Kinetics of photoinduced matter transport driven by intensity and polarization in thin films containing azobenzene

We investigate the kinetics of photoinduced deformation phenomena in azobenzene-containing thin solid films. We show that a light intensity pattern and a light polarization pattern produce two distinct material transport processes whose direction and kinetics can be independently controlled. The kinetics of the intensity-driven deformation scales with the incoming light power while the kinetics of the polarization-driven mass transport scales with the amplitude of the electromagnetic field pattern. We conclude that these two processes are fully independent one from the other and originate from two different microscopic mechanisms

A new experimental procedure for characterizing quantum effects in small magnetic particle systems

A new experimental procedure is discussed, which aims at separating thermal from quantum behavior independently of the energy barrier distribution in small particle systems. Magnetization relaxation data measured between 60 mK and 5 K on a sample of nanoparticles is presented. The comparison between experimental data and numerical calculations shows a clear departure from thermal dynamics for our sample, which was not obvious without using the new procedure presented here.Comment: LaTeX source, 6 pages, 5 PostScript figure

Thin films of calcium phosphate and titanium dioxide by a sol-gel route: a new method for coating medical implants

Titanium is a commonly used biomaterial for dental and orthopaedic applications. To increase its ability to bond with bone, some attempts were made to coat its surface with calcium phosphate (CaP). This paper describes a new type of coating. Instead of a pure CaP layer, a mixing of titanium dioxide (TiO2) and CaP is fabricated and deposited as a coating. These layers are deposited by a sol-gel route on pure titanium substrates using various pre-treatments. The method consists of mixing a solution of tetrabutyl ortho-titanate or a sol of titanium dioxide with a solution of calcium nitrate and phosphorous esters. This composite is deposited on to commercially pure titanium plates, mechanically polished or blasted with pure crystalline aluminum oxide, using the spin-coating technique. These coatings are then fired at 650 or 850°C for various times. The samples are characterized by X-ray diffraction for their crystallinity, X-ray photoelectron spectroscopy for their surface chemical composition and scanning electron microscopy for their topography. Samples treated at 850°C present a well-pronounced crystallinity, and a high chemical purity at the surface. The topography is strongly related to the viscosity of the precursor and the substrate pre-treatment. Possibilities to structure the outermost layer are presented. © 1999 Kluwer Academic Publisher

Non-monotonic field-dependence of the ZFC magnetization peak in some systems of magnetic nanoparticles

We have performed magnetic measurements on a diluted system of gamma-Fe2O3 nanoparticles (~7nm), and on a ferritin sample. In both cases, the ZFC-peak presents a non-monotonic field dependence, as has already been reported in some experiments,and discussed as a possible evidence of resonant tunneling. Within simple assumptions, we derive expressions for the magnetization obtained in the usual ZFC, FC, TRM procedures. We point out that the ZFC-peak position is extremely sensitive to the width of the particle size distribution, and give some numerical estimates of this effect. We propose to combine the FC magnetization with a modified TRM measurement, a procedure which allows a more direct access to the barrier distribution in a field. The typical barrier values which are obtained with this method show a monotonic decrease for increasing fields, as expected from the simple effect of anisotropy barrier lowering, in contrast with the ZFC results. From our measurements on gamma-Fe2O3 particles, we show that the width of the effective barrier distribution is slightly increasing with the field, an effect which is sufficient for causing the observed initial increase of the ZFC-peak temperatures.Comment: LaTeX file 19 pages, 9 postscript figures. To appear in Phys. Rev. B (tentative schedule: Dec.97

Magnetically textured y-Fe2O3 nanoparticles in a silica gel matrix: structural and magnetic properties

International audienceThis paper is devoted to magnetic and structural properties of anisotropic g -Fe2O3 superparamagnetic particles dispersed in a transparent xerogel matrix. The effect of frozen anisotropy axes and magnetic texture, induced by a magnetic field applied during the solidification of the matrix on the in-field magnetization process, is studied by alternating gradient force magnetometry and first and second order magneto-optical effects. The changes of magnetization curves with respect to the ferrofluid solution at the same particle concentration are interpreted on the basis of an existing statistical approach extended to systems with particle size distribution, which has to be taken into account for real samples. A very good agreement between the experiment and theory was achieved for a log-normal distribution of diameters which well resembles that deduced from electron microscopy observations in different imaging modes. This structural analysis states the parameter values used in calculations and confirms the relevance of basic assumptions of the model for the specimens studied. The experimental results and the related theoretical discussion should be of use to understand magnetic properties of other magnetically textured superparamagnetic system

Monitoring the orientation of rare-earth-doped nanorods for flow shear tomography

Rare-earth phosphors exhibit unique luminescence polarization features originating from the anisotropic symmetry of the emitter ion's chemical environment. However, to take advantage of this peculiar property, it is necessary to control and measure the ensemble orientation of the host particles with a high degree of precision. Here, we show a methodology to obtain the photoluminescence polarization of Eu-doped LaPO4 nano rods assembled in an electrically modulated liquid-crystalline phase. We measure Eu3+ emission spectra for the three main optimal configurations ({\sigma}, {\pi} and {\alpha}, depending on the direction of observation and the polarization axes) and use them as a reference for the nano rod orientation analysis. Based on the fact that flowing nano rods tend to orient along the shear strain profile, we use this orientation analysis to measure the local shear rate in a flowing liquid. The potential of this approach is then demonstrated through tomographic imaging of the shear rate distribution in a microfluidic system.Comment: 8 pages, 3 figures + supplementary files for experimental and numerical method