Aid Of Transmission Electron Microscopy Research Articles

Defects distribution and evolution in selected-area helium ion implanted 4H–SiC

An experimental demonstration of the generation of VSi, CSiVC, and NCVSi color centers in 4H–SiC using helium ion microscope irradiation of 5 × 5 μm2 areas with subsequent annealing treatment is presented. With the aid of transmission electron microscopy (TEM), photoluminescence (PL) and cathodoluminescence (CL) spectroscopy and Raman stress analysis, the evolution and distribution of color centers were thoroughly investigated. Cross-sectional TEM revealed the presence of helium bubbles in the center of the regions implanted with high doses which account for the observed quench of PL emission in the center of the implanted regions in both PL and CL measurements. PL spectra from the virgin, implanted and annealed samples proved the appearance of VSi after implantation and the transformation from VSi to CSiVC and NCVSi centers after annealing at 1000 °C. Moreover, with the increase of the implantation dose, the area of NCVSi centers increases whereas that of CSiVC decreases, which provide the first evidence of the competitive relationship between the formation of CSiVC and NCVSi defects. The comparison between stress distribution and CSiVC defect distribution illustrated that CSiVC centers predominantly distributed around the surface rupture region after thermal annealing where significant stress repair occurred. The results show that focused helium ion implantation holds promise for the precise coupling of VSi, CSiVC and NCVSi centers in predefined locations in integrated photonics applications.

Deformation mechanism and force modelling of the grinding of YAG single crystals

YAG single crystals are the primary host materials for solid-state lasers at multi-kW scale and must be processed using ultra-precision grinding to achieve a satisfactory dimensional precision and surface integrity. However, the deformation mechanism of YAG crystals is not well understood, which has thus hindered the development of high efficiency grinding technology for the crystals. In this work, precision grinding of YAG single crystals was investigated. Ductile-like surfaces that are free of cracks and brittle-ductile surfaces that consist of fractured spots and ductile striations were found after grinding. The deformation mechanisms associated with the two types of surfaces were explored with the aid of transmission electron microscopy (TEM). The results indicated that the deformation involved in the formation of the ductile-like surface was mainly caused by the slippage of (0 0 1) crystal planes, along with the formation of dislocations and stacking faults and the distortion of atomic planes. The brittle-ductile surfaces were generated by the plastic deformation due to the formation of nanocrystals and nanovoids, combined with brittle fracture caused by the crack propagation initiated at intersections of slip lines. A theoretical model was developed to predict the grinding force in the ductile-like grinding process, which has taken the combined effect of strain rate, random distribution of abrasive radii and elastic-to-plastic transition depth into account for the first time. The key model parameters were obtained using a genetic algorithm trained using the experimental force data. The modelled force agrees well with the measured. This model enabled an in-depth understanding of the deformation mechanism of a crystal solid involved in ultraprecision grinding and the effect of strain rate on its material removal.

Dilated Minute Chambers in Laryngeal Vocal Fold Polyps: Histopathological and Ultrastructural Features

In Reinke's space of human vocal fold, type III collagen forms a three dimensional network and this contains numerous minute chambers in between these fibers. These compartments are occupied by glycosaminoglycans and glycoproteins. In laryngeal fold lesions, such as Reinke's edema and vocal fold polyps, proteoglycan (PG)/hyaluronic acid (HA) components of extracellular matrix increased. We investigated the size and quantity of the minute chambers within Reinke's space, filled with PG/HA with the aid of transmission electron microscopy. Eight vocal fold polyps and 10 mucosal biopsies (as control group) were all evaluated by light microscopy and electron microscopy. We detected that PG/HA in extracellular matrix had been increased in vocal fold lesions when compared with control group, by Alcian Blue-pH 2.5 stain. The mean volume of the chambers in Reinke's space of normal larynx was measured as 0.040233 µm2 whereas the mean volume of these chambers in vocal fold polyps was measured as 6.420221 µm2. The difference between the volumes of these chambers in vocal fold polyps and in control group was statistically significant (P = 0.001). Within these chambers PG/HA were found and PG/HA filling these chambers were increased in vocal fold polyps. We think proteoglycan and glycosaminoglycans, especially HA, play an important role in determining biochemical properties of vocal fold lesions.

Deformation patterns and fracture stress of beta-phase gallium oxide single crystal obtained using compression of micro-pillars

The deformation of single-crystal beta-phase gallium oxide (or β-Ga2O3) micro-pillars under compression was investigated with the aid of transmission electron microscopy. High-density stacking faults were the dominant deformation defects in the plastically deformed micro-pillars. Micro-cracks were found along (200), (001) and (010) lattice planes and fracture occurred along (200) lattice plane when compressive strain was sufficiently great. Lattice bending was also observed in the fractured pillar. The average fracture stress and strain of β-Ga2O3 being measured are 7.25 ± 1.11 GPa and 3.80 ± 0.57%, respectively, which have never been reported previously.

Embedded Mesoporous Silica Silver Nanoparticles as potential antibacterial agent againstMultidrug-Resistant Bacteria

Many workers have paid more attention to eco-friendly mesoporous silica silver nanoparticles featuring smaller particle sizes to enhance their remarkable antimicrobial properties. A simple chemical method was developed for synthesize high valence silver nanoparticles immobilized on the mesoporoussilica nanomaterial, which showed strong antibacterial activity. Chemical reduction of silver ion has been regarded in the present work, and a reducing agent , such as hydrazine was used to promote the reduction of the silver ion – precursor. The average particle size of the synthesized mesoporous silica-silver nanoparticles (Ag/NH2-KIT-6(x)) with different concentrations of Ag (3.2 and 7.1%) calculated from Scherrer’s equation for (1 1 1)-plane were 8 and 6.5 nm respectively. The synthesized materials were characterized using X-Ray diffraction (XRD), FTIR spectra, X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM), which revealed the mesoporous silica nanoparticles. Antibacterial activities of mesoporous silver nanoparticles against Gram- negative Pseudomonas aeruginosa(ATCC 9027) and Gram-positive Staphylococcus aureus(ATCC 43300) were found to be increased with the increasing of Ag concentration in the Ag/NH2-KIT-6(x). The maximum inhibition zone diameter when the concentration 7.1 % was used obtained against P. aeruginosaand S. aureuswith diameters of 32 and 30 mm respectively. The antimicrobial activity of mesoporousAg/NH2-KIT-6(x) was evaluated also using the MIC&MBC tests. The surface structures of both the untreated and the treated bacterial cells were examined by the aid of TEM. The treated bacterial cells were significantly changed, and major damage was observed in the outer cell membrane. In conclusion the use of AgNPs as antibacterialagentwasfoundtobetoxicagainstpathogenicbacteriaandconsidered

Extracting elastic properties of an atomically thin interfacial layer by time-domain analysis of femtosecond acoustics

Modern devices adopting denser designs and complex 3D structures have created much more interfaces than before, where atomically thin interfacial layers could form. However, fundamental information such as the elastic property of the interfacial layers is hard to measure. The elastic property of the interfacial layer is of great importance in both thermal management and nano-engineering of modern devices. Appropriate techniques to probe the elastic properties of interfacial layers as thin as only several atoms are thus critically needed. In this work, we demonstrated the feasibility of utilizing the time-resolved femtosecond acoustics technique to extract the elastic properties and mass density of a 1.85-nm-thick interfacial layer, with the aid of transmission electron microscopy. We believe that this femtosecond acoustics approach will provide a strategy to measure the absolute elastic properties of atomically thin interfacial layers.

2D black phosphorous nanosheets as a hole transporting material in perovskite solar cells

We demonstrate for the first-time liquid exfoliated few layers of 2D Black phosphorus (BP) nanosheets as a hole transporting material (HTM) for perovskite based solar cells. The photoelectron spectroscopy in air (PESA) measurements confirm the low laying valence band level of BP nanosheets (−5.2 eV) favourable for hole injection from CH3NH3PbI3 (MAPbI3). Our results show that ∼25% improvement in power conversion efficiency (PCE) of η = 16.4% for BP nanosheets + Spiro-OMeTAD as an HTM as compared to spiro-OMeTAD (η = 13.1%). When BP nanosheets are exclusively utilised as an HTM, a PCE of η = 7.88% is noted, an improvement over the 4% PCE values observed for HTM free devices. Photoluminescence (PL) quenching of MAPbI3 and impedance measurements further confirm the charge extraction ability of BP nanosheets. The structural and optical characterization of liquid exfoliated BP nanosheets is discussed in detail with the aid of transmission electron microscopy, Raman spectroscopy, absorption spectroscopy and photo-electron spectroscopy.

Transmission electron microscopy studies and modeling of 3D reciprocal space of ω forming alloy

Initial stage of ω phase formation and associated anomalous features that appear in diffraction patterns of a metastable β transition metal alloy have been investigated in this study with the aid of transmission electron microscopy, simulation and modeling. The paper explores discrete features that emerge in selected area diffraction patterns of quenched Ti-15wt%Mo alloy and analyzes the correlation between ω reflections and diffuse arcs by considering all variants of ω phase as per the formation kinetics of ω phase in β matrix while quenching. Superimposed simulated diffraction patterns have been compared with experimental counterparts and it is deduced that there is lack of congruence between ω reflections and diffuse arcs even after considering trigonal ω with varying degrees of displacement. Direct lattice imaging of trigonal ω in β matrix has been demonstrated by phase contrast microscopy coupled with Fourier filtering techniques. By investigating the nature of ω reflections and diffuse arcs with the aid of electron diffraction pattern calculations and phase contrast microscopy, it is shown that, existing model of three-dimensional (3D) reciprocal space of ω forming alloy at quenched stage is not complete. A new model incorporating a patterned intensity distribution is fitted at the octahedral sites of an fcc reciprocal lattice whose planar intersections with Ewald’s sphere show a better fit with the observed experimental diffraction patterns.

Electrical transport properties of graphene nanowalls grown at low temperature using plasma enhanced chemical vapor deposition

In this work, we report the electrical transport properties of uniform and vertically oriented graphene (graphene nanowalls) directly synthesized on multiple substrates including glass, Si/SiO2 wafers, and copper foils using radio-frequency plasma enhanced chemical vapor deposition (PECVD) with methane (CH4) as the precursor at relatively low temperatures. The temperature for optimum growth was established with the aid of transmission electron microscopy, scanning electron microscopy, and Raman spectroscopy. This approach offers means for low-cost graphene nanowalls growth on an arbitrary substrate with the added advantage of transfer-free device fabrication. The temperature dependence of the electrical transport properties (resistivity and thermopower) were studied in the temperature range, 30–300 K and analyzed with a combination of 2D-variable range hopping (VRH) and thermally activated (TA) conduction mechanisms. An anomalous temperature dependence of the thermopower was observed for all the samples and explained with a combination of a diffusion term having a linear temperature dependence plus a term with an inverse temperature dependence.

Electrospun core-shell structured nanofilm as a novel colon-specific delivery system for protein

A novel core-shell structured nanofilm for the delivery of protein to the colon was developed by coaxial electrospinning using bovine serum albumin (BSA) as protein model. Firstly, the BSA-loaded chitosan nanoparticle was prepared by ionic gelation, and then the coaxial nanofilm was fabricated using alginate as shell layer and the BSA-loaded chitosan nanoparticle as core layer. Scanning electron microscopy analysis showed that the obtained nanofilm exhibited a smooth surface, and the core-shell structure was evidenced by the aid of transmission electron microscopy. There was little change in the secondary structure of encapsulated BSA and around 75% of BSA was released in the simulated colonic fluid. The corresponding kinetics models of BSA release in different simulated digestive fluids were built and the results revealed that the release of BSA in colon followed a complex mechanism. This study shows that electrospun nanofilm is a promising colon-specific delivery system for bioactive protein.

Induction Tempering vs Conventional Tempering of a Heat-Treatable Steel

An induction heat treatment is favorable compared to a conventional one mainly due to significant time and cost savings. Therefore, in this study, the microstructure property relationships during induction and conventional heat treatment of a heat treatable steel 42CrMo4 is investigated. The yield strength and hardness is slightly higher for the conventionally heat-treated steel, whereas the induction heat-treated condition exhibits a roughly 30 J/cm2 higher impact energy. In a previous investigation of the authors, it has been proved that the difference in yield strength originates from the smaller block size of the conventionally heat-treated steel, which was already present after hardening. In the present work, it can be shown that during tempering the martensitic blocks become equi-axed ferrite grains due to recrystallization as revealed by electron back scatter diffraction. Nevertheless, a larger grain size usually is less favorable for the impact toughness of steels. Therefore, another mechanism is responsible for the higher impact energy of the induction hardened and tempered steel. With the aid of transmission electron microscopy a finer distribution of cementite was observed in the induction heat-treated samples. The delay of recovery is the reason for the presence of finer cementite in case of the induction heat-treated steel. Here, the higher heating rates and shorter process times reduce the annihilation of dislocation and as a consequence provide more nucleation sites for precipitation of cementite during tempering. From the obtained experimental results, it is believed that the finer distribution of carbides causes the observed higher impact toughness.

TEM study of the evolution of sputtered Ni+CrAlYSiHfN nanocomposite coating with an AlN diffusion barrier at high temperature

MCrAlY (M denotes Ni and/or Co) coatings are widely used on the turbine blades to protect the aeroengine at high temperature. However, the interdiffusion between coating/substrate and the coefficient of thermal expansion (CTE) mismatch between protective oxides layer/coating are the main factors that limit the service lifetime of MCrAlY coatings. In this work, a Ni+CrAlYSiHfN/AlN nanocomposite duplex coating system was designed to improve the weakness of conventional MCrAlY coatings. The nanocomposite coating system exhibited a low oxidation rate in the 1000 °C isothermal oxidation test and the oxidation rate constant of the coating system was 6.33 ∗ 10− 13 g2 cm− 4 s− 1 at the first 20 h, and then the TGO grew at a low constant of 1.49 ∗ 10− 13 g2 cm− 4 s− 1 until 200 h. Besides, the AlN diffusion barrier effectively inhibited the interdiffusion between coating/substrate. The evolution of coating microstructures and thermal growth oxides (TGO) at high temperature were studied with the aid of transmission electron microscopy.

Coaxial nanofibers of chitosan–alginate–PEO polycomplex obtained by electrospinning

Electrospinning of mucoadhesive membranes is a new and promising field of investigation in the pharmaceutical and biomedical area. The present study explored the electrospinning of two mucoadhesive polymers, chitosan and alginate, to form a core–shell type nanofibers for future applications as controlled drug delivery. Due to the charged functional groups present in these natural polysaccharides, they can complex to yield various nanodevices to be used in controlled release of several active ingredients. In this work, the core–shell type coaxial nanofibers formation was evidenced by the aid of transmission electron microscopy (TEM). Other characterization techniques as scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Infrared spectroscopy (FTIR) and X-ray diffraction (XRD), strongly suggest the formation of different molecular structures of the membranes obtained by the complexation of chitosan and alginate. Swelling rate and weight loss tests followed by SEM analyses confirmed that the nanofiber structure of these membranes were kept even after incubating them for 24h in water. The results of this work confirmed that core–shell nanofibers made of chitosan and alginate polycomplex is possible to be obtained with success.

The role of hydrophilic organoclay in morphology development of poly(butylene terephthalate)/polypropylene blends

This work is concerned with the effect of hydrophilic organoclay on morphology development of poly(butylene terephthalate) (PBT)/polypropylene (PP) blends. The concentration of nanoclays is varied from 1, 3, and 5 phr of polymer blend. Morphological analysis of nanocomposites shows a pronounced refinement of phase morphology with the reduction of droplet size, as compared to neat PBT/PP blend. With the aid of transmission electron microscopy, X-ray diffractometry, and rheological measurements, it is found that organoclays are exclusively located in PBT matrix and at the interface. The nonhomogeneous distribution of organoclays at the interface results in coalescence suppression of droplets and reduction of interfacial tension. Moreover, viscosity and elasticity of matrix are increased with the confinement of organoclays in PBT, which ends up with easier breakup of droplets. According to our research, using nanoclay changes the elasticity ratio of phases that affects capillary number and morphology of the blend. Our calculation indicates that the minimum size of dispersed droplets occurs at elasticity ratio of 1.92.

Size Controlled Synthesis of FeCo Alloy Nanoparticles and Study of the Particle Size and Distribution Effects on Magnetic Properties

In this research the size controlled synthesis of FeCo nanoparticles was done using a quaternary microemulsion system. X-ray diffraction and high resolution transmission electron microscopy of as-synthesized nanoparticles confirm the formation of FeCo alloy nanoparticles. The effects of two process parameters, namely, water to surfactant molar ratio and molar concentration of metal salts, on the size and size distribution of nanoparticles were discussed by the aid of transmission electron microscopy. The size dependency of magnetic properties was also investigated using a room temperature vibrating sample magnetometer. The superparamagnetic-ferromagnetic and single domain-multidomain transition sizes were determined. Then the specific absorption rates at transition sizes were calculated and the best sample for magnetic hyperthermia treatment was introduced.

Virus associated with thickening of the cladodes of prickly pear (Opuntia ficus-indica Mill.)

Symptoms putative to phytoplasmas and virus as yellowing, mosaic, proliferation and deformation of fruits and thickening of the cladodes of prickly pear have been observed in Nopaltepec, Estado de México. The objective of this investigation was to detect the presence of virus in samples of prickly pear showing thickening syndrome of the cladodes. The analysis of double-stranded RNA in prickly pear tissue whit the symptoms mentioned above revealed the presence of viral RNA. In symptomatic tissue, flexible rods of 950-1700 nm in length were observed with the aid of transmission electron microscopy. The virus was transmitted mechanically to Nicotiana tabacum var. Xanthi, N. glutinosa, N. occidentalis, N. benthamiana, Chenopodium quinoa, C. amaranticolor and Datura stramonium. Results from RT-PCR indicate that the particle does not correspond to TMV, neither to member of the Potyviridae family or species of the genus Potexvirus.

Preparing conductive poly(lactic acid) (PLA) with poly(methyl methacrylate) (PMMA) functionalized graphene (PFG) by admicellar polymerization

We synthesized conductive poly(lactic acid) (PLA) polymer by spiking PLA matrices with poly(methyl methacrylate) (PMMA)-functionalized graphene (PFG) by virtue of admicellar polymerization. The PFG was prepared by admicellar polymerization of methyl methacrylate monomers adsorbed onto the graphite oxide. The electrical conductivity of the prepared PFG/PLA considerably increases up to 2.58×10−4S/cm with the percentage of PFG under experimented conditions, ∼12 orders of magnitude greater than the PLA. Aside from electrical conductivity, the tensile strength and Young’s modulus of the PFG/PLA also exhibit increases of ∼5MPa (∼10%) and ∼0.7GPa (>80%) after the 5wt.% addition of the PFG, respectively. Moreover, with the aid of transmission electron microscopy (TEM), it is clear that the graphene surface is covered by the PMMA films rather than usual discrete nanospheres. Our method may offer an alternative green procedure to synthesize conductive PLA polymer since the materials used in the experiments are bio-degradable and environment-begin.

Green synthesis of Au–Pd bimetallic nanoparticles: Single-step bioreduction method with plant extract

A facile and eco-friendly method for the preparation of Au–Pd bimetallic nanoparticles (~ 7 nm) has been developed based on simultaneous bioreduction of Au(III) and Pd(II) precursors with Cacumen Platycladi leaf extract in aqueous environment. The morphology, structure, and size were confirmed with the aid of transmission electron microscopy, selected area electron diffraction, UV–vis spectroscopy, X-ray diffraction, and energy dispersive X-ray spectroscopy. The results from Fourier transform infrared spectroscopy showed that the C O and C O groups in the plant extract played a critical role in capping the nanoparticles. Importantly, the process can be described as pure “green chemistry” technique since no additional synthetic reagents are used as reductants or stabilizers.

Structural characteristics and physical properties of lotus fibers obtained from Nelumbo nucifera petioles

Lotus fiber is a natural cellulose fiber isolated from lotus petiole. Botanically, the fiber is the thickened secondary wall in xylem tracheary elements. In order to obtain essential information for the preparation and processing of lotus fibers, the fine structure and properties of lotus fibers were investigated by the aid of transmission electron microscopy (TEM), confocal laser scanning microscopy (CLSM), atomic force microscopy (AFM), X-ray diffraction (XRD), and so on. The results show that lotus fibers display a rough surface topography and an internal structure different from common plant fibers. The percent crystallinity and preferred orientation of crystallites in lotus fibers are 48% and 84%, respectively. Considering the average breaking tenacity and Young's modulus, lotus fibers are similar to cotton. The elongation of lotus fibers is only about 2.6% while their moisture regain is as high as 12.3%.

Electron-microscopic examination of microstructural changes in structural martensitic steel after low-cyclic fatigue tests

Microstructural changes in a structural martensitic steel upon low-cyclic fatigue (LCF) deformation have been investigated. The micromechanics of plastic deformation and accompanying effects have been studied at the scale of martensite laths and packets with the aid of transmission electron microscopy (TEM). It has been shown that with increasing LCF deformation, changes in both the morphology and the internal structure of martensite occur. The changes are manifested in the form of a refinement of the structural units of martensite. It has been revealed that in the limits of a packet the fatigue deformation occurs inhomogeneously. However, the laths of the same orientation are deformed equally and almost simultaneously. The influence of the dimensions of former austenite grains and orientation of packets on the LCF process has been considered. The mechanics of the fatigue plastic deformation on the nano-, meso-, and microlevels and the processes that accompany this deformation have been studied.