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Assessment of Different Electron Microscopy Techniques for Particle Size Quantification of Potential
NanomaterialsPhilipp Müller1, Johannes Mielke2, Vasile-Dan Hodoroaba2, Ralf Kägi3 and Martin Ryner4
1. BASF SE, Department of Material Physics and Analytics, Ludwigshafen, Germany. 2. BAM Federal Institute for Materials Research and Testing, Berlin, Germany.
3. EAWAG aquatic research, Dübendorf, Switzerland.4. Vironova AB, Stockholm, Sweden.
NanoDefine is funded by the European Community's Seventh Framework Programme under Grant Agreement-604347
M&M 2015, Portland (OR); Session A17.03 – Paper 155
P. Müller; M&M 2015 Portland (OR), Session A17.03, Paper 155
Motivation: EC regulation
RECOMMENDATION on the definitionof nanomaterial (2011)
"Nanomaterial“ means a natural, incidental or manufactured material containing particles, in an unbound state or as an aggregate or as an agglomerate and
where, for 50 % or more of the particles in the number size distribution, one or more external dimensions is in the size range 1 nm - 100 nm.
P. Müller; M&M 2015 Portland (OR), Session A17.03, Paper 155
The NanoDefine approach
• Detailed assessment and benchmark of measuring techniques to develop a sustainable, flexible, cost efficient and easy to implement solution for nano-characterization
Among several other techniques; EM is evaluated by as potential gold standard for determination of number size distributions
integral methods:• Dynamic Light Scattering (DLS)• Small-Angle X-ray Spectroscopy (SAXS)• UltraSonic Spectroscopy (USSp)• X-Ray Diffraction (XRD)• Brunauer Emett Teller surface (BET)
• Field Flow Fractionation (FFF)• Centrifugal Liquid Sedimentation (CLS)
counting methods:• Electron Microscopy (EM)• Particle Tracking Analysis (PTA)• Nano Coulter counter• Single particle ICP-MS
check www.nanodefine.eu
P. Müller; M&M 2015 Portland (OR), Session A17.03, Paper 155
FEI Tecnai G2TEM/STEM800k€/$
VironovaminiTEM250k€/$
FEI MagellanFEI BAM?TSEMJeol JSM7500SEM250k€/$
Phenom G2tabletopSEM50k€/$
7 samples, 7 imaging techniques, 4 institutions
EM round robin
P. Müller; M&M 2015 Portland (OR), Session A17.03, Paper 155
Samples
BaSO4
CaCO3
substances coated TiO2
Au
Ag
SiO2
mono- and bimodal calibrants
250 nm 200 nm
500 nm
500 nm
250 nm
BaSO4 (fine) MWCNT
CaCO3 (fine)
kaolin clay
coated TiO2
P. Müller; M&M 2015 Portland (OR), Session A17.03, Paper 155
Sample preparationCalibrants Au, Ag and SiO2: drying of one drop of the suspension on a TEM grid
Real life material:• Dispersion in 2mg/ml SHMP solution (sodium hexametaphosphate - calgon)• 3 min ultrasonic probe treatment• 5 min ultrasonic bath treatment• 3 µl drop on TEM-grid• Removal of excess solvent by a tissue after 5 min
P. Müller; M&M 2015 Portland (OR), Session A17.03, Paper 155
Approach of the round robinFind a cheap but comparable EM method for Particle size determination
manual measurement
… a pragmatic and (biased?) approach!
automated measurement usingparticle analyzer
• final version of public and free “imageJ” and “R” plugin will be released in ~2 years
• standard configuration!
10 nm 500 nm
P. Müller; M&M 2015 Portland (OR), Session A17.03, Paper 155
the miniTEM processMiniTEM = BF TEM at 25 kV; low costs of ownershipEvaluation steps:1. Sample preparation for TEM (~15 min)2. Sample insertion + other manual steps (~10 min)3. Fully automated data acquisition (~2 h)4. Definition of analysis chain in the miniTEM Software (~1 h
but nearly the same protocol for all saples)5. Optional: manual optimization of results (5 min)
e.g. removing false positives
• 30 min of manual work/sample• Real- world price of 150 €/$ per sample possible
(reduction by factor 5-10) compared to TEM at BASF with manual evaluation
P. Müller; M&M 2015 Portland (OR), Session A17.03, Paper 155
resultsGreen: <25% deviation from HAADF-TEM manual
Yellow: >25%<50% deviation
Red: >50% deviation
automatic evaluation of tabletop SEM images impossible
Sample bimodal silica Nano Au Nano Ag BaSO4 fine coated TiO2 MWCNT Kaolin CaCO3 fineReferenceBASF HAADF manually 13.7 19.7 2.7 283.8 185.3 11.6 119.6 160.1TEM BF BASF manually 14.3 20.0 2.8 259.4 153.1 9.2 119.9 157.9BASF particlesizer 11.1 19.1 1.9 313.5 43.0 4.2 21.0 83.0BASF particlesizer_stack 9.5 11.8 0.9 367.5 78.0 4.4 33.0 68.0TEM HAADF-STEM BASF particlesizer 11.9 18.8 2.7 268.1 16.2 7.2 28.6 87.0BASF particlesizer_stack 11.7 18.3 2.3 238.2 32.7 7.0 32.2 42.2BASF auto iTEM 12.6 18.3 2.5 490.5 68.6 14.7 77.2 155.5MiniTEM BF Vironova manually @BASF 11.4 21.4 184.7 12.1 131.4 158.2Vironova custom auto 13.7 20.5 5.5 509.4 242.5 10.9 121.9 175.3Vironova particlesizer 13.8 22.5 4.7 429.8 190.8 5.9 33.6 265.5SEM SE BAM manually #1 17.6 201.5 157.4 11.5 120.8 171.9BAM manually #2 214.0 213.0 12.0 128.0 158.0BASF particlesizer 22.8 21.2 11.0 238.0 159.8 26.9 103.3 160.8TSEM BAM man 16.1 269.8 152.9 9.6 119.7 171.9BAM particlesizer 14.7 18.4 5.1 346.7 162.8 29.4 120.7 207.6
P. Müller; M&M 2015 Portland (OR), Session A17.03, Paper 155
~100 nm
BF-TEM HAADF-STEMBF-miniTEM
BF-TSEM HAADF-TSEM SE-SEM TableTop -SEM
Comparison of the techniques- nano Au
P. Müller; M&M 2015 Portland (OR), Session A17.03, Paper 155
~1µm
BF-TEM HAADF-STEMBF-miniTEM
BF-TSEM HAADF-TSEM SE-SEM TableTop -SEM
Comparison of the techniques- Kaolin
~ 1 µm
P. Müller; M&M 2015 Portland (OR), Session A17.03, Paper 155
BF-TEM HAADF-STEMBF-miniTEM
BF-TSEM HAADF-TSEM SE-SEM TableTop -SEM
Comparison of the techniques- CaCO3
~ 500 nm
P. Müller; M&M 2015 Portland (OR), Session A17.03, Paper 155
What do we learn for a pragmatic approach?• Spherical particles work perfect for automation• Even small particles are detected by all methods• Accuracy quickly drops for particles with a diameter of a few nm
HAADF-TSEM auto HAADF-TSEM manually
Nano Ag 10 nm
Sample bimodal silica Nano Au Nano AgReferenceBASF HAADF manually 13.7 19.7 2.7TEM BF BASF manually 14.3 20.0 2.8BASF particlesizer 11.1 19.1 1.9BASF particlesizer_stack 9.5 11.8 0.9TEM HAADF-STEM BASF particlesizer 11.9 18.8 2.7BASF particlesizer_stack 11.7 18.3 2.3BASF auto iTEM 12.6 18.3 2.5MiniTEM BF Vironova manually @BASF 11.4 21.4 Vironova custom auto 13.7 20.5 5.5Vironova particlesizer 13.8 22.5 4.7SEM SE BAM manually #1 17.6 BAM manually #2 BASF particlesizer 22.8 21.2 11.0TSEM BAM man 16.1 BAM particlesizer 14.7 18.4 5.1
P. Müller; M&M 2015 Portland (OR), Session A17.03, Paper 155
What do we learn for a pragmatic approach?Sample bimodal silica Nano Au Nano Ag BaSO4 fine coated TiO2 MWCNT Kaolin CaCO3 fineTEM BFBASF manually 14.3 20 2.8 259.4 153.1 9.2 119.9 157.9BASF particlesizer 11.1 19.1 1.9 313.5 43.0 4.2 21.0 83.0TEM HAADF-STEMBASF HAADF manually 13.7 19.7 2.7 283.8 185.3 11.6 119.6 160.1BASF particlesizer 11.9 18.8 2.7 268.1 16.2 7.2 28.6 87.0
• No significant difference between BF-TEM and HAADF-STEM
• HAADF-STEM has advantages if strongly agglomerated or contaminated
200 nm
coated TiO2
P. Müller; M&M 2015 Portland (OR), Session A17.03, Paper 155
What do we learn for a pragmatic approach?
• Manual evaluation can deal with all imaging modes
• For SEM and miniTEMagglomeration is an even larger issue
Sample bimodal silica Nano Au Nano Ag BaSO4 fine coated TiO2 MWCNT Kaolin CaCO3 fine
HAADF manually 13.7 19.7 2.7 283.8 185.3 11.6 119.6 160.1BF manually 14.3 20 2.8 259.4 153.1 9.2 119.9 157.9miniTEM manually 11.4 21.4 184.7 12.1 131.4 158.2SE SEM manually #1 17.6 201.5 157.4 11.5 120.8 171.9SE SEM manually #2 214.0 213.0 12.0 128.0 158.0TSEM manually 16.1 269.8 152.9 9.6 119.7 171.9
HAADF-STEM miniTEMCaCO3 fine
200 nm
P. Müller; M&M 2015 Portland (OR), Session A17.03, Paper 155
Issues with automatic evaluationNanoDefine Particle Sizer:• Excellent results for all materials demonstrated
(lab conditions)• Real-life drawbacks: agglomeration +
contamination
miniTEM:• Algorithm searches for unagglomerated particles• Less problems with agglomeration but possible
bias?!
1 µm
Coated TiO2 - miniTEM
100 nm
Coated TiO2 – HAADF-STEM
P. Müller; M&M 2015 Portland (OR), Session A17.03, Paper 155
Discussion of uncertancies
0100200300400500
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52la
rger
# of
par
ticle
s
size [nm]
particle size histogram of bimodal silicaautomated evaluation
100 nm
• manual: ~330 particles counted• auto.: several 1000 particles counted• Still not sufficient to reflect a bimodal distribution• No false negatives for all 80 studies
significant statistical error
Potentially even larger systematic error due to preparation artifacts
Sample coated TiO2 MWCNT Kaolin CaCO3 fine
HAADF manually 185.3 11.6 119.6 160.1BF manually 153.1 9.2 119.9 157.9miniTEM manually 184.7 12.1 131.4 158.2SE SEM manually #1 157.4 11.5 120.8 171.9SE SEM manually #2 213.0 12.0 128.0 158.0TSEM manually 152.9 9.6 119.7 171.9std. dev. 22.06358374 1.1561 4.6928 6.33614
Benchmark with CRM needed;Error seems to be tolerable for threshold-based categorization
P. Müller; M&M 2015 Portland (OR), Session A17.03, Paper 155
Summary• TableTop SEM
does not meet requirements for EC definition
~100 nm
TableTop –SEM (nano Au)
30 nm
TSEM (nano Ag)• SEM and
especially TSEM safely detects particles < 5 nm
• Sufficient for threshold based decisions
• Main error seems to result from sample preparation (despite dispersion protocol)
• Pragmatic approaches in evaluation should be tolerable
500 nm
500 nm
• Automation works perfect for spherical samples and is sufficient for ~50% of real life material
• No false negatives at all!
P. Müller; M&M 2015 Portland (OR), Session A17.03, Paper 155
Thank you for your attention!
Funding:
The research leading to these results has received funding from the European Union’s Seventh Framework Programme(FP7/2007-2013) under grant agreement n°604347 – NanoDefine(www.nanodefine.eu)
Special thanks to:
Thorsten Wieczorek(lab work at BASF)Wendel Wohlleben(work on BET-based assesment)Thorsten Wagner (imageJ plugin + discussion)
Amusement in the poolAgglomerate of TiO2 nanoparticles as
used in sunscreen
P. Müller; M&M 2015 Portland (OR), Session A17.03, Paper 155
Backup
P. Müller; M&M 2015 Portland (OR), Session A17.03, Paper 155
Overview
1.Motivation – EC Regulation and the NanoDefine Project
2.Experimental section - The Electron Microscopy (EM) “round robin”
3.Results and take-home messages
4.Discussion of precision and remaining issues
P. Müller; M&M 2015 Portland (OR), Session A17.03, Paper 155
Confidence interval of the medianbimodal silica Nano Au Nano Ag BaSO4 fine coated TiO2 MWCNT Kaolin CaCO3 fine
# of measureme 306 339 388 372 60 225 328 345Median 13.7 19.7 2.7 283.8 185.3 11.6 119.6 160.1upper limit CI 14.4 20.0 2.8 298.9 207.4 12.1 127.5 173.6lower limit CI 13.2 19.5 2.6 262.9 159.1 10.9 109.0 148.2
• Manual measurements on HAADF-STEM images• Despite low number of measurement: tolerable confidence interval• In all cases: clear assignment to nano/non-nano possible• All studies with a result of < 80 nm or >120 nm can be considered as clear cases
P. Müller; M&M 2015 Portland (OR), Session A17.03, Paper 155
What do we learn for a pragmatic approach?Kaolin- BF TEM
200 nm
• EM cannot measure the smallest dimension of the platelets
Possible solution:• Determine Volume Specific Surface Area (VSSA) by BET• Determine the number of small dimension by EM• Modify the cutoff value by which one would define a material as nano by BET:
Irregular particleD=3 small dimensions:
VSSA cut-off = 60 m²/cm³
PlateletD=1 small dimension:
VSSA cut-off = 20 m²/cm³
Rod / tubeD=2 small dimensions:
VSSA cut-off = 40 m²/cm³
VSSA cutoff = 60𝒎𝒎2
𝒄𝒄𝒎𝒎3 ∗𝑫𝑫3