Exposure and misuse of organophosphate (OP) compounds originated from insecticides, drugs and chemical warfare agents are potential hazard to health and environment. OP detection is one of the four strategies (deter, detect, delay, and defend) to protect vulnerable from this chemical threat. Among many methods to detect OP, electrical-based detection and graphene nanomaterials deliver higher sensitivity performance, technological compatibility, and versatility. The magic of graphene originates from its large surface area and excellent electrical conductivity, while electrical methods offer low cost, rapid, and easy handling. This article provides an overview of selected electrical and electrochemical methods employing graphene, reduced graphene oxide, graphene oxide, and other graphene forms reported for OP detection in the recent years. Strategies in using graphene, experimental challenges and fundamental material interactions including advantages using biomaterials as receptors in achieving better detection limit, specificity, and selectivity of OP compounds are the highlights of the paper. Every transformation of graphene has its merits in term of ease of processing, device functionality and sustainability. Since contemporary graphene had successfully reached low detection limit possible in OP sensing, graphene sensor device should be focused on developing rapid and in-situ OP monitoring in water and food resources to alert authorities on possible contamination in the community.
The origin of chemical vapor deposition (CVD) growth direction difference in graphene/hexagonal boron nitride (hBN) heterostructures is theoretically studied. The study is focused on the advance in energy gain by H termination of the bare hBN N edge on the Cu(111) surface comparing with that of the bare graphene edge. It is found that the difference in the van der Waals correction method affects largely the advance. However, when the most reliable van der Waals correction of the vdw-DF2-B86R method is used, the results consist with our speculation stating that the edge termination of the existing island rather automatically changes depending on whether the island is graphene or hBN. Thus, it is proposed that the graphene island edge is automatically bare and the hBN island edge is automatically terminated by H during the CVD growth.
Glass micropipettes and nanopipettes are widely used for injection to or aspiration from living cells, and nanopipettes can be also used for nano-fabrication by deposition. Here, we show a non-destructive and contamination-free method of examining the inside of glass micropipettes and nanopipettes by argon gas flow through the pipettes from the tip-top to the tube-end. The exit pressure for each pipette was measured at the entrance pressure of 50 kPa, and the semi-log plot of the vacuum conductance versus pipette inner diameter is compared with the calculation using tapered tube approximation assuming molecular flow. The experimental results were consistent in trend with the calculation, and the difference between the experimental results and the calculation was due to the intermediate gas flow as the pipette inner diameter increases. Therefore, the formula of the calculation was transformed using the Gompertz function to fit the experimental results well. By utilizing the plot of the inner diameter dependence of the exit pressure, the inner diameter of glass pipettes can be estimated from our developed gas flow method.
To enhance the photoluminescence (PL) from erbium-doped silicon, nanopillars were fabricated in a silicon-on-insulator (SOI) layer with erbium and oxygen. Photoluminescence measurements at room temperature demonstrated that a nanopillar with the diameter of 1435 nm exhibits the highest near-infrared PL from erbium atoms, which is 2.0 times higher than that from an unstructured erbium-doped SOI layer. Optical simulations revealed that the PL enhancement is mainly due to the resonance absorption of excitation light at the wavelength of 785 nm. The results show the potential of nanostructure fabrication for enhancing the near-infrared PL intensity.
The scanning atom probe (SAP) developed in the authors’ laboratory has a microelectrode that localizes the electric field around the sample apex. The scanning atom probe can be applied for the measurement of non-bulk, non-solid materials. The metal chelate compounds supported on carbon fiber (CF) were successfully analyzed by scanning atom probe using polyethylene glycol as matrix and CF as support and field emitter. The chelate bonds between Fe2+ metal ion and bidentate ligands 1,10-phenanthroline were found to be stable because the metal complex ions were detected keeping the number of ligands coordinating with the metal ion. On the other hand, the neutral chelate complex was found to dissociate isothiocyanate which was a negatively charged monodentate ligand.
In this paper, the current-voltage (I-V) characteristic and volt-tesla (V-T) characteristic of diodes with a p-n junction under the appearance of a magnetic field are considered. Analysis of the experimentally obtained magnetic diodes I-V characteristic and V-T characteristic with p-n junction, new formulas were derived for calculating the I-V characteristic and V-T characteristics. Based on the developed theoretical formulas, new I-V and V-T characteristics were calculated and graphs were obtained. Theoretically obtained graphs were compared with the experimental ones and similarities were found. Theoretical expressions have been developed to calculate the theoretical I-V and V-T characteristics. Theoretically, they were based on two reasons and their consistency with experience was shown.
Lead iron tantalate (PFT) is multiferroic material and has a complex perovskite structure. To analyze the local structure, we grew a PFT single crystal and applied X-ray fluorescence holography to the grown single crystal. We analyzed the temperature dependence of the first neighbor Pb atomic image around Fe and found that the atomic image intensity almost monotonically increased with decreasing temperature. This behavior is in marked contrast to the case of lead iron niobate, where the Pb atomic image intensity shows an abrupt decrease by cooling down below the magnetic transition temperature of about 150 K. This finding is discussed in relation to the energy gain of Ta and Nb due to the second order Jahn-Teller effect.
Bi-Pr-O composite nanoflakes were synthesized with the aid of polyvinyl pyrrolidone (PVP) as the surfactant. The characterization of Bi-Pr-O composite nanoflakes was performed by X-ray diffraction and electron microscopy. The prepared nanoflakes consisted of tetragonal Bi2O3, hexagonal Pr2O3, and hexagonal Bi0.4Pr0.6O1.5 with smooth surface. The size of whole nanoflakes is less than 1 μm and thickness is less than 100 nm. The formation of the Bi-Pr-O composite nanoflakes can be explained by a PVP-assisted growth mechanism. A systematic study of electrochemical catalysis of L-cysteine using a Bi-Pr-O-composite-nanoflake-modified electrode was carried out. A pair of quasi-reversible anodic and cathodic peaks are observed at −0.69 and +0.02 V, respectively, on the Bi-Pr-O-composite-nanoflake-modified electrode in 2 mM L-cysteine and 0.1 M KCl solution. The current response of the Bi-Pr-O-composite-nanoflake-modified electrode is proportional to the L-cysteine concentration in the range of 0.001—2 mM with a detection limit of 0.33 μM. In addition, the Bi-Pr-O composite nanoflakes display satisfactory reproducibility and stability for the detection of L-cysteine.
Precise second-harmonic generation spectra of monolayer (ML)-MoS2, trilayer (3L)-MoS2 with a 3R structure, and 3L-MoS2 with a 2H structure are measured in the two-photon energy region from 2.4 to 3.2 eV. The spectra are resolved into two components, C1 and C2. As the number of layers increases from ML- to 3L-MoS2, the peak energy of the low-energy component, C1, is red-shifted and its peak width broadens. Peak intensity is also higher for 3L-MoS2 compared with ML-MoS2. This trend reveals that the C1 component originates from interband transitions in a ring-shaped region with bands nesting around the Γ point, similar to the C exciton observed in linear optical spectra. In contrast, for the high-energy C2 component, the variation of peak energy and peak width with layer numbers from ML- to 3L-MoS2 is negligible. Compared with ML-MoS2, the peak intensity increases for the 3L-MoS2 with the 3R structure, but decreases for the 3L-MoS2 with the 2H structure. These behaviors indicate that the C2 component is different from the C excitons in the linear optical spectrum, coming from excitation in a region where the band structure is less modified by interlayer coupling, revealing the presence of a transition to a hidden state, which is specific to the nonlinear optical spectrum.
Theoretical O K-edge X-ray absorption near-edge structure (XANES) spectra of sucrose molecules forming intermolecular H-bonds were obtained by molecular dynamics (MD) and density functional theory (DFT) calculations. The calculated O K-XANES spectra of sucrose molecules forming intermolecular H-bonds suggested that the peaks of O atoms shift toward higher energies in the O K-XANES spectra. The results confirmed that O K-XANES can provide useful information about H-bonds in sugars and that XANES is a powerful tool for investigating the relationship between the melting-point fluctuation of sugars and H-bonds between sucrose molecules.
At room temperature, pure Co has a hexagonal close-packed (HCP) structure. When several percent of Fe is doped into a Co crystal, it changes to the face-centered cubic (FCC) structure. However, it is not clear why the FCC structure in the FexCo1−x system is so stable even with small amounts of Fe concentration. Therefore, we carried out X-ray fluorescence holography (XFH) on a Fe0.08Co0.92 single crystal to visualize the three-dimensional atomic images around both Fe and Co atoms. The intensities of the reconstructed images by XFH around Fe atoms at both 100 and 300 K are inversely proportional to the distance from the Fe emitter, and those at 100 K were always higher than those at 300 K due to the suppression of the thermal vibrations of atoms. However, the image intensities around Co did not increase by cooling unlike those around Fe. In particular, the distance dependence of the atomic image intensities at 100 K are roughly constant up to 0.8 nm. This suggests that the lattice around Co, i.e., matrix crystal lattice of Fe0.08Co0.92, is more distorted than that around dopant Fe.
Absorption efficiency and performances of nanoparticles (NPs) for solar irradiance harvesting were investigated using quasi-static approximation of electrodynamics. This work considered gold (Au)- and silver (Ag)-based NPs in five configurations: solid, metal–graphene (MG), dielectric–metal (DM), dielectric–metal–graphene (DMG), and dielectric–graphene–metal (DGM). SiO2 and HfO2 were the dielectric materials of the structure or the host medium. The size-dependent Drude–Lorentz model determines the permittivity of the metal and the Kubo formula determines the surface conductivity of the graphene. The calculated results show that DGM NPs have the highest absorption performance compared to others with the same radius of 15.34 nm (including a 0.34 nm graphene layer). A SiO2–graphene–metal NP in HfO2 gave the best performance when the dielectric material and environment in the structure were exchanged. Furthermore, adding a graphene layer to an NP generates a secondary peak at a low frequency but reduces the primary peak. Additionally, the performance was enhanced by varying the core radius from 5 to 20 nm for a fixed-size DGM NP with a radius of 25.34 nm until it declines after reaching the maximum performance point. Also, the thickness of graphene influenced the performance of this structure. As a result, a DMG NP can be chosen to be applied in solar irradiance harvesting devices because this structure enhances the solar irradiance absorption performance.
Gold nanoparticles (AuNPs) are used in many applications including in cancer therapy. One way to improve the quality of treatment is to design AuNPs to provide optimum adsorption to the radionuclides being employed. Therefore, we have to first understand the mechanism and quantify the strength of such adsorption process. This study looks at the adsorption characteristics of iodine and astatine on gold nanoparticles, specifically the (111) surface to learn more about adsorption of such heavy elements on Au surfaces. Both iodine and astatine are found to be able to bond with Au(111) via covalent bonding most stably on the face-centered cubic (fcc) site. We also found that the adsorption strength of iodine and astatine on gold are comparable, and that spin orbit coupling correction does not significantly affect the adsorption energies.
A VO2 film with a thickness of 400 nm was deposited on indium-tin-oxide/glass substrate by the inductively coupled plasma-assisted radio frequency magnetron sputtering method. A temperature-dependent Raman spectrum exhibits mixed VO2 M2 and triclinic (T) phases at room temperature. A resistance change of more than one order of magnitude is achieved in out-of-plane direction in the prepared sample. The current-voltage (I-V) characteristics of the prepared sample are investigated by varying the contact probe force on the VO2 side from 1 to 30 gf. At low probe forces, a multi-step like I-V characteristic is obtained. On the other hand, when the probe force is increased, the I-V characteristic similar to the usually reported I-V in VO2 is obtained. Moreover, it was found that the hysteresis width of the I-V characteristics became larger with increasing the probe force. In oscillation measurements, the self-sustained electrical oscillation was obtained until 20 gf. At 20 gf, the oscillation region became smaller than 1 and 5 gf. However, the oscillation was not found at 30 gf. This is responsible for the large hysteresis width in the I-V characteristics. The results suggested that there is a strong correlation between the hysteresis behavior of the I-V characteristics and the oscillation characteristics. We believe that the findings of the present study will contribute to the further acceleration of the application of the VO2 films in various fields.
The magnetic domains in a heterostructured film consisting of antiferromagnetic FeMn and ferromagnetic Co layers were investigated via photoemission electron microscopy combined with X-ray magnetic circular dichroism (XMCD-PEEM) under various magnetization and heat-treatment conditions. Further, these domains were visualized in the macroscopically exchange-biased state after the field-cooling process. By further heating the film above the Néel temperature of FeMn, followed the antiferromagnet (AFM), FeMn, which was restored from the paramagnetic state, aligned submissively according to the existing domain structure of the adjacent ferromagnet (FM), Co, without disturbing its domain structure. Such flexibility of the magnetization of the AFM to the magnetic domains of the neighboring FM during the magnetization from the paramagnetic state contradicts the well-known property of the AFM, i.e., robustness against the external magnetic field, following the determination of its magnetization directions.
We have studied nanometer-scale features observed with scanning tunneling microscopy on nitrogen (N)-adsorbed Cu(001) surfaces. Grid-like nanopattern aligned in  directions at a medium N-coverage and trenches along  appearing at a higher N-coverage are frequently reported. In addition, we observed “diagonal lines” along  on a grid-patterned surface and “dark curves” growing from the trench ends. All features above are responsible for relief of N-induced compressive stress. We propose structural models for the five features, based on a hard-sphere model, and estimate how much strain is absorbed by the feature. Nitrogen atoms are adsorbed on Cu(001) in c(2 × 2) arrangement. Since two energetically-equivalent c(2 × 2) arrangements are possible, two N-adsorbed domains can be “in-phase” or “antiphase” in a  direction at the domain boundary. We show also that each strain-relief feature has specific preference in phases. Looking out over the five mechanisms, we note that, the higher the N coverage is, the more effective relief mechanism is chosen, and that “monoatomic line” (a component of the grid) is very unique since it is formed between in-phase domains.
The effect of the different polishing conditions for niobium has been investigated as the basic data for polishing the superconducting quarter-wave resonators (QWRs) in the booster linac of the Tokai-tandem accelerator. Surface roughness and desorbed hydrogen amount of niobium samples with different polishing conditions such as polishing method (electropolishing: EP or chemical polishing: CP), polishing thickness, and electrode location, have been measured. For the hydrogen amount measurement, thermal desorption spectroscopy has been performed. The electrode arrangement in the EP to avoid hydrogen bubbles hitting the niobium surface is found to be important to obtain a smooth surface and less hydrogen content. The large polishing thickness resulted in a large amount of hydrogen content in the niobium or large surface roughness in the case of both EP and CP. The EP without hitting the hydrogen bubbles and with appropriate polished thickness will be the best solution for the actual polishing of the QWRs.
A non-destructive, fast 2D profile monitor for an ion beam accelerator can be achieved by creating a high-density gas-sheet target in vacuum. It is known that gas flow through a long rectangular channel with a very small gap-to-width ratio is effectual in forming a gas sheet. To obtain a gas sheet with the desired performance, the spatial distribution of the emitted molecules in the candidate channel should be examined in more detail. As part of the gas-sheet development, the gas load through the channel should also be investigated to maintain the accelerator tubes in ultra-high vacuum. For efficient investigation, we explored the possibility of using direct simulation Monte Carlo (DSMC) method instead of experiments. We measured the gas flow (N2 and Ar) through the channel with gap a = 0.1 mm, width b = 50 mm, and length L = 100 mm and derived the vacuum conductance C for the Knudsen number (Kn) in the range of 0.03–104. Then, for comparing with the Kn dependence of the measured conductance, the DSMC method was used to calculate the transmission probability (the Clausing factor Ck) of the molecules passing through a channel with infinite width. The changes in Ck and C are similar. As Kn decreases from ∼103, Ck and C begin to decrease rapidly and reach a minimum when Kn is between 1 and 0.5. Then they increase as Kn decreases further to <0.5. Furthermore, we successfully simulated the spatial distribution of the molecules ejected from the channel when molecular collisions occur with increasing inlet pressure.
In recent years, a durable target is required according to the increase of the beam power. Therefore, a liquid film was formed in a vacuum and was tested as a target. Ethanol and mercury were selected as liquid target materials, and it was investigated whether the liquid sheet could be formed stably in a vacuum, taking into account the vacuum pressure. The results confirmed that the liquid films were stably formed in both cases, and the pressure values with the films were about the vapor pressure of the materials.
Minimizing friction losses in mechanical systems is essential for realizing a low-carbon society, as it will result in energy and resource conservation. In this study, we focused on the suitability of ionic liquids that form an electric double layer for use as liquid lubricants. Ionic liquids have been reported to exhibit ultralow friction with friction coefficients of less than 0.01. However, it is necessary to elucidate the effects of water on their lubricating properties, as water can cause corrosive wear on metallic sliding materials during lubrication using fluorine-based ionic liquids. In addition, water destroys the layer formed at the friction interface and adversely affects the lubricating properties. Here, we investigated the lubricating properties and lubricating mechanisms of both hydrophilic (1-butyl-3-methylimidazolium dicyanamide [BMIM][DCN] and 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4]), and hydrophobic (1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF6] and 1-butyl-3-methylimidazolium tris (perfluoroalkyl) trifluorophosphate [BMIM][FAP]) ionic liquids at different relative humidity (RH) levels (15, 50, and 80%). [BMIM][DCN] exhibited good lubricating properties at 15% RH because of the formation of an adsorption layer derived from both types of ions. However, the adsorption layer was destroyed by water molecules as the humidity was increased. [BMIM][BF4] also exhibited good lubricating properties at 15% RH. This ionic liquid formed a chemical layer as well as an adsorption layer. However, these layers were destroyed by water molecules at 50 and 80% RH. In the case of [BMIM][PF6] too, a chemical layer and an adsorption layer were formed at 15 and 50% RH, and these layers exhibited the best lubricating properties. On the other hand, the layers were destroyed by water molecules at 80% RH. Finally, [BMIM][FAP] exhibited good lubricating properties even under high-RH conditions because this ionic liquid was the most hydrophobic.