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Rocksalt‐structured (RS) MgZnO crystals are grown on quartz glass substrates by the mist chemical vapor deposition (mist CVD) method. Cathodoluminescence (CL) emission properties are comparatively studied with those for the RS‐MgZnO epitaxial film prepared on MgO substrate to explore their potential for vacuum ultraviolet (VUV) emitter. In the experiment, the newly developed VUV spectroscopy system is employed, where the CL and optical transmittance spectra are simultaneously measured. Growths of RS‐MgZnO on quartz glass substrate indicate formation of microcrystals (MCs). The MCs dominantly exhibit a near‐band‐edge VUV emission at 6.20 eV (200 nm) at 6 K and 6.07 eV (204 nm) at 300 K. Moreover, the MCs show a noticeable higher energy shoulder at 6.6 eV (188 nm) at 6 K and 6.4 eV (194 nm) at 300 K. The results ensure potential of RS‐MgZnO crystals for active element in VUV emitter regardless of the substrate material. [ABSTRACT FROM AUTHOR]

Abstract: We report the fabrication of rhombohedral corundum-structured indium oxide (α-In2O3) thin films, which can complete a semiconductor quaternary alloy system with α-Al2O3 and α-Ga2O3, on sapphire substrates with α-Fe2O3 buffer layers. X-ray diffraction showed the formation of α-In2O3, and the α-In2O3 film exhibited n-type semiconductor properties with electron concentration of 1.2×1018 cm−3 and electron mobility of 83cm2/Vs. The α-In2O3 took grain structure with the lateral sizes of 300–600nm, and in a grain area α-In2O3 grew epitaxially on a sapphire substrate. [Copyright &y& Elsevier]

Abstract: Transparent conducting polymer, poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) thin films were fabricated by a vapor-deposition technique, ultrasonic spray-assisted mist deposition method. The thickness was well controlled from 40 to 600nm, keeping reasonable conductivity of 300–450S/cm. The films with thickness less than 180nm have high (>80%) transmission over a wide (270–800nm) spectral region. In addition, formation of ring-dot electrode pattern with a hard-mask was demonstrated, achieving lithography-less patterning. The results encourage that this deposition method is developed as an actual process technology of transparent electrodes in devices. [Copyright &y& Elsevier]

Abstract: Dot array formation of zinc oxide (ZnO) along the linear single steps was demonstrated on sapphire substrates under near atmosphere pressure by metalorganic chemical vapor deposition (MOCVD). Sapphire substrates of , (0001) and planes (A-plane, C-plane and R-plane, respectively) were employed as templates for manufacturing the nanostructures. For highly controlling dot array formation the substrates were prepared by annealing at 1000°C for 3h in air after chemical treatment. The step arrays were easily prepared on C-plane and R-plane sapphire. The linearly aligned ZnO nanodot arrays were formed on R-plane sapphire along the step edges over several ten micrometers. The result can be attributed to the smaller number of dangling bonds on R-plane than on A-plane and C-plane, enhancing the surface diffusion length. Sapphire can be a good template for manipulating II–VI semiconductor on it to form nanostructures even at near atmosphere pressure by a conventional MOCVD. [Copyright &y& Elsevier]

Temperature dependencies of optical reflectance and cathodoluminescence (CL) spectra were measured for the MgO single crystal using a custom-built vacuum ultraviolet (VUV) spectroscopic system. Simultaneous observation enabled us to identify free exciton (FE) and bound exciton (BE) emissions by comparing the CL emission with the exciton resonance structures. The results indicated that the BE emission dominates the near-band edge emission, and the FE emission was observed as a shoulder at 300 K. The results ensure strong excitonic nature and potential of a rock salt-structured MgO-based material system for an active element in the VUV light emitter. [ABSTRACT FROM AUTHOR]

Deep traps in n‐type α‐Ga2O3 grown by mist chemical vapor deposition are analyzed by the photocapacitance method and deep‐level optical spectroscopy. The trap levels at Ec−(≈2.0 eV) (E1), Ec−(≈2.5 eV) (E2), and Ec−(≈3.2 eV) (E3) are evident and their concentrations are 3.5 × 1014, 3.6 × 1014, and 6.2 × 1015 cm−3, respectively, which are much lower than ever reported for α‐Ga2O3. The Frank–Condon shift of all three traps is large as seen for β‐Ga2O3, indicating a high degree of lattice coupling in the midgap state in α‐Ga2O3. [ABSTRACT FROM AUTHOR]

Ultra-wide bandgap p-type α-(Ir,Ga)2O3 films with bandgaps of up to 4.3 eV have been obtained by unintentional doping or Mg doping. For Mg-doped films, Hall-effect measurements revealed a hole concentration of 9.9 × 1018 to 8.1 × 1019 cm−3 and a mobility of 0.13 − 0.92 cm2/V s, respectively. A preliminary test of a pn junction diode composed of p-type α-(Ir,Ga)2O3 and n-type α-Ga2O3 did not show catastrophic breakdown in the reverse direction until 100 V and the current on/off ratio at +3 V/−3V was 5 × 105. Since α-(Ir,Ga)2O3 and α-Ga2O3 take the same crystal structure and are well lattice-matched (with a lattice mismatch of <0.3%), the formation of a high-quality pn heterojunction is encouraged; this is one of the advantages of the corundum material system. [ABSTRACT FROM AUTHOR]

Highly crystalline corundum structured α-(Ga0.42Fe0.58)2O3 alloy thin film showed magnetic properties at room temperature. Microstructure analysis of cross-sectional transmission electron microscope (TEM) observation and TEM energy dispersive X-ray spectroscopy measurement indicated that different crystal phase could not be detected as well as there is no remarkable phase separating area, that is, Fe and Ga ions are distributed uniformly in the film. Magnetic measurements were performed on α-(Ga1-xFex)2O3 (x = 0.24, 0.44, 0.58, 1.00) alloy thin films at 110 K. The induced magnetic moment per a Fe ion of α-(Ga0.42Fe0.58)2O3 at 5000 Oe is about 6 times larger than α-Fe2O3 thin film. Compared to the α-Fe2O3 thin films, the value of coercivity is also about 6 times in α-(Ga0.42Fe0.58)2O3, in contrast, there is no significant difference in value of coercivity of α-(Ga1-xFex)2O3 (x = 0.24, 0.44, 1.00) thin films. These means that the origin of magnetism is not the separation region of α-Fe2O3 in α-(Ga0.42Fe0.58)2O3 thin film. [ABSTRACT FROM AUTHOR]

Corundum-structured iridium oxide (α-Ir2O3), showing p-type conductivity, is a strong candidate to form high-quality pn heterojunctions with α-Ga2O3. We fabricated α-Ir2O3/α-Ga2O3 pn heterojunction diodes and they showed well-defined rectifying current-voltage (I-V) characteristics with the turn-on voltage of about 2.0 V. The band alignment at the α-Ir2O3/α-Ga2O3 interface was investigated by X-ray photoemission spectroscopy, revealing a staggered-gap (type-II) with the valence- and conduction-band offsets of 3.34 eV and 1.04 eV, respectively. The total barrier height for electrons was about 2.4 eV, which reasonably agreed with the turn-on voltage in the I-V characteristics. This means that electrons are mainly attributed to electrical conduction around the turn-on voltage. [ABSTRACT FROM AUTHOR]

An annealed α‐(Al0.4Ga0.6)2O3 buffer layer is introduced to achieve either α‐Ga2O3 or ϵ‐Ga2O3 growth on sapphire substrates, depending on the growth temperature, using the mist chemical vapor deposition method. Transmission electron microscopy reveals that the epitaxial relationship between ϵ‐Ga2O3 and the α‐(Al0.4Ga0.6)2O3 buffer layer is ϵ‐Ga2O3 [10 1 ¯0] || α‐(Al0.4Ga0.6)2O3 [11 2 ¯0], and the two hexagonal lattices are consequently rotated in the ab plane by 30° with respect to each other. The lattice mismatch between the buffer layer and ϵ‐Ga2O3 is 1.2%, while that between the buffer layer and α‐Ga2O3 is 2.2%. When the growth temperature is below 600 °C, ϵ‐Ga2O3, which had the smaller lattice mismatch, is produced. On the other hand, higher temperature leads to a longer diffusion length, and atoms reach the step edges. Therefore α‐Ga2O3, which has the same structure as the buffer layer, is grown along the step edges above 600 °C. As a result, ϵ‐Ga2O3 and α‐Ga2O3 grow below and above 600 °C, respectively. [ABSTRACT FROM AUTHOR]

We report on the growth of very high-quality Al-doped n-type ZnO epilayers on sapphire substrates using a radio-frequency (rf) magnetron sputtering technique combined with a rapid-thermal annealing. Photoluminescence (PL) and Hall measurements show that both the optical and electrical properties of the ZnO layers are significantly improved with an increasing annealing temperature up to 900 °C. For example, the samples that are grown at 600 °C and a rf power of 100 W with an Ar/O2 gas ratio of 1 give an electron concentration of 1.83×1020 cm3 and a mobility of 65.6 cm2/V s, when annealed at 900 °C for 3 min in a nitrogen ambient. Furthermore, x-ray diffraction measurements show that both the as-grown and annealed samples are of excellent crystallinity. [ABSTRACT FROM AUTHOR]

We analyze the surface structure of an α-Fe 2 O 3 (0001) film grown on a c-plane sapphire substrate by mist chemical vapor deposition (CVD), which has been recently developed as a simple, safe, and cost-effective film growth method. Using coaxial impact-collision ion scattering spectroscopy, we found that the atomic-layer sequence of the surface termination of an α-Fe 2 O 3 (0001) film grown by mist CVD was Fe–O 3 –Fe– from the top layer. This surface termination is predicted to form in an oxygen-poor environment by density functional theory combined with a thermodynamical approach despite that the mist CVD process is performed with atmospheric-pressure air. The surface structure markedly changes after annealing above 600 °C in ultrahigh vacuum. We found that only a couple of layers from the top layer transform into Fe 3 O 4 (111) after 650 °C annealing, which would be so-called biphase reconstruction. Complete transformation into a Fe 3 O 4 (111) film occurs at 700 °C, whose atomic-layer sequence is determined to be Fe–O 4 –Fe 3 – from the top layer. [ABSTRACT FROM AUTHOR]

We report improved growth conditions for corundum-structured α-(Al x Ga 1− x ) 2 O 3 , followed by the growth characteristics of α-(Al x Ga 1− x ) 2 O 3 /Ga 2 O 3 heterostructures with the use of mist chemical vapor deposition (CVD) technology. Higher growth temperatures, 700–800 °C, were effective for better crystalline quality especially for higher Al composition x . Coherent growth of α-(Al x Ga 1− x ) 2 O 3 was achieved for x =0.03 and 0.11 with the film thickness of about 100 nm. The type-I band lineup was expected for the heterostructure. [ABSTRACT FROM AUTHOR]

(-201)-oriented beta gallium oxide (β-Ga2O3) thin films were grown on yttrium-stabilized zirconia (YSZ) substrates using a mist chemical vapor deposition (CVD) method. The lowest full-width at half maximum value in ω-scan X-ray diffraction was 0.50°, obtained for the growth temperature of 650 °C on a YSZ(100) substrate. Observation by a secondary electron microscope (SEM) revealed flat surface including large-scale precipitates. Electron diffraction patterns suggested that thin films basically possess β-type crystal structure though crystal precipitates were formed by poly-crystal. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Abstract: The structural and optical properties of ZnO thin films deposited at various oxygen partial pressure and rf-power of rf magnetron sputtering were investigated. The sputtered ZnO films are mainly formed with the oxygen which was supplied from a sputtering gas; therefore the film stoichiometry can be controlled by the oxygen partial pressure and rf-power. From photoluminescence study, it was found that the wide emission band above 550nm was observed due to an increase of oxygen vacancies when the ZnO film changed from O-rich to Zn-rich. The chemical stoichiometry of the film will help us to understand the formation mechanism of intrinsic defects in ZnO films. [Copyright &y& Elsevier]

Trap densities in the channel layers Dt of ZnO thin-film transistors have been extracted. First, the low-frequency (low-f) capacitance–voltage C–V characteristics are measured using the customized measurement system. Next, the surface potential is calculated from the low-f C–V characteristic, and the surface potential gradient is calculated by applying Gauss's law. Finally, the spatial profile of the electric potential is calculated by applying Poisson equation and carrier density equations, and Dt is extracted. It is found that, generally, the deep states are flatly distributed in the energy gap apart from the conduction band, and the shallow states seem to be the tail states. Moreover, the dependence on the oxygen partial pressure during the sputtering of ZnO films [p(\O2)] has been analyzed. It is found that for p(\O2) = \0.50 \sim \0.75\ \Pa, Dt changes little, whereas for p(O2) = \0.17 \sim \0.33\ \Pa, Dt increases. It is clarified that the abnormal shapes of the current–voltage and low-f C–V characteristics originate from the increase of Dt. [ABSTRACT FROM PUBLISHER]

Abstract: Ultrasonic spray-assisted metalorganic vapor phase epitaxy (MOVPE), where the ultrasonically sprayed liquid source solution is used as the precursor of the vapor phase reaction, has been developed to grow single-crystalline ZnO and ZnMgO thin films on sapphire substrates. By applying RF sputtering-deposited ZnO buffer layers of 10–80nm in thickness, the mobility reached 58–66cm2/Vs with the electron concentration of (4–9)×1017 cm−3 at the growth temperatures of 800–900°C. The temperature dependence of mobility revealed that at room temperature the lattice scattering competed with the ionized impurity scattering, suggesting that the remarkable increase of the mobility is expected by reducing the residual impurities with purified sources. The results suggest the promising potential of the present growth method, with using safe and inexpensive source materials, as one of the MOVPE technologies contributing to mass production. On the other hand, the surface morphology and electrical properties were markedly degraded in ZnMgO, and these problems are still found to be difficult to be resolved. [Copyright &y& Elsevier]

Abstract: The surface of β-Ga2O3 (100) single crystal grown with floating zone method was treated by chemical–mechanical-polishing (CMP) for 30–120min followed by annealing in oxygen atmosphere at temperature 600–1100°C for 3–6h. The evolution of the step arrangement was investigated with reflection high energy electron diffraction and atomic force microscopy. Atomically smooth surfaces with atomic step and terrace structure of β-Ga2O3 substrates were successfully obtained after just CMP treatment as well as CMP treatment and post annealing at 1100°C for 3h. The uniform step height was 0.57nm, and smooth terrace width was 100nm, where the misorientation angle was about 0.36°. The obtained atomically smooth surface provides a potential application for the high-quality epitaxial film growth. [Copyright &y& Elsevier]

Abstract: β-Ga2O3 thin films were grown on (100)-oriented β-Ga2O3 single crystal substrates by plasma-assisted molecular beam epitaxy. At the growth temperature over 800 °C and the Ga beam equivalent pressure of 1.1×10−7 Torr, the grown surfaces exhibited clear step and terrace structures and the root-mean-square roughness of 0.5 nm in atomic force microscopy. The successful step-flow growth is indebted to the strong cleavableness of (100) planes of β-Ga2O3. The off-axis direction, determined by the initial substrate polishing stage, significantly influences on the surface morphology, and it should be along [001] or [00-1] directions in order for smooth surfaces. [Copyright &y& Elsevier]

Selective formation of ZnO nanodots grown by metalorganic chemical vapor deposition (MOCVD) was achieved on focused-ion beam (FIB)-nanopatterned SiO2 and Si substrates. The selective formation characteristics, dimension, and density of ZnO nanodots on FIB-nanopatterned substrates strongly depended on the FIB-patterning and MOCVD-growth conditions. The mechanism of the selective formation of ZnO nanodots on FIB-nanopatterned SiO2 substrates is attributed to a surfactant effect of the implanted Ga which leads to the formation of the preferred nucleation sites for the growth of ZnO nanodots, while that of ZnO nanodots on nanopatterned Si substrates is mainly considered in terms of the generation of surface atomic steps and kinks, which are created by Ga+ ion sputtering, on the patterned Si areas. [Copyright &y& Elsevier]

The optical and structural properties of textured ZnCdO films that exibit a newly found distinct blue luminescence have been investigated. Microscopic compositional fluctuations of Cd, associated with hexagonal grain structures, were observed. Models for the blue-luminescence process are proposed. [Copyright &y& Elsevier]

The article focuses on the chemistry of expanded porphyrins that have pyrrolic subunits with more than four porphyrins. This new class of macrocycles has the ability to chelate two or more metal ions with the aid of large and flexible ligands. Examples of such macrocycles include the metalation of amethyrin and doubly N-confused hexaphyrin. Furthermore, this article describes the thermal splitting of bis-Cu(II) complex of octaphyrin into two Cu(II) porphyrins. To conclude, further studies are required for the novel activities and potentials of such macrocycles.

ZnO nanotips and nanorods were grown on screen-printed multi-walled carbon nanotube (MWCNT) films via thermal chemical vapor deposition at relative low growth temperatures of 400 and 500 °C. Uniform formation of ZnO nanotips and nanorods occurred on MWCNT-printed Si substrates, but were rarely observed on bare Si substrates at the same growth temperatures. In photoluminescence (PL) measurements, it was found that ZnO nanorods exhibit typical intrinsic optical properties, while ZnO nanotips revealed p-type like luminescence behavior. Acceptor-related emission bands originating from neutral acceptor-bound exciton, free-to-acceptor and donor-acceptor pair transitions are clearly observed in temperature-dependent PL spectra of ZnO nanotips.

[reaction: see text] Two derivatives of ethylenedioxy-substituted terthiophene-fullerene dyads were newly synthesized as the precursors for polythiophene having fullerene side chains. By electrolytic oxidation of dyad 1, the charm-bracelet type polythiophene, poly-1, was obtained as a purple film, which showed electrochemical activity, electrochromism, and photoelectronic response.