AFM Measurements and Tip Characterization of Nanoparticles with Different Shapes

Unambiguous identification of the measurement methodologies is fundamental to reduce the uncertainty and support traceability of particle shape and size at the nanoscale. In this work, the critical aspects in atomic force microscopy measurements, that is, drawbacks on sample preparation, instrumental parameters, image pre-processing, size reconstruction, and tip enlargement, are discussed in reference to quantitative dimensional measurements on different kinds of nanoparticles (inorganic and biological) with different shapes (spherical, cylindrical, complex geometry). Once the cross-section profile is extracted, top-height measurements on isolated nanoparticles of any shape can be achieved with sub-nanometer accuracy. Lateral resolution is affected by the pixel size and shape of the probe, causing dilation in the atomic force microscopy image. For the reconstruction of critical sizes of inorganic non-spherical nanoparticles, a geometric approach that considers the nominal shape because of the synthesis conditions is presented and discussed

AFM Measurements and Tip Characterization of Nanoparticles with Different Shapes

Unambiguous identification of the measurement methodologies is fundamental to reduce the uncertainty and support traceability of particle shape and size at the nanoscale. In this work, the critical aspects in atomic force microscopy measurements, that is, drawbacks on sample preparation, instrumental parameters, image pre-processing, size reconstruction, and tip enlargement, are discussed in reference to quantitative dimensional measurements on different kinds of nanoparticles (inorganic and biological) with different shapes (spherical, cylindrical, complex geometry). Once the cross-section profile is extracted, top-height measurements on isolated nanoparticles of any shape can be achieved with sub-nanometer accuracy. Lateral resolution is affected by the pixel size and shape of the probe, causing dilation in the atomic force microscopy image. For the reconstruction of critical sizes of inorganic non-spherical nanoparticles, a geometric approach that considers the nominal shape because of the synthesis conditions is presented and discussed

Quantitative three-dimensional characterization of critical sizes of non-spherical TiO2 nanoparticles by using atomic force microscopy

Since both size and shape of nanoparticles are challenging to be quantitatively measured, traceable 3D measurements are nowadays an issue. 3D nanometrology plays a crucial role to reduce the uncertainty of measurements, improve traceable calibration of samples and implement new approaches, models, and methodologies in the study of the nanomaterials. AFM measurement of nanoparticles with unusual shape represent a non-trivial challenge due to the convolution with the finite size of the tip. In this work, geometric approaches for the determination of critical sizes of TiO2 anatase bipyramids and nanosheets are described. An uncertainty budget is estimated for each nanoparticle size with the aim of assessing the different sources of error to obtain a more reliable and consistent result. The combined standard uncertainties are respectively less than 5% and 10% of the dimensions of bipyramids and nanosheets. Due to the stability and monomodal distribution of their critical sizes, bipyramids and nanosheets are suitable to apply as candidate reference materials at the nanoscale. Moreover, quantitative measurements of shape and texture descriptors are discussed in order to understand the quality of the synthetized batch

Tip-sample characterization in the AFM study of a rod-shaped nanostructure

Accurate measurements of line-width standards, sidewalls and non-spherical nanoparticles performed at the nanoscale by means of atomic force microscopy (AFM) suffer from errors due to the tip shape and size. To reduce the uncertainty, the study here presented aims to investigate a bio-plant nanostructure, namely the tobacco mosaic virus (TMV), as a candidate reference tip characterizer. The TMV has a rod-shaped structure with a diameter of about 18 nm, reported earlier from x-ray fibre diffraction, thus representing a reference at the nanoscale. When imaged by AFM, the diameter of the TMV is determined as the top height of the rod from the reconstructed cross-section profile of isolated virions, deposited on a flat substrate like mica. A mean diameter of 16.5 nm, smaller than the nominal value by fibre diffraction measurements, is determined with our metrological AFM. Meanwhile, tip–sample–substrate interactions are discussed with reference to experimental data and models in the literature, in order to determine deformations and the associated uncertainty of corrections, with which the difference between the AFM-reconstructed top-height diameter and the nominal value reduces to about 0.3 nm. Once the virus is fully characterized, a tip profile is estimated by the AFM-reconstructed cross-section profiles of the TMV. The approach is used to evaluate the tip-related enlargement from the nominal circle size, assumed undeformed, of the TMV cross-section profile. A good repeatability of the reconstructed tip shape is achieved from subsequent imaging of virions, while tip degradations are somewhat visible over the working time