nanoparticle characterisation instrumentation characterisation instrumentation nanometrology section...
TRANSCRIPT
Nanoparticle characterisation instrumentation
Nanometrology Section
Physical Metrology Branch
National Measurement Institute Australia
November 2012
Characterisation techniques
Choice of measurement technique
and knowledge of its limitations:
Dynamic light scattering (DLS)
magipics.com.au
DLS results for suspensions containing different fractions of 20 nm and 100 nm PSL particles.
Size range ~0.1 nm to ~ 6 µm.
Measurand Autocorrelation function of the scattered light intensity;
average hydrodynamic diameter.
Advantages Fast and accurate for monomodal suspensions. An
ensemble measurement technique, providing a good
statistical representation of the sample.
Limitations Particles must be in suspension and undergoing
Brownian motion. Large particles scatter much more light (I∝ x6); even a
small number of large particles can obscure the
contribution from smaller particles.
Differential centrifugal sedimentation (DCS)
magipics.com.au
DCS measurement of a suspension of PSL particles showing signs of aggregation. The inserts show scanning electron micrographs of different clusters of n individual particles with n=1...6 observed in this sample.
Size range < 5 nm to ~30 µm.
Measurand Light extinction as a function of sedimentation time,
from which the intensity‐weighted distribution of
the Stokes diameter can be derived.
Advantages Very high resolving power because the particles are
separated by their sedimentation rate before
detection. An ensemble technique, providing a good
statistical representation of the sample.
Limitations Small and/or low density particles sediment over
long time‐scales. The particles are detected
optically, thus their optical properties must be
known to derive volume or number based size
distributions.
Transmission electron microscopy (TEM)
Size range ~ 0.1 nm to ~ 2 µm.
Measurand Equivalent diameter, expressed as the diameter of a circle having the same area as the projected area of the particle, or Feret’s diameter, the mean value of the distance of parallel tangents of the projected outline the particle position.
of
Advantages Excellent for visualizing the sample and to produce representative EM images. Provides information about particle shape, size and sizedistribution. Enables visualisation of the degree of aggregation/agglomeration. Possibility to investigate crystalline phase and perform chemical analysis. Single particle technique.
Limitations Poor time
statistical representation of a sample. Imaging and analysis consuming. Sample preparation can be challenging.
can be
Nominally 20 nm SiO2 particles analysed for particle size distribution using ImageJ.
30 nm Au
Au nanorods
60 nm Au and 20 nm SiO2
ZnO
Asymmetric flow‐field flow fractionation (AFFFF)
magipics.com.au
Size range ~ 0.1 nm to ~ 2 µm.
Measurand Detector dependent, often equipped with light scattering detectors, e.g., for static and dynamic light scattering. Elution time can also be used to provide a measure of particle size.
Advantages A separation measurement technique. Very high resolution for both high and low molecular weight particles. Provides sequential separation of particles based on a size‐dependent interaction of the particles with an applied force field (flow). Fractions can be collected for off‐line processing. It is also possible to hyphenate to, for example, ICP‐MS.
Limitations Complex method development required to optimise particle separation.
Particle tracking analysis (PTA)
re
Liquid
Particles scatter in the laser beam
Particles to be viewed asuspended in liquid
Laser beam (approx 50 µm wide)
Glass Metallised surface
NanoSight Ltd.
Size range ~20 nm to ~ 1 µm.
Measurand Diffusion length based on 2‐D tracking of particles
moving under Brownian motion.
Advantages Qualitative differentiation between particles of
different composition based on scattering intensity. Allows measurements of particle number concentration
(particles/mL). Single particle measurement technique.
Limitations Strong dependence on operator through choice of
settings for imaging and analysis. Limited statistical
relevance due to limited number of particles analysed.
Mix of 100 nm PS and 100 nm Au
Examples of Reference Materials
NISTAu PSL•AFM • DMA• DLS• TEM• SEM• SAXS
EC‐JRC‐IRMMSiO2• DLS• DCS
• TEM/SEM • SAXS • Zeta potential*
Thermo ScientificPSL• DLS (20‐50 nm)• TEM (> 50 nm)
See www.nano‐refmat.bam.de/en/ for a (non‐exhaustive) list of currently available nanoscale reference materials.
Take home messages:
• Nanoparticle characterisation is important.
• Understand your instrumentation.
•
Use well‐characterised particles to check instrument performance.
•
Bi‐modal or multi‐modal mixes of particles may give a better understanding of the instrument limitations.
Take home messages:
• Characterise your particle suspension before,
during and after other experiments.
• Important to pose the right question, e.g.:
•
What is the primary particle size?
•
What is the size distribution of the agglomerates/aggregates?
• Use more than one technique.
• You can never know too much about a sample!
NMIA Nanometrology team: Bakir Babic, Heather Catchpoole, Victoria Coleman, Chris Freund, Jan Herrmann,
Åsa Jämting, Malcolm Lawn, Maitreyee Roy and John Miles.
Dr Jan Herrmann
Nanometrology Section
National Measurement Institute
Bradfield Road
West Lindfield NSW 2070 Australia
Email: [email protected]
www.measurement.gov.au/nano