Principles of
Nanometrology
A.A. 2011-2012
About nanometrology
The standardization of methods for measurement,
imaging and properties recording at nanoscale
undergo continuous updating.
The descriptions of methods and apparatuses represents
a selection and are proposed on the basis of the
Eighth Nanoforum Report: Nanometrology
Published by the Nanoforum.org, European
Nanotechnology Gateway, in July 2006.
(http://www.nano.org.uk/members/MembersReports/NANOMETROLOGY_Report.pdf)
Step by step
1.
Size determination: PSD for particles (GSD, Grain
Size Det., for polycrystalline materials)
2.
Surface Specific Area, SSA
3.
Z potential, hydrodynamic radius and
electrophoretic mobility
4.
Surface and 3D imaging, lattice properties
1. PSD, Particle Size Distribution
Photon Correlation Spectroscopy.
Fluctuations of the light scattered from dispersed objects in
suspension are due to Brownian motion and are
proportional to the size of these objects.
Smaller particles move faster, causing a rapid decay of
scattering
This method of measurement is standardised according to
ISO 13320-1.
Dynamic Scatter Light: in the exemple the powder
contains 50% of nanparticles sized 5 nm and 50% of their
aggregates, sized 50nm. The number and the volume of
particles, and the intensity of the scattered light are
shown.
Note that for particles of larger size the intensity is greater:
in fact, smaller particles move faster, causing a rapid
decay of scattering.
2. SSA, Specific Surface Area
The specific surface area, or the total surface area per
gram of material, is one of the main properties
characterizing nanomaterials, in which it is very larger than
in bulk materials.
Measurement
The material is inserted in a closed container, under
nitrogen. The gas adsorption to the surface causes
a drop of the pressure of nitrogen proportional to the surface
Area (B.E.T. method).
3a. Z potential and
hydrodynamic radius
An electrical double layer sorrounds charged particles in
liquid suspensions. Around them, two regions differentiate:
one (the lighter layer) where charges are diffuse, another
(darker) where the charges are stricly bonds (Stern layer).
It moves together with the atoms forming the sorrounded
sphere and represents the hydro-dynamic radius.
The electric potential at the boundary between Stern and
diffuse radius is called Z potential.
Measuring the Z potential.
A laser beam passes through a cell containing
the nanoparticles suspension.
When an electric field is applied to the cell, the
charged particles moves.
When interfering with the laser beam, they cause
the laser intensity fluctuate: the recorded signal
is proportional to the particle speed.
Decrease in Z potential is followed by dramatical
aggregation of nanoparticles, big aggregates
does not move in the beam light.
A scheme of the apparatus follows.
1) laser; 2) attenuator; 3) cell; 4) compensation optics;
5) computer
3b. Electrophoretical mobility.
Uε = 2 ε ζ f (k a) / 3 η
The Henry’s equation for measuring the electrophoretical
mobility (Uε) includes the following variables:
ε: dielectric constant
ζ : Z potential
η: viscosity
F (k a) : Henry’s function
Environmental variables, as pH, concentration of ions and
of sufractant-acting molecules, including polymers and
organics, affects the Z potential.
4. Surface and 3D imaging,
lattice properties
1. Dimensional Nanometrology
SEM: Scanning
Electron Microscope;
SPM: Scanning
Probe Microscop;
AFM: Atomic Force
Microscope.
The grey box
displays the
dimensional range of
nanomaterials.
4a. TEM: Transmission
Electron Microscopy
Basics: The electrons interacts with the ultra thin
specimen and are transmitted through that, than recorded,
The image corresponding to the transmitted electrons is
magnified on a screen, a photographic layer or another
sensor.
The tomographic reconstruction provides 3D images,
diffraction methods give informations about the
crystalline state of the sample, and the cryovitrification shows the macromolecule assemblies
inside the sample.
Resolution: depth: 200nm, lateral resolution: 2-20nm.
TEM: scheme
http://www.nobelprize.org/educational/physics/microscopes/tem/index.html
4b. SEM: Scanning Electron
Microscopy
Basics: SEM uses a high-energy beam of
electrons. The beam is condensed and directed
at the sample surface. The interactions occurring
during the scanning are recorded.
Resolution: depth: 1nm-5μm, lateral
resolution: 1-20nm.
SEM: Scheme
SEM image of Co3O4 nanoparticles in cluster
http://www-archive.mse.iastate.edu/microscopy/path2.html
4c. AFM: Atomic Force
Microscopy
Basics: The tip of a probe (cantilever) is slowly
scanned across the surface. A laser beam,
focused on the cantilever, records on a
photodetector the deflection of the cantilever,
caused by the interaction of its atoms with those
on the sample surface.
Resolution: depth: 0.5nm-5nm; lateral
resolution: 0.2-130 nm.
AFM: Scheme
AFM image of Co3O4 nanoparticles
AFM techniques and
applications
 Contact Mode (CM): The signal is the movement of the tip, or
the adjustments needed to maintain the deflection constant. The
stiffness of the lever must be lower than the interatomic forces at
the sample surface (1 - 10 nN/nm). For topological recordings.
 Lateral Force Microscopy (LFM): The twisting of the cantilever
is a function of the friction levels in different areas of the sample
surface.
 Force Modulation (FM): The tip (or the sample) is oscillated at a
high frequency and pushed into the repulsive regime. The slope
of the force-distance curve is correlated to the sample's surface
elasticity.
 Phase Imaging: The phase shift of the oscillating tip is related to
specific properties of the sample, such as friction, adhesion,
and viscoelasticity.
4d. NMR: Nuclear
Magnetic Resonance
Basics: NMR studies a magnetic nucleus by
aligning it with a very powerful external
magnetic field and perturbing this alignment
using an electromagnetic field. The relaxation
spectra is a function of nuclear identity, 3D
structure of macromolecules in solution or
pore dimensions.
Resolution: in the nm range.
4e. SAXS: Small Angle X Ray
Scattering
Basics: X ray is incident on to a sample and
scattered electrons from the sample are analyzed
at very low angles.
The lattice interplanar spacing of the crystal is
a function of the wavelength and of the incidence
angle of the x-ray.
Resolution: between 1 nm and >200 nm.
SAXS: Scheme
(http://pubs.usgs.gov/of/2001/of01-041/htmldocs/xrpd.htm)
SAXS: Scheme
(http://pubs.usgs.gov/of/2001/of01-041/htmldocs/xrpd.htm)
BRAGG law:
2d(sinΘ) = λo
d = lattice interplanar spacing of the crystal
Θ = x-ray incidence angle (Bragg angle)
λ = wavelength of the characteristic x-ray
Two-dimensional small-angle
X-ray scattering image.
Nanostructure of two
styrene-dienestyrene triblock
copolymers.
Left: a lamellaforming triblock
showing a biaxial
texture (four-spot
pattern).
Right: a cylinderforming triblock
showing a singlecrystal texture (sixspot pattern).
Images: Sasha Myers, http://www.princeton.edu/cbe/news/archive/
4f. SANS: Small Angle
Neutron Scattering
Basics: A neutron source generates a collimated
beam; neutrons are scattered by the sample,
placed in the beam.
A position sensitive neutron detector detects
scattered neutrons with 0.05° ≤ 2θ ≤ 3°.
The scattered intensity is a function of position.
Resolution: between 0.5 nm and 500 nm.
SANS: Scheme
(http://www.ncnr.nist.gov/instruments/usans/)