Stephan Keller | Technical University of Denmark (DTU) (original) (raw)
Papers by Stephan Keller
Electroanalysis, 2015
ABSTRACT In this work, we compare pyrolyzed carbon derived from the photoresist SU-8 alone or in ... more ABSTRACT In this work, we compare pyrolyzed carbon derived from the photoresist SU-8 alone or in combination with polystyrene and poly(styrene)-block-poly(dimethylsiloxane) copolymer (PS-b-PDMS), to be used as novel materials for micro- and nanoelectrodes. The pyrolyzed carbon films are evaluated with scanning electron microscopy, thermal gravimetric analysis, X-ray photoelectron spectroscopy, contact angle analysis, and Raman spectroscopy. Furthermore, the standard rate constant for electron transfer is determined from cyclic voltammograms and found to be lower for PS-b-PDMS compared to PS and SU-8 films. This may be related to the lower carbon content of PS-b-PDMS, as well as to its higher microstructural disorder.
Journal of Micromechanics and Microengineering, 2011
A microfluidic flow meter based on cantilever deflection is developed, showing a resolution down ... more A microfluidic flow meter based on cantilever deflection is developed, showing a resolution down to 3 nL min-1 for flows in the microliter range. The cantilevers are fabricated in SU-8 and have integrated holes with dimensions from 5 × 5 to 20 × 20 µm2. The holes make it possible to measure in a liquid environment. With a lithography optimization,
Proceedings of the IEEE International Conference on Micro Electro Mechanical Systems (MEMS), 2011
MICROMECHANICAL SENSORS FOR THE MEASUREMENT OF BIOPOLYMER DEGRADATION SS Keller, L. Gammelgaard, ... more MICROMECHANICAL SENSORS FOR THE MEASUREMENT OF BIOPOLYMER DEGRADATION SS Keller, L. Gammelgaard, MP Jensen, S. Schmid, ZJ Davis ... several months to determine degradation rates under specific conditions [3]. This method is very time consuming and ...
Proceedings of the IEEE International Conference on Micro Electro Mechanical Systems (MEMS), 2011
Microelectronic Engineering, 2010
This work presents a simple and low-cost SU-8 based wafer-level vacuum packaging method which is ... more This work presents a simple and low-cost SU-8 based wafer-level vacuum packaging method which is CMOS and MEMS compatible. Different approaches have been investigated by taking advantage of the properties of SU-8, such as chemical resistance, optical transparence, mechanical reliability and versatility. A novel technique of wafer level adhesive bonding, which uses SU-8 as structural and adhesive material, has been
Reports on Progress in Physics, 2011
Physical Chemistry Chemical Physics, 2010
We present a method to monitor the diffusion of liquid molecules in polymers. A microdrop of wate... more We present a method to monitor the diffusion of liquid molecules in polymers. A microdrop of water is deposited by a piezoelectric drop generator onto the upper surface of a cantilever made of SU-8 based photoresist. In response, the cantilever bends in the opposite direction. We find that this bending is mainly caused by the diffusion of water into the cantilever and the consequent swelling of SU-8. Using a one-dimensional diffusion model and assuming a simple swelling law, we qualitatively model the bending of the cantilever during in and out diffusion of water in SU-8. With a more sophisticated finite element model the diffusion coefficient of water in the SU-8 polymer can be determined quantitatively from the dynamics of cantilever bending.
Microelectronic Engineering, 2012
Microelectronic Engineering, 2011
The influence of various parameters on the spray-coating of thin films of poly(l-lactide) (PLLA) ... more The influence of various parameters on the spray-coating of thin films of poly(l-lactide) (PLLA) was investigated. The optimized processing conditions were used for deposition of the biodegradable polymer on arrays of SU-8 microcantilevers. The resonance frequency of the cantilevers before and after spray-coating was measured which allowed the characterization of the mechanical properties of the coatings. Initial experiments on enzymatic
Microelectronic Engineering, 2011
Microelectronic Engineering, 2011
Microelectronic Engineering, 2011
Langmuir, 2013
In this work we have performed a detailed study of the influence of various parameters on spray c... more In this work we have performed a detailed study of the influence of various parameters on spray coating of polymer films. Our aim is to produce polymer films of uniform thickness (500 nm to 1 μm) and low roughness compared to the film thickness. The coatings are characterized with respect to thickness, roughness (profilometer), and morphology (optical microscopy). Polyvinylpyrrolidone (PVP) is used to do a full factorial design of experiments with selected process parameters such as temperature, distance between spray nozzle and substrate, and speed of the spray nozzle. A mathematical model is developed for statistical analysis which identifies the distance between nozzle and substrate as the most significant parameter. Depending on the drying of the sprayed droplets on the substrate, we define two broad regimes, "dry" and "wet". The optimum condition of spraying lies in a narrow window between these two regimes, where we obtain a film of desired quality. Both with increasing nozzle-substrate distance and temperature, the deposition moves from a wet state to a dry regime. Similar results are also achieved for solvents with low boiling points. Finally, we study film formation during spray coating with poly (D,L-lactide) (PDLLA). The results confirm the processing knowledge obtained with PVP and indicate that the observed trends are identical for spraying of other polymer films.
Electroanalysis, 2015
ABSTRACT In this work, we compare pyrolyzed carbon derived from the photoresist SU-8 alone or in ... more ABSTRACT In this work, we compare pyrolyzed carbon derived from the photoresist SU-8 alone or in combination with polystyrene and poly(styrene)-block-poly(dimethylsiloxane) copolymer (PS-b-PDMS), to be used as novel materials for micro- and nanoelectrodes. The pyrolyzed carbon films are evaluated with scanning electron microscopy, thermal gravimetric analysis, X-ray photoelectron spectroscopy, contact angle analysis, and Raman spectroscopy. Furthermore, the standard rate constant for electron transfer is determined from cyclic voltammograms and found to be lower for PS-b-PDMS compared to PS and SU-8 films. This may be related to the lower carbon content of PS-b-PDMS, as well as to its higher microstructural disorder.
Journal of Micromechanics and Microengineering, 2011
A microfluidic flow meter based on cantilever deflection is developed, showing a resolution down ... more A microfluidic flow meter based on cantilever deflection is developed, showing a resolution down to 3 nL min-1 for flows in the microliter range. The cantilevers are fabricated in SU-8 and have integrated holes with dimensions from 5 × 5 to 20 × 20 µm2. The holes make it possible to measure in a liquid environment. With a lithography optimization,
Proceedings of the IEEE International Conference on Micro Electro Mechanical Systems (MEMS), 2011
MICROMECHANICAL SENSORS FOR THE MEASUREMENT OF BIOPOLYMER DEGRADATION SS Keller, L. Gammelgaard, ... more MICROMECHANICAL SENSORS FOR THE MEASUREMENT OF BIOPOLYMER DEGRADATION SS Keller, L. Gammelgaard, MP Jensen, S. Schmid, ZJ Davis ... several months to determine degradation rates under specific conditions [3]. This method is very time consuming and ...
Proceedings of the IEEE International Conference on Micro Electro Mechanical Systems (MEMS), 2011
Microelectronic Engineering, 2010
This work presents a simple and low-cost SU-8 based wafer-level vacuum packaging method which is ... more This work presents a simple and low-cost SU-8 based wafer-level vacuum packaging method which is CMOS and MEMS compatible. Different approaches have been investigated by taking advantage of the properties of SU-8, such as chemical resistance, optical transparence, mechanical reliability and versatility. A novel technique of wafer level adhesive bonding, which uses SU-8 as structural and adhesive material, has been
Reports on Progress in Physics, 2011
Physical Chemistry Chemical Physics, 2010
We present a method to monitor the diffusion of liquid molecules in polymers. A microdrop of wate... more We present a method to monitor the diffusion of liquid molecules in polymers. A microdrop of water is deposited by a piezoelectric drop generator onto the upper surface of a cantilever made of SU-8 based photoresist. In response, the cantilever bends in the opposite direction. We find that this bending is mainly caused by the diffusion of water into the cantilever and the consequent swelling of SU-8. Using a one-dimensional diffusion model and assuming a simple swelling law, we qualitatively model the bending of the cantilever during in and out diffusion of water in SU-8. With a more sophisticated finite element model the diffusion coefficient of water in the SU-8 polymer can be determined quantitatively from the dynamics of cantilever bending.
Microelectronic Engineering, 2012
Microelectronic Engineering, 2011
The influence of various parameters on the spray-coating of thin films of poly(l-lactide) (PLLA) ... more The influence of various parameters on the spray-coating of thin films of poly(l-lactide) (PLLA) was investigated. The optimized processing conditions were used for deposition of the biodegradable polymer on arrays of SU-8 microcantilevers. The resonance frequency of the cantilevers before and after spray-coating was measured which allowed the characterization of the mechanical properties of the coatings. Initial experiments on enzymatic
Microelectronic Engineering, 2011
Microelectronic Engineering, 2011
Microelectronic Engineering, 2011
Langmuir, 2013
In this work we have performed a detailed study of the influence of various parameters on spray c... more In this work we have performed a detailed study of the influence of various parameters on spray coating of polymer films. Our aim is to produce polymer films of uniform thickness (500 nm to 1 μm) and low roughness compared to the film thickness. The coatings are characterized with respect to thickness, roughness (profilometer), and morphology (optical microscopy). Polyvinylpyrrolidone (PVP) is used to do a full factorial design of experiments with selected process parameters such as temperature, distance between spray nozzle and substrate, and speed of the spray nozzle. A mathematical model is developed for statistical analysis which identifies the distance between nozzle and substrate as the most significant parameter. Depending on the drying of the sprayed droplets on the substrate, we define two broad regimes, "dry" and "wet". The optimum condition of spraying lies in a narrow window between these two regimes, where we obtain a film of desired quality. Both with increasing nozzle-substrate distance and temperature, the deposition moves from a wet state to a dry regime. Similar results are also achieved for solvents with low boiling points. Finally, we study film formation during spray coating with poly (D,L-lactide) (PDLLA). The results confirm the processing knowledge obtained with PVP and indicate that the observed trends are identical for spraying of other polymer films.