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Methods of Identifying Microbiological Hazards in Indoor Environments
Published in Rafał L. Górny, Microbiological Corrosion of Buildings, 2020
In the case of a transmission electron microscope (TEM), a beam of high-energy electrons produced by the electron gun is directed at a thin (e.g. several dozen or several hundred nanometres thick) sample, at which point it can be reflected, absorbed or transmitted. In transmission mode, reflected electrons are used to create an image of the sample structure, while in scanning mode, they image its surface. TEM has a resolution limit approaching 0.1 nm, which allows observation of even the atomic structure of the examined sample. Going further, an atomic force microscope (AFM) utilises a scanning probe to examine the surface by recording the forces which act on it as a function of position. AFM analyses deflection of a cantilever with a tip under the influence of interaction forces (primarily van der Waals forces) between the atoms of the tip and the atoms which make up the examined surface. A detector (a photodiode) converts the deflection of the cantilever into a current signal, which is then used to generate the sample image. In pulsed mode, the probe tip remains in contact with the sample surface for only a very short period of time, making visual representation of even soft and delicate microbiological samples possible [Bartoszek and Rosowski 2017; Jensen et al. 1994; Jonsson et al. 2014; Karlsson and Malmberg 1989; Macher 1999].
Metal Oxide/Sulphide-Based Nanocatalysts in Biodiesel Synthesis
Published in Bhaskar Singh, Ramesh Oraon, Advanced Nanocatalysts for Biodiesel Production, 2023
Juan S. Villarreal, José R. Mora
There are two types of electron microscopy that are widely used: scanning electron microscopy (SEM) and transmission electron microscopy (TEM) (Ealias and Saravnakumar, 2017). An electron beam is launched to the sample and then, backscattered electrons (Mayeen et al. 2018) and transmission electrons are detected (Mohan Bhagyaraj and Oluwafemi 2018) in SEM and TEM, respectively. SEM allows to obtain a visualization of the surface of the particles with a 3D reference, so it is possible to estimate its size, size distribution, morphology and agglomerations (Ali et al., 2016). On the other hand, TEM provides the possibility to visualize the contour, shape, size and also density of particles, which is appreciable by the colour intensity (Mohan Bhagyaraj and Oluwafemi, 2018).
Electrical characterization of electro-Ceramics
Published in Amit Sachdeva, Pramod Kumar Singh, Hee Woo Rhee, Composite Materials, 2021
An electron microscope uses electrons rather than light to form an image. The scanning electron microscope (SEM) images the sample surface by scanning it with a high-energy beam of electrons in a raster scan pattern. The electrons interact with the atoms that make up the sample, producing signals that contain information about the sample’s surface topography, composition, and other properties such as electrical conductivity. It has a large depth of field, which allows a large amount of the sample to be in focus at one time. The images produced have high resolution, which means that closely spaced features can be examined at a high magnification.
Colloidal lead in drinking water: Formation, occurrence, and characterization
Published in Critical Reviews in Environmental Science and Technology, 2023
Javier A. Locsin, Kalli M. Hood, Evelyne Doré, Benjamin F. Trueman, Graham A. Gagnon
In some cases, direct visualization of colloids may also be desired, which is impossible in methods previously discussed. Electron microscopes use electrons to produce an image of an object with magnification controlled by electric fields (Fig. 1). Two common electron microscopy methods are scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Since conventional SEM and TEM must be operated under a high vacuum, samples are dried. Thus, sample preparation is critical: the drying process may make it difficult to distinguish between agglomeration due to drying and aggregates already present in the sample or induce the crystallization of salts and structural alteration of colloids (Domingos et al., 2009). In contrast, environmental SEM (ESEM) and liquid TEM allows the in-situ observation of the sample (Daulton et al., 2001; Hülsey et al., 2019). However, they suffer from lower resolution due to electron interactions with the liquid layer (Peckys & de Jonge, 2011).
Dispersion stability of nano additives in lubricating oils – an overview of mechanisms, theories and methodologies
Published in Tribology - Materials, Surfaces & Interfaces, 2022
Amir Ashraf, Wani Khalid Shafi, Mir Irfan Ul Haq, Ankush Raina
In this method, a drop of nano lubricant is tested for sedimentation using different microscopy techniques. The various microscopy techniques used are optical microscope, scanning electron microscope (SEM), transmission electron microscope (TEM) and freeze etching replication transmission electron microscope (FERTEM). For SEM analysis, the nanoparticles are extracted from lubricating oil using n-heptane and the extracted nanoparticles are put on smooth silicon (Si) wafers. For TEM microscopy, the sample of nanoparticles is put in toluene or benzene and the solution obtained is then placed on a Cu grid plate which is covered by carbon film. The prepared sample is then dried at ambient temperature. For the FERTEM characterization technique, the sample is freezed using cryogenic liquid and then etched using the Pt/C coating. The nanoparticles present in the fractured sample are then washed with a hydrochloric acid solution (HCl). The main aim of the freezing technique is that structure of nanoparticles does not change in size and can be easily inspected for its stability. The drawback of this test is that the time duration of stability cannot be determined.
Post-processing noise reduction via all-photon recording in dynamic light scattering
Published in Science and Technology of Advanced Materials: Methods, 2021
Takashi Hiroi, Sadaki Samitsu, Kunie Ishioka
Precise determination of polymer and particle sizes is important in the development of novel materials functioning as catalysts [1–3], inks [4,5], biomaterials [6–8], and carriers for drug delivery [9–12]. For nanometer-scale targets, conventional optical microscopy or static light scattering using visible light offer insufficient spatial resolution. Electron microscopy can achieve much higher resolution, but it requires samples to be placed in a high vacuum, which limits its application to liquids and biological targets. Small-angle X-ray and neutron scattering (SAXS and SANS, respectively) [13,14], which are standard techniques for determining the sizes and shapes of nanoscale samples, also have drawbacks. Biological and polymer samples can be easily damaged by the high photon energies in SAXS, and in SANS, deuteration of the solvent is often employed to suppress the incoherent scattering from the hydrogen atoms and to obtain appropriate scattering contrast between the solute and the solvent. Furthermore, both SAXS and SANS typically require large-scale, expensive apparatus.