Showing papers on "Transmission electron microscopy published in 2012"
TL;DR: The results suggest that the growth here occurs via surface-mediated growth, which is similar to graphene growth on Cu under low pressure, which are particularly attractive for use as atomic membranes or dielectric layers/substrates for graphene devices.
Abstract: Hexagonal boron nitride (h-BN) is very attractive for many applications, particularly, as protective coating, dielectric layer/substrate, transparent membrane, or deep ultraviolet emitter. In this work, we carried out a detailed investigation of h-BN synthesis on Cu substrate using chemical vapor deposition (CVD) with two heating zones under low pressure (LP). Previous atmospheric pressure (AP) CVD syntheses were only able to obtain few layer h-BN without a good control on the number of layers. In contrast, under LPCVD growth, monolayer h-BN was synthesized and time-dependent growth was investigated. It was also observed that the morphology of the Cu surface affects the location and density of the h-BN nucleation. Ammonia borane is used as a BN precursor, which is easily accessible and more stable under ambient conditions than borazine. The h-BN films are characterized by atomic force microscopy, transmission electron microscopy, and electron energy loss spectroscopy analyses. Our results suggest that the...
1,069 citations
TL;DR: It is shown that TMDs can be doped by filling the vacancies created by the electron beam with impurity atoms, and this results shed light on the radiation response of a system with reduced dimensionality, but also suggest new ways for engineering the electronic structure of T MDs.
Abstract: Using first-principles atomistic simulations, we study the response of atomically thin layers of transition metal dichalcogenides (TMDs)--a new class of two-dimensional inorganic materials with unique electronic properties--to electron irradiation. We calculate displacement threshold energies for atoms in 21 different compounds and estimate the corresponding electron energies required to produce defects. For a representative structure of MoS2, we carry out high-resolution transmission electron microscopy experiments and validate our theoretical predictions via observations of vacancy formation under exposure to an 80 keV electron beam. We further show that TMDs can be doped by filling the vacancies created by the electron beam with impurity atoms. Thereby, our results not only shed light on the radiation response of a system with reduced dimensionality, but also suggest new ways for engineering the electronic structure of TMDs.
947 citations
TL;DR: In this paper, the synthesis of magnetic Fe3O4@graphene composite (FGC) and utilization in dye removal from aqueous media were investigated by the structural, surface, and magnetic characteristics of the nanosized composite.
528 citations
TL;DR: The synthesis of large-area h-BN film is reported using atmospheric pressure chemical vapor deposition on a copper foil, followed by Cu etching and transfer to a target substrate, and the mobility of the CVD graphene device remains the same before and after device integration.
Abstract: Hexagonal boron nitride (h-BN) is a promising material as a dielectric layer or substrate for two-dimensional electronic devices. In this work, we report the synthesis of large-area h-BN film using atmospheric pressure chemical vapor deposition on a copper foil, followed by Cu etching and transfer to a target substrate. The growth rate of h-BN film at a constant temperature is strongly affected by the concentration of borazine as a precursor and the ambient gas condition such as the ratio of hydrogen and nitrogen. h-BN films with different thicknesses can be achieved by controlling the growth time or tuning the growth conditions. Transmission electron microscope characterization reveals that these h-BN films are polycrystalline, and the c-axis of the crystallites points to different directions. The stoichiometry ratio of boron and nitrogen is close to 1:1, obtained by electron energy loss spectroscopy. The dielectric constant of h-BN film obtained by parallel capacitance measurements (25 μm2 large areas) ...
500 citations
TL;DR: Characterizations of HFCNs through high-resolution transmission electron microscopy, infrared/Raman spectroscopy, and X-ray diffraction indicate that abundant small oxygenous graphite domains existed and endowed the H FCNs with fluorescent properties.
Abstract: We propose an ingenious method for synthesizing cross-linked hollow fluorescent carbon nanoparticles (HFCNs) with green emission by simply mixing acetic acid, water, and diphosphorus pentoxide. This is an automatic method without external heat treatment to rapidly produce large quantities of HFCNs, in contrast to other syntheses of fluorescent carbon nanoparticles that required high temperature, complicated operations, or long reaction times. Characterizations of HFCNs through high-resolution transmission electron microscopy, infrared/Raman spectroscopy, and X-ray diffraction indicate that abundant small oxygenous graphite domains existed and endowed the HFCNs with fluorescent properties. After simple post-treatments, the cross-linked HFCNs can be used for cell-imaging applications. Compared with traditional dyes and CdTe quantum dots, HFCNs are the superior fluorescent bioimaging agent according to their low toxicity, stability, and resistance to photobleaching. The HFCNs were also applied to watermark ink and fluorescent powder, showing their promising potentials for further wide usage.
467 citations
TL;DR: ZnO nanoparticles have been synthesized by precipitation method from Zinc nitrate and have potential for application in manufacturing units due to ease processing and more economical reagents.
Abstract: ZnO nanoparticles have been synthesized by precipitation method from Zinc nitrate. The powder was characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, selected-area electron diffraction, UV-vis optical absorption, and photoluminescence spectroscopy analyses. XRD patterns showed that ZnO nanoparticles have hexagonal unit cell structure. SEM and TEM pictures reveal the morphology and particle size of prepared ZnO nanoparticles. The UV-vis absorption spectrum shows an absorption band at 355 nm due to ZnO nanoparticles. The photoluminescence spectrum exhibits two emission peaks one at 392 nm corresponding to band gap excitonic emission and another located at 520 nm due to the presence of singly ionized oxygen vacancies. The synthesis method has potential for application in manufacturing units due to ease processing and more economical reagents.
417 citations
TL;DR: Graphene domains prepared by an atmospheric pressure chemical vapor deposition method with suppressing nucleation on copper foils through an annealing procedure showed that the submillimeter graphene domains were monolayer single crystals.
Abstract: Submillimeter single-crystal monolayer and multilayer graphene domains were prepared by an atmospheric pressure chemical vapor deposition method with suppressing nucleation on copper foils through an annealing procedure. A facile oxidation visualization method was applied to study the nucleation density and morphology of graphene domains on copper foils. Scanning electron microscopy, transmission electron microscopy, atomic force microscopy, polarized optical microscopy, and Raman spectra showed that the submillimeter graphene domains were monolayer single crystals.
371 citations
TL;DR: It is shown that core/shell nanoplatelets can be obtained with a 2D geometry that is conserved and the core/ shell structure appears very clearly on high-resolution, high-angle annular dark-field transmission electron microscope images, thanks to the difference of atomic density between the core and the shell.
Abstract: We have recently synthesized atomically flat semiconductor colloidal nanoplatelets with quasi 2D geometry. Here, we show that core/shell nanoplatelets can be obtained with a 2D geometry that is conserved. The epitaxial growth of the shell semiconductor is performed at room temperature. We report the detailed synthesis of CdSe/CdS and CdSe/CdZnS structures with different shell thicknesses. The shell growth is characterized both spectroscopically and structurally. In particular, the core/shell structure appears very clearly on high-resolution, high-angle annular dark-field transmission electron microscope images, thanks to the difference of atomic density between the core and the shell. When the nanoplatelets stand on their edge, we can precisely count the number of atomic planes forming the core and the shell. This provides a direct measurement, with atomic precision, of the core nanoplatelets thickness. The constraints exerted by the shell growth on the core is analyzed using global phase analysis. The co...
337 citations
TL;DR: In this paper, the growth of vertically standing zincblende InP nanowire arrays on InP (100) substrates in the vapor-liquid-solid growth mode using low-pressure metal-organic vapor-phase epitaxy was investigated by electron beam lithography.
Abstract: We investigate the growth of vertically standing [100] zincblende InP nanowire (NW) arrays on InP (100) substrates in the vapor-liquid-solid growth mode using low-pressure metal-organic vapor-phase epitaxy. Precise positioning of these NWs is demonstrated by electron beam lithography. The vertical NW yield can be controlled by different parameters. A maximum yield of 56% is obtained and the tapering caused by lateral growth can be prevented by in situ HCl etching. Scanning electron microscopy, high-resolution transmission electron microscopy, and micro-photoluminescence have been used to investigate the NW properties.
331 citations
TL;DR: In this paper, a mesoporous Li4Ti5O12/C nanocomposite is synthesized by a nanocasting technique using the porous carbon material CMK-3 as a hard template.
Abstract: A mesoporous Li4Ti5O12/C nanocomposite is synthesized by a nanocasting technique using the porous carbon material CMK-3 as a hard template. Modified CMK-3 template is impregnated with Li4Ti5O12 precursor, followed by heat treatment at 750 °C for 6 h under N2. Li4Ti5O12 nanocrystals of up to several tens of nanometers are successfully synthesized in micrometer-sized porous carbon foam to form a highly conductive network, as confirmed by field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy, and nitrogen sorption isotherms. The composite is then evaluated as an anode material for lithium ion batteries. It exhibits greatly improved electrochemical performance compared with bulk Li4Ti5O12, and shows an excellent rate capability (73.4 mA h g−1 at 80 C) with significantly enhanced cycling performance (only 5.6% capacity loss after 1000 cycles at a high rate of 20 C). The greatly enhanced lithium storage properties of the mesoporous Li4Ti5O12/C nanocomposite may be attributed to the interpenetrating conductive carbon network, ordered mesoporous structure, and the small Li4Ti5O12 nanocrystallites that increase the ionic and electronic conduction throughout the electrode.
320 citations
TL;DR: This review provides a brief overview about both transmission electron microscopy (TEM) and scanning electron microscope (SEM) techniques which have been employed to characterise nanoemulsions and selected examples of electron microscopic studies of nanoemulsion studies are presented.
TL;DR: In this article, the effects of crystal structure and electronic structure on the photocatalytic activities of cubic NaNbO3 have been investigated by H2 evolution from aqueous methanol solution and CO2 photoreduction in gas phase.
Abstract: Cubic and orthorhombic NaNbO3 were fabricated to study the effects of crystal structure and electronic structure on the photocatalytic activities in detail. The samples were characterized by X-ray diffraction, field emission transmission electron microscopy, high-resolution transmission electron microscopy, UV–visible absorption spectroscopy, and X-ray photoelectron spectroscopy. The photocatalytic activities of the two phases of NaNbO3 have been assessed by H2 evolution from aqueous methanol solution and CO2 photoreduction in gas phase. The photocatalytic H2 evolution and CO2 reduction activities over cubic NaNbO3 were nearly twice of those over orthorhombic NaNbO3. The first-principles calculation reveals that the higher activity over cubic NaNbO3 can be attributed to its unique electronic structure, which is beneficial for electron excitation and transfer.
TL;DR: In this article, the evolutions of the structure occurring into the lithium rich cobalt free layered cathode material Li1.2Mn0.61Ni0.18Mg0.01O2 upon the first electrochemical cycle were investigated by the means of high angle annular dark field (HAADF) imaging in a scanning transmission electron microscope and electron diffraction in a transmission electron microscopy.
Abstract: The evolutions of the structure occurring into the lithium rich cobalt free layered cathode material Li1.2Mn0.61Ni0.18Mg0.01O2 upon the first electrochemical cycle were investigated by the means of high angle annular dark field (HAADF) imaging in a scanning transmission electron microscope and electron diffraction in a transmission electron microscope. They are coupled with electron energy loss spectroscopy (EELS) experiments in order to probe the chemical evolutions occurring during the first charge/discharge cycle. In the pristine material, the analysis of the HAADF images and electron diffraction patterns confirmed the ordering between the cations (Li or Ni with Mn) and the existence of disoriented domains stacked along the c axis. Moreover, the partial solid solution of Ni into Li2MnO3 leading to a composite material is evidenced. Upon the first charge, a loss of material is shown to have occurred, and the presence of a defect spinel phase due to the transfer of transition metal cations to the intersl...
TL;DR: In this article, the diffusional displacive 18R to 14H transformation rate is controlled by the diffusion rate of Y and Zn atoms into the segregation layers in a Mg-8Y-2Zn-0.6Zr alloy.
TL;DR: The direct determination of free reduced and total CySH in human urine samples has been successfully carried out without the assistance of any separation techniques and the morphological and structural characterizations evidence that the Au NCs can be efficiently decorated on the GO.
TL;DR: In this paper, the results of studies regarding the Al-Al3Ti-Ti composite are presented, which was fabricated by explosive welding and annealing under an air atmosphere of 630°C.
TL;DR: In this article, the evolution of the morphology during the evaporation of the mixed solvent, which comprises additive and chlorobenzene (CB), is investigated by in-situ grazing incidence X-ray scattering, providing insight into the key role the additive plays in developing a multi-length-scale morphology.
Abstract: Additives are known to improve the performance of organic photovoltaic devices based on mixtures of a low bandgap polymer, poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM). The evolution of the morphology during the evaporation of the mixed solvent, which comprises additive and chlorobenzene (CB), is investigated by in-situ grazing incidence X-ray scattering, providing insight into the key role the additive plays in developing a multi-length-scale morphology. Provided the additive has a higher vapor pressure and a selective solubility for PCBM, as the host solvent (CB) evaporates, the mixture of the primary solvent and additive becomes less favorable for the PCPDTBT, while completely solubilizing the PCBM. During this process, the PCPDTBT first crystallizes into fibrils and then the PCBM, along with the remaining PCPDTBT, is deposited, forming a phase-separated morphology comprising domains of pure, crystalline PCPDTBT fibrils and another domain that is a PCBM-rich mixture with amorphous PCPDTBT. X-ray/neutron scattering and diffraction methods, in combination with UV–vis absorption spectroscopy and transmission electron microscopy, are used to determine the crystallinity and phase separation of the resultant PCPDTBT/PCBM thin films processed with or without additives. Additional thermal annealing is carried out and found to change the packing of the PCPDTBT. The two factors, degree of crystallinity and degree of phase separation, control the multi-length-scale morphology of the thin films and significantly influence device performance.
TL;DR: Enhanced gas sensing properties are closely related to the change of nanostructure and activity of ZnO and NiO nanocrystals as well as combination of homo- and heterointerfaces in the optimum gas sensor, which are confirmed by a series of well-designed experiments.
Abstract: Novel NiO@ZnO heterostructured nanotubes (NTs) were fabricated by the coelectrospinning method, consisting of external hexagonal ZnO shell and internal cubic NiO NTs. They are carefully investigated by scanning electron microscopy, transmission electron microscopy, scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy mapping, X-ray diffraction, and X-ray photoelectron spectroscopy techniques. A reasonable formation mechanism of the hierarchical NiO@ZnO NTs is proposed, which is discussed from the view of degradation temperature of different polymers and the amount of inorganic salts. They were then explored for fabrication of H(2)S gas sensors. The gas sensing test reveals that compared with the pure ZnO, NiO, and the ZnO-NiO mixed gas sensors, hierarchical gas sensor exhibits highly improved sensing performances to dilute hydrogen sulfide (H(2)S) gas. The response of the optimum NiO@ZnO NTs sensor to 50 ppm H(2)S increases as high as 2.7-23.7 times compared to the other sensors, whereas the response and recovery times also become shorter considerably. These enhanced gas sensing properties are closely related to the change of nanostructure and activity of ZnO and NiO nanocrystals as well as combination of homo- and heterointerfaces in the optimum gas sensor, which are confirmed by a series of well-designed experiments.
TL;DR: In this article, Li-rich layered oxide is prepared and coated with an AlF3 layer by a chemical deposition method, and the layer with a thickness of about 5-7 nm is coated on the surface of the Li(Li0.17Ni0.25Mn0.58)O2 grains.
TL;DR: In this paper, surface morphological changes were examined using scanning electron microscopy after heat treatment in the temperature range of 600-900 °C for solid oxide fuel cell cathodes.
Abstract: Elemental enrichment behavior on the surface of La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) was investigated in order to understand potential degradation mechanism of solid oxide fuel cell cathodes. Surface morphological changes were examined using scanning electron microscopy after heat treatment in the temperature range of 600–900 °C. Submicron-sized precipitates were formed on grain surfaces after heat treatment. Their shapes appeared to be aligned along the surface orientations of the underlying grains. Auger electron spectroscopy and transmission electron microscopy characterization revealed that the precipitate was strontium (Sr)-oxygen (O) based. The formation of Sr–O precipitates was found to increase with increasing temperature and oxygen partial pressure. A defect chemistry model is presented based on the observed phenomena.
TL;DR: In this article, the synthesis of magnetite (Fe 3 O 4 ) nanoparticles by a sol-gel method was described by using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive analysis by X-rays (EDAX), transmission electron microscope (TEM), superconducting quantum interference device (SQUID), and Mossbauer spectrometry.
TL;DR: A green and facile approach to synthesize chemically bonded TiO2/graphene sheets (GS) nanocomposites using a one-step hydrothermal method was reported in this paper.
TL;DR: In this paper, the authors used a uniform coating of Ce and Sn precursors onto polystyrene (PS) spheres, followed by heat treatment at 550°C to remove the PS spheres core.
Abstract: The Ce-doped SnO2 hollow spheres were prepared by the uniform coating of Ce and Sn precursors onto polystyrene (PS) spheres, following by heat treatment at 550 °C to remove the PS spheres core. The observations of field emission gun scanning electron microscope (FESEM) and transmission electron microscopy (TEM) showed that Ce-doped SnO2 hollow spheres with a shell thickness of ∼200 nm, which were composed of nanoparticle aggregates with the crystallite size of 10–15 nm. X-ray diffraction (XRD) exhibited that all the diffraction peaks have been indexed to a rutile structure of SnO2. No diffraction peaks of cerium oxide were observed, suggesting that Ce4+ ions get uniformly substituted into the Sn4+ sites or interstitial sites in SnO2 lattice. The Ce-doped SnO2 hollow spheres showed perfect sensing performance toward acetone gas with rapid response, good stability and high response at 250 °C compared with pure SnO2 hollow spheres.
TL;DR: Transmission electron microscopy of cryogenically ion milled sections of fully-mineralized cortical bone is used to study the spatial and topological relationship between mineral and collagen and observes that hydroxyapatite occurs largely as elongated plate-like structures which are external to and oriented parallel to the collagen fibrils.
Abstract: The relationship between the mineral component of bone and associated collagen has been a matter of continued dispute. We use transmission electron microscopy (TEM) of cryogenically ion milled sections of fully-mineralized cortical bone to study the spatial and topological relationship between mineral and collagen. We observe that hydroxyapatite (HA) occurs largely as elongated plate-like structures which are external to and oriented parallel to the collagen fibrils. Dark field images suggest that the structures (“mineral structures”) are polycrystalline. They are approximately 5 nm thick, 70 nm wide and several hundred nm long. Using energy-dispersive X-ray analysis we show that approximately 70% of the HA occurs as mineral structures external to the fibrils. The remainder is found constrained to the gap zones. Comparative studies of other species suggest that this structural motif is ubiquitous in all vertebrates.
TL;DR: Real-time electron microscopy of dendritic growth dynamics and the associated local ionic concentrations can provide new insight into the functional electrochemistry of batteries and related energy storage technologies.
Abstract: An ideal technique for observing nanoscale assembly would provide atomic-resolution images of both the products and the reactants in real time. Using a transmission electron microscope we image in situ the electrochemical deposition of lead from an aqueous solution of lead(II) nitrate. Both the lead deposits and the local Pb2+ concentration can be visualized. Depending on the rate of potential change and the potential history, lead deposits on the cathode in a structurally compact layer or in dendrites. In both cases the deposits can be removed and the process repeated. Asperities that persist through many plating and stripping cycles consistently nucleate larger dendrites. Quantitative digital image analysis reveals excellent correlation between changes in the Pb2+ concentration, the rate of lead deposition, and the current passed by the electrochemical cell. Real-time electron microscopy of dendritic growth dynamics and the associated local ionic concentrations can provide new insight into the functiona...
TL;DR: Results indicate that MSNs-SS-mPEG nanoparticles can be used in the biomedical field and serve as efficient gatekeepers to control the on-off of the pores.
Abstract: Hybrid mesoporous silica nanoparticles (MSNs), which were synthesized using the co-condensation method and engineered with unique redox-responsive gatekeepers, were developed for studying the glutathione-mediated controlled release. These hybrid nanoparticles constitute a mesoporous silica core that can accommodate the guests (i.e., drug, dye) and the PEG shell that can be connected with the core via disulfide-linker. Interestingly, the PEG shell can be selectively detached from the inner core at tumor-relevant glutathione (GSH) levels and facilitate the release of the encapsulated guests at a controlled manner. The structure of the resulting hybrid nanoparticles (MSNs-SS-mPEG) was comprehensively characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (XRD), and nitrogen adsorption/desorption isotherms analysis. The disulfide-linked PEG chains anchored on MSNs could serve as efficient gatekeepers to control the on–off of the pores....
TL;DR: A cytotoxicity test suggested that the porous core/sheath nanofibers are non-toxic and support cell attachment, therefore, this fiber mat may find application in the design of wound-healing patches with long-term activity.
TL;DR: In this article, the epitaxial crystallization of polyethylene (PE) on reduced graphene oxide (RGO) nanosheets via a controlled solution crystallization method was reported.
Abstract: We report epitaxial crystallization of polyethylene (PE) on reduced graphene oxide (RGO) nanosheets via a controlled solution crystallization method. Polarized light microscopy, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy were used to investigate morphology of RGO-induced PE crystals. The PE edge-on crystals formed from randomly distributed rodlike nuclei on the basal plane of RGO nanosheets and further grew into larger lamellae with an average dimension of a few hundreds of nanometers. Selected area electron diffraction (SAED) pattern revealed that the c-axis of polymer chain is parallel to the basal plane of the RGO nanosheets. PE/RGO nanocomposites (PGNs) with different RGO loadings were fabricated through solution crystallization/precipitation using the PE-decorated RGO hybrid as the precursor. Both nonisothermal and isothermal crystallization behaviors of PGNs were studied using differential scanning calorimetry (DSC). Crystallization kinetics of PGNs w...
TL;DR: In this article, hollow structured CoFe2O4 nanospheres were synthesized by a hydrothermal method, which gave an outer diameter of 200-300 nm and a wall thickness of about 100nm.
Abstract: Hollow structured CoFe2O4 nanospheres were synthesized by a hydrothermal method. The uniform hollow nanosphere architecture of the as-prepared CoFe2O4 has been confirmed by field emission scanning electron microscopy and transmission electron microscopy analysis, which give an outer diameter of 200–300 nm and a wall thickness of about 100 nm. CoFe2O4 nanospheres exhibited a high reversible capacity of 1266 mA h g−1 with an excellent capacity retention of 93.6% over 50 cycles and an improved rate capability. CoFe2O4 could be a promising high capacity anode material for lithium ion batteries.
TL;DR: The results indicate that oxygen vacancies could be involved in the ferromagnetic exchange, and the possible mechanism of formation was discussed based on the experimental results.
Abstract: Ferromagnetism was observed at room temperature in monodisperse CeO2 nanospheres synthesized by hydrothermal treatment of Ce(NO3)3·6H2O using polyvinylpyrrolidone as a surfactant. The structure and morphology of the products were characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy, high-resolution transmission electron microscopy, and field-emission scanning electron microscopy (FE-SEM). The optical properties of the nanospheres were determined using UV and visible spectroscopy and photoluminescence (PL). The valence states of Ce ions were also determined using X-ray absorption near edge spectroscopy. The XRD results indicated that the synthesized samples had a cubic structure with a crystallite size in the range of approximately 9 to 19 nm. FE-SEM micrographs showed that the samples had a spherical morphology with a particle size in the range of approximately 100 to 250 nm. The samples also showed a strong UV absorption and room temperature PL. The emission might be due to charge transfer transitions from the 4f band to the valence band of the oxide. The magnetic properties of the samples were studied using a vibrating sample magnetometer. The samples exhibited room temperature ferromagnetism with a small magnetization of approximately 0.0026 to 0.016 emu/g at 10 kOe. Our results indicate that oxygen vacancies could be involved in the ferromagnetic exchange, and the possible mechanism of formation was discussed based on the experimental results.