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Hosono, Hideo

Publications and source records attributed to Hosono, Hideo.

16 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Unconventional excitonic states with phonon sidebands in layered silicon diphosphide

Complex correlated states emerging from many-body interactions between quasiparticles (electrons, excitons and phonons) are at the core of condensed matter physics and material science. In low-dimensional materials, quantum confinement affects the electronic, and subsequently, optical properties for these correlated states. Here, by combining photoluminescence, optical reflection measurements and ab initio theoretical calculations, we demonstrate an unconventional excitonic state and its bound phonon sideband in layered silicon diphosphide (SiP 2 ), where the bound electron–hole pair is composed of electrons confined within one-dimensional phosphorus–phosphorus chains and holes extended in two-dimensional SiP 2 layers. The excitonic state and emergent phonon sideband show linear dichroism and large energy redshifts with increasing temperature. Our ab initio many-body calculations confirm that the observed phonon sideband results from the correlated interaction between excitons and optical phonons. With these results, we propose layered SiP2 as a platform for the study of excitonic physics and many-particle effects.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Ship-in-a-Bottle Synthesis of High Concentration of N2 Molecules in a Cage-Structured Electride

We report the formation of neutral nitrogen molecules in the cages of [Ca12Al14O32]2+ (C12A7) framework compensated by extra-framework anions. NH3 treatment of C12A7 electride (C12A7:e–) at 800 °C leads to the formation of N2 and NH2– species in the C12A7 cages. N2 and NHx species in the cages are identified using the Raman spectroscopy of 14NH3 and 15NH3-treated C12A7:e–. The concentration of H and N in the C12A7 cages after NH3 treatment is ~1021 cm–3. We propose a two-step mechanism, supported by density functional theory (DFT) modeling, of N2 incorporation into the C12A7 cages: incorporation of NH2– formed from decomposition of NH3 at C12A7:e– surface followed by the NH2- species reacting to form N2 molecules. Encapsulation of neutral molecules, as opposed to negatively charged species reported in C12A7 previously, offers new opportunities for trapping and storing gaseous substances in nano-porous materials.

Nakao, Takuya↗
DOE OSTI2021

Field-induced topological Hall effect and double-fan spin structure with a $c$-axis component in the metallic kagome antiferromagnetic compound YMn 6 Sn 6

Geometric frustration in the kagome lattice makes it a great host for the flat electronic band, nontrivial topological properties, and novel magnetism. In this work, we use magnetotransport measurements to map out the field-temperature phase diagram of the centrosymmetric YMn 6 Sn 6 with a Mn kagome lattice and show that the system exhibits the topological Hall effect (THE) with an in-plane applied magnetic field around 240 K. In addition, our neutron diffraction results demonstrate that the observed THE cannot arise from a magnetic skyrmion lattice, but instead from an in-plane field-induced double-fan spin structure with c-axis components. This paper provides a platform to understand the influence of a field-induced novel magnetic structure on magnetoelectric response in topological kagome metals.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Air-Stable Calcium Cyanamide-Supported Ruthenium Catalyst for Ammonia Synthesis and Decomposition

Efficient ammonia synthesis and decomposition processes under mild conditions are important to meet the expanding demand in major applications of ammonia as the energy carrier and to provide feedstock for chemical industry. In this study, we report that air-stable calcium cyanamide-supported ruthenium (Ru/CaCN 2 ) works as an efficient and stable catalyst for ammonia synthesis and decomposition. Ru/CaCN 2 exhibits greater catalytic performances for both reactions than Ru/Ca 2 N electride and Ru–Cs/MgO. The kinetic analysis for ammonia synthesis suggests that Ru/CaCN 2 exhibits low apparent activation energy and high resistance to hydrogen poisoning, which has characteristics similar to the kinetic parameters of Ru-supported electride catalyst. H 2 -temperature programmed reaction and temperature programmed desorption revealed that Ru promoted the formation of CN 2 vacancies on the CaCN 2 surface which in turn capture hydrogen as H – ions during the reaction. Density functional theory calculations provide insights into how the formation of CN 2 vacancies is promoted by Ru, which leads to the decrease in the work function of the CaCN 2 surface and the hydrogen capture at the Ru-support interface. These results suggest that the high catalytic performance of Ru/CaCN 2 can be attributed to the formation of a quasi-electride structure at the Ru–CaCN 2 interface.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Particulate Generation on Surface of Iron Selenide Films by Air Exposure

Nanometer-sized particular structures are generated on the surfaces of FeSe epitaxial films directly after exposure to air; this phenomenon was studied in the current work because these structures are an obstacle to field-induced superconductivity in electric double-layer transistors using FeSe channel layers. Chemical analyses using field-effect scanning Auger electron spectroscopy revealed no clear difference in the chemical composition between the particular structures and the other flat surface region. This observation limits the possible origins of the particulate formation to light elements in air such as O, C, H, and N.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Ternary inorganic electrides with mixed bonding

A high-throughput screening based on first-principles calculations was performed to search for new ternary inorganic electrides. From the available materials database, we identified three new thermodynamically stable materials (Li 12 Mg 3 Si 4 , NaBa 2 O, and Ca 5 Ga 2 N 4 ) as potential electrides made by main group elements, in addition to the well known mayenite based electride (C12A7:e – ). Different from those conventional inorganic electrides in which the excess electrons play only the role of anions, the three new materials, resembling the electrides found in simple metals under high pressure, possess mixed ionic and metallic bonding. The interplay between two competing mechanisms, together with the different crystal packing motifs, gives rise to a variety of geometries in anionic electrons and rich physical phenomena such as ferromagnetism, superconductivity, and metal-insulator transition. Furthermore, our finding here bridges the gap between electrides found at ambient and high-pressure conditions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Superconducting transition temperatures in the electronic and magnetic phase diagrams of Sr 2 VFeAsO 3- δ , a superconductor

We elucidate the magnetic phases and superconducting (SC) transition temperatures (T c) in Sr 2 VFeAsO 3-δ (21113V), an iron-based superconductor with a thick-blocking layer fabricated from a perovskite-related transition metal oxide. At low temperatures (T<37.1 K), 21113V exhibited a SC phase in the range 0.031 ≤ δ ≤ 0.145 and an antiferromagnetic (AFM) iron sublattice in the range 0.267 ≤ δ ≤ 0.664. Mixed-valent vanadium exhibited a dominant AFM phase in 0.031 ≤ δ ≤ 0.088, and a partial ferrimagnetic (Ferri.) phase in the range 0.124 ≤ δ ≤ 0.664. The Ferri. phase was the most dominant at a δ value of 0.267, showing an AFM phase of Fe at T < 20 K. Increasing the spontaneous magnetic moments reduced the magnetic shielding volume fraction due to the SC phase. This result was attributed to the magnetic phase of vanadium, which dominates the superconductivity of Fe in 21113V. The T c–δ curve showed two maxima. Conclusively, the smaller and larger of T c maxima occurred at δ = 0.073 and δ = 0.145, respectively; the latter resides on the phase boundary between AFM and the partial Ferri. phases of vanadium. 21113V is a useful platform for verifing new mechanisms of T c enhancement in iron-based superconductors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Flux growth and magneto-transport properties of cubic antiperovskite Ca3PbO single crystals

Highlights: • Antiperovskite Ca{sub 3}PbO is predicted to be a three-dimensional Dirac fermion system. • Cubic crystals, 1 mm in size, were obtained by a Ca-self-flux method. • The crucible and sealing method were critical factors to reduce carrier density. • Shubnikov-de Haas oscillations were clearly observed, indicating its high purity. - Abstract: We report the single crystal growth of cubic antiperovskite Ca{sub 3}PbO by a Ca-self-flux method. Cubic crystals, 1 mm in size, were successfully obtained through the use of iron crucibles sealed in stainless steel capsules. The crucible material and sealing method were found to be critical factors for achieving large crystals with low carrier density. The crystals were subsequently characterized by powder and single-crystal x-ray diffraction experiments, electron-probe microanalysis, and Hall effect measurements. Through the use of short stainless steel rods as tight caps for the crucible and fillers to occupy extra space in the capsule, the Ca evaporation loss of the flux, which contributes to Ca vacancy formation, was effectively reduced. Hence, the hole carrier density in the single crystal was reduced to 4.0 × 10{sup 19} cm{sup −3}. The crystal synthesized under optimized growth conditions showed clear Shubnikov-de Haas oscillations, indicating its high purity and homogeneity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Roles of Pseudo-Closed s 2 Orbitals for Different Intrinsic Hole Generation between Tl–Bi and In–Bi Bromide Double Perovskites

Although metal halide double perovskites A 2 B(I)B(III)X 6 are expected as nontoxic alternatives for lead halide perovskites, recent studies have shown that only Tl(I)–Bi(III) and In(I)–Bi(III) bromides are thermodynamically stable and possess optoelectronic properties suitable for photovoltaic absorbers. In this work, we show, through density functional theory calculations, that Tl–Bi and In–Bi bromide double perovskites exhibit significantly different semiconducting behaviors due to the different energy levels of the highest-occupied pseudoclosed s 2 orbitals of Tl(I) and In(I). While Tl–Bi double perovskites can exhibit semiconducting $p$-type properties, In–Bi bromide double perovskites exhibit metallic $p$-type ones regardless of the synthesis condition due to the extremely low formation energy of In vacancy. Such difference makes Tl–Bi bromide double perovskites suitable for optoelectronic applications, but not In–Bi bromide double perovskites. Furthermore, there is a high probability for In to substitute a Bi site, forming a local In–In bromide double perovskite structure with a lower local conduction band minimum, detrimentally affecting the open circuit voltage of In–Bi bromide double perovskite-based thin film solar cells.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Structure and stability of CaH 2 surfaces: on the possibility of electron-rich surfaces in metal hydrides for catalysis

Structure, thermodynamic stability, and electronic properties of CaH 2 surfaces in (001),(110), and (111) crystallographic orientations are investigated using ab initio modeling. We show that stoichiometric surfaces terminated with a hydrogen atomic plane are the most energetically favorable and discuss properties of hydrogen vacancies (VH) at these surfaces. The average calculated work function of the most stable pristine surfaces (~5.2 eV) is in agree-ment with experimental data for powder samples. Neutral hydrogen vacancies host localized electrons and induce defect states in the band gap, thereby shifting the effective work function to much lower values of ~2.7 eV. Surface VH are predicted to aggregate into dimers and form electron-rich centers (e - )Ca 2+ (e - ) stable to over 800 K. These results suggest that hydrogen-deficient surfaces of CaH 2 can host a large concentration of localized electrons and, thus, give rise to new catalytic functionalities involving electron transfer between the surface, catalysts supported on it, and reacting species.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Rattling of Oxygen Ions in a Sub-Nanometer-Sized Cage Converts Terahertz Radiation to Visible Light

A simple and robust approach to visualization of terahertz (THz) light would open up opportunities to couple physical phenomena that occur at fundamentally different energy scales. Here we demonstrate how nanoscale cages of Ca 12 Al 14 O 33 crystal enable a novel method for conversion THz radiation to visible light. These crystallographic cages contain weakly bonded oxygen ions and give rise to a low-energy conduction band that can populated with localized yet mobile electrons. THz light excites a nearly stand-alone rattling motion of the encaged species, which promotes electron transfer from them to the neighboring cages. When the power of THz light reaches tens of watts, the coupling between forced rattling in the confined space, electronic excitation and ionization of oxygen species and corresponding recombination processes result in emission of bright visible light.

Toda, Yoshitake↗
DOE OSTI2016

Preface

Preface to the special issue of Thin Solid Films covering the 9th International Symposium on Transparent Oxide Thin Films for Electronics and Optics (TOEO-9).

14 SOLAR ENERGY↗