Combination of transmission electron and atomic force microscopy techniques to determine volume equivalent diameter of submicrometer particles

Abstract

Morphological properties of atmospheric particles are directly related to their residence time and transport behaviors, and their deposition patterns in human respiratory systems. The projected properties of particles measured by transmission electron microscopy (TEM) were combined with the particle height measured by atomic force microscopy (AFM) to determine volume equivalent diameter of submicrometer particles. For nonvolatile (refractory) laboratory-generated spherical polystyrene latex and cubic NaCl particles, the measured volume equivalent diameters agreed well with the true values (within 4%). However, for nonrefractory (NH(4))(2)SO(4) particles, the measured volume equivalent diameter was much smaller than the true value due to evaporation of volatile species at low vacuum pressure and high electron-beam intensity conditions in TEM, and deformation of particles in AFM. We observed that the volume equivalent diameter of 100 nm mobility-classified atmospheric particles was 35 ± 5 nm, suggesting that these particles contain nonrefractory species, whereas that of 20 nm mobility-classified atmospheric particles was found to be 19 ± 6 nm, suggesting that these particles were refractory and spherical.

Substrate-Deposited Sea Spray Aerosol Particles: Influence of Analytical Method, Substrate, and Storage Conditions on Particle Size, Phase, and Morphology

“…Particle size, phase, and shape are all important properties of atmospheric aerosol particles, as these properties determine the atmospheric lifetime, light scattering properties, and heterogeneous chemistry. − A variety of microscopy techniques are used to image particles and determine their size, phase, and shape. , These techniques require different operating conditions and are governed by different physical principles of operation. Conventional scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques operate under high vacuum conditions that can facilitate evaporation of semivolatile species and lead to underestimation of a particle’s size and alter its composition, while atomic force microscopy (AFM) operates at ambient conditions. Microscopy techniques require particle deposition onto substrates, such as quartz, TEM grids, silicon wafers, aluminum foil, titanium foil, or filters.…”

“…4,5 These techniques require different operating conditions and are governed by different physical principles of operation. Conventional scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques operate under high vacuum conditions that can facilitate evaporation of semivolatile species and lead to underestimation of a particle's size and alter its composition, 6 while atomic force microscopy (AFM) operates at ambient conditions. Microscopy techniques require particle deposition onto substrates, such as quartz, TEM grids, silicon wafers, aluminum foil, titanium foil, or filters.…”

Facile Method for Determining the Aspect Ratios of Mineral Dust Aerosol by Electron Microscopy

“…The height of the particles can be calculated based on the width of the uncoated region. Using the two dimensional projection of the particles visible in the TEM image and the height of the particle, the aspect ratios of the particle in the top-down and side-on orientations can be determined (Robertson et al 1954;Jepson and Rowse 1975;Nadeau 1985Nadeau , 1987Inoue and Kitagawa 1994;Becket et al 1997;Tumolva et al 2012). This method assumes that the particle has no surface irregularities that may affect the observed height of the particle and that the particles do not move during the coating process.…”

“…Aspect ratios for clay minerals have been as high as 1.68 for montmorillonite, 1.31 for kaolinite, and 5.33 for illite for the top-down orientation and as high as 448, 18, and 120, respectively, for the side-on orientation (Nadeau 1985). AFM has also been used to measure the dimensions of clay minerals without the use of a coating (Lindgreen et al 1991;Schleicher et al 1993;Bickmore et al 2002;Tumolva et al 2012). In addition to microscopy methods used to study the dimensions of the particles, surface area measurements through gas adsorption studies (described below) can be used with microscopy methods to find the dimensions of the particles (Hofmann et al 1961;Schuttlefield et al 2007).…”

Analytical Methods for Physicochemical Characterization and Toxicity Assessment of Atmospheric Particulate Matter: A Review

“…AFM utilizes a nanoscale cantilever tip traveling across the surface of the analyzed sample to map its 3-D topography [170]. This ability to generate 3-D particle models at a high spatial resolution and a vertical resolution of ≤0.1 nm are among the significant advantages of AFM [102,104,105,171]. AFM has been implemented to study particle properties including size, shape, mass, volume, hygroscopicity, surface roughness, and adhesion to other particles and surfaces [102,104,106,107,172].…”