High-resolution Transmission Electron Microscopy Techniques Research Articles

Optical, structural and electrical characterizations of stacked Hf-based and silicon nitride dielectrics

High-k stacked dielectric structures were fabricated by a combination of RF magnetron sputtering and plasma-enhanced chemical vapor deposition. Their structural properties were studied versus deposition and annealing conditions by means of attenuated total reflection and high-resolution transmission electron microscopy techniques. All samples demonstrated smoothed surface (with a roughness below 1nm) and abrupt interfaces between the different stacked layers. No crystallization of Hf-based layers was observed after annealing at 800°C for 30min, demonstrating their amorphous nature and phase stability upon annealing. Uniform capacitance–voltage characteristics were measured along the wafers for all stacks. Besides, after round-voltage sweep they demonstrate significant flat-band voltage hysteresis due to charging of the stack caused by carrier injection from the substrate. These phenomena were found to be more pronounced for the stacks with pure HfO2 layers. The stacked structures were implemented for the formation of Ge nanocrystals by means of ion implantation followed by the thermal treatment mentioned above. It was found that the spatial distribution of Ge crystallites in stacked dielectrics affects significantly their electrical properties including the trapping of charge.

Achieving excellent bandwidth absorption by a mirror growth process of magnetic porous polyhedron structures

A symmetrical Fe2O3/BaCO3 hexagonal cone structure having a height of 10 μm and an edge length of ~4 μm is reported, obtained using a common solvothermal process and a mirror growth process. Focused ion beam and high-resolution transmission electron microscopy techniques revealed that α-Fe2O3 was the single crystal feature present. Ba ions contributed to the formation of symmetrical structures exhibited in the final composites. Subsequently, porous magnetic symmetric hexagonal cone structures were used to study the observed intense electromagnetic wave interference. Electromagnetic absorption performance studies at 2–18 GHz indicated stronger attenuation electromagnetic wave ability as compared to other shapes such as spindles, spheres, cubes, and rods. The maximum absorption frequency bandwidth was at 7.2 GHz with a coating thickness d = 1.5 mm. Special structures and the absence of BaCO3 likely played a vital role in the excellent electromagnetic absorption properties described in this research.

Electrochemical Immunosensor for Detection of Atrazine Based on Polyaniline/Graphene

In this study, a novel layer-by-layer polyaniline/graphene (PANi/Gr) structure for electrochemical detection of atrazine was developed. Gr film was synthesized by thermal chemical vapor deposition (CVD) method and transferred onto the PANi-predeposited microelectrode. The properties of PANi/Gr film were thoroughly investigated by high-resolution transmission electron microscopy and Raman techniques. The most attractive feature of this system is a suitable microenvironment, which could provide an amplification of the conductive signal, thus may contribute to enhancing electron transfer and subsequently improve the sensitivity in electrochemical measurements. With low detection limit (∼ 43 × 10−12 g/L), acceptable stability and good reproducibility, the proposed electrochemical immunosensor could be advantageously extended for multiplexed detection of other agents of environmental pollution.

Aging behavior and precipitate characterization of a high Zn-containing Al-Zn-Mg-Cu alloy with various tempers

In the present work, the influence of one-step and two-step aging treatments on hardness, electrical conductivity and mechanical properties of a high Zn-containing Al-Zn-Mg-Cu alloy is investigated and detailed aging parameters subjected to various aging tempers, i.e., T6, T79, T76, T74 and T73, are proposed. The nanoscale precipitates under different tempers are qualitatively investigated by means of transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HREM) techniques. Based on the precipitate observations, precipitate size distributions and neighbor precipitates distances are extracted from bright-field TEM images projected along 〈110〉Al orientation with the aid of an imaging analysis. The results show that with the deepening of aging degree, the conductivity of one-step and two-step aging increase continuously while the hardness increases for one-step aging and decreases for two-step aging at the second preservation. The tensile strength decreases as the aging degree deepens and the yield strength shows a similar trend. In addition, as the degree of over-aging deepens, the precipitate size distribution interval becomes broader, the average precipitate size turns larger and the average distance of neighbor precipitates also becomes greater. The influence of precipitates on mechanical properties is discussed.

Preparation and Photocatalytic Performance of One-Dimensional In2O3 Nanofibers, CuO Microfibers and CuO/In2O3 Heterostructured Nanofibers by Electrospinning Process

One-dimensional (1D) CuO/In2O3 heterostructured nanofibers with the diameter of about 300 nm were successfully prepared through combining a facile single-capillary electrospinning with sintering process, and investigated by thermogravimetric and differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) techniques, etc. The photocatalytic activities were examined by degrading methylene blue (MB) under 500W xenon lamp, halogen lamp and mercury lamp irradiation, respectively. The heterostructured nanofibers exhibited a higher photocatalytic activity than P25-TiO2 under 500W xenon lamp irradiation due to the enhanced absorption for visible light and the efficient electron–hole separation and transportation. The single CuO microfibers and In2O3 nanofibers were also prepared as the control groups by the same method.

Surface enhanced Raman spectroscopy and quantum chemical studies on glycine single crystal

Adsorption characteristics of glycine (Gly) on silver surface were investigated based on density functional theory calculations and surface enhanced Raman spectroscopy (SERS) technique. The single crystals of Gly were grown by slow evaporation method and characterized by single crystal X-ray diffraction (XRD) technique. Silver nanoparticles (Ag NPs) were prepared by solution combustion method using Gly as fuel. The Ag NPs were characterized by XRD, ultraviolet–visible spectroscopy and high-resolution transmission electron microscopy techniques. The calculated structural parameters of Gly molecule were compared with the experimental observed single crystal XRD data. The structural parameters of Gly after adsorption on silver surface show the slight deviation, which indicates the interaction between the Gly and Ag3 cluster. Raman and SERS spectra for Gly single crystal were studied experimentally. Raman frequencies were calculated for Gly and Gly adsorbed on a silver surface. Raman and SERS frequencies were assigned on the basis of potential energy distribution calculation and compared with the experimental values. Frontier molecular orbital analysis was carried out for Gly and Gly adsorbed on a silver surface. The band gap value was significantly reduced for Gly after adsorption on the silver surface. The reduction in band gap indicates the delocalization of electrons, which leads to the higher bioactivity of the title molecule. SERS spectral analysis reveals that the Gly adsorbed as a stand-on orientation on the silver surface. Hence, the present investigation has been developed as a model system to understand the interaction of Ag NPs with amino acids.

D-sorbitol-induced phase control of TiO2 nanoparticles and its application for dye-sensitized solar cells.

Using a simple hydrothermal synthesis, the crystal structure of TiO2 nanoparticles was controlled from rutile to anatase using a sugar alcohol, D-sorbitol. Adding small amounts of D-sorbitol to an aqueous TiCl4 solution resulted in changes in the crystal phase, particle size, and surface area by affecting the hydrolysis rate of TiCl4. These changes led to improvements of the solar-to-electrical power conversion efficiency (η) of dye-sensitized solar cells (DSSC) fabricated using these nanoparticles. A postulated reaction mechanism concerning the role of D-sorbitol in the formation of rutile and anatase was proposed. Fourier-transform infrared spectroscopy, 13C NMR spectroscopy, and dynamic light scattering analyses were used to better understand the interaction between the Ti precursor and D-sorbitol. The crystal phase and size of the synthesized TiO2 nanocrystallites as well as photovoltaic performance of the DSSC were examined using X-ray diffraction, Raman spectroscopy, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, and photocurrent density-applied voltage spectroscopy measurement techniques. The DSSC fabricated using the anatase TiO2 nanoparticles synthesized in the presence of D-sorbitol, exhibited an enhanced η (6%, 1.5-fold improvement) compared with the device fabricated using the rutile TiO2 synthesized without D-sorbitol.

Combustion synthesis and enhanced 1.5 μm emission in Y2O3:Er3+ powders codoped with La3+ ions

Er3+ and La3+ codoped Y2O3 nanocrystalline powders were synthesized by gel combustion method and characterized with thermal analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM) techniques and fluorescence spectroscopy. After being calcined at 1200 °C, the (Y1-xLax)2O3:Er3+ powders were confirmed to be cubic Y2O3 phase with the crystalline grain size in the range of 20-40 nm. The Er3+ emission at 1.53 μm from the 4I13/2→4I15/2 transition was observed, which was found to be enhanced by introducing La3+ ions. Such enhancement could be attributed to the adjustment of Er3+ ions' local environment by the codoping of La3+ ions, leading to the increased ground state absorption cross section of Er3+ ions.

A multi-analytical study on the sulphur components in some high sulphur Indian Tertiary coals

The main source of industrial energy in the world is coal. To better understand the distribution of sulphur containing components in high sulphur Tertiary coals, a multi-analytical analysis was carried out on four industrially important high sulphur northeast region (NER) Indian coals. Some of the relevant information on the distribution and speciation of sulphur functionalities in these Tertiary coals were obtained by using chemical analysis, X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM) and Mossbauer spectroscopy techniques. The study revealed the presence of various sulphur compounds such as pyrite (FeS2), disulphides (S–S), sulphone (−SO2–) and aryl thioether (R1–S–R2) in the coals, which are essential to be removed before the coal could be utilised. Sulphur is present in high amounts in MEG (4.54 %) and NG (4.56 %) coal samples. The lowest amount of sulphur was found in TP coal. In the present study, it is shown that the NER Tertiary coals contain higher amounts (>50 %) of organic sulphur, which may be difficult to remove by conventional methods. X-ray photoelectron spectroscopy (XPS) analysis of these Tertiary coals revealed that sulphur is present in two forms namely inorganic and organic. TPR also provide information on sulphur association in coals as iron pyrite, sulphides, thiophene, thiols, etc. Fe components in NER coals contain typically pyrite and Mossbauer spectroscopy where pyrite, illite, marcasite and hematite were observed, which is in agreement with the results obtained with other techniques.

Electrospinning synthesis of novel lithium-rich 0.4Li2MnO3·0.6LiNi1/3Co1/3Mn1/3O2 nanotube and its electrochemical performance as cathode of lithium-ion battery

In this study, a lithium-rich layered 0.4Li2MnO3·0.6LiNi1/3Co1/3Mn1/3O2 nanotube cathode synthesized by novel electrospinning is reported, and the effects of temperature on the electrochemical performance and morphologies are investigated. The crystal structure is characterized by X-ray diffraction patterns, and refined by two sets of diffraction data (R-3m and C2/m). Refined crystal structure is 0.4Li2MnO3·0.6LiNi1/3Co1/3Mn1/3O2 composite. The inductively coupled plasma optical emission spectrometer and thermogravimetric and differential scanning calorimetry analysis measurement supply reference to optimize the calcination temperature and heat-treatment time. The morphology is characterized by scanning and high-resolution transmission electron microscope techniques, and the micro-nanostructured hollow tubes of Li-rich 0.4Li2MnO3·0.6LiNi1/3Co1/3Mn1/3O2 composite with outer diameter of 200–400 nm and the wall thickness of 50–80 nm are synthesized successfully. The electrochemical evaluation shows that 0.4Li2MnO3·0.6LiNi1/3Co1/3Mn1/3O2 sintered at 800 °C for 8 h delivers the highest capacity of the first discharge capacity of 267.7 mAh/g between 2.5 V and 4.8 V at 0.1C and remains 183.3 mAh/g after 50 cycles. The electrospinning method with heat-treatment to get micro-nanostructured lithium-rich cathode shows promising application in lithium-ion batteries with stable electrochemical performance and higher C-rate performance for its shorter Li ions transfer channels and stable designed structure.

Sonocatalytic removal of naproxen by synthesized zinc oxide nanoparticles on montmorillonite

ZnO/MMT nanocomposite as sonocatalyst was prepared by immobilizing synthesized ZnO on the montmorillonite surface. The characteristics of as-prepared nanocomposite were studied by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM) and X-ray diffraction (XRD) techniques. The synthesized samples were used as a catalyst for sonocatalytic degradation of naproxen. ZnO/MMT catalyst in the presence of ultrasound irradiation was more effective compared to pure ZnO nanoparticles and MMT particles in the sonocatalysis of naproxen. The effect of different operational parameters on the sonocatalytic degradation of naproxen including initial drug concentration, sonocatalyst dosage, solution pH, ultrasonic power and the presence of organic and inorganic scavengers were evaluated. It was found that the presence of the scavengers suppressed the sonocatalytic degradation efficiency. The reusability of the nanocomposite was examined in several consecutive runs, and the degradation efficiency decreased only 2% after 5 repeated runs. The main intermediates of naproxen degradation were determined by gas chromatography–mass spectrometry (GC–Mass).

Ethylene glycol (EG) solvothermal synthesis of flower-like LiMnPO4nanostructures self-assembled with (010) nanobelts for Li-ion battery positive cathodes

Flower-like LiMnPO4 nanostructures self-assembled with nanobelts were synthesized via a simple ethylene glycol (EG) solvothermal route, in which lithium acetate, manganese acetate and phosphoric acid are used as the reaction precursors. The primary block LiMnPO4 nanobelts are dominated with (010) facets. X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM, and N2-physisorption technique were employed to characterize the microstructure and morphologies of the synthesized samples. On the basis of the experimental results, a possible formation mechanism of the flower-like LiMnPO4 nanostructures self-assembled with nanobelts has been discussed. In addition, the electrochemical performance of the mesoporous LiMnPO4 nanostructures is further investigated as positive cathodes in Li-ion batteries.

Microstructure and mechanical property of TiSiN nanocomposite film with inserted CrAlN nanomultilayers

Abstract A series of TiSiN films inserted by CrAlN nanomultilayers with different thicknesses was prepared by reactive magnetron sputtering. The influences of CrAlN layer thickness on the microstructure and hardness of films were investigated by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and nano-indentation techniques. The insertion of CrAlN nanomultilayers destructs the nanocomposite structure of TiSiN film, leading to the decrease of hardness. As the CrAlN layer thickness increases to 2.5 nm, CrAlN layers are inclined to grow epitaxially with TiSiN layers in order to lower the interfacial energy. As a result, the TiSiN film can be further strengthened with the maximal hardness of 53.9 GPa. As the CrAlN layer thickness further increases to 3.0 nm, the epitaxial growth structure between TiSiN and CrAlN layers is broken, resulting in the deterioration of hardness.

Insights into the conversion behavior of SiO-C hybrid with pre-treated graphite as anodes for Li-ion batteries

A SiO/graphite/amorphous carbon (SiO-C) hybrid anode with superior electrochemical performance is successfully realized by using a low-cost and simple method. Here, we apply a pretreatment of commercialized graphite by ball-milling to realize evenly dispersion of the components and good effect of carbon coating, thus resulting in excellent cycling stability. Specifically, the as-prepared sample shows a high reversible capacity of 850mAhg−1 after 100 cycles at 100mAg−1 and excellent rate capability of 730mAhg−1 even at 500mAhg−1. Additionally, a relatively high initial coulombic efficiency of 77% is delivered among SiO-based anode materials. High-resolution transmission electron microscope (HRTEM) technique is used to further visually verify the conversion behavior of SiO in the first cycle: scattered amorphous silicon particles with size about 5nm and irreversible Li4SiO4 as the detected resultants. The result of electrochemical impedance spectroscopy (EIS) reveals that the polarization resistance (Rp) decreases with pre-treated graphite. This work presents a facile approach to prepare Si-based anode material for new generation lithium-ion batteries with high energy density and more insights into the conversion behavior of SiO.

Highly efficient anode catalyst with a Ni@PdPt core–shell nanostructure for methanol electrooxidation in alkaline media

To enhance the electrocatalytic activity of anode catalysts used in alkaline-media direct methanol fuel cells (DMFCs), a Ni@PdPt electrocatalyst was successfully prepared using a three-phase-transfer method. The Ni@PdPt electrocatalyst was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and high-resolution TEM (HRTEM) techniques. The experimental results indicate that the average particle size of the core–shell-structured Ni@PdPt electrocatalyst is approximately 5.6 nm. The Ni@PdPt electrocatalyst exhibits a catalytic activity 3.36 times greater than that of PdPt alloys for methanol oxidation in alkaline media. The developed Ni@PdPt electrocatalyst offers a promising alternative as a highly electrocatalytically active anode catalyst for alkaline DMFCs.

Factors Affecting the Growth Behavior of De-lonized Water Assisted Carbon Nanotube Forests.

The aim of this work is to analyze the conditions for producing water assisted carbon nanotubes (WA-CNT) forests by varying parameters that include growth temperature; de-ionized (DI) water flow; carbon-containing gas flow; and thereby determine the length, impurities and catalyst utilization in the CNT forest. Most importantly, the impact of water molecules on the length and catalyst utilization of the CNT forest was investigated. The CNT forests with lengths up to 140 microns were grown using a chemical vapor deposition technique at atmospheric pressure. The forest bundles had weak adhesion with the substrate which allows them to be peeled off easily, enabling easy transfer to other substrates. The characterization of CNT forest were carried out using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and high-resolution transmission electron microscopy (HR-TEM) techniques.

Spherulitic copper-copper oxide nanostructure-based highly sensitive nonenzymatic glucose sensor.

In this work, three different spherulitic nanostructures Cu–CuOA, Cu–CuOB, and Cu–CuOC were synthesized in water-in-oil microemulsions by varying the surfactant concentration (30 mM, 40 mM, and 50 mM, respectively). The structural and morphological characteristics of the Cu–CuO nanostructures were investigated by ultraviolet–visible (UV–vis) spectroscopy, X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy techniques. The synthesized nanostructures were deposited on multiwalled carbon nanotube (MWCNT)-modified indium tin oxide (ITO) electrodes to fabricate a nonenzymatic highly sensitive amperometric glucose sensor. The performance of the ITO/MWCNT/Cu–CuO electrodes in the glucose assay was examined by cyclic voltammetry and chronoamperometric studies. The sensitivity of the sensor varied with the spherulite type; Cu–CuOA, Cu–CuOB, and Cu–CuOC exhibited a sensitivity of 1,229, 3,012, and 3,642 µA mM−1·cm−2, respectively. Moreover, the linear range is dependent on the structure types: 0.023–0.29 mM, 0.07–0.8 mM, and 0.023–0.34 mM for Cu–CuOA, Cu–CuOB, and Cu–CuOC, respectively. An excellent response time of 3 seconds and a low detection limit of 2 µM were observed for Cu–CuOB at an applied potential of +0.34 V. In addition, this electrode was found to be resistant to interference by common interfering agents such as urea, cystamine, L-ascorbic acid, and creatinine. The high performance of the Cu–CuO spherulites with nanowire-to-nanorod outgrowths was primarily due to the high surface area and stability, and good three-dimensional structure. Furthermore, the ITO/MWCNT/Cu–CuOB electrode applied to real urine and serum sample showed satisfactory performance.

Effect of Ti diffusion on the microstructure of Ge2Sb2Te5 in phase-change memory cell.

The dependence of the microstructure of Ge2Sb2Te5 (GST) on Ti diffusion into GST by annealing in GST/Ti/TiN phase-change random access memory stack was studied by various transmission electron microscopy (TEM) techniques. The microstructure and crystal structure of GST were identified with high-resolution TEM (HRTEM) and image simulation technique, and the Ti diffusion into GST was revealed by scanning transmission electron microscope-energy-dispersive X-ray spectroscopy analysis. It was observed that Ti atoms of Ti/TiN thin layers were incorporated into GST cell through several thermal annealing steps and they could retard the phase transition from face-centered cubic (FCC) phase into hexagonal close-packed (HCP) phase partially and restrain the increase in grain size. Thus, it is concluded that Ti diffusion can affect the microstructure of GST including the type of the crystal phase and grain size of GST. It was shown that the insertion of diffusion barrier between TiN and GST could block Ti diffusion into GST and make it possible for FCC phase to completely transform into HCP phase.

Strong effects of gallia on structure and selective responses of Ga2O3–In2O3 nanocomposite sensors to either ethanol, CO or CH4

Gallia–In2O3 nanocomposite sensors containing 0–75wt% gallia calcined at 500–850°C are fabricated via co-precipitation method and their response to ethanol, CO, methane and volatile organic compounds is investigated at different operating temperatures. The samples were characterized by X-ray diffraction, energy-dispersive X-ray spectroscopy, high-resolution transmission electron microscopy and BET surface area measurement techniques. Depending on gallia content and calcination temperature, different phases of α- and β-Ga2O3 and c- and rh-In2O3 are formed. The sensors’ responses and selectivities strongly depend on their gallia content and operating and calcination temperatures. At 300°C, 10wt% Ga2O3–In2O3 and 25wt% Ga2O3–In2O3 sensors calcined at 500°C show maximum response to ethanol and CO, respectively, while the maximum response to methane is observed at 400°C by the sensor containing 65wt% Ga2O3. 25wt% Ga2O3–In2O3 calcined at 850°C is selective to methane at 400°C, however, 75wt% Ga2O3–In2O3 calcined at 650°C shows no response to methane. Also, this sensor calcined at 850°C is selective to either CO or methane at 350 and 650°C, respectively, in presence of ethanol and other volatile organic compounds. The sensor containing 65wt% gallia calcined at 500°C is selective to CO in presence of ethanol and methane at 250°C. In addition, the sensor containing 25wt% gallia is selective to VOCs in presence of CO and methane, at the low temperature of 200°C.

Mechanism in the β phase evolution during hot deformation of Ti–5Al–2Sn–2Zr–4Mo–4Cr with a transformed microstructure

The mechanism in the β phase evolution during hot deformation of a near β titanium alloy Ti–5Al–2Sn–2Zr–4Mo–4Cr with a transformed microstructure was investigated in the present work by the high-resolution electron backscatter diffraction (EBSD) and transmission electron microscope (TEM) techniques. The β phase exhibits significant variation in orientation, local texture and grain boundary during hot deformation, which is highly related to the globularization of α platelets. Kinking of the α platelets promotes the continuous dynamic recrystallization (CDRX) of β phase by increasing the misorientation, and formation of the globular α grains assists in the recrystallization of β phase via grain boundary sliding. The strain rate plays an important role in the β phase evolution as well which is greatly affected by the α phase evolution. The recrystallization of β phase is more evident during kinking at a higher strain rate where a structure with more and finer β recrystallized grains occurs, while dynamic recovery (DRC) is the main mechanism in the β phase where the globularization of α phase is relatively low at a larger strain.