Principles of Nanometrology A.A

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 (

1. 1.Size determination: PSD for particles (GSD, Grain Size Det., for polycrystalline materials) 2. 2.Surface Specific Area, SSA 3. 3.Z potential, hydrodynamic radius and electrophoretic mobility 4. 4.Surface and 3D imaging, lattice properties Step by step

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

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. U ε = 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

SEM SPM AFM SEM: Scanning Electron Microscope; SPM: Scanning Probe Microscop; AFM: Atomic Force Microscope. The grey box displays the dimensional range of nanomaterials. 1. Dimensional Nanometrology

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 cryo- vitrification shows the macromolecule assemblies inside the sample. Resolution: depth: 200nm, lateral resolution: 2-20nm.

TEM: scheme

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 Co 3 O 4 nanoparticles in cluster

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: nm.

AFM: Scheme AFM image of Co 3 O 4 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 ( 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 (

SAXS: Scheme BRAGG law: 2d(sinΘ) = λ o 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-diene- styrene triblock copolymers. Left: Left: a lamella- forming triblock showing a biaxial texture (four-spot pattern). Right Right: a cylinder- forming triblock showing a single- crystal texture (six- spot pattern). Images: Sasha Myers,

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 (