Condensed Matter Sciences (CMS)
Research in this group covers the following areas:
The physics of metal-hydride switchable mirrors.
Recently we discovered that palladium protected metal-hydride films of yttrium, lanthanum and Rare-Earth metals (RE) can be rapidly switched between a shiny metal and a transparent large gap semiconductor. In Mg- RE- and Mg-TM-hydrides even transitions to a highly absorbing state can be induced. We study the physical mechanisms responsible for the metal-insulator transition, the optical and electrical properties and the diffusion of hydrogen waves in switchable mirrors.
Light-weight metal-hydride storage materials.
Metal-hydrides absorb hydrogen to a higher density than liquid hydrogen. Metal-hydrides, however are considered too heavy for implementation in cars. Complex metal-hydrides could be "the" solution. Our search for new complex metal-hydride storage materials uses thin film sputter deposition in a combinatorial approach. The catalytic hydrogen uptake is investigated by Scanning Tunneling/ Spectroscopy/ Microscopy. In addition, structural/chemical modeling is developed to facilitate the prediction of new hydrogen storage compounds.
Smart coatings based on metal-hydrides.
The switchable metal-hydrides may have applications as large area displays, smart windows in buildings,variable reflectance coatings and active layer in fiber optic hydrogen sensors. Therefore, we study the fundamental issues involved in making such devices. This involves the deposition (by sputtering and pulsed laser deposition) and characterisation (High-resolution XRD, RBS, AFM/STM) of relevant thin films. In collaboration with ECN we develop a demonstrator variable reflectance device that is to be used within a hybrid photovoltaic/solar collector device.
Non-linear dynamics and pattern formation in superconductors.
Patterns of currents and magnetic flux in superconductors are investigated by means of high-resolution magneto-optics. Superconductors are an attractive model-system to study pattern formation because the experimental time scales can be made relatively short. We study frustration phenomena and front instabilities in type-I superconductors and roughening of interfaces in type-II superconductors. We also study the patterns induced by the non-linear current-voltage characteristics in inclined-field configurations and in nano-patterned thin films.
Experimental investigation of self-organized criticality.
Self-organized criticality (SOC) occurs in many systems in nature ranging from earthquakes to the extinction of species in biology. We study SOC in superconductors by means of high-resolution magneto-optics and in a rice-pile of one square meter floor area using a unique camera system to accurately measure the shape of the pile. Questions of main interest are whether the many exponent scaling relations that were found to hold analytically or in numerical simulations, can also be observed for a real physical system and whether it is possible to keep a system away from SOC behaviour such that e.g. devastating avalanches can be prevented. For our rice pile, both questions seem to have a positive answer.
Casimir effect: Fundamental problems and applications to micro- and nanotechnology.
The Casimir effect is the attraction between electrically neutral objects as a result of quantum fluctuations of the electromagnetic field. The aim of our group is to investigate the Casimir effect under suitably engineered conditions. These studies offer the opportunity to emphasize some tantalizing aspects of this interaction mechanism (e.g., non-additivity, sign-reversal, etc) and to explore the possibility to exploit the Casimir force for the development of conceptually new micro- and nanofabricated devices.
Fiber-top MicroElectroMechanical Systems.
Fiber-top sensors (VU patent pending) are plug-and-play monolithic micro-machined devices for multipurpose applications. They rely on the fabrication of mechanical structures on the edge of an optical fiber. In our group, we design new devices, investigate alternative fabrication techniques, and explore novel applications that span from atomic force microscopy in hostile environments to the development of medical instruments for in vivo chemical, biological, or physical measurements.
