While etching high aspect ratio trenches into silicon with reactive ion etching (POE) using an SFJO2 chemistry it is observed that the etch rate is depending on the mask opening. This effect is known as POE lag and is caused by the depletion of etching ions and radicals or inhibiting neutrals during their trench passage. In order to decide which source is the main cause, we constructed special "horizontal trenches" where only radicals are controlling the etching. The experiment showed that radicals are not responsible for POE lag. Inhibitor depletion will result in inverse POE lag. This effect is not found during our experimentation which leaves us with ion depletion to explain POE lag. Depletion of ions is caused by ions captured by the sidewalls due to the angular distribution of incoming ions into the trench opening and the deflection of ions in the trench due to electrostatic fields• The analysis given in this paper indicates that the influencing field causes ion deflection, ion depletion, and therefore POE lag in micron-sized Si trenches for low-energetic ions• In all cases, thus independent of the feature size, the angular distribution of incoming ions is thought to have a major contribution to RIE lag at higher pressures. These phenomena will be treated theoretically and simulated using a program, written in c++ under windows, in order to give a quantitative analysis of RIE lag.

The equilibrium shape of droplets on surfaces, functionalized with stripes of alternating wettability, have been investigated using simulations employing a finite element method. Experiments show that a droplet deposited on a surface with relatively narrow hydrophobic stripes compared to the hydrophilic stripes adopts a strongly elongated shape. The aspect ratio, the length of the droplet divided by the width, decreases toward unity when a droplet is deposited on a surface with relatively narrow hydrophilic stripes. The aspect ratio and the contact angle parallel to the stripes show unique scaling behavior as a function of the ratio between the widths of the hydrophobic and hydrophilic stripes. For a small ratio, the contact angle parallel to the stripes is low and the aspect ratio high, while for a large ratio, the contact angle parallel is high and the aspect ratio low. The simulations exhibit similar scaling behavior, both for the aspect ratio of the droplets and for the contact angles in the direction parallel to the stripes. Two liquids with different surface tensions have been investigated both experimentally and in simulations; similarities and differences between the findings are discussed. Generally, three parameters are needed to describe the droplet geometry: (i) the equilibrium contact angles on the hydrophilic and (ii) hydrophobic areas and (iii) the ratio of the widths of these chemically defined stripes. Furthermore, we derive a simple analytical expression that proves to be a good approximation in the quantitative description of the droplet aspect ratio.

The motion of droplets under the influence of lithographically created anisotropic chemically defined patterns is described and discussed. The patterns employed in our experiments consist of stripes of alternating wettability: hydrophobic stripes are created via fluorinated self-assembled monolayers, and for hydrophilic stripes, the SiO(2) substrate is used. The energy gradient required to induce the motion of the droplets is created by varying the relative widths of the stripes in such a way that the fraction of the hydrophilic area increases. The anisotropic patterns create a preferential direction for liquid spreading parallel to the stripes and confine motion to the perpendicular direction, giving rise to markedly higher velocities as compared to nonstructured surface energy gradients. Consequently, the influence of the distinct pattern features on the overall motion as well as suggestions for design improvements from an application point of view are discussed.

An acoustic wave consists of two elements, the acoustic pressure and the acouslic flow. Up to now one has to measure the pressure and calculale the flow to determine the acoustic flow, so it would be convenient to have a sensor Ibat is able to measure acoustic flows. At the University of Twente a novel device has been de ~eloped which fulfils this need. In this p~per a short introduction to Ihe governing priaciples of this dynamic flow sen~or, the fabrication process, the electronics and some of its interesting applications will be presented. This micromachined device measuring acoastie flows is called the microflown or ~-flown.

A reproducible wafer-scale method to obtain 3D nanostructures is investigated. This method, called corner lithography, explores the conformal deposition and the subsequent timed isotropic etching of a thin film in a 3D shaped silicon template. The technique leaves a residue of the thin film in sharp concave corners which can be used as structural material or as an inversion mask in subsequent steps. The potential of corner lithography is studied by fabrication of functional 3D microfluidic components, in particular i) novel tips containing nano-apertures at or near the apex for AFM-based liquid deposition devices, and ii) a novel particle or cell trapping device using an array of nanowire frames. The use of these arrays of nanowire cages for capturing single primary bovine chondrocytes by a droplet seeding method is successfully demonstrated, and changes in phenotype are observed over time, while retaining them in a well-defined pattern and 3D microenvironment in a flat array.