In this work, manipulating width and equilibrium position of fluorescent microparticles in spiral microchannel fractionation devices by embedding microchambers along the last turn of a spiral is reported.

A pressure resistant and optically accessible deterministic lateral displacement (DLD) device was designed and microfabricated from silicon and glass for high-throughput fractionation of particles between 3.0 and 7.0 µm comprising array segments of varying tilt angles with a post size of 5 µm. The design was supported by computational fluid dynamic (CFD) simulations using OpenFOAM software. Simulations indicated a change in the critical particle diameter for fractionation at higher Reynolds numbers. This was experimentally confirmed by microparticle image velocimetry (µPIV) in the DLD device with tracer particles of 0.86 µm. At Reynolds numbers above 8 an asymmetric flow field pattern between posts could be observed. Furthermore, the new DLD device allowed successful fractionation of 2 µm and 5 µm fluorescent polystyrene particles at Re = 0.5–25.

Deterministic lateral displacement (DLD) microsystems are suitable for the size fractionation of particle suspensions in the size range of 0.1 to 10 µm. To be able to fractionate real particles beyond a laboratory scale, these systems have to be designed for higher throughputs. High flow resistances and increasing the clogging of the systems impose substantial challenges for industrial operation. Simulative parameter studies are suitable for improving the design of the systems; for example, the position and shape of the posts. A high-resolution, two-way coupled 6-DOF CFD-DEM approach was used to study the flow and particle behavior of different post shapes (circular and triangular) and post sizes at different Reynolds numbers. The results were compared with the classical first streamline width theory. It was shown that the streamline theory does not account for all effects responsible for the separation. Furthermore, a shift in the critical particle diameter to smaller values could be obtained when increasing the Reynolds number and also when using triangular posts with reduced post sizes compared to the post spacing. These findings can help to improve the efficiency of the systems as the post spacing could be extended, thus reducing the flow resistance and the probability of clogging.

This work presents a method for measuring the electrical resistivity, carrier concentration and Seebeck coefficient of electroplated thermoelectric layers in the presence of electrically conducting seed layers, and suitable for in-line characterization. The method is based on measuring the initial properties of the seed layer, and of the combination of seed layer and deposited film after the electroplating process. Using only these values and the individual layer thicknesses, the properties of the deposited film can then be calculated based on a theoretical model of the two-layer system. Additionally, it is possible to use seed layers with different geometry and size when compared to the deposited film. The model is experimentally verified by a full characterization of electroplated Bi 2 Te 3 on Pt seed layers, with varying thickness for both layers. Reference values for the properties of the deposited films are obtained by removing the Bi 2 Te 3 layers from the seed layers and their subsequent characterization. By using the proposed method, the thermoelectric properties of the deposited film can be determined with an accuracy of 15% or better as long as the sheet resistance ratio of deposited and seed layer is smaller than 0.4. Electrodeposition of thermoelectric thin film materials is an attractive synthetic approach, offering the advantages of a relatively simple setup, low associated costs, efficient use of material and high growth rates. 1 The deposited materials are typically evaluated with regards to their thermoelectric power factor PF, which includes the Seebeck coefficient S of the material and its electrical resistivity ρ:Additionally, measurements of the carrier concentration are a useful tool for the further optimization of the thermoelectric materials. 2 The measurement of these properties of electroplated films presents a fundamental challenge, as the electroplating process necessitates the existence of an electrically conductive seed layer underneath the deposited film.The most common approach to avoid this problem is the removal of the deposited film from the seed layer after the electroplating process. 3-6 This allows the direct measurement of the thermoelectric properties without the interference of the seed layer. However, the disadvantage of this method is that the deposited material is potentially damaged during the release process by introducing cracks or other defects. Furthermore, this requires a rather poor adhesion between the deposited film and the seed layer, which is the opposite of the typical requirement for the fabrication of thermoelectric devices. Another possible approach is the deposition of thin films on seed layers which are composed of similar or ideally identical materials, and will therefore have no influence on the measured properties. 7,8 While these methods generally yield good results and are useful in a research environment, they are not necessarily applicable for actual fabrication processes, or any environment where high throughput, inline monitoring or non-destruc...