Temperature and concentration dependence of SANS spectra of aqueous solutions of short-chain amphiphiles

The small-angle neutron scattering (SANS) of some aqueous solutions of short-chain amphiphiles (glycols, diglycols, diols) has been measured as a function of concentration and temperature. The analysis of the spectra in terms of the Teubner-Strey phenomelogical formula indicates that, on increasing the concentration of the amphiphile, the structure of all these systems evolves in a similar way, i.e. a transition from disordered structures toward correlated aggregates (microstructures). The transition is depressed by increasing the temperature.     

Shrinkage dynamics of a vesicle in surfactant solutions

We develop a theory for shrinkage dynamics of a vesicle interacting with surfactant molecules. A stepwise shrinkage is formulated in such a way that it consists of two processes. One is a nucleation process of a pore under increasing of the membrane tension. The other is a closure process of the pore due to the line tension of the pore edge after leakage of the inner fluid. We carry out numerical simulations and show that the results agree with experiments semi-quantitatively. An analytical study is also carried out to understand the periodic shrinkage.     

Size and viscoelasticity of spatially confined multilamellar vesicles

We studied viscoelastic properties and scaling behavior of multilamellar vesicles (MLVs) confined between two parallel plates as a function of the shear rate and sample thickness (gap size between parallel plates). The rheological properties are classified into two regimes; the shear-thinning regime at high shear rates and the shear-thickening regime at low shear rates. In the former, the MLV radius results from the mechanical balance between the effective surface tension σ_eff and viscous stress force. The MLV radius is independent of the gap size. σ_eff estimated by van der Linden model is 2.1 ±0.15 ×10^-4 Nm^-1 corresponding to the same value obtained by SANS measurement. Power law exponents for the steady state viscosity and yield stress against pre-shear rate ( , ) well agree with prediction based on the layering of membranes. Therefore, viscoelastic properties in this regime could be modeled by assuming that the dynamics of MLVs are driven by layering of MLV polydomains, which could be accompanied by the viscous dissipation, i.e., the stress relaxation on the MLV, induced by continuous sequence of yields of MLVs. The flow curve is empirically explained by the assumption of a relaxation time for the MLV shape. In the latter, however, scaling laws observed in the shear-thinning regime break down. The MLV radius increases when the gap size is reduced below the threshold value and MLV is no longer formed at very small gap sizes. Different dynamics from the shear-thinning regime seem to dominate the viscoelasticity.     

Hard disk magnetic domain nano-spatial resolution imaging by using a near-field scanning microwave microscope with an AFM probe tip

A near-field scanning microwave microscope (NSMM) incorporating an atomic force microscope (AFM) probe tip was used for the direct imaging of magnetic domains of a hard disk under an external magnetic field. We directly imaged the magnetic domain changes by measuring the change of reflection coefficient S₁₁ of the NSMM at an operating frequency near 4.4 GHz. Comparison was made to the magnetic force microscope (MFM) image. Using the AFM probe tip coupled to the tuning fork distance control system enabled nano-spatial resolution. The NSMM incorporating an AFM tip offers a reliable means for quantitative measurement of magnetic domains with nano-scale resolution and high sensitivity.     

Characterization of the electronic excitations in Alq3 using electron energy-loss spectroscopy

We have studied the electronic excitations of tris-(8-hydroxyquinoline)-aluminium(III) (Alq₃) thin films using electron energy-loss spectroscopy in transmission. This allowed us to derive an effective dielectric function of such films in a large energy range. Moreover, an analysis of the momentum dependence of the lowest lying excitation allowed us to gain information on its localization. We show that this excitation does not disperse, i.e., is localized in the condensed phase. In contrast to many other molecular organic semiconductors, its spectral weight does not follow the behavior of a simple dipole-allowed electronic transition.     

The formation of V–Al–N thin films by reactive ion beam mixing of V/Al interfaces

The reactive ion beam mixing (IBM) of V/Al interfaces by low-energy N₂⁺ ions at room temperature leads to the formation of V–Al–N ternary nitride thin films. The kinetics, growth mechanisms, composition and electronic structure of those films have been studied using X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, Factor Analysis and Monte Carlo TRIDYN simulations. The comparison of experimental results with those obtained from TRIDYN simulations suggests that the chemical reaction with the nitrogen partial pressure and processes driven by residual defects are the rate-controlling mechanisms during the reactive IBM of V/Al interfaces. The kinetics of mixing is characterized by two stages. During the first stage (≤4×10¹⁶ ions/cm²), the formation of vanadium nitride is observed. In the second stage, vanadium nitride is transformed into a V–Al–N ternary nitride due to Al incorporation in the near surface region. Moreover, the V/Al ratio can be varied in a broad range, whereas the nitrogen concentration slightly decreases with increasing the aluminium content of the film.     

Propagation oscillations in the near-field response of traveling surface waves launched by metallic nanoapertures

We discuss the implications of a frequency-dependent complex dielectric function ε(ω) of a metal for the interpretation of scanning near-field optical microscopy (SNOM) measurements in the vicinity of metallic nanoapertures. For subwavelength slits in gold films we observe distinct spatial intensity oscillations in the near-field signal for specific wavelengths in the visible spectrum. These oscillations of the SNOM signal far away from the nanoslit are ascribed to a constructive interference between the propagating surface plasmon (SP) with light scattered parallel to the gold–air interface. In these spatial SNOM-signal oscillations information about the surface plasmon dielectric function is encoded which can be extracted, for example, in surface plasmon interferometry for applications as sensors or waveguides.     

Analysis of bit rate dependence up to 80 Gbit/s of a simple wavelength converter based on XPM in a SOA and a shifted filtering

This paper provides the analysis of wavelength converted pulses obtained with a simple semiconductor optical amplifier (SOA)-based wavelength conversion scheme, which exploits cross phase modulation (XPM) in an SOA in conjunction with shifted filtering. The analysis includes experimental measurements of the back-to-back system performances as well as frequency-resolved optical gating (FROG) characterisations of the wavelength converted pulses. These measurements are implemented at different bit rates up to 80 Gbit/s and for both red and blue-shifted filtering, particularly showing different patterning effect dependencies of red and blue-shifting techniques. This analysis is developed by the addition of a numerical study which corroborates the experimental results. A further understanding of the different performances of red and blue filtering techniques, presented in the literature, can thus be proposed. The placement of the filter to undertake red-shifted filtering (RSF) allows us to achieve very short pulse widths but high bit rate operation is limited by pattern effects. The blue-shifted filtering (BSF) technique shows optimum performance as regards to patterning effects even if the wavelength converted pulses can be larger.     

Emission of positronium in a nanometric PMMA film

Positron beam experiments have been performed for the first time on a self-supporting polymethyl metacrylate (PMMA) film of 310 nm-thick made by spin coating. The positronium (Ps) emission from the PMMA surface is studied as a function of the positron implantation energy by using Doppler profile spectroscopy and Compton-to-peak ratio analysis. When the sample and the Ge-detector are perpendicular to the positron beam, the emission of para-positronium (p-Ps) is detected as a narrow central peak. By rotating the sample 45° with respect to the beam, the emission of p-Ps is detected as a blue-shifted fly-away peak. The bulk Ps fraction, the efficiency for the emission of Ps by picking up an electron from the surface, and the diffusion lengths of positrons (thermal and or epithermal), p-Ps and ortho-positronium (o-Ps) are obtained.