Structure and magnetic properties of hcp and fcc nanocrystalline thin Ni films and nanoparticles produced by radio frequency magnetron sputtering

We report on the growth of thin Ni films by radio frequency magnetron sputtering in Ar-plasma. The growth temperature was about 350 K and the films were deposited on various substrates such as glass, silicon, sapphire and alumina. The thickness of the thinnest films was estimated by the appearance of Kiessig fringes up to about 2theta = 8 degrees in the small-angle X-ray diffraction pattern, as expected for high-quality atomically-flat thin films. With the help of this, a quartz balance system was calibrated and used for measuring the thickness of thicker samples with an accuracy of better than 5%. Structural characterization via X-ray diffraction and high resolution transmission electron microscopy revealed an Ar-gas pressure window, where single phase hcp Ni films may be grown. The magnetic response of the Ni films was checked at room temperature via a newly established and fully automatic polar magneto-optic Kerr effect magnetometer. The hcp films show no magnetic response. Interestingly, the magnetic saturation field of fcc films deposited at low Ar pressure is comparable to the one of bulk Ni, while the one of fcc films deposited at high Ar pressures is decreased, revealing the presence of residual strain in the films. Finally, it is shown that it is possible to form films which contain magnetic Ni fcc nanoparticles in a non-magnetic hcp matrix, i.e., a system interesting for technological applications demanding a single Ni target for its production.     

Complementarity effect of governance mechanisms on environmental collaboration: does it exist?

This study evaluates the effect of pre-existing relational governance mechanisms on environmental collaboration. Specifically, our study distinguishes between structural and process dimensions of relational governance mechanisms so as to facilitate a more nuanced investigation into the inherent complementarities and performance implications. Using data collected from 145 US firms and a combination of methodologies – three-stage least squares and structural equation modelling, a number of direct, complementary and mediation effects are hypothesised and tested. The three-stage least squares methodology was adopted to overcome endogeneity and simultaneity issues inherent in the hypotheses covering complementarity. Contrary to conventional wisdom, structural and process governance mechanisms were not found to act as complements for environmental collaboration. Instead, the effect of structural mechanisms was found to be completely mediated by the process mechanisms. Thus, process mechanisms of relational governance were found to be much more important in promoting advanced practices such as environmental collaboration. Our results also document the significant mediating role of environmental collaboration. Implications for future research and practice are offered.     

The Role and the Effect of Calcium Ion Content of Photographic Gelatins on Coating Defects

The influence of the calcium ion content of some photographic gelatins on the adhesion of gelatin solutions to emulsion layers was investigated by surface tension, pH and viscosity measurements and by coating using the dip method.

Adhesion of the gelatin layers was examined in the coating process under the following conditions:

Surface tension at varying wetting agent concentrations, for gelatin solutions which contain calcium ions from 0 to 5760 ppm concentration.

Surface tension at varying gelatin concentrations.

Surface tension at varying pH values of the gelatin solutions used in the coating process.

The experimental results demonstrate that, at gelatin concentrations between 2 and 4%, the adhesion ability of a gelatin solution on a dry or wet gelatin (emulsion) layer depends on the Ca2* content of the coating solution. It is necessary to have at least 1000 ppm Ca2* concentration to guarantee a perfect adhesion and a perfect coating. Gelatin source, pH and the viscosity of the system are unimportant.     

Preconditioned Conjugate Gradient and Multigrid Methods for Numerical Solution of Multicomponent Mass Transfer Equations I. Diffusion-Reaction Equations

In a series of two papers, we analyze the numerical performances of the preconditioned conjugate gradient algorithms (BICGSTAB and GMRES) and multigrid method in solving two-dimensional multicomponent mass transfer equations. The present test problems are steady-state, linear and nonlinear diffusion-reaction equations. The nonlinear algorithm used in connection with the preconditioned conjugate gradient methods is the modified Picard iteration. Theoretical results about the preconditioning are presented. The multigrid algorithm used is the Full Approximation Storage algorithm. The finite difference method was used to discretize the mathematical model equations. The numerical results obtained show good numerical performances.     

Light interactions with gold nanorods and cells: implications for photothermal nanotherapeutics

Gold nanorods (AuNR) can be tailored to possess an intense and narrow longitudinal plasmon (LP) absorption peak in the far-red to near-infrared wavelength region, where tissue is relatively transparent to light. This makes AuNRs excellent candidates as contrast agents for photoacoustic imaging, and as photothermal therapeutic agents. The favorable optical properties of AuNR which depend on the physical parameters of shape, size and plasmonic coupling effects, are required to be stable during use. We investigate the changes that are likely to occur in these physical parameters in the setting of photothermal therapeutics, and the influence that these changes have on the optical properties and the capacity to achieve target cell death. To this end we study 3 sets of interactions: pulsed light with AuNR, AuNR with cells, and pulsed light with cells incubated with AuNR. In the first situation we ascertain the threshold value of fluence required for photothermal melting or reshaping of AuNR to shorter AuNR or nanospheres, which results in drastic changes in optical properties. In the second situation when cells are exposed to antibody-conjugated AuNR, we observe using transmission electron microscopy (TEM) that the particles are closely packed and clustered inside vesicles in the cells. Using dark-field microscopy we show that plasmonic interactions between AuNRs in this situation causes blue-shifting of the LP absorption peak. As a consequence, no direct lethal damage to cells can be inflicted by laser irradiation at the LP peak. On the other hand, using irradiation at the transverse peak (TP) wavelength in the green, at comparative fluences, extensive cell death can be achieved. We attribute this behavior on the one hand to the photoreshaping of AuNR into spheres and on the other hand to clustering of AuNR inside cells. Both effects create sufficiently high optical absorption at 532 nm, which otherwise would have been present at the LP peak. We discuss implications of these finding on the application of these particles in biomedicine.     

Amorphous alumina coatings: processing, structure and remarkable barrier properties

Amorphous aluminium oxide coatings were processed by metalorganic chemical vapour deposition (MOCVD); their structural characteristics were determined as a function of the processing conditions, the process was modelled considering appropriate chemical kinetic schemes, and the properties of the obtained material were investigated and were correlated with the nanostructure of the coatings. With increasing processing temperature in the range 350 degrees C-700 degrees C, subatmospheric MOCVD of alumina from aluminium tri-isopropoxide (ATI) sequentially yields partially hydroxylated amorphous aluminium oxides, amorphous Al2O3 (415 degrees C-650 degrees C) and nanostructured gamma-Al2O3 films. A numerical model for the process allowed reproducing the non uniformity of deposition rate along the substrate zone due to the depletion of ATI. The hardness of the coatings prepared at 350 degrees C, 480 degrees C and 700 degrees C is 6 GPa, 11 GPa and 1 GPa, respectively. Scratch tests on films grown on TA6V titanium alloy reveal adhesive and cohesive failures for the amorphous and nanocrystalline ones, respectively. Alumina coating processed at 480 degrees C on TA6V yielded zero weight gain after oxidation at 600 degrees C in lab air. The surface of such low temperature processed amorphous films is hydrophobic (water contact angle 106 degrees), while the high temperature processed nanocrystalline films are hydrophilic (48 degrees at a deposition temperature of 700 degrees C). It is concluded that amorphous Al2O3 coatings can be used as oxidation and corrosion barriers at ambient or moderate temperature. Nanostructured with Pt or Ag nanoparticles, they can also provide anti-fouling or catalytic surfaces.     

Structural and physical properties of antibacterial Ag-doped nano-hydroxyapatite synthesized at 100°C

ABSTRACT: Synthesis of nanosized particle of Ag-doped hydroxyapatite with antibacterial properties is in the great interest in the development of new biomedical applications. In this article, we propose a method for synthesized the Ag-doped nanocrystalline hydroxyapatite. A silver-doped nanocrystalline hydroxyapatite was synthesized at 100°C in deionized water. Other phase or impurities were not observed. Silver-doped hydroxyapatite nanoparticles (Ag:HAp) were performed by setting the atomic ratio of Ag/[Ag + Ca] at 20% and [Ca + Ag]/P as 1.67. The X-ray diffraction studies demonstrate that powders made by co-precipitation at 100°C exhibit the apatite characteristics with good crystal structure and no new phase or impurity is found. The scanning electron microscopy (SEM) observations suggest that these materials present a little different morphology, which reveals a homogeneous aspect of the synthesized particles for all samples. The presence of calcium (Ca), phosphor (P), oxygen (O), and silver (Ag) in the Ag:HAp is confirmed by energy dispersive X-ray (EDAX) analysis. FT-IR and FT-Raman spectroscopies revealed that the presence of the various vibrational modes corresponds to phosphates and hydroxyl groups. The strain of Staphylococcus aureus was used to evaluate the antibacterial activity of the Ca10-xAgx(PO4)6(OH)2 (x = 0 and 0.2). In vitro bacterial adhesion study indicated a significant difference between HAp (x = 0) and Ag:HAp (x = 0.2). The Ag:Hap nanopowder showed higher inhibition.     

Effectiveness of the use of steel fibres on the torsional behaviour of flanged concrete beams

The behaviour under torsion of reinforced concrete beams with steel fibres as mass reinforcement is experimentally investigated. Short hooked-ended steel fibres with aspect ratio l_f/d_f = 37.5 are used. Test results of 35 beams with rectangular, L-shaped and T-shaped cross-sections tested in pure torsion are presented and discussed. Various configurations of conventional and fibre steel reinforcement are examined. The experimental program includes (i) plain concrete beams (control specimens), (ii) specimens with longitudinal reinforcing bars and (iii) specimens with bars and stirrups. All cases are examined with 0%, 1% and 3% steel fibre volume fractions. The use of steel fibres as the only shear torsional reinforcement is also reported herein, in an attempt to examine the effectiveness of fibres as a potential replacement of stirrups. Test results indicated that fibrous concrete beams exhibited improved overall torsional performance with respect to the corresponding non-fibrous control beams. The addition of steel fibres was essential to the tested beams without or with inadequate conventional steel reinforcement. Fibres prevented the sudden brittle failure of both rectangular and non-rectangular beams and proved to be under some circumstances adequate to provide for enhanced torsional moment capacities, even in the case of full replacement of stirrups with steel fibres.