Dynamics of driven three-dimensional thin films: from hdrophilic to superhydrophobic substrates

We study the forced displacement of a thin film of fluid in contact with vertical and inclined substrates of different wetting properties, that range from hydrophilic to hydrophobic, using the lattice-Boltzmann method. We study the stability and pattern formation of the contact line in the hydrophilic and superhydrophobic regimes, which correspond to wedge-shaped and nose-shaped fronts, respectively. We find that contact lines are considerably more stable for hydrophilic substrates and small inclination angles. The qualitative behavior of the front in the linear regime remains independent of the wetting properties of the substrate as a single dispersion relation describes the stability of both wedges and noses. Nonlinear patterns show a clear dependence on wetting properties and substrate inclination angle. The effect is quantified in terms of the pattern growth rate, which vanishes for the sawtooth pattern and is finite for the finger pattern. Sawtooth shaped patterns are observed for hydrophilic substrates and low inclination angles, while finger-shaped patterns arise for hydrophobic substrates and large inclination angles. Finger dynamics show a transient in which neighboring fingers interact, followed by a steady state where each finger grows independently.

Magnetic properties of amorphous Fe-Si compositionally modulated thin films

The present paper reports on a magnetometric study of Fe‐Si compositionally modulated thin films. The low‐temperature dependence of the magnetization exhibit Bloch's T3/2 dependence with a minor T5/2 correction term. The spin‐wave stiffness constant deduced from the temperature coefficient depends on the characteristic modulation length and its values are much lower that in glassy alloys.

Structural disorder in two-dimensional random magnets: Very thin films of rare earths and transition metals

The low-temperature isothermal magnetization curves, M(H), of SmCo4 and Fe3Tb thin films are studied according to the two-dimensional correlated spin-glass model of Chudnovsky. We have calculated the magnetization law in approach to saturation and shown that the M(H) data fit well the theory at high and low fields. In our fit procedure we have used three different correlation functions. The Gaussian decay correlation function fits well the experimental data for both samples.

Evidence of extended orientational order in amorphous Fe/Sm thin films

Amorphous thin films of Fe/Sm, prepared by evaporation methods, have been magnetically characterized and the results were interpreted in terms of the random magnets theory. The samples behave as 2D and 3D random magnets depending on the total thickness of the film. From our data the existence of orientational order, which greatly influences the magnetic behavior of the films, is also clear.

Competing tunneling and capacitive paths in Co-ZrO2 granular thin films

The ac electrical response is studied in thin films composed of well-defined nanometric Co particles embedded in an insulating ZrO2 matrix which tends to coat them, preventing the formation of aggregates. In the dielectric regime, ac transport originates from the competition between interparticle capacitive Cp and tunneling Rt channels, the latter being thermally assisted. This competition yields an absorption phenomenon at a characteristic frequency 1/(RtCp), which is observed in the range 1010 000 Hz. In this way, the effective ac properties mimic the universal response of disordered dielectric materials. Temperature and frequency determine the complexity and nature of the ac electrical paths, which have been successfully modeled by an Rt-Cp network.

Mossbauer and magnetization studies of amorphous NdFeB compositionally modulated thin films

Several NdFeB compositionally modulated thin films are studied by using both conversion electron Mossbauer spectra and SQUID (superconducting quantum-interference-device) magnetometry. Both the hyperfine fields and the easy magnetization magnitude are not correlated with the modulation characteristic length (lambda) while the magnetization perpendicular to the thin-film plane decreases as lambda increases. The spectra were recorded at room temperature being the gamma rays perpendicular to the substrate plane. The magnetization measurements were recorded by using a SHE SQUID magnetometer in applied magnetic fields up to 5.5 T and in the temperature range between 1.8 and 30 K.

Mossbauer studies of amorphous FeSi compositionally modulated thin films

Conversion electron Mossbauer spectra of composition modulated FeSi thin films have been analysed within the framework of a quasi shape independent model in which the distribution function for the hyperfine fields is assumed to be given by a binomial distribution. Both the hyperfine field and the hyperfine field distribution depend on the modulation characteristic length.

Influence of ohmic heating on the flow field in thin-layer electrodeposition

In thin-layer electrodeposition the dissipated electrical energy leads to a substantial heating of the ion solution. We measured the resulting temperature field by means of an infrared camera. The properties of the temperature field correspond closely with the development of the concentration field. In particular, we find that the thermal gradients at the electrodes act similar to a weak additional driving force to the convection rolls driven by concentration gradients.

Nanomechanical properties of molecular organic thin films

Using atomic force microscopy we have studied the nanomechanical response to nanoindentations of surfaces of highly oriented molecular organic thin films (thickness¿1000¿nm). The Young¿s modulus E can be estimated from the elastic deformation using Hertzian mechanics. For the quasi-one-dimensional metal tetrathiafulvalene tetracyanoquinodimethane E~20¿GPa and for the ¿ phase of the p-nitrophenyl nitronyl nitroxide radical E~2GPa. Above a few GPa, the surfaces deform plastically as evidenced by discrete discontinuities in the indentation curves associated to molecular layers being expelled by the penetrating tip.

Fingerlike aggregates in thin-layer electrodeposition

Electrodeposition experiments conducted in a thin-layer horizontal cell containing a nonbinary aqueous electrolyte prepared with cupric sulfate and sodium sulfate gave rise to fingerlike deposits, a novel and unexpected growth mode in this context. Both the leading instability from which fingers emerge and some distinctive features of their steady evolution are interpreted in terms of a simple model based on the existing theory of fingering in fluids.

Structural and electrical properties of Fe-doped TiO2 thin films

The present study discusses the effect of iron doping in TiO2 thin films deposited by rf sputtering. Iron doping induces a structural transformation from anatase to rutile and electrical measurements indicate that iron acts as an acceptor impurity. Thermoelectric power measurement shows a transition between n-type and p-type electrical conduction for an iron concentration around 0.13 at.%. The highest p-type conductivity at room temperature achieved by iron doping was 10(-6) S m(-1).

Linear relations between writhe and minimal crossing number in Conway families of ideal knots and links

We showed earlier how to predict the writhe of any rational knot or link in its ideal geometric configuration, or equivalently the average of the 3D writhe over statistical ensembles of random configurations of a given knot or link (Cerf and Stasiak 2000 Proc. Natl Acad. Sci. USA 97 3795). There is no general relation between the minimal crossing number of a knot and the writhe of its ideal geometric configuration. However, within individual families of knots linear relations between minimal crossing number and writhe were observed (Katritch et al 1996 Nature 384 142). Here we present a method that allows us to express the writhe as a linear function of the minimal crossing number within Conway families of knots and links in their ideal configuration. The slope of the lines and the shift between any two lines with the same

Performance of a Nongrouted Thin Bonded PCC Overlay, HR-291, 1992

The use of a thin bonded concrete overlay atop an older surface has been widely incorporated for pavement rehabilitation in Iowa since the early 70's. Two test sections were constructed in 1985 on county road T61 on the Monroe-Wapello County line without the use of grout as a bonding agent to determine if adequate bond could be achieved and structural capacity uncompromised. Both test sections have performed well with one section having higher bond strengths, lower roughness values, higher structural capacity, and less debonding at the joints than the other section. Overall, both ungrouted sections have performed well under substantial truck traffic with minimal surface distress. More attention should be given, however, to rectifying apparent debonding at the joints when no grout is used as a bonding agent.