Observation of DC field-evaporated ion species extracted from transition metal nitride thin film deposited on tungsten-tip

The ion species extracted from transition metal nitride thin films were investigated in order to understand the field evaporation mechanism of nitrogen in atom probe analysis. Nitrides of group IV transition metal, ie, titanium (Ti), zirconium (Zr), and hafnium (Hf) nitrides, were chosen for analysis, owing to their good electrical conductivities. The samples were prepared by sputtering deposition of nitride thin film on a tungsten needle. Measurements were performed at 3 different direct current voltages, and for each voltage, we observed different ion species. For TiN and ZrN, both atomic metal ions and molecular ions were detected and TiN and ZrN tended to evaporate in the form of triple-charged molecular ions. For ZrN, Zr²⁺, Zr³⁺, ZrN³⁺, and (ZrN)₂³⁺ were observed at lower direct current voltages. For a higher tip voltage, N⁺ ions were detected in addition to these ions. These results suggest that the evaporation field of nitrogen is higher than those of Zr³⁺ and (ZrN)₂³⁺. In the analysis of an HfN tip, no ions could be detected. These results can be explained in terms of the differences between evaporation fields that were roughly estimated from the work functions and the bond energies of the analyzed nitrides.     

High‐Pressure Synthesis of A2NiO2Ag2Se2 (A=Sr,Ba) with a High‐Spin Ni2+ in Square‐Planar Coordination

Square‐planar coordinate Ni²⁺ ions in oxides are exclusively limited to a low‐spin state (S=0) owing to extensive crystal field splitting. Layered oxychalcogenides A₂Ni^IIO₂Ag₂Se₂ (A=Sr, Ba) with the S=1 NiO₂ square lattice are now reported. The structural analysis revealed that the Ni²⁺ ion is under‐bonded by a significant tensile strain from neighboring Ag₂Se₂ layers, leading to the reduction in crystal field splitting. Ba₂NiO₂Ag₂Se₂ exhibits a G‐type spin order at 130 K, indicating fairly strong in‐plane interactions. The high‐pressure synthesis employed here possibly assists the expansion of NiO₂ square lattice by taking the advantage of the difference in compressibility in oxide and selenide layers.     

Specific Ion Effects on an Oligopeptide: Bidentate Binding Matters for the Guanidinium Cation

Ion–protein interactions are important for protein function, yet challenging to rationalize owing to the multitude of possible ion–protein interactions. To explore specific ion effects on protein binding sites, we investigate the interaction of different salts with the zwitterionic peptide triglycine in solution. Dielectric spectroscopy shows that salts affect the peptide's reorientational dynamics, with a more pronounced effect for denaturing cations (Li⁺, guanidinium (Gdm⁺)) and anions (I^?, SCN^?) than for weakly denaturing ones (K⁺, Cl^?). The effects of Gdm⁺ and Li⁺ were found to be comparable. Molecular dynamics simulations confirm the enhanced binding of Gdm⁺ and Li⁺ to triglycine, yet with a different binding geometry: While Li⁺ predominantly binds to the C‐terminal carboxylate group, bidentate binding to the terminus and the nearest amide is particularly important for Gdm⁺. This bidentate binding markedly affects peptide conformation, and may help to explain the high denaturation activity of Gdm⁺ salts.     

Development of Surface Fluorescence X‐Ray Absorption Fine Structure Spectroscopy Using a Laue‐Type Monochromator

Surface fluorescence X‐ray absorption fine structure (XAFS) spectroscopy using a Laue‐type monochromator has been developed to acquire structural information about metals with a very low concentrate on a flat highly oriented pyrolytic graphite (HOPG) surface in the presence of electrolytes. Generally, surface fluorescence XAFS spectroscopy is hindered by strong scattering from the bulk, which often chokes the pulse counting detector. In this work, we show that a bent crystal Laue analyzer (BCLA) can efficiently remove the scattered X‐rays from the bulk even in the presence of solution. We applied the technique to submonolayer (～10¹⁴ atoms cm^?2) Pt on HOPG and successfully obtained high signal/noise in situ XAFS data in combination with back‐illuminated fluorescence XAFS (BI‐FXAFS) spectroscopy. This technique allows in situ XAFS measurements of flat electrode surfaces to be performed in the presence of electrolytes.     

Wavelength tunability of L-band fiber ring lasers using mechanically induced long-period fiber gratings

We report on oscillation wavelength control in erbium-doped fiber ring lasers by adjusting the period of a mechanically induced long-period fiber grating (LPFG) inserted into the fiber ring resonator. Pump light is provided by a 974 nm laser diode (LD), the emission of which is coupled into the fiber ring resonator through a wavelength-division multiplexing coupler. Laser oscillation occurs with a threshold pump LD current of 40 mA, corresponding to a threshold pump power of 5 mW. When a periodic pressure of 0.81 N/mm is applied to form the LPFG, the fiber ring laser exhibits the tunable range of 40.9 nm, i.e., from 1563.1 to 1604 nm, by changing the grating period.     

The relationship between chemical composition distributions and specific grain boundary conductivity in Y-doped BaZrO3 proton conductors

The relationship between chemical composition at a grain boundary and specific grain boundary conductivity is studied in Y-doped BaZrO₃ ceramics sintered at 1800 °C. Y enrichment at the grain boundary as yttrium concentration increased and Ba deficiency in ceramics as an increase of sintering time are observed. At the grain boundary, phase segregation, i.e. existence of secondary phase and amorphous phase which prevent proton migration, is not observed. The results indicate that at the grain boundary, concentration of Ba vacancy and Y substituted into Zr site is changed. Grain boundary conductivity shows significant dependences to Ba deficiency and Y concentration in ceramics. It is due to significant dependences of specific grain boundary conductivity to Ba deficiency and Y concentration in ceramics. The results indicate that proton migration across the grain boundary is sensitive to concentration of those effectively charged defect, i.e. Y substituted into Zr site and Ba vacancy at grain boundary.     

Fabrication of CoPt magnetic nanodot arrays by electrodeposition process

We attempted to fabricate patterned media using the electrochemical deposition process along with nanopatterned substrates prepared by the electron beam lithography (EBL), UV nanoimprint lithography (UV-NIL), and spin-on-glass nanoimprint lithography (SOG-NIL) approaches. CoPt was electrodeposited into the nanopatterned substrates and chemical mechanical polishing was carried out to planarize the surface. It was clarified that CoPt nanodot arrays were successfully deposited into the patterned nanopores fabricated by UV-NIL and SOG-NIL as well as by EBL with high area selectivity and uniformity. The density of the CoPt nanodot arrays deposited into the nanopores fabricated by EBL was equal up to an areal recording density of 250 Gbit/in².     

High energy x-ray satellites ofL 2,3 emission bands of Na,Mg, Al,and Si

The x-ray satellites found on the high energy sides of theL _2,3 emission bands of Na, Mg, Al, and Si have previously been attributed to the radiative decay of double ionization states. However, in some recent papers it has been proposed that the satellites in Al and Si may arise from the simultaneous radiative decay of a core ionization state and a volume plasmon. A detailed investigation of the high energy satellites of theL _2,3 x-ray emission bands of Na, Mg, Al, and Si have been made for incident electron energies from 500 eV to 5 keV and the results compared with the double ionization theory. Plasmon involvement is also considered. The present results lend additional support to the first interpretation; namely, that the satellites arise from the radiative decay of atoms with a double vacancy in theL _2,3 (2p) shell and not from the plasma phenomenon.     

Hot photoluminescence of GaAs-AlGaAs multiple quantum well structures under high excitation by a single shot of 30 ps, 532 nm laser

Energy-resolved decay times and time-resolved spectra of hot photoluminescence of GaAs-AlGaAs multiple quantum well structures at 77 K under high excitation (50 MW/cm²) were measured by single shot experiments with the use of a 30 ps, 532 nm laser, a streak camera, and an optical multichannel analyzer. It was found that the transition between higher subbands (n=2 e-hh) appears and its intensity relaxes with a decay time of about 200 ps. The theoretical expression for carrier relaxation in a two-dimensional quantum well was obtained. We found that the calculated energy loss rate due to Lo-phonon scattering (10 meV/ps) is at least four times larger than the observed one (2.7 meV/ps).