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The effect of nanoscale Ag film thickness on the electrical and optical properties in transparent conducting oxide films consisting of an IZTO/Ag/IZTO multilayer were investigated. The homoge- neous morphologies of the Ag films sandwiched between the IZTO films affected the optical and electrical properties of the IZTO/Ag/IZTO multilayer films. The transmittance and resistivity of the IZTO/Ag/IZTO multilayer films decreased with increasing Ag film thickness. The resistivities of the IZTO/Ag/IZTO multilayer films grown on glass substrates were decreased by using an Ag thin inter- layer in comparison with that of the IZTO single layer.

Thin film transistors (TFTs) with indium–zinc tin-oxide (IZTO) dual-channel layers were fabricated on heavily-doped p-type Si substrates by using a tilted dual-target radio-frequency magnetron sputtering system. The number of oxygen vacancies in the IZTO channel layer decreased with increasing oxygen partial pressure, resulting in a decrease in the conductivity. The threshold voltage ( V th ) shifted toward positive gate-source voltage with increasing oxygen partial pressure for the growth of the IZTO layer because of a decrease in the carrier concentration. The V th , the mobility, the on/off-current ratio, and the subthreshold swing of the dual-channel IZTO TFTs were 3.5 V, 7.1 cm 2 /V s, 1.3 V/decade, and 8.2 × 10 6 , respectively, which was enhanced by utilizing dual-channel layers consisting of a top channel deposited at a high oxygen partial pressure and a bottom channel deposited at a low oxygen partial pressure.

ZnO nanostructures were formed on Al-doped ZnO (AZO)/Ag/AZO-multilayer-film-coated flexible polyethersulfone (PES) substrates at low temperature by using an electrochemical deposition method. The resistivity of the AZO/Ag/AZO multilayer films decreased with increasing thickness of the Ag film. X-ray diffraction patterns for the ZnO nanostructures showed that the crystal structure of the ZnO was hexagonal wurtzite and that the orientation was along the c-axis perpendicular to the substrate. Scanning electron microscopy images showed that the ZnO nanostructures grown at current densities of −1.0 and −1.5 mA/cm2 were ZnO nanorods with diameters of 150 nm and ZnO nanoflowers with a planar dimension, respectively. Photoluminescence spectra showed that the band-edge emission peak of the ZnO nanostructures dominantly appeared in the ultraviolet region. These results showed that ZnO nanorods and nanoflowers with high quality were synthesized on AZO/Ag/AZO-multilayer-film-coated PES substrates.

Effects of Ag film thickness on the optical and the electrical properties in CuAlO 2 /Ag/CuAlO 2 multilayer films grown on glass substrates were investigated. Atomic force microscopy images showed that Ag films with a thickness of a few nanometers had island structures. X-ray diffraction patterns showed that the phase of the CuAlO 2 layer was amorphous. The resistivity of the 40 nm-CuAlO 2 /18 nm-Ag/40 nm-CuAlO 2 multilayer films was 2.8 × 10 −5 Ω cm, and the transmittance of the multilayer films with an Ag film thickness of 8 nm was approximately 89.16%. These results indicate that CuAlO 2 /Ag/CuAlO 2 multilayer films grown on glass substrates hold promise for potential applications as transparent conducting electrodes in high-efficiency solar cells.

ZnO nanoparticles embedded in a Si3N4 layer by using spin-coating and thermal treatment were fabricated to investigate the feasible applications in charge trapping regions of the metal/oxide/nitride/oxide/p-Si memory devices. The magnitude of the flatband voltage shift of the capacitance-voltage (C-V) curve for the Al/SiO2/ZnO nanoparticles embedded in Si3N4 layer/SiO2/p-Si memory device was larger than that of Al/ZnO nanoparticles embedded in SiO2 layer/p-Si and Al/SiO2/Si3N4/SiO2/p-Si devices. The increase in the flatband voltage shift of the C-V curve for the Al/SiO2/ZnO nanoparticles embedded in Si3N4 layer/SiO2/p-Si memory device in comparison with other devices was attributed to the existence of the ZnO nanoparticles or the interface trap states between the ZnO nanoparticles and the Si3N4 layer resulting from existence of ZnO nanoparticles embedded in the Si3N4 layer.

We have investigated the characteristics of flexible indium zinc oxide (IZO) electrode grown on polyethylene terephthalate (PET) substrates using a specially designed roll-to-roll (RTR) sputtering system for use in flexible optoelectronics It was found that both electrical and optical properties of the flexible IZO electrode were critically dependent on the DC power and Ar/O(2) flow ratio during the roll-to-roll sputtering process At optimized conditions (constant working pressure of 3 mTorr.Ar/O(2) flow ratio of Ar at only 30 sccm, DC power 800 W and rolling speed at 0 1 cm/s) the flexible IZO electrode exhibits a sheet resistance of 17 25 Omega/sq and an optical transmittance of 89 45% at 550 nm wavelength. Due to the low PET substrate temperature, which is effectively maintained by cooling drum system, all IZO electrodes showed an amorphous structure regardless of the DC power and Ar/O(2) flow ratio Furthermore. the IZO electrodes grown at optimized condition exhibited superior flexibility than the conventional amorphous ITO electrodes due to its stable amorphous structure This indicates that the RTR sputter grown IZO electrode is a promising flexible electrode that can substitute for the conventional ITO electrode, due to its low resistance, high transparency, superior flexibility and fast preparation by the RTR process. (C) 2009 Elsevier B.V All rights reserved

We have investigated the electrical, optical, structural, and annealing properties of indium zinc tin oxide (IZTO) films prepared by an unbalanced radio frequency (RF) magnetron sputtering at room temperature, in a pure Ar ambient environment. It was found that the electrical and optical properties of unbalanced RF sputter grown IZTO films at room temperature were influenced by RF power and working pressure. At optimized growth condition, we could obtain the IZTO film with the low resistivity of 3.77 × 10− 4 Ω cm, high transparency of ~ 87% and figure of merit value of 21.2 × 10− 3Ω− 1, without the post annealing process, even though it was completely an amorphous structure due to low substrate temperature. In addition, the field emission scanning electron microscope analysis results showed that all IZTO films are amorphous structures with very smooth surfaces regardless of the RF power and working pressure. However, the rapid thermal annealing process above the temperature of 400 °C lead to an abrupt increase in resistivity and sheet resistance due to the transition of film structure from amorphous to crystalline, which was confirmed by X-ray diffraction examination.

Optoelectronic materials compatible with silicon substrates are important from the viewpoint of practical applications for silicon photonics. ZnO nanocrystals were fabricated directly on Si substrates by tuning both of the composition and postannealing conditions of ZnSiOx composite films deposited by sputtering Si and ZnO targets simultaneously. The high-resolution TEM analysis showed that ZnSiOx nanocomposite film containing ZnO nanocrystals could be obtained by postannealing the ZnSiOx film with Zn/Si ratio = ∼1.6 at 700 °C. In this film, ZnO nanocrystals with a size of ∼5 nm, which could be identified as ZnO from electron diffraction pattern, were densely distributed in the amorphous matrix. This film exhibited a stronger and broader cathodoluminescence emission ranging from 350 nm to 550 nm compared to that of ZnO film fabricated with the same deposition conditions. These results lead to a practical application of ZnO nanocrystals to optoelectronic devices using Si substrates. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Dependence of the stored charges and the tunneling voltages on the tunneling SiO2 thickness for Si nanoparticles embedded in a SiO2 layer formed by the sonochemical method was investigated by using electrostatic force microscopy (EFM) measurements. Bright-field transmission electron microscopy images showed that Si nanoparticles were embedded in a SiO2 layer. EFM images for the Si nanoparticles embedded in a SiO2 layer under applied bias voltages showed that the localized charges remained in the Si nanoparticles embedded in a SiO2 layer. The stored charge in the Si nanoparticles embedded in a SiO2 layer increased with a decrease in the tunneling SiO2 thickness. While the threshold tunneling voltage increased with an increase in the tunneling oxide thickness, the mean amplitude of the tunneling voltage increased with a decrease in the thickness of the tunneling SiO2 layer.

Recently, evidence was presented that certain single-walled carbon nanotubes (SWNTs) possess helical defective traces, exhibiting distinct cleaved lines, yet their mechanical characterization remains a challenge. On the basis of the spiral growth model of SWNTs, here we present atomic details of helical defects and investigate how the tensile behaviors of SWNTs change with their presence using molecular dynamics simulations. SWNTs have exhibited substantially lower tensile strength and strain than theoretical results obtained from a seamless tubular structure, whose physical origin cannot be explained either by any known SWNT defects so far. We find that this long-lasting puzzle could be explained by assuming helical defects in SWNTs, exhibiting excellent agreement with experimental observation. The mechanism of this tensile process is elucidated by analyzing atomic stress distribution and evolution and the effects of the chirality and diameter of SWNTs on this phenomenon are examined based on linear elastic fracture mechanics. This work contributes significantly to our understanding of the growth mechanism, defect hierarchies and mechanical properties of SWNTs.

Capacitance–voltage ( C – V ) and electrostatic force microscopy (EFM) measurements on Si nanocrystals (Si-NCs) formed by using the sonochemical method were carried out to investigate the charging effects of the Si-NCs. Transmission electron microscopy images and atomic force microscopy images showed that the Si-NCs were created inside the SiO 2 layer. The C – V curve and the EFM image showed that the Si-NCs embedded in the SiO 2 layer experienced charging effects. The macroscopic surface charge density determined from the C – V curve was in reasonable agreement with the microscopic local value obtained from the EFM image. The present results indicate that the EFM technique might provide a promising method for investigating charging effects in various kinds of nanocrystals embedded in the insulating layer.

The effects of hydrogenation and aging on the optical properties in porous Si (PS) layers were investigated by using photoluminescence (PL) measurements. When the hydrogenated PS layers were aged in air, the intensity of the PL spectrum increased. The emission peak for the hydrogenated PS layers shifted to higher energy with decreasing H2/N2 ratio. The relation of the dehydrogenized states in the as-formed PS surface to the quantum states of Si nanoparticles with relatively small sizes is discussed. These results indicate that the optical properties of PS layers are significantly affected by hydrogenation and aging.

The characteristics of an SiN x passivation layer grown by a specially designed inductively coupled plasma chemical vapor deposition (ICP-CVD) system with straight antennas for the top-emitting organic light emitting diodes (TOLEDs) are investigated. Using a high-density plasma on the order of ∼ 10 11 electrons/cm 3 formed by nine straight antennas connected in parallel, a high-density SiN x passivation layer was deposited on a transparent Mg–Ag cathode at a substrate temperature of 40 °C. Even at a low substrate temperature, single SiN x passivation layer prepared by ICP-CVD showed a low water vapor transmission rate of 5 × 10 − 2 g/m 2 /day and a transparency of ∼ 85% respectively. In addition, current–voltage–luminescence results of the TOLED passivated by the SiN x layer indicated that the electrical and optical properties of the TOLED were not affected by the high-density plasma during the SiN x deposition process.

LiCoO2 thin films, which could be used as a cathode material in microbatteries, have been deposited by radio-frequency (rf) magnetron sputtering with various substrate biases as process parameter. The substrate bias during deposition has influenced the electrochemical properties of thin film electrode, and it could be found by charge–discharge test and cyclic voltammogram. We could obtain LiCoO2 thin film cathodes, which can be used directly, without annealing, for the complete thin film battery. The variations of electrochemical properties with substrate bias are related to micro-structural changes due to the ion bombardment, which delivers energy to the growing film. The bias sputtering of LiCoO2 is suggested as the promising method to fabricate thin film microbatteries.

The effect of In x Ga 1− x As ( x = 0.1 , 0.2) asymmetric strain release layers (ASRLs) on the microstructural and the interband transition properties of InAs/GaAs quantum dots (QDs) grown by using molecular beam epitaxy (MBE) and atomic layer epitaxy was investigated by using high-resolution transmission electron microscopy (HRTEM) and photoluminescence (PL) measurements. When the thickness of the ASRL covering the QDs was increased in the range between 0 and 5 nm, the PL peak corresponding to the interband transitions shifted to longer wavelengths due to strain relaxation. However, when the thickness of the ASRL was increased above approximately 7 nm, the peak shifted to shorter wavelengths due to the local interdiffusion of In and Ga atoms between the In x Ga 1− x As capping layer and the InAs QDs as a result of the localized strains in the In x Ga 1− x As capping layer and the InAs QDs. These results provide important information on the tunable feasibility of the interband transitions in the InAs/GaAs QDs utilizing the In x Ga 1− x As capping layer.

Structural and optical properties of In 0.5 Ga 0.5 As/GaAs quantum dots (QDs) grown at 510°C by atomic layer molecular beam epitaxy technique are studied as a function of n repeated deposition of 1-ML-thick InAs and 1-ML-thick GaAs. Cross-sectional images reveal that the QDs are formed by single large QDs rather than closely stacked InAs QDs and their shape is trapezoidal. In the image, existence of wetting layers is not clear. In 300 K-photoluminescence (PL) spectra of InGaAs QDs (n = 5), 4 peaks are resolved. Origin of each peak transition is discussed. Finally, it was found that the PL linewidths of atomic layer epitaxy (ALE) QDs were weakly sensitive to cryostat temperatures (16-300 K). This is attributed to the nature of ALE QDs; higher uniformity and weaker wetting effect compared to SK QDs.

Silicon nanocrystals in a range from 2 nm to 5 nm were prepared from Zintl salt, soldium silicide (NaSi) by sonochemical method. This synthesis permits that the reaction be completed in only a few hours and the easy alkyl-modification of nanocrystals surface at room temperature and ambient pressure. The average size of nanocrystals measured by the dynamic light scattering analysis was 2.7 nm. The high-resolution transmission electron micrograph confirmed the material identity of nanocrystals as crystalline silicon. FT-IR spectra are consistent with the surface states of nanocrystals that are chlorine-or butyl-capped. The emission peak center moved to a longer wavelength (up to 430 nm) with the reaction time, under a 325 nm excitation.

We exploited the practical sonochemical route for preparing silicon nanocrystals at room temperature and ambient pressure. This synthesis provided the very fast reaction within a few hours and the useful modification for the surface of silicon nanoparticles. The average size of prepared nanocrystals was 2.8 nm and confirmed by TEM images. The chlorine-capped nanoparticles were characterized by FT-IR spectroscopy. The luminescence of silicon colloid was observed in the wide range between 340 nm and near 700 nm and showed white color with commercial low-intensity UV-lamp exposure. This synthetic strategy is potentially applicable for illuminating devices such as white light emitting diodes.

The annealing effect on the surface and the microstructural properties of ZnO thin films grown on p-Si (1 0 0) substrates by radio-frequency magnetron sputtering have been investigated using atomic force microscopy (AFM), X-ray diffraction (XRD), and transmission electron microscopy (TEM) measurements. The AFM images and the XRD patterns showed that the crystallinity of the annealed ZnO films was enhanced by annealing in comparison with that of the as-grown ZnO films, and XRD patterns, pole figures, and TEM images showed that the as-grown and the annealed ZnO films grown on Si (1 0 0) substrates had a c-axis preferential orientation in the [0 0 0 1] crystal direction. These results indicate that the surface and the microstructural qualities of the ZnO films grown on p-Si (1 0 0) substrates are improved by thermal treatment.

Impurity free vacancy disordering (IFVD) of InGaAs self-assembled quantum dots (SAQDs) grown by metal organic chemical vapor deposition (MOCVD) method has been carried out at 700�°C for the time range from 1 min to 4 min by using SiO2 and SiNx–SiO2 dielectric capping layers. The photoluminescence (PL) peak was blue shifted up to 157 meV and its full width at half maximum (FWHM) was narrowed from 76 meV to 47 meV as the annealing time increased. The integrated PL intensity was increased after the thermal annealing, which may be attributed to a defect quenching. There was an optimum annealing condition to get the largest integrated PL intensity for each dielectric capping. SiNx–SiO2 double capping layers have been found to induce larger integrated PL intensity and better carrier confinement after the thermal annealing of SAQDs compared to SiO2 single capping layer, even though SiNx–SiO2 double capping induced larger blue-shift than SiO2 single capping.

ZrO2:Er thin films for active waveguide applications were fabricated by the metal-organic chemical vapor deposition (MOCVD) method. X-ray diffraction demonstrated that there is a rapid change of preferred orientation, from (001) to (100), in samples of which the Er contents are 2.39 mol% and 10.41 mol%, respectively. The observed phase change from monoclinic to tetragonal was attributed to the c/a ratio reduction with Er ion incorporation into the ZrO2 matrix. A considerable increase in oxygen deficiency leads to the phase change, as revealed by X-ray photoelectron spectroscopy (XPS). The near-infrared photoluminescence of 4I13/2 → 4I15/2 transition was investigated and the quenching concentration for the luminescence was found to be 2.39 mol%. It was proposed that the oxygen deficiency observed at 10.41 mol% Er concentration is mainly responsible for the quenching phenomenon.

Theoretical modeling and fabrication of polarization-insensitive semiconductor optical amplifiers that use a multi-quantum-well structure as the gain media are reported. Polarization insensitivity of gain is achieved through the introduction tensile strain into the quantum wells. Gain calculations, using the k/spl middot/p method, were performed to obtain the required amount of tensile strain to obtain polarization insensitivity over a wide energy spectrum. Fabricated amplifiers show a polarization-insensitive (

Composite polymer electrolyte membranes were fabricated by depositing Pd films on the surface of Nafion™ membranes by sputtering, and the modified membranes were investigated for their morphologies, methanol permeabilities, protonic conductivities and performances for direct methanol fuel cells (DMFCs). The Pd film acted as a barrier to methanol crossover, but at the same time it also reduced proton conductivity. Though both the methanol permeability and the protonic conductivity through the modified membranes decreased with increasing Pd thickness, the cell performances were almost independent of the Pd thickness. The effects of methanol concentration on the protonic conductivity and the cell performance were also investigated. And, the role of Pd films in DMFCs is discussed in some detail.

AB2-type alloy, a kind of hydrogen storage alloys used as an anode of Ni-MH batteries, has a large discharge capacity but still has several problems such as initial activation, cycle life and self-discharge. In this study, we have investigated the effects of Cr addition and fluorination after La addition on AB2-type alloy with Zr0.7Ti0.3V0.4Mn0.4Ni1.2 composition. The EPMA and SEM surface analysis techniques were used and the crystal structure was characterized by XRD analysis. Metal hydride negative was characterized by galvanostatic cycling test, electrochemical impedance spectroscopy and potentiodynamic polarization. Cr-addition is found to be effective to improve cycle life and self-discharge characteristics but ineffective to promote initial activation due to the formation of stable oxide film on alloy surface. Highly reactive particles have been formed by fluorination after La-addition to the alloys and those particles may remarkably improve the initial activation of MH-negative electrodes.

The results of investigating $SiL_{2,3}$ / X-ray emission valence spectra of amorphous silicon films irradiated by excimer laser are presented. It is found that laser annealing leads to crystallization of amorphous silicon films and the crystallinity increases with the laser energy density from 250 to 400 mJ/ $\textrm{cm}^2$ . The vertical structure of the film is investigated by changing the accelerating voltage on the X-ray tube, and the chemical and structural state of Si $_3$ N $_4$ buffer layer is found not to be changed by the excimer laser treatment.

Thin films of pure SnO2, of the Sn/Li2O layered structure, and of Sn/Li2O were fabricated by sputtering method, while a `lithium-reacted tin oxide thin film' was assembled by the evaporation of lithium metal onto a SnO2 thin film. Film structure and charge/discharge characteristics were compared. The lithium-reacted tin oxide thin film, the Sn/Li2O layered structure, and the Sn/Li2O co-sputtered thin films did not show any irreversible side reactions of forming Li2O and metallic Sn near 0.8 V vs Li/Li+. The initial charge retention of the Sn/Li2O layered structure and Sn/Li2O co-sputtered thin films was about 50% and a similar value was found for the lithium-reacted tin oxide thin film (more than 60%). Sn/Li2O layered structure and Sn/Li2O co-sputtered thin films showed better cycling behavior over 500 cycles than the pure SnO2 and lithium-reacted tin oxide thin film in the cut-off range from 1.2 to 0 V vs Li/Li+. Keywords: Lithium batteries, Anode, Layered structure, Co-sputtering, Tin oxide, Lithium oxide

The effect of fluorination on the surface of an AB 2 -type hydrogen-storage alloy with the composition Zr 0.7 Ti 0.3 V 0.4 Mn 0.4 Ni 1.2 is investigated. Electron probe microanalysis (EPMA), scanning electron microscopy (SEM), Auger electron spectroscopy (AES), and X-ray diffraction (XRD) techniques show that the fluorinated AB 2 -type alloys have a unique surface morphology and high reactivity with a protective film. The treatment is found to be effective when lanthanum is incorporated in the alloy. The cycle-life of the metal hydride (MH) electrode increases significantly as a result of a decrease in the overpotential by electrode polarization. The degradation rate of the MH electrode is less than 3% after 100 cycles when lanthanum is added at 1–3 wt.%.

Transmission electron microscopy images of annealed ZnO/silicon nitride (SiN x ) multilayer grown on Si (1 0 0) substrates showed that the ZnO nanoparticles were formed inside the SiN x layer. The photoluminescence (PL) spectrum of a sample consisting of ZnO/SiN x multilayer with a SiN x buffer layer annealed at 800 °C showed that only a strong ultraviolet (UV) emission peak around 376 nm, corresponding to the ZnO nanoparticles, appeared in the visible range. The full width at half maximum of the UV peak of the PL spectrum was approximately 13 nm indicative of the high-quality of the ZnO nanoparticles. The optical properties of the ZnO nanoparticles were enhanced with increasing thickness of the deposited ZnO thin film

In these days, the researches of non-volatile memory device using nano-crystal(NC)-Si are actively progressing to replace flash memory devices. Many kinds of non-volatile memory devices such as phase-change(P)-RAM, resistance(Re)-RAM, polymer(Po)-RAM, and nano-floating gate memory(NFGM) are being studied. In this work, we study NFGM device in which information is memorized by storing electrons in silicon nanocrystal. The NFGM device has shown great promise for ultra-dense high-endurance memory device for low-power applications [S. Tiwari, et al., Appl. Phys. Lett. 68 (1996) 1377], and it is able to fabricate 1T-type device. Thus, the NFGM is considered to replace existing flash memory device. Non-volatile memory device has been fabricated by using NC-Si particles. The NC-Si particles have broad size range of 1-5nm and an average size of 2.7nm, which are sufficiently small to indicate the quantum effect for silicon. The memory window has been analyzed by C-V characteristic of NC-Si particles. V"d-I"d and V"g-I"d characteristics of the fabricated device have also been measured.

An examination is made of the discharge and cycle life of Zr 0.5 Ti 0.5 V 0.6 Ni 1.4 alloys when a fraction (0.2 at.%) of the Ni-component is substituted by Cr or Mn. In addition, the Zr:Ti component ratios are varied to extend the cycle life of high capacity, Mn-substituted Zr 1− x Ti x V 0.6 Ni 1.2 Mn 0.2 ( x =0.0, 0.25, 0.5, 0.75) alloys. The metallurgical microstructure is observed by X-ray diffraction analysis, scanning electron microscopy, and energy dispersive X-ray analysis. Active–passive potentiodynamic behaviour, as well as charge–discharge cycle characteristics, is evaluated, and dissolved V-species in the electrolytic solution is analyzed by inductively coupled plasma spectroscopy. The corrosion behaviour of the V–Cr or the V–Mn phase in the alkaline electrolyte solution is found to determine the cycle life of an AB 2 alloy. Cr-substituted (Zr 0.5 Ti 0.5 Ni 1.2 Cr 0.2 ) alloy, containing a V–Cr phase, is estimated to involve a dissolution rate of 0.028 wt.% vanadium per cycle in an alkaline electrolytic solution, while Mn-substituted (Zr 0.5 Ti 0.5 V 0.6 Ni 1.2 Mn 0.2 ) alloy, containing a V–Mn phase, is estimated to have a dissolution rate of 0.138 wt.% vanadium per cycle. For Mn-substituted alloys, an optimum Zr:Ti ratio of 3:1, i.e., Zr 0.75 Ti 0.25 V 0.6 Ni 1.2 Mn 0.2 , is found to have the most stable cycle life. The improvement in cycle life caused by increasing the Zr content in the alloy is attributed to increase in the corrosion resistance of the alloy due to less formation of the corrosive V–Mn phase.

Thickness dependence of ferroelectric and structural properties of BaTiO3 thin films was investigated. BaTiO3 thin films were prepared by rf magnetron sputtering on polycrystalline Pt substrates at 700°C. Film thickness range was 2,100-20,000 A. Room temperature permittivity, and D-E hysteresis loops were measured as a function of the film thickness. It has been found that these properties had the strong dependence on film thickness, which has mainly due to grain sizes of BaTiO3 thin films. The variation in permittivity according to grain size was discussed in terms of crystallinity, film stress, and recrystallization process.

Polycrystalline BaTiO3 thin films with thickness ranging from 2100 to 20 000 A were prepared on platinum substrates using off-axis radio-frequency magnetron sputtering. The variation in room temperature permittivity of the films was investigated with respect to thickness using x-ray diffraction and transmission electron microscopy. All films were ferroelectric and their room temperature permittivity, which was significantly higher than previously reported values, showed a strong dependence on film thickness. Higher permittivity was attributed primarily to the presence of ferroelectric domains. The room temperature permittivity of the thin films showed large variations with grain size, as in the case of BaTiO3 ceramics. The increase in permittivity with increasing film thickness was attributed to the decrease in defect concentration with grain growth. The 20 000 A film showed an abrupt decrease in permittivity and the presence of an intergranular phase having titanium-excess composition; these phenomena ar...

We report the theoretical modeling and the fabrication of polarization-insensitive optical amplifiers at 1300 nm in AlInGaAs-InP material system. Gain calculations, using the k.p method, show that the introduction of 0.33% tensile strain into a three-quantum-well structure can achieve gain-matching over a wide energy spectrum. The amplifiers, fabricated and tested, show excellent polarization insensitivity (less than 0.3 dB) at 1280 nm with a gain of 11 dB at 150 mA. Gain-bandwidth needs to be improved by employing antireflection coatings to suppress the facet reflectivity.

ZnO nanoparticles embedded in a Si3N4 layer by using spin-coating and thermal treatment were fabricated to investigate the feasible applications in charge trapping regions of the metal/oxide/nitride/oxide/p-Si memory devices. The magnitude of the flatband voltage shift of the capacitance-voltage (C-V) curve for the Al/SiO2/ZnO nanoparticles embedded in Si3N4 layer/SiO2/p-Si memory device was larger than that of Al/ZnO nanoparticles embedded in SiO2 layer/p-Si and Al/SiO2/Si3N4/SiO2/p-Si devices. The increase in the flatband voltage shift of the C-V curve for the Al/SiO2/ZnO nanoparticles embedded in Si3N4 layer/SiO2/p-Si memory device in comparison with other devices was attributed to the existence of the ZnO nanoparticles or the interface trap states between the ZnO nanoparticles and the Si3N4 layer resulting from existence of ZnO nanoparticles embedded in the Si3N4 layer.

Nonvolatile memory device was fabricated by using Nano-Crystal(NC)-Si particles. NC-Si particles had a wide size distribution of 1∼5nm and an average size of 2.7nm, which were sufficiently small to indicate the quantum effect for silicon. The memory window was analyzed by C-V characteristic of NC-Si particles. V d -I d , V g -I d characteristics of the fabricated device were also measured.

Dependence of the charging effects on the tunneling oxide thickness in Si nanoparticles embedded in a SiO 2 layer was investigated by using electrostatic force microscopy (EFM) measurements. EFM images showed that the stored charge in the Si nanoparticles increased with an increase in the applied bias voltage of the EFM tip. The variation of tunnel oxide thickness affected the tunneling threshold voltages, at which the carriers begun to tunnel from the Si substrate to the Si nanoparticles. These results indicate that the observed charging effects of Si nanoparticles embedded in a SiO 2 layer provide important informations on potential applications in nonvolatile memories with floating gates consisting of Si nanocrystals embedded in a SiO 2 layer.

The amounts of cesium and uranium released from crushed spent PWR fuel in the gel-state clays with a few ml of supernatant at hot cell temperature under Ar-atmosphere have been measured. The fractions of cesium dissolved from the fuel for 873 days were 0.29 and 0.25% in Boom clay/Boom-clay water and Ca-bentonite/synthetic granitic groundwater, respectively. These cesium fractions were very close to the gap inventory of cesium, which was determined to be around 0.30% in the previous experiment. The fraction of uranium released up to 193 days in the Boom clay media was 0.011% and this fraction has been retained until 873 days. Such this phenomenon was also obtained in the Ca-bentonite media even though the released fraction was higher than that in Boom clay. The increase of less than 0.001% in the dissolved uranium fraction between 193 and 873 days suggests that the long-term leach rate of uranium from spent fuel would be much less than 24 μg·m−2·day−1.

The water-soluble silicon quantum dots (QDs) of average diameter ~3 nm were prepared in organic solvent by ultrasound-induced solution route. This speedy rout produces the silicon QDs in the size range from 2 nm to 4 nm at room temperature and ambient pressure. The product yield of QDs was estimated to be higher than 60 % based on the initial NaSi weight. The surfaces of QDs were terminated with organic molecules including biocompatible ending groups (hydroxyl, amine and carboxyl) during simple preparation. Covalent attached molecules were characterized by FT-IR spectroscopy. These water-soluble passivation of QDs has just a little effect on the optical properties of original QDs.

Influence of quantum dot growth on the electrical properties of Au/GaAs Schottky diode structures containing self-assembled InAs quantum dots fabricated via atomic layer molecular beam epitaxy is investigated. Current-voltage characteristics and low frequency noise measurements were performed and analyzed. Employing four different structures; containing single quantum dot layer, without quantum dot layer for a reference, thicker capping layer with single quantum dot layer, three quantum dot layers, we find the diode containing single quantum dot layer show largest leakage current and all the dots show 1/f behavior in low frequency noise characteristics. Current dependence of the noise current power spectral density shows that all the dots have linear current dependence at low bias which is explained by the mobility and diffusivity fluctuation. The Hooge parameter was determined to be in the range of 10 -7 to 10 -8 . At high bias, the diodes containing quantum dot layer(s) show I F β dependence with the value of β larger than 2 (3.9, and 2.7), and the diode without quantum dot layer and thicker capping layer show the value of β smaller than 2 (1.6). The deviation of the values of β from two is explained by the random walk of electrons involving interface states at the metal-semiconductor Schottky barrier interface via barrier height modulation. It seems that the growth of quantum dots induces generation of the interface states with its density increasing towards the conduction band edge. The value of β smaller than 2 means that the interface states density is increasing towards the midgap. Typical value of the interface states density was found to be on the order of 10 11 to 10 12 cm 2 /Vs.

Summary form only given, as follows. Summary form only given. We have studied optical and structural properties of a-SiN/sub x/ thin films prepared by plasma method. While there are several methods of preparing a-Si based alloy (a-SiN/sub x/), plasma methods, such as PECVD and sputtering, have been widely used because of its good film quality and low deposition temperature. a-SiN samples were prepared on c-Si substrates by PECVD at 270/spl deg/C with pure NH/sub 3/ and 5%-diluted SiH/sub 4/ in N/sub 2/ as a precursor, and plasma was generated by RF power. All the deposition conditions were fixed except plasma power. We have observed two photolummescence (PL) peaks at about 3.0 eV and 2.5 eV at room temperature by He-Cd laser with 3.82 eV excitation energy. The former peak is due to the defect structures in SiN/sub x/ and the latter small silicon cluster. With the increase of plasma power, the PL properties of green band were improved with the increase of intensity, and the narrowing of full width at half-maximum. This result is attributed to the enhancement of nano-crystal silicon because the plasma power enhances the formation of radicals such as SiH, SiH/sub 2/, and SiH/sub 3/from precursors.

Summary form only given, as follows. Summary form only given. Detection wavelength tuning of a quantum well infrared photodetector (QWIP) has been carried out by using the dielectric cap quantum well intermixing technique with plasma enhanced chemical vapor deposited SiO/sub 2/ capping layer.

Summary form only given, as follows. Summary form only given. Intermixing effects of MBE (Molecular Beam Epitaxy) grown InGaAs SAQDs (Self-Assembled Quantum Dots) covered with SiO/sub 2/ dielectric capping layers, which was grown by PECVD, were investigated. After the thermal annealing, photoluminescence (PL) measurement has been carried for the optical characterization at the room temperature quantum well with PECVD-grown SiO/sub 2/ capping layer.

Intermixing effects of MOCVD (metal organic chemical vapor deposition) grown InGaAs SAQDs (self-assembled quantum dots) covered with SiO2 and SiNx-SiO2 dielectric capping layers were investigated. The intermixing of SAQDs was isothermally performed at 700°C by varying annealing time under the N2-gas ambient. It was confirmed from the PL measurement after the thermal annealing that, the emission energy of SAQDs was blue-shifted by 190 meV, the FWHM (full width at half maximum) was narrowed from 76 meV to 47 meV and the PL intensity was increased. SiNx-SiO2 double capping layer have been found to induce larger PL intensity after the thermal annealing of SAQDs compared to SiO2 single capping layer. The results can be implemented for increasing quantum efficiency and tuning the detection wavelength in quantum dot infrared photodetector (QDIP).

Silicon nanoparticles in the range from 2 nm to 5 nm was prepared from Zintl salt, soldium silicide (NaSi) by sonochemical method. This synthesis permits the reaction completed as fast as in a few hours and the easy alkyl-modification of nanocrystals surface at room temperature and ambient pressure. The average size of nanoparticles measured by the dynamic light scattering analysis was 2.7 nm. The high-resolution transmission electron micrograph cofirmed the material identity of nanoparticles as crystalline silicon. FT-IR spectra are consistent with the surface states of nanocrystals that is chlorine- or butyl-capped. The emission peak center moved to longer wavelength (up to 430 nm) with the reaction time, under a 325 nm excitation. The luminescence of silicon colloids looks bright bluish-white under excitation using a commercial low-intensity UV lamp.

Effects of In x Ga 1-x As strain relaxation layers on the optical and structural properties of InAs quantum dots (QDs) were studied systemically. 300 K-photoluminescence (PL) shows that PL peak energy of the QDs is blue-shifted in GaAs/InAs QDs/5 nm-thick In 0.1 Ga 0.9 As structure compared to GaAs/InAs QDs/GaAs structure. This is attributed to the intermixing of materials between the QDs and the InGaAs layer below the QDs, whereas capping of a 5 nm-thick In 0.1 Ga 0.9 As layer leads to red shift due to strain relaxation effect. As thickness of In x Ga 1-x As capping layer ( TI ) increases, 300 K-PL peaks experience red shift below TI TI above 7 nm results in blue shift. Considering average height of the QDs is ~ 7 nm, this is attributed to intermixing of material between the QDs and InGaAs capping layers. The blue shift in x = 0.2 over TI > ~7 nm is relatively smaller compared to that in x = 0.1. It is noteworthy that strain difference between the InAs QDs and the In x Ga 1-x As is smaller in x = 0.2 rather than in x = 0.1. Finally, InAs QDs are sandwiched by asymmetric thickness (7.5 nm-thick capping InGaAs, 0, 1.2, and 2.5 nm-thick bottom InGaAs) of In 0.2 Ga 0.8 As layers. 300 K-PL spectrum shows that 1.2 nm-thick bottom InGaAs leads to the longest wavelength (1306 nm) among this sample set. This is attributed to reduced barrier height and ignorable accumulated strain effect in thin bottom InGaAs layers. In this report, we justify merit of dots in an asymmetric well structure over conventional dots in a symmetric well structure and strain relaxation structure for the control of PL peak energy.

Numerical calculations have been performed for polarization insensitive amplifiers in AlInGaAs material system for the 1550 nm wavelength window. SOAs fabricated and tested at 1527 nm show a maximum gain difference of 0.9 dB at 60 mA of drive current between the TE and the TM modes. A polarization insensitive spectral bandwidth of 40 nm was observed where the gain difference between the two polarizations was found to be less than 1 dB.