires
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Assembly of nanowires via Langmuir-Blodgett techniqueWhang, Nano Lett. 3, 951 (2003).
Spacing can also be controlled via a sacrificial shell layer
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Assembly and integration Jin, Nano Lett. 4, 915 (2004)
Large scale application may be realized without registration
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Si nanowires directly bridging contactsHe, Adv. Mater. 17, 2098 (2005)
Si nanowires can be epitaxiallygrown on Si <111> surface
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Si nanowires directly bridging contacts
He, Adv. Mater. 17, 2098 (2005)
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Dick, Nature Mater 3, 380 (2004) Branched nanowires
GaP nanowires via VLS and MOCVD
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Fabrication of single crystalline metallic nanowires from SiNWs
•Single Crystal
•NiSi 1:1 phase confirmed by EDS
•Diameter control inherited from Si nanowire
Si nanowire
NiSi nanowire
Rapid Anneal
Etch off excess Ni, Post Anneal
Evaporate Ni
5nm5nm
Si+Ni NiSi
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Pure NiSi Nanowires: Transport Measurement
50 100 150 200
2400
2800
3200
R (O
hm)
T (K) •Metallic•Low resistivity: 9.5 µΩ.cm
•Diffusive transport, electron phonon scattering dominates
•Very High Jmax: 3×108 A/cm2 due to elimination of grain boundaries (electromigration)
500nm
Imax=1.8mA
Compare: Metallic Carbon Nanotube: Jmax=1×109 A/cm2
1 10 100
10
100
1000
R-R
0 (Ω)
T (K)
Bloch-Gruneisen formula fit,θD=200K
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NiSi/Si Nanowire Heterostructure
1µm
Ni evaporation
40µm
Si
NiSi
(221)
(112)
5nm atomic sharp interface
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Integrated NiSi/Si/NiSi FET Devices
Electrode
gm=275nS @ -1V bias; µ=325cm2/Vs
Gate response only observed on p-Si
+9V, reduced conductance
-9V, enhanced conductance
3µm
10nm
L=3µm, dox=600nm
NW mask
NiSi
NiSiSi
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Nanowires as temperaturesFan, J. Am. Chem. Soc. 125, 5254, (2003)
Si as template
From SiO2/Si core/shell structure, resulting in SiO2nanotubes
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Single-crystalline Si naotubes
Timko, et al, unpublished
10 nm
Si nanotube
10 nm
GeSi nanowire
Ge core as templateSi tubes obtained from the Ge/Si core/shell nanowires
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Single-crystalline Si naotubes
Timko, et al, unpublished
10nm
0
-2
-4
-2
Bias Voltage VSD (Volts)
Cur
rent
(A) Cur
rent
(nA)
0 4 8-4-8
-8 -4 0 4
100
µ
50 nm
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Diameter and Wall Thickness Control
20nm
20nm 20nm 20nm
20nm20nm
5min Shell growth
20min Shell growth
50min Shell growth
5nm core 20nm core 80nm core
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Variations of Si Nanotubes
200nm
200nm
200nm
T=380C
T=400C
20nm
20nm
Si cones Si nanotube networks
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Nanofluidics with Si nanotubes
Timko, et al, unpublished
Nanoparticles inserted inside Si nanotubes
20nm
Trapped gas bubbles
20nm20nm 20nm
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Nanofluidics with Si nanotubes
Timko, et al, unpublished
V
20µm
20µmOnOff
•Fluidic properties at the nanoscale•DNA stretching•Bio-sensing
Electro-osmosis