High-resolution Transmission Electron Micrographs Research Articles

Comparative study on different coupling agents used as surfactants: effect on dispersion properties of TiN nanoparticles

Γ-methacryloxypropyl trimethoxy silane (KH-570) and macromolecular coupling agents (MCA) (St/AN/KH-570 random copolymer) were used as surfactants for the surface modification of titanium nitride (TiN) nanoparticles (nanoTiN). The structure and dispersion properties of the modified nanoTiN were investigated by Fourier transform infrared (FTIR) spectra, X-ray photoelectron spectroscopy (XPS), a sedimentation stability experiment (SSE), a contact angle measuring instrument (CAMI) and a high-resolution transmission electron micrograph (HRTEM). According to the spectra of FTIR and XPS, it can be inferred that the KH-570 and MCA covalently bonded on the surface of nanoTiN and an organic coating layer was formed. The SSE and the CAMI showed that the stable dispersion and the hydrophobic property were improved significantly. The results of the HRTEM showed that the surfactants improved the dispersibility of particles in the organic solution and the SBR matrix. It is found that the MCA can more effectively improve the dispersion stability of nanoTiN because of a more strong steric stabilisation of the macromolecular structure, which facilitated to hinder the aggregation of nanoparticles.

Electrical transport and morphological studies of polyaniline nanostructures

Polyaniline nanostructures have been synthesized by self‐assembly method by varying the dopant to monomer molar ratio. High resolution transmission electron micrographs show how the dopant to monomer molar ratio influences on the morphology and structure. The temperature dependence of dc conductivity study shows semiconducting behavior. From dc conductivity study it has been observed that conductivity increases with increasing dopant concentration and maximum conductivity is attained at dopant to monomer molar ratio of 3:4. From the slope of the reduced activation energy versus temperature plot it is confirmed that the charge transport in polyaniline nanostructures is in insulating regime and dominated by variable range hopping mechanism. In particular, a crossover from 1D to 3D variable range hopping conduction is observed by changing the dopant to monomer molar ratio. With increasing the dopant concentration the 680 nm absorption peak shifted towards higher wavelength range. The red shifting of this peak indicates the increased extent of π‐conjugation length. The enhancement of characteristic band intensity at 1336 cm−1 in Micro‐Raman spectra indicates the increase of delocalization degree. Temperature profiles of the degradation processes have been mapped using thermogravimetry analyzer and it is observed three‐step weight losses for all the samples. POLYM. ENG. SCI., 55:995–1002, 2015. © 2014 Society of Plastics Engineers

Synthesis and luminescence properties of CeF3:Tb3+ nanodisks via ultrasound assisted ionic liquid method

CeF3 and CeF3:Tb3+ nanocrystals were successfully synthesized by the ultrasound assisted ionic liquid (IL) method at room temperature. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), high-resolution transmission electron micrographs (HRTEM) and photoluminescence (PL) spectra were employed to characterize the nanocrystals. The results of XRD indicated that the obtained samples crystallized well with a hexagonal phase crystal structure. SEM and TEM images demonstrated that the obtained CeF3:Tb3+ nanocrystals had a discoid shape in the presence of ultrasound and IL, whereas only granular nanoparticles were obtained by magnetic stirring. The possible formation mechanisms of the crystal growth were proposed. The PL spectra of the CeF3:Tb3+ nanodisks exhibited a strong green emission when excited at 254 nm. Furthermore, the photoluminescence intensity of CeF3:Tb3+ of the discoid particles was largely improved compared with that of the granular nanoparticles.

Phase transformation and microstructure study of nano-structured austenitic and ferritic stainless steel powders prepared by planetary milling

In the present work, nano-structured austenitic and ferritic stainless steel powders were prepared in bulk by milling elemental powders in a specially designed dual-drive planetary mill (DDPM) and Fritsch pulverisette planetary mill (P5 mill) for 10 and 40h respectively. The progress of milling and phase transition of stainless steel have been studied by means of X-ray diffraction. The crystallite size and the lattice strain of the austenitic stainless steel after 10h of milling are 9nm and 5.59×10−3 respectively. Similarly, the crystallite size and the lattice strain of the ferritic stainless steel after 10h of milling are 8nm and 9.05×10−3 respectively. Annealing of milled powder at 750°C promotes ferritic to austenitic transformation in both argon and nitrogen atmospheres as limited transformation takes place after milling. However, nitrogen favors the transformation to a greater extent than argon. Lattice parameters calculated from both high resolution transmission electron micrographs (HRTEM) and Nelson–Riley method match with austenitic and ferritic stainless steels. It has been found that initially particles are flattened and finally become almost spherical of size around 10–15μm in both cases.

Enamel proteins mitigate mechanical and structural degradations in mature human enamel during acid attack

A hydrazine deproteination process was used to investigate the role of enamel proteins in the acid erosion of mature human dental enamel. Bright field high resolution transmission electron micrographs and x-ray diffraction analysis show no crystallographic changes after the hydrazine treatment with similar nanoscale hydroxyapatite crystallite size and orientation for sound and de-proteinated enamel. However, the presence of enamel proteins reduces the erosion depth, the loss of hardness and the loss of structural order in enamel, following exposure to citric acid. Nanoindentation creep is larger for sound enamel than for deproteinated enamel but it reduces in sound enamel after acid attack. These novel results are consistent with calcium ion-mediated visco-elasticty in enamel matrix proteins as described previously for nacre, bone and dental proteins. They are also in good agreement with a previous double layer force spectroscopy study by the authors which found that the proteins electrochemically buffer enamel against acid attack. Finally, this suggests that acid attack, and more specifically dental erosion, is influenced by ionic permeation through the enamel layer and that it is mitigated by the enamel protein matrix.

Evaluation of in vitro macrophage response and in vivo host response to growth factors incorporated chitosan nanoparticle impregnated collagen-chitosan scaffold.

The purpose of this study was to evaluate the in vitro macrophage compatibility, the inflammatory response and in vivo host response to a novel collagen-chitosan (COL-CS) scaffold containing growth factors incorporated Chitosan Nanoparticle (CNP). The scaffold was obtained by freezing a blend of COL-CS solution and growth factor incorporated CNP followed by lyophilization. High Resolution Transmission Electron Micrograph (HR-TEM) indicated that growth factors incorporated CNP were in the size range of 50-100 nm, while Scanning Electron Microscopic (SEM) analysis of the scaffold surface suggests that the pores of the scaffolds (COL-CS) were well interconnected, with a mean diameter of 75-150 microm. Macrophages grown on growth factors containing scaffold exhibited poor inflammatory response compared to scaffold without growth factors. In vivo biocompatibility and host response study of scaffold was performed by subcutaneous implantation and examination of the implanted material on day 3 and 15 post implant. The dual growth factors viz. EGF (Epidermal Growth Factor) and FGF (Fibroblast Growth Factor) incorporated implant showed a distinct fibrous capsule boundary on the surface. Secondly, the immunofluoresence assay and zymography respectively for TNFalpha and MMP9 exhibited low expression of these inflammatory markers. These observations divulge that the growth factors when incorporated, can suppress the inflammatory properties of the scaffolds and thus such scaffolds could be used in tissue engineering for minimal host response and enhanced tissue-scaffold interaction.

Size and Crystallinity Dependence of Magnetism in Nanoscale Iron Boride, α-FeB

A nanoscale boride, α-FeB, with grains of variable size and crystallinity was synthesized by precipitation from solution followed by heat treatment (450 °C, 550 °C, 750 °C, 1050 °C). Analysis of transmission electron micrographs, electron diffraction, and magnetic measurements suggests superparamagnetism at room temperature for the smaller, more disordered particles of FeB, while the larger, more crystalline particles of α-FeB, with a particle size of approximately 20 nm, display open magnetic hysteresis loops and blocking. In contrast to the soft ferromagnetism of bulk β-FeB, which was synthesized by conventional solid state reaction at 1500 °C, the sample of α-FeB annealed at 1050 °C is a harder ferromagnet, possibly due to stacking faults that pin the magnetic domains; these stacking faults are apparent in the high resolution transmission electron micrographs. The changes in magnetic behavior are visible from the varying blocking temperatures (63 K, 94 K, 150 K, and >320 K from the smallest to the largest particles) and correlate with the transformations from amorphous to α-FeB and from α-FeB to β-FeB.

Tailoring the formation of metastable Mg through interfacial engineering: A phase stability analysis

A classical thermodynamic approach has been used for describing the pseudomorphic growth in Mg/Nb multilayer films. The bi-phase diagram of these films has been predicted theoretically and the predictions were verified experimentally by growing multiple Mg/Nb thin films that were characterized through high resolution transmission electron micrograph (HRTEM) and X-ray diffraction (XRD) measurement. The good agreement between predictions and experiments shows that the stability of multilayer films can be explained through simple thermodynamic analysis on the competition between bulk and interfacial energies.

Effect of nitrogen passivation on the interfacial property and band offset of HfLaO/SiGe

The effect of NH3 plasma treatment on the interfacial and dielectric property between ultrathin HfLaO and strained Si0.65Ge0.35 substrate is investigated by high-resolution cross-sectional transmission electron micrographs (HR-TEM), Auger electron spectroscopy (AES), x-ray photoelectron spectroscopy (XPS), near edge x-ray absorption fine structure (NEXAFS), valence-band spectra and current density–voltage (J–V). TEM, AES and XPS results confirm that the interfacial layer with N–Hf, La–N and Si–N/Si–O–N bonds acts as a barrier layer against interdiffusions during annealing to some degree. In addition, the signals of N 1s core-level and N K-edge NEXAFS spectra are seen to disappear completely after post-deposition annealing (PDA) at 900°C due to the dissociation of unstable N chemical states during high-temperature annealing. The valence-band offsets ΔEV of HfLaO/SiGe interfaces with and without nitridation are determined to be 3.38 ± 0.01 eV and 3.20 ± 0.01 eV, respectively. While the corresponding conduction-band offsets ΔEC are found to be 1.10 ± 0.01 eV and 1.28 ± 0.05 eV, respectively. Moreover, the nitrided capacitor after PDA shows a low leakage current density (J) of ∼9.15 × 10−8 A cm−2 at a gate bias of Vg = −2.0 V.

Preparation of PbS nano‐microcrystals with different morphologies and their optical properties

PbS nano‐microcrystals were prepared from Pb(OAc)2·3H2O and sulfur in a solution without any surfactant using the solvothermal process. Different morphologies, mainly including polyhedron microcrystals and sphere‐like assemblies, were characterized using a scanning electron microscope (SEM) and a transmission electron microscope (TEM). PbS nano‐microcrystals with cubic crystal structure were detected using X‐ray diffraction (XRD), electron diffraction (ED) and high resolution transmission electron micrograph (HRTEM) techniques. The optical properties were investigated by ultraviolet‐visible (UV‐vis) spectroscopy, and photoluminescence spectroscopy (PL). The UV‐vis absorption peaks of PbS exhibited a large blue‐shift and the PL spectra had a strong and broad emission bands centered at 408 nm. The crystal growth mechanism of PbS was also discussed.

Dopant size dependent variable range hopping conduction in polyaniline nanorods

The present work investigates the electrical transport and dielectric relaxation of polyaniline (PAni) nanorods doped with organic camphorsulfonic acid (CSA) and inorganic hydrochloric acid (HCl) synthesized by interfacial polymerization technique. High resolution transmission electron micrographs (HRTEM) depict that initially spherical nuclei directionally grow into nanorods and CSA doped PAni produces more uniform and aligned structures. The electrical transport studies reveal that the CSA doped nanorods follow 1D Mott variable-range hopping (VRH), whereas the HCl doped nanorods exhibit 2D VRH conduction mechanism. The value of interchain charge transfer integral is found to be higher for smaller size HCl doped PAni than that for larger size CSA doped PAni. The resistivity measurements exhibit semiconducting behavior for both organic and inorganic dopants and the resistivity of the CSA doped nanorods is found to be smaller than that of the HCl doped nanorods. The dielectric relaxation studies suggest Debye type relaxation with a single relaxation peak for both the dopants and the relaxation time of the carriers of the CSA doped PAni nanorods is smaller than that of the HCl doped nanorods.

Engineering polypyrrole nanotubes by 100 MeV Si9 + ion beam irradiation: Enhancement of antioxidant activity

In this work, the effect of 100MeV Si9+ ion beam with four different fluences on antioxidant and structural properties of polypyrrole nanotubes has been investigated. Polypyrrole nanotubes have been synthesized by reactive self degrade template method. Fragmentation of the polypyrrole nanotubes at higher fluence is revealed from the high resolution transmission electron micrograph (HRTEM) and X-ray diffraction (XRD) results. The decrease in characteristics band of polypyrrole in Fourier transmission of infrared spectra (FTIR) spectra suggests the main chain scission of polypyrrole during irradiation. The free radical scavenging activity of pristine and irradiated samples are evaluated by using α, α-diphenyl-β-picrylhydrazyl (DPPH) assay. The decline of the UV–visible absorbance at 516nm suggests the neutralization of DPPH free radicals through the reaction with polypyrrole. Significant increase in antioxidant activity of polypyrrole nanotubes is observed with increase in ion fluence.

The structural and magnetic properties of Fe/(Ga, Mn)As heterostructures

Fe/(Ga, Mn)As heterostructures were fabricated by all molecular-beam epitaxy. Double-crystal X-ray diffraction and high-resolution cross-sectional transmission electron micrographs show that the Fe layer has a well ordered crystal orientation and an abrupt interface. The different magnetic behavior between the Fe layer and (Ga, Mn)As layer is observed by superconducting quantum interference device magnetometry. X-ray photoelectron spectroscopy measurements indicate no Fe2As and Fe—Ga—As compounds, i.e., no dead magnetic layer at the interface, which strongly affects the magnetic proximity and the polarization of the Mn ion in a thin (Ga, Mn)As region near the interface of the Fe/(Ga, Mn)As heterostructure.

Microwave-assisted solvothermal synthesis of 3D carnation-like SnS2 nanostructures with high visible light photocatalytic activity

Novel 3D carnation-flowerlike hexagonal SnS2 hierarchical structures have been successfully synthesized through a simple microwave-assisted solvothermal process. The as-prepared products were characterized by power X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), high-resolution transmission electron micrographs (HRTEM), selected area electron diffraction (SAED), X-ray photoelectron spectroscopy (XPS) and UV–vis diffuse reflectance spectra (DRS). The photocatalytic activity of the sample under visible-light irradiation (λ>420nm) was evaluated by the degradation of two different organic pollutants, rhodamine B (RhB) and phenol. The results reveal that the carnation-flowerlike SnS2 architectures show much higher photocatalytic activity than the SnS2 nanoparticles. The high catalytic performance of the SnS2 architectures comes from their hierarchical mesoporous structures, high BET surface area, high surface-to-volume ratios, and increased light absorbance. In addition, the SnS2 hierarchical architectures are stable during the photocatalytic reaction and can be used repeatedly.

Fabrication and magnetic properties of NiFe–ZnO nano-granular films

Excellent soft magnetic and high frequency properties were obtained successfully in the (Ni75Fe25)x(ZnO)1−x granular films fabricated on the glass substrate by RF magnetron oblique sputtering. The microstructure, magnetic and high frequency properties were investigated systematically. High resolution transmission electron micrographs show that the film consists of fcc Ni75Fe25 particles uniformly embedded in an amorphous insulating matrix ZnO with particle size a few nanometers. The (Ni75Fe25)x(ZnO)1−x films exhibit excellent soft magnetic properties in a wide x range from 0.50 to 0.80 with coercivity not exceeding 5 × 10−4 T, which is ascribed to the exchange coupling between magnetic particles. Especially for the sample with x = 0.64, coercivities in hard and easy axes are 5.0 × 10−5 and 3.6 × 10−4 T, respectively, and the electric resistivity ρ reaches 1,790 μΩ·cm. The dependence of complex permeability u = u′ − ju″ on frequency f shows that the real part u′ is more than 130 below 500 MHz, and the ferromagnetic resonance frequency fr reaches 1.32 GHz, implying the promising for high frequency application.

Ambient-temperature fabrication of microporous carbon terminated with graphene walls by sputtering process for hydrogen storage applications

A very thin amorphous carbon film (10–30nm), has been bombarded with sputtered Cr nanoparticles, resulting in inelastic collision between the nanoparticles and the nuclei of the C-atoms causing atom displacement and re-arrangement into graphene layers. The process occurs at ambient temperature. Fabrication of graphitic microporous carbon terminated with few-to-multilayer graphene walls has been verified by Raman spectroscopy and scanning transmission electron microscopy. High resolution transmission electron micrographs reveal that the formation of graphene layers is highly sensitive to the sputtering parameters. With a gradual increase in the sputtering voltage/current density/time from 3.5kV/40mA–cm−2/1.0min to 5.0kV/70mA–cm−2/3.0min the graphitic domains are found to transform from semi-graphitized layers to well-defined, highly ordered, larger-area graphene walls within the microporous network. The mechanism of this graphitic microporous carbon formation is assumed to be due to two simultaneous processes: in one hand, the sputtering plasma, containing energetic ions and sub-atomic particles, act as dry-etchant to activate the a:C film to transform it into microporous carbon, whereas on the other hand, the charged metal nanoparticle/ion bombardment under sputtering resulted in the inelastic collision between the nanoparticles/ions and the nuclei of the C atoms followed by atom displacement (and displacement cascade) and re-arrangement into ordered structure to form graphitic domains within the microporous carbon network. H2 storage experiment of the samples depicts excellent hydrogen storage properties. This simple, cost-effective, complementary-metal-oxide-semiconductor-compatible, single-step process of metal-graphene hybrid nanomaterial formation may find interesting applications in the field of optoelectronics and biotechnology. Additionally, this method can be adopted easily for the incorporation of transition metals into graphene and similar graphitic carbon nanostructures and may enhance the hydrogen storage capacity for energy-related applications.

Thermoelectric properties of PbSe0.5Te0.5: x (PbI2) with endotaxial nanostructures: a promising n-type thermoelectric material

In the present investigation, we report on the thermoelectric properties of PbSe0.5Te0.5: x (PbI2) from room temperature to 625 K. High-resolution transmission electron micrographs of the samples reveal endotaxial nanostructures embedded in a PbSe0.5Te0.5 matrix. The combined effect of mass fluctuation and nanostructures reduces the thermal conductivity to a great extent compared to PbTe and PbSe, without affecting the carrier mobility. As a result, a thermoelectric figure of merit with a value of 1.5 is achieved at 625 K. This value is significantly higher than that of the available state-of-the-art n-type materials.

Diameter dependent antioxidant property of polypyrrole nanotubes for biomedical applications

In this work we investigate the diameter dependent antioxidant activity of polypyrrole (PPy) nanotubes synthesized by the reactive self degrade template method. HRTEM (High Resolution Transmission Electron Micrograph) micrograph confirms the formation of nanotubes with smaller diameter at higher cetyltrimethylammonium bromide (CTAB) concentration. The formation of amorphous PPy is revealed by X-ray diffraction pattern exhibiting its characteristic broad peak centred at 2θ=25°. Antioxidant activity of the nanotubes has been carried out through the α, α-diphenyl-β-picrylhydrazyl (DPPH) assay. All the samples quenched DPPH in a dose dependent manner. The antioxidant activity of the nanotubes enhances with decrease in average diameter of the nanotubes and may be used as a potential candidate for food storage and biomedical applications.

Quantitative evaluation of size selective precipitation of Mn-doped ZnS quantum dots by size distributions calculated from UV/Vis absorbance spectra

We demonstrate the quantitative evaluation of the sharp classification of manganese-doped zinc sulfide (ZnS:Mn) quantum dots by size selective precipitation. The particles were characterized by the direct conversion of absorbance spectra to particle size distributions (PSDs) and high-resolution transmission electron micrographs (HRTEM). Gradual addition of a poor solvent (2-propanol) to the aqueous colloid led to the flocculation of larger particles. Though the starting suspension after synthesis had an already narrow PSD between 1.5 and 3.2 nm, different particle size fractions were subsequently isolated by the careful adjustment of the good solvent/poor solvent ratio. Moreover, due to the fact that for the analysis of the classification results the size distributions were available, an in-depth understanding of the quality of the distinct classification steps could be achieved. From the PSDs of the feed, as well as the coarse and the fine fractions with their corresponding yields determined after each classification step, an optimum after the first addition of poor solvent was identified with a maximal separation sharpness κ as high as 0.75. Only by the quantitative evaluation of classification results leading to an in-depth understanding of the relevant driving forces, a future transfer of this lab scale post-processing to larger quantities will be possible.

Bismuth oxyiodide–graphene nanocomposites with high visible light photocatalytic activity

A series of chemically bonded Bismuth oxyiodide (BiOI)–graphene (GR) nanocomposites have been synthesized by a facile one-step hydrothermal method. Both the reduction in graphene oxide (GO) and the formation of BiOI nanocrystals were achieved simultaneously during the hydrothermal reaction. The prepared materials were characterized by means of powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectra, high-resolution transmission electron micrographs (HRTEM), UV–vis diffuse reflectance spectra (DRS), and photoluminescence (PL) emission spectroscopy. The photocatalytic activities of these BiOI–GR nanocomposites were evaluated by the degradation of methyl orange. Under visible irradiation (λ>420nm), the BiOI–GR photocatalysts were found to exhibit higher photocatalytic activities than pure BiOI, and the activity was increased by almost 6 times when loaded with 2.0wt% graphene. The enhanced photocatalytic activity can be attributed to more effective charge transportations and separations arisen from the strong chemical bonding between BiOI and graphene, the high dye adsorption performance, and the increased light absorption.