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We systematically investigated electronic evolutions of non-symmorphic borophene with chemical environments that were realized by the ion exchange method. Electronic structures can be characterized by the topological $Z_2$ invariant. Spectroscopic experiments and DFT calculations unveiled that a sheet of hydrogenated borophene (borophane) is the Dirac nodal loop semimetal ($Z_2=-1$), while a layered crystal of YCrB$_4$ is an insulator ($Z_2=1$). The results demonstrate the electronic topological transition by replacement of the counter atoms on the non-symmorphic borophene layer.

2,2',7,7'-Tetrakis(N,N-di-p-methoxyphenylamino)-9,9'-spirobifluorene (spiro-OMeTAD) is utilized as a p-type semiconductor layer in perovskite solar cells and solid-state dye-sensitized solar cells. Spiro-OMeTAD has been known to have a spiro center, leading to a random orientation. Although the molecular orientation of organic semiconductor materials influences the conductivity, which is directly related to semiconductor device characteristics, the molecular orientation of spiro-OMeTAD has not been fully discussed. In this study, we prepared spiro-OMeTAD layers on various substrates and investigated their orientation by grazing-incidence wide-angle X-ray scattering (GIWAXS) and near-edge X-ray absorption fine structure (NEXAFS). Additionally, we demonstrated that the molecular orientation of spiro-OMeTAD could be controlled by changing their surface energies by changing the substrate materials. Consequently, we could improve the electrical conductivity by improving its molecular orientation. The results of this study provide a guideline for the preparation of organic semiconductor material layers using the wet-coating method.

An inexpensive, simple, and high-activity catalyst preparation method has been introduced in this work. Pt and RuO x catalysts were fabricated by soaking inexpensive graphite electrodes (pencil-lead graphite rod: PGR) in catalyst precursor solutions and using a simple flame-annealing method, which results in lower amount of Pt and RuO x catalyst layers. From X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure analysis, it has been found that platinum and ruthenium were deposited as zero-valence metal (Pt) and oxide (RuO x ), respectively. Catalytic activities of Pt/PGR and RuO x /PGR for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) were evaluated using neutral 1 M Na2SO4 aqueous electrolyte, respectively. Although HER and OER currents using PGR without catalysts were -16 mA cm-2 (at -1.5 V vs Ag/AgCl) and +20 mA cm-2 (at +2.0 V vs Ag/AgCl), they were improved to -110 and +80 mA cm-2 with catalysts (Pt and RuO x ), respectively. Such an inexpensive and rapid catalyst electrode preparation method on PGR using flame-annealing is a very significant method in the initial catalyst activity evaluation requiring a large amount of trial and error.

We studied electronic states of borophene in a crystal of rare-earth aluminum/chromium boride and the hydrogenated sheet, borophane, successfully prepared by ion exchange and liquid exfoliation of the crystal. The layer has a boron network with five-membered and seven-membered rings. Electronic structures of all the boron-derived layers are found to be gapless by soft x-ray absorption and emission spectroscopy measurements at the B K-shell absorption edge and density functional theory calculations. The present results support the existence of a Dirac nodal loop at the Fermi level in the borophane layer with five- and seven-membered rings, predicted recently by topological calculations.

Inexpensive and sensitive graphite electrodes were fabricated by applying flame annealing to pencil-graphite rods (PGRs) as electrodes for water electrolysis cells. The resin (polymer, binder) on t...

The structural and electrical properties of the nanographene prepared from pentacene by hot mesh deposition (HMD) and soft X-ray irradiation have been investigated. The three regions in the carbon film were observed in the center of soft X-ray beam and around it. The color change of the HMD carbon film by soft X-ray irradiation was discussed from the distribution of film property.

A new technical method is developed for soft X-ray spectroscopy of near-edge x-ray absorption fine structure (NEXAFS). The measurement is performed with continuously rotating linearly polarized light over 2 π , generated by a segmented undulator. A demonstration of the rotational NEXAFS experiment was successfully made with a 2D film, showing detailed polarization-dependence in intensity of the molecular orbitals . The present approach provides varieties of technical opportunities that are compatible with the state-of-the-art experiments in nano-space and under the o p e r a n d o condition.

The effect of soft X-ray irradiation on hydrogenated silicon-containing diamond-like carbon (Si-DLC) films intended for outer space applications was investigated by using synchrotron radiation (SR). We found that the reduction in film thickness was about 60 nm after 1600 mA·h SR exposure, whereas there was little change in their elemental composition. The reduction in volume was attributable to photoetching caused by SR, unlike the desorption of hydrogen in the case of exposure of hydrogenated DLC (H-DLC) film to soft X-rays. The ratio of the sp2 hybridization carbon and sp3 hybridization carbon in the hydrogenated Si-DLC films, sp2/(sp2 + sp3) ratio, increased rapidly from ~0.2 to ~0.5 for SR doses of less than 20 mA·h. SR exposure significantly changed the local structure of carbon atoms near the surface of the hydrogenated Si-DLC film. The rate of volume reduction in the irradiated hydrogenated Si-DLC film was 80 times less than that of the H-DLC film. Doping DLC film with Si thus suppresses the volume reduction caused by exposure to soft X-rays.

Diamond-like carbon (DLC) films are an amorphous carbon film with sp2 and sp3 bonding structures of carbons. The DLC films have been used widely in industry owing to have superior properties such as high mechanical hardness and low friction coefficient. The DLC films are divided into the following of four categories: ta-C and a-C films are hydrogen-free DLC with high and low C–C sp3 bonds, respectively, and ta-C:H and a-C:H films are hydrogenated DLC with high and low C–C sp3 bonds, respectively. As the industrial application of DLC films is expanding, it is important to clarify the definition of these DLC film types and to able to easily evaluate the types. There are various DLC deposition methods. Filtered arc deposition (FAD) method which is one of the vacuum arc deposition methods is a few deposition methods can form hydrogen-free DLC films with high hardness. In addition, hydrogenated DLC films can be prepared under the deposition condition in which a hydrogen or a hydrocarbon gas is introduced into the chamber on the FAD system. Various DLC films prepared using T-shape FAD system were characterized by the sp3 fraction and hydrogen content measured using near edge X-ray absorption fine structure spectroscopy and Rutherford back scattering/elastic recoil detection analysis, respectively. It was found that the sp3 fraction, nanoindentation hardness, and film density of DLC films have a correlation. Based on these results, DLC films were classified from the film density and hydrogen content.

The electronic structure of the ($3\ifmmode\times\else\texttimes\fi{}3$)-ordered phase of a silicon (Si) layer on Al(111) has been studied by angle-resolved photoemission spectroscopy using synchrotron radiation and modeled by a trial atomic model. A closed Fermi surface originating from a linearly dispersing band is identified. A band structure calculation of a trial atomic model of the honeycomb silicene on Al(111) implies that the metallic band originates from the Al-Si hybrid state that has the Dirac-cone-like dispersion curve. The Si layer on Al(111) can be a model system of Xenes to realize the massless electronic system through the overlayer-substrate interaction.

The existence of a topological Dirac nodal loop is predicted for hydrogenated monolayer boron sheets with a nonsymmorphic symmetry. The three-center two-electron bonds in boron compounds restrict the electronic system to be insulating or semimetallic with a Dirac nodal loop. Two types of electronic structures are distinguished by the Z_2 topological index and confirmed by first-principles total-energy calculations. The topological taxonomy, developed in this research, can be applied to other two-dimensional materials and to seek novel Dirac fermions.

Al0.24Ga0.76N thin film surfaces were irradiated simultaneously with CF4 plasma and ultraviolet (UV) at wavelengths of 280 and 310 nm. The UV wavelength and intensity were varied without changing the plasma-generating conditions. These UV photon energies were larger than the band-gap energy of AlGaN film. A compositional change in the simultaneously-irradiated surface depended on the UV wavelength. The 280-nm UV irradiation caused a greater degree of nitrogen deficiency than that introduced by 310-nm UV irradiation, causing the Ga- and Al-rich surface. Moreover, the 280-nm UV irradiation increased the amounts of F atoms and CFx fluorocarbons incorporated into the surface, in comparison with CF4 plasma-only irradiation. In contrast, the 310-nm UV irradiation reduced the amount of the incorporated F atoms and hardly increased the amount of the incorporated CFx fluorocarbons from those caused by CF4 plasma-only irradiation. These became more prominent with increasing UV intensity. These UV wavelength-dependent results can be discussed in terms of four factors: the UV photogenerated-hole-assisted oxidation, the localized surface plasmon resonance, the UV-induced migration of gallium and aluminum vacancies forming stable complexes with F, and the sticking of F-related radicals from CF4 plasma onto the surface.

In this paper, the local structure of silicon-containing diamond-like carbon (Si-DLC) films is discussed based on the measurement of C K-edge and Si K-edge near-edge x-ray absorption fine structure (NEXAFS) spectra using the synchrotron radiation of 11 types of Si-DLC film fabricated with various synthesis methods and having different elemental compositions. In the C K-edge NEXAFS spectra of the Si-DLC films, the * band shrunk and shifted to the lower-energy side, and the * peak broadened with an increase in the Si content in the Si-DLC films. However, there were no significant changes observed in the Si K-edge NEXAFS spectra with an increase in the Si content. These results indicate that Si&ndash, Si bonding is not formed with precedence in Si-DLC film.

TiO2 thin films were treated with plasma with the assistance of external heating. This plasma was produced with an O2 dielectric barrier discharge (DBD) at atmospheric and near-atmospheric gas pressures. For comparison, the samples were annealed in O2 gas and also treated with O2 DBD plasma alone. The effects of these treatments on photocatalytic activity were compared by evaluating the photodecomposition of methylene blue dye in aqueous solution. The photocatalytic activity of the heat-assisted plasma-treated sample was the most enhanced among the treatment processes. The net photodecomposition of the heat-assisted plasma-treated sample was slightly higher than or comparable to that of TiO2 anatase-phase nanoparticle powder. The photocatalytic activity enhancement can be attributed to an increase in the effective concentration of photogenerated carriers on the surface. This increase is driven by the synergistic effect between an increase in the depletion layer width and an increase in the optical absorption due to the crystalline transition from the bronze to the anatase phases. This crystalline transition occurred at a lower temperature than the annealing transformation temperature.

We have measured the soft X-ray absorption and emission spectra of near B-K and C-K absorption edges of highly oriented pyrolytic graphite (HOPG) doped with a small amount (0.32 at.%) of boron (B), including incident/takeoff angle dependence.The main peak intensities at the B-K edge around 182 eV were almost independent on the change of takeoff angle. On the other hand, the satellite peak around 185 eV becomes larger as the takeoff angle becomes smaller. Based on this result, unlike the previous assignment of the main peak predicted from the quantum chemical calculation (π orbitals), it is reasonable to attribute the main peak to the σ orbitals. The takeoff angle dependence of the B-K emission is similar to the angle dependency of the C-K emission of undoped HOPG. Based on this and the theoretical consideration, it is presumable that the doped B atom does not intercalate between the layers of HOPG; it replaces the C atom of the hexagonal network structure and has a wave function similar to that of C atoms (sp2 type hybridized orbital). (Less)

Highly oriented pyrolytic graphite (HOPG) is a unique source material for the synthesis of new types of diamond. It can transform to layered nano-polycrystalline diamond (NPD) under static high pressure and high temperature (HPHT) and to “amorphous diamond” by introducing structural defects by neutron irradiation followed by shock compression. Here, we investigated the structural change of the neutron-irradiated HOPG through a HPHT treatment at 2300 °C and 15 GPa by Raman, X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray absorption near edge structure (XANES) analyses. The recovered sample consists of randomly oriented nanodiamonds (50–100 nm), showing clearly a different microtexture from those of the layered NPD and “amorphous diamond” reported by the previous studies. This is likely as a result of competing effects of the introduction of irradiation-induced defects, which provided the preferential nucleation sites for cubic diamond, and their partial recovery upon annealing during the HPHT treatment. The present result suggests that NPDs with various crystalline structures can potentially be synthesized from neutron-irradiated HOPG by controlling the density and distribution of the defects introduced.

Photodecomposition and photobactericidal activities of anatase/rutile-mixed phase TiO2 nanoparticles annealed with low-temperature O2 plasma were clarified by comparing them with those annealed in ambient air. The photocatalytic activities of plasma-assisted-annealed sample greatly enhanced as compared with the untreated sample, under not only ultraviolet irradiation but also visible-light irradiation. The photocatalytic activities of air-annealed samples did not enhance under ultraviolet irradiation but enhanced under visible-light irradiation. The enhanced photocatalytic activities due to the plasma-assisted annealing (PAA) originated from the increased photoexcited carrier concentration. This enhancement was discussed from PAA-induced characteristic factors. PAA facilitated the phase transformation to anatase, contributing directly to extending the photoexcited carrier lifetime. PAA introduced more oxygen vacancies, contributing to trapping more photogenerated electrons. PAA also introduced more bridging/terminal oxygen groups adsorbed on the surface, increasing the upward band-bending, the depletion layer width at the surface, and the charge transfer from rutile to anatase. These two introductions contributed to facilitating the separation of photoexcited carriers. Furthermore, PAA reduced the aggregate size of TiO2 nanoparticles formed on the surface, contributing to increasing optical absorptions. More reactive oxygen species produced from the bridging/terminal oxygen groups by the photoexcited carriers would also enhance the photocatalytic activities.

In situ X-ray diffraction observation was done for neutron-irradiated and un-irradiated HOPG samples with synchrotron radiation to clarify the effect of irradiation-induced defects on the transformation to diamond under high-pressure and high-temperature treatment. At 16 GPa, no remarkable change appeared for the irradiated HOPG with increasing the temperature up to 800 °C. At temperatures of 1200 and 1400 °C, hexagonal diamond was formed, along with the formation of cubic diamond. This is probably due to annealing of the irradiation defects that led to partial restoration of the structure to the original HOPG and then enables the formation. On the other hand, in un-irradiated HOPG, hexagonal diamond was formed at 400 °C, which changed to cubic diamond at 1200 °C or higher. We guess that irradiation defects promote the nucleation of cubic diamond in the irradiated sample and then contribute to the formation of isotropic polycrystalline diamond or amorphous diamond.

The irradiation effect on fluorinated diamond-like carbon (F-DLC) film was investigated by measuring the dose dependence of various film properties using synchrotron radiation (SR) in the soft X-rays in the SR dose region from 0 to 2000 mA h. Film flatness was maintained but various film properties and surface properties were found to be changed by the SR irradiation. Wettability of the F-DLC film surface increased dramatically within 20 mA h SR exposure, which was ascribed to the decrease in fluorine on the film surface. Film thickness, film density, composition ratio of fluorine atom in film decreased and sp 2 / ( sp 2 + sp 3 ) ratio of carbon atoms increased within 300 mA h SR exposure, which were ascribed to the desorption of species containing fluorine atoms. In addition, dominant desorbed species emitted from F-DLC film were found in the fluorocarbon group, CF x . Changes in film properties and film thickness did not proceed, when fluorine content in the F-DLC film decreased to about 10% after the 300 mA h SR exposure.

Low-energy Ar ions (0.5–2 keV) were irradiated onto vertically aligned multiwalled carbon nanotube (VA-MWCNT) films, and the chemical states, orientation, and oxygen content of the irradiated VA-MWCNT films were investigated by soft X-ray absorption spectroscopy (XAS). After irradiation, two additional peaks appeared in the XAS spectra in the C K region, indicating a significant change in the electronic structure. Furthermore, it was found that the VA-MWCNT films were oxidized after irradiation. The results of chemical-state analyses of the XAS spectra in both the C K and O K regions indicated the formation of carboxyl groups ( COOH) on the surface of the VA-MWCNT films upon irradiation. The oxygen content of the VA-MWCNT films increased with increasing ion energy and fluence.

Al0.24Ga0.76N thin film surfaces were etched with CF4 plasma, with and without the assistance of near-ultraviolet (UV) irradiation. The near-UV source was a black light lamp, which emitted wavelengths of 300–400 nm. The chemical compositions and morphologies of surfaces etched under the two plasma conditions were compared, to clarify the effect of near-UV irradiation on the properties of the AlGaN surface. Near-UV irradiation during CF4 plasma etching reduced the amounts of F atoms, AlFx fluorides, and GaFx fluorides incorporated into the surface, and enhanced the amount of CFx fluorocarbons. Near-UV irradiation did not influence the depth distribution of incorporated fluorine-related impurities, or the degree of nitrogen deficiency caused in the surface. These compositional changes in the surface occurred irrespective of the gas pressure. Near-UV irradiation caused a significant change in the morphology of surfaces etched at high gas pressure (13 Pa), as the etching time was increased to 60 and 100 min. Near-UV irradiation did not change the morphologies of surfaces etched at lower gas pressures (1.3 and 6.7 Pa), irrespective of etching time.

Electronic states of a free-standing hydrogenated monolayer boron (HB) sheet were studied via soft X-ray spectroscopies at the B K-shell absorption edge and first-principles calculations. The HB sheet is semimetallic with electron and hole pockets at the Y and Γ points, respectively. The electron band results from the B-H-B bonds formed during synthesis from a MgB2 crystal, while the hole band is kept through the process and originates from a honeycomb lattice boron layer or borophene in MgB2. Our results suggest that the HB sheet is a promising two-dimensional material for realizing new boron-based or superconducting nanodevices.

The molecular orientation and partial density of states were evaluated using NewSUBARU by soft X-ray absorption spectroscopy (XAS) and soft X-ray emission spectroscopy measurements. The degree of molecular alignment was degraded by increasing mesh temperature in hot mesh deposition (HMD), in other words, was changed from pentacene (Pn) to 6,13-dihydropentacene (DHP). At a mesh temperature of 1450 °C, the different XAS was obtained due to the mixing effect of Pn and DHP, and presence of Pn oligomer. The HMD carbon film transformed into the graphite-like film and the graphene on the quartz substrate and the Ni/quartz substrate after soft X-ray irradiation, respectively. The HMD carbon film after soft X-ray irradiation showed the peaks due to terminal carbon such as CH n and COOH in comparison with the reported large graphene sheet. It indicates that the flake size of the graphene on the Ni/quartz substrate was small and had many edges.

Development of fine grain 316L with small amount of TiC for high radiation-tolerant performance was tried considering the fabrication process of thermo-mechanical treatments. The materials obtained are UFG316L+2.0 mass% TiC with the grain size of 90–270 nm, depending on the final annealing temperature from 700 ℃ to 900 ℃. The materials were examined by transmission electron microscopy observation, X-ray absorption near-edge structure spectroscopy, high voltage electron microscope electron irradiation and stress corrosion cracking by crevice bent beam method in high-temperature water with 8 ppm dissolved oxygen. The test results showed that the material is generally of excellent quality. Especially void swelling induced by the electron irradiation at 400 ℃ is less than 1/10 compared to the commercial SUS316L.

Hydrogenated amorphous carbon (a-C:H) films containing isotopes of carbon and hydrogen were deposited, and their structure and physical properties were evaluated to investigate the isotopic effects in an attempt to reduce the defect density of carbon films. These isotope films such as deuterated amorphous carbon (a-12C:D) and hydrogenated 13C carbon (a-13C:H) films were deposited under the same deposition condition by the radio frequency plasma CVD method from isotope methane gas. The ratio of sp2/sp3 carbon was same, the deuterium content of a-12C:D was smaller than hydrogen contents of other films. Although the smallest content of hydrogen or deuterium as the termination structure of the carbon network was observed for the a-12C:D film, the density of defects was also smallest in the film. The Tauc gap of the a-12C:D film was approximately 30% larger than the that of the other films. From these results, the deposition process of a-C:D film brings lower defect density compared with the deposition system for a-C:H.

We have constructed a compact soft X-ray emission spectrometer at the BL-09A beamline of the NewSUBARU synchrotron radiation facility at the University of Hyogo, Japan. Using this spectrometer, we observed a large take-off angle dependence of C-K emissions in highly oriented pyrolytic graphite (HOPG). At an excitation photon energy of 310 eV, far from the absorption edge of HOPG, we detected large take-off angle dependence of π → 1s emission. The π emission intensity was much higher than that of σ emission, which has not been reported before. One reason for the apparent discrepancy between these results and previous ones probably originates from the difference in energy resolving power of the emission spectrometers used. According to a band calculation for HOPG, the large angle dependence observed here could be attributed to the resonant transition of 1s electrons to a π state 25 eV higher than the Fermi level.

The manipulation of central atom coordination environments can greatly boost catalytic performances and promote the understanding of associated mechanisms in both sub-nanometer clusters and atomically dispersed catalysts. In this study, sub-nanometer “raft”-like PtNx clusters were synthesized on a TiO2 support, and the significant enhancement effects of the Pt–N coordination structure on the performance of hydrogen evolution reaction (HER) are demonstrated. In acidic media, the PtNx catalyst display a superior HER activity (37.5 A mg-1 Pt) and turnover frequencies (37.9H2 s-1) at overpotential of 50 mV; outperforming commercial Pt/C by a factor of 13.3 and 3.9, respectively. Density functional theory (DFT) calculation results reveal that the charge transfer occur from the N to the neighboring Pt atoms when the hydrogen is adsorbed on N atoms; such a charge redistribution within Pt–N coordination structure leads to a smaller H* free energies on the activated N atoms, and is believed to account for the higher HER activity.

In synchrotron radiation (SR) optical devices coated with oxidation-prone metal, such as Ni and Cr, the UV-O3 ashing method cannot be used for removal of the contaminated carbon film deposited during use in the beamline. We have demonstrated that surface treatment technology using atomic hydrogen is effective as a new contaminated carbon film removal technology. Hydrogen gas was flowed into contact with a tungsten mesh (catalyst) heated to 1700°C to obtain atomic hydrogen. By flowing this atomic hydrogen on the surface of the SR mirror, deposited contaminants could be almost completely removed. The reflectance of the mirror recovered from about 14% to about 70% at the C-K absorption region. The reflectance also increased by about 20% at a photon energy greater than 300 eV because of the removal of carbon film and the reduction of native oxide at the mirror surface.

The effect of irradiation by a hyperthermal-atomic-oxygen beam on hydrogenated titanium-doped diamond-like carbon (hydrogenated Ti-DLC) films, applied as a solid lubricant for equipment used in low-earth orbit was investigated. Unlike the film thickness of hydrogenated non-doped DLC films, that of hydrogenated Ti-DLC films was found to be constant after the films were exposed to atomic oxygen. In addition, bulk composition of the hydrogenated Ti-DLC film stayed constant, and in particular, hydrogen content in the film did not decrease. These results indicate that a hydrogenated Ti-DLC film can keep its low friction properties under vacuum. Surface chemical analysis showed that a titanium-oxide layer is form on the film by exposure to atomic oxygen. The thickness of the titanium oxide layer was estimated to be about 5 nm from the element distribution in the depth direction of the hydrogenated Ti-DLC films. The titanium-oxide layer was interpreted to protect the bulk film from erosion by hyperthermal atomic oxygen.

Compositional and morphological changes in Al 0.24 Ga 0.76 N surfaces etched by CF 4 and Ar plasmas were investigated in order to clarify the effect of fluorine impurities incorporated in the surface by the CF 4 plasma. The CF 4 plasma effectively incorporated the fluorine impurities in the surface even at a short etching time. A small number of the incorporated fluorine impurities only contributed to the formations of Al(OH) x F y and GaF x on the surface even as the etching time increased. Although the CF 4 and Ar plasma etchings preferentially remove nitrogen atoms from the surfaces, the preferential removal induced by the CF 4 plasma etching was suppressed compared with the case of the Ar plasma etching. The CF 4 plasma etching caused a smooth surface regardless of the gas pressure and the etching time, whereas the Ar plasma etching changed the surface morphology depending on the gas pressure and the etching time. The incorporation of the fluorine impurities, which bonded with the cation vacancies such as gallium and aluminum vacancies introduced in the surface by the plasma etching, was considered to concern the suppression of the preferential removal and the formation of the smooth surface.

Damage characteristics of n-GaN thin film surfaces etched by ultraviolet (UV) light-assisted He plasmas at various gas pressures have been investigated from the viewpoint of the UV light irradiation effect. During the plasma etching, the surface is additionally irradiated with UV light emitted from a black light lamp. The peak wavelength of the emitted UV light corresponds to that of the GaN band-gap energy. The result is compared with that obtained only by use of He plasma. A morphological change in the surface etched by the UV light-assisted He plasma depends on gas pressure, whereas the He plasma only does not cause the morphological change in the surface regardless of gas pressure. The additional UV light irradiation causes a morphological change in the surface etched for a long time of more than 60 min at high gas pressures between 6.7 and 13 Pa. The morphology of the surface etched at a low gas pressure of 1.3 Pa does not change from that of the as-grown surface even with increasing etching time. The additional UV light irradiation also enhances the etch depth and suppresses a decrease in N/Ga ratio at the surface compared with that obtained only by use of the He plasma.

Polypropylene (PP) film surfaces were treated using air-based nonequilibrium atmospheric pressure plasma jets generated with a twisted wires-cylindrical electrode configuration. For comparison, PP samples were also processed with Ar plasma jets. The flux of charged particles imparted to the polymer surface by the air plasma jet greatly increased with decreases in both the gas flow rate and nozzle-to-sample distance, which was not the case for the Ar plasma jet. Reducing the gas flow rate and the nozzle-to-sample distance greatly enhanced the extent to which the surface was rendered hydrophilic by the air plasma within a short treatment time of 1 min. This enhanced effect is believed to originate from a high concentration of oxygen-based functional polar groups (FPGs) containing C O/C OH and C O/C O OH bonds grafted onto the surface. The hydrophilic surfaces resulting from this process also exhibited nanopore structures. The large number of oxygen-based FPGs produced by the air plasma can be attributed primarily to oxygen radical ions impinging from the air plasma on the surface. This can further be attributed secondarily to heat-induced oxidation rather than the sticking of oxygen radicals and UV-induced oxidation from the plasma. The nanoporous structure can also be ascribed to oxidation from UV photogenerated holes.

Surface structural changes of Ti-doped diamond-like carbon (Ti-DLC) film exposed to a hyperthermal atomic oxygen beam were investigated using near-edge X-ray absorption fine structure (NEXAFS) spectroscopy using synchrotron radiation. The spectral shape of the C K NEXAFS spectrum of as-deposited Ti-DLC film resembled that of DLC film. After exposure to atomic oxygen, the spectrum resembled that of TiC powder. The sp 2 /( sp 2 + sp 3 ) ratio of as-deposited Ti-DLC film decreased drastically by exposure to a hyperthermal atomic oxygen beam. On the other hand, the spectral shape in the Ti L NEXAFS spectrum of as-deposited Ti-DLC film resembled that of TiC powder and became similar to that of TiO 2 powder after exposure to atomic oxygen. These changes are ascribable to the desorption of C atoms as CO and/or CO 2 from Ti-DLC film due to the irradiation of atomic oxygen beam. On the other hand, oxidized Ti was not desorbed from the Ti-DLC film. As a result, the sp 2 /( sp 2 + sp 3 ) ratio of C in the Ti-DLC film decreased, because residual C atoms were bonded to Ti atoms.

Low-energy Ar ions (0.5–2 keV) were irradiated to multi-layer graphenes and the damage process, the local electronic states, and the degree of alignment of the basal plane, and the oxidation process upon ion irradiation were investigated by Raman spectroscopy, soft X-ray absorption spectroscopy (XAS) and in situ X-ray photoelectron spectroscopy (XPS). By Raman spectroscopy, we observed two stages similar to the case of irradiated graphite, which should relate to the accumulations of vacancies and turbulence of the basal plane, respectively. XAS analysis indicated that the number of sp 2 -hybridized carbon (sp 2 -C) atoms decreased after ion irradiation. Angle-resolved XAS revealed that the orientation parameter (OP) decreased with increasing ion energy and fluence, reflecting the turbulence of the basal plane under irradiation. In situ XPS shows the oxidation of the irradiated multi-layer graphenes after air exposure.

Damage characteristics of SiC surfaces etched by capacitively coupled radio frequency Ar plasmas at various gas pressures have been studied from the viewpoint of synergy effect of Ar plasma ion and plasma-induced ultraviolet (UV) light irradiations. In the absence of UV light emission at the low gas pressure of 10 mTorr, morphology of the etched SiC surface is similar to that of the as-grown surface regardless of an increase in etching time. In contrast, the experimental Si/C ratio at the surface decreases with an increase in etching time, which agrees with the simulation that Si atoms at the surface are preferentially removed by Ar + ions impinging on the surface. The agreement indicates that the physical etching effect, which originates from the Ar + impact, contributes to the decrease in the Si/C ratio. In the presence of the UV light emission, the surface morphology at the high gas pressure of 50–100 mTorr depends on the etching time. The surface morphology changes as the etching time increases to 200 min. The experimental etch depth at the etching time of 200 min does not agree with that of the simulation. The experimental etch depth is much higher than the simulated one. The difference connecting with the gas pressures can be related to the factor whether the UV light is emitted from the plasma: the result at the high gas pressure suggests the contribution of the synergy effect caused by the following possible phenomenon: Si–C bonding at the surface is weakened.

Damage characteristics of n-GaN surfaces etched by capacitively-coupled radio frequency N2 plasma, generated with a high applied voltage of 400 V, was studied in terms of synergistic effect between ion bombardment and ultraviolet (UV) light irradiation. The result was compared with that obtained with a low applied voltage of 200 V. Morphology of the surface etched at a low gas pressure of 10 mTorr is similar to that of the as-grown surface even with increasing etching time, whereas N/Ga ratio at the surface decreases. The result can be explained in terms of the physical etching, though the surface is irradiated with the UV light emitted from the plasma. The result obtained at the low gas pressure is independent of the applied voltage. In contrast, the characteristic at the surface etched at a high gas pressure of 50-100 mTorr depends on the applied voltage. A morphological change in the surface etched with the high applied voltage occurs, whereas the N/Ga ratio increases The increase in the N/Ga ratio is not reproduced by the simulation, which implies the contribution of the UV light irradiation. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Amorphous hydrogenated carbon (a-C:H) and amorphous deuterated carbon (a-C:D) films were prepared using plasma-enhanced chemical vapor deposition (PECVD) from CD4, H2, CD4 and D2 source gases. Fourteen different samples were prepared by changing the source gas ratios of CH4/H2, CH4/D2, CD4/H2, and CD4/D2. The concentrations of hydrogen (H) and deuterium (D) relative to carbon (C) in the films were determined by elastic recoil detection analysis (ERDA) and Rutherford backscattering spectroscopy (RBS). The sp2/(sp2 + sp3) ratios of the films were analyzed by near-edge X-ray absorption fine structure (NEXAFS) measurements. Hardness and mass density of the films were measured using a nanoindenter and X-ray reflectivity (XRR), respectively. For all combinations of source gas, the H and D concentrations varied by only 4.0 at.%. For the CH4/D2 source gas, the D concentration in the film increased from 0 at.% with the D2/(CH4 + D2) source gas combination to 11.2 at.% for the 80% D2/(CH4 + D2) source gas combination. The increase in D concentration exceeded the increase in total H and D concentration (3.4 at.%). For CH4/D2 source gas, the H concentration decreased as the D concentration increased. For the CD4/H2 source gas, we observed the opposite tendency. Additionally, an isotope effect between the a-C:H films and the a-C:D films was observed, with preferential incorporation of H over D. From the NEXAFS measurements, the sp2/(sp2 + sp3) ratios in all of the samples were between 38.8% and 40.8%. A correlation between the sp2/(sp2 + sp3) ratio and the H2 or D2 gas source ratio was not observed. The hardness and density of the films decreased when the H2 or D2 source gas ratio increased. Even though the H concentration in the a-C:H films was higher than the D concentration in the a-C:D films, the a-C:D films had lower hardness and mass density values. These findings suggest that information concerning the voids, nanostructures, sp2/sp3 ratios and H concentrations of hydrogenated amorphous carbon films is crucial for evaluation of their mechanical properties.

By comparing differences between characteristics of Al 0.24 Ga 0.76 N thin film surfaces irradiated with ultraviolet (UV) light-assisted CF 4 plasma and with CF 4 plasma, we clarified the effect of UV light irradiation on the surfaces. A black light lamp, which emitted photons with energies of 3.1 to 4.1 eV, was used as the UV light source. The UV light irradiation under a high gas pressure of 13 Pa changed the surface morphology as the irradiation time increased. In the case of low gas pressures of 1.3 and 6.7 Pa, the UV light irradiation did not contribute to the morphological change in the surface. The UV light irradiation also suppressed not only the amount of F atoms incorporated but also the amount of fluorides, Al(OH x )F y and GaF x , formed in the surface. In contrast, the amount of CF x incorporated in the surface was enhanced. These compositional change in the surface occurred irrespective of gas pressure.