Lecture by:
Rose Farahiyan Munawar , PhD
Models of 3-D nanostructures made
from DNA.
Pre-Quiz
Nanowires
quantum wire, metallic nanowire, semiconductor
nanowire, insulating nanowire, molecular nanowire,
nanowire arrays, nanowire, alumina nanowire, bismuth
nanowire, boron nanowire, cadmium selenide
nanowire, copper nanowire, gallium nitride nanowire,
gold nanowire, gallium phosphide
nanowire, germanium nanowire, indium phosphide
nanowire, magnesium oxide nanowire, manganese
oxide nanowire, nickel nanowire, palladium nanowire,
platinum nanowire, silicon nanowire, silicon carbide
nanowire, silicon nitride nanowire, titanium dioxide
nanowire, zinc oxide nanowire, gold microwire, silicon
microwire,
Nanowire (Nw)
Why Nanowires?
Why Nanowires?
The nanowires could be used, in the near future, to
link tiny components into extremely small
circuits.
Using nanotechnology, such components could be
created out of chemical compounds.
Advantages of NWs:
• NW devices can be assembled in a rational and
predictable because:
– NWs can be precisely controlled during synthesis,
– chemical composition,
–diameter,
–length,
– doping/electronic properties
• Reliable methods exist for their parallel assembly.
Advantages of NWs:
• It is possible to combine distinct NW building
blocks in ways not possible in conventional
electronics.
• NWs thus represent the best-defined class of
nanoscale building blocks, and this precise
control over key variables correspondingly
enabled a wide range of devices and
integration strategies to be pursued
Structure of NWs
• Whiskers, fibers:1D structures ranging from
several nanometers to seve ral hundred
microns
• Nanowires: Wires with large aspect ratios
(e.g.>20),
• Nanorods: Wires with small aspect ratios.
• NanoContacts: short wires bridged between
two larger electrodes.
Structure of NWs
Structure of NWs
A nanowire is a nanostructure, with the
diameter of the order of a nanometer (10-9
meters).
Alternatively, nanowires can be defined as
structures that have a thickness or diameter
constrained around tens of nanometers or less
and an unconstrained length.
Structure of NWs
At these scales, quantum mechanical effects are
important — hence such wires are also known
as "quantum wires".
Presently diameters as small as 12 nanometers
Structure of NWs
Typical nanowires exhibit aspect ratios (lengthto-width ratio) of 1000 or more.
As such they are often referred to as onedimensional (1-D) materials.
Nanowires Structure
The nanowires can show peculiar shapes.
Single crystal formation- common
crustallographic orientation along the
nanowire axis
Sometimes they can show noncrystalline order,
assuming e.g. a pentagonal symmetry or a
helicoidal (spiral) shape.
Helical Nanowire
Nanowires Structure
The lack of crystalline order is due to the fact
that a nanowire is periodic only in one
dimension (along its axis).
Minimal defects within wire
Minimal irregularities within nanowire.
Nanowires Structure
Electrons zigzag along pentagonal tubes and
spiral along helicoidal tubes.
Hence it can assume any order in the other
directions (in plane) if this is energetically
favorable.
thin, brittle, can be electrically conductive,
quantum effects can be important
Structure of NWs
• Hence it can assume any order in the other
direction NWs are observed spontaneously in
nature.
• Nanowires can be either suspended,
deposited or synthesized from the elements.
Types of nanowires (diameter)
1
2
•Classical Nanowires
•Quantum Nanowires
Properties of NWs
Nanowires have many interesting properties
that are not seen in bulk or 3-D materials.
This is because electrons in nanowires are
quantum confined laterally and thus occupy
energy levels that are different from the
traditional continuum of energy levels or
bands found in bulk materials.
NW Properties
Depending on what it's made from, a NW
can have the properties of an insulator, a
semiconductor or a metal.
NW Properties
SEM characterization of as-synthesized
silicon oxide
nanowires.
Indium arsenide (InAs) nanowires
grown by the VLS technique
NW Properties
Insulators won't carry an electric charge
While metals carry electric charges very well.
Semiconductors fall between the two, carrying a
charge under the right conditions.
NW Properties
By arranging semiconductor wires in the proper
configuration, engineers can create
transistors, which either acts as a switch or an
amplifier
Semiconductors are most useful in making
transistors for computers.
NW Properties
Optical properties
• Controlling the flow of optically encoded
information with nanometer-scale accuracy
over distances of many microns, which may
find applications in future high-density optical
computing .
• Silicon NWs coated with SiC show stable
photoluminescence at room temperature
Building Blocks Synthesis
How do we make NWs?
There is no single fabrication method for NWs
All the materials (metallic, semiconductor etc)
hane been grown as 2D nanomaterials (thin
films) in the last three decades
How do we make NWs?
NW fabrication is challenging
Challenging is to grow 1D NWs
Alignment is a critical first step for developing
devices that use NWs
Methods
• Spontaneous growth:
Evaporation condensation
Dissolution condensation
Vapor-Liquid-Solid growth (VLS)
Stress induced re-crystallization
• Electro-spinning
• Solution Synthesis
Methods
• Template-based synthesis:
Electrochemical deposition
Electrophoretic deposition
Colloid dispersion, melt, or solution filling
Conversion with chemical reaction
• Lithography (top-down)
General Idea of Spontaneous Growth
A growth driven by reduction of Gibbs free
energy or chemical potential.
This can be from either recrystallization or a
decrease in supersaturation.
Anisotropic growth is required → growth along
a certain orientation faster than other
direction.
General Idea of Spontaneous Growth
Crystal growth proceeds along one direction,
where as there is no growth along other
direction.
Uniformly sized NWs (i.e. the same diameter
along the longitudinal direction of a given
NW)
Fundamentals of evaporation (dissolution)condensation growth
Fundamentals of evaporation (dissolution)condensation growth
(1) Diffusion of growth species from the bulk (such as
vapor or liquid phase) to the growing surface, which,
in general, is considered to proceed rapid enough
and, thus, not at a rate limiting process.
(2) Adsorption and desorption of growth species onto
and from the growing surface. This process can be
rate limiting, if the supersaturation or concentration of
growth species is low.
(3) Surface diffusion of adsorbed growth species. During
surface diffusion, an adsorbed species may either be
incorporated into a growth site, which contributes to
crystal growth, or escape from the surface.
Fundamentals of evaporation (dissolution)condensation growth
(4)
Surface growth by irreversibly incorporating the
adsorbed growth species into the crystal structure.
When a sufficient supersaturation or a high
concentration of growth species is present, this step will
be the rate-limiting process and determines the growth
rate.
(5) If by-product chemicals were generated on the
surface during the growth, by-products would desorb
from the growth surface, so that growth species can
adsorb onto the surface and the process can
continue.
(6) By-product chemicals diffuse away from the surface so
as to vacate the growth sites for continuing growth.
Evaporation condensation
Nanowires and nanorods grown by this method
are commonly single crystals with fewer
Imperfections
The formation of nanowires or nanorods is due
to the anisotropic growth.
Evaporation condensation
The general idea is that the different facets in a
crystal have different growth rates
There is no control on the direction of growth of
nanowire in this method
Dissolution condensation
Differs from Evaporation-condensation
The growth species first dissolve into a solvent
or a solution, and then diffuse through the
solvent or solution and deposit onto the surface
resulting in the growth of nanorods or
nanowires.
The nanowires in this method can have a mean
length of <500 nm and a mean diameter of ~60
nm
E-Beam Lithography
Nanowires Typical Applications
• in electronic, opto-electronic and devices
• as additives in advanced composites
• for metallic interconnects in nanoscale
quantum devices
• as field-emittors and as leads for biomolecular
nanosensors.
• also optical, sensing, solar cells, magnetic, and
electronic device applications
Applications in Electronic
Applications in Electronic
Applications in Biomedical
Engineering
Applications in Structural, Mechanical
Applications in Sensors
Conclusion
Challenges:
The insufficient control of the properties of
individual building blocks
Low device-to-device reproducibility
Lack of reliable methods for assembling and
integrating building blocks into circuits
Conclusion
Advances:
• Synthesis of nanoscale building blocks with
precisely controlled chemical composition,
physical dimension, and electronic, optical
properties
• Some strategies for the assembly of building
blocks into increasingly complex structures
• New nanodevice concepts that can be
implemented in high yield by assembly
approaches
References
• Synthesis, Characterization, and Manipulation
of Helical SiO2 Nanosprings, Hai-Feng Zhang et
al.
• One-Dimensional Nanostructures, Sharif
Hussein Sharif Zain
• An Introduction to NanoWires And Their
Applications, Amir Dindar and Shoeb Roman
• Nanostructures, Raul J. Martin-Palma et al.
References
• Nanostructures and Nanomaterials, GuoZhong
Chao
• Synthesis and applications of one-dimensional
Semiconductors, Sven Barth et al.
• Nanomaterials, nanotechnology and design:
an introduction for engineer, M. F. Ashby et al.
• http://www.reade.com/home