Effect of laser annealing using high repetition rate pulsed laser on optical properties of phosphorus-ion-implanted ZnO nanorods

The effect of high repetition rate pulsed laser annealing with a KrF excimer laser on the optical properties of phosphorus-ion-implanted zinc oxide nanorods has been investigated. The recovery levels of phosphorus-ion-implanted zinc oxide nanorods have been measured by photoluminescence spectra and cathode luminescence images. Cathode luminescence disappeared over 300 nm below the surface due to the damage caused by ion implantation with an acceleration voltage of 25 kV. When the annealing was performed at a low repetition rate of the KrF excimer laser, cathode luminescence was recovered only in a shallow area below the surface. The depth of the annealed area was increased along with the repetition rate of the annealing laser. By optimizing the annealing conditions such as the repetition rate, the irradiation fluence and so on, we have succeeded in annealing the whole damaged area of over 300 nm in depth and in observing cathode luminescence. Thus, the effectiveness of high repetition rate pulsed laser annealing on phosphorus-ion-implanted zinc oxide nanorods was demonstrated.     

Color vision: "OH-site" rule for seeing red and green

Eyes gather information, and color forms an extremely important component of the information, more so in the case of animals to forage and navigate within their immediate environment. By using the ONIOM (QM/MM) (ONIOM = our own N-layer integrated molecular orbital plus molecular mechanics) method, we report a comprehensive theoretical analysis of the structure and molecular mechanism of spectral tuning of monkey red- and green-sensitive visual pigments. We show that interaction of retinal with three hydroxyl-bearing amino acids near the β-ionone ring part of the retinal in opsin, A164S, F261Y, and A269T, increases the electron delocalization, decreases the bond length alternation, and leads to variation in the wavelength of maximal absorbance of the retinal in the red- and green-sensitive visual pigments. On the basis of the analysis, we propose the "OH-site" rule for seeing red and green. This rule is also shown to account for the spectral shifts obtained from hydroxyl-bearing amino acids near the Schiff base in different visual pigments: at site 292 (A292S, A292Y, and A292T) in bovine and at site 111 (Y111) in squid opsins. Therefore, the OH-site rule is shown to be site-specific and not pigment-specific and thus can be used for tracking spectral shifts in any visual pigment.     

Magnetism of fcc/fcc, hcp/hcp twin and fcc/hcp twin-like boundaries in cobalt

The magnetic moments of the fcc/fcc, hcp/hcp twin and fcc/hcp twin-like boundaries in cobalt were investigated by first-principles calculations based on density functional theory. The magnetic moments in fcc/fcc were larger than those of the bulk fcc, while the variations in the magnetic moment were complicated in hcp/hcp and fcc/hcp. The magnetovolume effect on the magnetic moment at the twin(-like) boundaries was investigated in terms of the local average atomic distance and the average deviation from equilibrium; however, the complicated variations in the magnetic moment could not be explained from the magnetovolume effect. Next, the narrowing (or broadening) of the partial density of states (PDOS) width of 3d orbitals, the number of occupied states for the spin-down channel, and the PDOS around the Fermi level were investigated. The entire variation in the magnetic moment at the twin(-like) boundaries could be understood in terms of these factors. Charge transfer occurred in hcp/hcp. In this case, the contributions of 4s and 4p electrons to the variation in the magnetic moment were relatively large.     

Synthesis and Aromaticity of Benzene-Fused Doubly N-Confused Porphyrins

A bicyclo[2.2.2]octadiene(BCOD)-fused bis(dipyrromethane) derivative was reacted with methylal in the presence of trifluoroacetic acid followed by oxidation with chloranil to give a doubly N-confused phlorin derivative, which did not undergo the retro-Diels–Alder reaction extruding an ethylene molecule on heating. In contrast, a 7-tert-butoxybicyclo[2.2.1]heptadiene(7-BuOBCHD)-fused bis(dipyrromethane) yielded benzene-ring-fused doubly N-confused porphyrins by following similar reaction sequences.     

Synthesis of chlorophyll-a derivatives possessing the 3-(2-acylethenyl) group by cross-aldol condensation and their optical properties

Chlorophyll-a derivatives possessing a trans-2-acylethenyl group at the C3-position were prepared by cross-aldol (Claisen-Schmidt) condensation of methyl pyropheophorbide-d having the C3-formyl group with ketones bearing α-hydrogen atoms including (un)substituted acetophenones, acetylarenes, and alkanones under basic conditions. The Qy absorption and fluorescence emission bands of the synthetic chalcone analogs in dichloromethane were largely dependent on the C3³-substituents. Especially, the introduction of electron-donating and withdrawing groups to the C3³-phenyl ring resulted in bathochromic and hypsochromic shifts of the maxima, respectively. Furthermore, fluorescence quantum yields and lifetimes were largely suppressed by the substitution with a nitro group on the C3³-phenyl ring.     

Bivariate distributions in statistical spectroscopy studies: IV. Interacting particle Gamow-Teller strength densities and β-decay rates offp-shell nuclei for presupernova stars

A method to calculate temperature dependent-decay rates is developed by writing the expression for the rates explicitly in terms of bivariateGT strength densities (I _O ^H _(GT)) for a given hamiltonianH=h+V and state densities of the parent nucleus besides having the usual phase space factors. The theory developed in the preceding paper (III) for constructing NIP strength densities is applied for generatingI _O ^h _(GT) and thenI _O ^H _(GT) is constructed using the bivariate convolution formI _O ^H _(GT)= _S I _O(GT) ^h,S _O(GT) ^V,S ; _BIV-G . The spreading bivariate Gaussian _O(GT) ^V ;BIV-G, forfp-shell nuclei, is constructed by assuming that the marginal centroids are zero, the marginal variances are same as the corresponding state density variances and fixing the bivariate correlation coefficient using experimental-decay half lifes. With the deduced values of 0.67,-S-decay rates for^61,62Fe and^62–64Co isotopes are calculated at presupernova matter densities=10⁷–10⁹ gm/cc, temperaturesT=(3–5)×10⁹ K and electron fractions Y_e=0.43–0.5. The convolution form forI _O(GT) ^H led to a simple expression for calculatingGT non-energy weighted sum rule strength and it describes (within 10%) the shell model results offp-shell nuclei.The work presented in this paper has grown out of many discussions and correspondence one of the authors (VKBK) has with J.B. French in the last five years and also out of an ongoing project one of the authors (VKBK) is carrying out with J.B. French and R.U. Haq. Thanks are due to K. Kar and S. Sarkar for supplying some of their results before publishing. The authors thank V. Potbhare for his interest in the work presented in this paper.     

Facile iodination of the vinyl groups in protoporphyrin IX dimethyl ester and subsequent transformation of the iodinated moieties

Iodination of protoporphyrin IX dimethyl ester using phenyliodine bis(trifluoroacetate) (PIFA) and I₂ was studied. Iodine added to both the C3- and C8-vinyl groups equally to afford the iodohydrin or iodoether in the presence of water or alcohol, respectively. Any meso-hydrogen atom was not substituted by an iodine atom under these conditions, although both the vinyl group and one of the meso positions of methyl pyropheophorbide-a bearing a chlorin π-system, a chlorophyll-a derivative, was modified with PIFA and I₂. The reaction intermediates derived from the porphyrin were more reactive than those from the chlorin and liable to form intermolecular linkages. The obtained 2-iodo-1-hydroxyethyl group was transformed into a formyl group by a mild treatment. The corresponding iodoether moiety was readily converted into the acetyl group under basic conditions. These transformations were also applicable to smaller olefins such as styrene.     

XPS study on surface modification of NiTi alloy by acidic solution immersion and subsequent heating in air

Changes in the surface chemical state of a nearly equiatomic nickel–titanium (NiTi) alloy caused by immersion in aqueous solutions of HNO₃ and H₂SO₄ as well as subsequent heating in air at 723 K were analyzed using X-ray photoelectron spectroscopy (XPS). An XPS analysis using angle-resolved technique and a mathematical deconvolution technique revealed that a passive layer formed in an ambient atmosphere contained TiO₂ as a major state and Ni(OH)₂ and NiO as minor states. The Ni(OH)₂ on the alloy remained in the region even when heated in air at 723 K. Therefore, the resulting layer became a Ti-oxide layer with Ni segregated region at the surface, which was NiO formed via dehydration of Ni(OH)₂. However, immersion in an aqueous solution of HNO₃ or H₂SO₄ enables Ni(OH)₂ state to dissolve in the passive layer of a NiTi alloy; thereby, the Ni segregated region rarely appeared in the oxide layer by heating. The Ni segregated region at the surface becomes an obstacle for the inward diffusion of oxygen; thus, the annihilation of such a segregated region results in an increase in the thickness of the oxide layer.