High-resolution Transmission Electron Micrographs Research Articles

Features of noise in ultrathin gold nanowire structures

Bundles of ultrathin gold nanowires (Au NWs, 2 nm in diameter) were fabricated and subsequently assembled onto electrodes. Electrical measurements and noise spectroscopy techniques were applied for sample characterization. The peculiarities of noise behavior in the system of bundles of ultrathin gold nanowires were studied. The measured power spectral density of flicker noise was proportional to current squared, which reflects ohmic behavior in NW structures. Lorentzian-shaped components were revealed in the noise spectra. They are suggested to be the result of the participation of molecules adsorbed on the NW surface in transport phenomena. The presence of molecular interfaces was confirmed by high-resolution transmission electron micrographs. The adsorbed molecules play an important role in charge transport and therefore determine electrical and noise properties of the NW structures. The results should be taken into account for the development of NW devices for sensing and molecular electronics applications.

High energy density layered-spinel hybrid cathodes for lithium ion rechargeable batteries

High energy density Li2MnO3 (layered)–LiMn1.5Ni0.5O4 (spinel) composite cathodes have been synthesized using auto-combustion route. Rietveld refinements together with the analyses of high resolution transmission electron micrographs confirm the structural integration of Li2MnO3 nano-domains into the LiMn1.5Ni0.5O4 matrix of the composite cathodes. The discharge capacity of the composite cathodes are due to the intercalation of Li+ ion in the tetrahedral (8a) and octahedral (16c) sites of the spinel component and also the insertion of Li+ in the freshly prepared MnO2 lattice, formed after Li2O extraction from the Li2MnO3 domains. The capacity fading of the composite cathodes are explained to be due to the layered to spinel transition of the Li2MnO3 component and Li+ insertion into the octahedral site of the spinel lattices which trigger cubic to tetragonal phase transition resulting volume expansion which eventually retard the Li+ intercalation with cycling.

Solid phase epitaxial growth of high mobility La:BaSnO3 thin films co-doped with interstitial hydrogen

This work presents the solid phase epitaxial growth of high mobility La:BaSnO3 thin films on SrTiO3 single crystal substrates by crystallization through thermal annealing of nanocrystalline thin films prepared by pulsed laser deposition at room temperature. The La:BaSnO3 thin films show high epitaxial quality and Hall mobilities up to 26 ± 1 cm2/Vs. Secondary ion mass spectroscopy is used to determine the La concentration profile in the La:BaSnO3 thin films, and a 9%–16% La doping activation efficiency is obtained. An investigation of H doping to BaSnO3 thin films is presented employing H plasma treatment at room temperature. Carrier concentrations in previously insulating BaSnO3 thin films were increased to 3 × 1019 cm−3 and in La:BaSnO3 thin films from 6 × 1019 cm−3 to 1.5 × 1020 cm−3, supporting a theoretical prediction that interstitial H serves as an excellent n-type dopant. An analysis of the free electron absorption by infrared spectroscopy yields a small (H,La):BaSnO3 electron effective mass of 0.27 ± 0.05 m0 and an optical mobility of 26 ± 7 cm2/Vs. As compared to La:BaSnO3 single crystals, the smaller electron mobility in epitaxial thin films grown on SrTiO3 substrates is ascribed to threading dislocations as observed in high resolution transmission electron micrographs.

Gnidia glauca Leaf and Stem Extract Mediated Synthesis of Gold Nanocatalysts with Free Radical Scavenging Potential

Development of eco-friendly and novel method for the synthesis of metal nanoparticles is one of the most popular and emerging aspect of nanobiotechnology. In this report, Gnidia glauca leaf and stem extract are used to synthesize gold nanoparticles (AuNPs). As compared to other biological methods, the syntheses were extremely rapid leading to complete reduction within 20 min. Transmission and high resolution transmission electron micrographs clearly indicated that majority of the bioreduced nanoparticles were spherical within a size range of 10 to 60 nm. Exotic shapes like gold nanotriangles and nanohexagons were found in a range between 100 to 300 nm. Dynamic light scattering validated the size range that was observed in TEM and HRTEM. Unique pattern confirming the self-assembly of spheres into anisotropic nanoparticles of larger dimensions was exhibited in HRTEM images. X-ray diffraction pattern and energy dispersive spectroscopic analysis confirmed the purity of elemental gold in the bioreduced nanoparticles. Fourier infrared spectral analysis indicated the role of the phenolic groups in reduction of chloroauric acid into AuNPs. Efficient reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the presence of AuNPs and NaBH4 with apparent rate constants (k) 1.99 × 10-3 min-1 and 4.498 × 10-3 min-1, for AuNPs reduced by GGLE and GGSE, respectively provided strong evidence for the catalytic potential. AuNPs synthesized by GGSE and GGLE showed a second order rate constant of 1.78 × 107 and 1.31 × 107 respectively confirming the scavenging of ABTS•+ radicals.

Influence of Li1+ co-doping defects on luminescence and bandgap narrowing of ZnO:Co2+ nanoparticles due to band tailing effects

Microstructure and optical studies confirm the hexagonal structure of Zn0.96−yCo0.04LiyO (0.00≤y≤0.10) nanoparticles. No diffracted planes related to secondary or clustering phases of Co and Li were observed from high resolution transmission electron micrographs (TEM). Electron energy loss spectroscopy (EELS) and mapping analysis show homogeneous distribution of dopants in the host structure. Two transition energies are derived from fitted UV luminescence spectra and are assigned to free exciton (FX) and donor–acceptor pairs (DAP). The shift in the energy of FX versus Li content shows non-monotonic trend in the range of energy ~3.28–3.23eV. The presence of yellow luminescence in co-doped samples may be due to Li defects. Red luminescence at 680nm interprets a mixed d–d radiative transition of the internal Co2+ ions in a tetrahedral crystal. Green emission band at 520nm indicating the existence of oxygen vacancies in samples. The Co2+ crystal field splitting transition bands 4A2(F)→2E1(G), 4A2(F)→4T1(P) and 4A2(F)→2A1(G) are clearly observed at 565nm, 615nm and 660nm respectively in reflectance spectra. With increasing Li concentration a nonmonotonic trend of energy bandgap was observed in the range 3.30±0.017eV–2.99±0.012eV from reflectance spectra. We observed that the reflectance and photoluminescence spectra show change in band structure and provide clear evidence for narrowing in bandgap energy. The band tailing mechanism seems to be responsible for energy bandgap narrowing due to carrier–carrier, carrier–phonon, carrier–impurity interactions in co-doped samples.

Antibacterial effect of Ag-doped TiO2 nanoparticles incorporated natural rubber latex foam under visible light conditions

Ag-doped TiO2 nanoparticles (Ag-TiO2 NPs) incorporated into natural rubber latex foam (NRLF) showed enhanced antimicrobial activities under visible light. Synthesis of Ag-TiO2 NPs and their incorporation into NRLF are investigated in this paper. Synthesized Ag-TiO2 nanopowder was evaluated by powder X-ray diffraction (XRD) technique, surface electron microscopy (SEM), and high-resolution transmission electron micrograph (HRTEM) coupled with energy dispersive X-ray (EDX) technique. The modified NRLF materials were also evaluated by SEM-EDX analysis, XRD analysis, and antibacterial susceptibility tests. It was found that the XRD peaks obtained for the Ag-TiO2 NP perfectly matched with the reference code of 98-010-5393 which was the tetragonal type anatase phase of TiO2. Most of XRD peaks obtained for the modified NRLF matched with those of Ag-TiO2 NPs which confirmed the presence of nano Ag-TiO2 NPs in the modified NRLF. The particle size analysis carried out by HRTEM images and the EDX mapping results showed that the Ag nanoparticles with a diameter of 5 nm were simply attached to the surface of TiO2 nanoparticles. Modified NRLF showed antimicrobial activity against Gram positive Staphylococcus epidermidis, Gram-positive methicillin-resistant Staphylococcus aureus and Gram-negative Escherichia coli (strain numbers HB101, DH5d) bacteria species.

Synthesis of α-Fe2O3-functionalised graphene oxide nanocomposite by a facile low temperature method and study of its magnetic and hyperfine properties

Reduced graphene oxide/α-Fe2O3 nanocomposites were synthesized by a simple sol–gel method. Initially, the samples were investigated by X-ray diffraction, high resolution transmission electron microscopy and Raman spectroscopy. High resolution transmission electron micrographs indicate that the magnetic nanoparticles are well dispersed in the reduced graphene oxide sheet-like structure. Fourier transform infrared spectroscopy studies corroborate the results obtained by X-ray diffraction. Temperature as well as field dependent magnetic measurements revealed ferromagnetism in the pristine α-Fe2O3 as well as in the nanocomposite sample that is attributed to surface canted spins and defects present in the samples. The enhanced value of coercivity in case of the nanocomposite sample could be ascribed to the Ruderman–Kittel–Kasuya–Yosida type of interaction between the isolated reduced graphene oxide spin and the magnetic ions. Presence of super paramagnetic doublet as well as sextet patterns related to hematite phase is confirmed by the 57Fe-Mössbauer spectroscopy.

Synthesis of rattle-type Ag@Al2O3 nanostructure by laser-induced heating of Ag and Al nanoparticles

A simple and flexible method has been presented for the fabrication of rattle-type Ag@Al2O3 nanostructures in water and polyvinyl pyrrolidone polymer solution based on laser-induced heating of mixture of silver (Ag) and aluminium (Al) nanoparticles by 532-nm laser. Silver and aluminium nanoparticles were prepared by pulsed laser ablation in liquid using same laser wavelength. The transmission electron micrographs revealed morphological changes from sintered-/intermediate-type structure in water medium and jointed structure (heterostructures) in polymer solution to rattle-type structure with changing irradiation time. At longer irradiation time, the Kirkendall effect becomes dominant due to diffusion rate mismatch between the two metals at the interface and facilitates the formation of porous alumina shell over silver core. The morphology and chemical composition of the nanostructures were characterized by transmission electron micrograph, high-resolution transmission electron micrograph and energy-dispersive X-ray analysis. The melting response of alumina (Al2O3), aluminium and silver nanoparticles with 532-nm laser wavelength provides novel pathway for rattle-type formation.

Charge-carrier relaxation dynamics and ac conductivity scaling of poly(3,4-ethylenedioxythiophene) nanoparticles

An investigation of the dielectric characteristics of poly(3,4-ethylenedioxythiophene) nanoparticles has been conducted in the frequency range 20 Hz–2 MHz and the temperature range of 80–300 K through the studies of dielectric permittivity, modulus formalism and ac conductivity. High-resolution transmission electron micrographs confirm the formation of well-ordered spherical nanoparticles. Micro-Raman spectra confirm the conformational transition from benzenoid to quinoid structure with increasing dopant concentration. Linear variation of imaginary permittivity with frequency suggests that the dc conduction process is more significant than interfacial polarisation. The presence of single relaxation peak in the imaginary modulus formalism indicates the Debye-type relaxation. The decrease of frequency exponent with temperature confirms that the charge transport takes place through correlated barrier hopping mechanism. The scaling of ac conductivity spectra confirms that the relaxation dynamics of charge carriers in the poly(3,4-ethylenedioxythiophene) nanoparticles system is temperature independent.

Reduction of silver (I) using defatted cashew nut shell starch and its structural comparison with commercial product

In this current study, we report on the reduction of noble metal silver into silver nanoparticles using defatted cashew nut shell (CNS) starch as both the reducing and capping agents. Furthermore, it was compared with commercially available silver nanopowder for the first time. Color changes, ultraviolet–visible spectra (433.76nm), X-ray diffraction peaks (2θ=37.8, 46.3, 66.2, and 77.92) revealed the face-centered cubic (fcc) geometry of silver nanoparticles, scanning electron microscopy–energy dispersive spectroscopy confirmed the presence of elemental silver nanoparticles and the defatted CNS starch silver nanoparticle structures was in accordance to commercial silver nanopowder. The size of both the nanoparticles was found to be similar in the range of 10–50nm as analyzed using high resolution-transmission electron micrographs. The FT-IR spectroscopy revealed the shifting of NH and OH of defatted CNS starch, starch based silver nanoparticle and commercial silver nanopowder has parallel functional groups. The use of environmentally benign and renewable materials like defatted CNS starch offers an alternative to large scale synthesis of silver nanoparticle and includes numerous benefits like eco-friendly and compatibility for pharmaceutical and biomedical applications.

Synthesis and characterization of highly organized crystalline rutile nanoparticles by low-temperature dissolution-reprecipitation process

Abstract

Electrical conduction mechanism of poly(3,4-ethylenedioxythiophene) nanofiber bundles at low temperature

The nature of charge transport mechanism in poly(3,4-ethylenedioxythiophene) nanofiber bundles has been studied as a function of temperature, magnetic field and AC electric field. High-resolution transmission electron micrographs show the formation of nanofibers with an average diameter of 14 nm. X-ray diffraction analysis depicts the enhancement of polymer chains ordering with increasing dopant concentration. Analysis of the temperature dependence of resistivity reveals a three-dimensional variable range hopping electrical conduction mechanism in the synthesized nanofibers system. A large positive magnetoresistance has been observed at low temperature, which shows a decreasing trend with increasing temperature as well as dopant concentration. The high value of positive magnetoresistance at low temperature has been explained by the wave function shrinkage model. The decrease in frequency exponent s with increasing temperature suggests that the AC conduction takes place through correlated barrier hopping mechanism.

Charge carrier relaxation studies in poly (3, 4-ethylenedioxythiophene) nanofibers

The electrical conductivity and carrier relaxation in poly (3, 4-ethylenedioxythiophene) (PEDOT) nanofibers have been studied over a wide range of frequency and temperature by means of impedance spectroscopy. High resolution transmission electron micrographs confirm the formation of nanofibers with average diameter of 14 nm. The linear increase of imaginary permittivity with decreasing frequency in the log-log plot of e″ versus ω is attributed to the higher contribution of dc conductivity than that of the electrode polarization. The presence of single semicircle in the complex impedance Cole-Cole plot indicates the presence of single charge carrier relaxation mechanism. The perfect matching of the relaxation peak in Z″ and M″ vs. frequency at different temperature confirms the presence of Debye type relaxation. From the temperature dependent behavior of frequency exponent study it is confirmed that the charge transport takes place through correlated barrier hopping mechanism. Decrease of barrier height and increase of density of states with increasing dopant concentration can be corroborated with the conductivity enhancement.

Synthesis of core-shell particles based on hyperbranced polyester and zirconium slag nanoparticles and its influence on the impact resistance of epoxy resin thermosets

Core–shell particles (CSPs) were prepared by hyperbranched polyesters (HBPs), which synthesized by the polycondensation of succinic anhydride and diethanolamine, grafted on zirconium slag nanoparticles (ZSN), a kind of solid waste in zirconium industry. The CSPs were characterized by attenuated total internal reflectance infrared spectroscopy (ATR-IR), nuclear magnetic resonance spectroscopy (NMR), high resolution transmission electron micrographs (HRTEM), and thermogravimetric analysis (TGA). Then the effect of CSPs on impact enhancement of epoxy resin thermosets modified by HBP with different kinds of functional terminal groups, such as hydroxyl group, epoxide group, and amino group, was studied. The results indicated that the addition of CSPs resulted to a strong interfacial adhesion and thus improve the impact resistance of epoxy resin thermosets. POLYM. COMPOS., 2015. © 2015 Society of Plastics Engineers

On the synthesis of nickel oxide nanoparticles by sol–gel technique and its electrocatalytic oxidation of glucose

Nickel oxide nanoparticles (nano-NiOx) of peculiar shape are prepared by sol–gel technique and its electrocatalytic activity is evaluated at different conditions. The thus prepared nanoparticles are annealed at three different temperatures, i.e., 200, 400 and 600 °C and anchored on glassy carbon (GC) electrode. Nano-NiOx modified GG (nano-NiOx/GC) electrodes are subjected to surface analysis techniques such as field emission scanning electron microscopy (FE-SEM) high resolution transmission electron micrograph (TEM) and X-ray diffraction (XRD). Electrochemical characterizations are performed using cyclic voltammetry and chronoamperometric techniques. The effects of annealing temperature on the morphological structure, surface concentration and subsequently on the electrochemical properties of nano-NiOx/GC are examined. Experimental results indicate that the grain size and electrochemical characteristics of the nano-NiOx/GC are significantly affected by the annealing temperature. The electrocatalytic oxidation of glucose at nano-NiOx/GC electrode is significantly enhanced especially with nano-NiOx annealed at 200 °C compared to those annealed at 400 and 600 °C. Nano-NiOx is believed to play a crucial role as a catalytic mediator to facilitate the charge transfer during the oxidation of glucose.

A new zeolite formed from interlayer expansion of the precursor COK-5

The layered silicate COK-5 has been used for an interlayer expansion reaction with dichlorodimethylsilane (DCDMS) at 180 °C to interconnect neighboring layers, yielding a new and crystalline microporous framework. The samples containing the methyl functional groups in the as-made form and having OH groups in the calcined form were designed as COE-5 and calcined COE-5. These samples were characterized with X-ray diffraction (XRD), N2 sorption isotherms, inductively coupled plasma optical emission spectrometry (ICP-OES), infrared spectroscopy (IR), high-resolution transmission electron micrograph (HRTEM), thermogravimetry-differential thermal analysis (TG-DTA), and 29Si and 13C solid-state magic-angle spinning nuclear magnetic resonance (MAS NMR), as well as the contact angle techniques. XRD patterns and HRTEM images suggest that the sample interlayer spacing has been expanded by nearly 0.5 Å. The N2 sorption isotherms of the materials show the BET surface areas are 165 m2/g for COE-5 and 340 m2/g for calcined COE-5. 29Si and 13C MAS NMR as well as IR spectroscopy confirm the insertion of the linker group -Si(CH3)2- connecting neighboring layers. Interestingly, calcined COE-5 shows enhanced catalytic performance in the acetalisation of glycerol with acetone to produce solketal, compared with COK-5.

In-situ synthesis of chromium carbide (Cr3C2) nanopowders by chemical-reduction route

Chromium carbide nanopowder (Cr3C2) has been synthesized from chromium oxide (Cr2O3) by chemical-reduction route under autogenic pressure of hydrogen and CO gases at 87MPa. The reduction of Cr2O3 to Cr3C2 has taken place at a relatively low temperature (700°C) in the presence of Mg in an autoclave. The increased pressure of hydrogen and CO gases facilitates the reduction and carburization simultaneously which helps in reducing the reaction temperature. The nanopowder shows faceted morphology as observed in TEM. High resolution transmission electron micrographs reveal that the size of Cr3C2 powders varies in the range of 30–40nm and is coated by 12–13 layers of carbon with average thickness of 3.5–4nm. Thermal stability of the as-obtained product was investigated by TGA/DTA analysis. Based on the experimental results, possible reaction mechanism for the transformation and formation of nanopowder is discussed in the light of the obtained structure.

Electrical, optical, photocatalytic, and bactericidal properties of polyethylene glycol-assisted sol–gel synthesized ZnTiO3-implanted ZnO nanoparticles

ZnTiO3-implanted ZnO nanoparticles were prepared by sol–gel method employing polyethylene glycol (PEG) 4000 and 20 000. The high resolution transmission electron micrographs, selected area electron diffraction pattern, energy dispersive x-ray spectra and powder x-ray diffractograms show the prepared materials as core/shell nanoparticles. Increase of the molecular mass of PEG decreases the d-spacing in ZnO of ZnTiO3-implanted ZnO and pristine ZnO nanoparticles. The charge transfer resistances of ZnTiO3-implanted ZnO nanoparticles are larger than those of pristine ZnO and precursor ZnTiO3 nanoparticles. The optical properties of ZnTiO3/ZnO nanoparticles are similar to those of pristine ZnO nanoparticles. The photocatalytic activity of ZnO is enhanced by the presence of ZnTiO3 core in the ZnO lattice. The bactericidal activity of core/shell ZnTiO3/ZnO nanoparticles is not less than that of ZnO nanoparticles.

The [formula omitted] structure type and its relation to some complex amalgam structures

A plethora of binary and ternary intermetallic compounds has been assigned to the Gd14Ag51 structure type, crystallising in the hexagonal system (space group P6/m, a=1264.30(18)pm, c=933.58(11)pm for Gd14Ag51). Starting in the late 1960s, much work has been invested in the structural elucidation of these crystal structures. However, reliable single crystal data are scarce, and most structure type assignments have been performed merely on the basis of powder data. We have redetermined four representatives of the binary RE14Ag51 structure type (RE=Y, Ce, Gd, Tb) with modern high-precision single crystal X-ray methods. The assignment of the Gd14Ag51 structure type to space group P6/m was additionally verified by careful analysis of high resolution transmission electron micrographs. We emphasise the close relation of the Gd14Ag51 structure type to the structures of some recently described amalgams of similar composition focussing on disorder phenomena and structural complexity. Furthermore, we provide detailed information on synthesis as well as electrical and magnetic properties for Gd14Ag51, the parent compound of this structure family.

Novel 3D flowerlike Au/BiOBr0.2I0.8 composites with highly enhanced visible-light photocatalytic performances

A series of 3D flowerlike Au/BiOBr0.2I0.8 composites with different Au contents have been synthesized by a hydrothermal combinated with photodeposition method. The as-prepared samples 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), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectra (DRS), and photoluminescence (PL) emission spectroscopy. The photocatalytic activities of these Au/BiOBr0.2I0.8 composites under visible-light irradiation (λ>420nm) were evaluated by the degradation of methyl orange (MO), rhodamine B (RhB) and phenol. The results revealed that the Au/BiOBr0.2I0.8 composites exhibited much higher photocatalytic activities than pure BiOBr0.2I0.8. And the 0.6%Au/BiOBr0.2I0.8 sample exhibited the highest photocatalytic activity. The enhanced photocatalytic activity could be attributed to Au deposits by acting as electron traps and the surface plasma resonance effect of Au. A possible photocatalytic mechanism of Au/BiOBr0.2I0.8 composites was also proposed.