Scientific Internship: Switchable friction at randomly rough multi-asperity interfaces through capillary condensation?
In this project, you will investigate the interplay between nanometric water films and mechanical contacts.
The research field of tribology, devoted to contact formation, friction and wear phenomena down to the atomic scale, is of direct and pressing relevance to the manufacture of semiconductor devices. Friction-induced stresses and deformations on the scale of only a few atomic spacings are starting to challenge the future of nanolithography technology, limiting the achievable feature size in semiconductor chips.
In this project, you will investigate the interplay between nanometric water films and mechanical contacts. Under ambient conditions, almost all surfaces are covered by a thin water layer. Silicon oxide for instance is covered by 0-3 nm of water as the relative humidity of the surrounding air is varied from 0-100%. Whenever two surfaces that are covered by such water layers – for instance an AFM tip and a silicon oxide substrate – approach to within a few nanometers, a capillary bridge can form around the contact point and contribute to the contact force, and thus to the friction force. The attractive force exerted by a single capillary bridge is well understood and roughly equal to the product of its circumference and the water surface tension. At an interface with roughness, the total contact circumference over which capillary effects can contribute to the effective normal force – and thus the friction – is not trivial. The larger this circumference, however, the larger the contrast in friction measured in dry or humid environments. In order to establish friction that can be switched from low to high and vice versa, by externally changing the humidity, we therefore need to understand the roughness- and humidity-dependent capillary force.
In this project we will perform rough sphere-on-smooth substrate friction experiments, conducted in a controlled humidity environment. We will show that friction can be switched from low to high and vice versa by changing the humidity, and compare the friction measurements to multi-asperity contact models that account for capillary effects.
Recommended articles for further reading on this subject:
- B. Asay and S. H. Kim. Evolution of the adsorbed water layer structure on silicon oxide at room temperature. J. Phys. Chem. B 109, 16760-16763 (2005).
- Bartošík, L. Kormoš, L. Flajšman et al. Nanometer-sized water bridge and pull-off force in AFM at different relative humidities: Reproducibility measurement and model based on surface tension change. J. Phys. Chem. B 121, 610−619 (2017).
- Bazrafshan, M. B. de Rooij and D. J. Schipper. Adhesive force model at a rough interface in the presence of thin water films: The role of relative humidity. Int. J. Mech. Sci. 140, 471–485 (2018).
- J. Vogel and P. H. Steen. Capillarity-based switchable adhesion. Proc. Natl. Acad. Sci. USA 107, 3377–3381 (2010).
- N. J. Persson. Capillary adhesion between elastic solids with randomly rough surfaces. J. Phys Condens. Matter 20, 315007 (2008).
About the group
At the Advanced Research Center for Nanolithography (ARCNL) we carry out exciting fundamental physics research at the highest possible level with relevance to key technologies in nanolithography. We contribute to the production of ever smarter and smaller electronics, while at the same time pushing the boundaries of our fundamental insight into the workings of nature.
You will be embedded in the Contact Dynamics team at ARCNL but will also be closely associated with the University of Amsterdam and ASML, the world leading manufacturer of high tech lithography machines for chip making.
You have or will soon have a Bachelors degree in physics or a related field and participate in a Master study during the entire internship duration. The internship must be a mandatory part of your curriculum. You have a nationality of an EU-member state and/or you are a student at a Netherlands University. Please note: as from 01-01-2021 the UK is no longer an EU-member state. You must be available for at least 5 months.
Terms of employment
At the start of the traineeship your trainee plan will be set out, in consultation with your ARCNL supervisor, including a small allowance.
Prof. Steve Franklin
Group leader Contact Dynamics
Phone: +31 (0)20-754 7100
Postdoc Contact Dynamics
Phone: +31 (0)20-754 7100
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