Correlation of AFM/SEM/EDS Images
Figure 4: EDS maps giving chemical information (data corrected for noise using MountainsLab®
software).
right) provides height information on the agglomerate, which is about 800 nm. Finally, EDS provides information on the chemical com-
position of the particles and the silicon chip they are attached to (Figure 4). Te presence of zinc corresponds exactly to constituent particles of isotropic shape of these agglomerates, and iron precisely corresponds to the nanorods. Te presence of oxygen corresponds exactly to the location of the constitu- ent particles of these agglomerates. Tese results confirm that these agglomerates consist of a mixture of oxides, namely zinc oxide and iron oxide particles. Tese results also show that it is possible to distinguish the
constituent particles of zinc and iron oxide particles within the observed agglomerates. Digital
Surf ’s MountainsLab® software allows the
correlation of images and combining of data from differ- ent measurement instruments. The resulting 3D image is presented in Figure 5. Moreover, it is possible to perform particle analysis based on each image layer. In Figure 6, the particle analysis was performed on the EDS map of zinc. It provides the surface area of each detected grain composing the total agglomerate. The distribution of these statistics is shown in Figure 6. It is also possible to perform this type of analysis on the SEM and AFM layers to obtain the size of nanoparticles (height from the AFM layer, equivalent diam- eter or Feret diameters from the SEM layer) when they are well-isolated. Te proportion of ZnO and Fe2
O3 particles in the agglom-
erate can also be determined. In this example (Figure 7), the results on the projected surface show a proportion of ZnO par- ticles three times higher in area (13.88% versus 4.288%) than that of Fe2
O3 particles.
Discussion In this
paper, we independently discriminate two
populations of nanoparticles within an agglomerate by combining measurements from several instruments. Te ultimate aim of this type of experiment is to measure particles in mixtures independently, type by type, even if the particles are similar in size and shape.
2021 May •
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Figure 5: 3D view of the colocalized data (AFM-SEM-EDS) with (above left as thumbnails) the layers (or “channels”) composing the dataset.
Tis preliminary work clearly shows that this kind of study involves critical steps:
• A real effort must be made with regards to sample preparation. Ideally, the particles must be dispersed on the substrate homogeneously. Tis is particularly true if the mixture is extracted from commercial products, due to agglomeration issues and the presence of residues.
• A system must be employed to easily locate the same area of the sample across a set of different instruments.
• During the imaging, the sample must not be degraded. In particular, contamination occurring during SEM and EDS analysis can be a critical issue. Preventing this phenomenon by plasma cleaning, for example, is essential.
• Obtaining EDS maps of nanoparticles requires the detector to work at very low voltage for lateral resolution issues. Driſt correction during all phases of acquisition is indispensable.
• A soſtware program allowing the colocalization of images from different instruments is required. Not only must this soſtware allow basic correction operations on each layer of the correlated data, but it must also offer correction of
relative distortions between the correlated images:
ultimately, the soſtware must be capable of handling the dataset thus created, that is, manage multi-layer images in the same way as single-channel images.
Conclusions Te proof of concept presented here shows that it is possible
to discriminate nanoparticles by their chemical composition within a mixture and thus measure them independently. Tis achievement was accomplished by use of a combination of AFM/SEM/EDS data and the appropriate soſtware tools. Here we demonstrate extraction of the proportion of Fe2
O3 and ZnO
nanoparticles within an agglomerate. In the near future, it will also 49
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