Cold Field Emission Scanning Electron Research Articles

Effect of Ni Content on Microstructure and Characterization of Cu-Ni-Sn Alloys.

Cu-xNi-5Sn (wt %) alloys with a different Ni content were prepared by a powder metallurgy method. The effect of Ni content on the hardness and yield strength of Cu-xNi-5Sn (wt %) alloys was investigated. The microstructure, composition, and morphology of Cu-xNi-5Sn (wt %) alloys were observed by X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), and cold field emission scanning electron microscope (FESEM), respectively. Results indicate that the hardness and yield strength firstly increase and then decrease with the increase of Ni content and reach up to a maximum when Ni content is 12.5 wt %. Furthermore, the formation of the sandwich structure and needle-like phase is found in the grain, the grain boundary and intragranular precipitates are rich in both the Ni and Sn phase. The formation of the inerratic and suitable lamellar precipitates of sandwich structure and needle-like phase can be responsible for the good mechanical properties of the Cu-12.5Ni-5Sn alloy after aging treatment. The sandwich structure and need-like phase that were observed by FESEM can contribute to clarify the morphology of Cu-Ni-Sn alloys.

Optimization study of direct morphology observation by cold field emission SEM without gold coating

Gold coating is a general operation that is generally applied on non-conductive or low conductive materials, during which the morphology of the materials can be examined by scanning electron microscopy (SEM). However, fatal deficiencies in the materials can result in irreversible distortion and damage. The present study directly characterized different low conductive materials such as hydroxyapatite, modified poly(vinylidene fluoride) (PVDF) fiber, and zinc oxide nanopillar by cold field emission scanning electron microscopy (FE-SEM) without a gold coating. According to the characteristics of the low conductive materials, various test conditions, such as different working signal modes, accelerating voltages, electron beam spots, and working distances, were characterized to determine the best morphological observations of each sample.

Research on Quantitative Analysis for Nanopore Structure Characteristics of Shale Based on NMR and NMR Cryoporometry

Shale gas is a key natural gas resource of very great significance in China. On the basis of the differences in pore structure characteristics between marine and continental shale in China, the Weiyuan marine shale (sample #1), Jiao Shiba marine shale (sample #2), and Yaoqu continental shale (samples #5 and #6) were selected to study the pore structure characteristics and controlling factors using cold field-emission scanning electron microscopy and nuclear magnetic resonance (NMR). NMR cryoporometry (NMRC) was employed to determine the nanoscale pore structure. This method can be extended to micron measurements combining NMR relaxation analysis to detect in detail the pore structure of shales on different aperture scales. The smaller the test temperature gradient is, the finer is the pore distribution result. The test results show decreasing porosity in going from sample #5 to samples #2, #6, and #1 to #4. NMRC, low-field NMR (LFNMR), mercury intrusion porosimetry (MIP), and gas adsorption (GA) methods show good agreement for the pore distribution in their respective scopes of application. The NMR methods result in a much better estimate for the total pore volume than the more common MIP and GA methods. Hence, the pore structure of the reservoir shale can be evaluated more accurately by combining NMRC and LFNMR with GA and MIP. Thus, the nanopores of continental shale (sample #5, Yaoqu shale) are clearly better developed and will more likely have a higher commercial exploitation value than marine shale.

Formation of cavitation-induced nanosize precipitates on the eroded surface for Inconel 718 alloy

The cavitation erosion of Inconel 718 nickel-base alloy was investigated using an ultrasonic vibratory apparatus. The morphologies and microstructure evolution of the eroded surface were observed by scanning electron microscopy (SEM) and cold field emission scanning electron microscope (FESEM) and the cavitation-induced nanosize precipitates are found in the local zones of eroded surface.

Rotation contour contrast reconstruction using electron backscatter diffraction in a scanning electron microscope

The microstructure of a deformed Mg–Al–Ca alloy was imaged using an electron-beam energy of 20 keV in a cold field-emission scanning electron microscope. The backscattered electron (BSE) micrographs showed a non-uniform contrast, the simplest being in the form of parallel contours inside a number of grains. This contrast is described as rotation contour contrast (RCC) and is attributed to local rotation of the crystal during the deformation of the grain. A model is presented to relate the rotation of crystal planes about one rotation axis to the channeling contrast in the channeling pattern and, consequently, to RCC in the BSE micrograph. This model was validated with the electron backscatter diffraction technique such that the RCCs in the BSE micrograph were reconstructed using the electron backscatter diffraction pattern intensities. The appearance of the RCCs was attributed to the change in the electron-beam position across a Kikuchi band due to local crystal rotation.

Rotation axes analysis of deformed magnesium based on rotation contour contrast in a scanning electron microscope

A crystallographic orientation contrast in the form of cross-shaped and intersecting contours was observed in a backscattered electron (BSE) micrograph of deformed magnesium (Mg) grains in a cold field emission scanning electron microscope (CFE-SEM). This contrast was identified as rotation contour contrast (RCC). A model is presented to link the RCC in the BSE micrograph to the channeling contrast in the corresponding channeling pattern. Based on this model, the appearance of the cross-shaped RCC in the BSE micrograph was attributed to the rotation of the crystal about two rotation axes and the RCC was related to a two dimensional angular scan of the corresponding channeling pattern. This model was experimentally validated using the selected area channeling pattern (SACP) technique. The crystallographic directions of the rotation axes were identified using the electron backscatter diffraction (EBSD) technique.

Detection of Human Ig G Using Photoluminescent Porous Silicon Interferometer.

Photoluminescent porous silicon (PSi) interferometers having dual optical properties, both Fabry-Pérot fringe and photolumincence (PL), have been developed and used as biosensors for detection of Human Immunoglobin G (Ig G). PSi samples were prepared by electrochemical etching of p-type silicon under white light exposure. The surface of PSi was characterized using a cold field emission scanning electron microscope. The sensor system studied consisted of a single layer of porous silicon modified with Protein A. The system was probed with various fragments of aqueous human immunoglobin G (Ig G) analyte. Both reflectivity and PL were simultaneously measured under the exposure of human Ig G. An increase of optical thickness and decrease of PL were obtained under the exposure of human Ig G. Detection limit of 500 fM was observed for the human Ig G.

Microstructural Characterization of Mg–0.3Al–0.2Ca Alloy Using Ion Milling Surface Preparation Technique

The Vickers microindentation and spherical nanoindentation tests were carried out on a polycrystalline Mg–0.3Al–0.2Ca alloy specimen. Specimens were prepared with chemical polishing and ion milling techniques. The electron channeling contrast imaging (ECCI) and electron backscattered diffraction (EBSD) were used to study the plastic deformation inside and around the indents with a cold-field emission scanning electron microscope. The distribution of strain fields, slip lines, and twins was imaged on an indented surface. A crystallographic orientation mapping was performed to map the local crystallographic misorientation associated with channeling contrast variations. The chemical polishing technique was used to remove the material from the surface and allow the study of deformed microstructure at a maximum depth of the indent. The combination of ECCI and EBSD with chemical polishing and ion milling surface preparation techniques proved to be beneficial to study the indentation-induced plastic deformation in a polycrystalline Mg–0.3Al–0.2Ca alloy specimen.

Application of Low Energy STEM with the In-lens Cold FE-SEM

We have developed a high resolution STEM imaging method using accelerating beam voltages of 30 kV and less. In this study, we examined and determined the low accelerating voltage parameters necessary for obtaining lattice resolution in STEM images, using the cold field emission scanning electron microscope (CFE-SEM), Hitachi SU9000. We also investigated and optimized the objective lens conditions for optimum lattice fringe imaging. The STEM images and associated Fourier transform image obtained at 30 kV show the Si (222) lattice fringes and reflection spots, corresponding to the d-lattice spacing of 0.157 nm. The STEM images and associated Fourier transform image at 15 kV show the Si (111) lattice fringes and reflection spot, corresponding to the d-lattice spacing of 0.314 nm.

Fabrication and Characterization of Free-Standing DBR Porous Silicon Film

Distributed Bragg reflector porous silicon of different characteristics were formed to determine their optical constants in the visible wavelength range using a periodic square wave current between low and high current densities. The surface and cross-sectional SEM images of distributed Bragg reflector porous silicon were obtained using a cold field emission scanning electron microscope. The surface image of distributed Bragg reflector porous silicon indicates that the distributions of pores are even. The cross-sectional image illustrates that the multilayer of distributed Bragg reflector porous silicon exhibits a depth of few microns and applying of square current density during the etching process results two distinct refractive indices in the contrast. Distributed Bragg reflector porous silicon exhibited a porosity depth profile that related directly to the current-time profile used in etch. Its free-standing film was obtained by applying an electro-polishing current.

Electron channelling contrast observations in deformed Mg alloys prepared with ion milling

Electron channelling contrast imaging (ECCI) was used in the cold-field emission scanning electron microscope (CFE-SEM) to image the microstructure on deformed bulk specimen. Imaging was conducted with a pole-piece mounted silicon photodiode detector at 5 keV to collect backscattered electrons generated from a low-tilted (0 – 3 degrees) specimen. Broad ion beam milling surface preparation technique was used to remove surface layers and reveal near-surface deformation features. The uniaxial hot-compression tests were conducted on Mg-0.3 wt% Al-0.2 wt% Ca alloy. ECCI observations on deformed bulk specimen showed irregular and complex channelling contrast variations inside parent grains and low angle grain boundaries originated from parent grain boundaries. ECCI on an ion milled prepared surface provides non-destructive and rapid visualisation and characterisation of strain fields along with near-surface deformation substructures in CFE-SEM.

Deposition, characterization, and in vivo performance of parylene coating on general-purpose silicone for examining potential biocompatible surface modifications

In this study, a thorough investigation of parylene coatings was conducted, as follows: microstructure (i.e., X-ray diffractometer (XRD) and cold field emission scanning electron microscope (FESEM)), mechanical property (i.e., pencil hardness and cross-cut adhesion test), surface property (i.e., water contact angle measurement, IR, and X-ray photoelectron spectroscopy (XPS)), and biocompatibility tests (i.e., fibroblast cell culture, platelet adhesion, and animal studies). The results revealed that parylene, a crystalline and brittle coating, exhibited satisfactory film adhesion and relative hydrophobicity, thereby contributing to its effective barrier properties. Fibroblast cell culturing on the parylene-deposited specimen demonstrated improved cell proliferation and equivalent to or superior blood compatibility than that of the medical-grade silicone (currently used clinically). In the animal study, parylene coatings exhibited similar subcutaneous inflammatory reactions compared with the medical-grade silicone. Both in vitro and in vivo tests demonstrated the satisfactory biocompatibility of parylene coatings.

Lattice imaging at an accelerating voltage of 30kV using an in-lens type cold field-emission scanning electron microscope

We reported investigation of lattice resolution imaging using a Hitachi SU9000 conventional in-lens type cold field emission scanning electron microscope without an aberration corrector at an accelerating voltage of 30kV and discuss the electron optics and optimization of observation conditions for obtaining lattice resolution. It is possible to visualize lattice spacings that are much smaller than the diameter of the incident electron beam through the influence of the superior coherent performance of the cold field emission electron source. The defocus difference between STEM imaging and lattice imaging is found to increase with spherical aberration but it is possible to reduce the spherical aberration by reducing the focal length (f) of the objective lens combined with an experimental sample stage enabling a shorter distance between the objective lens pre-field and the sample. We demonstrate that it is possible to observe the STEM image and crystalline lattice simultaneously. STEM and Fourier transform images are detected for Si{222} lattice fringes and reflection spots, corresponding to 0.157nm. These results reveal the potential and possibility for a measuring technique with excellent precision as a theoretically exact dimension and established the ability to perform high precision measurements of crystal lattices for the structural characterization of semiconductor materials with minimal radiation beam damage.

Multi‐walled carbon nanotubes decorated by platinum catalyst nanoparticles—Examination and microanalysis using scanning and transmission electron microscopies

Carbon nanotubes (CNTs) decorated with platinum (Pt) nanoparticles (NPs) have been characterized using a cold field-emission scanning electron microscope (SEM) and a high resolution field-emission transmission electron microscope (TEM). With this particular composite material, the complementary nature of the two instruments was demonstrated. Although the long CNTs were found to be mostly bent and defective in some parts, the nucleation of Pt occurred randomly and uniformly covered the CNTs. The NPs displayed a large variation in size, were sometimes defective with twins and stacking faults, and were found to be faceted with the presence of surface steps. The shape and size of the NPs and the presence of defects may have significant consequences on the activity of the Pt catalyst material. Also, thin layers of platinum oxide were identified on the surface of some NPs.

Characterisation of rare earth minerals with field emission scanning electron microscopy

Rare earth elements are becoming increasingly in demand, due to their prevalence in both renewable energy devices and high end electronics. The characterisation of the composition and morphology of the various phases that have valuable rare earth elements in the ores are needed in conjunction with the study of their physicochemical properties to optimise industrial process to extract the minerals containing the rare earth elements. Rare earth bearing minerals contain many elements with overlapping X-ray peaks (L- and M-lines) with an energy dispersive spectrometry detector, requiring a high degree of X-ray energy resolution. A program was developed to obtain the intensity of each peak by deconvolution of the X-ray spectrum. Low accelerating voltage of less than 5 kV and small beam diameter of less than 10 nm of a cold field emission scanning electron microscope allow x-ray microanalysis on the nanometre scale. A 100 nm wide phase was observed at 4 kV on a backscattered electron micrograph. Furthermore, a small beam diameter of less than 10 nm was used for identification of small phases of a few micrometres.Les éléments de terre rare sont de plus en plus en demande, grâce à leur prévalence tant dans les dispositifs d’énergie renouvelable que dans l’électronique de haute gamme. On a besoin de caractériser la composition et la morphologie des différentes phases qui contiennent des terres rares de valeur dans les minerais, en combinaison avec l’étude de leurs propriétés physico-chimiques, afin d’optimiser le procédé industriel d’extraction des minéraux contenant les terres rares. Les minéraux porteurs de terre rare contiennent plusieurs éléments ayant des pics de rayons x qui se chevauchent (lignes L et M) avec un détecteur de spectroscopie à dispersion d’énergie, nécessitant une haute résolution énergétique. On a développé un programme visant à obtenir l’intensité de chaque pic par déconvolution du spectre de rayons x. Un faible voltage d’accélération de moins que 5 kV et un faisceau à faible diamètre de moins que 10 nm d’un microscope électronique à balayage par cathode froide permettent la microanalyse des rayons x à l’échelle du nanomètre. On a observé une phase de 100 nm de largeur à 4 kV sur une micrographe d’électrons rétrodiffusés. De plus, on a utilisé un faisceau de faible diamètre de moins que 10 nm pour l’identification de petites phases de quelques μm.

Acquisition parameters optimization of a transmission electron forward scatter diffraction system in a cold‐field emission scanning electron microscope for nanomaterials characterization

Transmission electron forward scatter diffraction (t-EFSD) is a new technique providing crystallographic information with high resolution on thin specimens by using a conventional electron backscatter diffraction (EBSD) system in a scanning electron microscope. In this study, the impact of tilt angle, working distance, and detector distance on the Kikuchi pattern quality were investigated in a cold-field emission scanning electron microscope (CFE-SEM). We demonstrated that t-EFSD is applicable for tilt angles ranging from -20° to -40°. Working distance (WD) should be optimized for each material by choosing the WD for which the EBSD camera screen illumination is the highest, as the number of detected electrons on the screen is directly dependent on the scattering angle. To take advantage of the best performances of the CFE-SEM, the EBSD camera should be close to the sample and oriented towards the bottom to increase forward scattered electron collection efficiency. However, specimen chamber cluttering and beam/mechanical drift are important limitations in the CFE-SEM used in this work. Finally, the importance of t-EFSD in materials science characterization was illustrated through three examples of phase identification and orientation mapping.

Detection of nerve agent stimulants based on photoluminescent porous silicon interferometer

Porous silicon (PSi) exhibiting dual optical properties, both Fabry-Pérot fringe and photolumincence, was developed and used as chemical sensors. PSi samples were prepared by an electrochemical etch of p-type silicon under the illumination of 300-W tungsten lamp during the etch process. The surface of PSi was characterized by cold field-emission scanning electron microscope. PSi samples exhibited a strong visible orange photoluminescence at 610 nm with an excitation wavelength of 460 nm as well as Fabry-Pérot fringe with a tungsten light source. Both reflectivity and photoluminescence were simultaneously measured under the exposure of organophosphate vapors. An increase of optical thickness and quenching photoluminescences under the exposure of various organophosphate vapors were observed.

Fabrication and characterization of tunable wettability surface on copper substrate by poly(ionic liquid) modification via surface‐initiated nitroxide‐mediated radical polymerization

AbstractPoly(ionic liquid) surfaces with tunable wettability were successfully prepared on micro/nanoscale CuO/Cu composite substrates by a surface‐initiated nitroxide‐mediated radical polymerization technique. Various characterization techniques including X‐ray photoelectron spectroscopy, cold field emission scanning electron microscopy, and static water contact angle measurement were used to characterize the surfaces for each surface modification step. Kinetic studies revealed that the polymer chain growth from the surface was a controlled/“living” polymerization process. The surface with tunable wettability, reversible switching between hydrophilicity and hydrophobicity can be easily achieved by sequential counteranion exchange. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Solvothermal Synthesis and Optical Performance of One-dimensional Strontium Hydroxyapatite Nanorod

One-dimensional strontium hydroxyapatite (Sr-HAp) nanorods were successfully synthesized by a simple solvothermal method. The products were characterized via X-ray diffraction (XRD), Fourier transform infrared (FT-IR), cold field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), photoluminescence (PL) excitation and emission spectra. The experimental results indicated that oleic acid as a surfactant played a key role in confining the growth of the Sr-HAp powders. A possible formation mechanism of the one-dimensional nanorod was proposed and elaborated. Moreover, the as-obtained Sr-HAp samples showed an intense and bright emission band centered at 460 nm under long-wavelength UV light excitation and the contents of NaOH used in the synthetic process had an obvious impact on the optical performance of Sr-HAp powders. The possible luminescent mechanism of the Sr-HAp samples was discussed.

Fabrication of Gradient Optical Filter Containing Anisotropic Bragg Nanostructure

New gradient optical filters containing asymmetric Bragg structure were prepared from the distributed Bragg reflector (DBR) porous silicon (PSi). Anisotropic DBR PSi displaying a rainbow-colored reflection was generated by using an asymmetric etching configuration. Flexible anisotropic DBR PSi composite films were obtained by casting of polymer solution onto anisotropic DBR PSi thin films. The surface and cross-sectional images images of anisotropic DBR PSi composite films obtained with cold field emission scanning electron microscope indicated that the average pore size and the thickness of porous layer decreased as the lateral distance increased. As lateral distance increased, the reflection resonance shifted to shorter wavelength.