Student Projects

Reducing water loss in immersion lithography (Master)

In collaboration with ASML.

In immersion lithography, semiconductor wafers are contacted with a liquid immersion medium in order to enhance the achievable optical resolution. It is desirable that no residues of the immersion medium remain behind on a processed semiconductor wafer, despite the high wafer-liquid relative velocities on order of 0.5 m/s. unfortunately, any kind of surface irregularity - such as chemical heterogeneities or topographical steps - leads to liquid entrainment and the occurrence of residual droplets. The top and bottom figures show numerical simulations of two substrates moving (upwards) through a liquid meniscus that contain either a chemical defect (top figure) or a circular elevated patch of only 0.5 micron step height (down figure). In both cases undesirable residual droplets are left behind on the substrate.

The goals of this MSc thesis project are 1) to study this entrainment process as a function of speed as well as the ‘strength’ of the irregularity (size, step-height and contact angle difference) and 2) to identify procedures that minimize or prevent liquid entrainment. You will have the opportunity to perform both experiments as well as numerical simulations. 

For more information please contact: prof. Anton A. Darhuber (

Enhancing the critical wafer scan speed in immersion lithography (Master)

In collaboration with ASML.

In immersion lithography, semiconductor wafers are contacted with a liquid immersion medium in order to enhance the achievable optical resolution. It is desirable that no residues of the immersion medium remain behind on a processed semiconductor wafer, despite the high wafer-liquid relative velocities on order of 0.5 m/s. There exists a critical scan speed, above which massive liquid entrainment occurs. The scan speed in a lithography machine must remain below this critical value, which limits the achievable throughput. The goal of this MSc thesis project is to do proof-of-principle experiments to determine whether the critical scan speed can be enhanced 1) by means of a suitable gas flow field in the vicinity of the contact line of the liquid meniscus or 2) by optimizing the flow field inside the liquid. Figure 1 shows a droplet on a moving substrate that is held in place by a vertical needle. If the scan speed is increased, water will stick to the substrate at some point and part of the drop will break away from the needle. The question to be addressed is whether 1) a suitable air flow in the vicinity of the droplet or 2) an optimized supply flow can delay that process, i.e. increase the critical scan speed. Numerical simulations will accompany the experiments. 

For more information please contact: prof. Anton A. Darhuber (

Immersion cooling of electronic devices (Master)

In collaboration with Prodrive Technologies.

High-end switching amplifiers and drives are characterized by high accuracy and low drift. The power performance of these products can reach up to 1MW at voltages up to 1kV. They are used in applications such as high-precision motion control systems or as gradient amplifiers for magnetic resonance imaging (MRI). The critical factor in achieving high accuracy and low drift is heat removal from the system and the thermal stability of the integrated control electronics. Classical solutions use modules that are mounted on an air-cooled heatsink or a liquid-cooled cold plate. The next step is to replace this classical solution by immersion cooling, where the electronics is fully immersed in a non-conductive liquid. In such a system cooling is achieved by phase transition (liquid to gas) and this potentially results in a very high heat transfer capacity and a stable temperature. The goals of this project are:

  • To estimate the maximum possible cooling capacity
  • To characterize the stability of the phase transition process and of the overall temperature 
  • To identify potential problems such as bubble trapping/arrest
  • In-depth analysis of most promising solution concept(s) 

They will be addressed using proof-of-principle experiments and numerical simulations (Comsol).

For more information please contact: prof. Anton A. Darhuber (

Hydrodynamically mediated particle collisions (Bachelor/Master)

Plastic recycling is hampered by the multitude of different chemical composition of plastics in use. Magnetic density separation allows to sort different plastics according to small differences in their mass density. For this purpose, plastic objects are ground into flakes and immersed in a magnetic liquid. Collisions of such particles in the liquid are one of the phenomena limiting the throughput and resolution of magnetic-density separators in plastic recycling technology. To gain an in-depth understanding, experiments will be performed where two well-defined, 3D-printed plastic particles (one heavier than water, one lighter) will be released at the top and the bottom of a transparent water tank. The ensuing collision will be recorded with 2 cameras providing 3D resolution and analyzed using particle-tracking software. The next steps are 1) to study the effect of a background turbulence level present in the tank before releasing the particles, 2) to modulate the effective buoyancy forces by using a salt solution or a strong magnet and a transparent magnetic fluid and 3) using 3 or more particles.

For more information please contact: Rik Dellaert (

Magnetic levitation (Bachelor)

For the magnetic density project we are searching for a Bachelor student who can investigate a start-up about magnetic levitation of plastic particles in a magnetic fluid with strong magnets (200+ kg lifting power).

The project will consist about making a safety protocol, a literature review and experiments. Working with strong magnets could be harmful and therefore the safety protocol is needed. The literature review should point out what is already known about magnetic levitation. In the experiment we will try to duplicate a previous experiment. Where a non-magnetic object floats in a magnetic fluid with the help of strong magnets as can be seen in this youtube video:

For more information please contact: Rik Dellaert (

Fun with ferrofluids (Bachelor)

Liquids that contain suspended magnetic nanoparticles can be manipulated with magnetic fields. The left image shows the instability of a droplet in a vertical magnetic field of increasing strength. The right image shows the actuation of a droplet due to a horizontal magnetic field gradient. The goal of this project is to measure the shape of a droplet as a function of magnetic field, the critical field strength for droplet splitting as well as the achievable droplet propulsion speeds.

For more information please contact: Rik Dellaert (

Rheology and jamming of dense suspension of soft capsules (Bachelor/Master)

Suspensions of hard spheres become jammed when they approach the close-packing ratio, and are not able to flow anymore. For a suspension of soft capsules we can reach filling fractions well above those of hard spheres, and there exists a rich variety in dynamics of the suspension which depends on many different parameters.In this project you will use our in-house developped lattice Boltzmann code to simulate such suspensions under a shearing load, and investigate and characterise the influence of a mixture of shear thinning and shear thickening capsules.

For more information please contact: Maarten Wouters (

Further read:

  1. Rheology of dense suspensions of elastic capsules: normal stresses, yield stress, jamming and confinement effect, {M. Gross, T. Krueger, and F. Varnik}, Soft matter 10, 2014
  2. Motion and deformation of elastic capsules and vesicles in flow, {D. Barthès-Biesel}, An. Rev. Fluid Mech., 2016

Building microscopic structures with evaporating colloidal suspensions (Bachelor)

Evaporation-driven particle self-assembly is an ideal mechanism for constructing micro-and nanostructures at scales where direct manipulation is impossible. This technique has many possible applications in the printing industry, to create new kinds of electronic devices or devices for medical applications. However, predicting and controlling the exact properties of the assembled structures remains a challenge and central goal. In this project you will investigate the cluster formation of spherical and ellipsoidal colloidal particles with state of the art computer simulations. You will work at the boundary between physics, chemistry, material sciences and computer sciences and gain insight into the current state of research in this field.

For more information please contact: Qingguang Xie (

Deformation of thin liquid films by means of deep UV exposure (Bachelor)

Thin liquid films can be driven by local variations in the surface tension. One way to induce such a Marangoni flow is by exposing the liquid film to deep UV irradiation. The irradiation creates reaction products that locally increase the surface tension, which drives the flow of liquid towards the irradiation zone.  In this project you will experimentally study this process, by varying parameters such as the exposure dose and the properties of the liquid film. 

For more information please contact: Bèr Wedershoven (

Dewetting of solid-liquid-solid systems (Bachelor)

Adhesive labels do not stick on wet surfaces. The goal of the project is to study the dynamics of thin liquid films between two soft surfaces being pushed together. Illustration shows dewetting in such a system, a few dry spots growing and leaving trapped liquid where they met. You will use a reflective interference contrast microscope that allows measuring liquid film thickness between 0.1 and 10 um to study the dynamics of this process.

For more information please contact: Maciej Chudak (

Impact of contact line speed on dynamic contact angles (Bachelor)

In the context of immersion lithography (as developed by ASML, Veldhoven), water droplets come in contact with and move along polymeric photoresist surfaces. The so-called advancing and receding contact angles are crucial for the likelihood of droplets to get stuck, i.e. of residual droplets to occur, which is undesirable. In this project you will study the dynamic contact angles for water on photoresist surfaces and determine their velocity dependence.  You will use an experimental setup based on video microscopy and develop a data extraction routine for the dynamic contact angles from the raw video frames e.g. by using Matlab or other image analysis tools.

For more information please contact: Bojia He (

Droplets and Particles in Rotating Flow (Bachelor)

A vortex tube is an apparatus where gas is taken into a strong swirl motion. In order to understand the radial and tangential flow velocities in a swirl flow small tracer droplets are added that can be detected with optical means. The photo shows our Laser Doppler set-up combine with a vortex tube. The question is now: how well do the velocities of these droplets represent the real fluid velocity in the vortex tube. This traineeship offers you to set-up your own theoretical analytical, MATLAB or Mathematica tools to study the phenomenon of droplets in rotating flows.

For more information please contact: Jos Zeegers (

Ranque Hilsch vortex cryocooler (Bachelor)

In a novel study the performance of a cryogenic miniature vortex tube is explored. The idea is to use gas that is precooled to 120 K and investigate how well a vortex tube performs under these conditions. A master student is currently exploring the ins and outs of such a cryogenic vortex tube system. There are two options for a semi-independent traineeship for this subject and those are shown below:

1: Sound speed nozzle and the vortex tube
For a vortex tube the injection of the gas into the swirl chamber is relevant. Currently conical nozzles are implemented and we like to know how well a simple conical nozzle injects compressed gas in comparison with an idealized ISO or ASME nozzle. You will need to assist in the design of a set-up and make measurements of the performance of such nozzles. Of course the analysis and comparison with available literature is of importance.

2: Supersonic Laval nozzles in a vortex tube
As far as we know there is no scientific literature available where supersonic nozzles have been implemented in a vortex tube. We would like to know how a small supersonic nozzle has to be designed. You would need to search in the scattered literature in this field, and in related fields like rocket exhaust nozzle literature. If possible you generate a design and we have it made in the workshop, and if possible be tested in the similar set-up as is discussed under 1.

For more information please contact: Jos Zeegers (