SiO coatings on aluminum substrates were prepared using hard-facing performed at ambient conditions. Well-integrated SiO/aluminum interfaces are created via electrodiffusion that takes place during processing. Analysis of surfaces with scanning electron microscopy/EDS and nanoindentation confirm atomic stoichiometries and hardness values consistent with SiO. Hard-facing performed at ambient conditions is a way to coat aluminum with SiO that otherwise would decompose at elevated temperatures typically created using conventional hard-facing.
We designed a segmented undulator composed of four units of an APPLE undulator, such as an APPLE-II, and three phase-shifters. By simulating the optical performance in a 1-nm-rad emittance ring of synchrotron radiation, the novel undulator generates various polarized light that have high flux, high polarization, and fast-switching with a marginal perturbation to an electron beam in the storage ring. Varieties of polarization combinations in undulator segments allow for novel research, such as experiments using orbital angular momentum in X-ray photons. Furthermore, they provide a high flux third harmonic beam for both linear and circular polarizations, extending the photon energy range significantly at a beamline. The high degree of freedom in polarization controls of the segmented undulator provides opportunities for new experiments with low-emittance synchrotron radiation or X-ray free electron lasers.
We developed thermocouple probes consisting of constantan and chromel segments with nanoscale sharpness. The ends of wires made of these alloys were polished utilizing a single step drop-off electrochemical procedure in a H3PO4 solution. The macroscopic shapes of the etched wires were designed to detect ultra-small heat inputs with high sensitivity after assembling a thermocouple. After electrochemical treatment, ultimately smooth, mirror-polished wire surfaces were observed. The etched wires were then assembled in a transmission electron microscope (TEM) to create a miniature thermocouple by using which we successfully detected a small temperature increase induced by focused TEM electron beam irradiation. Judging from high-resolution TEM imaging, a thermocouple with the tip-end of only ∼5 nm in diameter was fabricated.
Transition-metal doping for titanium dioxide (TiO2) is attracting attention for the study of visible-light responsive photocatalyst. Its photocatalytic properties were investigated via various spectroscopic approaches, though surface studies had not yet progressed owing to the difficulty in obtaining its well-defined surface. In this report, we propose that a well-defined crystalline TiO2(110) surface may be obtained by the codoping of chromium (Cr) and antimony (Sb) with commercially available wafers. Cr and Sb are codoped by a solid-state reaction of TiO2(110) wafer and dopant powder. The prepared wafer exhibited visible-light responsivity on absorption below wavelengths of 600 nm. The surface morphology characterization, performed by atomic force microscopy (AFM) revealed that the Cr and Sb codoped TiO2(110) surface has a well crystallized step-terrace structure that is atomically flat, while monodoped TiO2(110) surface does not. The codoping of Cr and Sb with TiO2(110) wafer should contributes towards retaining the stable rutile-TiO2 lattice structure and produces a well-defined TiO2(110) surface structure with visible-light responsive characteristics.
In this work, various ternary cerium oxide/lanthanum oxide/cobalt oxide (Ce/La/Co) nanocatalysts were synthesized by co-precipitation method based on response surface methodology (RSM). The optimum predicted surface area was found to be 67.6 m2 g−1 at calcination temperature of 650°C, La content of 10.0 wt%, and Co content of 8.0 wt%. Average crystal size of optimum ternary Ce/La/Co catalyst was estimated 11.4 nm. The confirmation tests revealed that experimental data can be predicted well by the model. Furthermore, the prepared catalysts were evaluated by Brunauer-Emmett-Teller (BET), Barrett-Joyner-Halenda (BJH), X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), energy-dispersive X-ray (EDX) and NH3 temperature programmed desorption (NH3-TPD) analyses. The characterization results confirmed that ternary Ce/La/Co catalysts were successfully synthesized. Also, the NH3-TPD result showed that total active sites of optimum ternary Ce/La(10)/Co(8) catalyst with La content of 10.0 wt% and Co content of 8.0 wt% was greater than that of single cerium oxide catalyst. The optimum synthesized catalyst was tested for SO2 reaction by methane to sulfur. SO2 conversion and selectivity of catalysts at various temperatures were determined. The better performance of Ce/La/Co optimum catalyst at different temperatures was obtained for SO2 reduction. Also the selectivity of the optimum catalyst for production of sulfur is better than other catalysts.
A high-density convergent plasma sputtering device has been developed for magnetic film deposition. The external convergent magnetic field is produced by a solenoid coil and a permanent magnet positioned behind the ferromagnetic metal target. The ion density and the ion accelerating voltage are individually controlled since the ion production and sputtering areas are separated like an ion beam sputtering device. Iron (Fe) thin films are deposited on an unheated substrate using argon plasmas under the target to substrate distance of 54 mm. The films consist of the α-Fe phase with a body-centered cubic crystal structure. The deposition rate was about 25 nm min−1 at a sputtering gas pressure of 0.2 Pa.
Carbonaceous films, adsorptive for a range of volatile organic compounds (VOCs), were prepared by radio-frequency (rf) sputtering of biomedical-grade polypeptide gelatin crystals. The film was composed of densely packed nitrogen-rich microcolumns, resulting in a groove-poor structure. The gelatin-sputtered quartz crystal resonator was characterized by a high capability to adsorb VOCs, especially for the small, dielectric molecules of ethanol and water. Using the sorption capacities of 17 kinds of 500 ppm VOCs, we modeled the linear solvation energy relationship, which was substantially governed by electrostatic intermolecular interactions. Kelvin force microscopy (KFM) revealed that surface charging of the gelatin-sputtered film increased with the exposure time of the VOCs. Moreover, the dynamic force mode (DFM) in scanning probe microscopy (SPM) was used to elucidate the interaction force between the tip and the sample surface. The retarding phase shift increased with the exposure time of the VOCs. Deviation of the interaction force, induced by adsorption of the VOCs, was higher for hexane than for ethanol. The polar VOCs and the non-polar VOCs were roughly separated by the principal component analysis using the KFM and DFM data.
Recent advances in the molecular design of organic materials have uncovered various novel functional properties. One of them is the coupling of proton dynamics and electrical conductivity, which can only be achieved in 3D organic crystals. However, reduction of dimensionality to two dimensions is essential in organic electronics application. In this study, we prepared and characterized a 2D organic bilayer with “proton-electron” concerted functionality on a solid surface. It consisted of catechol-fused bis(methylthio)tetrathiafulvalene (H2Cat-BMT-TTF) deposited onto an imidazole-terminated alkanethiolate self-assembled monolayer (Im-SAM) on a Au surface. Direct evidence of interfacial hydrogen bonding (H-bonding) was obtained by scanning tunneling microscopy (STM), infrared reflection absorption spectroscopy (IRAS), and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. STM images showed the deposited H2Cat-BMT-TTF molecules as grains with the thickness of a single molecular layer. The OH stretching vibrational modes of H2Cat-BMT-TTF in the IRAS spectra showed a large red shift and substantial broadening upon adsorption on Im-SAM, indicating that the OH groups of H2Cat-BMT-TTF act as the H+ donor sites. The counterpart H+ acceptor sites were pinpointed by N K-edge NEXAFS. The π* peak of the imino N atoms of the imidazole rings in Im-SAM shifted to higher energy upon the adsorption of H2Cat-BMT-TTF. Therefore, H-bonds form between the imino N atoms (H+ acceptor sites) of Im-SAM and the OH groups (H+ donor sites) of H2Cat-BMT-TTF. The present work is a steady step toward the realization of 2D organic functional materials, and the experimental methods adopted herein will serve as powerful tools for the detection of their functions.
We obtained the energy distribution of the interface states at the SiO2/4H-SiC(0001) interface using operando hard x-ray photoelectron spectroscopy. Two types of interface states were observed: one with continuous interface states in the entire SiC band-gap and the other with sharp interface states formed below the conduction band minimum (CBM). The continuous interface states in the whole gap were attributed to carbon clusters while the sharp interface states observed near the CBM were due to the Si2—C=O state and/or the Si2—C=C—Si2 state at the SiO2/SiC interface.
In this study, we introduce a novel algorithm that can recognize the concavo-convex shapes of X-ray photoelectron spectroscopy (XPS) data and estimate the optimum background (BG) in XPS spectra with fine structures near the endpoints. In this algorithm, the active Shirley method was improved by incorporating a function for automatically selecting the analytical range. This autoselection function first investigates all the candidates for the initial endpoints. These estimates are then used to decide the BG shape according to the Shirley method. In order to exclude false-positive candidates caused by the recognition of noise peaks as small XPS peaks, the function evaluates the concavo-convex shape of the XPS spectrum after the long-period noise is removed using a smoothing process. The proposed algorithm was demonstrated to successfully estimate the optimal spectral BG from an XPS spectrum with a poor signal-to-noise ratio of about 40%.
In the present work, an experimental exploration was made to study the bond strength on solid-state coating of aluminum 6063 over EN24 carbon steel by friction surfacing process using different mechtrode diameter. Friction surfacing was carried out by different combinations of elemental process parameters with different mechtrode rods of 12 mm, 18 mm, and 24 mm in diameters. The result showed that the applied axial force and rotational speed has a strong correlation on diameter of mechtrode for obtaining a successful coating during the process. A non-contact infrared (NC-IR) thermometer provided the temperature profile, and the highest temperatures recorded were 358°C, 389°C, and 422°C for the 12 mm, 18 mm, and 24 mm rod diameters, respectively. The mechanical strength of the successful coating was analyzed using the Vickers microhardness and bending tests. The result exhibited that the coating sample obtained by the 18 mm rod diameter gave higher hardness value (142 HV at interface) and bending strength (481 MPa at 120° bend angle) compared to coating samples obtained from the 12 mm and 24 mm rod diameters. The coating was analyzed using field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray analysis (EDAX) techniques to know the feature of microstructure and intermetallic bonding. The result revealed the formation of better martensite attributes and more oxide compounds at the interface of sample made by the 18 mm rod diameter, indicating adequate molecular interlocking between aluminium and iron particles.
The dominant photon detectors and focal plane arrays (FPAs) in the mid-wave infrared (MWIR) range (λ = 3 μm to 5 μm) use single crystal InSb and HgCdTe materials. The cost of these detectors is high, and cooling at approximately 80 K to 120 K is required to reduce the dark current. Colloidal quantum dots (CQDs) can be used to provide the speed and detectivity (D*) of the quantum detectors with lower fabrication costs than those of single crystal epitaxial materials. The aim of this study is to develop a MWIR area array sensor with an HgCdTe-ternary alloyed semiconductor CQD using a commercially available silicon readout integrated circuit (ROIC). First, we synthesized a solution processed HgCdTe CQD responsive in the MWIR range at room temperature and developed a Schottkey junction photodiode array of 10 × 10 pixels based on the same quantum dots (QDs) to produce a HgCdTe-Si interface suitable for a MWIR photodiode at room temperature. After ensuring its functionality, we developed a 320 × 256-pixel focal plane array (FPA) responsive in the MWIR region by hybridization of the HgCdTe CQD layer over a silicon ROIC die with a direct injection input circuit. The FPA was operated using an indigenously developed Field Programmable Gate Array (FPGA)-based drive unit, and different IR targets were imaged to evaluate its use as a low-cost MWIR FPA. NEΔT value of 4 K achieved at room temperature.
We calculate the Casimir force acting on randomly stacked graphene layers and investigate the impact of diamagnetism on the Casimir force. The randomly stacked graphene layers are predicted to have a much smaller permeability than regularly stacked graphene layers such as graphite. We show that the Casimir force between randomly stacked graphene layers and a conducting plate is enhanced as the permeability of the randomly stacked graphene layers decreases from 1 to 0, especially for large separations. Conversely, the magnitude of the Casimir force between the randomly stacked graphene layers and a magnetic-dielectric plate such as yttrium-iron-garnet decreases as the permeability of the randomly stacked graphene layers decreases, and the force can be repulsive if the permittivity of the magnetic-dielectric plate contains a permeability much smaller than its permeability.
In this work, water adsorption and dissociation on Ni3- and Ni5-decorated Y- and Sc-stabilized zirconia (YZO and ScZO respectively), were probed using planewave, pseudopotential-based density functional theory calculations, to assess water splitting and subsequent hydrogen evolution potential of these metal-on-zirconia structures. It is found that the strength of Ni cluster binding on zirconia depends on the size of the cluster, at least for Ni3 and Ni5, and on the nature of the stabilizing atom. The Ni3 and Ni5 clusters tend to bind more favorably on the Sc site of ScZO compared to that of the Y site of YZO. Water is found to adsorb strongly on Ni3-YZO, Ni3-ScZO, and Ni5-ScZO. Water dissociation barrier for both the first and second hydrogen atoms tends to decrease for larger Ni cluster, with the Ni5-YZO system giving the lowest energy barriers. With relatively fine dissociation barriers, such systems could potentially be tapped for electrocatalytic water dissociation reactions leading to hydrogen evolution. These results are of importance and could contribute significantly in the further search and design of electrocatalytic materials for water dissociation and eventual hydrogen evolution for sustainable hydrogen production.
Group III elements doping for zinc oxide is currently attracting much attention for the study of absorber layer in nano-optoelectronic and photovoltaic devices as an alternative route to indium tin oxide (ITO) due to their optimized properties. In this report, Al-doped ZnO (AZO, Al: 1—7 at%) nanoparticles have been successfully deposited onto glass substrates using sol-gel process, and investigated by techniques such as X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The coated ZnO:Al nanoparticles at Al concentration up to 5 at% showed a nanosized polycrystalline structure with a c-plane preferred orientation. In AZO (7 at%), lower diffraction peaks were observed. The crystallite size calculated from XRD was ranged 38.7—43.5 nm. SEM showed spherical nanoparticles in shape with a smooth surface. The Raman results provided peaks located at 434, 435, 559, 851, and 1090 cm−1. According to XPS, the as-grown nanoparticles present the most intense peak located at about 1021.8 eV, assigned to the Zn 2p3/2 corresponding to zinc oxide. It was concluded that the structural properties of AZO thin films were improved with Al (5 at%), and these samples may be considered as an alternative of costly ITO in thin-film photovoltaic applications.
The article describes a new possibility of study by the method of computer simulation the energy and angular distribution of Xe+ ions scattered from the InP(001)❬110❭ surface at glancing incidence by initial energies of 1 keV and 3 keV. It is shown that glancing scattered ions formed double peaks in energy distribution curves which corresponded to the scattered ions from surface atomic rows and semichannels. It was shown that, at grazing surface semichanneling conditions, an intense peak arising from the effect of ion focusing was observed in the angular distribution. The results allow studies of semiconductor surfaces by using low energy ion scattering spectroscopy.
Titanium is a highly reactive metal and its high-temperature processing has to be done at a high-vacuum atmosphere. In this research, porous titanium scaffolds were fabricated using the space holder method for dental reconstruction purposes. Accordingly, the samples were sintered in two different vacuum furnaces at the vacuum level of 0.013 Pa, including high-vacuum leak rate (HLR) and low-vacuum leak rate (LLR). The microstructural study using the scanning electron microscope revealed that there was no significant difference in the microstructure of the samples. A compression test on the porous titanium scaffolds indicated that the HLR sample had less strength than the LLR sample. X-ray diffractometry also revealed that, besides the titanium peaks, the HLR sample included titanium oxide phases, unlike the LLR sample. Therefore, both vacuum chamber design and a vacuum leak rate of the furnace are parameters which are effective on the sintering of the porous titanium scaffold and should be considered.
Graphene, an ultra-thin derivative of carbon, has hindered a lot of applications because of its unique characteristics. It was found that superb improvements on properties can be made on further by creating nanopores or nanoholes on the surface of the graphene film. Such holed graphene can be used in energy storage, fuel cells, biosensors, biochemical applications, plasmonic tweezers, etc. This is because pores can contribute toward more surface area and eventually toward transportation and storage for electron/ion, gas, and liquid. This paper is a review of graphene nanohole fabrication methods.
Raman spectroscopy provides a meaningful fingerprint for sensing and discriminating materials, and surface-enhanced Raman scattering (SERS) can dramatically increase Raman signals up to the single-molecule level of sensitivity. Graphene, a monolayer carbon sheet, has recently attracted considerable attention as a unique SERS substrate. However, there are various types of graphene materials, and the SERS application category is significantly correlated to the structure and quality of the graphene. This review provides a broad perspective on this research area, intended for researchers of diverse fields. First, we categorize the graphene-based SERS applications based on their structure. Second, we introduce the types of graphene (graphene oxide, reduced graphene oxide, chemical vapor deposited graphene, and carbon nanowalls) and their synthesis methods. Thereafter, we highlight state-of-the-art studies for each category of graphene-based SERS.
When the mean free paths of acoustic phonons are larger than half the MoS2 island size, the generated acoustic phonons remain at nonequilibrium and are confined within the island or form standing waves. In contrast, when the island size decreases to less than 1 μm, surface softening increases, reducing the barrier of the tip—surface interaction potential. Unexpectedly, the friction force from an island with a size of 0.2 μm abruptly decreases to below 10 pN. The superlubricity described here is a novel type involving phonon confinement and surface softening that is easily achievable and very simple because it uses only nanostructures smaller than 1 μm.
Establishing an accurate view of the photocatalytic mechanism of titanium dioxide (TiO2) has been a challenging task since the discovery of the Honda-Fujishima effect. Despite the great success of catalytic studies in elucidating the chemical and physical aspects of photocatalysis, many questions remain. A surface science approach, which is characterized by the use of atomically well-defined surfaces in precisely controlled environments, is a powerful tool to shed light on the fundamental mechanism, especially the dynamics of photoexcited carriers. In the present contribution, recent progress in photocatalytic research that correlates photocatalytic activity and carrier dynamics on rutile and anatase TiO2 is reviewed. A special focus is placed on the lifetime of photoexcited carriers. We present a method to determine the carrier lifetime; pump-probe time-resolved soft X-ray photoelectron spectroscopy, utilizing an ultraviolet laser as a pump light and a synchrotron radiation as a probe light. The carrier lifetime is found to be linearly correlated with the photocatalytic decomposition/desorption rate of acetic acid adsorbed on single-crystal TiO2 surfaces. The important role of a potential barrier on the TiO2 surface, which influences the carrier lifetime and the photocatalytic activity, is discussed.
Scanning transmission electron microscopy combined with electron energy-loss spectroscopy and energy-dispersive X-ray spectroscopy is useful for analyzing chemical states and elemental components in a new material. Using these instruments, the spectra over the spatial grid points in a region of interest can be observed. This measurement technique is called spectral imaging (SI). Because of the large size of SI data, the analysis cost is a bottleneck in the evaluation process of the material. To reduce the analysis cost, machine learning techniques can be applied, which can automatically extract essential information from the data. This paper reviews our developed machine learning method, which is based on non-negative matrix factorization and its extensions. A spatial orthogonality constraint and a generalized noise model, which includes Gaussian and Poisson noise models, are introduced. Numerical experiments demonstrate the effectiveness and characteristics of our developed methods.
Surface X-ray diffraction is a powerful tool for studying the atomic structure of buried interfaces nondestructively. The analysis is often limited to the static structures, since the acquisition of crystal truncation rod (CTR) profile dataset is lengthy. Recently, high-speed methods have been developed by several groups, aiming for the in operando study of interface phenomena. Our method uses energy-dispersive convergent X-rays and area detector, and allows the quantitative structure analysis during irreversible phenomena in a typical time frame of 1 s. In this review, the energy-dispersive method is compared with the other high-speed methods which use high-energy X-rays with a grazing incidence geometry and transmission geometry, and then two examples of the real-time monitoring are presented, the photo-induced wettability transition of the rutile-TiO2(110) surface and an electrochemical reaction on the Pt(111) electrode surface, to show the capability of the energy-dispersive method.
In-situ analysis of heterogeneous catalysts under reaction condition is indispensable to understand reaction mechanisms and nature of active sites. Ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) is one of the powerful methods to investigate chemical states of catalysts and reaction intermediates adsorbed on the surface. In this review, reaction of carbon dioxide on Cu(997) and Zn-deposited Cu(997) surfaces are discussed as an example of surface chemistry of weakly adsorbed molecules, together with a brief overview of recent progress in AP-XPS methods.
Figures 3 and 4 in the original article [e-J. Surf. Sci. Nanotechnol. 16, 36 (2018)] were inappropriately displayed. Correct figures are shown in this erratum. “Table 1” and “Table 3” that appear in the text on p. 39 in the original article should be replaced by “Table I” and “Table III”, respectively. The publisher found that they occurred during the production process. None of the corrections change any discussion and conclusions of the article.
Figure 1 in the original article should be corrected. The parameter g means not the gap between the center of two silver nano-particles but the gap between two silver nano-particles. This revision does not affect the conclusion.