V.-D. Hodoroaba, S. Rades, K. Natte, G. Orts-Gil and W. E. S. Unger

Traceable Size Characterization of Nanoparticles at BAMwith a Zeiss Supra 40 Scanning Electron Microscope

and a Transmission Setup

T STEM detector

thin foils

SEM with the Top surface and in-depth observation,Thin samples on

1. SEM in mode (TSEM or LV-TEM): transmission How does it work?

2. calibration of image magnification with CRMsTraceable

4.1 Image processing for NP size measurementmetrological

Figs. 6 Steps in image processing for SiO NPs: after calibration (Fig. 6a), binarization (Fig. 6b), delimitation 2

of the NPs Results of the 6(Fig. 6c); size distribution found with the Image J processing software package (Fig. 6d).

5Significant sources

T single-unit transmission setup

thin foils

SEM with the Zeiss Top surface and in-depth observation,Thin samples on

Calibration of the image magnification ® certified NPs or certified pitch patterns.

Threshold selection for the delimitation of the NPsThickness correction for the applied coating ®

additional measurement of witness specimens (Si).

Monte-Carlo simulation of TSEM images as important tool in the evaluation of the measurement

1uncertainties.

SEMTop surface observation,Bulk substrates

Fig. 1c Sketch of an SEM equipped with the Zeiss single-unit transmission setup for the analysis of electron transparent samples by converting the transmitted electrons (TE) with the gold electron multiplier into secondary

2,3electrons to be analysed with the available E-T detector.Foto right: Foto of the Zeiss single-unit transmission setup.EDX detection is possible only by extra removal of the screening ring.

Fig. 1a Sketch of conventional SEM for analysis of samples on bulk substrates;

. Most SEMs have attached an EDS detector enabling elemental analysis.

with Everhart-Thornley (E-T) electron detector and In-Lens detector

BAM Federal Institute for Materials Research and Testing, Berlin, Germany

Dan.Hodoroaba@bam.de

High-resolution SEM with the sensitive detection

of the specimen surface bottom-up with In-Lens

detectors enables excellent evaluation of the

sample (NP) surface morphology at the nanoscale.Complimentary valuable in-depth information,

1,3but also accurate lateral dimensional one are

gained when the NPs are deposited on thin

substrates and analysed in the transmission mode

at a high-resolution SEM (TSEM).

Fig. 1b Sketch of a modern SEM equipped with a STEM detector (BF= bright field, DF= dark field) for the analysis of electron transparent samples on thin substrates additionally to the E-T and In-Lens detectors.Note the necessity of a large area EDS X-ray detector for enhanced

3sensitivity at the elemental analysis of NPs.

Poor contrast of the micrographs obtained by

conventional E-T barely enables the identification 3of non-conductive NPs.

Low-voltage facilities at modern SEMs makes

possible acceptable analysis of uncoated 5conductive NPs.

High-resolution cathodes, in-the-lens

detectors and electrically conductive supports

enhance significantly the quality of the

morphological analysis of NPs. However, a slight

overestimation of the NP size due to a saturation 3effect at the NP boundaries has been observed.

References:

[1] E. Buhr, N. Senftleben, T. Klein, D. Bergmann, D. Gnieser, C. G. Frase and H. Bosse, Meas. Sci. Technol. 20 (2009) 413.[2] U. Golla and B. Schindler (2004) US patent 6,815,678 B2.[3] V.-D. Hodoroaba, S. Benemann, C. Motzkus, T. Macé, P. Palmas and S. Vaslin- Reimann, Microsc. Microanal. 18 (Suppl 2) (2012), 1750.[4] V.-D. Hodoroaba, S. Rades, K. Natte, G. Orts Gil and W. E. S. Unger, GIT Imaging and Microscopy 1 (2013) 54.[5] C. Motzkus et al., submitted.[6] http://rsb.info.nih.gov/ij/

5.2 Nominal SiO NPs210 nm

Figs. 8 a) TSEM micrograph of SiO NPs, and b) equivalent “conventional” TEM 2

micrograph of the same sample for comparison. The determined size distributions are overlapped onto the micrographs.

SiO NPs of 10 nm nominal size as a potential NP 2

CRM candidate has been manufactured and characterized at BAM.

Once carefully taken the SEM images can be automatically processed with respect to the NP size distribution.

(1a) (1b) (1c)Screening ring

Au electronmultiplier

TEM grid

Aperture(BF or DF)

Sample holder of„dovetail “ type

Combining top surface observation (for ) with in-depthobservation (for measurement)

nano-morphologysize

Figs. 2 SEM micrographs of SiO particles obtained with: a) the high-resolution In-Lens detector and b) with the 24conventional E-T detector of the transmitted electrons (i. e. TSEM mode) coming from the same scanned area.

100 nm

0 5 10 15 20 25 300

20

40

60

80

100

%pa

rtic

les

size /nm

4. Image processing

(2b)(2a)

(3) (4a) (4b) (5)

SEM:PTB CD (pitch) structure

TNP CRMs

SEM (with TEM grids and electron transparent foils):5

: Au NPs, PSL NPs, etc.TGrating BAM-L200

SEM (with a FIB lamella): CRM:

5. on NP samples from Study cases NanoValid

(8a)

0 5 10 15 20 25 300

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40

60

80

100

%pa

rtic

les

size /nm

(7)

Fig. 7 Ag NPs acquired in the TSEM mode.

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0 25 50 75 100 125 150 175 2000

20

40

60

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120

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160

180

NP

num

ber

size /nm

(6d)

3. Measurement uncertainty

5.1 What is the ?NP shape

Quick high-resolution SEM in combination with TSEM observation of NP shape/morphology as accompanying m e a s u r e m e n t s d u r i n g N P

4manufacturing.

Acknowledgement:

The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement n° 263147 (NanoValid Development of reference methods for hazard identification, risk assessment and LCA of engineered nanomaterials).

Mrs. S. Benemann is greatly acknowledged for her calm hands during all the TSEM measurements.

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