1. An Introduction to Nano-Science
& Nano-Technology
Dr. Abdul Waheed Anwar
Nanotechnology Research Center
Department of Physics
UET Lahore

2. Nano-materials
 What is “nano-material” and why we are
interested in it?
 Optical and electronic properties of nano-
materials

3. Nano-materials
 Definition: low dimension structures including
quantum wells, quantum wires, and quantum dots
 Expecting different behavior of electrons in their
transport (for electronic devices) and correlation (for
optoelectronic devices) from conventional bulk material

4. Nano-materials
Electron behavior:
Quantum well – 1D confined and in parallel plane 2D Bloch
wave
Quantum wire – in cross-sectional plane 2D confined and 1D
Bloch wave
Quantum dot – all 3D confined

5. Nano-materials
Bulk semiconductor
– plane wave like with effective mass, two different type
of electrons identified with opposite sign of their
effective mass, i.e., electrons and holes
– parabolic band dispersion (E~k) relation
– density of states in terms of E: continues square root
dependence, with different parameters for
electrons/holes in different band

6. Nano-materials
• Quantum well
– discrete energy levels in 1D for both electrons and holes
– different effective masses in 2D parallel plane for electrons and holes
– dispersion (E~k) relation: parabolic bands with discrete states inside the stop-
band
– density of states in terms of E: additive staircase functions, with different
parameters for electrons/holes in different band
• Quantum wire
– discrete energy levels in 2D cross-sectional plane for both electrons and holes
– different effective masses in 1D for electrons and holes
– dispersion (E~k) relation: parabolic bands with discrete states inside the stop-
band
– density of states in terms of E: additive staircase decayed functions, with
different parameters for electrons/holes in different band

7. Nano-materials
• Quantum dot
– discrete energy levels for both electrons and holes
– discrete energy states only
– density of states in terms of E: -functions for
electrons/holes

8. Nano-materials
 Electrons in semiconductors: easily controllable and
accessible
 Electrons in atomic systems: hardly controllable or
accessible

9. Nano-materials
 Geometrical dimensions in the artificial structure
can be tuned to change the confinement of electrons
and holes, hence to tailor the correlations (e.g.,
excitations, transitions and recombinations)
 The reduced probability of inelastic and elastic
collisions (much expected for quantum computing,
could be a drawback for light emitting devices)
 Definite polarization (spin of photons are regulated)
(Coulomb) binding between electron and hole is
increased due to the localization

10. Nano-materials
• Current technologies
– Top-down approach: patterning  etching  re-
growth
– Bottom-top approach: patterning  etching 
selective-growth
– Uneven substrate growth: edge overgrowth, V-
shape growth, interface QD, etc.
– Self-organized growth: most successful approach
so far

11. Carbon Nanotubes
Carbon nanotubes: an important 1-D
material in Nanoscience and nanotechnology
with exceptional properties such as
Properties SWNT Comparison
Very low density 1.33-1.44 Al 2.7g/cm3
g/cm3
High tensile Upto 63 GPa Steel <2GPa
strength
High current ≈109 A/cm2 Cu <106 A/cm2
density
Excellent heat ≈ 4000 W/mK Diamond ≈ 4000
transmission W/mK
Strong temperature Upto 2800 oC Metal in
stability in vaccum μchips <1000 oC

12. Carbon Nanotubes
Wide range of applications:
 Molecular Electronics
 Fibres and Fabrics
 Conductive Plastics
 Field Emission
 Conductive Adhesives
 Sensors DNA-Functionalized
 Thermal Materials CNT-FET for
 Medical diagnostic Chemical Sensing
 medical treatment Cristian Staii et al, Nano Letters, 5, 1774 (2005)

13. Carbon Nanotubes
CNT is a tubular form of two dimensional
graphene
Zigzag (n1,0)
Armchair (n1,n1)
 Chiral indices n1(4),n2(2) Chiral (n1,n2)
 Chiral vector Ch=n1a1+n2a2
 Chiral angle θ: between Ch and a1

14. Carbon Nanotubes
SWCNT MWCNT
diameter : 1.2 nm
http://www.almaden.ibm.com/st/past_projects/nanotubes/?page3 http://www.nano-lab.com/nanotube-image3.html
DWCNT DWCNT
 CCVD
 Peapods C60@SWCNT
 Arc Discharge
Nanoscience and Technology,2005,Part III,203-224

15. Carbon Nanotubes
C1
Metallic SWCNT
M Constant DOS at
E11 Fermi level
V1
Semiconducting SWCNT C1 SC
E11 Zero DOS at
V1 Fermi level
The band structure Densities of states
SWCNT Optical properties depend on the
allowed electronic transitions between van
Hove singularities (vHs)

16. Carbon Nanotubes
Metallic :(n1-n2)mod3=0
Semiconducting:(n1-n2)mod3=1
or
:(n1-n2)mod3=2
SWCNT optoelectronic
properties depend on
chiral indices & diameter
www.sustainability.rit.edu/nanopower/rcn.html

17. Gold, Silver and Platinum Nano-materials
 Metals are unique in their physical and chemical
properties as compared to other compound materials
such as metal oxides, sulphides and nitrides.
 Metals have ductility, malleability, luster, high
density, fewer defects and are generally crystalline in
nature.

18. Gold, Silver and Platinum Nano-materials

19. Nano-materials
Gold is one of the few metallic elements that can be used in
nano scale system and devices due to its resistance to
oxidation.
More over gold has some additional properties at nano scale

20. Gold, Silver and Platinum Nano-materials
The coloring nature of Au and Ag nano-particles was
fundamental identification for their nano-particle colloid
formation.
Making use of this, they have been used as coloring
agents in decorative glasses and clothing.
This is due to light-absorbing nature of the
surface of Au and Ag nano-particles because of the surface
plasmon resonance.

21. What Is Nano?
 Pt nano-particles are catalytically active for oxidation and
reduction reactions.
 As a result, these nano-materials find applications for catalytic
use.
 Since Au, Ag and Pt nano-particles have considerable stability
as compared to other metals, they have gained importance.
However, in the near future, all metals will be possibly shaped
in nano size by using suitable stabilizing agents and medium.

22. Electronic Properties
• Ballistic transport – a result of much reduced
electron-phonon scattering, low temperature
mobility in QW (in-plane direction) reaches a rather
absurd value ~107cm2/s-V, with corresponding mean
free path over 100m
• Resulted effect – electrons can be steered, deflected
and focused in a manner very similar to optics, as an
example, Young’s double slit diffraction was
demonstrated on such platform

23. Electronic Properties
• If excitation (charging) itself is also quantized
(through, e.g., Coulomb blockade), interaction
between the excitation quantization and the
quantized eigen states (i.e., the discrete energy levels
in nano-structure) brings us into a completely
discrete regime
• Resulted effect – a possible platform to manipulate
single electron to realize various functionalities, e.g.,
single electron transistor (SET) for logical gate or
memory cell

24. Optical Properties
• Discretization of energy levels increases the density
of states
• Resulted effect – enhances narrow band correlation,
such as electron-hole recombination.

25. Optical Properties
• Discretization of energy levels reduces broadband
correlation
• Resulted effect –reduces temperature dependence;
which is very much needed in quantum computing
and reduces device performance temperature
dependence

26. Optical Properties
• Quantized energy level dependence on size
(geometric dimension)
• Resulted effect – tuning of optical gain/absorption
spectrum

27. Quantum Dot
Quantum dots are semiconductor very small nano
crystalswhich can be considered as dimensionless.
Quantum dots range from 2-10 nanometers (10-50 nm) in
diameters
An exciton pair is defined as an electron and hole pair.
An exciton Bohr radius is the distance in an electron hole
pair
 The size of QD is of the same order as the radius of exciton
Bohr radius

28. What Is Nano?