Nanomaterials 1
Nanoscopic Materials
NANO -particles, crystals, powders
-films, patterned films
-wires, rods, tubes
-dots
Nanostructured materials = nonequilibrium character
good sinterability
high catalytic activity
difficult handling
adsorption of gases and impurities
poor compressibility
Nanomaterials 2
Properties on Nanostructured Materials
 Metallic behavior
Single atom cannot behave as a metal
nonmetal to metal transition : 100-1000 atoms
 Magnetic behavior
Single domain particles, large coercive field
 Depression of melting points in nanocrystals
bulk Au mp 1064 C 10 nm Au 550 C
Unique Features of the Nano-scale
Nanomaterials 3
Smallness: physical size
Size compatibility with the basic biological structures (cells,
liposomes, enzymes…)
delivery vehicles for medical applications
surface chemistry - functionalization
Smallness: surface versus bulk forces
A large to surface to volume ratio
Bulk forces - gravity - unimportant for nanoparticles
Surface forces - Brownian motion - colloidal particles never
settle
Unique Features of the Nano-scale
Nanomaterials 4
Smallness: surface versus bulk atom properties
Increasing surface to bulk atom number ratio with decreasing
size enhances the role of surface (boundary)
• surface phonon scattering
• surface electron scattering
• surface atom electric charge distribution
• surface atom spins in ferromagnetic, ferrimagnetic, and
antiferromagnetic materials - transition to superparamagnetic
state
Unique Features of the Nano-scale
Nanomaterials 5
Chemical bonding in nanostructures
Single wall carbon nanotubes (SWCNT)
hexagonal bonding of C in graphite and graphene - sp2
C bonding in SWCNT is contorted sp2  sp3
Chirality - variable amounts of twisting
Unique Features of the Nano-scale
Nanomaterials 6
Self-assembly
combination of particles, atoms, or molecules, selfassemble
into predetermined new materials and structures (micelles, SAM,
MOF, DNA, proteins, ....)
Unique Features of the Nano-scale
Nanomaterials 7
Quantum confinement and tunneling
Electron quantum confinement - the spatial restrictions of
nanoscale structures confine electrons resulting in the presence
of energy levels whose values and spacing depend on the degree
of confinement = size
Quantum tunneling (the opposite of confinement) - an electron
wave function leaks across classically forbidden energy barriers
of nano-scale size
Unique Features of the Nano-scale
Nanomaterials 8
Quantum confinement and tunneling
Electron in a box - an infinitely deep 3D box
the difference between two energetically adjacent electron
energy levels:
h is Planck’s constant, me is the electron mass, Lx L x L is the
confining volume
Decreasing L increases the inter-level spacing
Nanoscale - quantization of energy due to confinement
Micro- and larger scales - energy appears as a continuum
Unique Features of the Nano-scale
Nanomaterials 9
Wave-particle duality
Quantum interference between particle waves that are scattered
off the boundaries of a nanostructure thereby forming a standing
wave
Atoms arranged on a surface form a corral confining their
valence electrons. The probability density image determined by
the wave function distribution captured by STM - wave function
leakage into a positively biased scanning probe
Unique Features of the Nano-scale
Nanomaterials 10
Relativistic phenomena at the nano-scale
In 2D materials, graphene - mass-less Dirac electrons
Mass-less behavior can produce
• ballistic (collision-free) charge transport
• unusual Hall effects
• enormously high carrier mobilities
• topologically dependent phases
Unique Features of the Nano-scale
Nanomaterials 11
Electromagnetic interactions with nanostructures
Plasmonic mode of a metal nanoparticle excited by the electric
field of an incoming light wave - a cooperative excitation of free
valence electrons
Relaxation
- reradiation of photons from the nanoparticle
- collisions of oscillating valence electrons within the particle
The electric field distribution of the metal nanoparticle
• radiating far-field component = the emitted photons
• near-field component around the nanoparticle
Unique Features of the Nano-scale
Nanomaterials 12
Fluctuations
Thermodynamic fluctuations - a system gets smaller, fluctuations
away from the thermodynamic equilibrium distribution become
important, the statistics of huge numbers of particles
Quantum fluctuations - the small separation distances between
objects at the nano-scale, the temporary change ΔE in the
amount of energy (or mass of particles) that can occur in a
region for a time Δt, the fluctuation time - conservation of
energy is violated during the fluctuation time
Unique Features of the Nano-scale
Nanomaterials 13
Fluctuations
Casimir force (theor. 1948, exp. 1996) - quantum phenomenon, a
pressure that pushes objects having a nano-scale separation
together, vacuum energy, fluctuating electromagnetic waves,
restricted wavelengths of standing waves between nanoobjects =
lower energy of vacuum between nanoobjects, pressure form
outside
The Casimir force affects friction and results in striction (the
permanent adhesion of surfaces)
- a critical problem for moving systems at the nano-scale
- the force increases with decreasing distance
Nanomaterials 14
Synthesis Methods
Top-down: from bulk to nanoparticles
Bottom-up: from atoms to nanoparticles
Nanomaterials 15
Bottom-up Synthesis: Atom Up
Nanomaterials 16
Bottom-up Synthesis
 Atom Aggregation Method
GEM – gas evaporation method
 Evaporation by heating – resistive, laser, plasma, electron beam, arc
discharge
 The vapor nucleates homogeneously owing to collisions with the cold gas
atoms
 Condensation
- in an inert gas (He, Ar, 1kPa) on a cold finger, walls - metals,
intermetallics, alloys, SiC, C60
- in a reactive gas O2 TiO2, MgO, Al2O3, Cu2O
N2, NH3 nitrides
- in an organic solvent matrix
Nanomaterials 17
Carbide formation
Ni(g) + pentane NixCyHz Ni3C
77 to 300 K 180 C, octane
Bottom-up Synthesis
SMAD – the solvated metal atom dispersion
1 – 2 g of a metal, 100 g of solvent, cooled with liquid N2
more polar solvent (more strongly ligating) gives smaller particles
Ni powder: THF < toluene < pentane = hexane
Nanomaterials 18
 Thermal or Sonocative Decomposition of Precursors
Fe(CO)5 nc-Fe + 5 CO sono
[Co(en)3]WO4 nc-WC – 23% Co
PhSi(OEt)3 + Si(OEt)4 + H2O gel -SiC
(CH3SiHNH)n (l) Si3N4 + SiC laser
M(BH4)4 (g) borides MB2+x (M = Ti, Zr, Hf)
Si(OEt)4 + Ag+
or Cu2+
+ H2O SiO2/Ag+
/Cu2+
SiO2/Ag/Cu
Ar, 1500 C
300-400C
H2, 550 C
Bottom-up Synthesis
Nanomaterials 19
Bottom-up Synthesis
Fe(CO)5 oleic acid
trioctylamine
350 o
C, 1 h
350 o
C, 1 h
Fe
Me3NO
Fe2O3
6 nm
Separation of nucleation and growth
Fe(CO)5 thermal decomposition at 100 oC contributes to nucleation
Fe(oleate) thermal decomposition at 350 oC contributes to growth
OH
O
Thermal decomposition of precursors
Nanomaterials 20
 Reduction of Metal Ions
Borohydride Reduction - Manhattan Project
Aqueous, under Ar
2 Co2+
+ 4 BH4
+
9 H2O Co2B + 12.5 H2 + 3 B(OH)3
Under air
4 Co2B + 3 O2 8 Co + 2 B2O3
Nonaqueous
Co2+
+ BH4
+
diglyme Co + H2 + B2H6
TiCl4 + 2 NaBH4 TiB2 + 2 NaCl + 2 HCl + H2
MXn + n NR4[BEt3H] M + NR4X + n BEt3 + n/2 H2
M = group 6 to 11; n = 2,3; X = Cl, Br
mixed-metal particles
Bottom-up Synthesis
Nanomaterials 21
Bottom-up Synthesis
Thermometer
Vacuum/N2
Stopper/Septum
230 °C
Solution of
precursors
in OLA
M(acac)n
acetylacetonates
Hot-injection
OLA oleylamine
ODE octadecene
MO
O
O
O
O
O
Me
Me
Me
Me
Me
Me
Nanomaterials 22
Bottom-up Synthesis
180 °C in octylamine
200 °C in dodecylamine
Phase Control
[NnBu4]2[Fe4S4(SPh)4]
pyrrhotite Fe7S8
greigite Fe3S4
thiospinel, the sulfide analogue of
magnetite
Bottom-up Synthesis
Nanomaterials 23
Sonocative decomposition of precursors
Cavity interior
Filled with gases and vapors
5 000 – 20 000 C / 500 – 1500 bar
Surrounding
liquid layer
2000 C
Bulk liquid
shock waves
shear forcesCavitation
creation, growth, and
implosive collapse
of bubbles in a liquid
Bottom-up Synthesis
Nanomaterials 24
Sonocative decomposition of precursors
Fe2O3
amorphous
Fe2O3
maghemite
Fe2O3
hematite
)))))
300 o
C
340 o
C
linear
dynam/isothermal
Fe(acac)3
TG
MO
O
O
O
O
O
Me
Me
Me
Me
Me
Me
Particle size 20 - 30 nm
Spherical shape
Uniform size distribution
Nanomaterials 25
Au
fcc
S
S
S
S
S
S
S
S
S
S
S S
S
Bottom-up Synthesis
Au colloidal particles
HAuCl4 + NaBH4 in toluene/H2O system, TOABr as a
phase transfer agent, Au particles in the toluene layer,
their surface covered with Br, addition of RSH gives
stable Au colloid
Nanomaterials 26
Bottom-up Synthesis
SH
Nanomaterials 27
Two-dimensional array of
thiol-derivatised Au particles
(mean diam 4.2 nm)
Nanomaterials 28
TEM micrograph of hexagonal arrays
of thiolized Pd nanocrystals:
a) 2.5 nm, octane thiol
b) 3.2 nm, octane thiol
Nanomaterials 29
The d-l phase diagram for Pd nanocrystals thiolized with different alkane thiols.
The mean diameter, d, obtained by TEM.
The length of the thiol, l, estimated by assuming an all-trans conformation of the alkane chain.
The thiol is indicated by the number of carbon atoms, Cn.
The bright area in the middle - systems which form close-paced organizations of nanocrystals
The surrounding darker area includes disordered or low-order arrangements of nanocrystals
The area enclosed by the dashed line is derived from calculations from the soft sphere model
Nanomaterials 30
K +
K+
Mg
Mg
Alkali Metal Reduction
in dry anaerobic diglyme, THF, ethers, xylene
NiCl2 + 2 K  Ni + 2 KCl
AlCl3 + 3 K  Al + 3 KCl
Reduction by Glycols or Hydrazine
“Organically solvated metals”
Bottom-up Synthesis
Nanomaterials 31
Bottom-up Synthesis
Alkalide Reduction
13 K+(15-crown-5)2Na + 6 FeCl3 + 2CBr4
THF
30 °C
2 Fe3C (nano) + 13 K(15-crown-5)2Cl0.43Br0.57 + 13 NaCl
Anealed at 950 °C / 4 h
Fe3C: 2 – 15 nm
Nanomaterials 32
 Reactions in Porous Solids – Zeolites, Mesoporous materials
Ion exchange in solution, reaction with a gaseous reagent inside the
cavities
M2+
+ H2E ME M = Cd, Pb; E = S, Se
Ship-in-the-Bottle Synthesis
Ru3+
+ Na-Y Ru(III)-Y
Ru(III)-Y + 3 bpy Ru(bpy)3
2+
reduction of Ru(III)
Conducting carbon wires
Acrylonitrile introduced into MCM-41 (3 nm diam. channels)
Radical polymerization
Pyrolysis gives carbon filaments
Bottom-up Synthesis
Nanomaterials 33
 Gel or Polymer Matrices
 Sol-Gel Method
Aerogels, supercritical drying
 Aerosol Spray Pyrolysis
Aqueous solution, nebulization, droplet flow, solvent evaporation,
chemical reaction, particle consolidation, up to 800 C
3Gd(NO3)3 + 5 Fe(NO3)3 Ga3Fe5O12 + 6 O2 + 24 NO2
MnCl2 + 2 FeCl3 + 4 H2O MnFe2O4 + 8 HCl
Mn(NO3)2 + Fe(NO3)3 no go, why?
Bottom-up Synthesis
2 MCln (g) + n H2  M0 + 2n HCl
850-900 C
3-11 nm
Nanomaterials 34
H2O +
octane
H2O
H2O
Cd2+ Se2-
CdSe
CdSe
PhSeSiMe3
Bottom-up Synthesis
 Inverse Micelles
Nanomaterials 35
Polymeric Nanoparticles from Rapid Expansion of Supercritical
Fluid Solution
Bottom-up Synthesis
Nanomaterials 36
Polymeric Nanoparticles from Rapid Expansion of Supercritical
Fluid Solution
Bottom-up Synthesis
Bottom-up Synthesis
Nanomaterials 37
Nanomaterials 38
Bottom-up Synthesis
Spinning Disc Processing (SDP)
A rapidly rotating disc (300-3000 rpm)
Ethanolic solutions of Zn(NO3)2 and NaOH, polyvinylpyrrolidone (PVP) as a
capping agent
Very thin films of fluid (1 to 200 m) on a surface
Synthetic parameters = temperature, flow rate, disc speed, surface texture
influence on the reaction kinetics and particle size
Intense mixing, accelerates nucleation and growth,
affords monodispersed ZnO nanoparticles
with controlled particle size down to a size of 1.3 nm
and polydispersities of 10%
Bottom-up Synthesis
Nanomaterials 39
Crystallization free energy
S > 1 supersaturation
Bottom-up Synthesis
Nanomaterials 40
Nucleation rate
experimentally controllable parameters:
a) level of supersaturation
b) temperature
c) surface free energy
Vm = 3.29 × 10−5 m3 mol−1 (CdSe)
Nanomaterials 41
Bottom-up Synthesis
Accumulation of the monomers
Supersaturated solution
Burst of nucleation
Slow growth of particles without
additional nucleation
the size focusing
Separation of nucleation and growth
LaMer mechanism
Nanomaterials 42
Bottom-up Synthesis
Hot-injection
N = the number concentration of the nanocrystals
σ( r ) = relative standard deviation of their radii r
< r > = mean radius
dN / dt = nucleation rate
Nanomaterials 43
Bottom-up Synthesis
Heat-up
N = the number concentration of the nanocrystals
σ( r ) = relative standard deviation of their radii r
< r > = mean radius
dN / dt = nucleation rate
Nanomaterials 44
Watzky-Finke mechanism
Slow continuous nucleation
Fast autocatalytic surface growth
Nanomaterials 45
Seed-mediated mechanism
Au nanoclusters as seeds
Bi, Sn, In, Au, Fe, Fe3O4
Nanomaterials 46
Other mechanisms
Digestive rippening
Surfactant exchange
Surface Modification
Nanomaterials 47
A nanoparticle of 5 nm core diameter
with different hydrophobic ligands
NP and molecules drawn to scale
The particle is idealized as a smooth
sphere
trioctylphosphine oxide (TOPO)
triphenylphosphine (TPP)
dodecanethiol (DDT)
tetraoctylammonium bromide (TOAB)
oleic acid (OA)
Bottom-up Synthesis
Nanomaterials 48
Continuous Synthesis of Inorganic Nanoparticles
rapid mixing of two precursor solutions and the fast removal of the nuclei
from the reaction environment
a very short mixing time
transport from the reactor to a tubing for the particle growth, the length of
tubing up to the collection vessel influences the particle growth
Nanomaterials 49
Top-down Synthesis: Bulk Down
 Introduction of Crystal Defects (Dislocations, Grain Boundaries)
High-Energy Ball Milling
final size only down to 100 nm, contamination
 Extrusion, Shear, Wear
High-Energy Irradiation
 Detonative Treatment
 Crystallization from Unstable States of Condensed Matter
 Crystallization from Glasses
Precipitation from Supersaturated Solid or Liquid Solutions
Nanomaterials 50
Top-down Synthesis
Lithographic Techniques
electron beam and focused ion beam (FIB) lithography
Nanomaterials 51
Top-down Synthesis
Lithographic Techniques
electron beam and focused ion beam (FIB) lithography
Top-down Synthesis
Nanomaterials 52
Laser ablation synthesis in solution
SEM image of Pt target
after ablation at 355 nm
for 15 min at 14 J/cm2
Top-down Synthesis
Nanomaterials 53
Laser ablation synthesis in solution
HRTEM images of AgNP
(left) and AuNP (right)
obtained by LASiS in DMF
and water, respectively