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The strain effect from a substrate is an important experimental route to control electronic and magnetic properties in transition-metal oxide (TMO) thin films. Using hard x-ray photoemission spectroscopy, we investigate the strain dependence of the valence states in LaNiO$_{3}$ thin films, strongly correlated perovskite TMO, grown on four substrates: LaAlO$_{3}$, (LaAlO$_{3}$)$_{0.3}$(SrAl$_{0.5}$Ta$_{0.5}$O$_{3}$)$_{0.7}$, SrTiO$_{3}$, and DyScO$_{3}$. A Madelung potential analysis of core-level spectra suggests that the point-charge description is valid for the La ions while it breaks down for Ni and O ions due to a strong covalent bonding between the two. A clear x-ray photon-energy dependence of the valence spectra is analyzed by the density functional theory, which points to a presence of the La 5$p$ state near the Fermi level., 6 pages, 4 figures, and 2 tables

This work explores the mechanism of interfacial coupling in LaMnO${}_{3}$/SrIrO${}_{3}$ superlattices by x-ray spectroscopies and first-principles calculations. The superlattice-period dependent properties of the Ir magnetic moments can be attributed to the realignment of electron spin during the formation of the interfacial molecular orbital.

We studied the effect of post-deposition annealing (PDA) on the electrical property and the structure of aluminum oxide (AlOx) passivation films prepared by the atomic layer deposition with various temperatures. Surface recombination velocity (S max), interface trap density (D it), and fixed charge density (Q eff/q) before and after the PDA were evaluated employing lifetime and capacitance-voltage measurements. The structural change by the PDA was investigated by a Stokes ellipsometer and X-ray reflectivity measurements at SPring-8. The S max of all samples was improved by the PDA. The improvement of S max in the samples deposited at the temperature of 200 and 300 °C was due to the D it decrease, but that in the sample deposited at the temperature of 25 °C was due to both the D it decrease and the Q eff/q increase. From the XRR measurements, it revealed that the formation of the interfacial thin-layer is essential for the appearance of negative fixed charges.

The concept of the tricolor superstructure (TCS), which is a triple-layer stack structure containing two types of high dielectric constant (high-k) layers (designated HK1 and HK2) and a SiO2 layer, is proposed to control the moment and the polarity of the interface dipole layer that are induced at the high-k/SiO2 interfaces. The interface dipole layer is formed by oxygen ion migration from the layer with higher oxygen areal density (σ) to that with lower σ. When the two high-k materials are selected with the order of σHK1 > σSiO2 > σHK2 in a SiO2/HK2/HK1/SiO2 TCS, the dipole directions of the interface dipole layers at the SiO2/HK2 and the HK1/SiO2 interfaces are aligned. Additionally, in the transposed SiO2/HK1/HK2/SiO2 TCS, the total polarity is reversed. The concept is demonstrated using Al2O3 and Y2O3 layers because they offer the order of σAl2O3 > σSiO2 > σY2O3. The two stacking sequence samples composed of SiO2/Y2O3/Al2O3/SiO2 and SiO2/Al2O3/Y2O3/SiO2 that were fabricated using superlattice technique by pulsed laser deposition obviously show opposite dipole polarities. Increasing repetition of the deposited TCS unit also causes the dipole moments to increase systematically. The TCS technique enables control of the properties of the interface dipole layer at high-k/SiO2 interfaces in amorphous systems.The concept of the tricolor superstructure (TCS), which is a triple-layer stack structure containing two types of high dielectric constant (high-k) layers (designated HK1 and HK2) and a SiO2 layer, is proposed to control the moment and the polarity of the interface dipole layer that are induced at the high-k/SiO2 interfaces. The interface dipole layer is formed by oxygen ion migration from the layer with higher oxygen areal density (σ) to that with lower σ. When the two high-k materials are selected with the order of σHK1 > σSiO2 > σHK2 in a SiO2/HK2/HK1/SiO2 TCS, the dipole directions of the interface dipole layers at the SiO2/HK2 and the HK1/SiO2 interfaces are aligned. Additionally, in the transposed SiO2/HK1/HK2/SiO2 TCS, the total polarity is reversed. The concept is demonstrated using Al2O3 and Y2O3 layers because they offer the order of σAl2O3 > σSiO2 > σY2O3. The two stacking sequence samples composed of SiO2/Y2O3/Al2O3/SiO2 and SiO2/Al2O3/Y2O3/SiO2 that were fabricated using superlattice techniqu...

Relaxor type ferroelectrics are treasure boxes both for basic physics and practical applications. Among them, Ba(Zr, Ti)O3 is one of the candidate materials for elucidating the mechanism of relaxor phenomena. It has homo-valent B-site ions of Zr4+ and Ti4+. Therefore, there is no driving force to push the ions into ordered structure. On the other hand, it has a possibility of co-existence of multi phases (so-called pinching effect). In case of the bulk state, we have found that the relaxor behavior is strongly affected by the annealing conditions. To make clear the intrinsic parameter for the relaxor, we have demonstrated the artificial control of the positioning of the B-site ions by the superlattice technique. The stacking periodicity and the compositional combination of BaTiO3 and BaZrO3 are changed systematically with this method and the sign of the relaxor is detected.

We studied the effective net charge density (Qeff) of strontium silicate (SrxSiOx+2, x = 1, 2, 3) films grown on silicon (Si) (100) substrates. The SrxSiOx+2 layers were deposited from a Sr2SiO4 polycrystalline target by pulsed laser deposition, and then annealed at 400–600 °C in an oxygen atmosphere with a tube furnace. The Qeff values of the SrxSiOx+2/Si (100) samples were obtained from the shift in the voltage of the flat band state in their capacitance–voltage curves. The SrxSiOx+2/Si (100) samples with a thickness of 15 nm annealed at 400 °C showed the maximum Qeff/q value of 1.03 × 1013 cm−2, where q is the elementary charge. With increasing annealing temperature, the SrxSiOx+2 layer penetrated into the Si (100) substrate. This penetration may degrade the interfacial properties and decrease the Qeff value of the layers. For all the samples, the charges concentrated near the SrxSiOx+2/Si (100) interface. Our results suggest that anion and cation migration plays an important role in charge generation ...

We have grown YMnO3 (YMO) thin films on Si(111) using silicon oxynitride (SiON) as a buffer layer. Thickness of SiON buffer layer was well controlled within 2 nm. High resistance of ultrathin SiON layer (dSiON∼0.7 nm) to Si oxidation was confirmed by x-ray photoelectron spectroscopy (XPS). Using the ultrathin SiON layer, we obtained c-axis oriented ferroelectric phase of YMO. Although capacitance–voltage curves of Al/YMO/SiON/Si(111) showed hystereses attributed to ferroelectricity of the YMO films, the memory window was not sufficient (0.2 V), seemingly due to poor crystallinity of the YMO films. On the other hand, leakage current characteristic was good enough for application. The typical value of leakage current density was 10−8 A/cm2 at a drive voltage of ±5 V. In this article, the details of the characterization elucidated by using x-ray diffraction, atomic force microscopy, and XPS will be shown as well.

To investigate the effect of initial oxidized layer condition on passivation quality of AlOx films deposited at room temperature by means of ozone-based atomic layer deposition technique, crystalline silicon substrates were exposed to ozone before deposition. This ozone exposure pre-treatment increased the thickness of over-layer as compared with standard samples, and deteriorate interface quality of as-deposited samples. For 10nm-thick samples, the ozone exposure pre-treatment is effective for generation of negative fixed charges. The effective lifetime of the sample with ozone exposure and post-deposition annealing is 1.8 msec at the injection level of 1015 cm-3. For 30nm-thick samples, ozone exposure pre-treatment improves the effective lifetime.

The authors studied the correlation between the chemical bonding (CB) states and fixed charge (FC) states of Sr-silicate films grown on Si(100) substrates [Sr-silicate/Si(100)]. The Sr-silicate/Si(100) samples were synthesized by silicate reaction of SrO layers on the Si substrates through the diffusion of Si atoms from the substrates by thermal annealing in oxygen atmosphere. The CB states and the FC states of the Sr-silicate/Si(100) samples were obtained from their O 1s core-level x-ray photoemission spectra and the shift in voltage from the flat band state in their capacitance–voltage curves, respectively. Peak fittings of the O 1s core-level spectra for each sample were carried out with the three components of Si–O, Si–O–Sr, and Sr–O bonds to determine the CB state. The thin Sr-silicate layers were mainly constructed of the Si-O-Sr component. With increasing thickness, the amount of Si-O-Sr component decreased while that of Sr-O increased. The thickness dependency of the FC density showed a good agreement with that of the Si-O-Sr component, revealing a clear correlation between FC and Sr–O–Si bonding. Our results suggest that silicate bonding plays an important role in FC generation in Sr-silicate systems.

We investigated the room temperature growth of HfO2 layers on Si substrates by pulsed laser deposition under ultra-high vacuum conditions. The laser fluence (LF) during HfO2 layer growth was varied as a growth parameter in the experiments. X-ray photoemission spectroscopy (XPS) was used to observe the interface chemical states of the HfO2/Si samples produced by various LFs. The XPS results indicated that an interface Hf-silicate layer formed, even at room temperature, and that the thickness of this layer increased with increasing pulsed LF. Additionally, Hf-Si bonds were increasingly formed at the interface when the LF was more than 2 J/cm2. This bond formation process was related to decomposition of HfO2 to its atomic states of Hf and O by multiphoton photochemical processes for bandgap excitation of the HfO2 polycrystalline target. However, the Hf-Si bond content of the interface Hf-silicate layer is controllable under high LF conditions. The results presented here represent a practical contribution to the development of room temperature processing of Hf-compound based devices.

Thin films of ferroelectric binary mixed II–VI compounds such as (ZnxCd1−x)S, as well as (ZnyCd1−y)Te and (ZnzCd1−z)Se (0⩽x,y,z⩽1), were examined from the standpoint of the application to Si-based nonvolatile memories. Electronic-band discontinuities at the ferroelectric–Si interface decreased significantly with increase in the atomic number of the constituent chalcogenide atoms, which favored (ZnxCd1−x)S as the most potential gate ferroelectrics among the three compounds. Polarization-field (P–E) characteristics of the (ZnxCd1−x)S films were found to largely depend on the cation composition. No hysteretic behaviors in the P–E curves were observed for high-Zn concentrations above x=0.5, while the P–E curves traced hysteretic loops due to the ferroelectricity for x

Electrical properties of Bi4Ti3O12 (BiT) films on Si(100) were improved due to insertion of silicon oxynitride (SiON) buffer layers with thicknesses of 1–2 nm. Capacitance–voltage measurements indicated that the improvement was largely attributable to better Si interface properties rather than to the difference of the BiT film quality. By means of x-ray photoelectron spectroscopy and high-resolution transmission microscopy, the Si interfaces of the specimens with and without the SiON buffer layers were investigated. Consequently, we found that a postannealing treatment at 680 °C inevitably resulted in nonuniform growth of Si oxide layers at the Si interface of the specimen without the SiON buffer layer, and that the layer thickness mounted to approximately 10 nm. In contrast, 1–2-nm-thick SiON buffer layers terminated the growth of the additional oxide layer of less than about 3 nm, and the resulting Si oxide layers were quite uniform.

Electrical properties of ferroelectric Bi4Ti3O12 (BiT) films on Si(100) using a 1 nm thick silicon oxynitride (SiON) buffer were investigated. The capacitance–voltage (C–V) characteristics of Au/BiT/SiON/Si(100) exhibited hysteresis loops with a memory window of 2 V due to the ferroelectricity, and did not show large carrier injections. The effects of the SiON buffer were demonstrated in current–voltage characteristics. In the reverse bias region, a leakage current density of the specimen without the SiON buffer was much larger than that of the specimen with the buffer. Apart from these electrical measurements, anomalous features appeared in C–V characteristics of the illuminated specimen, which were likely to be due to the ac response of the optically generated electrons in some trap states at the interface.

We have obtained ferroelectric characteristics from nonoxide (ZnxCd1−x)S (x=0.1–0.3) thin films. On the basis of x-ray photoelectron and visible–ultraviolet light absorption spectroscopy measurements, the conduction-band discontinuity at the (ZnxCd1−x)S/Si(100) interfaces is found to vary between 0.4 and 1.3 eV with a change in composition x between 0.1 and 0.9. The leakage current density, which strongly depends on the conduction-band discontinuity, is reduced to less than 10−6 A/cm2 at a gate voltage of 4 V.

Spinel ferrite oxides doping non-magnetic ions show the photo-induced magnetization (PIM) effect at high temperature [1-3]. Such a magnetization enhancement by light irradiation is a unique property in this material. In order effectively to use the PIM effect and precisely to control the magnetism, direct light-emission from light-emitting element substrates would be a useful technique. In this study, spinel ferrite Al0.2Ru0.8Fe2O4 (ARFO) thin films, with the high temperature PIM effect, were prepared on GaAs(001) substrates by a pulsed laser deposition technique to aim integration with light-emitting devices based on GaAs lattice-matched materials in the future. Results showed that (001)-oriented ARFO thin films were successfully grown by using MgO buffer layers. The magnetic properties were approximately the same as ARFO films using other substrates such as Al2O3(0001) or MgO(001).

Aluminum oxide (AlOx) films were deposited by mist chemical vapor deposition (MCVD) in air for p-type crystalline silicon, and the effects of the deposition temperature (Tdep) and AlOx film thickness on the maximum surface recombination velocities (Smax) were evaluated. It was found that Smax was improved with increasing Tdep. The AlOx film deposited at 400 °C exhibited the best Smax value of 2.8 cm/s, and the passivation quality was comparable to that of AlOx deposited by other vacuum-based techniques. Smax was also improved with increasing film thickness. When the film thickness was above 10 nm, Smax was approximately 10 cm/s. From the Fourier transform infrared spectra, it was found that the AlOx films deposited by MCVD consisted of an AlOx layer and a Si-diffused AlOx layer. In addition, it is important for the layers to be thick enough to obtain high-quality passivation.

The authors fabricated 2 × 1 Sr-reconstructed Si(100) substrates using thin SrO layers, and used them to direct growth of crystalline perovskite oxide on Si. The SrO layers used to reconstruct the Si(100) substrates were grown by pulsed laser deposition from a SrO single crystal target, followed by postdeposition-annealing (PDA) of the SrO/Si(100) structure. In situ observations of reflective high-energy electron diffraction during PDA confirmed a 2 × 1 reconstruction of the Si surface and x-ray photoemission spectroscopy of the annealed samples confirmed the existence of Sr atoms in a silicate phase, which indicated that a 2 × 1 Sr-reconstructed Si surface was achieved. The optimal fabrication conditions were annealing at 720 °C for 1 min and an equivalent SrO layer thickness (MLeq) of 2.5 MLeq. The temperature condition was very narrow, at 720 ± 20 °C, for an acceptable product. Subsequently, the authors demonstrated the growth of crystalline SrTiO3 films on the 2 × 1 Sr-reconstructed Si(100) surfaces.

We have demonstrated the presence of ferroelectric properties in non-oxide (II-VI type semiconductor) ferroelectric thin films, such as (Zn,Cd)Te, (Zn,Cd)Se and (Zn,Cd)S (thickness: 3000–5000 Å). They have shown the ferroelectric hysteresis feature with memory windows of 0.2V, 0.3V and 0.8V, respectively. The materials design for getting the ferroelectric nature is as follows: when the size of the replaced atom is smaller than the host atom, then the substituent atoms can occupy off-centered positions, thus locally induce electric dipoles, thereby leading to ferroelectric behavior. These II-VI wide gap semiconducting ferroelectric films will open the door for new memory devices.

Eu doped rare-earth orthovanadates are known to be good red phosphor materials. In particular, LaVO{sub 4}:Eu is a promising candidate due to the low Eu-site point symmetry, and thus high dipole transition probability within Judd-Ofelt theory. However, the low solubility limit (< 3 mol %) of Eu in LaVO{sub 4} prevents its efficient use as a phosphor. We present optical evidence of enhanced Eu solubility as high as 10 mol % in LaVO{sub 4}:Eu thin films grown by pulsed laser deposition and postannealing. The photoluminescent intensity exceeded that of YVO{sub 4}:Eu thin films when excited below the host bandgap, indicating stronger direct emission of Eu in LaVO{sub 4}.

We demonstrated signal transmission using the nonlinearity of VO2 in the manner of stochastic resonance (SR). A correlated insulator state of VO2 changes nonlinearly to a metallic state when an applied bias voltage increases beyond a threshold. The transition of the states between insulator and metal is adaptable to the SR theory. In this study, the response to a weak pulse signal was optimized by a particular level of noise via SR. Numerical SR simulations suggests the existence of multiple threshold channels in the insulating state, spontaneously enhancing the reliability of signal transmission.

Room-temperature-photoinduced magnetization (PIM) was observed in spinel ferrite Al0.2Ru0.8Fe2O4 thin films with a spin-cluster-glass structure. Additionally, the films exhibited significant properties as spintronic materials, showing a low saturation magnetization under 0.6μB/unit cell and good conductivity with a high spin polarized electron level of over 75%. A combination of high-temperature PIM and the electronic properties associated with spintronics would generate an area of research and development that utilize the degrees of freedom offered by optical systems in the field of spintronics.

Surface segregation effects play an important role in the growth of traditional III-V semiconductor heterointerfaces. Here we show that segregation processes can also set an upper limit to the obtainable interface sharpness in perovskite oxide heterostructures. In particular, the structure of LaVO3∕SrTiO3 superlattices was studied on the atomic scale by electron microscopy and spectroscopy. The vanadate layers exhibit a growth asymmetry, with diffuse lower and atomically abrupt upper interfaces, caused by preferential Sr surface segregation. Switching the SrTiO3 termination layer does not change the interface abruptness, which excludes the interfacial polar discontinuity as the driving force for the observed growth asymmetry.

We characterized the electronic structure of LaVOx thin films by x-ray photoemission spectroscopy. We could distinguish the photoemission spectra among the x=3 phase (LaV3+O3), the x=4 phase (LaV5+O4), and the mixed phase regime. In the mixed phase, the surface was found to be mostly LaVO4. We could observe the evolution of the electronic structure in the growth phase diagram by systematically measuring core-level photoemission spectra. The V4+ component present in the x=3 phase may be due to charge transfer to avoid the polar catastrophe of the polar LaVO3 thin-film surface and/or to the oxidation of the surface.

We have studied the phase diagram of LaVOx films grown on (001) SrTiO3 substrates by pulsed laser deposition. With increasing oxygen partial pressure, the growth phase diagram varies between epitaxial perovskite LaV3+O3 single crystal films and polycrystalline monoclinic LaV5+O4. An interesting feature is the lack of an accessible phase corresponding to V4+, resulting in an extended region of phase coexistence of LaVO3 and LaVO4. Atomically flat LaVO3 could be grown in both layer-by-layer and step-flow growth modes, making this a promising candidate for incorporating strongly correlated electrons in atomic-scale perovskite heterostructures.

The in-plane dielectric and ferroelectric properties of c-axis oriented epitaxial strontium bismuth tantalate (SBT) thin films were investigated by interdigital surface electrode measurement. The four types of SBT thin films, which have various Sr∕Bi atomic ratios, were prepared on MgO substrates by pulsed laser deposition. The dielectric properties at kilohertz and megahertz frequencies were studied from 20to870K. Above room temperature, all the films show the phase transition. Sr0.99Bi1.61Ta2O9, Sr0.97Bi2.10Ta2O9, and Sr0.88Bi1.79Ta2O9 thin films show frequency dispersions near phase transition temperature. At low temperatures, dielectric and ferroelectric properties of Sr0.97Bi2.10Ta2O9 and Sr0.83Bi2.08Ta2O9 thin films were investigated. Both dielectric constant and remanent polarization show a tendency to decrease as temperature decreases, and the rapid change, which may indicate a phase transition, was observed in Sr0.97Bi2.10Ta2O9 near 80K.

Using pulsed-laser deposition, ferroelectric Bi4Ti3O12 (BiT) films were grown on Si(100) with and without an ultrathin buffer layer of silicon oxynitride (SiON), and the interface states were investigated using X-ray photoelectron spectroscopy. For both as-grown specimens, the additional oxidation of the interface Si was observed, and their thicknesses were almost identical. Due to the postannealing at 700°C in an oxygen ambient, on the other hand, a large difference in the Si oxidation was observed between the two specimens. The BiT films on Si(100) without the SiON buffer layer failed in preventing the significant development of the interfacial Si oxidation. On the contrary, it was clarified that the 1.3-nm-thick SiON buffer layers suppressed the additional oxidation to less than 3.5 nm.

A seriously fouled condenser of the Sakai-Port Power Station which started in 1965 has been renovated by in-situ artificial protective film (APF) coating of the condenser tubes. The condenser of the No.2 unit with a capacity of 250 MW has two-water boxes called "A" and "B" condensers installed with aluminum -brass tube. The gradual decrease in heat transfer performance of the condenser tubes has been revealed by inspections of removed tubes. Based on measurements carried out in October 1983 for evaluating in-situ APF coating, in march 1984 in-situ APF coating was applied to only A condenser being more heavily fouled than B condenser. The comparative measurement conducted in October 1984 proved that the condenser vacuum was improved by about 0.6 kPa. The removed APF coated tubes presented sound coated surfaces, except for some tiny blisters at both ends, and no indication of corrosion after six months duration. In-situ APF coating is concluded as being a good countermeasure against corrosion and fouling.