High-resolution Scanning Electron Microscopy Images Research Articles

High resolution SEM imaging of gold nanoparticles in cells and tissues.

The growing demand of gold nanoparticles in medical applications increases the need for simple and efficient characterization methods of the interaction between the nanoparticles and biological systems. Due to its nanometre resolution, modern scanning electron microscopy (SEM) offers straightforward visualization of metallic nanoparticles down to a few nanometre size, almost without any special preparation step. However, visualization of biological materials in SEM requires complicated preparation procedure, which is typically finished by metal coating needed to decrease charging artefacts and quick radiation damage of biomaterials in the course of SEM imaging. The finest conductive metal coating available is usually composed of a few nanometre size clusters, which are almost identical to the metal nanoparticles employed in medical applications. Therefore, SEM monitoring of metal nanoparticles within cells and tissues is incompatible with the conventional preparation methods. In this work, we show that charging artefacts related to non-conductive biological specimen can be successfully eliminated by placing the uncoated biological sample on a conductive substrate. By growing the cells on glass pre-coated with a chromium layer, we were able to observe the uptake of 10nm gold nanoparticles inside uncoated and unstained macrophages and keratinocytes cells. Imaging in back scattered electrons allowed observation of gold nanoparticles located inside the cells, while imaging in secondary electron gave information on gold nanoparticles located on the surface of the cells. By mounting a skin cross-section on an improved conductive holder, consisting of a silicon substrate coated with copper, we were able to observe penetration of gold nanoparticles of only 5nm size through the skin barrier in an uncoated skin tissue. The described method offers a convenient modification in preparation procedure for biological samples to be analyzed in SEM. The method provides high conductivity without application of surface coating and requires less time and a reduced use of toxic chemicals.

Synchrotron-based X-ray tomographic microscopy for visualization of three-dimensional collagen matrices.

Three-dimensional collagen matrices (3D-CMs) may be visualized by cumbersome reconstructions of serial sections. We report here on the method of synchrotron-based X-ray tomographic microscopy (SRXTM) to image 3D-CMs in native tissue probes. SRXTM of 3D-CMs (mucoderm®, mucograft®) was performed at the TOMCAT beamline of the Swiss Light Source (SLS) at the Paul Scherrer Institute (Villigen, Switzerland). SRXTM combines the advantages of high-resolution scanning electron microscopy (SEM) imaging with the low-resolution reconstructions of micro-CT (μCT) imaging. It may be used to non-destructively visualize and analyze structures within the 3D-CMs without the need of serial sectioning and reconstruction. High-resolution SRXTM is a useful tool in analyzing the topology and morphometry of structures in 3D-CMs. The outcome justifies the efforts in sophisticated data processing. SRXTM may help to understand the clinical characteristics of 3D-CMs in more detail.

Structural, optical and magnetic characterization of Zn1−xNixAl2O4 (0≤x≤5) spinel nanostructures synthesized by microwave combustion technique

Zn1−xNixAl2O4 (0≤x≤0.5) spinel nanostructures were synthesized by microwave combustion technique. Structural, vibrational, optical, morphological and magnetic properties were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), diffuse reflectance (DRS) and photoluminescence (PL) spectroscopy, high resolution scanning electron microscopy (HR-SEM), and vibrating sample magnetometry (VSM), respectively. The XRD pattern confirmed the formation of a single phase cubic spinel structure of ZnAl2O4 (gahnite), except for higher dopant concentrations for which a secondary phase was observed and validated by Rietveld refinement analysis. Different concentration levels of Ni2+ was used as the dopant in the zinc aluminate matrix. Decrease in lattice parameter and increase in porosity were observed on increasing Ni2+ concentration. The average crystallite size of the nanoparticles estimated using Debey–Scherrer׳s method was found to be in the range of 8.89–13.84nm. The William–Hall (W–H) analysis was used to study the effects of lattice strain over the crystallite size. FT-IR spectra showed the vibrational stretching frequencies corresponding to the zinc aluminate spinels. The optical band gap value of undoped zinc aluminate nanostructure is higher than the reported bulk zinc aluminate. The direct band gap estimated using the Kubelka–Munk method decreased with increasing Ni2+ content (5.05–3.98eV), due to the formation of subbands in the energy gap. The HR-SEM images depict the formation of well developed nano-sized clusters with homogeneous well crystallized grains without any agglomerations. The PL characteristics of undoped and Ni2+ doped zinc aluminates are suggestive of defect controlled process. Magnetic measurements revealed that the undoped ZnAl2O4 has diamagnetic behavior while the Ni2+ doped ZnAl2O4 system has superparamagnetic behavior, despite NiO impurities.

Smaller is less stable: Size effects on twinning vs. transformation of reverted austenite in TRIP-maraging steels

Steels containing reverted nanoscale austenite (γRN) islands or films dispersed in a martensitic matrix show excellent strength, ductility and toughness. The underlying microstructural mechanisms responsible for these improvements are not yet understood, but are observed to be strongly connected to the γRN island or film size. Two main micromechanical effects are conceivable in this context, namely: (i) interaction of γRN with microcracks from the matrix (crack blunting or arresting); and (ii) deformation-induced phase transformation of γRN to martensite (TRIP effect). The focus here is on the latter phenomenon. To investigate size effects on γRN transformation independent of other factors that can influence austenite stability (composition, crystallographic orientation, defect density, surrounding phase, etc.), a model (TRIP-maraging steel) microstructure is designed with support from diffusion simulations (using DICTRA software) to have the same, homogeneous chemical composition in all γRN grains. Characterization is conducted by in-situ tension and bending experiments in conjunction with high-resolution electron backscatter diffraction mapping and scanning electron microscopy imaging, as well as post-mortem transmission electron microscopy and synchrotron X-ray diffraction analysis. Results reveal an unexpected “smaller is less stable” effect due to the size-dependent competition between mechanical twinning and deformation-induced phase transformation.

FIB-SEM Instrument with Integrated Raman Spectroscopy for Correlative Microscopy

Confocal Raman Microscope (CRM) is integrated with Scanning Electron Microscope (SEM) and its standard analyzers such as Energy Dispersive X-ray spectroscope (EDX), that can be further equipped with Focused Ion Beam (FIB). This yields valuable chemical information about molecular composition and chemical bonds in the sample on top of the high resolution SEM image, elemental composition map by EDX, nano-prototyping capability by FIB, etc. In presented system, confocal setup of the Raman Microscope provides lateral resolution of 360 nm (with the 532 nm excitation laser). This is a high standard in the world of light microscopy, however, electron microscopy offers resolution more than 2 orders of magnitude better. Combining the CRM spectral image and high resolution SEM image acquired in-situ is therefore of great benefit. State-of-the-art Raman analyzers inside SEM use parabolic mirror for focusing the primary laser beam on the sample and collecting the Raman-scattered light. The lateral resolution of these systems typically does not exceed 2-5 μm. We achieve the resolution comparable with stand-alone instruments by integrating a full confocal light microscope with SEM. The integrated system is capable of Raman imaging which is an important property. When just a single spectrum is acquired, one can never be sure, whether the position calibration is off. Besides lateral scanning, vertical movement is also supported, which allows non-destructive 3D tomography of laser transparent samples. Combination of CRM chemical analysis and SEM high resolution imaging makes this tool ideal for use in chemistry, medicine, biology, geology, forensic science and many other fields. The integration is feasible with two types of electron columns: conventional (LYRA) and immersion (GAIA). The immersion column [1] is recommended for non-conductive or fragile samples, because it offers better resolution at low acceleration voltages (1 nm at 15 kV and 1.4 nm at 1 kV). Its three-lens design is equipped with a Schottky field-emission gun and it offers multiple display modes (for ultrahigh resolution, large field of view or increased depth of focus) as well as a field-free mode for investigating magnetic samples.

Quaternary deep-sea ostracode taxonomy of Ocean Drilling Program Site 980, eastern North Atlantic Ocean

Ocean Drilling Program (ODP) Holes 980 B and C, Feni Drift at the eastern slope of the Rockall Plateau, eastern North Atlantic, were examined for late Quaternary deep-sea ostracode taxonomy. Nineteen genera and 32 species were examined and (re-)illustrated with high-resolution scanning electron microscopy images. One new speciesCytheropteron paramassonin. sp. is described and one new nameEucytherura zehaliis proposed forEucytherura hazeliYasuhara et al., 2009. This study provides updated taxonomic information for deep-sea ostracode genera and species from the eastern North Atlantic, which is an important baseline for application of deep-sea ostracodes to paleoceanographical reconstructions and paleoecological studies in this region.

In-situ preparation and characterization of acid functionalized single walled carbon nanotubes with polyimide nanofibers.

Nanofiber composites (Polyimide/f-SWCNT) of Pyromellitic dianhydride, 4,4'-Oxydianiline, and 4,4'-(4,4'-isopropylidene diphenyl-1,1'-diyl dioxy) dianiline (PMDA-ODA/IDDA) and surface-functionalized single walled carbon nanotubes (f-SWCNT) were made by electrospinning a solution of poly(amic acid) (PAA) containing 0-2 wt% f-SWCNT followed by thermal imidization. X-ray photoelectron spectroscopy spectra verified the oxidation of SWCNT surface after acid treatment, and indicated possible hydrogen bonding interactions between the f-SWCNTs and polyamic acid. High-resolution scanning electron microscopy images showed the average diameter of nanofibers to be below 150 nm, and transmission electron microscopy images showed that SWCNTs were aligned inside the polymer nanofiber. In thermogravimetric analysis, all composites showed increased thermal stability with increasing f-SWCNT content compared to neat PI. Storage modulus also increased from 124 MPa to 229 MPa from neat PI to 2% f-SWCNT composite.

Structural and Magnetic Properties of Co diffused CdTe Nanocrystalline Thin Films Deposited by Electron Beam Evaporation

Co diffused cadmium telluride (CdTe) nanocrystalline thin films with different Co content were prepared by depositing CdTe/Co stacked layers on glass substrates at 373 K using electron beam evaporation technique. The effect of Co content on structural, morphological, chemical, Raman, and magnetic studies were carried out. X-ray diffraction (XRD) patterns confirmed that all Co diffused CdTe films are in zinc blende structure. The lattice parameter increased with increase of Co content. The high-resolution scanning electron microscopy (HRSEM) images illustrated the grain size of the films. EDAX data confirmed the presence of Co, Cd, and Te with nearly stoichiometic. Raman spectra revealed peaks corresponding to A1, TO, and LO modes of CdTe and gradual shift in peak position. The increase in intensity confirmed the incorporation of Co into CdTe host lattice. Magnetic measurements showed a clear well-defined room temperature ferromagnetic hysteresis loop.

LaNiO3 nanotubes produced using a template-assisted method.

We have studied the experimental conditions needed to produce LaNiO3 (LNO) nanostructures using a template-assisted method. In this route, a mesoporous anodic aluminum oxide template was filled with a chemical solution that had been prepared with polymeric precursors route. The precursor solutions and synthesized samples were characterized by X-ray diffraction (XRD), thermogravimetric analysis, infrared spectroscopy and high-resolution scanning electron microscopy (HRSEM). The XRD results for the samples that were heat-treated at 700 degrees C revealed that these samples crystallize in a perovskite-like LaNiO3 structure. HRSEM images revealed that the samples prepared with different deposition times (0.5, 1 and 2 h) promoted the formation of LaNiO3 nanotubes with different wall thicknesses.

Facile Construction of Heterostructured BiVO4–ZnO and Its Dual Application of Greater Solar Photocatalytic Activity and Self-Cleaning Property

Development of coupled semiconductor oxides makes a significant advancement in catalytic functional materials. In this article, we report the preparation of nanobundle-shaped BiVO4–ZnO photocatalyst by a simple hydrothermal process followed by thermal decomposition. The photocatalyst was characterized by X-ray powder diffraction (XRD), high-resolution scanning electron microscopy (HR-SEM), field emission scanning electron microscopy (FE-SEM), energy-dispersive spectroscopy (EDS), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), photoluminescence spectroscopy (PL), and UV–vis diffuse reflectance spectroscopy (DRS). The XRD pattern confirmed formation of monoclinic scheelite BiVO4 and the hexagonal wurtzite structure of ZnO. HR-SEM images show nanobundle-like structure, and the size of the nanospheres ranges from 20 to 40 nm. BiVO4–ZnO has increased absorption in the UV and visible region when compared to ZnO. The cata...

Atomic Layer Deposition of Al-Doped ZnO/Al2O3 Double Layers on Vertically Aligned Carbon Nanofiber Arrays

High-aspect-ratio, vertically aligned carbon nanofibers (VACNFs) were conformally coated with aluminum oxide (Al2O3) and aluminum-doped zinc oxide (AZO) using atomic layer deposition (ALD) in order to produce a three-dimensional array of metal-insulator-metal core-shell nanostructures. Prefunctionalization before ALD, as required for initiating covalent bonding on a carbon nanotube surface, was eliminated on VACNFs due to the graphitic edges along the surface of each CNF. The graphitic edges provided ideal nucleation sites under sequential exposures of H2O and trimethylaluminum to form an Al2O3 coating up to 20 nm in thickness. High-resolution transmission electron microscopy (HRTEM) and scanning electron microscopy images confirmed the conformal core-shell AZO/Al2O3/CNF structures while energy-dispersive X-ray spectroscopy verified the elemental composition of the different layers. HRTEM selected area electron diffraction revealed that the as-made Al2O3 by ALD at 200 °C was amorphous, and then, after annealing in air at 450 °C for 30 min, was converted to polycrystalline form. Nevertheless, comparable dielectric constants of 9.3 were obtained in both cases by cyclic voltammetry at a scan rate of 1000 V/s. The conformal core-shell AZO/Al2O3/VACNF array structure demonstrated in this work provides a promising three-dimensional architecture toward applications of solid-state capacitors with large surface area having a thin, leak-free dielectric.

Synthesis, structural and property studies of Ni doped cadmium sulphide quantum dots stabilized in DETA matrix

Pure and Nickel doped cadmium sulphide nanoparticles at pH value 10 with three different concentrations have been synthesized by chemical precipitation method. Diethylene triamine was used as stabilizing agent to control the particle size as quantum dots without any agglomeration. The synthesized samples were characterized with X-ray diffraction (XRD), High resolution scanning electron microscopy (HRSEM), Energy dispersive X-ray analysis (EDAX), Transmission electron microscopy (TEM), Ultraviolet–Visible absorption spectroscopy (UV–VIS), Fourier transform infrared (FTIR) spectroscopy and photoluminescence (PL) studies. The nano crystalline nature of the as prepared samples is confirmed using XRD analysis. The average size of Ni doped cadmium sulphide nanoparticles calculated from Debye Scherer formula was of the order of 1.5–3nm and that of pure CdS nanoparticles was of the order of 6–7nm. The same value of the particle size was confirmed by using Williamson Hall plot as well as Henglein’s formula. X-ray peak broadening analysis was carried out using Williamson–Hall plot. The surface morphology studies of the sample using HRSEM images show the formation of nanoclusters and the EDAX spectra confirms the presence of cadmium sulphide and nickel elements in the sample. TEM images establish the stabilization of CdS nanoparticles in DETA. The UV–VIS absorption spectra of the sample show blue shift in the absorption region due to the quantum confinement effect. FTIR studies have been carried out to establish the presence of bonding by capping agent in the Ni doped samples. The synthesized samples show photoluminescence in the spectral region from 350 to 550nm, the visible region of the electromagnetic spectrum.

Taxonomic revision of deep-sea Ostracoda from the Arctic Ocean

Taxonomic revision of deep-sea Ostracoda from the Arctic Ocean was conducted to reduce taxonomic uncertainty that will improve our understanding of species ecology, biogeography and relationship to faunas from other deep-sea regions. Fifteen genera and 40 species were examined and (re-)illustrated with high-resolution scanning electron microscopy images, covering most of known deep-sea species in the central Arctic Ocean. Seven new species are described: Bythoceratina lomonosovensis n. sp., Cytheropteron parahamatum n. sp., Cytheropteron lanceae n. sp.,Cytheropteron irizukii n. sp., Pedicythere arctica n. sp., Cluthiawhatleyi n. sp., Krithe hunti n. sp. This study provides a robust taxonomic baseline for application to paleoceanographical reconstruction and biodiversity analyses in this climatically sensitive region.

Facile fabrication of highly efficient, reusable heterostructured Ag–ZnO–CdO and its twin applications of dye degradation under natural sunlight and self-cleaning

A metal doped coupled semiconductor oxide, Ag–ZnO–CdO was fabricated by a simple co-precipitation method and characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), elemental mapping, high-resolution scanning electron microscopy (HR-SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET) surface area measurement, UV-Vis diffuse reflectance spectroscopy (DRS) and photoluminescence spectroscopy (PL). XRD and EDS reveal the presence of CdO and metallic Ag in the catalyst. FESEM shows a mixture of hexagonal nanosheets, nanoclusters and nanoparticles with a large number of cavities. HR-SEM and TEM images of the catalyst show that ZnO particles have pentagonal or hexagonal plate-like structure. Cadmium oxide and silver clusters are formed on the clear smooth surface of ZnO. Ag–ZnO–CdO has increased absorption in the UV and Visible region when compared to ZnO. This three component nanojunction system exhibited enhanced photocatalytic activity for the degradation of acid black 1 (AB 1) and acid violet 7 (AV 7) under sunlight far exceeding those of the single and two component systems. Ag–ZnO–CdO was found to be stable and reusable without appreciable loss of catalytic activity up to five runs. This metal doped coupled oxide shows increased hydrophobicity, when compared to CdO or ZnO. Our results provide new insights of the performance of a solar active photocatalyst with self-cleaning properties.

Characterization and reduction of spectral distortions in Silicon-on-Insulator integrated Bragg gratings

A major issue in the fabrication of integrated Bragg grating filters in highly confined waveguides is the average effective index fluctuations caused by waveguide dimension variations. Lateral variations are caused by the sidewall roughness created during the etching process while vertical variations are coming from the wafer silicon layer thickness non-uniformity. Grating spectral distortions are known to result solely from the low spatial frequency components of these variations. As a result, in this work, we present an experimental method to quantify such relevant spatial components by stitching a hundred high-resolution scanning electron microscope images. Additionally, we propose two techniques to reduce, in the design, the phase noise impact on integrated Bragg gratings without relying on fabrication process improvements. More specifically, we show that the use of hybrid multimode/singlemode waveguides reduce by more than one order of magnitude the effect of sidewall roughness on integrated Bragg gratings while we show that the fabrication of ultra-compact gratings in spiral waveguides mitigate the impact of the silicon layer thickness variations.

Optical and magnetic properties of Mg-doped ZnFe2O4 nanoparticles prepared by rapid microwave combustion method

Mg-doped ZnFe2O4 samples were prepared by a microwave combustion method. The obtained samples were characterized by powder X-ray diffraction (XRD), high resolution scanning electron microscopy (HR-SEM), energy dispersive X-ray analysis, UV–Visible diffuse reflectance spectra (DRS), photoluminescence (PL) spectra and vibrating sample magnetometer (VSM). XRD results confirm the formation of cubic spinel-type structure with an average crystallite size in the range of 15–43nm. Lattice parameter decreases with increasing Mg concentration, due to the smaller ionic radius of Mg2+ ion. The HR-SEM images show the morphology of the samples as spherical shaped particles in agglomeration. The broad visible emission band is observed in the entire PL spectrum. The estimated band gap energy is found to decrease with increasing Mg content (2.15–1.42eV). The magnetization showed an increasing trend with increasing Mg concentration (x=0.5), due to the rearrangement of cations at tetrahedral and octahedral sites.

Development of nano-catalyzed membrane for PEM fuel cell applications

Nano-catalyzed membrane with different platinum (Pt) catalyst loadings (0.25 to 1 mg cm−2) was investigated for proton exchange membrane fuel cell applications, and the Pt loading on the Nafion membrane was prepared by non-equilibrium impregnation reduction method. The prepared catalyzed membranes were subjected to various characterisations, namely, X-ray diffraction, high-resolution scanning electron microscopy (HRSEM) with energy-dispersive X-ray, cyclic voltammetry, polarisation and electrochemical impedance spectroscopy. The polycrystalline fcc cubic structure and the particle size of Pt catalyst were estimated by X-ray diffraction analysis. The membrane with 0.4 mg cm−2 of Pt loading exhibits a favourable surface morphology which is confirmed by HRSEM image. Electrochemical investigations were clearly evident that the uniform distributions of Pt particles with fine pores on Nafion membrane facilitated the three-phase boundary which leads to a better cell performance. Electrochemical impedance spectroscopy demonstrated that the cell constructed using 0.4 mg cm−2 of platinum-loaded membrane has lower resistance than the other Pt loading.

Microwave combustion synthesis, structural, optical and magnetic properties of Zn1−xCoxAl2O4 (0 ⩽ x ⩽ 0.5) spinel nanostructures

Cobalt doped zinc aluminate spinel type nanostructures were synthesized by microwave combustion method. The structural, vibrational, optical, morphological and magnetic properties were studied by using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), diffuse reflectance spectroscopy (DRS), photoluminescence (PL), high resolution scanning electron microscopy (HR-SEM), energy dispersive X-ray diffraction (EDX) and vibrating sample magnetometry (VSM) respectively. The XRD patterns confirmed the formation of single phase ZnAl2O4 cubic spinel without impurities. The lattice parameter increased from 8.081 to 8.116Å with increasing Co2+ content. The average crystallite size of the nanoparticles estimated using Debey–Scherrer’s method was found to be in the range of 11.80–20.21nm. The presence of tensile strain in the zinc aluminates was determined from Williamson–Hall (W–H) analysis. FT-IR spectra showed the vibrational stretching frequencies corresponding to the zinc aluminate spinel structure. The direct band gap estimated using Kubelka–Munk method decreased with increasing Co2+ content (5.01–2.89eV), due to the formation of sub bands in between the energy gap. Optical absorption spectra confirmed the cobalt substitution by the occurrence of a triplet of bands at 542, 584, and 624nm, which is the characteristic of Co2+ ions in the tetrahedral sites. For ZnAl2O4 and Co substituted ZnAl2O4, PL spectra showed the emission bands in UV as well as in the visible regions, due to the defect centers acting as the trap levels. The elemental compositions of Co, Zn and Al were quantitatively obtained from the EDX analysis. HR-SEM images showed the features of well created pore structures and nano sized grains. Magnetic measurements revealed that the undoped ZnAl2O4 has diamagnetic behavior while the Co doped ZnAl2O4 system has superparamagnetic behavior.

Interaction of preosteoblasts with surface-immobilized collagen-based nanotubes

In a previous work, we demonstrated the successful use of electrophoretic deposition (EPD) to immobilize collagen-based nanotubes onto indium-tin-oxide-coated glass (ITO glass), leading to the creation of biointerfaces with protein-based chemistry and topography [1]. In this work, we present a first study of preosteoblasts behavior in contact with surface-immobilized collagen-based nanotubes. Changes in cell morphology after their interaction with ITO glass modified with collagen-based nanotubes were studied using fluorescence microscopy and compared to those observed on virgin ITO glass as well as on ITO glass on which a collagen layer was simply adsorbed. Scanning electron microscopy (SEM) was used to study interactions of cell filopodias with the deposited nanotubes. Cytotoxicity of these biointerfaces was examined as well in short term cultures, using Alamar blue assay.Cells showed particular morphologies on ITO glass coated with nanotubes compared to virgin ITO glass or collagen adsorbed layer on ITO glass. High resolution SEM images suggest that apart from cell morphology, length and thickness of filopodias seem to be significantly affected by surface modification with collagen-based nanotubes. Moreover, nanotube-coated ITO glass did not show any obvious cytotoxicity in short term culture, opening new perspectives for the surface modification of biomaterials. We show the versatility of the proposed surface modification procedure by tailoring biointerfaces with a mixture of micro- and nanometer-scale collagen-based tubes.

2D plasmonic gold nano-patches for linear and nonlinear applications

We demonstrate the fabrication of a 2D periodic arrangement of gold square nano-patches on both silicon and borosilicate glass substrates whose optical properties can be exploited for both linear and nonlinear applications. The comparison between numerical and experimental results, combined with high-resolution scanning electron microscopy images highlights the importance of the geometry and the fine shape in the determination of the square gold nano-patches optical properties.