Seedless growth of zinc oxide flower-shaped structures on multilayer graphene by electrochemical deposition

A seedless growth of zinc oxide (ZnO) structures on multilayer (ML) graphene by electrochemical deposition without any pre-deposited ZnO seed layer or metal catalyst was studied. A high density of a mixture of vertically aligned/non-aligned ZnO rods and flower-shaped structures was obtained. ML graphene seems to generate the formation of flower-shaped structures due to the stacking boundaries. The nucleation of ZnO seems to be promoted at the stacking edges of ML graphene with the increase of applied current density, resulting in the formation of flower-shaped structures. The diameters of the rods/flower-shaped structures also increase with the applied current density. ZnO rods/flower-shaped structures with high aspect ratio over 5.0 and good crystallinity were obtained at the applied current densities of −0.5 and −1.0 mA/cm². The growth mechanism was proposed. The growth involves the formation of ZnO nucleation below 80°C and the enhancement of the growth of vertically non-aligned rods and flower-shaped structures at 80°C. Such ZnO/graphene hybrid structure provides several potential applications in sensing devices.     

Electrochemically deposited gallium oxide nanostructures on silicon substrates

We report a synthesis of β-Ga₂O₃ nanostructures on Si substrate by electrochemical deposition using a mixture of Ga₂O₃, HCl, NH₄OH, and H₂O. The presence of Ga³⁺ ions contributed to the deposition of Ga₂O₃ nanostructures on the Si surface with the assistance of applied potentials. The morphologies of the grown structures strongly depended on the molarity of Ga₂O₃ and pH level of electrolyte. β-Ga₂O₃ nanodot-like structures were grown on Si substrate at a condition with low molarity of Ga₂O₃. However, Ga₂O₃ nanodot structures covered with nanorods on top of their surfaces were obtained at higher molarity, and the densities of nanorods seem to increase with the decrease of pH level. High concentration of Ga³⁺ and OH^- ions may promote the reaction of each other to produce Ga₂O₃ nanorods in the electrolyte. Such similar nature of Ga₂O₃ nanorods was also obtained by using hydrothermal process. The grown structures seem to be interesting for application in electronic and optoelectronic devices as well as to be used as a seed structure for subsequent chemical synthesis of GaN by thermal transformation method.     

Crystal structure and fluorescence behavior of N,N'-bis (1-naphthylmethyl)-diazonia-18-crown-6 diisothiocyanate

N,N'-bis (1-naphthylmethyl)-diaza-18-crown-6 (1) showed weak emissions, suggesting that photoinduced electron transfer (PET) from the amine group to the excited naphthalene occurs. The PET fluoroionophore (1) was found to display unique photophysical properties in the presence of a guest cation. Single crystals of the HNCS salt of 1 were grown from 1 and NH(4)SCN. The crystal structure of the HNCS salt of 1 was elucidated by X-ray crystallographic analysis. The HNCS salt of 1 consists of a 1·2H(+) and 2NCS(-) ion pair. The 1·2HNCS salt gave an emission band at 332 nm. Complexation of 1 with HNCS increased the fluorescence intensity of the host by a factor of 29. The emission enhancement of 1 with HNCS was caused by the proton which dissociates from HNCS.     

Structure–Activity Relationships of 1,2‐Disubstituted Benzimidazoles: Selective Inhibition of Heme Oxygenase‐2 Activity

Devising ways to up‐ or down‐regulate heme oxygenase activity is attracting much interest as a strategy for the treatment of a variety of disorders. With a view of obtaining compounds that exhibit high potency and selectivity as inhibitors of the heme oxygenase‐2 (HO‐2) isozyme (constitutive) relative to the heme oxygenase‐1 (HO‐1) isozyme (inducible), several 1,2‐disubstituted 1H‐benzimidazoles were designed and synthesized. Specifically, analogues were synthesized in which the C2 substituent was the following: (1H‐imidazol‐1‐yl)methyl, (N‐morpholinyl)methyl, cyclopentylmethyl, cyclohexylmethyl, or (norborn‐2‐yl)methyl. Compounds with the cyclic system in the C2 substituent being a carbocyclic ring, especially cyclohexyl or norborn‐2‐yl, and the N1 substituent being a ring‐substituted benzyl group, especially 4‐chlorobenzyl or 4‐bromobenzyl, best exhibited the target criteria of high potency and selectivity toward inhibition of HO‐2. The new candidates should be useful pharmacological tools and may have therapeutic applications.     

Electron microscopy of pathogenic yeasts Cryptococcus neoformans and Exophiala dermatitidis by high-pressure freezing

A high-pressure freezing method was used to observe the ultrastructure of pathogenic yeasts, Cryptococcus neoformans and Exophiala dermatitidis, after freeze-substitution and ultrathin sectioning. The method well preserved the cell structure in its natural state, since the capsule, cell wall, plasma membrane, nucleus, outer and inner nuclear membranes, nuclear pores, nucleolus, mitochondria, mitochondrial membrane and cristae, vacuoles, endoplasmic reticulum, Golgi apparatus, spindle pole body, ribosomes, lipid droplets, microtubules, actin filaments, and glycogen granules were clearly visible. The method was shown to freeze cells as deep as 0.1 mm by sectioning the sample perpendicular to specimen surface. The quality of the cell image was similar to that obtained by a rapid freezing method when compared using the same materials. Thus, high-pressure freezing would be useful for making serial ultrathin sections for three-dimensional analysis of cells, which should give basic information of structure and function of pathogenic yeast cells necessary for finding an effective therapy for mycoses.     

Seed/catalyst-free growth of zinc oxide nanostructures on multilayer graphene by thermal evaporation

We report the seed/catalyst-free growth of ZnO on multilayer graphene by thermal evaporation of Zn in the presence of O₂ gas. The effects of substrate temperatures were studied. The changes of morphologies were very significant where the grown ZnO structures show three different structures, i.e., nanoclusters, nanorods, and thin films at 600°C, 800°C, and 1,000°C, respectively. High-density vertically aligned ZnO nanorods comparable to other methods were obtained. A growth mechanism was proposed based on the obtained results. The ZnO/graphene hybrid structure provides several potential applications in electronics and optoelectronics.     

Synthesis of gallium nitride nanostructures by nitridation of electrochemically deposited gallium oxide on silicon substrate

Gallium nitride (GaN) nanostructures were successfully synthesized by the nitridation of the electrochemically deposited gallium oxide (Ga₂O₃) through the utilization of a so-called ammoniating process. Ga₂O₃ nanostructures were firstly deposited on Si substrate by a simple two-terminal electrochemical technique at a constant current density of 0.15 A/cm² using a mixture of Ga₂O₃, HCl, NH₄OH and H₂O for 2 h. Then, the deposited Ga₂O₃ sample was ammoniated in a horizontal quartz tube single zone furnace at various ammoniating times and temperatures. The complete nitridation of Ga₂O₃ nanostructures at temperatures of 850°C and below was not observed even the ammoniating time was kept up to 45 min. After the ammoniating process at temperature of 900°C for 15 min, several prominent diffraction peaks correspond to hexagonal GaN (h-GaN) planes were detected, while no diffraction peak of Ga₂O₃ structure was detected, suggesting a complete transformation of Ga₂O₃ to GaN. Thus, temperature seems to be a key parameter in a nitridation process where the deoxidization rate of Ga₂O₃ to generate gaseous Ga₂O increase with temperature. The growth mechanism for the transformation of Ga₂O₃ to GaN was proposed and discussed. It was found that a complete transformation can not be realized without a complete deoxidization of Ga₂O₃. A significant change of morphological structures takes place after a complete transformation of Ga₂O₃ to GaN where the original nanorod structures of Ga₂O₃ diminish, and a new nanowire-like GaN structures appear. These results show that the presented method seems to be promising in producing high-quality h-GaN nanostructures on Si.     

Delay fault simulation of sequential circuits

This article proposes a 7-valued logic appropriate for test generation and fault simulation, in the area of robust tests for gate delay faults, and a straightforward simulation strategy for sequential circuits. It is shown that a purely qualitative logic of robust testing is inadequate for circuits with edge-triggered flip-flops. The relation between the 7-valued logic and the similar logic proposed before by Smith, Schulz et al., and Lin and Reddy are discussed.     

Self-checking CMOS circuits using pass-transistor logic

This article presents a new approach to implementing self-checking circuits in CMOS technology. Implementations are made self-checking with respect to a single line stuck-at 0/1 fault. It is assumed that stuck faults at a common gate of neighboring PMOS and NMOS are not independent and the contact between a PMOS (NMOS) source and a power (ground) line is fault free. Self-checking error checkers for parity, two-rail code, and m-out-of-n code are designed using pass-transistor logic and then verified by fault simulation.     

Moment analysis of mass-transfer kinetics in C18-silica monolithic columns

The moment analysis of elution peak profiles based on new moment equations provides information on the mass-transfer characteristics of C(18)-silica monolithic columns. The flow rate dependence of the HETP data was analyzed using the generalized van Deemter equation, after correction of these data by subtraction of the external mass-transfer contribution to band broadening. Kinetic parameters and diffusion coefficients related to the mass-transfer processes in monolithic columns were derived by taking advantage of the different flow velocity dependence of their contributions to band broadening. At high flow rates, axial dispersion and diffusive migration across the monolithic C(18)-silica skeleton contribute much to band broadening, suggesting that it remains important to reduce the influence of eddy diffusion and the mass-transfer resistance in the stationary phase to achieve fast separations and a high efficiency. Surface diffusion plays a predominant role for molecular migration in the monolithic stationary phase. Although the value of the surface diffusion coefficient (D(s)) depends on an estimate of the external mass-transfer coefficient, D(s) values of the order of 10(-7) cm(2) s(-1) were calculated for the first time for the C(18)-silica monolithic skeleton. The value of D(s) decreases with increasing retention of sample compounds. Analysis of a kind of time constant calculated from D(s) suggests that the "chromatographic corresponding particle size" is approximately 4 microm for the C(18)-silica monolithic stationary phase used in this study. The accuracy of the D(s) values determined was discussed.