Field-emission Microscopy Research Articles

Osseointegrated membranes based on electro-spun TiO2/hydroxyapatite/polyurethane for oral maxillofacial surgery.

Membranes which have an osseointegration abilty are often selected as biomaterials in oral and maxillofacial surgery. Although these membranes are often the best option for certain uses, it is a challenge to create functionally attractive membranes. In this research, electro-spun titanium oxide (TiO2)/hydroxyapatite (HA)/polyurethane (PU) membranes were fabricated with different ratios of HA and TiO2: 100: 0, 70:30, 50:50, 30:70 and 0:100 w/w. The morphologies of the different mixtures were assessed with a Scanning Electron Microscope (SEM) and Field Emission Microscope (FESEM). Element analysis was performed with EDX. The physical properties of the water contact angles and mechanical strength were tested and the membranes cultured with osteoblasts to evaluate their biological functions, cell adhesion, viability, proliferation, alkaline phosphatase (ALP) activity, and calcium content. The results showed that the membranes with TiO2 and HA had smaller fibers than those without TiO2 and HA. The TiO2- and HA-including compounds showed the formation of particle aggregation on the surface of the fibers. They also had higher water contact angles, mechanical strength, and stiffness than those without TiO2 and HA, and they had better cell adhesion, viability, proliferation, ALP activity and calcium content. The membrane with a 50:50 TiO2:HA ratio had more unique biological functions than the others. Finally, our research demonstrated that osseointegrated membranes with 50:50 TiO2:HA are promising for oral and maxillofacial surgery.

Field emission microscopy pattern of a single-crystal diamond needle under ultrafast laser illumination

We report herein on the spatial beam properties of a field emission electron source based on a single-crystal diamond needle illuminated by ultrashort light pulses. We show that the increasing of the laser intensity strongly modifies the emission pattern, leading to the emergence of a new emission region at high peak power. This region is situated on the opposite side of the diamond needle to the one irradiated by the laser. By spatially-resolved energy spectrometry, we prove that the electrons emitted from this region are governed by a multi-photon absorption process. The occurrence of this emission pattern can be explained by accounting for the inhomogeneous distribution of the optical field enhancement and the laser absorption induced by light diffraction within the nanometric needle. The numerical simulations performed on a real sub-wavelength tip confirm this localization of the optical field enhancement and reveal that the electrons trajectories match the spatial beam distribution evidenced experimentally. This work underlines the need to closely monitor the surface roughness of the field emitter as well as the laser illumination conditions to finely control its emission pattern.

Neuroprotective and Antioxidant Effect of Naringenin-Loaded Nanoparticles for Nose-to-Brain Delivery

Parkinson’s disease (PD) is a neurodegenerative disorder resulting in a decreased nigrostriatal availability of dopamine. Oxidative stress is one factor contributing to PD. Naringenin (NAR), a flavonoid, is a potent antioxidant shown to be beneficial in experimental PD. The clinical development of NAR has been hampered due to its low bioavailability resulting from gastrointestinal degradation, inefficient permeability, and low aqueous solubility. The objective of the present research was to formulate and characterize naringenin-loaded chitosan nanoparticles (NAR NPs) for nose-to-brain delivery. The cellular uptake, cytotoxicity, and neuroprotective effects of NAR NPs were determined using the SH-SY5Y cell line in vitro. NAR NPs were prepared using the ionic gelation method and characterized by zetasizer, transmission electron microscopy (TEM), and field emission microscopy (FESEM). The average particle size, polydispersity index (PDI), zeta potential, entrapment efficiency, and 24 h in vitro release profile were 87.6 ± 8.47 nm, 0.31 ± 0.04, 15.36 ± 2.05 mV, 91.12 ± 2.99%, and 54.80 ± 4.22%, respectively. The percentage NAR permeation through nasal mucosa from NPs was found to be 67.90 ± 0.72%. Cellular uptake of prepared NPs was confirmed by fluorescence microscopy. Neuroprotective activity of NAR NPs was evaluated through viability assays and by estimating reactive oxygen species (ROS) levels. NAR NPs showed enhanced neuroprotective ability and antioxidant effect against 6-OHDA-induced neurotoxicity in SH-SY5Y cells. However, animal studies are necessary to establish the potential of NAR NPs to be an effective carrier for the treatment of PD for nose-to-brain delivery.

Physical properties of cerium doped-yttrium iron garnet ultrathin films for photovoltaic application

In this study, cerium incorporated yttrium iron garnet ultrathin films (CexY3-xFe5O12) (where x = 0, 0.1, 0.3, and 0.5) were prepared by the sol-gel method, spin coating technique, and heat treatment on quartz substrates. The effect of Ce on structural properties, morphology of thin films surface, and optical properties was explored by X-ray diffraction (XRD), field emission microscopy (FESEM), and atomic force microscopy (AFM). According to the XRD results, the films were crystalline with the cubic phase, while the FESEM indicated the YIG nanoparticles with approximately spherical shapes. The growth process of crystallite in YIG nanoparticles was investigated by X-ray peak broadening. The Williamson-Hall (W–H) analysis was utilized to maintain the contributions of crystallite size on the peak broadening of Ce:YIG nanoparticles. The structural features of thin films such as strain and stress for all of the peaks of XRD were accurately determined from the uniform deformation model (UDM) according to the YIG cubic phase. According to the AFM pictures, it seemed that thin films had a continuous and smooth surface. The absorption and transmission were measured in the visible and infrared region from 400 to 1200 nm.

Inhibitory effects of tangeretin on osteoclastogenesis and titanium particle-induced osteolysis

Objective To explore the effects of tangeretin on osteoclastogenesis and bone resorption. Methods Primary bone marrow mononuclear macrophages were isolated and purified from C57BL/6 mice, and different concentrations of tangeretin were added for co-culture. Cell count kit (CCK-8) method was used to detect the cytotoxicity of tangeretin. Macrophage-colony stimulating factor (M-CSF) and receptor activator of nuclear factor-κB ligand (RANKL) were used to induce the differentiation of primary bone marrow mononuclear macrophages into osteoclasts. No tangeretin was given in the control group, and different concentrations of tangeretin (3.125, 6.250 μmol/L) were added in the experimental groups. The number of osteoclasts was counted by tartrate resistant acid phosphatase (TRAP) staining. Cells were planted on bone slices and treated with different concentrations of tangeretin until osteoclasts formed, and bone slices were imaged and analyzed using field-emission scanning electron microscopy. Twenty mice were randomly assigned to four groups (n=5 for each): sham PBS control (sham), Ti particles with PBS (vehicle), and Ti particles with low [10 mg/(kg·day)] or high [20 mg/(kg·day)] concentrations of tangeretin. After 14 days, the effects of tangeretin on osteoclasts in vivo were studied using the titanium particle-induced calvarial osteolysis model. Results Tangeretin cytotoxicity was concentration-dependent. Cell viabilities at 6.250, 12.500 and 25.000 μmol/L of tangeretin were not significantly different from those in the control group (P>0.05). The maximum concentration used in our study was 25.000 μmol/L, which was proven to have no cytotoxic effects on primary bone marrow mononuclear macrophages. Compared to the control group, the number of TRAP positive multinucleated osteoclasts in tangeretin 3.125 μmol/L group (P<0.01) and 6.250 μmol/L group (P<0.01) was significantly decreased. Similarly, the bone resorption area in tangeretin 3.125 μmol/L group (P<0.01) and 6.250 μmol/L group (P<0.01) was also significantly decreased. The In vivo results showed significant osteolysis of the skull in the control group compared to the sham group (P<0.01). As compared with the control group, the osteolysis was significantly inhibited in both the low-concentration tangeretin group (P<0.01) and the high-concentration tangeretin group (P<0.01), and the degree of osteolysis in the high-concentration tangeretin group was significantly lower than that in the low-concentration tangeretin group (P<0.01). Conclusion Tangeretin could inhibit the osteoclastogenesis and osteolysis. Key words: Tangeretin; Osteoclasts; Bone resorption; Osteoporosis

Changes in Ion-Current Composition in the Process of Field Evaporation of Tungsten at High Temperatures

Field evaporation of tungsten at T ~ 2000 K was studied using a sector magnetic mass spectrometer with a field ion source and a field emission microscope. Only low-charge ions W+2 and W+ of all W isotopes were observed in the process of evaporation. The mass distribution of ion currents of isotopes agreed roughly with the standard isotopic ratio for natural tungsten, although certain deviations from it, which were attributed to fluctuations and the erratic nature of evaporation process, were also detected.

Activated Carbons from Thermoplastic Precursors and Their Energy Storage Applications.

In this study, low-density polyethylene (LDPE)-derived activated carbons (PE-AC) were prepared as electrode materials for an electric double-layer capacitor (EDLC) by techniques of cross-linking, carbonization, and subsequent activation under various conditions. The surface morphologies and structural characteristics of the PE-AC were observed by field-emission scanning electron microscope, Cs-corrected field-emission transmission electron microscope, and X-ray diffraction analysis, respectively. The nitrogen adsorption isotherm-desorption characteristics were confirmed by Brunauer–Emmett–Teller, nonlocal density functional theory, and Barrett–Joyner–Halenda equations at 77 K. The results showed that the specific surface area and total pore volume of the activated samples increased with increasing the activation time. The specific surface area, the total pore volume, and mesopore volume of the PE-AC were found to be increased finally to 1600 m2/g, 0.86 cm3/g, and 0.3 cm3/g, respectively. The PE-AC also exhibited a high mesopore volume ratio of 35%. This mesopore-rich characteristic of the activated carbon from the LDPE is considered to be originated from the cross-linking density and crystallinity of precursor polymer. The high specific surface area and mesopore volume of the PE-AC led to their excellent performance as EDLC electrodes, including a specific capacitance of 112 F/g.

Field electron emission induced glow discharge in a nanodiamond vacuum diode

The present paper extends the prior findings on self-induced heating of solid state field emission devices. It was found that a vacuum diode (base pressure ∼10−9 Torr), that makes use of graphite-rich polycrystalline diamond as cathode material, can switch from a diode regime to a resistor regime to a glow discharge plasma regime without any external perturbation, i.e. all transitions are self-induced. Combined results of in situ field emission microscopy, ex situ electron microscopy and Raman spectroscopy suggest that it is the nanodiamond cathode of the diode heated to about 3000 K which causes self-induced material evaporation, ionization and eventually micro-plasma formation. Our results confirm that field emission, commonly called cold emission, is a very complex phenomenon that can cause severe thermal load. Thermal load and material runaway could be the major factors causing vacuum diode deterioration, i.e. progressive increase in turn-on field, decrease in field enhancement factor, and eventual failure.

Scanning Field Emission Microscopy with Polarization Analysis (SFEMPA)

In the Fowler-Nordheim regime of Scanning Tunneling Microscopy (STM) the tip-target distance is few nanometers to few tens of nanometers. In this situation the tunneling between tip and target is completely suppressed. Instead, electrons can be field-emitted from the tip and their impact with the target might excite electrons off the surface. Under certain circumstances, the excited electrons escape the tip-target junction and build a new electronic system, absent in the tunneling regime of STM. A recent experiment discovered that this electronic system is spin polarized at nanoscale tip-target distances. Here we provide a comprehensive review of all strategies that have been adopted to perform the spin polarized experiments in the Fowler-Nordheim regime of STM. We also present new data that complement the proof of spin polarization and specifically underline the magnetic imaging potential of this new technology, which we call Scanning Field Emission Microscopy with Polarization Analysis (SFEMPA).

(Invited) Self-Supported Nanoporous Carbon Scaffold As a Novel Material for Use in Fuel Cells and Electrolysis Cells

Several years ago, our group pioneered the use of mesoporous colloid imprinted carbon (CIC) powders (1-3) for a wide variety of electrochemical applications, including as catalyst supports in PEM fuel cells, as electrodes in supercapacitors and redox-flow batteries, sensors, and for water deionization. The CICs have an ordered, close-packed internal porous (spherical) structure and are typically prepared by imprinting a mesophase carbon pitch powder with a colloidal silica template, followed by carbonizing the imprinted pitch and then removal of the silica template. One of the biggest advantages associated with the CICs is the tunability of their pores, controlled by the size of the silica colloid (from ca. 10 to 100’s of nanometers) used in the templating step, with our CICs having pore sizes ranging from ca. 8 – 100 nm. This pore size is ideal for the deposition of catalytic nanoparticles inside the pores, as well as the infiltration of an ionomer phase, such as Nafion, for use in PEM fuel cell catalyst layers. However, one disadvantage of the CIC powders, especially in PEMFC applications, is that there are variable pore sizes between the CIC particles and thus varying access to Nafion and water. Also, the use of powders makes it challenging to image the same particle or region before and after catalyst testing to determine any changes that have occurred, including carbon corrosion.Partly for these reasons, as well as the desire for improved reproducibility of the catalyst layer microstructure, our team recently developed a novel, self-supported, nanoporous carbon scaffold (NCS) material (4,5) for use in PEMFCs, but also in electrolysis systems. The preparation method used to produce the NCS membranes is similar to what was used by our group to make the CIC powders, employing mesophase pitch as the carbon precursor and imprinting with silica colloids of controlled diameter. The pore size can be similarly tailored (from 5 nm to > 100 nm) and the thickness can be controlled to 1-100 microns, with the NCS being formed using a tape casting method. We have also successfully modified the internal wettability of the NCS through surface functionalization, examples being a hydrophilic group (e.g., -PhSO3H) or a hydrophobic group (e.g., PhF5), and have also successfully loaded the NCS with Pt nanoparticles using a variety of approaches. The electrochemistry of the NCS materials, carried out in aqueous solutions using 3-electrode circuitry, shows that the internal surface of the NCS is fully percolating, with all of the pores being 3-D interconnected. Similar to the CICs, the ink bottle-shaped pores within the NCS material are connected bypore necks, which are typically 25-50% of the diameter of the corresponding spherical pores. The necks may hinder mass transport within the NCS during device operation and thus efforts have been made to tailor the pore neck size. The performance of the NCS material within a full PEMFC MEA has also been determined as a function of NCS pore and pore neck size. As well, the behavior of the NCS material in a flow through mode, including for CO2reduction in an electrolysis cell, has been demonstrated, while also having been characterized using nitrogen gas sorption, field emission microscopy (FE-SEM), transmission electron microscopy (TEM), 3-D TEM, TEM tomography, and elemental analysis.

A Comparative Study of Field Emission From Pristine, Ion‐Treated and Tungsten Nanoparticle‐Decorated p‐Type Silicon Tips

The field electron emission characteristics of individual tips of a silicon field emitter array are analyzed. The array of conical‐shaped tips is fabricated on a p‐type silicon wafer by using reactive ion etching and sharpening oxidation. The tips are decorated with single tungsten nanoparticles at their apexes. Furthermore, the focused ion beam is also used to increase surface conductivity of some of the tips. Comparative measurements of field emission are performed by using the scanning anode probe field emission microscopy technique. All types of tips demonstrated emission activation consisting of a sudden current increase at a certain value of the applied voltage. Compared to the pristine tips, a noticeable reduction of the saturation effect in the current–voltage characteristics and a smaller light sensitivity for the decorated tips is found. For ion‐treated tips, saturation effects and light sensitivity are completely suppressed. Scanning electron microscopy observations reveal the formation of single nanoscale protrusions extending from the metal particles and from the apexes of bare ion‐treated tips after exposure under strong electric fields during the field emission measurements. The influence of protrusions growth on characteristics of silicon field emitter arrays is discussed.

MgO nanoparticles confined in ZIF-8 as acid-base bifunctional catalysts for enhanced glycerol carbonate production from transesterification of glycerol and dimethyl carbonate

Abstract MgO-loaded ZIF-8 catalysts (MgO@ZIF-8) with various MgO loadings were prepared and characterized using atomic absorption spectroscopy (AAS), powder X-ray diffraction (PXRD), Fourier-transform infrared spectroscopy (FT-IR), N2 sorption isotherms, field-emission transmission electron microscopy (FE-TEM), and thermogravimetric analysis (TGA). Our results indicate that MgO nanoparticles could deposit onto the ZIF-8 surface with high atom efficiency while maintaining the ZIF-8 structure through a wet-impregnation and calcination process. It is suggested that the surface sites and microporosity of ZIF-8 support provide an adequate environment for the initial deposition of Mg precursor and subsequent growth of MgO nanoparticles through a nanoconfinement effect. MgO@ZIF-8 catalysts were tested for catalytic transesterification of glycerol and dimethyl carbonate to yield glycerol carbonate. It is found that the 50 wt% MgO@ZIF-8 catalyst display an improved catalytic activity than those of MgO and ZIF-8. Furthermore, the MgO@ZIF-8 catalysts showed higher catalytic activities than their physically-mixed counterparts, indicative of a synergistic effect between MgO and ZIF-8, which is explained by a proposed mechanism based on acid-base bifunctional sites on the surface.

Surfactant-assisted spray pyrolyzed SnO2 nanostructures for NO2 gas-sensing application

Well-defined morphologies of tin oxide (SnO2) nanostructures assisted by cationic surfactant such as cetyl trimethyl ammonium bromide (CTAB) have been obtained by simple and cost-effective spray pyrolysis technique (SPT) for NO2 gas detection. The effect of concentrations of CTAB on the structural, morphological, electrical, optical, and gas-sensing properties of SnO2 nanostructures was investigated using X-ray diffraction, field-emission scanning electroscope microscopy, two probe resistivity, and photoluminescence techniques. The XRD results revealed that high concentration of CTAB in the precursor solution leads to decrease in crystallite size with significant changes in the morphology of SnO2 nanostructures. Photoluminescence studies of the SnO2 nanostructures showed the emissions in visible region, which exhibit marked changes in the intensities upon variation of surfactants in the precursor solutions. The calculated crystallite size was found to be 10.78–24.57 nm. The optical band-gap energy was found to be in the range of 3.95–2.78 eV. Using indigenously built gas-sensing unit, the gas-sensing properties of synthesized thin film were studied. For NO2 gas at 150 °C as an operating temperature and for 20 ppm concentration of the gas, the gas response for CTAB4 thin film is found to be 19.43.

Surface Modification of SiO₂ for Highly Dispersed Pd/SiO₂ Catalyst.

Surface modification of SiO₂ supports was shown to significantly affect the properties of Pd/SiO₂ catalysts. The surface of SiO₂ can be modified by various pretreatment methods. In this study, the effect of different calcination temperatures on support surface was investigated. Pd supported on pretreated SiO₂ was characterized by H2 temperature-programmed reduction (TPR), XRD, CO chemisorption measurements, and field-emission transmission electron microscopy (FE-TEM). The silanol group (-OH), which is one of the functional groups of SiO₂, interferes with the reduction of palladium because it strongly bonds with palladium ions (-PdO) during the preparation of the catalyst. Due to the complete removal of silanol (Si-OH) groups following calcination at 700 °C, the metal reducibility was enhanced, and the catalyst pretreated at this calcination temperature exhibited the highest metal dispersion of 13.02%. Further, to confirm the catalytic activity of the prepared catalysts, hydrogenation of D-glucose was conducted. The HPLC results demonstrated that Pd/SiO₂_700 has the highest catalytic activity toward hydrogenation of D-glucose. Therefore, it was confirmed that the removal of silanol groups increase the metal dispersion and catalytic activity of Pd/SiO₂ catalyst.

Glass fiber supported BiOI thin-film fixed-bed photocatalytic reactor for water decontamination under solar light irradiation

BiOI powder has been proved to be an efficient photocatalyst, but the difficulty in removing it from water after reaction limits its application in real water treatment. To solve this problem, a thin-film fixed-bed reactor (TFFBR) was set-up by developing a BiOI thin film on glass fiber cloth (GFC). The composition and structure of the as-prepared films were characterized with X-ray diffraction, X-ray photoelectron spectroscopy, field emission microscopy, transmission electron microscopy and Fourier transform infrared spectroscopy. The BiOI thin film was made by painting a silica sol containing BiOI on GFC, which could be tailored to desired sizes to accommodate the TFFBR. The mass of BiOI on the GFC increased with the number of iterations of the painting process. SiO2 sol glued the BiOI particles tightly onto the GFC, making the thin film strong enough to resist fluid flushing in the TFFBR. The photocatalytic activity of the BiOI thin film was investigated by degrading bisphenol A (BPA) under simulated sunlight. Ninety eight percent of BPA (20 mg/L in 2 L) was degraded by the BiOI thin film sample of seven layers (GFC-7) on the TFFBR within 8 hr irradiation. The GFC-7 displayed good photocatalytic ability toward artificial sewage containing BPA in a wide pH range (5–9), and also demonstrated excellent durability and reusability. The working conditions were optimized and it was found that the thickness of the fluid film and residence time over the thin film were key factors affecting the photocatalytic efficiency.

Micro-Spectroscopy in the Low-Energy Regime:Secondary Electron Detection and Energy Analysis in the Scanning Field-Emission Microscope

Micro-Spectroscopy in the Low-Energy Regime:Secondary Electron Detection and Energy Analysis in the Scanning Field-Emission Microscope

Deformation mechanism of metastable titanium alloy showing stress-induced α′-Martensitic transformation

In this study, the deformation mechanism of a metastable Ti-4Al-4Fe-0.25Si-0.1O alloy was investigated via ex-situ electron backscattering diffraction (EBSD) and field-emission transmission electron microscopy (FE-TEM). A stress-induced α′-martensitic transformation occurred from the retained β phase. New variants of α′-martensite were nucleated and grew in the transformed α′-martensite under increasing levels of applied stress. Microstructural observations revealed that the orthorhombic nanodomains were sheared in the prior α′-martensite; these sheared nanodomains contributed to the formation of different variants of α′-martensite. This additional martensitic transformation resulted in an excellent combination of strength (ultimate tensile strength; UTS: 1340 MPa) and ductility (30%).

The Effects Of Phthalic Anhydride On R-Hdpe / Eva / Cff Composites: Tensile And Physical Properties

Phthalic anhydride is one of the compromise coupling agents that enhance the dispersion and hydrophobicity of fiber which consequently improved the interfacial adhesion of composites. This article is concerned with the mechanical properties, morphology, and functional groups towards recycled high density polyethylene (r-HDPE)/ethylene vinyl acetate (EVA)/chicken feather fiber (CFF)/phthalic anhydride (PAH) composites. In this study, the r-HDPE/EVA/CFF/PAH composites with varies loading of phthalic anhydride (2, 4, 6 and 8 phr) were moulded into compression moulding machine and tested using conventional universal testing machine. Morphology and functional groups properties were characterized using field emission microscope (FESEM) and Fourier transform infrared spectroscopy (FTIR), respectively. The results showed that the tensile and physical properties (water absorption and oven aging) of r-HDPE/EVA/CFF/PAH composites were slightly affected by the phthalic anhydride loading.

The Influences of Chicken Feather Loading on Tensile and Physical Properties of R-Hdpe/Eva/Cff Composites

PE/EVA blends are one of the popular existing commercial polymers which catch many attentions among researchers and manufacturing industry. This article is concerned with the mechanical properties, morphology, and functional groups towards recycled high density polyethylene (r-HDPE)/ethylene vinyl acetate (EVA) reinforced with chicken feather fiber (CFF). In this study, the r-HDPE/EVA/CFF composites with varies ratio of chicken feather (2.5, 5.0, 7.5, 10.0, and 12.5 phr) were moulded into compression moulding machine and tested using conventional universal testing machine. Morphology and functional groups properties were characterized using field emission microscope (FESEM) and Fourier transform infrared spectroscopy (FTIR), respectively. The results showed that the tensile and physical properties (water absorption and oven aging) of r-HDPE/EVA/CFF composites were slightly affected by the chicken feather fiber content.

Peculiarities of the Condensation of Silicon on the Surface of a Tungsten Single Crystal

Using the methods of the field emission microscopy, the condensation of Si on the W surface at various temperatures T of the substrate and numbers n of monatomic layers of the deposited condensate is studied. At low temperatures of T ~ 600 K, a low-temperature Si monolayer with the structure of pure W is formed on the surface, whereas another structure of a high-temperature monolayer, namely, surface silicide, is formed at T ≥ 1000 K. The low-temperature monolayer and surface silicide also differ in their orienting effect when constructing the Si layers. In the case of condensation on a low-temperature monolayer, crystallites of Si are formed starting already from the third monolayer at n ≥ 3, whereas the Si crystallites grow during the condensation on surface silicide starting from n ≥ 300 monolayers.