Fabrication Techniques and Characterization of Metal and semi-Conductor Nanowires is Presented in this Lecture delivered at AMITY University, Jaipur.

1. Fabrication and Characterization
of Nanowire Devices
Hardev Singh Virk
Professor Emeritus, Eternal
University, Baru Sahib (HP), India

2. Birth of Nanotechnology
“There's Plenty of Room at the Bottom”
• On December 29, 1959, Richard P. Feynman
gave the seminal talk at a meeting at Caltech
of the American Physical Society. He
presented a vision of the precise manipulation
of atoms and molecules so as to achieve
amazing advances in information technology,
mechanical devices, medical devices, and
other areas.

3. Changing Idea into Reality
Eric Drexler of MIT, the Chemist, established
the modern field of nanotechnology, with a
draft of his seminal Ph.D. thesis in the mid
1980s. His 1991 doctoral thesis at MIT was
revised and published as the book
"Nanosystems, Molecular Machinery
Manufacturing and Computation" (1992),
which received the Association of American
Publishers award for Best Computer Science
Book of 1992.

4. The Incredible Tininess of Nano
The pinhead
sized dot is a
million nm
Billions of nanometers
A two meter tall male is
two billion nanometers.
Biological
cells size is
Thousands
of nm
DNA Molecules
are about 2.5
nm in width
Hydrogen atom
spans 0.1 nm
2 Uranium
atoms span 1 nm

5. • AFM Imaging of ATOMS of GOLD (Au 111)

6. Atomic Lattice Structure of HOPG in 3D
Topography using Atomic Force Microscope

7. Introduction to Nanowires
Nanowires of metallic and semi-conducting
materials have drawn a lot of research
interest because of their potential
applications in fields like nanoelectronics,
opto-electronics and sensors. Nanowires
exhibit unique electrical, magnetic, optical,
thermoelectric and chemical properties
compared to their bulk counterpart. Electronic
conduction takes place both by bulk
conduction and through tunneling
mechanism.

8. Special Characteristics
• Nanowires exhibit high density of electronic
state.
• They have diameter-dependant band gap.
• They show enhanced surface scattering of
electrons and phonons.
• They have increased excitation energy, high
surface to volume ratio and large aspect ratio.

9. Fundamental Features
• One-dimensionality
• – Wire diameter: several nm ~ hundreds of nm’s
• – Aspect ratio: L:D >10:1
• Material integrity
• – Single crystalline nanostructure
• Availability of numerous materials
• – Superconductor, metal, semiconductor, insulator
• Unique physical properties
• – Large surface-to-volume ratio
• – High transport/carrier mobility
• – Quantum confinement/tunable band structure

10. Quantum Confinement Effects
– Quantum dots (0-D): confined states, and no
freely moving ones
– Nanowires (1-D): particles travel only along the
wire direction
– Quantum wells (2-D): confines particles within a
thin layer
There is no confinement
effect in Bulk materials.
Refer to energy distribution.

11. Chemical Routes of Synthesis
• Solution-Based Synthesis
• – Solution-Liquid-Solid (SLS) Method
• – Solvothermal Chemical Synthesis
• – Template-Based Synthesis
• Gas-Phase Synthesis
• – Vapor-Liquid-Solid (VLS) Method
• -- Laser abrasion
• -- PVD
• -- CVD (LPCVD, MOCVD)
• – Vapor-Solid (VS) Method
• – Oxide-Assisted Growth (OAG)

12. Growth of Semiconductor Nanowires
by VLS method
Laser ablation overcomes thermodynamic
equilibrium constraints and enables liquid
nanocluster formation.

13. GaN Nanowires Grown by VLS method
SEM image of GaN nanowires of diameters
10nm and lengths on the order of 10m (Huang
et al., 2002).

14. ZnO Nanowires on Sapphire by VLS
method
SEM images of ZnO nanowire arrays grown on a sapphire substrate, (a)
shows patterned growth, (b) shows a higher resolution image of the
parallel alignment of the nanowires, and (c) shows the hexagonal cross-section
of the nanowires (Huang et al., 2001).

15. Nano-Lasers using ZnO Nanowires
ZnO nanowires Emission spectrum from ZnO nanowires. grown by VLS method.

16. Nanowire Fabrication
Template synthesis using polymer and anodic
alumina membranes
Electrochemical deposition
Ensures fabrication of electrically continuous wires
since only takes place on conductive surfaces
Applicable to a wide range of materials
High pressure injection
Limited to elements and heterogeneously-melting
compounds with low melting points
Does not ensure continuous wires
Does not work well for diameters < 30-40 nm
 Chemical Vapor Deposition (CVD) or VLS technique
Laser assisted techniques

17. Polymer Template Synthesis of
Nanowires

18. LLaarrggee EEttcchheedd IIoonn TTrraacckkss

19. Anodic Alumina Template Preparation
 Anodization of aluminum
 Start with uniform layer of ~1mm Al
 Al serves as the anode, Pt may serve as the cathode, and
0.3M oxalic acid is the electrolytic solution
 Low temperature process (2-50C)
 40V is applied
 Anodization time is a function of sample size and distance
between anode and cathode
 Key Attributes of the process (per M. Sander)
 Pore ordering increases with template thickness – pores are
more ordered on bottom of template
 Process always results in nearly uniform diameter pore, but not
always ordered pore arrangement
 Aspect ratios are reduced when process is performed when in
contact with substrate

20. Electrochemical mechanism
• The overall reaction that takes place during
anodization is:
2Al + 3H2O => Al2O3 + 3H2
At the anode:
2Al + 3O2- => Al2O3 + 6e-
At the cathode:
6H+ + 6e- ==> 3H2
• The Al is oxidized at the metal/oxide
interface
• The oxide is etched away by the acid with
the applied potential
• The pores are induced by the roughness of
the top surface
TEM micrographs

21. Anodic alumina (Al2O3) Template
(T. Sands/ HEMI group http://www.mse.berkeley.edu/groups/Sands/HEMI/nanoTE.html)
alumina template
Si substrate 100nm
(M. Sander)

22. EElleeccttrroollyyttiicc CCeellll

23. Replica of Nanowires

24. Microtubule Fabrication

25. Electrochemical Synthesis
• Electrochemistry has been used to fabricate
nanowires of Cu and heterojunctions of Cu-Se
and Cd-S. The results of our investigations can
be exploited for fabrication of nanodevices for
application in opto-electronics and nano-electronics.
During failure of our Experiments,
exotic patterns ( nanoflowers, nanocrystals,
nanobuds) were produced under nature’s self
assembly.

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ffoorr mmoorrpphhoollooggiiccaall aanndd ssttrruuccttuurraall ssttuuddiieess..

27. Atomic Force Microscope(NT-MDT)

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AAnnooddiicc AAlluummiinnaa MMeemmbbrraannee ((AAAAMM))

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36. Copper Nanoflowers grown in Polymer
Template (100nm pores)

37. Copper Marigold Flower

38. SiC Crystalline Nanowire Flowers
G. W. Ho (Nanotechnology, 2004)

39. Crystalline Nano-comb of ZnO NW
H. Yan (JACS 2003)

40. SEM micrograph of Copper Buds

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PPoollyyccrryyssttaalllliinnee CCooppppeerr

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CCooppppeerr nnaannooccrryyssttaallss
Position [°2Theta] (Copper (Cu))
10 20 30 40 50 60 70
Counts
0
20000
40000
60000
36.637 [ ° ]
38.283 [ °]
43.461 [ ° ]
45.448 [ ° ]
48.920 [ ° ]
50.580 [ ° ]
54.304 [ ° ]
54.956 [ ° ]
64.809 [ ° ]
74.299 [ °]
KK1

43. XXRRDD ssppeeccttrruumm ooff CCuu nnaannoowwiirreess
30 40 50 60 70 80 90
Position [°2Theta] (Copper (Cu))
Counts
1600
400
0
Cu polycrystalline

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ddiiooddee cchhaarraacctteerriissttiiccss

49. A Billion Dollar Question …
• What can nanowires offer for semiconductor
nanoelectronics?
• Nonlithographic & extremely cost-effective
• Reduced phonon scattering: High carrier
mobility but reduced thermal conductance(?)
• Tunable electrical/optical properties
• Large surface-to-volume ratio: Sensor
sensitivity & memory programming efficiency

50. Advantages of 1-D Nanowires
• High-quality single-crystal wires with nearly
perfect surface
• Scalable nanostructure with precisely
controlled critical dimensions
• Best cross-section for surround-gate CMOS
• Very cost-effective materials synthesis
• High transport low-dimensionality structure
• May use as both device and interconnect for
ultra-compact logic (e.g., SRAM)

51. Nanowire Field-Effect Transistor
A single device for numerous applications
Device physics study
• Ambipolar transport
• Carrier mobility study
• Quantum effect

52. Quantum-Wire Device
M. Bjork (Nano Letters, Sept. 2004)
1. In-situ control of nanowire synthesis allows design of strongly confined
quantum mechanical systems inside nanowires, possibly useful for SET .
2. Next-generation nanoelectronic devices with extremely-low power, high
performance, and radiation tolerance.

53. 3-D Nanowire Logic Chip
H. Ng (Nano Letters, July 2004)

54. Si NW Thermal Conductance
D. Li (APL Oct. 2003)

55. Thermoelectric (TE) Conversion
E.J. Menke (Nano Letters, Oct. 2004)
Bismuth Telluride (Bi2Te3) nanowires

56. Role of Nanowires for Next-
Generation Electronics
• The chemical and physical characteristics of
nanowires, including composition, size,
electronic and optical properties, can be
rationally controlled during synthesis in a
predictable manner, thus making these
materials attractive building blocks for
assembling electronic and optoelectronics
nanosystems.

57. Some Observations & Remarks
• Nanotechnology will be the driving force for
next technology revolution.
• Nanowires open door to a wonderland where
the next generation electronics would emerge.
• Scope for innovating new synthesis method
and complex functional nanostructures.
• New device and interconnect concepts will
emerge from horizon, driven by materials
synthesis.

58. Our Publications
• My website: http:// drhsvirk.weebly.com
for list of our published research papers.
Go to www.docstoc.com for purchase of
reprints.
Free download of Review Paper on Nanowires:
visit: ttp://www.intechopen.com/articles/show
• Chapter 20 of Book “Nanowires - Implementations
and Applications”, InTech Open, Abbass Hashim
(Ed).

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60. Thank
You !!!