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We report the single crystal growth of cubic antiperovskite Ca3PbO 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 × 1019 cm−3. The crystal synthesized under optimized growth conditions showed clear Shubnikov-de Haas oscillations, indicating its high purity and homogeneity.

Co-Mo bimetallic nanoparticles (NPs) with various compositions were prepared on a CeO2 support (Co-Mo/CeO2) by sodium naphthalenide driven reduction. The Co-Mo/CeO2 catalyst exhibits much higher activity for ammonia synthesis than monometallic catalysts such as Co/CeO2 and Mo/CeO2, and the optimum activity is obtained at Co:Mo = 4:6. X-ray absorption fine structure (XAFS) analyses reveal that Co3Mo3N NPs are formed after ammonia synthesis reaction. Nitrogen temperature programmed desorption (N2-TPD) measurements indicate that the Co-Mo/CeO2 catalyst possesses a large number of nitrogen adsorption sites with an intermediate nitrogen adsorption energy between that of Co and Mo. Furthermore, nitrogen vacancy sites, which are active sites for N2 dissociation, are more easily formed on the Co-Mo/CeO2 catalyst than on bulk-type Co3Mo3N. As a consequence, the turnover frequency of the Co-Mo/CeO2 catalyst is much higher than that of bulk-type Co3Mo3N and is comparable to that of the efficient Ru/CeO2 catalyst.

Layered iron oxyarsenides are novel interesting semimetallic compounds that are itinerant antiferromagnets in their ground state with a transition to high-temperature superconductivity upon charge carrier doping. The rare earth containing mother compounds offer rich physics due to different antiferromagnetic orderings: the alignment of Fe magnetic moments within the FeAs sublattice, which is believed to play a role for the superconducting pairing mechanism, and the ordering of the rare-earth magnetic moments at low temperatures. Here, we present thin film preparation and a film growth study of SmFeAsO on MgO(100) substrates using pulsed laser deposition (PLD). In general, the PLD method is capable to produce iron oxyarsenide thin films, however, competition with impurity phase formation narrows the parameter window. We assume that the film growth in an ultra-high vacuum (UHV) environment results in an oxygen-deficient phase, SmFeAsO 1− δ . Despite the large lattice misfit, we find epitaxial oxyarsenide thin film growth on MgO(100) with evolving film thickness. Bragg reflections are absent in very thin films although they locally show indications for pseudomorphic growth of the first unit cells. We propose the possibility for a Stranski-Krastanov growth mode as a result of the large in-plane lattice misfit between the iron oxypnictide and the MgO unit cells. A columnar 3-dimensional film growth mode dominates and the surface roughness is determined by growth mounds, a non-negligible parameter for device fabrication as well as in the application of surface sensitive probes. Furthermore, we found evidence for a stratified growth in steps of half a unit cell, i.e. alternating growth of (FeAs) − and (SmO 1− δ ) + layers, the basic structural components of the unit cell. We propose a simple model for the growth kinetics of this compound.

We report the origins of the coloration of Bi2O3–SiO2, Bi2O3–B2O3, and Bi2O3–P2O5 glasses. The glasses were quantitatively analyzed to reveal the Bi valence state and network connectivity of silicate, borate, and phosphate. The electronic structure was correlated with Bi valence states, giving two types of signals: those related to optical bandgaps with Bi3+ s–p intra-transition states at 3.6–4.7 eV and visible absorption bands at 2.5–2.7 eV originating from the charge transfer between Bi3+ and Bi5+ and/or plasmonic Bi0 clusters in the colored glasses. These Bi oxide glasses with tvisible transparent and high refractive index are attractive to replace toxic Pb-containing optical glasses.

The thermoelectric properties of perovskite-type Sr 1−x La x SnO 3 ceramics with x=0.01–0.05 were evaluated from the Seebeck coefficient S , electrical conductivity σ , and thermal conductivity κ measured at high temperatures. The La-doped ceramics were n -type semiconductors exhibiting thermally activated electrical conduction behaviors in the temperature range of 473–1073 K. Eelectron carriers were introduced into the conduction band from doped La atoms up to x=0.03, which was the solubility limit of La at Sr site. The temperature dependence of the κ values for the ceramics was unaffected by both the La content and the microstructures. Estimations of the electronic thermal conductivities by the Wiedemann-Franz law revealed that the phonon thermal conductivities were dominant for all ceramics. The dimensionless figure of merit ZT increased with increasing temperature for all ceramics and reached 0.02–0.05 at 1073 K. In contrast to cubic Ba 1−x La x SnO 3 ceramics, bending of the Sn–O–Sn bonds due to octahedral tilting distortion in Sr 1−x La x SnO 3 lowered the electron mobility, decreasing the power factor S 2 σ and ZT values, although it effectively reduced the phonon mean free path, decreasing the κ values.

The discovery of novel lightweight materials with metallic properties is important for future smart applications, and two-dimensional materials with metallic conductivity are quite rare in this regard. Herein, we report an electrically conductive two-dimensional hydrogen boride material (borophane) that was synthesized in powder form by an ion-exchange reaction. The produced freestanding borophane was amorphous by X-ray diffractometry and found to consist of curved layers of elongated hexagonal networks of boron and hydrogen atoms that bridge pairs of boron atoms with H/B ratio of 1.0. This hexagonal borophane exhibits metallic conduction with a conductivity of 0.13 S cm−1 at around room temperature, and a unique metal-to-insulator transition at around 30 °C.

We fabricated amorphous oxide semiconductor films, a-(Ga1–xZnx)Oy, at room temperature on glass, which have widely tunable band gaps (Eg) ranging from 3.47–4.12 eV. The highest electron Hall mobility ~ 7 cm2 V− 1 s− 1 was obtained for Eg = ~ 3.8 eV. Ultraviolet photoemission spectroscopy revealed that the increase in Eg with increasing the Ga content comes mostly from the deepening of the valence band maximum level while the conduction band minimum level remains almost unchanged. These characteristics are explained by their electronic structures. As these films can be fabricated at room temperature on plastic, this achievement extends the applications of flexible electronics to opto-electronic integrated circuits associated with deep ultraviolet region.

We investigated the effects of thermal annealing for high-density subgap states in amorphous In–Ga–Zn–O (a-IGZO) films by focusing on low-quality defective films deposited without O 2 supply (LQ films). It was found that most of the subgap states were thermally unstable and decreased dramatically by annealing at ≤ 400 °C in O 2 . These defects (but with different shapes) were further reduced by 600 °C annealing, whose subgap states appeared similar to that of a-IGZO films deposited at an optimum condition (high quality, HQ films) and annealed at 300 °C. However, electron Hall mobilities and field-effect mobilities of their thin-film transistors (TFTs) were low for the LQ films/TFTs even annealed at 600 °C compared to those for the HQ films/TFTs. It implies that not only the subgap states but also heavier structural disorder deteriorated the electron transport in the LQ films. The present results also suggest that although a-IGZO deposition without O 2 supply is sometimes employed in particular for DC sputtering, supplying some O 2 gas would be better to produce good TFTs at lower temperatures.

Experimental contributors to the field of Superconducting Materials share their informal views on the subject., Epilogue to Physica C Special Issue on Superconducting Materials, Volume 514 (2015)

We report an electron tunneling study of SmFeAsO 1− x F x in the low doping region ( x =0, 0.045, 0.046, 0.069) by low temperature UHV-STM/STS. Superconducting gaps are observed for each superconducting sample x =0.045 ( T c =12.9 K), x =0.046 ( T c =32.9 K) and x =0.069 ( T c =46.9 K). We obtained corresponding superconducting gap size of Δ SC = 9.5 ± 0.5 meV , 9.75±0.25 meV and 11±1 meV. While T c increases, Δ SC is kept the same. This suggests that the effective attractive interaction is the same and that there is some mechanism that suppresses the superconductivity in the low doping region. On the other hand, similar gap structures were found in a non-superconducting sample with x =0 at 7.8 K. The obtained gap size was Δ N = 8.5 ± 1.5 meV , which is almost the same as the superconducting gap in the superconducting samples ( x =0.045, 0.046, 0.069).

Metallic oxide conductor 12CaO·7Al2O3 (C12A7) electride with high affinity to CO2, a new candidate for the cathode material in electrochemistry, is used for the selective monocarboxylaiton of various olefins. The galvanostatic electrolysis was performed under carbon dioxide atmosphere without sacrificial anode in a divided cell. The monocarboxylic products were obtained in moderate to high yield (58−91%), which were significantly higher than those at Pt (9−83%) and glassy carbon (32−72%) cathode. Keywords: Mayenite, Electride, Cyclic voltammetry, Carboxylation, Carbon dioxide

A device model for amorphous In–Ga–Zn–O thin-film transistors ( a -IGZO TFTs) that explains temperature dependence is proposed. It incorporates a carrier-density dependent mobility and a density of subgap traps of a -IGZO. The model parameters were extracted from only one transfer curve of an a -IGZO TFT at a low drain voltage through a simple analytical model. Device simulation based on this model reproduced current- and mobility-gate voltage characteristics of the a -IGZO TFT well over a wide range of bias voltage and temperature (253–393 K).

We fabricated ZnS:(Cu,Al) thin film phosphors on glass substrates by pulsed laser deposition (PLD) using a KrF 248 nm laser in a H 2 S gas flow. Firstly, we investigated effects of annealing temperature, stress and crystallinity on photoluminescence properties of powder samples. For thin films, photoluminescence intensity increased with increasing the substrate temperature up to 700 °C and then decreased. The former increase is attributed to improvement of crystalline quality and strain, while the latter degradation is attributed to reduction of the Cu acceptors. Intense photoluminescence is observed under an ambient light when excited by 325 nm monochromated light from a fluorescence spectrophotometer. It was confirmed that the PLD process stabilized the wurtzite structure, which is not stable in bulk samples at the thermal equilibrium.

We perform first principles band calculation of electron doped iron-based superconductors adopting the virtual crystal approximation. We find that when electrons are doped by element substitution in the blocking layer, the band structure near the Fermi level is affected due to the increase of the positive charge in the layer. On the other hand, when Fe in the conducting layer is substituted by Co, the band structure is barely affected. This difference should be a key factor in understanding the phase diagram of the heavily doped electron doped systems Ln FeAsO 1-x H x .

Thermoelectric properties and figure of merit were evaluated from the Seebeck coefficient S, electrical conductivity σ, and thermal conductivity κ measured at high temperatures for perovskite-type ceramics of Ba1−xLaxSnO3 with x=0.002, 0.005, and 0.008, which were prepared by a polymerized complex method and a subsequent spark plasma sintering technique. All the polycrystalline dense ceramics showed n-type degenerate semiconducting behavior in the temperature range of 373–1073 K. The La content dependence of the S values revealed successful increase in the electron carriers with the La doping in this x range. The κ values remained almost unchanged with x showing ~9.6 Wm−1 K−1 at room temperature and decreased with increasing temperature. The electronic thermal conductivities calculated by the Wiedemann–Franz law as well as the T−1 dependence of the κ values indicate that the phonon thermal conductivity was dominant. The dimensionless figure of merit ZT increased with increasing temperature for all the ceramics and showed ~0.1 at 1073 K for the ceramics with x=0.002 and 0.005.

An insight is given into recent experimental advances in the spectroscopic studies of oxygen-excess intrinsic defects, in glassy SiO 2 and α-quartz. By controlling excess oxygen in a-SiO 2 , and the conditions of F 2 -laser irradiation, SiO 2 glass samples can be obtained with optical absorption almost exclusively dominated by single defect, oxygen dangling bonds (“non-bridging oxygen hole centers” or NBOHCs), without the presence of complementary Si dangling bonds (generic “E′-centers”). This allows for a more accurate determination of the spectral shape of NBOHC optical absorption in UV and vacuum UV spectral regions. The temperature dependence of NBOHC electron paramagnetic resonance (EPR) signal intensity is stronger than predicted by Curie’s law (1/ T ) even at temperatures at and below 77 K. Dangling bonds are characteristic of an amorphous state and do not exist in a regular crystal lattice. However, site-selective luminescence shows that highly ordered NBOHCs exist in particle-irradiated α-quartz, evidently either on the border between the damage tracks and the crystalline phase or as a part of Si vacancies. They are different from the common “glass-like” NBOHCs in a-SiO 2 by giving distinct sharp zero-phonon lines with characteristic energies in luminescence spectra instead of a continuous distribution of lines. Two distinct types of luminescent NBOHCs, associated with the long and short Si–O bonds in α-quartz are suggested. EPR data corroborate the presence of oriented NBOHCs in neutron-irradiated α-quartz and confirm distinct NBOHCs at the sites of “long” and “short” Si–O bonds in α-quartz.

Relationships between microstructure and transport properties of bicrystal grain boundary (BGB) junctions were studied in cobalt-doped BaFe2As2 (BaFe2As2:Co) epitaxial films grown on [0 0 1]-tilt bicrystal substrates of MgO and (La, Sr)(Al, Ta)O3 with misorientation angles θGB = 3–45°. The θGB of BaFe2As2:Co BGBs were exactly transferred from those of the bicrystal substrates. No segregation of impurities was detected at the BGB junction interfaces, and the chemical compositions of the BGBs were uniform and the same as those in the bulk film regions. A transition from a strongly-coupled GB behavior to a weak-link behavior was observed in current density–voltage characteristics under self-field around θGB ∼ 9°. The critical current density decreased from (1.2–1.6) × 106 A/cm2 of the intragrain transport to (0.7–1.1) × 105 A/cm2 of θGB = 45° because supercurrent becomes more governed by Josephson current with increasing θGB.

Photovoltaic properties and electronic structures of n-type amorphous In–Ga x –Zn–O/ p -type Si heterojunction solar cells ( x = 1, 2, and 3) were investigated focusing on the effects of Ga content based on expectation that Ga-rich films have larger band gaps and improve open circuit voltages (V OC ) of solar cells. To know the electronic structures such as the conduction band minimums (CBMs) and the valence band maximums (VBMs) of these materials, hard x-ray photoemission spectroscopy (HX-PES) was performed. Contrary to the above expectation, the best result was obtained for x = 1 with an energy conversion efficiency of 5.3%. Although the Ga-rich films had larger optical band gaps and higher CBMs, V OC were remained low and poorer fill factors were obtained due to larger densities of defects. The low V OC were partly resulted from the deep VBM levels of the Ga-rich films. The defect densities are discussed in relation also to near-VBM states and near-CBM states observed in HX-PES and subgap optical absorptions.

We characterized epitaxial thin films of Co-doped BaFe 2 As 2 deposited on MgO substrate by resistivity, Hall resistivity and magneto-optical imaging measurements. The Hall coefficient R H is negative at all temperatures and decreases with decreasing temperature. The films have high critical current density J c greater than 1 MA/cm 2 at low temperatures as determined from transport measurements. While the differential magneto-optical images of the remanent state in the film confirm the high J c values they also show the presence of extended defects. Furthermore, the angular dependence of J c in these films exhibit a larger peak for H // c than for H // ab at low fields which probably arises from the presence of defects along the c -axis.

The terahertz (THz) conductivity of FeSe 0.5 Te 0.5 (‘11’-type) and Co-doped BaFe 2 As 2 (‘122’-type) thin films are investigated. For ‘11’-type, the frequency dependence of the complex conductivity can be understood as that of BCS-type superconductor near the superconducting gap energy, and we estimated the superconducting gap energy to be 0.6 meV. For ‘122’-type, we estimated the superconducting gap energy to be 2.8 meV, which is considered to be the superconducting gap opened at the electron-type Fermi surface near the M point.

Indium-free and acid-resistant anatase Nb-doped TiO 2 (NTO) electrodes are promising as economical substitutes for high-cost Sn-doped In 2 O 3 (ITO) films used in organic photovoltaics. By rapid-thermal annealing under an ambient vacuum, an insulating amorphous NTO film of low transparency was changed dramatically into a transparent and conductive anatase NTO electrode. Metallic conductivity of the annealed NTO electrode could be attributed to formation of the anatase phase and activation of the Nb dopant. Based on synchrotron X-ray scattering and high-resolution transmission electron microscopy, the electrical properties of the NTO electrode could be correlated with the microstructure of the NTO film. The acid-stability of NTO film also supports its use as a substitute for ITO electrode. Unlike Ga:ZnO and Al:ZnO films, which were easily etched by acidic PEDOT:PSS solution, the NTO film was stable against this reagent. Importantly, the annealing temperature influenced the performance of the organic solar cell fabricated with the NTO electrode. This indicates that activation of Nb dopants and formation of the anatase phase play an important role in the extraction of carrier from the organic layer to the anode electrode.

Exchange between oxygen molecules embedded in amorphous SiO 2 (interstitial O 2 ) and oxygen atoms in the a -SiO 2 network is found to be remarkably slow at 500 °C. Thermal loading of 18 O 2 at this temperature yields a -SiO 2 containing 18 O-labeled interstitial O 2 whose 18 O fraction is as high as ~ 90%. The 18 O fraction of interstitial O 2 in this sample is quickly decreased by thermal annealing at or above 700 °C because of the oxygen exchange accompanied by the release of 16 O from the a -SiO 2 network. This finding indicates that the oxygen exchange starts at much lower temperatures than indicated by previous works, based on monitoring of the isotopic composition of oxygen atoms in the a -SiO 2 network.

Creation of point defects by ArF (6.4 eV) and F2 laser (7.9 eV) irradiation in synthetic “wet” silica glass thermally loaded with interstitial O2 molecules was studied by optical absorption, electron paramagnetic resonance and infrared absorption. The presence of excess oxygen caused a significant increase of laser-induced ultraviolet (UV) absorption, which was 4 times (7.9 eV-irradiation) and > 20 times stronger (ArF irradiation) as compared to O2-free samples. The spectral shape of photoinduced absorption nearly completely coincided with the spectral shape of oxygen dangling bonds (NBOHC) in 3 to 6.5 eV regions. The contribution of Si dangling bonds (E' centers) was less than few % and was not dependent on oxygen content. Peroxy radical defects were not detected. The photoinduced NBOHCs thermally decayed at 400...500 C. However, a subsequent brief 7.9 eV irradiation restored their concentration up to 70%. This sensitization can be in part attributed to generation of interstitial Cl2 and HCl. These data show that oxygen stoichiometry is an important factor for maximizing laser toughness of wet silica.

12CaO·7Al2O3 (C12A7) is an electrical insulator with a band gap ∼7.5 eV. Contrary to conventional ultra-large gap oxides, electrical conductivity of C12A7 is controllable over a very wide range of 10−10 to 103 S cm−1 by electron doping to a unique conduction band arising from 3-dimensionally connected sub-nanometer-sized cages constituting the crystal structure. This feature provides opportunities to develop a new electronic device. In this study, we fabricated side-gated transistors using C12A7:e− nanowire (NW) channels. The carrier concentration in the as-doped NW channel (Ne > 1020 cm−3) was too high to operate transistors, and therefore Ne was reduced by low-temperature oxidation and controlled to be ∼1014 cm−3. Current modulation by gate voltage sweep was clearly observed in semiconducting C12A7:e− NW channels at room temperature. Moreover, by reducing the channel length from ∼2 μm to ∼100 nm, the magnitude of the current modulation was drastically increased and the on–off current ratio larger than 102 was obtained.

Electronic and magnetic structures of MnP-based compounds, LaMnOP, BaMn 2 P 2 , KMnP and MnP, are calculated by density functional theory at the generalized gradient approximation (GGA) + U level. It reveals that the anti-ferromagnetic (AFM) configuration between the adjacent MnP layers is more stable by ∼80 meV than the ferromagnetic (FM) configuration for BaMn 2 P 2 , while LaMnOP and KMnP have almost no spin interaction between the MnP layers. This difference is explained by the shorter inter-layer spacing in BaMn 2 P 2 . The defect formation energies calculated for LaMnOP suggest that oxygen substitution at the P sites and P vacancies are the most easily formed point defects and explain the observed n-type conduction in nominally undoped polycrystalline samples.

Effects of fluorine doping on the diffusion of interstitial oxygen molecules (O2) in amorphous SiO2 (a-SiO2) were compared to those obtained from a-SiO2 containing SiOH groups. Incorporation of moderate concentration ( ∼ 1 0 19 cm−3) of SiF groups gives rise to minor changes in diffusion parameters between 800 and 1100 ° C: only a slight decrease in solubility and an increase in the activation energy for diffusion can be detected. Incorporation of SiOH groups has similar weak effects on the solubility and activation energy for diffusion. These minor changes are most likely due to the enhancement of the flexibility of local Si–O network as a result of the dissociation of the network by SiOH and SiF groups. However, in contrast to the SiF doping, SiOH doping leads to a notable decrease in the diffusion coefficient. The heat of solution changes by ∼ 0.1 –0.2 eV at ∼ 1000 ° C and it is attributed to the glass transition of a-SiO2.

In order to understand the growth mechanism of magnesium doped LaCuOSe thin film on MgO, the atomic structure of the interface between the epitaxial thin film and the substrate was investigated. Electron diffraction confirmed the orientation relationship between the film and the substrate as (0 0 1)[1 0 0]LaCuOSe:Mg//(0 0 1)[1 0 0]MgO. High resolution Z -contrast imaging based on the high angle annular dark field scanning transmission electron microscope (HAADF-STEM) technique clearly revealed the alternate stacking of La–O layers and Cu–Se layers, and identified a peculiar stacking sequence of La layers at the interface. With the aid of first principles calculations of the interfacial adhesive energy, it was found that the different La layers at the interface play a key role in stabilizing the interface.

We recently report that a superconducting transition is invoked by exposure to water vapor in undoped SrFe 2 As 2 , which occurs accompanied by shrinkage of the c -axis length of the unit cell. In this paper, we calculated structures and formation energies of O-/OH-related impurities and vacancies in SrFe 2 As 2 by first-principles calculations in order to find a model that explains the c -axis shrinkage in SrFe 2 As 2 . It was found that the incorporation of an O, OH or H 2 O molecule at an interstitial site cannot explain the c -axis shrinkage, and that formation of an As vacancy needs a large formation energy. While, Sr and Fe vacancies are formed with negative formation energies, and the Fe vacancy can explain the c -axis shrinkage.

Electronic and optical properties of layered compounds Ln MnPO ( Ln = Nd, Sm, Gd) are investigated in comparison with an antiferromagnetic semiconductor LaMnPO. Diffuse reflectance spectra and temperature dependent electrical conductivity indicate that the Ln MnPO compounds are semiconductors with band gap energies of 0.7–0.8 eV. Electrical conductivity at RT is varied from 4 × 10 −3 to 2.5 S cm −1 by Cu doping for NdMnPO. Nominally undoped Ln MnPO compounds exhibit negative Seebeck coefficients due presumably to P deficiency, while the sign of the Seebeck coefficients is changed to positive by doping of Ca or Cu to the Ln sites, indicating that the polarity of the predominant carriers in Ln MnPO is controlled by doping. Mn spins in NdMnPO are already in an antiferromagnetic ordering state below 350 K, while antiferromagnetic ordering of Nd spins occurs at ∼10 K.

To elucidate the thermoelectric properties at high temperatures, perovskite-type La-doped BaSnO3 ceramics were fabricated by a polymerized complex (PC) method and subsequent spark plasma sintering (SPS) technique. Fine powders of Ba1−xLaxSnO3 (x = 0.00–0.07) were prepared by the PC method using citrate complexes, and SPS treatment converted the powders into dense ceramics with relative densities of 93–97%. The La content dependence of the lattice parameter suggested that the solubility of La for Ba sites was approximately x = 0.03. The temperature dependence of the electrical conductivity σ and Seebeck coefficient S showed that each La-doped ceramic was an n-type degenerate semiconductor in the measured temperature range of 373–1073 K. The La content dependence of the S values indicated that the electron carrier concentration increased successively up to x = 0.03, which was the solubility limit of the La atoms. The thermoelectric power factors S2σ increased drastically with La doping, and reached a maximum for x = 0.01 with values of 0.8 × 10−4 W m−1 K−2 at 373 K to 2.8 × 10−4 W m−1 K−2 at 1073 K.

Epitaxial (0001) films of GaN were grown on (111) YSZ substrates using single-crystalline InGaZnO 4 (sc-IGZO) lattice-matched buffer layers by molecular beam epitaxy with a NH 3 source. The epitaxial relationships are (0001) GaN //(0001) IGZO //(111) YSZ in out-of-plane and [112¯0] GaN //[112¯0] IGZO //[11¯0] YSZ in in-plane. This is different from those reported for GaN on many oxide crystals; the in-plane orientation of GaN crystal lattice is rotated by 30° with respect to those of oxide substrates except for ZnO. Although these GaN films showed relatively large tilting and twisting angles, which would be due to the reaction between GaN and IGZO, the GaN films grown on the sc-IGZO buffer layers exhibited stronger band-edge photoluminescence than GaN grown on a low-temperature GaN buffer layer.

Epitaxial growth and electron doping of 12CaO·7Al 2 O 3 (C12A7) and 12SrO·7Al 2 O 3 (S12A7) are reported. The C12A7 films were prepared on Y 3 Al 5 O 12 (YAG) single-crystal substrates by pulsed laser deposition at room temperature and subsequent thermal crystallization. X-ray diffraction patterns revealed the films were grown epitaxially with the orientation relationship of (001)[100] C12A7 || (001)[100] YAG. For S12A7, pseudo-homoepitaxial growth was attained on the C12A7 epitaxial layer. Upon electron doping, metallic conduction was achieved in the C12A7 film and the S12A7/C12A7 double-layered films. Analyses of optical absorption spectra for the S12A7/C12A7 films provided the densities of free electrons in each layer separately. Hall measurements exhibited larger electron mobility in the S12A7/C12A7 film than those in C12A7 and S12A7 films, suggesting free electrons may be accumulated at the S12A7/C12A7 interface due presumably to a discontinuity of the cage conduction bands.

Amorphous In–Ga–Zn-O ( a -IGZO) thin-film transistors (TFTs) with a coplanar homojunction structure are demonstrated. The coplanar source and drain regions made of a -IGZO were formed by depositing a hydrogenated silicon nitride (SiN X :H) layer onto the a -IGZO layer. The a -IGZO regions on which the SiN X :H layer was directly deposited showed the low resistivity of 4.7 × 10 −3 Ω cm and degenerated conduction. The fabricated TFT showed excellent transfer and output characteristics with a field-effect mobility of 11 cm 2 V − 1 s − 1 , a subthreshold swing of 0.17 V decade − 1 , and an on-to-off current ratio larger than 1 × 10 9 . The width-normalized source-to-drain resistance ( R sd W ) calculated using a channel resistance method was 51 Ω cm. This TFT also showed good stability over environment change and under electrical stress.

The epitaxial growth of Fe-based superconductors such as Co-doped SrFe 2 As 2 (SrFe 2 As 2 :Co) was reported recently, but has still insufficient properties for a device application because they have rough surfaces and are decomposed by reactions with water vapor in an ambient atmosphere. This paper reports that epitaxial films of Co-doped BaFe 2 As 2 grown at 700 ∘ C show the onset superconducting transition temperature of ∼20 K. The transition is sharper than those observed on the SrFe 2 As 2 :Co films, which would originate from their improved crystallinity. These films also have atomically-flat surfaces with step-and-terrace structures and exhibit chemical stability against exposure to water vapor.

We report experimental results of 75As and 139La nuclear magnetic resonance (NMR) in the layered oxypnictide system LaFeAs ( O 1 - x F x ) ( x = 0.0 , 0.04, 0.07 and 0.11) where superconductivity occurs in x greater than 0.04. In the undoped LaFeAsO, 1 / T 1 of 139La exhibits a distinct peak at T N ~ 142 K below which the La NMR spectra become broadened due to the internal magnetic field attributed to an antiferromagnetic (AFM) ordering. In the x = 0.04 sample, 1 / T 1 T of 75As exhibits a Curie–Weiss temperature dependence down to 30 K, suggesting the development of AFM spin fluctuations with decreasing temperature. In the x = 0.11 sample, in contrast, pseudogap behavior is observed in 1 / T 1 T at the 75As site with a gap value of Δ PG ~ 175 K . The spin dynamics vary markedly with F-doping, which is ascribed to the change of the Fermi-surface structure by the electron-doping. As for the superconducting properties for x = 0.04 , 0.07 and 0.11, 1 / T 1 of 75As in all compounds does not exhibit a coherence peak just below T c and follows a T 3 dependence at low temperatures. These results seemingly suggests that unconventional superconductivity with zero gap along lines, whereas the lack of the residual density of states at the low temperatures is incompatible with the presence of the line-nodes. We discuss similarity and difference between LaFeAs ( O 1 - x F x ) and cuprates, and also discuss the relationship between spin dynamics and superconductivity on the basis of F-doping dependence of T c and 1 / T 1 .

Thin films of tungsten phosphate glasses were deposited on a Pd substrate by a pulsed laser deposition method and the flux of hydrogen passed thorough the glass film was measured with a conventional gas permeation technique in the temperature range 300–500 °C. The glass film deposited at low oxygen pressure was inappropriate for hydrogen permeation because of reduction of W ions due to oxygen deficiency. The membrane used in the hydrogen permeation experiment was a 3-layered membrane and consisted of Pd film (~ 20 nm), the glass film (≤ 300 nm) and the Pd substrate (250 µm). When the pressure difference of hydrogen and thickness of the glass layer were respectively 0.2 MPa and ~ 100 nm, the permeation rate through the membrane was 2.0 × 10− 6 mol cm− 2 s− 1 at 500 °C. It was confirmed that the protonic and electronic mixed conducting glass thin film show high hydrogen permeation rate.

12CaO·7Al2O3 (C12A7) with a unique nano-porous structure and free O2− ions entrapped in sub-nanometer-sized cages is a fast oxygen-ion-conducting material. These free O2– may be replaced by various oxygen-related species, OH−, O2− and O−, by tuning the atmosphere during the heat treatment. We examined the conduction mechanism for stoichiometric C12A7 (C12A7:O2−), in which O2− ions exist as counter anions in sub-nanometer-sized cages, by Raman measurement of C12A7:O2− annealed in a dry 18O2 atmosphere. It was revealed that the primary ion conducting species is an O2− ion which diffuses via exchange with O2− in the cage wall. An experimental result on the sample containing O− ions implied that O− is more mobile than O2− in C12A7. Ab initio calculations on the diffusion paths of O2− and O− ions in C12A7 supported the above experimental results.

Pressure dependence on superconducting transition temperature ( T c ) was examined for iron-based superconductor LaFeAsO 1− x F x , SmFeAsO 1− x F x and LaFePO. The T c ’s increase largely for LaFePO and LaFeAsO 1− x F x with a small increase of pressure. The electrical resistivity measurements reveal the pressure-induced superconductivity in undoped LaFeAsO and SmFeAsO. X-ray diffraction measurements were also performed under high pressure up to 10 GPa for LaFePO and LaFeAsO 1− x F x system, where the anisotropic decrease of the lattice constants was observed with applying pressure.

FeAs-based layered superconductors such as F-doped LaFeAsO have recently been investigated intensively because of their high superconducting transition temperatures. Epitaxial films of these compounds are important to examine their intrinsic materials properties as well as to transfer them to device applications. In this review, we first present our research route from transparent p-type oxides semiconductors to the Fe-based superconductors. Then we review growth of epitaxial thin films for the layered oxychalcogenides and oxypnictides. Reactive solid-phase epitaxy technique was inevitable to prepare epitaxial thin films of the oxychalcogenides and Zn-based oxypnictides. On the other hand, epitaxial thin films of Mn-based oxypnictides were grown by standard pulsed laser deposition. These techniques, however, did not grow epitaxial thin films for LaFeAsO. Thus, we developed a modified pulsed laser deposition process and succeeded in obtaining epitaxial thin films of FeAs-based superconductors, LaFeAsO and cobalt-doped SrFe 2 As 2 .

Fluorine-doped synthetic SiO2 glass is suitable for investigating intrinsic defect processes in SiO2 glass because of the high radiation hardness and the low concentrations of defect precursors such as the strained Si O Si bonds and impurity-related network modifiers including SiOH, SiH, and SiCl groups. When the concentrations of the defect precursors are minimized by moderate fluorine doping into SiO2 glass, formation of oxygen vacancy–interstitial pairs (Frenkel pairs) is the primarily Co60γ-ray-induced defect process. However, heavy fluorine doping tends to degrade the radiation hardness and enhance the formation of the silicon and oxygen dangling bonds, suggesting the presence of another type of defect precursors in heavily fluorine-doped SiO2 glasses.

12CaO·7Al2O3 (C12A7) is a typical band insulator, but may be converted to a metallic conductor C12A7:e− by electron-doping via removal of free oxygen ions sitting in the subnanometer-sized cages as the counter ions. Also, C12A7 is known as a fast oxygen ion conductor. These unique features let us expect that it would be possible to dope electrons to C12A7 by removing the free oxygen ions by an external electric field. In this study, we fabricated C12A7/C12A7:e− stacking devices and examined their current–voltage characteristics. The thickness of the top C12A7 layer was controlled by low-temperature oxidation with an aid of an optical model analysis of spectroscopic ellipsometry. We found that the C12A7/C12A7:e− devices exhibited a bistable resistance switching effect with an on-to-off resistance ratio of ∼102 and operated as a resistive random access memory.

A homologous series compound ScAlO3(MgO) (SCAM) has a superior lattice matching as small as ∼1.4% in a-axis with GaN. This paper reports an efficient fabrication process of a single-crystalline SCAM buffer layer on a (1 1 1) yttria-stabilized zirconia (YSZ) substrate using pulsed laser deposition (PLD). A 10-nm thick ZnO epitaxial layer was used to induce solid-phase epitaxial growth of an amorphous (a-) SCAM layer formed at room temperature on (1 1 1) YSZ. It was found that the addition of excess Sc2O3 and ZnO to a SCAM target used for PLD was needed to obtain single-crystalline SCAM films with atomically flat terraces-and-steps surfaces. The resulting single-crystalline SCAM films were examined as buffer layers to grow GaN by molecular beam epitaxy with a plasma nitrogen source. The GaN films were grown epitaxially on the SCAM/YSZ substrates with the epitaxial relationship of [0 0 0 1] GaN||[0 0 0 1] SCAM||[1 1 1] YSZ and [1 0 0] GaN||[11-20] SCAM||[1-10] YSZ. The SCAM buffer layers enhanced lateral growth of the GaN films owing to the good lattice matching.

Single-crystalline thin films of ScAlMgO 4 (SCAM) were fabricated on YSZ (111) substrates by reactive solid-phase epitaxy (R-SPE) using ScGaO 3 (ZnO) m (SGZO) single-crystalline buffer layers, which suppress interface reactions between the SCAM layers and the YSZ substrates. First, post-annealing of the SCAM layers fabricated by the R-SPE process was examined. When annealing temperature was raised to > 1200 °C, the formation of a spinel MgAl 2 O 4 phase was observed. This is due probably to out-diffusion of Sc ions from the SCAM layers to the YSZ substrates. By introducing an SGZO buffer layer, a single-phase SCAM layer with a step-and-terrace surface was obtained by annealing at 1450 °C without the spinel formation. The SCAM layer was grown heteroepitaxially with an epitaxial relationship of (000 l) SCAM (111) YSZ and (110) SCAM (11–0) YSZ . Atomically flat surfaces were eventually formed by chemical-mechanical polishing. The SCAM layer was applied to a lattice-matched buffer layer for the growth of ZnO film, leading to marked lateral growth of ZnO domains.

A p-type transparent oxide semiconductor, CuGaO 2 , was grown epitaxially on (111) single-crystalline yttria-stabilized zirconia (YSZ) substrates by pulsed laser deposition (PLD). Single-phase epitaxial films were obtained in narrow conditions: i.e. 725 ≤ T s ≤ 780 °C at P O 2 = 6 Pa, and 3 Pa ≤ P O 2 ≤ 6 Pa at T s = 750 °C. The electrical conductivity of the as-deposited films was controlled from 3.3 × 10 − 5 S∙cm − 1 to 1.7 × 10 − 2 S∙cm − 1 by increasing the oxygen partial pressure from 3 to 6.5 Pa. The hole concentration and Hall mobility of the most conductive film were 5 × 10 17 cm − 3 and 0.2 cm 2 ∙V − 1 ∙s − 1 , respectively. Estimated from the conductivity, the hole concentration was controlled from ∼ 10 14 cm − 3 to ∼ 10 17 cm − 3 by the oxygen partial pressure. Post-annealing at 1215 °C smoothed the films surface to 0.56 nm in the root-mean-squares roughness and increased the Hall mobility to 0.8 cm 2 V − 1 ∙s − 1 , which is the largest value among CuGaO 2 films reported to date.

Single crystals of 12CaO·7Al2O3 (C12A7) have been grown by the Czochralski method with three different growth directions of , , and . Employment of a 2.0% oxygen-containing nitrogen atmosphere and use of an iridium crucible were the critical factors for obtaining the single crystal. The crystal exhibited orange color resulting from the incorporation of Ir4+ ions of ∼ 5 × 1017 cm− 3, presumably occupying at Ca2+ sites. High resolution X-ray diffraction analyses indicated that the C12A7 single crystal shows the tetragonal symmetry belonging to the space group I 4 ― 2 m .