A study of electron-beam-evaporated MgO films using electron diffraction,optical absorption and cathodoluminescence

Reflection high energy electron diffraction, optical absorption and cathodoluminescence were used to study MgO films deposited onto fused silica, single- crystal silicon and LiF substrates at various temperatures. Results showed that some of the same optical absorption and emission bands observed in X- or UV- irradiated, additively colored or mechanically deformed MgO crystals were observed in evaporated MgO films. The peak positions and the relative peak intensities of the optical absorption and emission bands depended on the substrate temperature during film deposition as well as on the structure of the film. The effect of heating the films in air and vacuum on the optical absorption and emission bands is also discussed.     

Carbon films: Structure and microtexture (optical and electron microscopy,Raman spectroscopy)

Nearly pure carbon films (150 and 500 Å thick) were prepared by condensing carbon vapour in vacuum. They were then heat treated under an inert gas flow from 25 to 2700 °C. The samples were studied comparatively with (1) a conventional transmission electron microscope (structure and microtexture), (2) a Raman microprobe (for quantification of the different types of defect by Raman spectroscopy) and (3) an optical microscope (for determination of the optical indices). The carbon films were found to graphitize in five stages. Each stage is characterized by the release of a given type of defect. Crystal growth occurs first in thickness and then in diameter. Perfect aromatic layers are formed progressively and the three-dimensional order improves. Polycrystalline graphite is then obtained. The graphitization is faster and more complete for thick films (about 500 Å thick) than for thin films (about 150 Å).     

Individual cathodoluminescence and photoluminescence spectroscopy of zinc oxide nanoparticles in combination with in situ transmission electron microscopy

The functions of scanning near-field optical microscopy (SNOM) were installed in high-resolution transmission electron microscopy (TEM) for cathodoluminescence spectroscopy and photoluminescence spectroscopy of individual nanostructures. Optical fiber probes used in SNOM were allowed to approach nanoparticles by piezomanipulation with simultaneous observation by TEM. As an application of this method, cathodoluminescence and photoluminescence from zinc oxide nanoparticles were measured at room temperature and 130 K. It was demonstrated that the present method directly provides the relationships between structural features of individual nanoparticles and spectra.     

Quantitative characterization of clay dispersion in polypropylene-clay nanocomposites by combined transmission electron microscopy and optical microscopy

This paper presents a novel method to describe the microstructure of polymer/clay nanocomposites quantitatively. Based on the image analyses of transmission electron microscopy (TEM) and optical microscopy micrographs, two parameters, degree of dispersion (χ) and mean interparticle distance per unit volume of clay (λ_V) are proposed to describe the level of clay dispersion. The degree of dispersion gives the percentage of exfoliation, and λ_V is a measure of spatial separation between particles relative to clay loading. A polypropylene/clay system was chosen as an example to show the effects of processing conditions and biaxial stretching on clay dispersion using the proposed quantifiers. It provides insights into the ‘real’ clay dispersion using a combination of both microscopical and macroscopical aspects.     

Local structure modulation of the low La-doped layered strontium manganite Sr4Mn3O10 studied by transmission electron microscopy and electron energy-loss spectroscopy

Transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS) have been used to characterize the structure and microstructure of the low La-doped layered manganite La _x Sr_4−x Mn₃O₁₀ (x ≤ 0.15). The structure of the perfect phase has been identified as an n = 3 layered structure of the hexagonal series by electron diffraction (ED), high-resolution electron microscopy (HRTEM) together with numerical image simulations. The presence of local superstructure modulation associated with La ordering in the compounds was revealed by electron diffraction and high-resolution electron microscopy. Electron diffraction data indicate that this superstructure modulation is two-dimensional, and the modulation plane lies in the ac plane. The two primary modulation vectors are and In addition, another type of modulated structure associated with periodic lattice distortion was occasionally visible in the La_0.15Sr_3.85Mn₃O₁₀ phase. Energy-loss spectroscopy data indicate that the periodic lattice distortion is led by ordered oxygen deficiency.     

A transmission electron microscopy study of particulate concentrations in seven individual snowflakes

An electron microscope analysis of seven individual snowflakes, which were collected over a six-hour period and allowed to dry upon collodion support films, showed the particle concentration to increase with elapsed time of snowfall, reach a maximum at $\text{3}\text{4}$ of the duration, and to essentially stabilize thereafter. The size of the particles ranged from less than 0.01 μm to 4.5 μm in diameter, with average particle size first increasing then decreasing with elapsed time of snowfall. The particle concentration in individual snowflakes was observed to be roughly 5 times greater than that observed previously in individual raindrops in the same geographic area, and there was no evidence of asbestiform fibers.     

Recent advances in electron imaging, image interpretation and applications: environmental scanning electron microscopy

One of the latest developments in electron microscopy is the environmental scanning electron microscope (ESEM), which enables soft, moist and/or electrically insulating materials to be viewed without pre-treatment, unlike conventional scanning electron microscopy, in which specimens must be solid, dry and usually electrically conductive. Such an advance has significant implications for studies of the 'native' surfaces of specimens including rocks and minerals, polymers, biological tissues and cells, food and pharmaceutical products, precious artefacts and forensic material, for example. Previous types of electron microscopes made scientists think carefully about the physics of electron-beam interactions with specimens and, hence, the interpretation of images. We now face additional factors influencing the emission and detection of electron signals, unique to the imaging of specimens in the partial vacuum of an ESEM. Just as importantly, we must consider the thermodynamic and kinetic stability of specimens, as appropriate, and explore the possibilities for new applications, particularly those of a dynamic nature. This paper briefly describes some of the issues involved and reviews the current state of understanding.     

Quantitative detection of individual cleaved DNA molecules on surfaces using gold nanoparticles and scanning electron microscope imaging

Single-nucleotide polymorphisms (SNPs) are the most frequent type of human genetic variation. Recent work has shown that it is possible to directly analyze SNPs in unamplified human genomic DNA samples using the surface-invasive cleavage reaction followed by rolling circle amplification (RCA) labeling of the cleavage products. The individual RCA amplicon molecules were counted on the surface using fluorescence microscopy. Two principal limitations of such single-molecule counting are the variability in the amplicon size, which results in a large variation in fluorescence signal intensity from the dye-labeled DNA molecules, and a high level of background fluorescence. It is shown here that an excellent alternative to RCA labeling is tagging with gold nanoparticles followed by imaging with a scanning electron microscope. Gold nanoparticles have a uniform diameter (15 +/- 0.5 nm) and provide excellent contrast against the background of the silicon substrate employed. Individual gold nanoparticles are readily counted using publicly available software. The results demonstrate that the labeling efficiency is improved by as much as approximately 15-fold, and the signal-to-noise ratio is improved by approximately 4-fold. Detection of individual cleaved DNA molecules following surface-invasive cleavage was linear and quantitative over 3 orders of magnitude in amount of target DNA (10(-18)-10(-15) mol).     

Polarized light microscopy and spectroscopy of individual single-walled carbon nanotubes

Polarized light microscopy (PLM) is used to image individual single-walled carbon nanotubes (SWNTs) suspended in air across a slit opening. The imaging contrast relies on the strong optical anisotropy typical of SWNTs. We combine PLM with a tunable light source to enable hyperspectral excitation spectroscopy and nanotube chirality assignment. Comparison with fluorescence microscopy and spectroscopy confirms the assignment made with PLM. This represents a versatile new approach to imaging SWNTs and related structures.      

Synthesis, electron tomography and single-particle optical response of twisted gold nano-bipyramids

A great number of works focus their interest on the study of gold nanoparticle plasmonic properties. Among those, sharp nanostructures appear to exhibit the more interesting features for further developments. In this paper, a complete study on bipyramidal-like gold nanostructures is presented. The nano-objects are prepared in high yield using an original method. This chemical process enables a precise control of the shape and the size of the particles. The specific photophysical properties of gold bipyramids in suspension are ripened by recording the plasmonic response of single and isolated objects. Resulting extinction spectra are precisely correlated to their geometrical structure by mean of electron tomography at the single-particle level. The interplay between the geometrical structure and the optical properties of twisted gold bipyramids is further discussed on the basis of numerical calculations. The influence of several parameters is explored such as the structural aspect ratio or the tip truncation. In the case of an incident excitation polarized along the particle long axis, this study shows how the plasmon resonance position can be sensitive to these parameters and how it can then be efficiently tuned on a large wavelength range.     

Malayaite ceramic pigments: A combined optical spectroscopy and neutron/X-ray diffraction study

Ceramic pigments based on the Cr-doped malayaite structure were synthesized by solid state reaction and characterized by optical spectroscopy and combined X-ray and neutron powder diffraction in order to elucidate the still unclear chromium substitution mechanisms. The results show that coloration is actually due to simultaneous occurrence of Cr⁴⁺ and Cr³⁺ ions in the crystal lattice. Spectroscopy data confirm that Cr⁴⁺ is replacing Sn⁴⁺ in the octahedral site and, in minor amount, Si⁴⁺ in the tetrahedral site. In addition, neutron powder diffraction data suggest that Cr³⁺ substitution for octahedral Sn⁴⁺ is charge balanced by the formation of oxygen vacancies with no preference over the different oxygen sites. Upon incorporation of Cr ion, the SnO₆ octahedra exhibit an off-centre displacement of central cation which in turn induces a rearrangement of both the octahedral and tetrahedral coordination shells.     

Transmission electron microscopy study of individual carbon nanotube breakdown caused by Joule heating in air

We present repeated structural and electrical measurements on individual multiwalled carbon nanotubes, alternating between electrical measurements under ambient conditions and transmission electron microscopy (TEM). The multiwalled carbon nanotubes made by chemical vapor deposition were manipulated onto cantilever electrodes extending from a specially designed microfabricated chip. Repeated TEM investigations were then made of the progressive destruction of the nanotube structure induced by Joule heating in air. The electrical measurements indicate that the studied nanotubes behave as diffusive conductors with remarkably predictable electrical properties despite extensive structural damage.     

Transmission electron microscopy study of a dental gallium alloy

Analytical transmission electron microscopy (TEM) studies of a dental gallium alloy have been carried out. This commercial Ga alloy was made by triturating a Ag-Sn-Cu-rich alloy powder with a liquid Ga alloy containing Ga, In and Sn. Ga alloys are of increasing interest as an alternative to amalgam. The dental material studied in the present work was found to be a composite consisting of remaining, undissolved particles from the Ag-based alloy powder in a matrix of reaction products with the liquid Ga alloy. The phases in the matrix and the remaining Ag-based alloy particles have been identified by electron diffraction, high resolution electron microscopy and energy dispersive X-ray spectroscopy. the following phases were identified: orthorhombic Ag₃Sn, cubic -Cu₉Ga₄, cubic Ag₉In₄, tetragonal -Sn and hexagonal Ag₂Ga. In addition to these well-known phases Ga-rich regions of Cu-Ga were observed consisting of an intergrowth of the tetragonal CuGa₂ and one of the cubic -Cu₉Ga₄ phases.     

Characterisation of nano-structured titanium and aluminium nitride coatings by indentation, transmission electron microscopy and electron energy loss spectroscopy

Titanium and aluminium nitride Ti_1 − xAl_xN films deposited by radiofrequency magnetron reactive sputtering onto steel substrate are examined by transmission electron microscopy over all the range of composition (x = 0, 0.5, 0.68, 0.86, 1). The deposition parameters are optimised in order to grow nitride films with low stress over all the composition range. Transmission electron microscopy cross-section images of Vickers indentation prints performed on that set of coatings show the evolution of their damage behaviour as increasing x Al content. Cubic Ti-rich nitrides consist of small grains clustered in rather large columns sliding along each other during indentation. Hexagonal Al-rich films grow in thinner columns which can be bent under the Vickers tip. Indentation tests carried out on TiN and AlN films are simulated using finite element modelling. Particular aspects of shear stresses and displacements in the coating/substrate are investigated. The growth mode and the nanostructure of two typical films, TiN and Ti_0.14Al_0.86N, are studied in detail by combining transmission electron microscopy cross-sections and plan views. Electron energy loss spectrum taken across Ti_0.14Al_0.86N film suggests that a part of nitrogen atoms is in cubic-like local environment though the lattice symmetry of Al-rich coatings is hexagonal. The poorly crystallised domains containing Ti and N atoms in cubic-like environment are obviously located in grain boundaries and afford protection of the coating against cracking.     

Microstructural examination of layered coatings by scanning electron microscopy, transmission electron microscopy, and atomic force microscopy

The structure of r.f. sputtered multilayer Ti-BN coatings was investigated by low-voltage scanning electron microscopy, energy-dispersive X-ray spectrometry, transmission electron microscopy, and atomic force microscopy. Appropriate specimen preparation methods are described for each technique; these included fracture of the substrate, masking the growing film to produce a taper section, and ion-beam milling of embedded cross sections. Correlation of scanning electron micrographs with atomic force images was facilitated by the presence of similar composition contrast in both cases. Quantitative X-ray microanalysis of the layers was performed using the φ(z) approach. The crystal structures of nanocrystalline grains nucleated as a result of interdiffusion reactions during thermal annealing were identified by selected-area electron diffraction and convergent-beam microdiffraction as -titanium and f.c.c. titanium nitride.     

Study of electropolymerised polyaniline films using cyclic voltammetry, atomic force microscopy and optical spectroscopy

Electropolymerisation of polyaniline (PANI) has been investigated using cyclic voltammetry in aqueous bath. The effect of dopant on the structure, morphology & optical properties of electrodeposited PANI has also been studied using x-ray diffraction (XRD), atomic force microscopy (AFM), optical absorbance & luminescence spectroscopy. It is shown that the presence of a neutral salt (KI) in the deposition matrix imparts enhanced crystallinity to PANI films.     

Electron microscopy and optical properties of small gold and silver particles in glass

Transmission electron micrographs of small gold and silver particles grown in glass show uniform particle size in a particular sample. The silhouettes of the particles are those expected for pure particles of f c c metals. From the particle sizes measured from the micrographs and the kinetics of particle growth, the diffusion coefficient of gold in the glass is calculated. This calculation allows particle sizes early in the growth process to be estimated. The optical absorption spectrum for particles containing about 100 atoms is shown.