A new method for measuring nanoparticle diameter from a set of SEM images using a remarkable point.

Scanning Electron Microscopy (SEM) is considered as a reference technique for the determination of nanoparticle (NP) dimensional properties. Nevertheless, the image analysis is a critical step of SEM measuring process and the initial segmentation phase consisting in determining the contour of each nano-object to be measured must be correctly carried out in order to identify all pixels belonging to it. Several techniques can be applied to extract NP from SEM images and evaluate their diameter like thresholding or watershed. However, due to the lack of reference nanomaterials, few papers deals with the uncertainty associated with these segmentation methods. This article proposes a novel approach to extract the NP boundaries from SEM images using a remarkable point. The method is based on the observation that, by varying the electron beam size, the secondary electron profiles crosses each other at this point. First, a theoretical study has been performed using Monte Carlo simulation on silica NP to evaluate the robustness of the method compared with more conventional segmentation techniques (Active Contour or binarization at Full Width at Half-Maximum, FWHM). The simulation results show especially a systematic discrepancy between the NP real size and the measurements performed with both conventional methods. Moreover, generated errors are NP size-dependent. By contrast, it has been demonstrated that a very good agreement between measured and simulated diameters has been obtained with this new technique. As an example, this method of the remarkable point has been applied on SEM images of silica particles. The quality of the segmentation has been shown on silica reference nanoparticles by measuring the modal equivalent projected area diameter and comparing with calibration certificate. The results show that the NP contour can be very accurately delimited with using this point. The measurement uncertainty has been also reduced from 4.3 nm (k = 2) with conventional methods to 2.6 nm (k = 2) using the remarkable point.

Development of a new hybrid approach combining AFM and SEM for the nanoparticle dimensional metrology.

At this time, there is no instrument capable of measuring a nano-object along the three spatial dimensions with a controlled uncertainty. The combination of several instruments is thus necessary to metrologically characterize the dimensional properties of a nano-object. This paper proposes a new approach of hybrid metrology taking advantage of the complementary nature of atomic force microscopy (AFM) and scanning electron microscopy (SEM) techniques for measuring the main characteristic parameters of nanoparticle (NP) dimensions in 3D. The NP area equivalent, the minimal and the maximal Feret diameters are determined by SEM and the NP height is measured by AFM. In this context, a kind of new NP repositioning system consisting of a lithographed silicon substrate has been specifically developed. This device makes it possible to combine AFM and SEM size measurements performed exactly on the same set of NPs. In order to establish the proof-of-concept of this approach and assess the performance of both instruments, measurements were carried out on several samples of spherical silica NP populations ranging from 5 to 110 nm. The spherical nature of silica NPs imposes naturally the equality between their height and their lateral diameters. However, discrepancies between AFM and SEM measurements have been observed, showing significant deviation from sphericity as a function of the nanoparticle size.

Evidence of dislocation cross-slip in MAX phase deformed at high temperature.

Ti2AlN nanolayered ternary alloy has been plastically deformed under confining pressure at 900°C. The dislocation configurations of the deformed material have been analyzed by transmission electron microscopy. The results show a drastic evolution compared to the dislocation configurations observed in the Ti2AlN samples deformed at room temperature. In particular, they evidence out-of-basal-plane dislocations and interactions. Moreover numerous cross-slip events from basal plane to prismatic or pyramidal planes are observed. These original results are discussed in the context of the Brittle-to-Ductile Transition of the nanolayered ternary alloys.

Structural characterization of self-assembled monolayers of neoglycoconjugates using atomic force microscopy.

Thiolated self-assembled monolayers of carbohydrates may serve as useful polyvalent tools to mimic the organized presentation of such molecules at the cell surface. SAMs presenting the disaccharide maltose as a neoglycoconjugate were produced, and the structure was studied by high resolution atomic force microscopy. The molecules form highly ordered structures on a gold (111) surface, with lattice parameters determined by the linker moiety rather than the headgroup.