Nanotechnology is used in the characteristics imported to leather and textiles in the footwear industry, which include self-cleaning fabrics, dye capability enhancement, flame retardation, UV and anti-static protection, anti-bacteria, wrinkle resistance, soil resistance, and water repellence

1. NANOMATERIAL SYNTHESIS
METHOD
TANVIR SIDDIKE MOIN

2. Nanomaterial Synthesis Method
“There's Plenty of Room at the Bottom’’
By Richard Feyman in 1959
Nanotechnology application in nowadays
Targeted drug delivery
Super nano-capacitors
CNTTransistor

3. Outline
Emergence and Challenges in Nanotechnology
Bottom-Up andTop-Down Approaches
Introduction to synthesis of nanoparticles
Evaporation and Condensation growth
Lithography technology
Method to nano composite structure

4. Emergence of Nano
• Moore’s Law
Moore’s Law plot of transistor size versus year
Original contact transistor
1947
~cm
Transistor
in Integrated circuit
Nowadays
~micrometer
CNTTransistor
Future
~nanometer
To meet the Moore’s Law, the size of transistor should be decreased

5. Emergence of Nano
• In our life
1. LED for display
2. PV film
3. Self-cleaning window
4. Temperature control fabrics
5. Health Monitoring clothes
6. CNT chair
7. Biocompatible materials
8. Nano-particle paint
9. Smart window
10. Data memory
11. CNT fuel cells
12. Nano-engineered cochlear
• The nanotechnology is changing our life, but not enough.
• Energy crisis, environmental problem, health monitoring, Artifical joints

6. Challenges in Nano
• Atomic scale imaging
• Understand and manipulate the target in nano scale
LaSrMnO and SrTiO superlattice
TEM in biology

7. Challenges in Nano
• Interdisciplinary Investigation
Nano drug delivery
ProteinTEM image
Nano mechanics
Biology
&
Medicine
Physics
&
Chemistry
&
Materials
Mechanics
&
Electronics
Nano

8. Emergence and Challenges in Nanotechnology
Approaches
Introduction to synthesis of nanoparticles
Evaporation and Condensation growth
Lithography technology
Method to nano composite structure
Bottom-Up andTop-Down Approaches

9. Approaches
• Obviously there are two approaches to the synthesis of nanomaterials and the
fabrication of nanostructures:
• Top-down
• Bottom-up
Lithography
Self-assembly

10. Emergence and Challenges in Nanotechnology
Synthesis of Nanoparticles
Introduction to synthesis of nanoparticles
Evaporation and Condensation growth
Lithography technology
Method to nano composite structure
Bottom-Up andTop-Down Approaches

11. Synthesis of Nanoparticles
•Homogeneous nucleation
A solution with solute exceeding the solubility or supersaturation possesses a high Gibbs free energy, the
overall energy of the system would be reduced by segregating solute from the solution.
G △G
△T
GV
S
GV
L
Tm
T*
At any temperature belowTm there is a driving force fro solidification.
G: Gibbs free energy
△G: Driving force for solidication

12. Synthesis of Nanoparticles
• Homogeneous nucleation
For nucleus with a radius r > r*, the Gibbs
free energy will decrease if the nucleus
grow. r* is the critical nucleus size, △G*
is the nucleation barrier.

13. Synthesis of Nanoparticles
• Synthesis of metallic nanoparticles
Influences factors
Differenct reagents
A:sodium citrate
B: citric acid
A B
A weak reduction reagent
induces a slow reaction rate
and favors relatively larger
particles.
Concentration
A: 0.25M AgNO3
B: 0.125MAgNO3
A B
A large precursor concentration
induces a large critical radius
and favors relarively larger
particles.
Other factors: the surfactants, polymer stabilizer, temperature, ect

14. Emergence and Challenges in Nanotechnology
Evaporation and Condensation
Introduction to synthesis of nanoparticles
Evaporation and Condensation growth
Lithography technology
Method to nano composite structure
Bottom-Up andTop-Down Approaches

15. Evaporation and Condensation
• The evaporation and condensation are the fundamental phenomena in preparing thin
films with nano meters thickness.
Substrate
Condensation
Source
vapor
energy
Evaporation
If a condensible vapor is produced by physical means
and subsequently deposited on a solid substrate, it is
called physical vapor deposition.
If a volatile compound of a material react, with or
without other gases, to produce a nonvolatile solid
film, it is called the chemical vapor deposition.
Although both are nonequilibrium processes, the
kinetics and transport phenomena are the
fundamental theory.

16. Evaporation and Condensation
• The Kinetic theoryLet’ s start with the equilibrium process.
Adsorption
Condensation
Substrate
The impingement rate:
the number of collisions per unit area per
second that a gas makes with a surface, such
as a chamber wall or a substrate
Supersaturation condition:
P, the gas pressure;m, the particle mass; k, Boltzmann’s constant, 1.38×10-23 J/K;T, the temperature
ji, incident flux
Tsub, temperature of substrate
• The substrate should be placed at relactively low temperature to meet the supersaturation condition.
• The impingement rate indicates the equilibrium process between evaporation and condensation.

17. Evaporation and Condensation
•The vapor source
The vapor is usually produced from a effusion cell, rather than a open system, therefore, we can solve the flow density from the
implingement rate.
z
A
J 

Tsource Peq
J: flow density
A: area of the leak
z: implingement rate
On a certain angle cos
4
av
n v
J


 
Source
substrate
The angle distribution is
important for a co-sputtering
condition.
Co-sputtering

18. Evaporation and Condensation
• The vapor source
If we use a beer can as source material, what vapor will we obtain? Al 97.7%
Mg 1%
Mn 1.3%
Consider the the implingement rate
beer can
Diffusion cell at 900 K
Mn atom
Al atom
Mg atom
Alloy source
Al, Mg, Mn have different atomic mass.
Al: 0.0001%
Mn: 0.01%
Mg:99.99%
It is not practical to use a congruent
evaporation temperature to deposit a
compound (or alloy) film from a compound
(or alloy ) film with a certain stoichiometric.
This result is obtained under consideringt the adsorption and desorption effect.

19. Evaporation
• How to get the stoichiometric vapor
Flash Evaporation
AC
Heater
substrate
Flash Evaporation
Flash evaporation utilizes very
rapid vaporization, typically by
dropping powders or grains of
the source material onto a hot
surface.The vapor condenses
rapidly onto a relatively cold
substrate, usually with the same
gross composition as that of the
source material.
The substrate was placed at a temperature
that was a supersaturation temperature for
each component.

20. Evaporation
• How to get the stoichiometric vapor
E-Gun
AC
substrate
Molten End
E-Gun
Rod-Fed Source
e-
In a rod-fed source, typically an electron-beam-heated
evaporator, the source material evaporators from the
molten end of the rod. The rod advances as material is lost
from the molten end. In steady state, the composition of the
vapor stream must equal that of the rod. This requires that
the molten end be enriched in the less volatile component.
The adjustment is automatic, since diffusion in the liquid
state is rapid.

21. Evaporation
• How to get the stoichiometric vapor
Coevaporation
substrate
A B
Effusion
Cells
Co-evaporation
T1 T2
T3
The covaporation with the three-temperature method
has been an effective technique for the compositionally
accurate deposition of compound semiconductor films
whose components’ vapor pressure differ greatly. It was
the forerunner of molecular beam epitaxy (MBE).

22. Evaporation
• How to get the stoichiometric vapor
Sputtering
Sputtering of certain materials, whose ejected
particles are molecules, was utilized to obtain a
stoichiometric vapor.
•Direct current sputtering
•Direct current reactive sputtering
•Radio-frequency sputtering

23. Evaporation
• The evaporation source
The simplest sources to produce vapors of materials may be thermal sources.These are sources where
thermal energy is utilized to produce the vapor of the evaporant material. Even when the energy that is
supplied to the evaporant may come from electrons or photons, the vaporizing mechanism may still be
thermal in nature.
quasiequilibrium
nonequilibrium
Evaporation
Sources Effusion cell
Effusion cell

24. Evaporation source
• Ideal Effusion Cell
δA
aorifice
L
Liquid
Gas, Peq
Lbody
1. The liquid and vapor are in equilibrium within the
cell. Pliq=Pvap,Tliq=Tvap, Gliq=Gvap
2. The mean free path inside the cell is much
greater than the orifice diameter.λ>>aorifice
3. The orifice is flat.
4. The orifice diameter is much less than the
distance to the receiving surface.
5. The wall thickness is much less than the orifice
diameter. L<<aorifice
How to design a effusion cell

25. Evaporation source
• Near-ideal Effusion cell
It is impossible to design an ideal effusion cell
Direct
Re-emitted
L
Liquid
Gas, Peq
Lbody Lbody
With a thick orifice lid,
diffuse and specular
reflection off the sidewalls
are possible.
It is the restriction due to the long cell
body that cause a nonequilibrium
behavior of vapor.

26. Evaporation source
• Open-Tube Effusion Cell
a
A quasiequilibrium source An open-tube effusion cell
L
The relative beam intensity of the open-tube effusion cell
calculated for various tube length-to-tube radius ratios (L/a)

27. Evaporation source
• E-Gun
A target anode is bombarded with an electron beam
given off by a charged tungsten filament under high
vacuum. The electron beam causes atoms from the
target to transform into the gaseous phase. These
atoms then precipitate into solid form, coating
everything in the vacuum chamber (within line of sight)
with a thin layer of the anode material.

28. Evaporation source
• Pulsed Laser Deposition
A high power pulsed laser beam is focused inside
a vacuum chamber to strike a target of the
material that is to be deposited. This material is
vaporized from the target (in a plasma plume)
which deposits it as a thin film on a substrate.

29. Evaporation source
• Sputtering
• In sputtering, energetic ions from the plasma of a
gaseous discharge bombard a target that is the
cathode of the discharge. Target atoms are ejected
and impinge on a substrate, forming a coating.

30. Evaporation source
• Plasma-enhanced chemical vapor deposition
Plasma-enhanced chemical vapor depostion is a process used to deposit thin films from a gas state (vapor) to
a solid state on a substrate. Chemical reactions are involved in the process, which occur after creation of a plasma of
the reacting gases. The plasma is generally created by RF (AC) frequency or DC discharge between twoelectrodes, the
space between which is filled with the reacting gases. A plasma is any gas in which a significant percentage of the
atoms or molecules are ionized. Fractional ionization in plasmas used for deposition and related materials processing
varies from about 10−4 in typical capacitive discharges to as high as 5–10% in high density inductive plasmas.

31. Condensation
• Condendation is the change of the physical state of matter from gaseous phase into liquid phase or
solid phase, and the reverse is vaporization.
condensation re-evaporation
adsorption
at special sit
surface
diffusion
nucleation
Inter diffusion
film growth
Adsorption of atoms from gaseous phase
Cluster formation
Critical size islands growth
Coalescence of neighboring islands
Percolation of islands network
Continuous film growth
film

32. Condensation
• Adsorption
physisorption
chemisorption
gas
substrate
Van derWaals force
chemical bond
re-evaporation
transition
• It is defined as chemisorption coefficient
that he fraction of adsorbated atoms
transferred from physisorption into
chemisorption but not re-evaporated.
• An critical condition is that the adsorption
is equall to the reevaporation.
• Only the atoms adsorpted on the
substrate and condensed, grow bigger the
critical radius, then the film would be
deposited.

33. Condensation
• Condensation coefficient
substrate
incident flux
re-evaporation
condensation
The fraction of the incident
flux that actually condenses
c c i
j a j

ji: the incident flux density
ac: the condensation coefficient
jc: the condensation flux

34. Condensation
• Deposition Rate
Growth speed
a
5.430A
Si
cubic lattice parameter, 5.430 A
8 atoms per conventional unit cell
The volume per unit cell, (5.430 A)3=160.10 A3
The particle density, 8/(160.10 A3)=0.05 A-3
The growth speed
2
3
0.703 /
14.06 /
0.05
c
n
f
j A s
v s
n A


   
c
n
f
j
v
n

The deposition rate, or the growth speed
jc, the condensation flux
nf, the particle density,
how many particles per volume
An example

35. Condensation
• Growth mode

36. Condensation
• Non-epitaxial growth
For most film-substrate material combinations, film grow in theVolmer-Weber (VW) mode which
leads to a polycrystalline microstructure.

37. Condensation
• Epitaxial growth---molecular beam epitaxy
Molecular beam epitaxy is a technique for epitaxial growth via the interaction of one
or several molecular or atomic beams that occurs on a surface of a heated crystalline
substrate.

38. Condensation
• Epitaxial growth-Atomic layer deposition
based on the sequential use of a gas phase chemical process.

39. Condensation
• Monolayer monitoring---RHEED
Reflection high energy electron diffraction, an extremely popular technique for monitoring the
growth of thin films.
• In RHEED, electrons beam strikes a single crystal surface at
a grazing incidence, forming a diffraction pattern on a
screen.
• Electrons with tenth of KeV order energy are focused and
incident onto the surface.
• Then, electrons are scattered by the periodic potential of
the crystal surface, which results in a characteristic
diffraction pattern on the screen.
• The diffracted intensity is displayed directly on a screen, so
the information is available instantly, i.e, real-time analysis
is possible.
• Further, RHEED arrangement in UHV chamber allows it to
be used for in-situ observation of MBE thin film growing
process.

40. Methods for deposition
Method ALD MBE CVD Sputtering Evapor PLD
Thickness Uniformity good fair good good fair fair
Film Density good good good good fair good
Step Coverage good poor varies poor poor poor
Interface Quality good good varies poor good varies
Low Temp. Depostion good good varies good good Good
Deposition Rate fair fair good good good Good
Industrial Application varies varies good good good poor

41. Emergence and Challenges in Nanotechnology
Lithography
Introduction to synthesis of nanoparticles
Evaporation and Condensation growth
Lithography technology
Method to nano composite structure
Bottom-Up andTop-Down Approaches

42. Lithography
• We have discussed various routes for the synthesis and fabrication of variety of nanomaterials; however,
the synthesis routes applied have been focused mainly on the chemical methods approaches, or the
physical vapor deposition. Now, we will discuss a different approach: top-down approach, fabrication of
nanoscale structures with various physical techniques---lithography.

43. Lithography
Lithographic techniques
(a)Photolithography
(b)Phase shifting opitcal lithography
(c)Electron beam lithography
(e)Focused ion beam lithography
(f) Neutral atomic beam lithography
Nanomanipulation and nanolithography
(a)Scanning tunneling microscopy
(b)Atomic force microscopy
(c)Near-field scnning optical microscopy
(d)Nanomanipulation
(e)Nanolithography

44. Photolithography
• Typical photolithographic process consists of producing a mask carrying the requisite pattern
information and subsequently transferring that pattern, using some optical technique into a
photoactive polymer or photoresist.

45. Photolithography
• Wafer preparation---cleaning
Typical contaminants that must be removed prior to photoresist coating:
•dust from scribing or cleaving (minimized by laser scribing)
•atmospheric dust (minimized by good clean room practice)
•abrasive particles (from lapping or CMP)
•lint from wipers (minimized by using lint-free wipers)
•photoresist residue from previous photolithography (minimized byperforming oxygen plasma ashing)
•bacteria (minimized by good DI water system)
•films from other sources:
–solvent residue
–H2O residue
–photoresist or developer residue
–oil
–silicone
Standard degrease:
– 2-5 min. soak in acetone with ultrasonic agitation
– 2-5 min. soak in methanol with ultrasonic agitation
– 2-5 min. soak in DI H2O with ultrasonic agitation
– 30 sec. rinse under free flowing DI H2O
– spin rinse dry for wafers; N2 blow off dry for tools and chucks
• For particularly troublesome grease, oil, or wax stains:
– Start with 2-5 min. soak in 1,1,1-trichloroethane (TCA) or trichloroethylene (TCE) with ultrasonic agitation prior to acetone

46. Photolithography
• Wafer preparation---primers
 Adhesion promoters are used to assist resist coating.
 Resist adhesion factors:
•moisture content on surface
•wetting characteristics of resist
•type of primer
•delay in exposure and prebake
•resist chemistry
•surface smoothness
•stress from coating process
•surface contamination
Ideally want no H2O on wafer surface
– Wafers are given a “singe” step prior to priming and coating
•15 minutes in 80-90°C convection oven
Used for silicon:
– primers form bonds with surface and produce a polar (electrostatic) surface
– most are based upon siloxane linkages (Si-O-Si)
•1,1,1,3,3,3-hexamethyldisilazane (HMDS), (CH3)3SiNHSi(CH3)3
•trichlorophenylsilane (TCPS), C6H5SiCl3
•bistrimethylsilylacetamide (BSA), (CH3)3SiNCH3COSi(CH3)3

47. Photolithography
• Photoresist Spin Coating
•Wafer is held on a spinner chuck by vacuum and resist is coated to uniform thickness by spin coating.
•Typically 3000-6000 rpm for 15-30 seconds.
• Resist thickness is set by:
– primarily resist viscosity
– secondarily spinner rotational speed
• Resist thickness is given by t = kp2/w1/2, where
– k = spinner constant, typically 80-100
– p = resist solids content in percent
– w = spinner rotational speed in rpm/1000
• Most resist thicknesses are 1-2 mm for commercial Si processes

48. Photolithography
• Prebake
Used to evaporate the coating solvent and to densify the resist after spin coating.
•Typical thermal cycles:
– 90-100°C for 20 min. in a convection oven
– 75-85°C for 45 sec. on a hot plate
• Commercially, microwave heating or IR lamps are also used in production lines.
• Hot plating the resist is usually faster, more controllable, and does not trap solvent like convection
oven baking.

49. Photolithography
• Align/Expose/Develop

50. Photolithography
• Etching/remove photoresist
photoresist has same polarity as final film;
photoresist never touches the substrate wafer.

51. Photolithography
• Etching/remove photoresist
photoresist has opposite polarity as final film; excess
deposited film never touches the substrate wafer.

52. Phase-shifting Photolithography
• Photolithography has a resolution limit. In order to improve the resolution in
photolithography, the phase-shifting method was developed.

53. E-beam lithography
• The theoretical resolution of photolithography is
)
2
(
3
2 min
d
s
b 
 
 The wavelength of the exposing radiation
s The gap width maintained between the masi and the photoresist surface
d The photoresist thickness
The wavelenght of electron beam is much smaller than UV light, electron beams can be focused to a
few nanometers in diameter and can be deflected accurately and precisely over a surface.

54. E-beam lithography
• Resist film
Negative resist: After development, the exposed structure is higher than the
surrounding due to crosslinking of polymer chains.
Positive resist: After development, the exposed structure is deeper than the
surrounding due to chopping of polymer chains.
PMMA (Poly-methyle-metacrylate)
-one of the first e-beam resists (1968)
-standard positive resist
-resolution<10 nm
-medium sensitivity (150-300μC/cm2 )
-available with high (950K) and low (50k) molecular weight
-contrast: high for 950k-resist, low for 50k-resist

55. E-beam lithography
• Challenge
Charging effect: Complicate exact focusing ofelectron-
beam, displacement and distortion of exposed structures.
Proximity effect: Scattering of electrons in resist film
and substrate, unwanted additional exposure.

56. Focused ion beam lithography
• Advantages
-Ions have heavy mass than electrons.
-Less proximity effect than E-beam
-Less scattering effect
-High resolution patterning than UV, E-beam lithography
-Even smaller wavelength than E-beam

57. Neutral atomic beam lithography
• In neutral atomic beams, no space charge effects make the beam divergent; therefore, high kinetic
particle energies are not required. Diffraction is no severe limit for the resolution because the de
Broglie wavelength of thermal atoms is less than 1 angstrom.

58. Nanomanipulation and nanolithography
(a)Scanning tunneling microscopy
(b)Atomic force microscopy
(c)Near-field scnning optical microscopy
(d)Nanomanipulation
(e)Nanolithography
Nanomanipulation and nanolithography are
based on scanning probe microscopy.

59. Scanning tunneling microscopy
• STM relies on electron tunneling, which is a phenomenon based on quantum mechanics.
Principle
A famous sample

60. Atomic force microscopy
• In spite of atomic resolution and other advantages, STM is limited to an electrically conductive surface
since it is dependent on monitoring the tunneling current between the sample surface and the tip. AFM
was developed as a modification of STM for dielectric materials.

61. Atomic force microscopy
• Local oxidation nanolithography
Schematic diagram for the AFM based local oxidation lithography on both silicon andAg monolayer.

62. Atomic force microscopy
• Effects of tip bias potentials on the lithography patterns.

63. Atomic force microscopy
• AFM and KPFM(Kelvin probe force microscopy) images of the patterned silver nanoparticle
monolayer. Shaped patterns were written on to the monolayer.

64. Nanomanipulation and nanolithography
• Some examples

65. •Describe a typical photolithographic process

66. THANKYOU