In lab-on-chip devices, on which complete (bio-)chemical analysis laboratories are miniaturized and integrated, it is essential to manipulate fluids in sub-millimetre channels and sub-microlitre chambers. A special challenge in these small micro-fluidic systems is to create good mixing flows, since it is almost impossible to generate turbulence. We propose an active micro-fluidic mixing concept inspired by nature, namely by micro-organisms that swim through a liquid by oscillating microscopic hairs, cilia, that cover their surface. We have fabricated artificial cilia consisting of electro-statically actuated polymer structures, and have integrated these in a micro-fluidic channel. Flow visualization experiments show that the cilia can generate substantial fluid velocities, up to 0.6 mm s(-1). In addition, very efficient mixing is obtained using specially designed geometrical cilia configurations in a micro-channel. Since the artificial cilia can be actively controlled using electrical signals, they have exciting applications in micro-fluidic devices.

A method is presented where the morphology of screen printed carbon nanotube pastes is modified using an adhesive tape. In this way, the organic matrix material is preferentially removed leaving an optimal emitter surface of sparsely distributed and well-aligned carbon nanotubes. From these emitter surfaces, homogeneous emission was observed with emitter site densities of at least 104 emitters cm−2 and extracted current densities over 500 mA cm−2.

In this study, we present observations of red‐line (630 nm) pulsating auroras using the camera system of Red‐line Emission Geospace Observatory (REGO), during a geomagnetic storm interval. We also develop a time‐dependent model to simulate the 630 nm auroral pulsations in response to modulated precipitation inputs and compare the model outputs with REGO observations. Key results are as follows. (1) Notwithstanding the long radiative timescale of the 630 nm emission, red‐line auroras can still be modulated by pulsating electron precipitations and feature noticeable oscillations, which constitute the red‐line pulsating auroral phenomena. (2) In a majority of cases, the oscillation magnitude of red‐line pulsating auroras is substantially smaller than that of the concurrent pulsating auroras seen on Thermal Emission Imaging System whitelight images (generally dominated by 557.7 nm green‐line emissions). Under certain circumstances, e.g., when the characteristic energy of the precipitation is very high, some of the pulsating auroras may not show discernible imprints on red line. (3) The altitude range contributing most to the red‐line pulsating aurora is systematically lower than that of the steady‐state red‐line aurora, since the slower O(1D) loss rate at higher altitudes tends to suppress the oscillation range of the 630 nm emission rate. (4) We find that some pulsating auroral patches are characterized by enhanced red‐to‐green color ratio during their on time, hinting that the percentage increase of the red‐line auroral component exceeds that of the green‐line auroral component for those patches. We suggest that those special patches might possibly be associated with lower energy (<1 keV) electron precipitations.

This article presents results of a study initiated to characterize the plasma-oxidation process of very thin Al films, a technology commonly used to produce good barrier layers for magnetic spin-tunnel junctions. The behavior of oxygen in the oxidizing Al layer is determined using both quantitative (Rutherford backscattering spectrometry, transmission electron microscopy) and qualitative (x-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry) analytical techniques. We have applied in situ XPS and experimented with O218 to unravel details of the oxidation mechanism. In addition, the influence of the oxygen pressure on the oxidation rate was established, both with and without a plasma being present. From optical emission spectra it is concluded that this pressure has a minor effect on the relative abundance of excited species in the oxygen plasma. When combined, these data constitute the basis of a model that distinguishes several steps in the plasma oxidation of Al. At the start, oxygen penetrates rapidly throughout the total Al layer, followed by a period of increasing oxygen concentration but constant oxide thickness. Finally, the Co underlayer becomes involved in the oxidation process, which marks the deterioration of the spin-tunnel junction. Evidence is obtained that for the thicker initial Al layers the Co electrode layer starts to oxidize before completion of the Al oxidation. This explains why for 0.8-nm-thick Al films the highest tunnel-magnetoresistance effect is obtained for stoichiometric Al2O3, whereas for 1.5 nm Al this occurs while the oxide is still substoichiometric.