Nm For Specimens Research Articles

Green chemistry synthesis of wolframites: An investigation about stoichiometric ratios, optical, structural, vibrational, and physico-chemical properties

This work aims to use a new route to synthesize nanostructured materials. The method has an eco-frendly perspective, which seeks to produce materials with dual characteristics (fluorescence and/or plasmon band) with various applications in luminescent sensors or particles for spectral optimization. Cobalt tungstate nanoparticles (CoWO4 - wolframite), with non-stoichiometric ratios of 2:1 and 1:2 of the precursor materials (ammonium paratungstate and cobalt nitrate), were prepared by the proteic sol-gel method. For the synthesis of the nanoparticles, two types of polymerizing agents were used: animal gelatin (collagen) and vegetal gelatin extracted from red algae (Rhodophyta). The prepared materials were calcined between 773 and 1073 K for 2 h. XRD results evidenced a variation of the lattice parameters and a monoclinic symmetry of the P21/c type for CoWO4 and of the P21/n type for WO3. Particle sizes, evaluated by the Scherrer equation, ranged from 13 to 30 nm for specimens synthesized at 773 K and from 20 to 51 nm for specimens synthesized at 1073 K. Raman spectroscopy revealed anharmonicity in the vibrational system and its damping according to the presence of distinct symmetries. The experiment was successful in obtaining a reproducible sol-gel procedure for the synthesis of the CoWO4 nanosystem. The procedure allowed the obtaining of plasmonic and photoluminescent properties only by stoichiometric modification of the precursors. Finally, the process was optimized, and the best synthesis conditions were defined. Furthermore, fluorescence and plasmon band investigation revealed that the nanostructures have maximum emission and absorption at 468 and 410 nm, respectively.

Influence of Cementite Precipitation on Work Hardening Behavior in Ultrafine Grain Steels Rolled at Room and Cryogenic Temperatures

The work hardening behavior of α + θ UFG steel related to α + θ two phase microstructure is more complicated than that of single-phase materials. Very few studies have been conducted on the work hardening of α + θ UFG steels. Therefore, it is necessary to study the correlation between the work hardening and α + θ microstructure. In this study, the work hardening behavior of low-carbon ultrafine grain (UFG) steels with different grain size of ferrite and cementite particles, fabricated by rolling and annealing process, was studied. The α grain size was decreased to 132 ± 11 and 200 ± 19 nm in specimens cryorolled and annealed at 450 and 550 °C, which were smaller than that in specimen cold-rolled and annealed at 550 °C. However, the specimen cryorolled and annealed at 550 °C had a tensile strength of 740.3 MPa, which was lower than that in the other specimens. Results indicate that the work hardening is affected by ferrite and cementite in the UFG steels. The relatively coarse ferrite phase and the large number of fine intragranular cementite particles contribute to better work hardening. The intragranular cementite particles play a significant role in the improvement of work hardening, because the geometrically necessary dislocations are apt to form and store around intragranular cementite particles, while the intergranular cementite particles result in the decreased dislocation accumulation ability of ferrite and impair the strength of grain boundaries and work hardening of ferrite + cementite ultrafine grain steels.

Elektronsko-optična študija in Augerjeva elektronska spektroskopija konverzijske prevleke na osnovi cirkonija, nanešene na čisti aluminij

The techniques of scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultramicrotomy and energy dispersive X-ray analysis (EDX) were employed to examine conversion coatings on aluminium developed from a zirconium nitrate/fluoride solution. The coating developed slowly on a microscopic metal substrate with islands of zirconium-rich centres within the coating matrix. According to the TEM assessment, the coating thickness was 30 nm for specimens treated for 60 s and 50 nm for those treated for 900 s. The population of the zirconium-rich centers ranged from 2.8 × 1012 m–2 to 6 × 1012 m–2 over the treatment period. According to Auger-electron-spectroscopy in-depth analyses, the coating is composed of three diffused layers with an outer region of zirconium oxide followed by a layer of aluminium oxide/hydroxide and an inner layer at the metal/coating interface comprising compounds of aluminium and fluorides. The corrosion-resistance and paint-adhesion characteristics of the zirconium conversion coating are superior to those of bare aluminium.

1064 nm dispersive Raman spectroscopy of tissues with strong near-infrared autofluorescence

Raman spectroscopy is an established technique for molecularly specific characterization of tissues. However, even with near-infrared (NIR) excitation, some tissues possess background autofluorescence, which can overwhelm Raman scattering. Here, we report collection of spectra from tissues with strong autofluorescence using a 1064 nm system with a high-throughput dispersive spectrometer and deep-cooled InGaAs array. Spectra collected at 1064 nm were compared with those collected at 785 nm in specimens from human breast, liver, and kidney. The results demonstrate superior performance at 1064 nm in the liver and kidney, where NIR autofluorescence is intense. The results indicate the feasibility of new biomedical applications for Raman spectroscopy at 1064 nm in tissues with strong autofluorescence.

Low energy Xe milling for the quantitative profiling of active dopants by off-axis electron holography

Off-axis electron holography is a powerful technique that can be used to measure the active dopants in semiconductors. The preparation of thin transmission electron microscopy specimens containing nm-scale regions of interest is extremely challenging and as a consequence ion milling is an essential tool. The exposure of doped specimens to energetic ions creates defects deep in the specimens that trap the active dopants, being the principle cause of what is known as the inactive region. The inactive thickness leads to an underestimation of the dopant potential in the specimens. Here we show that this artifact can be significantly reduced from 140 nm for specimens prepared using only Ga ions at 30 kV to only 10 nm by preparing specimens using 1.5 keV Xe ions for specimens containing p-n junctions with dopant concentrations of 2 × 1018 cm−3.

Improvement in the Mechanical Properties of Silicon Nitride Ceramic in High-Temperature Deformation Processes

Studies have been made on the changes in structure and properties of sintered materials: Si3N4 - 5 mass% Y2O3 - 2 mass% Al2O3, Si3N4 - 5 mass% Y2O3 - 5 mass% Al2O3, and Si3N4 - 40 mass% TiN on deformation in a high-pressure chamber of toroid type (pressure 4–5 GPa, temperature 1000–1600 °C), and also by direct extrusion with degrees of reduction of 55 and 72% (temperature 1750–1850 °C, pressure on the plunger 20–30 MPa). After pressure-chamber treatment, the materials have elevated mechanical characteristics: HV10 ≈ 16.7 GPa, KIc up to 8.4 MPa · m1/2 for the system Si3N4 - Y2O3 - Al2O3; and HV10 ≈ 16.9 GPa, KIc up to 9.4 MPa · m1/2 for Si3N4 - TiN. A structure feature is the small size of the coherent-scattering regions: 51 nm for Si3N4 and 65 nm for TiN in the system Si3N4 - TiN, and 33 nm for specimens in the system Si3N4 - Y2O3 - Al2O3. High-temperature extrusion results in a structure with β-Si3N4 grains elongated along the deformation direction. The anisotropic structure has KIc values in directions perpendicular to and parallel to the direction of extrusion of 11.5–12.0 MPa · m1/2 and 7.5–7.8 MPa · m1/2, respectively. The hardness after extrusion becomes 16.0 GPa.

Properties of severe plastically deformed Mg alloys

In this present investigation, mechanical properties of bulk Mg alloys synthesized by mechanical alloying (MA) and equal channel angular pressing (ECAP) were investigated. For mechanically alloyed samples, a dramatic increase in yield strength to 498 MPa has been achieved after 5 h milling. Strain softening accompanied by increased ductility of the longer milled samples is observed through the gradual decrease in yield strength. The lowest yield strength of 200 MPa was observed after 30 h milling while the elongation at fracture was dramatically increased to 45%. The average grain size was about 75 nm for specimens milled for 30 h. In ECAP, the accumulation of redundant shear strain and dynamic recrystallisation refine the microstructure while increasing the material's yield strength. Consequently, ductility is reduced. The mechanical properties of the Mg alloy are also found to be sensitive to the processing temperature at which ECAP is conducted and to the number of ECAP passes.

Microstructural evolution in nanocrystalline Y–TZP containing a silicate glass

Abstract Nanocrystalline yttria stabilized tetragonal zirconia polycrystal (NC–Y–TZP) powders were coated with a sodium strontium silicate glass using the sol-gel technique. The compact powders were sintered at 1400°C for 1 h resulting in dense nanocrystalline pellets with 5, 10 and 15 vol.% glass. Short pre-sintering heat treatment at 800°C caused the full stabilization of the tetragonal phase while long treatments led to the devitrification of the glassy phase. The mean grain size decreased from 196 nm in the glass-free specimen to 140, 110 and 100 nm in the specimens containing 5, 10 and 15 vol.% glass, respectively. The grain size distribution width also decreased with increase in the glass content. TEM revealed the morphological changes of the highly facetted polyhedral grains in the glass-free specimens into the round-shape grains with increase in the glass content. The effect of the glass on the phase formation, densification and microstructure have been discussed.

Morphologies of metastable inert gas precipitates in aluminum observed with in situ HRTEM

Inert gases of Xe, Ar and Ne were ion-implanted into Al at room temperature under the observation in a transmission electron microscope (TEM). The precipitation and the structure of inert gas precipitates were studied with conventional and high-resolution transmission electron microscopy (CTEM and HRTEM). An in situ observation revealed that Xe ions aggregate as atomic clusters, and the clusters change to crystalline particles in the size around 2.0 nm. It is a minimum size for the observable crystalline Xe precipitates, below which the Xe ion clusters are not stable either in shape or in structure. The Xe precipitates have sizes ranging from about 2.0 to 10 nm in specimens implanted with Xe to a dose of 5×10 19 ions m −2 . The precipitates larger than about 6 nm are usually in non-crystalline state, but the maximum size of crystalline precipitates also depends on the surrounding environment. Ar precipitates began to be visible with a size of about 1.4 nm at an implantation dose of 8×10 18 ions m −2 . The solid Ar precipitates in the specimen implanted with Ar to a dose of 1.9×10 20 ions m −2 range from 1.4 to 5 nm in size and have a truncated cuboctahedron shape faceted by {1 1 1} and {1 0 0} of Al. Ne precipitates in Al are in non-crystalline state, with sizes ranging from about 1.5 to 15 nm. The Ne precipitates are also in a truncated cuboctahedron shape, similar to the Ar precipitates. Analysis of growth dynamics of Ar and Ne precipitates suggests that dissolution of clusters and precipitates take place during the implantation, and that the growth rate of the precipitates increased with the implanted dose.

The bcc-to-9R martensitic transformation of Cu precipitates and the relaxation process of elastic strains in an Fe-Cu alloy

Abstract High-resolution electron microscopy experiments have been performed to explore the bcc—9R transformation and the subsequent elastic relaxation of Cu precipitates in an Fe—Cu alloy aged at 550°C. It was found that both electron irradiation (at an electron energy of 400 kV) and thermal annealing caused rotation of the close-packed (009)9R planes in twinned 9R Cu precipitates. For 400 kV electron irradiation, such rotations were observed in precipitates smaller than about 12nm in diameter. For specimens cooled from the ageing temperature of 550°C to a given temperature up to −60°C, and then annealed at 400°C, the rotation of (009)9R planes was found to occur only in precipitates above a size which depended on the temperature to which the specimen had been cooled. This critical size ranged from about 9 nm for specimens cooled to 400°C, to 4 nm for specimens cooled to −60°C. It is argued that these critical sizes are indicative of the sizes at which coherent bcc precipitates transform martensitically ...

Scanning soft X-ray imaging at 10 nm resolution

The potential imaging and selected-area near-edge X-ray absorption fine structure spectroscopic (NEXAFS) performance of a new scanning probe X-ray microscope (SPXM) for soft X-rays from synchrotron radiation is examined by computer modelling; an optical design for the microscope is also given. Acceptable dwell times per pixel in image collection are predicted. The microscope is expected to have a spatial resolution for “water-window” X-ray wavelengths (2.3–4.4 nm) of about 10 nm for specimens up to 200 nm thick. The central component of the optical system is a tube collimator forming a probe a few wavelengths in diameter above a scanned specimen. The collimator is illuminated at near-normal incidence by a Fresnel zoneplate condenser, and its exit aperture is positioned a few wavelengths above the specimen. Physical understanding is gained by a two-dimensional (2D) waveguide approach, and by calculations using the full-vector theory of Maxwell's equations. The calculations, because of computational limitations, are carried out mainly in 2D. The vector results agree well with a multislice scalar calculation in 2D which is then applied to 3D to describe the 3D probe imaging and to estimate the energy throughput.

A Comparative High-Resolution Electron Microscope Study of Ag Clusters Produced by a Sputter-Gas Aggregation and Ion Cluster Beam Technique

Ag clusters were formed by a sputter-gas-aggregation process [H. Haberland et al..: J. Vac. Sci. Technol. A 10 (1992) 3266] and the ionized cluster beam (ICB) [T. Takagi: Ionized-Cluster Beam Deposition and Epitaxy (Noyes, Park Ridge, 1988)] technique. The Ag clusters deposited on collodion-coated microgrids were investigated by high-resolution transmission electron microscopy. The diameter of those clusters, d, ranges from 1 nm up to about 10 nm for specimens produced by the sputter-gas aggregation technique, depending on the sputter condition and the deposition time. Comparable times of the ICB deposition lead to a broader distribution up to d≈20 nm, suggesting the formation of islands with extremely flat shapes. High percentages of crystalline particles obtained by both techniques are either single crystals or multiple twins with clear lattice images.

Growth kinetics and martensitic transformation of large Fe particles in a Cu-1.5 mass% Fe alloy

The growth kinetics and martensitic transformation induced by simple cooling of large Fe particles in Cu-1.5 mass % Fe single crystals aged at 973 K for up to 60 days are examined by transmission electron microscopy and magnetic measurement. The growth kinetics of large Fe particles can be described by the Lifshitz-Slyozov-Wagner theory and the interfacial energy between the Fe particles and the Cu matrix is estimated as 0.24 to 0.40 J m−2. The volume fraction of α-Fe particles increases with the mean particle size and with lowering of the cooling temperature. The critical sizes below which the transformation by simple cooling does not occur, are found to be 290 and 350 nm for specimens cooled to 77 K and room temperature, respectively. The saturation magnetization of the Cu-Fe alloy containing large α-Fe particles increases by further annealing of the cooled specimens. These facts imply that α-Fe particles are not produced during the prolonged ageing but are formed martensitically during the cooling process.

Macular corneal dystrophy: The macromolecular structure of the stroma observed using electron microscopy and synchrotron X-ray diffraction

The distribution of sulphated proteoglycans within the stromas of three patients (A,B,C) suffering from macular corneal dystrophy was studied using the specific dye Cuprolinic Blue in a 'critical electrolyte concentration' method. The corneas were examined using transmission electron microscopy and A and C were further studied by low-angle synchroton X-ray diffraction. Sera from all three patients were analyzed for the presence of keratan sulphate using a monoclonal antibody in an enzyme-linked immunosorbent assay. The serum from Patient A contained keratan sulphate, but the chains were thought to be shorter or less sulphate in their sera. Electron microscopy showed many electron-transparent lacunae randomly distributed throughout the specimens. The average collagen fibril diameter was normal but there were differences in packing between the specimens. Specimen A was closely-packed with most collagen fibrils in contact with their neighbours. Specimens B and C showed fewer regions of close packing; in most of the tissue the interfibrillar spacing appeared normal. Staining with Cuprolinic Blue revealed an unusual distribution of proteoglycans in some parts of the interfibrillar matrix, particularly in A, with 'small' proteoglycans running exclusively parallel to the collagen fibrils. Furthermore in A, and to a lesser extent in B and C, some lacunae were filled with clusters of abnormal sulphated proteoglycan filaments (of various sizes) which were chondroitinase ABC susceptible. Clearly defined regions, both within the lacunae and elsewhere, failed to stain with Cuprolinic Blue; this suggests an absence of sulphated proteoglycans within these areas. Equatorial X-ray diffraction of the wet tissues (A and C) gave values for the mean interfibrillar centre-to-centre separation of 43 +/- 2 nm in Specimen A and 52 +/- 3 nm in Specimen C. The differences observed in the serum keratan sulphate levels, the packing of the collagen fibrils and the distribution of chondroitin/dermatan sulphate proteoglycans confirm the heterogeneity that exists within the macular corneal dystrophies.

Discrimination of normal and atherosclerotic aorta by laser-induced fluorescence.

Precise targeting of laser energy to atherosclerotic plaque is crucial for the safe performance of laser angioplasty. The present study was designed to evaluate whether laser-induced fluorescence could distinguish atherosclerotic from normal aorta. Segments of human aorta obtained at necropsy were classified grossly and histologically as normal aorta (n = 7), thin yellow fatty plaque (n = 5), and thick white atheromatous plaque (n = 9), and analyzed by laser-induced fluorescence spectroscopy using a pulsed nitrogen laser. Fluorescence spectra were recorded over a wavelength range from 385 to 725 nm. Normal specimens had maximal fluorescence intensity at 514 nm. A prominent fluorescence peak at 448 nm was present in specimens characterized as white atheromatous plaque and at 538 nm in specimens characterized as yellow fatty plaque. The ratios of fluorescence intensity at 448 nm/514 nm and at 538 nm/514 nm correctly classified all specimens according to their gross and histologic type (p less than .001). Thus, a "smart" laser angioplasty catheter system might incorporate low-power laser radiation for arterial fluorescence spectroscopy to guide delivery of high-power laser radiation for plaque ablation.

Segregation and domain structure in rapidly solidified Ni3Al

Rapid solidification processing (RSP) in conjunction with microalloying is being used to enhance the ductility of Ni3Al. Boron which strengthens grain boundaries was added for significant improvement in ductility of Ni3Al. Specimens of Ni3Al (24 at. % Al) with additions of 0, 500, and 1000 wt ppm boron were splat-cooled in an arc-hammer apparatus. The specimens without boron were brittle while specimens with boron were ductile for all but the fastest quench rates. Microstructural characterization was performed with a Philips EM400T/FEG and JEM 120CX transmission electron microscopes.Antiphase boundaries (APB) are not observed in Ni3A1 alloys fabricated from cast ingots, but are present following RSP. The average domain sizes were 50 and 80 nm for specimens with and without boron, respectively, but were independent of solidification rate. Near the surface of the splats the domain size was approximately the same as in the center even though the grain size was much smaller. Regions of small domains which were always in the center of the grains were surrounded by larger domains.