Search

We present the development of time-of-flight/energy (TOF-E) telescope for elastic recoil detection analysis (ERDA) in UTTAC at the University of Tsukuba. The designs of the TOF tube are introduced. The performance for the quantification and mass resolution for light elements is confirmed on a CaTaOxNy film deposited on a Si substrate. The results are cross-checked by the data taken by an existing ΔE-E telescope ERDA system, which was previously installed in MALT at The University of Tokyo. The newly developed system can be used to reveal the relationship between the film deposition condition and the contamination quantitatively on a Si-Al-N (SiAlN) film on a SiO2 substrate. Finally, the analysis of a triple-layered metal nitrides film on a soda glass substrate, in which each layer has a thickness of 10 to15 nm, is shown. From the analysis of the surface peak of oxygen, the time resolution corresponds to depth resolution of 2.1 nm at the surface. The overall practical depth resolution conservatively estimated as better than 10 nm, because the depth profiles of various elements show clear counters corresponding to the three layers.

We demonstrated a position-sensitive-like detector (PSD) based on a scanning solidstate detector (scanning-SSD) in HERDA for improvement of detection limit for hydrogen. The new detection system enables us to separate the signals of interest from background noises, which can be attributed to the signals produced by particles of non-interest, by measuring the particle energies from a detected position and SSD outputs. As results, we succeeded to improve the detection limit for hydrogen and deuterium down to 2.0 × 1019 at./cm3 (~0.02 at.%) and 1.6 × 1020 at./cm3 (~0.16 at.%) with the data acquisition time of ~220 s and 120 s at each position of the SSD, respectively. The main contributions to the improvement of the detection limits are the high detection efficiency of the new detection system and the removal of stray particles, which mainly consist of low energy H0 and H+. We simulated the leading edge shape of the obtained HERDA spectra of hydrogen by SIMNRA and Monte Carlo simulation (CORTEO). The comparative studies between the experiments and simulations revealed the non-negligible contribution of H+ recoils generated by multiple scattering.

Epitaxial thin films of nitrogen-substituted Fe3O4 (Fe3O4–yNy) were synthesized on MgO (001) substrates by using nitrogen-plasma-assisted pulsed laser deposition. The obtained Fe3O4–yNy thin films ...

A double MCP (micro channel plate) system is developed for the improvement of detection limit in HERDA (high-resolution elastic recoil detection analysis) for hydrogen (H) and its isotope. One MCP detects the recoils of hydrogen (or deuterium (D)), the other one detects the secondary electrons emitted from stopper foil. While the dark current noise is reduced down to 2%, the detection efficiency still remains as 80%. The improved detection limit for H and D achieved ∼6.3 × 1019 atoms/cm3 (∼0.06 at.%) for 360 s and ∼2.3 × 1020 atoms/cm3 for 114 s, respectively. It is also found that the contributions of recoils of other light elements to the detection limit are crucial from the comparison with the previous study, in which both H and D are included in the samples. The developed system successfully determines the D depth profile in a SiO2 thin film (t = 5 nm) caused by the D2 annealing.

Metal oxynitride semiconductors with the d0 or d10 electron configuration are promising materials for nontoxic pigments and photocatalysts, but their electrical properties have scarcely been studied. Anatase TaON (δ-TaON) is a metastable polymorph of TaON, and its epitaxial thin films show good semiconducting properties such as a wide tunability of electrical conductivity and a rather high electron mobility comparable to that of anatase TiO2. However, the density of carrier electrons (ne) provided by anion vacancies is limited to ∼1 × 1020 cm–3, so establishing a method for carrier doping of anatase TaON remains a critical issue for its use in electronics applications. In this report, we used soft chemical insertion of Li into interstitial sites of anatase TaON epitaxial thin films by using an n-butyllithium solution, and the resulting material showed a higher ne (3.5 × 1020 cm–3) than anion-deficient anatase TaON films. Additionally, the Li-inserted anatase TaON showed an enhanced Hall mobility (μH) of o...

A-site cation-ordered perovskite cobaltite, RBaCo2Ox (R = rare earth element), exhibits fascinating physical properties, such as spin-state ordering and high oxygen conductivity, because of the large tetragonal distortion of the Co orbital. However, the distorted coordination geometry prefers oxygen vacancies, resulting in a difficulty in obtaining the stoichiometric phase (x = 6). For example, x in YBaCo2Ox, which has largely distorted Co orbitals because of the small size of Y3+, has so far been limited to 5.52. To expand the available range of x, in this study, we performed a low-temperature topotactic oxidation of YBaCo2O5.3 epitaxial films using a strong oxidizing agent NaClO. The x value can be varied in a wide range of 5.3–6.0, maintaining the A-site cation-ordered perovskite structure, by changing the pH and temperature of NaClO. The single crystalline film with x = 6 exhibits large tetragonal distortion (c/a = 0.968) because of the small ionic radius of Y3+ and substrate-induced tensile strain. Unlike antiferromagnetic insulating YBaCo2O5.5, the fully oxidized film with x = 6 exhibits in-plane ferromagnetism and metallicity with a Curie temperature of 130 K possibly because of the double-exchange interaction between Co3+ and Co4+. Moreover, the YBaCo2O6 film exhibits huge magnetic anisotropy with a magnetic anisotropy constant of 1.5 × 108 erg cm−3, demonstrating that the A-site cation-ordered perovskite structure is promising for obtaining high magnetocrystalline anisotropic materials.

A newly developed high-resolution elastic recoil detection analysis (HERDA) system installed at the 1 MV Tandetron in UTTAC at the University of Tsukuba is introduced. The effective solid angle of detector, energy resolution and detection limit for hydrogen are, for the first time, determined quantitatively by the measurements on an a-C:H (and D) film deposited on a Si substrate. In the case of a 500 keV 16 O + as the incident beam, an energy resolution of ∼0.45 keV and a detection limit of ∼3.8 × 10 20 atoms/cm 3 (∼0.18 at.%) with a data acquisition time of ∼310 s are derived.

Perovskite nickel oxides are of fundamental as well as technological interest because they show large resistance modulation associated with phase transition as a function of the temperature and chemical composition. Here, the effects of fluorine doping in perovskite nickelate NdNiO3 epitaxial thin films are investigated through a low-temperature reaction with polyvinylidene fluoride as the fluorine source. The fluorine content in the fluorinated NdNiO3–xFx films is controlled with precision by varying the reaction time. The fully fluorinated film (x ≈ 1) is highly insulating and has a bandgap of 2.1 eV, in contrast to NdNiO3, which exhibits metallic transport properties. Hard X-ray photoelectron and soft X-ray absorption spectroscopies reveal the suppression of the density of states at the Fermi level as well as the reduction of nickel ions (valence state changes from +3 to +2) after fluorination, suggesting that the strong Coulombic repulsion in the Ni 3d orbitals associated with the fluorine substitutio...

Baddeleyite niobium oxynitride (NbON) is a possible low-cost alternative to baddeleyite TaON, which is a well-known oxynitride semiconductor with high photocatalytic activity for visible light. In this study, baddeleyite NbON thin films were epitaxially grown on yittria-stabilized zirconia (YSZ) (100) substrates by using nitrogen-plasma-assisted pulsed laser deposition. Low temperature growth at 500 °C on a thin self-seed layer, which was deposited at 600 °C, was key to obtain baddeleyite NbON with almost stoichiometric chemical composition. X-ray diffraction measurement revealed multiple domain structure of the film with an epitaxial relationship of (100)NbON//(100)YSZ and [001]NbON//[001]YSZ. Band gap of the baddeleyite NbON films was 2.3 eV, which is smaller than that of baddeleyite TaON (2.5 eV). The NbON films showed n-type conduction with rather low mobility of 1.6 × 10−3 cm2 V−1 s−1, which is probably attributable to high defect density and grain boundaries.

We have developed a compact Δ E-E telescope elastic recoil detection analysis (ERDA) system, for the first time at Micro Analysis Laboratory, Tandem Accelerator (MALT) in the University of Tokyo, which consists of a gas ionization chamber and solid state detector (SSD) for the quantitative analysis of light elements. The gas ionization chamber is designed to identify the recoils of O and N from metal oxynitrides thin films irradiated with 40 MeV 35 Cl 7+ . The length of the electrodes along the beam direction is 50 mm optimized to sufficiently separate energy loss of O and N recoils in P10 gas at 6.0 × 10 3 Pa. The performance of the gas ionization chamber was examined by comparing the ERDA results on the SrTaO 2 N thin films with semi-empirical simulation and the chemical compositions previously determined by nuclear reaction analysis (NRA) and Rutherford backscattering spectrometry (RBS). We also confirmed availability of the gas ionization chamber for identifying not only the recoils of O and N but also those of lithium, carbon and fluorine.

We have performed an experiment on charged droplet formation in a humidified N2 gas with trace SO2 concentration and induced by 20MeV proton irradiation. It is thought that SO2 reacts with the chemical species, such as OH radicals, generated through the reactions triggered by N2+ production. Both droplet number and droplet size increased with SO2 consumption for the proton irradiation. The total charged droplet numbers entering the differential mobility analyzer per unit time were proportional to the 0.68 power of the SO2 consumption. These two findings suggest that coagulation among the small droplets contributes to the formation of the droplets. The charged droplet volume detected per unit time is proportional to the SO2 consumption, which indicates that a constant amount of sulfur atoms is contained in a unit volume of droplet, regardless of different droplet-size distributions depending on the SO2 consumption.

Thin films of aluminum nitride (AlN) fabricated by reactive deposition were characterized in order to examine the electrical insulation properties suitable for a gate insulator. For a series of AlN films deposited with a variation of the amount of Al flux at a fixed N flux, compositional and chemical analyses were performed using X-ray photoelectron spectroscopy (XPS) and elastic recoil detection analysis (ERDA). Combined with the result of current-voltage (I-V) measurement, it is found that the insulation properties are correlated with the compositional ratio between Al and N estimated by the ERDA measurement; a good electrical insulation with a minimal leak current of the order of 10- 9 A/cm2 at a high electric field 1 MV/cm is achieved in the film of nearly stoichiometric compositional ratio of Al/N, in which the dominance of the Al-N bonding state is confirmed in the XPS measurement. On the other hand, the incorporation of oxygen, probably caused by the surface oxidization due to the exposure to the air, has little effect on the electrical properties.

Perovskite nickel oxides are of fundamental as well as technological interest because they show large resistance modulation associated with phase transition as a function of the temperature and chemical composition. Here, the effects of fluorine doping in perovskite nickelate NdNiO

InOxFy thin films were epitaxially grown on Y-stabilized ZrO2 (111) substrates by reactive pulsed laser deposition. By changing the substrate temperature (TS), we were able to control the fluorine content of the film. Phase-pure epitaxial thin films with bixbyite-like ordering in the anion-site occupancy were obtained at high TS (≥ 240 °C), where fluorine was inserted into the vacancy sites in the bixbyite lattice up to y / (x + y) ~ 0.3. By decreasing TS, y / (x + y) increased and the bixbyite-like ordering disappeared; simultaneously, fluorine-rich and fluorine-poor subphases emerged. The films grown at TS ≤ 150 °C were amorphous and exhibited higher optical absorbance and electrical resistivity than the epitaxial films.

We investigated the effects of epitaxial strain on the anion composition, crystal structure, and electrical transport properties of topotactically hydrogen substituted SrTiOxHy epitaxial thin films grown on (LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7(001) (LSAT), LaSrAlO4(001) (LSAO), and DyScO3(110) (DSO) substrates. Hydrogen substitution for oxygen (y ≈ 3 − x) was confirmed by X-ray diffraction measurements, elastic recoil detection analysis, and energy dispersive X-ray spectroscopy. Tensile-strained SrTiOxHy/DSO films exhibited a higher hydrogen content (y = 0.87) than compressive-strained SrTiOxHy/LSAT films (y = 0.20) and almost relaxed SrTiOxHy/LSAO films (y = 0.56) after a reaction with CaH2 at 500 °C for 72 h, probably owing to enhanced oxygen diffusion under tensile strain. Metallic conduction was observed in the SrTiOxHy thin films with a low hydrogen content (y = 0.10 and 0.16 on LSAT, y = 0.20 on LSAO, and y = 0.40 on DSO), while further hydrogen substitution (y = 0.56 on LSAO and y = 0.57 and 0.87 on DSO) induced insulating behavior at low temperatures. Furthermore, comparing SrTiOxHy/LSAO (y = 0.56) and SrTiOxHy/DSO (y = 0.57) films revealed that the carrier activation ratio is drastically reduced by tensile strain. These results demonstrate the potential to strain-engineer chemical and physical properties of transition metal oxyhydride thin films.We investigated the effects of epitaxial strain on the anion composition, crystal structure, and electrical transport properties of topotactically hydrogen substituted SrTiOxHy epitaxial thin films grown on (LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7(001) (LSAT), LaSrAlO4(001) (LSAO), and DyScO3(110) (DSO) substrates. Hydrogen substitution for oxygen (y ≈ 3 − x) was confirmed by X-ray diffraction measurements, elastic recoil detection analysis, and energy dispersive X-ray spectroscopy. Tensile-strained SrTiOxHy/DSO films exhibited a higher hydrogen content (y = 0.87) than compressive-strained SrTiOxHy/LSAT films (y = 0.20) and almost relaxed SrTiOxHy/LSAO films (y = 0.56) after a reaction with CaH2 at 500 °C for 72 h, probably owing to enhanced oxygen diffusion under tensile strain. Metallic conduction was observed in the SrTiOxHy thin films with a low hydrogen content (y = 0.10 and 0.16 on LSAT, y = 0.20 on LSAO, and y = 0.40 on DSO), while further hydrogen substitution (y = 0.56 on LSAO and y = 0.57 and 0.87 on DSO)...

We investigated the polyvinylidene fluoride (PVDF)-mediated topotactic fluorination of two perovskite ruthenate thin films with different crystallographic structures, non-layered perovskite SrRuO3 and layered perovskite Sr2RuO4. While the former ruthenate did not react with PVDF, the latter was fluorinated to form Sr2RuO3F2 with a structure that exhibited a largely expanded c-axis. These results indicate that fluorine ions are preferentially inserted into the SrO rocksalt blocks in perovskite ruthenates, and that the oxygen atoms in the precursor oxide were partially removed upon fluorination. Finally, we noted that the Sr2RuO3F2 film was insulating, with a resistivity of 4.1 × 10 Ω cm at 300 K. It should be noted that this resistivity is five orders of magnitude higher than that of the metallic Sr2RuO4 film (6.7 × 10−4 Ω cm).

Zinc oxynitride (ZnOxNy) has attracted much attention as an amorphous semiconductor with high electron mobility. Recent studies reported that ZnOxNy thin films grown by sputtering contained nanocrystals, which might reduce their electron mobility through grain boundary scattering. In this study, we fabricated amorphous ZnOxNy thin films on a glass substrate by a less-energetic nitrogen-plasma-assisted pulsed laser deposition (PLD) to suppress the formation of the nanocrystals. Grown by PLD under optimized conditions, these ZnOxNy thin films exhibited extremely flat surfaces with a root-mean-squared roughness (Rrms) of less than 0.3 nm. The Hall mobility of these films exceeded 200 cm2 V−1 s−1 at a critical carrier concentration of ∼1 × 1019 cm−3, which was twice as high as the reported values for sputter-deposited films. Meanwhile, the mobility of films with larger Rrms was limited to ∼160 cm2 V−1 s−1 even at the critical carrier concentration and comparable with that of the sputter-deposited ZnOxNy films...

Synthesis of mid- to late-transition metal oxynitrides is generally difficult by conventional thermal ammonolysis because of thermal instability. In this letter, we synthesized epitaxialthin films of AX-type phase-pure cobalt oxynitrides (CoOxNy) by using nitrogen-plasma-assisted pulsed laser deposition and investigated their structural, electrical, and magnetic properties. The CoOxNythin films with 0 ≤ y/(x + y) ≤ 0.63 grown on MgO (100) substrates showed a structuralphase transition from rock salt (RS) to zinc blend at the nitrogen content y/(x + y) ∼ 0.5. As the nitrogen content increased, the room-temperature electrical resistivity of the CoOxNythin films monotonically decreased from the order of 105 Ω cm to 10−4 Ω cm. Furthermore, we observed an insulator-to-metal transition at y/(x + y) ∼ 0.34 in the RS-CoOxNy phase, which has not yet been reported in Co2+/Co3+ mixed-valence cobalt oxides with octahedral coordination. The low resistivity in the RS-CoOxNy phase, on the 10−3 Ω cm order, may have originated from the intermediate spin state of Co3+ stabilized by the lowered crystal field symmetry of the CoO6−nNn octahedra (n = 1, 2,…5). Magnetization measurements suggested that a magnetic phase transition occurred in the RS-CoOxNyfilms during the insulator-to-metal transition. These results demonstrate that low-temperature epitaxialgrowth is a promising approach for exploring novel electronic functionalities in oxynitrides.

Multi-phonon excitations, indicating a strong electron–phonon coupling, were observed by soft X-ray resonant inelastic X-ray scattering of Mg2FeH6 and Mg2FeD6. The Fe–H/D stretch and bend modes are selectively activated by the tuned electron excitation to eg brach of Fe 3d states in octahedral symmetry. The energy deviation with the factor of \( {\sim} \sqrt{2} \) due to the isotope effect was clearly observed.