Improvement of carrier diffusion length in silicon nanowire arrays using atomic layer deposition

To achieve a high-efficiency silicon nanowire (SiNW) solar cell, surface passivation technique is very important because a SiNW array has a large surface area. We successfully prepared by atomic layer deposition (ALD) high-quality aluminum oxide (Al₂O₃) film for passivation on the whole surface of the SiNW arrays. The minority carrier lifetime of the Al₂O₃-depositedSiNW arrays with bulk silicon substrate was improved to 27 μs at the optimum annealing condition. To remove the effect of bulk silicon, the effective diffusion length of minority carriers in the SiNW array was estimated by simple equations and a device simulator. As a result, it was revealed that the effective diffusion length in the SiNW arrays increased from 3.25 to 13.5 μm by depositing Al₂O₃ and post-annealing at 400°C. This improvement of the diffusion length is very important for application to solar cells, and Al₂O₃ deposited by ALD is a promising passivation material for a structure with high aspect ratio such as SiNW arrays.     

X-ray studies of multiple melting behavior of poly(butylene-2,6-naphthalate)

Multiple melting behavior of poly(butylene-2,6-naphthalate) (PBN) was studied with X-ray analysis and differential scanning calorimetry (DSC). Double endothermic peaks L and H attributed to the α-form crystal modification, a small peak attributed to the β-form crystal modification, and a new shoulder peak S at a lower temperature of peak H appeared in the DSC melting curves. Wide-angle X-ray diffraction patterns of the samples isothermally crystallized at 200 and 220 °C were obtained at a heating rate of 1 K min⁻¹, successively. In this heating process, change of crystal structure and increase of quantity of the β-form crystallites could not be observed up to the final melting. With increasing temperature, the diffraction intensity decreased gradually and then increased distinctly before a steep decrease due to the final melting. The X-ray analysis clearly proved the melt-recrystallization during heating. The β-form crystal modification was formed during slow heating process in the high temperature region.     

Synthesis of chemically modified chitosans with a higher fatty acid glycidyl and their adsorption abilities for anionic and cationic dyes

Novel chitosan‐based materials with a higher fatty acid glycidyl as the chemically modified agent were synthesized and the adsorption ability of the resulting polymers has been evaluated for typical anionic and cationic dyes. The successful modification was confirmed by the infrared spectroscopic measurements. As the degree of substitution was decreased, the adsorption ability of the chemically modified chitosans for anionic dyes at the higher dye concentration was increased, and the modified chitosans with a lower degree of substitution showed a higher adsorption ability than that of an activated carbon at the higher dye concentration. For cationic dyes, the chemically modified chitosan showed a good adsorption power, especially when the adsorption power was evaluated by the flow methods. The improved adsorption ability of a chemically modified chitosan material was also confirmed by comparing it with that of a crosslinked chitosan material. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2423–2428, 2005     

Immunomodulatory Properties and Osteogenic Activity of Polyetheretherketone Coated with Titanate Nanonetwork Structures

Polyetheretherketone (PEEK) is a potential substitute for conventional metallic biomedical implants owing to its superior mechanical and chemical properties, as well as biocompatibility. However, its inherent bio-inertness and poor osseointegration limit its use in clinical applications. Herein, thin titanium films were deposited on the PEEK substrate by plasma sputtering, and porous nanonetwork structures were incorporated on the PEEK surface by alkali treatment (PEEK-TNS). Changes in the physical and chemical characteristics of the PEEK surface were analyzed to establish the interactions with cell behaviors. The osteoimmunomodulatory properties were evaluated using macrophage cells and osteoblast lineage cells. The functionalized nanostructured surface of PEEK-TNS effectively promoted initial cell adhesion and proliferation, suppressed inflammatory responses, and induced macrophages to anti-inflammatory M2 polarization. Compared with PEEK, PEEK-TNS provided a more beneficial osteoimmune environment, including increased levels of osteogenic, angiogenic, and fibrogenic gene expression, and balanced osteoclast activities. Furthermore, the crosstalk between macrophages and osteoblast cells showed that PEEK-TNS could provide favorable osteoimmunodulatory environment for bone regeneration. PEEK-TNS exhibited high osteogenic activity, as indicated by alkaline phosphatase activity, osteogenic factor production, and the osteogenesis/osteoclastogenesis-related gene expression of osteoblasts. The study establishes that the fabrication of titanate nanonetwork structures on PEEK surfaces could extract an adequate immune response and favorable osteogenesis for functional bone regeneration. Furthermore, it indicates the potential of PEEK-TNS in implant applications.     

Discovery of a Novel Scaffold as an Indoleamine 2,3‐Dioxygenase 1 (IDO1) Inhibitor Based on the Pyrrolopiperazinone Alkaloid,Longamide B

Indoleamine 2,3‐dioxygenase 1 (IDO1) has emerged as a key target for cancer therapy, as IDO1 plays a critical role in the capacity of tumor cells to evade the immune system. The pyrrolopiperazinone alkaloid longamide B and its derivatives were identified as novel IDO1 inhibitors based on docking studies and small library synthesis. The thioamide derivative showed higher IDO1 inhibitory activity than longamide B, and displayed an activity similar to that of a representative IDO1 inhibitor, 1‐methyl‐tryptophan. These results suggest that the pyrrolopiperazinone scaffold of longamide B could be used in the development of IDO1 inhibitors.     

Formation of Exclusive Al2O3 Scale on Nb and Nb-Rich Alloys by Two-Step Oxygen–Aluminum Diffusion Process

External Al₂O₃ scale formation behavior by a diffusion aluminizing process on Nb and Nb–X (X?=?Mo, Re, and Ta) alloys with different oxygen solubilities was investigated. The oxygen content in Nb and Nb–X alloys was controlled by oxygen diffusion treatment at 1,100?°C using Nb/NbO mixture. Nb–aluminide, NbAl₃ and Nb₂Al, layers were developed on the low-oxygen Nb substrate by an aluminum diffusion treatment using Al/Al₂O₃/NH₄Cl mixture at 1,100?°C; whereas an adhesive Al₂O₃ scale developed on the Nb substrate with higher oxygen content. The alloy oxygen content decreased by an addition of Ta, Mo and Re, in this order, and the decrease in alloy oxygen content resulted in the transition of Al₂O₃ formation from external scale to internal precipitates. This transition was not observed when low Al activity powder mixture, Ni50Al/Al₂O₃/NH₄Cl, was used for Al diffusion process, and only external Al₂O₃ scale was developed on all samples. In the present study, the effects of oxygen solubility limit, oxygen content, and the activity of Al in diffusion process on the formation of Al₂O₃ scale will be discussed.     

Characterization of carbon nanofibers synthesized by microwave plasma-enhanced CVD at low-temperature in a CO/Ar/O2 system

The low-temperature synthesis of carbon nanofibers by microwave plasma-enhanced chemical vapor deposition using a CO/Ar/O₂ system and their characterizations were performed. At the optimum oxygen concentration of O₂/CO = 7/1000, vertically aligned CNFs can be synthesized at temperatures as low as 180 °C with growth rates of 4–6 nm/s. The diameter of bulk CNFs is about 50–100 nm and the surface of CNFs is covered by branching fibers and their nuclei with a diameter of about 5–20 nm. Not only the peaks originating from carbon chains, but also oxygen containing groups, such as CO and COC, are observed in the FTIR spectra. The CNFs growth rate is almost independent from the substrate temperature and it is concluded that an elementary process not on the substrates, but in the gas phase, is the rate-determining step in the present CO/Ar/O₂ microwave-plasma-enhanced CVD system.     

Thermal and electrical properties of perovskite-type strontium molybdate

Polycrystalline samples of perovskite-type strontium molybdate, SrMoO₃, have been prepared and the thermal and electrical properties have been measured from room temperature to about 1000 K. The electrical resistivity is of an order of magnitude of 10⁻⁵ to 10⁻⁶ (Ω m) in the whole temperature range. The Seebeck coefficient is around 4–9 μV K⁻¹. At room temperature, the thermal conductivity is about 30 W m⁻¹ K⁻¹, and it decreases with increasing temperature.     

Reinforcement of polypropylene by cellulose microfibers modified with polydopamine and octadecylamine

Cellulose microfibers (CMFs) having surfaces modified with polydopamine (PDPA) and octadecylamine (ODA) were prepared, and their reinforcing abilities for polypropylene (PP) were investigated. The PDPA coating was made via self-polymerization of dopamine (P-CMF), and subsequent alkylation was conducted by the reaction with ODA (OP-CMF). The modified CMFs exhibited improved dispersibility in the PP matrix due to the reduced hydrophilicity. The OP-CMF/PP composite prepared by batch mixing had a higher tensile modulus compared to that for the pure PP and composites with unmodified CMFs. However, excess alkylation lowered the tensile modulus, and the presence of an optimal degree of alkylation was demonstrated. The CMF/PP-IM composites fabricated by injection molding exhibited improved tensile properties compared to those prepared by batch mixing. Both the tensile modulus and yield stress were increased by increasing the CMF content and improved by the surface modification of the CMFs.     

Pervaporation via silicon-based membranes: Correlation and prediction of performance in pervaporation and gas permeation

Pervaporation (PV) is a membrane technology that holds great promise for industrial applications. To better understand the PV mechanism, PV dehydrations of various types of organic solvents (methanol, ethanol, iso-propanol, tert-butanol, and acetone) were performed on five types of organosilica and two types of silicon carbide-based membranes, all with different pore sizes. Water permeance was dependent on the types of organic aqueous solutions, which suggested that organic solvents penetrated the pores and hindered the permeation of water. In addition, water permeance of various types of membranes in PV was well correlated with hydrogen permeance in single-gas permeation. Furthermore, a clear correlation was obtained between the permeance ratio in PV and that in single-gas permeation, which was confirmed via the modified-gas translation model. These correlations make it possible to use single-gas permeation properties to predict PV performance.