Methodology to evaluate the uncertainty associated with nanoparticle dimensional measurements by SEM

Abstract

The scanning electron microscopy (SEM) technique is widely used for the characterizing of nanoparticle (NP) size, but very few papers deal with NP dimensional metrology. This article reports on a methodology with which to evaluate the uncertainty budget associated with the measurement of the mean diameter of a standard silica NP population by SEM. In this context, the effects of potential error sources have been evaluated though a metrological qualification of the instrument. The measuring method, consisting of determining the area equivalent diameter taken at middle height (D eq-FWHM ), has been tested on a reference silica NP with an indicative certification value given by SEM/TEM (number-based modal diameter). Because agglomeration phenomena can cause measurements errors, semi-automatic homemade software has been employed to build the diameter distribution histogram, selecting only isolated particles. Finally, an uncertainty budget, including the main experimental components, has been established for the mean diameter measurement of this silica NP population. The main contributors to this uncertainty budget are the resolution linked to the dimension of the electron beam diameter at the focal plane, the calibration uncertainty on reference NPs, and the measurement repeatability.

An Adaptable Device for Scalable Electrospinning of Low- and High-Viscosity Solutions

“…However, we observed undercounting of fiber diameter by the software relative to human counts, similar to the DiameterJ authors' original finding ( Figure 5C and D in [36]). Our hand-produced measurements were in close agreement to a sample of more time-consuming measurements made following the work of Crouzier et al [34]. As reported, DiameterJ was substantially faster, and collected many more datapoints.…”

“…Using the test dataset provided in [37], we were able to reproduce their results, which was especially useful for confirming that we used the software correctly. Although Crouzier et al [34] measured nanoparticles (not fibers), their use of measurement standards is well discussed in the literature, and their well-described uncertainty budget supports our decision to use their approach for quantification of our described measurements. We do not report any fiber values obtained from DiameterJ.…”

“…As is best practice for reporting measured values from micrographs [34], we have constructed an uncertainty budget as outlined in the "Evaluation of measurement data-Guide to the expression of uncertainty in measurement" [35]. We have modeled our uncertainty budget after Crouzier et al, which discuss the construction of an uncertainty budget for nanoparticle diameter determination and use a similar Zeiss scanning electron microscope [34]. Adobe CS3 and CC graphic software (Illustrator, Fireworks, and Photoshop) were used to prepare and analyze fibers.…”

“…The edges of the fibers are diffuse in the micrographs, which adds uncertainty as to where the physical edge of the fiber begins. Crouzier et al and Delvallée et al both discuss this problem in relation to their nanoparticles, and determined that selecting the full width half max (FWHM) of their features (all smaller than 100 nm) resulted in measurements most accurate to AFM measurements [34,39]. However, we were concerned with the transferability of the high-quality SEM work demonstrated in both publications to our own capabilities, and instead decided upon base measurement (described in Crouzier et al as D Eq-base ).…”

“…However, we were concerned with the transferability of the high-quality SEM work demonstrated in both publications to our own capabilities, and instead decided upon base measurement (described in Crouzier et al as D Eq-base ). According to previous work, a base measurement will result in an over estimation of the diameter [34,39]. No image threshold was selected due to complication of the fiber mat presenting both blank background, and fiber on fiber backgrounds.…”