High-resolution Transmission Electron Microscopy Micrographs Research Articles

Materials growth and band offset determination of Al2O3/In0.15Ga0.85Sb/GaSb/GaAs heterostructure grown by metalorganic chemical vapor deposition

The ternary InxGa1-xSb epilayers grown on GaAs substrates by metalorganic chemical vapor deposition using a GaSb buffer layer have been demonstrated. High–resolution transmission electron microscopy micrographs illustrate an entirely relaxed GaSb buffer grown by the interfacial misfit dislocation growth mode. A high quality In0.15Ga0.85Sb epilayer was obtained on the GaSb surface with the very low threading dislocation densities (∼8.0 × 106 cm−2) and the surface roughness was 0.87 nm. The indium content of the InxGa1-xSb epilayer depends significantly on the growth temperature and approaches to a saturated value of 15% when the growth temperature was above 580 °C. Based on the X-ray photoelectron spectroscopy analyses, the valence band offset and the conduction band offset of Al2O3 with the In0.15Ga0.85Sb/GaSb/GaAs heterostructure are 3.26 eV and 2.91 eV, respectively. In addition, from the O1s energy-loss spectrum analysis, the band gap of Al2O3 is found to be ∼6.78 ± 0.05 eV.

Graphene quantum dots prepared from glucose as optical sensor for glucose

Quantum Dots (QDs) show promise materials for many technological applications. In this work we utilized a simple route to prepare graphene quantum dots (GQDs) using glucose carbonization. GQDs functionalized with phenylboronic acid receptors were employed as a sensing material for a nonenzymatic glucose sensor. Photoluminance spectra of GQDs were used as a property of optical sensor for glucose. GQDs considered as a good sensing probe because of its low toxicity, high photoluminance, water solubility and excelent photochemical properties. The prepared GQDs were characterized using UV-visible, Raman and photoluminance spectroscopies, X-ray diffraction and high resolution transmission electron microscopy (HRTEM). HRTEM micrographs confirmed the preparation of 7–10nm GQDs and the emission peak of the GQDs appeared at 450nm. The developed sensor has linear response to glucose over a concentration range of 4–40mM with a correlation coefficient of 0.97 and a low detection limit of approximately 3.0mM.

Size distribution and visible luminescence of silicon nanoparticles embedded in SiNx thin film: Role of RF power in PECVD

This paper presents, the studies of the influence of (radio frequency) RF power on the size distribution and visible photoluminescence (PL) of SiNx thin film deposited at 300[Formula: see text]C of substrate temperature by plasma enhanced chemical vapor deposition. RF power was varied (5–50[Formula: see text]W), and its aftereffect on the optical properties of thin films was investigated. By increasing the RF power between 5[Formula: see text]W and 25[Formula: see text]W, main PL peak showed a red shift with an increase in PL intensity, which is associated with an increase in the silicon nanocrystals size and density, respectively. Results obtained were confirmed with High-resolution transmission electron microscopy micrographs and from the statistical calculations. By attaining a precise RF power value, stable silicon nitride thin film with suitable optical properties can be achieved for the potential fabrication of optoelectronic devices.

Impact of interfacial misfit dislocation growth mode on highly lattice-mismatched InxGa1-xSb epilayer grown on GaAs substrate by metalorganic chemical vapor deposition

Highly lattice-mismatch (over 8%) ternary InxGa1-xSb alloy directly grown on GaAs substrates was demonstrated by metalorganic chemical vapor deposition (MOCVD). The influence of growth parameters, such as growth temperature, indium vapor composition, and V/III ratio, on the film properties was investigated, and it was found that the growth temperature has the strongest effect on the surface morphology and the crystal quality of the InxGa1-xSb epilayer. An optimized growth temperature of ∼590 °C and a V/III ratio of 2.5 were used for the growth of the InxGa1-xSb epilayer on GaAs that displays a lower surface roughness. High-resolution transmission electron microscopy micrographs exhibit that InxGa1-xSb epilayer growth on GaAs was governed by the interfacial misfit dislocation growth mode. Furthermore, the variation of the intermixing layer thickness at the InxGa1-xSb/GaAs heterointerface was observed. These results provide an information of growing highly lattice-mismatched epitaxial material systems by MOCVD growth process.

The use of castor oil and ricinoleic acid in lead chalcogenide nanocrystal synthesis

A green solution-based thermolysis method for the synthesis of lead chalcogenide (PbE, E = S, Se, Te) nanocrystals in castor oil (CSTO) and its isolate ricinoleic acid (RA) is described. The blue shift observed from the optical spectra of CSTO and RA-capped PbE nanocrystals (NCs) confirmed the evidence of quantum confinement. The dimensions of PbE NCs obtained from NIR absorption spectra, transmission electron microscopy (TEM), and X-ray diffraction (XRD) studies were in good agreement. The particle sizes estimated were in the range of 20, 25, and 130 nm for castor oil-capped PbS, PbSe, and PbTe, respectively. Well-defined close to cubic-shaped particles were observed in the scanning electron microscopy (SEM) images of PbSe and PbTe nanocrystals. The high-resolution TEM and selective area electron diffraction (SAED) micrographs of the as-synthesized crystalline PbE NCs showed distinct lattice fringes with d-spacing distances corroborating with the standard values reported in literature.

A novel method of synthesis and microstructural investigation of calcium titanate powders

A novel method, using calcium chloride bihydrate (CaCl2·2H2O and TiO2) as raw materials, to synthesize crystalline calcium titanate (CaTiO3) has been investigated by thermodynamic calculation and X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), differential scanning calorimetric-thermogravimetric analysis (DSC-TG), high resolution transmission electron microscopy (HR-TEM) etc. Using XRD technique analyzed experimental results revealed success of thermal sintering process, in which the mass ratio of M CaCl2·2H2O/MTiO2 = 2:1, holding temperature of 1073 K, preservation time 2 h, could be used to produce crystalline CaTiO3 powders. Ratio of Ca/Ti/O = 1:1:3 was verified by EDS pot-scan. According to SEM observation, the crystalline CaTiO3 powders are mainly composed of many separated particles with average size approximately 10 μm and have been demonstrated a strongly faceted morphology. The lattice plane, (112) is clearly observed in the HR-TEM micrograph and the lattice distance was measured as 0.27 nm.

Preparation and Catalytic Activity of Thermosensitive Ga2O3 Nanorods

Gallium oxide (β-Ga2O3) nanorods were prepared by ultrasonic irradiation of molten gallium in warm water to form α-GaO(OH). This precursor was then subjected to calcination in air at 600 °C for 3 h to form β-Ga2O3, as confirmed by X-ray diffraction (XRD). Field emission scanning electron microscopy (FE-SEM)/high-resolution transmission electron microscopy (HRTEM) micrographs revealed the formation of well-organized nanotubes/nanorods with homogeneous size distribution. The average length of the β-Ga2O3 nanorods was affected by the temperature of the water during sonication, decreasing from 480 to 72 nm with an increase in the temperature from 25 to 50 °C. A sharp decline in the particle size was also observed when the temperature was above 35 °C. The catalytic activity of the β-Ga2O3 nanorods was examined, as a model, during the dehydration reaction of xylose to furfural. Furfural is a versatile biomass-derived platform compound used for the synthesis of several strategic chemicals. This nanoscale catalys...

Nanostructure investigation of the layered ternary compound Ni3–xSn1–yTe2

The structure of Ni3−xSn1–yTe2 is characterized by layered structural motifs related to an average NiAs/Ni2In-type. Order/disorder phenomena were analyzed via a detailed nanostructure investigation including electron diffraction and high resolution transmission electron microscopy (HRTEM) in conjunction with image simulation. Dependent on the stoichiometry, commensurate and incommensurate satellite reflections with respect to the parent NiAs structure were observed in Fourier transform and electron diffraction pattern as a result of occupational modulation of Te and Sn atoms. For the commensurate case a triplication of the c-lattice parameter is evident as a result of Sn–Te–Te stacking. Further, HRTEM micrographs indicate additional ordering phenomena along the c* direction depending on Ni/vacancy ordering which was rationalized by an alternating filling of van der Waals gaps with Ni. Also morphological defects in bright field images were observed. HRTEM investigations prove that these morphological defects are of structural nature, i.e. they are based on domains shifted relative to each other (antiphase boundaries).

Characterization of Thin Carbon Films Produced by the Magnetron Sputtering Technique

Thin carbon films containing both amorphous and crystalline structures were produced by RF magnetron sputtering. The depositions of the carbon films were performed on Co buffer layers previously deposited on c-plane (0001) sapphire substrates. The thin carbon films were characterized by high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy, energy dispersive X-ray spectroscopy (EDS), and field emission scanning electron microscope (FEG-SEM). The Raman spectra confirmed the presence of amorphous and crystalline structures by the existence of an intense D band separated from the G band, indicating early stages of crystallization. The interplanar distance corresponding to the graphite structures was determined by using HRTEM micrographs.

The Two-Dimensional Nanocomposite of Molybdenum Disulfide and Nitrogen-Doped Graphene Oxide for Efficient Counter Electrode of Dye-Sensitized Solar Cells.

In this study, we reported the synthesis of the two-dimensional (2D) nanocomposite of molybdenum disulfide and nitrogen-doped graphene oxide (MoS2/nGO) as a platinum-free counter electrode (CE) for dye-sensitized solar cells (DSSCs). X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), and Raman spectroscopy were used to examine the characteristics of the 2D nanocomposite of MoS2/nGO. The cyclic voltammetry (CV), electrochemical impedance spectra (EIS), and the Tafel polarization measurements were carried out to examine the electrocatalytic abilities. XPS and Raman results showed the 2D behaviors of the prepared nanomaterials. HRTEM micrographs showed the direct evidence of the 2D nanocomposite of MoS2/nGO. The results of electrocatalytic examinations indicated the MoS2/nGO owning the low charge transfer resistance, high electrocatalytic activity, and fast reaction kinetics for the reduction of triiodide to iodide on the electrolyte–electrode interface. The 2D nanocomposite of MoS2/nGO combined the advantages of the high specific surface of nGO and the plenty edge sites of MoS2 and showed the promoted properties different from those of their individual constituents to create a new outstanding property. The DSSC with MoS2/nGO nanocomposite CE showed a photovoltaic conversion efficiency (PCE) of 5.95 % under an illumination of AM 1.5 (100 mW/cm2), which was up to 92.2 % of the DSSC with the conventional platinum (Pt) CE (PCE = 6.43 %). These results reveal the potential of the MoS2/nGO nanocomposite in the use of low-cost, scalable, and efficient Pt-free CEs for DSSCs.

Montmorillonite-mediated aggregation induces deformation of influenza virus particles

The interaction between influenza virus [subtype A/Puerto Rico/8/1934 H1N1, (PR8)] and montmorillonite (Mt) is investigated by transmission electron microscopy and biochemical methods to determine how PR8 morphology and viability is affected. The majority of the PR8 particles formed aggregates with the Mt. TEM analysis showed that the virus particles retained structural integrity after aggregation but exhibited changes in morphology when compared to isolated PR8 and Mt aggregated with bromelain-treated PR8 (surface glycoproteins removed). Virus deformation shows that the virions exhibit an attraction to the Mt faces, possibly through hydrophobic interaction. The mean projection area of the aggregated PR8 was (10.4±6.1)×103nm2 compared to (9.5±3.3)×103nm2 for PR8 missing the surface glycoproteins; and (8.0±3.9)×103nm2 for non-aggregated PR8 controls. The increase in projection area of the aggregated PR8 suggests that the viruses deformed to increase contact region with the Mt faces with a subsequent compression normal to the face. PR8 missing the surface protein also exhibited an increase in projection area, although to a lesser extent, indicating that both the surface glycoproteins and viral envelope are attracted to the Mt faces. Circularity calculations indicate that the aggregated PR8 (circularity: 0.69±0.16) are less round, i.e. more distorted, than either control PR8 (0.78±0.14) or aggregated PR8 without surface glycoproteins (0.76±0.12). The pleomorphic nature of influenza virus may allow it to survive the deformation induced by the Mt platelets. High resolution TEM micrographs revealed that the otherwise-round viruses flattened when in contact with platelet faces, thus increasing contact area with the Mt.The PR8 was found to remain infectious after aggregation although at a lower rate than PR8 controls. The apparent reduced infectivity is likely a result of each aggregate (containing ~102 viral particles) acting as a single infectious unit.

Morphological and chemical characterization of soot emitted during flaming combustion stage of native-wood species used for cooking process in western Mexico

The morphology, microstructure and chemical composition of soot particles emitted directly from biofuel cook stoves have been studied by using high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and ion beam analysis (IBA) techniques. Freshly emitted soot particles were collected using an eight stage cascade impactor that separates particles according to their size. The particulate matter is impacted on thin aluminum foil and copper grids for Transmission Electron Microscope. The analysis of HRTEM micrographs revealed the nanostructure and the particle size of soot chain. Results from the border-based fractal dimension indicated that main morphological differences observed in soot particles perhaps are associated to cook-stove chamber design. XPS analysis shows that particles are mainly composed by carbon and oxygen. The XPS C-1s spectra show carbon with three peaks corresponding to sp2, sp3 hybridization and carbon oxygen bond. Additionally, we determined the areal density (atoms/cm2) of the soot films and the purity of the substrates by means of IBA techniques.

Synthesis, characterization and application of luminescent silica nanomaterials

Monodispersed luminescent nanoparticles for ink-jet printing and bioimaging.

Room temperature NO2 gas sensing of Au-loaded tungsten oxide nanowires/porous silicon hybrid structure**Project supported by the National Natural Science Foundation of China (Grant Nos. 61274074 and 61271070) and the Key Research Program of Application Foundation and Advanced Technology of Tianjin, China (Grant No. 11JCZDJC15300).

In this work, we report an enhanced nitrogen dioxide (NO2) gas sensor based on tungsten oxide (WO3) nanowires/porous silicon (PS) decorated with gold (Au) nanoparticles. Au-loaded WO3 nanowires with diameters of 10 nm–25 nm and lengths of 300 nm–500 nm are fabricated by the sputtering method on a porous silicon substrate. The high-resolution transmission electron microscopy (HRTEM) micrographs show that Au nanoparticles are uniformly distributed on the surfaces of WO3 nanowires. The effect of the Au nanoparticles on the NO2-sensing performance of WO3 nanowires/porous silicon is investigated over a low concentration range of 0.2 ppm–5 ppm of NO2 at room temperature (25 °C). It is found that the 10-Å Au-loaded WO3 nanowires/porous silicon-based sensor possesses the highest gas response characteristic. The underlying mechanism of the enhanced sensing properties of the Au-loaded WO3 nanowires/porous silicon is also discussed.

Room temperature mechanosynthesis and microstructure characterization of nanocrystalline Si0.9Al0.1C

This article reports the synthesis and microstructure characterization of nanocrystalline Si0.9Al0.1C powder obtained by mechanical milling the mixture of Si, Al and graphite powders at room temperature under inert atmosphere. XRD patterns of ball-milled powders clearly reveal the nucleation of Si0.9Al0.1C phase after 5 h of milling and the stoichiometric cubic Si0.9Al0.1C is formed after 10 h of milling with crystallite size of ∼3 nm. Microstructure of ball-milled powders in terms of different lattice imperfections is characterized by employing both Rietveld's method of structure refinement using XRD data and high resolution transmission electron microscope (HRTEM). HRTEM micrographs of 10 h milled powder substantiate the formation of nanocrystalline Si0.9Al0.1C compound without any contamination and confirm the findings of Rietveld analysis using XRD data.

The effect of HNO3 on morphology, phase transformation, and luminescence properties of LaPO4:Eu3+ phosphors

LaPO4:Eu3+ powders with different morphologies were hydrothermally constructed by adjusting the amount of HNO3 without using a catalyst, surfactant, or template. The as-prepared products were characterized by photoluminescence spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution-transmission electron microscopy (HR-TEM), selected area electron diffraction (SAED), X-ray diffraction (XRD), infrared (IR) spectra, and X-ray photoelectron spectroscopy. The SEM study revealed that the amount of HNO3 played a crucial role in the morphology of the final products. The XRD results indicated that the as-prepared samples were in the monoclinic phase when 3mL of HNO3 was used. The HR-TEM micrographs and SAED results demonstrated that the prepared nanorods were single and crystalline in nature with HNO3, and that they grew preferentially along the [012] direction. The emission spectra showed that the LaPO4:Eu3+ samples had the strongest emission intensity when prepared with HNO3.

Substrate bias induced synthesis of flowered-like bunched carbon nanotube directly on bulk nickel

This paper reports the effect of substrate bias on the multiwalled carbon nanotube (MWCNT) deposited on nickel foil by microwave plasma enhanced chemical vapor deposition technique. The MWCNTs have been characterized by the scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), Raman spectroscopy, field emission and current–voltage characteristic of the heterojunction diode. The SEM images exhibit unique hierarchical flowered-like bunched and conformally coated MWCNTs. Substrate bias induced ion bombardment helps in the enhancement of hydrocarbon dissociation and is responsible for flowered-like MWCNTs growth. The HRTEM micrographs show the base growth mechanism for MWCNTs. The value of turn on field for emission decreases from 5.5 to 1.9V/μm and field enhancement factor increases from 927 to 4770, respectively, with the increase of substrate bias. The diode ideality factor of CNT/ n-Si heterojunction is evaluated as 2.4 and the on/off current ratio is found to be 7 at ±2V, respectively.

High resolution transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction studies of nanocrystalline manganese borohydride (Mn(BH4)2) after mechano-chemical synthesis and thermal dehydrogenation

Abstract In order to synthesize manganese borohydride, Mn(BH4)2, mechano-chemical activation synthesis (MCAS) of the (2LiBH4 + MnCl2) powder mixture was carried out by ball milling in a magneto ball mill. Both X-ray diffraction and TEM selected area electron diffraction patterns (SAEDPs) clearly confirm the presence of the Mn(BH4)2 and LiCl phases in the synthesized nanocomposite. No other phases were detected. Bright field high-resolution TEM imaging of the synthesized composite powder particles reveals the presence of nanograins consistent with LiCl and Mn(BH4)2 within the powder particles. Their respective grain sizes, estimated as the equivalent circle diameters (ECD) from the high-resolution TEM micrographs with the corrected sample standard deviations, are within the range of 14.1 ± 3.7 nm and 10.0 ± 2.9 nm for LiCl and Mn(BH4)2, respectively. The XRD patterns of the thermally dehydrogenated (Mn(BH4)2 + 2LiCl) nanocomposite do not exhibit any Bragg diffraction peaks belonging to either crystalline Mn or B. In contrast, the SAED patterns and EDS elemental maps provide strong evidence that both Mn and B exist in the dehydrogenated powder as crystalline phases α-Mn and β-B, respectively. The results show that the lack of XRD Bragg diffraction peaks is insufficient evidence that the Mn and B elemental products of Mn(BH4)2 thermolysis can be classified as being amorphous.

Size dependent electrical and magnetic properties of mechanically-activated MnFe2O4 nanoferrite

The manganese nanoferrite (MnFe2O4) with an average particle diameter of 15nm was synthesized by mechanical activation followed by low-temperature thermal treatment. The milling energy induced during activation of precursors for the synthesis of MnFe2O4 nano-powders has been calculated using the basic principles of the collision model. X-ray structural analysis using Rietveld refinement confirmed the formation of spinel phase of the material in the Fd3m space group. The diameter of the nano-powder of the material was confirmed from a high-resolution transmission electron microscope (HRTEM). From the HRTEM micrographs study reveals that the size of the nanoparticles can be controlled by the application of required milling energy or time. Dependence of relative dielectric constant and tangent loss of the material on the crystallite size has been thoroughly studied and correlated in our present study. Variation of dielectric parameters with frequency and temperature has been explained using different mechanisms. The resistive characteristics, dielectric relaxation and negative-temperature-co-efficient of resistance (NTCR) of the material obtained from complex impedance measurements has been correlated with the particle size. The change in activation energy with particle size suggests the presence of a typical conduction mechanism in the material. The saturation magnetization is found to be particle size dependent. The synthesized manganese nanoferrite has potential applications in magnetic storage device, site specific drug delivery systems (particularly in magnetic hypothermia for cancer treatment), magnetic imaging etc.

Quantitative compositional analysis of InxGa1−xN/GaN multiquantum wells in light-emitting diodes

Abstract