Field Emission-type Scanning Electron Microscopy Research Articles

Electrochemical noise assessment of effect of sol parameters on the performance of an eco-friendly silane sol-gel coating on 304L stainless steel

ProposeThis paper aims to access the protective function of hybrid sol-gel coatings deposited on 304L stainless steel substrate in silane solutions containing a mixture of tetraethoxysilane, methyltriethoxysilane and glycidyloxypropyltrimethoxysilane with different pH values during various immersion periods.Design/methodology/approachThe 304L stainless steels coated through 10 and 30 s of immersion in the silane solutions with pH values of 2.1 and 2.8 were exposed to NaCl solution. The corrosion resistance of the coated substrates was studied through taking advantage of electrochemical noise method as well as atomic force microscopy (AFM), water contact angle and field emission-type scanning electron microscopy (FESEM) surface analysis.FindingsThe electrochemical current noise, PSD (I) plot, noise resistance and characteristic charge as parameters extracted from electrochemical noise method indicated the superiority of eco-friendly silane coating deposited on the substrate surface during 10 s exposure to the solution, due to the film uniformity and homogeneity as confirmed by FESEM and AFM. Moreover, immersion of the stainless steel in the silane solution with pH 2.1, characterized by higher hydrolysis ratio, led to more effective corrosion control in the NaCl electrolyte according to the results of electrochemical noise and FTIR measurements.Research limitations/implicationsThe noise resistance and characteristic charge as electrochemical noise parameters were only used in this research to evaluate the protective behavior of the water-based silane sol-gel coatings. Future studies should examine the correlation between electrochemical noise data and the parameters extracted from other electrochemical methods, e.g. electrochemical impedance spectroscopy.Practical implicationsThe data obtained in this research may provide an effective approach based on electrochemical noise method to screen the silane sol-gel coatings for protection of metallic substrates against corrosion.Originality/valueAccording to the literature, no report can be found studying the effect of immersion time on a silane solution, including glycidyloxypropyltrimethoxysilane, tetraethoxysilane and methyltriethoxysilane, as well as the silane solution pH on the corrosion resistance of 304L stainless steel in NaCl solution through electrochemical noise method.

Mechanism of formation, structural characteristics and photocatalytic activities of hierarchical-structured bismuth-tungstate particles

The mechanism of the formation of flake ball-shaped (FB) bismuth-tungstate (BWO) particles was studied with samples prepared by hydrothermal reactions under standard conditions (tungsten/bismuth ratio of 0.55 in feed; 433K; 20h) and other modified conditions, and the structural characteristics of the samples were analyzed by powder X-ray diffraction (composition and crystal structure), field emission-type scanning electron microscopy (FE-SEM) (morphology), focused ion-beam etching followed by FE-SEM (inner void structure), ultrahigh-voltage transmission electron microscopy (inner void structure) and low-voltage scanning electron microscopy with energy-dispersive X-ray spectroscopic analysis (morphology and elemental distribution). Based on the results, a novel two-step mechanism of (1) formation of aqueous bismuth-oxyhydroxide droplets covered by tungstic acid (BOx@HWO) with fluidity and (2) reaction of inner bismuth and outer tungsten components at the BOx@HWO surface to yield BWO flakes is proposed as a one of the most plausible pathways that are consistent with the hollow structure of FB BWO and observations of the products prepared with shorter hydrothermal reaction. Photocatalytic activities of FB BWO samples in relation to their structure were studied.

Preparation of Low Molecular Weight Polyvinyl alcohol)/Montmorillonite Composite Nanoparticles Using an Electrospraying Technique

Composite nanoparticles composed of low molecular weight poly(vinyl alcohol) (LMW-PVA) and montmorillonite (MMT) were prepared using the electrospraying technique by regulating PVA solution concentration. Field-emission type scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, reflection type X-ray diffraction and thermal gravimetric analysis were utilized to characterize the LMW-PVA/MMT composite nanoparticles morphology and properties. MMT platelets were exfoliated and well distributed within the composite nanoparticles. It was also found that the thermal stability was enhanced by the addition of MMT.

Preparation of SrTiO 3-supported TiO 2 photocatalyst

Strontium titanate (SrTiO 3) nano particles were supported on titania (TiO 2) particles P25, which is commercially available photocatalysts with a high activity, by reacting with strontium hydroxide aqueous solution under hydrothermal condition at 70 °C. SrTiO 3-supported TiO 2 powders were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), field emission type scanning electron microscopy (FE-SEM), and energy dispersive spectrometer (EDS). The photocatalytic activity of SrTiO 3-supported TiO 2 was examined by decolorisation of methylene blue (MB) under UV irradiation in the photocatalyst-dispersed solution. Enhancement on the photocatalytic activity of TiO 2 by supporting of SrTiO 3 was confirmed.

Standing wave type surface acoustic wave atomizer

A new standing wave type surface acoustic wave (SAW) atomizer is proposed and tested. To investigate atomization characteristics, the earlier progressive wave and the proposed standing wave types of atomizer are compared by means of vibration mode, atomization speed, and electrostatic deposition tests. In the case of the vibration mode and atomization speed tests, the standing wave type showed higher standing wave ratio (SWR) and slower atomization speed than the progressive wave type. In the electrostatic deposition test, a liquid sample is atomized by two types of SAW atomizer combined with two different driving modes, namely continuous and intermittent drive. The deposited dry particles are then measured by field-emission type scanning electron microscopy (FE-SEM) and particle sizes are calculated by image processing software. In the results, only the standing wave with continuous drive showed no second peak within size distribution.

Removal Properties of Diesel Exhaust Particles by a Dielectric Barrier Discharge Reactor

The removal properties of diesel exhaust particles (DEP) were investigated using an engine exhaust particle size spectrometer (EEPS), field emission-type scanning electron microscopy (FE-SEM) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). DEP were treated using a dielectric barrier discharge (DBD) reactor installed in the tail pipe of a diesel engine, and a model DBD reactor fed with DEP in the mixture of N(2) and O(2). When changing the experimental parameters of both the plasma conditions and the engine load conditions, we obtained characteristic information of DEP treated with plasma discharges from the particle diameter and the composition. In evaluating the model DBD reactor, it became clear that there were two types of plasma processes (reactions with active oxygen species to yield CO(2) and reactions with active nitrogen species to yield nitrogen containing compounds). Moreover, from the result of a TOF-SIMS analysis, the characteristic secondary ions, such as C(2)H(6)N(+), C(4)H(12)N(+), and C(10)H(20)N(2)(+), were strongly detected from the DEP surfaces during the plasma discharges. This indicates that the nitrogen contained hydrocarbons were generated by plasma reactions.

Characteristics of graphene-layer encapsulated nanoparticles fabricated using laser ablation method

Graphene layer-encapsulated Ni nanoparticles with diameters between 3 and 10 nm were fabricated by laser ablation techniques and deposited directly on the Si substrate at room temperature. It was found from the field-emission type scanning electron microscopy (FE–SEM) and transmission electron microscopy(TEM) analyses that any carbon nanotubes were not fabricated in the deposited nano-materials. High-resolution TEM observation showed the core-shell structure of Ni–C particles with crystalline nickel core surrounded by graphite-like layers. The X-ray diffraction(XRD) pattern also revealed that nanoparticles embedded in graphene capsules are crystalline nickel. With these Ni–C nanoparticles, we demonstrated the growth of vertically aligned carbon nanotubes with low spatial density on a silicon substrate by thermal CVD.

Effect of Thermal Oxidation Treatment on Surface Characteristic and Corrosion Resistance of Ni-Ti Shape Memory Alloy

In this study, a mechanically polished Ni-Ti alloy was subjected to isothermal oxidation (TO) in N2-20vol.%O2 at temperatures ranging from 300 to 800°C. TO-treated surfaces were then characterized by field emission type scanning electron microscopy (FE-SEM), energy dispersive X-ray spectrometer (EDX), X-ray electron spectroscopy (XPS) and X-ray diffraction (XRD). Electrochemical corrosion tests were also carried out using a three electrochemical cell connected to a computer driven potentiostat. Results showed that Ni-Ti alloy exhibited different oxidation behavior depending on the treatment temperatures. A Ni free layer was observed in the oxide layer for the specimens TO-treated at temperatures 500°C and above. Specimens TO-treated at temperatures ranging from 300 to 500°C showed higher corrosion resistance compared to that of the surface finished by polishing. This was because the TO-treatment created a thick oxide layer with an amorphous structure. Specimens TO-treated at above 600°C showed very low passive current densities, but lower pitting potential. This was because these samples were covered with crystalline oxide. Consequently, the TO-treatment at 500°C produced a smooth protective nickel free oxide layer, which contributes to good biocompatibility of Ni-Ti implants.

Synthesis and H 2 gas sensing properties of tin oxide nanohole arrays with various electrodes

Tin oxide nanohole arrays have been prepared by a liquid phase deposition method. Field emission-type scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) are used to characterize the surface morphologies and crystal structures of the tin oxide nanohole arrays. Two types of noble metal (Au, Pt, and Pd) electrodes covered with the surface of the tin oxide nanohole arrays, and the gas response of the sensors was measured to H 2 balanced with air. Tin oxide nanohole array sensors exhibited reversible response to H 2 in air. Temperature dependence of the gas response differed between the sensors equipped with a pair of electrodes on both surfaces and the sensors equipped with a couple of inter-digitated electrodes on one side. And H 2 response of the sensors equipped with a pair of electrodes on both surfaces was much higher than that of the sensors equipped with inter-digitated electrodes on one side.

Characterization of amorphous carbon film-coated nanotubes as electron field emission material

Effects of amorphous carbon (a-C) thin film coating over carbon nanotubes (CNTs) on the field emission characteristics have been studied. Large-area surface-wave plasma (SWP) device was used both for growth of multi-wall CNTs on Ni-evaporated Si substrate and for deposition of a-C thin layer over CNTs. Field emission characteristics of the a-C film-coated CNTs prepared with different CVD durations were investigated. Experimental results show that the emission performance was significantly improved by coating a-C film typically with a thickness of 0.6–1 μm, that is, the ignition voltage for electron emission was reduced from 240 V for the sample of CNTs only to 110 V for that of CNTs deposited with a-C film during 60 min. The surface morphology has been also studied using the field emission type scanning electron microscopy (FE-SEM). It was deduced that the reduction of ignition voltage was due to the field enhancement originated from grain shape structures of the surface after a-C film deposition.

Photoinduced formation and aggregation of silver nanoparticles at the surface of carboxymethylcellulose films

Formation and aggregation of photolytic silver nanoparticles at the surface of silver salt of carboxymethylcellulose films (CMCAg films) have been investigated. Detailed X-ray photoelectron spectroscopy (XPS) study and field emission type scanning electron microscopy (FE-SEM) observation have been carried out to characterize silver nanoparticles at the film surface. When the CMCAg films were irradiated with UV light in wet air at room temperature for 30–60 min, silver nanoparticles of ca. 10 nm size were formed at the irradiated surface. According to the FE-SEM observation, the growth of the particle diameter and aggregation of nanoparticles took place after prolonged irradiation, and finally, the irradiated side of the film surface was densely covered with the silver nanoparticles of ca. 35 nm size. Chemical composition analysis by the XPS measurements has confirmed the increase in the atomic concentration of silver with irradiation time. It is suggested that silver atoms and clusters can move in the film and precipitate at the irradiated surface.

Visualization of subgrain structure for a ferritic 12Cr–2W steel using backscattered scanning electron microscopy

A new observation method was developed for visualizing subgrain structure on the chemical–mechanically polished surface of a ferritic heat-resisting steel that contained 12 mass% chromium and 2 mass% tungsten, using field emission-type scanning electron microscopy (FE-SEM). The backscattered electron images revealed clearly visualized subgrain structures that were not influenced by the presence of precipitated particles.

Aggregation of Photolytic Gold Nanoparticles at the Surface of Chitosan Films

Formation and aggregation of photolytic gold nanoparticles at the surface of chitosan (CTO) films have been investigated. When thin films of chloroauric acid salt of CTO were irradiated with UV light in wet air at room temperature for 10 min, gold nanoparticles of approximately 10 nm size are formed at the film surface. Detailed X-ray photoelectron spectroscopy (XPS) study and field emission type scanning electron microscopy (FE-SEM) observation have been carried out to characterize gold nanoparticles at the film surface. The shift of Au(4f) peak to the higher energy side and broadening of full width at half-maximum in the XPS spectrum are the direct evidence of the existence of gold atoms and small clusters in the early stage of photolysis. According to FE-SEM observation, growth in the particle diameter and aggregation of nanoparticles were observed after prolonged irradiation, and, finally, the film surface was densely covered with gold particles of 20-100-nm size. Gold atoms and clusters could move in the film and precipitate to the irradiated surface. Chemical composition analysis further suggests that gold particles at the surface are covered with an ultrathin CTO layer, which is partly oxidized by oxygen and chlorinated by chlorine during photochemical reactions.

Observation of Multi-Scale Structure for a Creep-Fatigued Ferritic 12Cr-2W Steel

Microstructural analyses by field emission-type scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) were performed on a ferritic heat-resisting steel that contained 12 mass% chromium and 2 mass% tungsten to characterize its multi-scale structure, consisting of prior austenite grains, packets, blocks, subgrains and precipitates. The size distributions of the blocks, subgrains and precipitates were quantitatively evaluated before and after a creep-fatigue test to relate them to their creep-fatigue property. Our results showed that the occupancy of precipitates on prior austenite grain boundaries increased markedly and subgrains became coarse during the creep-fatigue test, while the block size did not change. It is suggested that the growth of grain boundary precipitates and coarse subgrains plays an important role in the intergranular fracture mechanism caused by creep-fatigue.

Effects of Ion-Beam-Irradiation on Morphology and Densification of CeO2 Films Prepared by Ion-Beam-Assisted Deposition

Cerium oxide (CeO2) films were prepared by ion-beam-assisted deposition (IBAD). The films were synthesized on Si wafers by depositing CeO2 vapor under simultaneous bombardment with O2, Ar and Xe ions in the energy range of 1.0 to 5.0 keV. Film characterizations were performed using field-emission-type scanning electron microscopy (FE-SEM) for cross-sectional observation of film morphology and film crystallization was examined by X-ray diffractometry (XRD). Rutherford backscattering spectrometry (RBS) was used for measuring the film composition and the packing density. Refractive indices of the films were measured by ellipsometry to investigate their optical properties. With increasing the transport rate ratio of ions to CeO2 vapor, the morphology of the specimens prepared with O2 and Xe ion beams was changed from columnar to granular structure. The increase in the transport ratio also had a significant effect on the enhancement of the film densification, leading to an increase in the refractive index.

Miscibility and phase structure of at-polypropylene/ethylene- block-(ethylene- co-butylene)- block-ethylene-copolymer blend

Miscibility and phase structure in blends of atactic-polypropylene (aPP) with poly[ethylene- b-(ethylene- co-butylene)- b-ethylene] (E-b-EB-b-E) containing different butylene content in the mid-block were investigated by differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and field emission type scanning electron microscopy (FE-SEM). In DSC measurement, blends showed single glass transition temperature in no relation to the blend composition and the butylene contents of mid-block in the block copolymers. On the other hand, the melting point of PE block in the block copolymers was not varied systematically with variation of the blend composition with no relation to the butylene content. From these results, it is assumed that aPP dissolves in the EB block in the copolymers. In morphological observation, it was revealed that all blends have the islands–sea structures containing PE domain. In the blends using the high butylene content copolymer, it was observed that PE domain became smaller than that of neat block copolymer. On the other hand, in the lower butylene content copolymer, the microphase structure was not observed but fine dispersed phase separated structures were observed in the blends of aPP and the copolymer.

Quantitative assessment of pores in oxidized carbon spheres using scanning tunneling microscopy

Surface heterogeneity, particularly shape and size of pores on the surface of activated carbon spheres were studied by using scanning tunneling microscopy (STM) and field-emission type scanning electron microscopy (FE-SEM). Spheres were carbonized either in N2 or CO2 atmosphere and oxidized ones were used as samples. A new numerical method based on the determination of contour maps from STM images was proposed in order to determine the size distribution in micropores. These results were discussed with respect to the adsorption of gas and liquid molecules. A good correlation between Brunaner, Emmett, and Teller (BET) surface area determined from adsorption isotherms of N2 at 77 K and the number of pores with the size of 0.5–1.8 nm was observed, indicating that the proposed procedure to analyze the pore size distribution is effective.

Phase Structure in Blends of Poly(ethylene glycol) and Poly(styrene-co-methacrylic acid)

Phase structures in blends of poly(ethylene glycol) (PEG) and poly(styrene-co-methacrylic acid) (P(S-co-MAA)) with several contents of methacrylic acid units are investigated by using both optical microscopy and field emission type scanning electron microscopy (FE-SEM). It is found that phase-separated domains are diminished with increasing MAA content in PEG/P(S-co-MAA) blends. Further, in the blends in which the ratio of MAA/−CH2CH2O− is larger than 0.2 (mol/mol), macroscopic phase structures disappeared despite the presence of two Tg's meaning separation into two phases in differential scanning calorimetry (DSC) measurements. In PEG/P(S-co-MAA) blends in which MAA/−CH2CH2OEnDash− > 0.2 (mol/mol), phase-separated structures like interpenetrating networks are found by FE-SEM observations.

Hydrothermal-electrochemical deposition of hydroxyapatite.

Hydroxyapatite crystals were formed on a titanium electrode using the hydrothermal-electrochemical method in an autoclave with two electrodes. The electrolyte dissolving NaCl, K2HPO4, CaCl2.2H2O, trishydroxyaminomethane, and hydrochloric acid was maintained at 80 degrees - 200 degrees C. After loading of a constant current at 12.5 mA/cm2 for 1 h, the deposited amounts were measured through the weight gain of the electrode. The deposits were characterized by X-ray diffractometry, Fourier transform infrared spectroscopy, field emission-type scanning electron microscopy, field emission-type transmission electron microscopy, and energy dispersive X-ray spectroscopy. The deposited amount increased with electrolyte temperatures up to 150 degrees C and slightly decreased above that temperature. The deposits were identified as hydroxyapatite crystal rods grown along the c axis and perpendicular to the substrate. The crystallinity of the deposited hydroxyapatite increased continuously with the electrolyte temperature and closed to stoichiometric hydroxyapatite. At 150 degrees - 160 degrees C, the hydroxyapatite rod grew very homogeneously perpendicular to the substrate, and the edge of the needle had a flat hexagonal plane.

Hydrothermal–electrochemical deposition of hydroxyapatite

Hydroxyapatite crystals were formed on a titanium electrode using the hydrothermal–electrochemical method in an autoclave with two electrodes. The electrolyte dissolving NaCl, K2HPO4, CaCl2 · 2H2O, trishydroxyaminomethane, and hydrochloric acid was maintained at 80°–200°C. After loading of a constant current at 12.5 mA/cm2 for 1 h, the deposited amounts were measured through the weight gain of the electrode. The deposits were characterized by X-ray diffractometry, Fourier transform infrared spectroscopy, field emission-type scanning electron microscopy, field emission-type transmission electron microscopy, and energy dispersive X-ray spectroscopy. The deposited amount increased with electrolyte temperatures up to 150°C and slightly decreased above that temperature. The deposits were identified as hydroxyapatite crystal rods grown along the c axis and perpendicular to the substrate. The crystallinity of the deposited hydroxyapatite increased continuously with the electrolyte temperature and closed to stoichiometric hydroxyapatite. At 150°–160°C, the hydroxyapatite rod grew very homogeneously perpendicular to the substrate, and the edge of the needle had a flat hexagonal plane. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 42, 387–395, 1998.