Introduction of nanoscience/nanotechnology ,properties/potential applications of nanomaterials and electrodeposition of metal single component and alloy nanowires in AAO template

1. Introduction of
nanoscience/nanotechnology ,properties/potential
applications of nanomaterials and electrodeposition of metal
single component and alloy nanowires in AAO template
By
Aiman Mukhtar
Post Doctoral Researcher
Wuhan University of Science and Technology

2. Content
Introduction of nanoscience
Properties of nanomaterials
Applications of nanomaterials
Preparation of AAO template
Electrodeposition of metal nanowires

3. What is Nanoscience
Nanoscience primarily deals with synthesis, characterization,
exploration, and exploitation of nanostructured materials.
 These materials are characterized by at least one dimension in the
nanometer range.
A nanometer (nm) is one billionth of a meter, or 10–9 m. One
nanometer is approximately the length equivalent to 10 hydrogen or 5
silicon atoms aligned in a line.

4. How big is a nanometer?
It is a million times smaller than the smallest measurement you can see
on a ruler!
It is a millionth of a millimeter or a billionth of a meter

6. Categorization of nanomaterial's according to
their dimensions

9. Surface effect
Dispersion F of a simple is defined as the fraction or percentage of atom
at the surface, relative to total No. of atom in the sample.
F=A/V
𝐴 = 4𝜋𝑟2
V= 4/3𝜋𝑟3
F=3/r or 6/d
If neglecting the edge effects for long cylindrical thin wire F becomes
F=1/d

11. What is quantum Confinement
quantum confinement effect is observed
when the size of the particle is too small to be
comparable to the wavelength of the electron.
For an electron with KE = 1 eV and rest mass
energy 0.511 MeV, the associated DeBroglie
wavelength is 1.23 nm
we break the words in to quantum and
confinement, the word confinement means
to confine the motion of randomly moving
electron to restrict its motion in specific
energy levels( discreteness) and quantum
reflects the atomic realm of particles.
So as the size of a particle decrease till we a
reach a nano scale the decrease in confining
dimension makes the energy levels discrete
and this increases or widens up the band gap
and ultimately the band gap energy also
increases.

13. Localized Surface Plasmon
when light hits a metal surface (of any size) some of the light wave propagates along the metal
surface giving rise to a surface plasmon — a group of surface conduction electrons that propagate
in a direction parallel to the metal/dielectric interface.
When a plasmon is generated in a conventional bulk metal, electrons can move freely in the
material and no effect is registered.
In the case of nanoparticles, the surface plasmon is localised in space, so it oscillates back and
forth in a synchronised way in a small space, and the effect is called Localised Surface Plasmon
Resonance (LSPR). When the frequency of this oscillation is the same as the frequency of the light
that it generated it (i.e. the incident light), the plasmon is said to be in resonance
with the incident light
One of the consequences of the LSPR effect in metal nanoparticles is that they have very strong
visible absorption due to the resonant coherent oscillation of the plasmons. As a result, colloids of
metalnanoparticles such as gold(Au), silver(Ag), pllatinum(pt) and palladium(pd) can display
colours which are not found in their bulk form.
The properties of metal nanoparticles make them useful in sensing

15. Quantum fluorescence
Ten distinguishable emission colours of
Cdse(cadmium selenide) QDs excited with a
near-UV lamp size range from 5nm-1.5nm
Quantum confinement causes the energy of the
band gap to increase: therefore, more energy is
needed in order to be absorbed by the band gap
of the material.
Higher energy means shorter wavelength (blue
shif). The same applies to the wavelength of
the fluorescent light emitted from the nano-
sized material, which will be higher, so the
same blue shift will occur

16. Hysteresis loop
The typical size of expected magnetic
domains is around 1 µm. When the size of
a magnet is reduced, the number of surface
atoms becomes an important fraction of the
total number of atoms, surface effects
become important, and quantum effects
start to prevail.
When the size of these domains reaches
the Nano scale, these materials show new
properties due to quantum confinement, for
example the giant magnetoresistance effect
(GMR). This is a fundamental nano-effect
used in modern data storage devices

17. single-walled(SWCNT) and
multi-walled(MWCNT)
Some nano-materials have inherent
exceptional mechanical properties
which are connected to their structure.
One such material is carbon nanotubes
these are extremely small tubes having
the same honeycomb structure of
graphite, but with different properties
compared to graphite. They can
be single-walled or multi-walled, as
illustrated in Figure .
Carbon nanotubes are 100 times
stronger than steel but six times lighter!!

19. Overview of nano-materials
In 1985, a new allotrope of carbon was
discovered formed of 60 atoms of carbons
linked together through single covalent
bonds arranged in a highly symmetrical,
closed shell that resembles a football. This
material was officially named
Buckminsterfullerene.
In the early 1990s, an incredible new carbon
form was discovered: carbon nanotubes.
These appear to be like graphite sheets
rolled up with fullerene-type end caps, but
have totally different properties
compared to graphite.

23. Metal/alloy nanowires

24. Applications
Logic gates
P-n junction
diodes
LED’s
Solar cells
sensors
Optical switches
Magnetic
information
storage medium

26. Applications
Indium tin oxide (ITO) is a
semiconducting material whose
main feature is the combination
of electrical conductivity and
optical transparency.
 It is widely used in its thin-film
form as transparent electrodes in
liquid crystal displays, touch
screens, LEDs, thin-film solar
cells, semiconducting sensors.

27. Electroplating to make metal single
and alloy nanowires

28. Synthesis of Nanowires
Electrochemical deposition
 Attractive synthesis method
 Inexpensive
 Controllable
 Do not require large laboratory equipment
• Use of AAO template
 Inexpensive
 Simple process
 Capable of depositing materials in extremely confined and ordered spaces

29. Experimental Procedure
Preparation of AAO template
Electrolyte
Applied Voltage (V) Temperature (◦C) Pore Diameter (nm)
Composition Concentration
H2SO4 0.3 M 15-20 0±2 10-20
(COOH)2 0.3 M 40 0±2 40-50
H3PO4 0.3 M 160-170 0±2 >150

30. Two-step Anodization Procedure
a. Pretreatment: annealing (vacuum of 10-5 Torr at 500 °C for 5 hrs.)
b. First anodization: 0.3 M oxalic acid for 6 hrs. (40V, and 0-5 °C)
c. Removed alumina layer in a mixture of phosphoric acid (6 wt.%) and chromic acid (1.8
wt.%) for 12 hrs. (60 °C)
d. Anodized again at the same conditions for 12 hrs.
e. Etched in a saturated CuCl2 solution to remove the remaining aluminum on the back side
f. Dissolved in a 5 wt.% phosphoric acid solution (40 °C)
g. A gold film was sputtered onto the back side.

31. Schematic illustration of AAO template
SEM image of
home-made AAO template

32. Electrodeposition
• Potentiostatic deposition
 Direct current electrodeposition
 electrons are provided from the external electron source
 applied voltage is remain same for the whole deposition process
• Potentiodynamic deposition
Cyclic voltammetry (CV)
 CV is obtained by measuring the current at the working electrode during the potential scans
 the rate of voltage change over time (scan rate)
 Measure, current density vs. applied potential curves

33. Electrochemical cell for electrodeposition of nanowires
 Area of working electrode (WE) = 0.608cm2
 Area of counter (Graphite) electrode (CE) = 14.7cm2
 Saturated calomel electrode (RE)

34. Growth mechanism of nanowire during
Electrodeposition

35. Experimental conditions
• Composition of electrolytes
 0.356M CoSO4. 7H2O and 0.68M H3BO3 for Co
 0.356M NiSO4. 6H2O and 0.68M H3BO3 for Ni
 0.356M CuSO4 and 0.68M H3BO3 for deposition of Cu
• Potential ranges
CV (potentiodynamic) deposition is performed
For, Co = -0.522 to -1.4V (SCE)
Ni = -0.492 to -1.492V (SCE)
Cu = 0.098 to -0.8V (SCE)
• Scan rate = 0.1mV/s
• pH = 2.5 (adjusted by 1M H2SO4 solution)
• Room temperature
Electrodeposition of Co, Ni and Cu

36. 0.2 0.0 -0.2 -0.4 -0.6 -0.8 -1.0 -1.2
10
0
-10
-20
-30
-40
-50
-60
-70
-80
CurrentDensity(mA/cm
2
)
overpotential (V)
Ni
Co
Cu
Current Density VS Overpotential curves
Results and Discussions (1)

37. SEM images
(a) Ni nanowires
(b) Co nanowires
(c) Cu nanowires
• Diameter of the deposited nanowires is the same as that of the pores of
AAO template (~50nm)
• cylindrical pores of the AAO template were fully filled during CV
deposition
Results and Discussions (1)

38. Experimental conditions
• Compositions of electrolytes
normalized concentrations of Co2+ and Ni2+ ions in the electrolyte were 80% Co and 20%
Ni
 Room temperature
 Applied potential
-1.6V,
-3.0 V
• pH values
2.5 (pH value is adjusted by 1 M H2SO4 solution)
Deposition of Co-Ni alloy nanowires
332424 65.0606.0724.0 BOMHOHMNiSOOHMCoSO 

39.  The Co-Ni phase
diagram shows that Co
and Ni exhibit complete
solid solution in the fcc
phase at temperatures
between the solidus and
the allotropic
transformation
temperature
 The fcc Co84.45Ni15.55 is
a high temperature
phase, and metastable at
room temperature
Co-Ni alloy phase diagram

40. SEM images of Co-Ni nanowires deposited at –1.6 V and -3V: (a) lying nanowires,
measured from four different positions of single nanowire; (b) standing nanowires,
measured from top of nanowires.

41. Thanks