Volume changes upon heating of aerosol particles from biomass burning using transmission electron microscopy

The responses of aerosol particles to heating are important for measurements of their chemical, physical, and optical properties, classification, and determination of origin. However, the thermal behavior of organic aerosol particles is largely unknown. We provide a method to analyze such thermal behavior through heating from room temperature to >600°C by using a heating holder within a transmission electron microscope (TEM). Here we describe in-situ shape and size changes and variations in the compositions of individual particles before and after heating. We use ambient samples from wildland and agricultural biomass fires in North America collected during the 2013 Biomass Burning Observation Project (BBOP). The results indicate that individual tar balls (TB; spherical organic material) from biomass burning retained, on average, up to 30% of their volume when heated to 600°C. Chemical analysis reveals that K and Na remain in the residues, whereas S and O were lost. In contrast to bulk sample measurements of carbonaceous particles using thermal/optical carbon analyzers, our single-particle results imply that many individual organic particles consist of multiple types of organic matter having different thermal stabilities. Beyond TBs, our results suggest that because of their thermal stability some organic particles may not be detectable by using aerosol mass spectrometry or thermal/optical carbon analyzers. This result can lead to an underestimate of the abundance of TBs and other organic particles, and therefore biomass burning may have more influence than currently recognized in regional and global climate models.

Copyright © 2018 American Association for Aerosol Research     

In situ transmission electron microscopy of solid-liquid phase transition of silica encapsulated bismuth nanoparticles

The solid-liquid phase transition of silica encapsulated bismuth nanoparticles was studied by in situ transmission electron microscopy (TEM). The nanoparticles were prepared by a two-step chemical synthesis process involving thermal decomposition of organometallic precursors for nucleating bismuth and a sol-gel process for growing silica. The microstructural and chemical analyses of the nanoparticles were performed using high-resolution TEM, Z-contrast imaging, focused ion beam milling, and X-ray energy dispersive spectroscopy. Solid-liquid-solid phase transitions of the nanoparticles were directly recorded by electron diffractions and TEM images. The silica encapsulation of the nanoparticles prevented agglomeration and allowed particles to preserve their original volume upon melting, which is desirable for applications of phase change nanoparticles with consistently repeatable thermal properties.     

Visualization and quantitative analysis of nanoparticles in the respiratory tract by transmission electron microscopy

Nanotechnology in its widest sense seeks to exploit the special biophysical and chemical properties of materials at the nanoscale. While the potential technological, diagnostic or therapeutic applications are promising there is a growing body of evidence that the special technological features of nanoparticulate material are associated with biological effects formerly not attributed to the same materials at a larger particle scale. Therefore, studies that address the potential hazards of nanoparticles on biological systems including human health are required. Due to its large surface area the lung is one of the major sites of interaction with inhaled nanoparticles. One of the great challenges of studying particle-lung interactions is the microscopic visualization of nanoparticles within tissues or single cells both in vivo and in vitro. Once a certain type of nanoparticle can be identified unambiguously using microscopic methods it is desirable to quantify the particle distribution within a cell, an organ or the whole organism. Transmission electron microscopy provides an ideal tool to perform qualitative and quantitative analyses of particle-related structural changes of the respiratory tract, to reveal the localization of nanoparticles within tissues and cells and to investigate the 3D nature of nanoparticle-lung interactions.     

Applications of transmission electron microscopy to coal chemistry

Transmission electron microscopy can be applied to several aspects of coal chemistry. First, examination can be made of the structure and characteristics of the mineral constituents. Second, the concentration and distribution of organic elements can be determined. These techniques are closely related to methods by which materials scientists have examined alloys and ceramic materials for many years. This Paper describes the methods, shows typical applications and indicates the relation between the measurements and progress in electron microscopy generally.     

Morphological characterization of the core–shell latex particle by transmission electron microscopy and image analysis

To describe the morphology of the core–shell latex particle of methyl methacrylate–butadiene–styrene graft copolymer (MBS) quantitatively, we propose four parameters, that is, the diameter of the core, the shell thickness (TH), the roundness of the core, and the eccentricity (E); we calculated these parameters with geometrical parameters determined by the analysis of transmission electron microscope images. The mean values and distributions of the four parameters based on a certain amount of particles were used for quantitative characterization of MBS latex samples. With increasing monomer‐to‐polymer ratios of the graft polymerization, both the MBS TH and the numbers of homopolymer particles increased, and the core–shell morphology tended to be irregular. For the MBS latices derived from poly(styrene–butadiene) latex with a wide distribution of particle sizes, the core–shell structures of the larger particles were different from those of smaller ones to a certain extent, and both the TH and the E decreased with increasing core size. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 855–861, 2003     

High-resolution transmission electron microscopy of Os-clusters supported on model alumina-films

Thin planar model alumina films can be successfully used as supports for metal species in the size range 1 nm, provided the electron optical conditions (defocus setting) are optimized. Os₃(CO)₁₂-clusters were anchored on the model support intact and the triatomic clusters ( 0.6 nm diameter) could be made visible. Metal aggregation in H₂-atmospheres and redispersion in CO and O₂ atmospheres has been studied. It is suggested that CO-induced fragmentation of small osmium particles exposing low-coordinated surface atoms probably leads to mononuclear surface carbonyl complexes.     

Impurities identification in a synthetic diamond by transmission electron microscopy

Three types of impurities, which were trapped in diamond single crystal during process of the diamond crystal growth under high temperature and high pressure in the presence of iron–nickel solvent catalyst, have been successfully and directly investigated by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Both the chemical composition and the crystal structure of the impurities were identified and determined. The impurities may be derived from the starting materials and the medium (pyrophillite) for transmitting the pressure, they consisted of amorphous graphite, f.c.c. (FeNi)₂₃C₆ and orthorhombic FeSi₂.     

Visualizing dispersion morphology via ultra-rapid freezing/transmission electron microscopy

Optical microscopy has been a useful technique for visualizing aqueous dispersions, but it lacks the high resolution available with transmission electron microscopy (TEM). In order to withstand the vacuum of the electron microscope, water-based systems must be either dried or frozen, but this distorts morphology. The ultra-rapid freezing technique can be used in such studies to preserve microstructure and also be compatible with the vacuum of the electron microscope. Also known as cryo-TEM, this technique has been used in coatings research to visualize the morphologies of a variety of aqueous dispersions. Besides being consistent with what we already know optically, these complementary techniques of ultra-rapid freezing and transmission electron microscopy now permit us a unique view of fluid microstructure far below the limit of optical microscopy.     

Orientation analysis of individual electrospun PE nanofibers by transmission electron microscopy

A systematic orientation analysis of individual electrospun polyethylene (PE) nanofibers was performed by transmission electron microscopy (TEM). PE nanofibers with a wide diameter distribution, ranging from 150 nm to several micrometers, and a variety of morphologies, including cylindrical, beaded- and ribbon-like fibers, were produced by the high-temperature solution electrospinning. In each fiber, crystalline orientation and its morphology were investigated by TEM. In the cylindrical fibers, development of fiber structure was strongly related to the fiber diameter. Depending on the diameter, three different structural models based on 1) the random-oriented crystalline structure, 2) the shish-kebab structure, and 3) the fibrillar structure composed of extended-chain crystals were proposed. In addition, orientation analysis of beaded fibers and that of ribbon-like fibers was also performed.     

Mass loss of wood and its components during transmission electron microscopy

The loss of mass of wood and its polymeric constituents in transmission electron microscopy has been determined by measurement of the decrease in the continuum x-ray intensity for various doses of irradiation. It was found that for doses higher than 5 × 10^?8 C/μm², 42% of the original mass of the wood remained on the grid. The corresponding percentages for cellulose, xylan, and lignin were 32, 45, and 70, respectively. The significance of these results in the use of transmission electron microscopy for imaging and for quantitative microbeam analysis is discussed.     

Scanning transmission electron microscopy of multiphases in graphite-alkali metal intercalation compounds

Structural and micro-analytical evidence is presented for the presence of multiphase regions in graphite-Rb intercalation compounds for stages n ? 2. The intercalate layers are composed of islands of alkali metal, ordered incommensurately with respect to the adjacent graphite layers and embedded in a background of disordered rubidium in the intercalate layer. The results confirm the non-integral stoichiometry of graphite alkali metal intercalation compounds for stages n ? 2.     

3D Nanotomography of calcium silicate hydrates by transmission electron microscopy

Calcium silicate hydrate (C-S-H), is the principal hydration product of Portland cement that mainly contributes to the physical and mechanical properties of concrete. This paper aims to investigate the three-dimensional structure of C-S-H with Ca/Si ratios of 1.0 and 1.6 at the nanoscale using electron tomography. The 3D reconstructions and selected region of interest analysis confirm that the morphology of both C-S-H materials are foil-like structures. The difference between the two materials is the density of elongated structures. C-S-H with Ca/Si ratio 1.6 is clearly composed of denser particles compared to the other C-S-H material due to overlapping of the foil-like structure. Pore analysis shows that C-S-H 1.0 and C-S-H 1.6 have porosities 69.2% and 49.8% respectively. Pore size distribution also reveals that C-S-H 1.0 has pore size range between 0-250 nm and C-S-H 1.6 between 0-100 nm. The pore network's size of C-S-H 1.0 is significantly larger than 1.6. This study illustrates the capability of using electron tomography to determine the 3D nanoscale structure of cementitious products and to distinguish between C-S-H 1.0 and 1.6.     

Microstructure of Athabasca bituminous sand by freeze-fracture preparation and transmission electron microscopy

The technique of freeze-fraclure has been used to prepare samples of bituminous sand and emulsions for electron microscopy. This provides substantial information about the volatile (primary aqueous) fractions of these systems. Evidence is presented that the water component in the bituminous sands occurs mainly as a water-in-oil emulsion in the interstitial spaces, not as a layer around the mineral particles.     

Sinter-free phase conversion and scanning transmission electron microscopy of FePt nanoparticle monolayers

Thermally robust monolayers of 4-6 nm diameter FePt nanoparticles (NPs) were fabricated by combining chemical synthesis and atomic layer deposition. Spin-cast monolayers of FePt NPs were coated with thin, 11 nm-thick layers of amorphous Al(2)O(3), followed by annealing to convert the FePt NPs from an alloy (A1) into intermetallic FePt (L1(0)) and FePt(3) (L1(2)) phases. The Al(2)O(3) layer serves as a barrier that prevents sintering between NPs during annealing at temperatures up to 730 °C. Electron and X-ray diffraction in conjunction with high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) show that as-synthesized A1 FePt NPs convert into L1(0) and L1(2) phase NPs through annealing. HAADF-STEM measurements of individual NPs reveal imperfect ordering and show that the NP composition determines which intermetallic phase is obtained. Mixed-phase NPs with L1(0) cores and FePt(3) L1(2) shells were also observed, as well as a smaller number of unconverted A1 NPs. These results highlight the need for improved control over the compositional uniformity of FePt NPs for their use in bit-patterned magnetic recording.     

Distribution of carbon black in semicrystalline polypropylene studied by transmission electron microscopy

Polypropylene (PP) samples filled with different carbon blacks (CB) were prepared by the conventional melt‐mixing method. The distribution of the CB in the PP matrix was investigated by using the RuO₄ vapor‐staining technique and transmission electron microscopy (TEM). Our results indicate that amorphous regions of PP are sandwiched between the crystalline lamellae. The thickness of individual amorphous layers is a few nanometers. The amorphous region was measured to be about 45 wt % using a differential scanning calorimeter (DSC). The thickness of the lamellae is much smaller than the dimensions of the CB particles, and the CB particles or aggregates are dispersed inside the spherulites. There is a thin layer of amorphous PP encapsulating the CB particles and aggregates. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 358–365, 2002     

Analysis of sub-micron mineral matter in coal via scanning transmission electron microscopy

The fine-scale mineral matter in three US coals has been analysed via scanning transmission electron microscopy (STEM). The samples observed were a North Dakota lignite, a Kentucky bituminous, and a Pennsylvania semi-anthracite. Specific mineral types, differing among the three coals examined, appear to predominate at this fine size scale (particles ? 200 nm in diameter). Fe-rich and Ba-rich minerals in the lignite, a Ti-rich mineral in the bituminous and Ca-rich and Ti-rich minerals in the semianthracite were the predominant species found. The inherent mineral content in the observed organic background also differed from coal to coal. The distributions of mineral species in the size range ? 200 nm reported herein do not reflect the distributions in the larger size ranges obtained by more macroscopic techniques.     

Structural features of pyrocarbon atomistic models constructed from transmission electron microscopy images

We report on atomistic models of laminar pyrocarbons constructed using a combination of 2D high resolution transmission electron microscopy (HRTEM) lattice fringe image analysis, 3D image synthesis and atomistic simulated annealing. In a first step, the effectiveness of the method and the convergence of the models with respect to the quench rate are checked on small systems. Then, the nanostructural features of large fully carbonaceous atomistic models obtained from the HRTEM images of a rough laminar pyrocarbon, as-prepared and after partial graphitization, are discussed. Both models show a very pronounced sp² character (?97%), essentially made of hexagonal rings (?88%) and pentagonal and heptagonal rings in similar amounts (≈6%). The latter mostly form pentagon-heptagon pairs or networks of line defects between misoriented hexagonal domains. Numerous pairs of screw dislocations, connecting different graphene domains, are also observed while edge dislocations with unsaturated carbon atoms are almost absent. The models are validated with respect to experimental pair distribution functions, showing excellent agreement.     

High-resolution scanning electron microscopy for the characterization of supported metal catalysts

A scanning electron microscope with a short-focal-length immersion lens and subnanometer resolution has been used to characterize several oxide-supported metal particle catalysts. Nanometer-sized metal particles in the Pt/TiO₂ and Pd/SiO₂ systems could be imaged with best clarity at the upper end of the operating voltage range (20–30 kV). However, visibility depended upon an adequate yield of secondary electrons relative to the support: small Pt particles on CeO₂ could not be located by secondary electron imaging. Best visibility of the surface topography of the support was obtained at lower accelerating voltages.