Silvan Schmid | Technical University of Denmark (DTU) (original) (raw)

Papers by Silvan Schmid

Micro- and Nanotechnology Sensors, Systems, and Applications V, 2013

Airborne nanoparticles can cause severe harm when inhaled. Therefore, small and cheap portable ai... more Airborne nanoparticles can cause severe harm when inhaled. Therefore, small and cheap portable airborne nanoparticle monitors are highly demanded by authorities and the nanoparticle producing industry. We propose to use nanomechanical resonators to build the next generation cheap and portable airborne nanoparticle sensors. Recently, nanomechanical mass spectrometry was established. One of the biggest challenges of nanomechanical sensors is the low efficiency of diffusion-based sampling. We developed an inertial-based sampling method that enables the efficient sampling of airborne nanoparticles on a nanomechanical sensor operating directly in air. We measured a sampling rate of over 1000 particles per second, for 28 nm silica nanoparticles with a concentration of 380000 #/cm 3 , collected on a 500 nm wide nanomechanical string resonator. We show that it is possible to reach a saturated sampling regime in which 100% of all nanoparticles are captured that are flowing in the projection of the nanostring. We further show that it is possible to detect single airborne nanoparticles by detecting 50 nm Au particles with a 250 nm wide string resonator. Our resonators are currently operating in the first bending mode. Mass spectrometry of airborne nanoparticles requires the simultaneous operation in the first and second mode, which can be implemented in the transduction scheme of the resonator. The presented results lay the cornerstone for the realization of a portable airborne nanoparticle mass spectrometer. Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/11/2013 Terms of Use: http://spiedl.org/terms Proc. of SPIE Vol. 8725 872525-2 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/11/2013 Terms of Use: http://spiedl.org/terms Proc. of SPIE Vol. 8725 872525-7 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/11/2013 Terms of Use: http://spiedl.org/terms

2013 Conference on Lasers & Electro-Optics Europe & International Quantum Electronics Conference CLEO EUROPE/IQEC, 2013

Polymer coated ceramic cantilevers are highly sensitive to temperature changes, due to the large ... more Polymer coated ceramic cantilevers are highly sensitive to temperature changes, due to the large difference in coefficient of thermal expansion of the two materials. Silicon rich nitride (SRN) cantilevers coated with SU-8 for temperature sensing were fabricated and tested. The devices were coated with SU-8 through spin coating before they were released to obtain bimorph cantilevers. Deflection versus temperature measurements were carried out in ambient and nitrogen atmosphere. In ambient atmosphere, two different effects were observed as the temperature was cycled between 20 and 50°C; (i) shrinkage of SU-8 with increasing temperature, due to evaporation of absorbed moisture and (ii) thermal expansion of SRN and SU-8. Separately, these two effects generate bending in opposite direction. The observed overall bending was seen to be a combination of both. In nitrogen atmosphere, the cantilevers showed a unidirectional deflection versus temperature characteristic. Transverse bending of the cantilevers resulted in an increased rigidity of the cantilevers which could explain the $50% lower temperature response compared to the theoretical values.

ABSTRACT We present an extensive study shedding light on the role of surface and bulk losses in m... more ABSTRACT We present an extensive study shedding light on the role of surface and bulk losses in micromechanical resonators. We fabricate thin silicon nitride membranes of different sizes and we coat them with different thicknesses of metal. We later characterize the 81 lowest out-of-plane flexural vibrational modes to achieve a total of more than 3000 experimental points that allow us to quantify the contribution of surface and volume intrinsic (material related) losses in MEMS resonators. We conclude that the losses in the interface between silicon nitride and aluminum is a very important contributor to the overall energy loss.

ABSTRACT Plasmonic nanostructures (hotspots) are key components e.g. in plasmon-enhanced spectros... more ABSTRACT Plasmonic nanostructures (hotspots) are key components e.g. in plasmon-enhanced spectroscopy, plasmonic solar cells, or as nano heat sources. The characterization of single hotspots is still challenging due to a lack of experimental tools. We present the direct photothermal probing and mapping of single plasmonic nanoslits via the thermally induced detuning of nanomechanical string resonators. A maximum relative frequency detuning of 0.5 % was measured for a single plasmonic nanoslit for a perpendicularly polarized laser with a power of 1350 nW. Finally, we show the photothermal scan over a nanoslit array.

The resonance frequency of strings is highly sensitive to temperature. In this work we have inves... more The resonance frequency of strings is highly sensitive to temperature. In this work we have investigated the applicability of micro string resonators as temperature sensors. The resonance frequency of strings is a function of the tensile stress which is coupled to temperature by the thermal expansion of the string and the frame clamping it. The sensitivity improves when the length and pre-stress are reduced and the difference in thermal expansion, Young's modulus and resonant mode are increased. At low tensile stress, the sensitivity becomes highly dependent on temperature. The investigation was done with silicon rich silicon nitride (SiNx), nickel (Ni) and aluminum (Al) micro strings. Aluminum strings show a relative sensitivity of up to 15 1 %/ºC, which is more than 100 times higher than values reported by other groups for similar devices. Sub-millisecond time constants can be achieved due to the low thermal mass of the strings. A temperature resolution of 2.5×10 -4 ºC has been achieved with silicon nitride strings. The theoretical limit for the temperature resolution of 8×10 -8 ºC has not been reached yet and requires further improvement of the sensor.

Micromechanical photothermal infrared spectroscopy is a promising technique, where absorption-rel... more Micromechanical photothermal infrared spectroscopy is a promising technique, where absorption-related heating is detected by frequency detuning of microstring resonators. We present photothermal infrared spectroscopy with mechanical string resonators providing rapid identification of femtogram-scale airborne samples. Airborne sample material is directly collected on the microstring with an efficient nondiffusion limited sampling method based on inertial impaction. Resonance frequency shifts, proportional to the absorbed heat in the microstring, are recorded as monochromatic IR light is scanned over the mid-infrared range. As a proof-of-concept, we sample and analyze polyvinylpyrrolidone (PVP) and the IR spectrum measured by photothermal spectroscopy matches the reference IR spectrum measured by an FTIR spectrometer. We further identify the organic surface coating of airborne TiO2 nanoparticles with a total mass of 4 pg. With an estimated detection limit of 44 fg, the presented sensor demonstrates a new paradigm in ultrasensitive vibrational spectroscopy for identification of airborne species.

Physical characterization of viscous samples is crucial in chemical, pharma and petroleum industr... more Physical characterization of viscous samples is crucial in chemical, pharma and petroleum industry. For example, in the refining industry of petroleum, water percentage is verified by measuring the density of a sample. In this article we present a suspended microchannel resonator (SMR) which uses 5 pL of a fluid sample and measures its density with a resolution of 0.01 kg/m 3 and a sensitivity of 16 Hz/kg/m 3 . The resonator can also simultaneously measure viscosity of the solutions with an accuracy of 0.025 mPa s. The SMR is part of a system which contains packaging and tubing to deliver samples to the resonator. The system can easily handle multiple viscous fluids to measure their densities and viscosities. The SMR is transparent, facilitating visual inspection of the microchannel content.

Integration of promising technologies that can enhance sensitivity, selectivity, and throughput i... more Integration of promising technologies that can enhance sensitivity, selectivity, and throughput into micro total analysis systems (μTAS) are important in making them useful in precise screening of reaction byproducts in analytical chemistry, cellular biology and pharmaceutical industries. But unfortunately so far a method to precisely determine molecular signatures of reagents is missing in μTAS. We have developed a technique whereby molecular signatures of 50 pL of liquid reagents confined within a bimetallic microchannel cantilever can be obtained. This is achieved using wavelength dependent mechanical bending of the cantilever under infrared (IR) radiation. This technique also allows simultaneous physical characterization of the liquid reagent using variations in resonance frequency. It is useful in lab-on-a-chip devices and has a myriad of applications in drug screening, bioreactor monitoring, and petrochemical analysis.

CLEO: 2014, 2014

ABSTRACT We experimentally demonstrate, for the first time, quadratic measurement of Brownian mec... more ABSTRACT We experimentally demonstrate, for the first time, quadratic measurement of Brownian mechanical motion in an optomechanical system. We use this nonlinear measurement to conditionally prepare classical non-Gaussian states of motion of a micro-mechanical oscillator.

Nanomechanical resonators have an unprecedented mass sensitivity sufficient to detect single mole... more Nanomechanical resonators have an unprecedented mass sensitivity sufficient to detect single molecules, viruses or nanoparticles. The challenge with nanomechanical mass sensors is the direction of nano-sized samples onto the resonator. In this work we present an efficient inertial sampling technique and gravimetric detection of airborne nanoparticles with a nanomechanical resonant filter-fiber. By increasing the nanoparticle momentum the dominant collection mechanism changes from diffusion to more efficient inertial impaction. In doing so we reach a single filter-fiber collection efficiency of 65 6 31% for 28 nm silica nanoparticles. Finally, we show the detection of single 100 nm silver nanoparticles. The presented method is suitable for environmental or security applications where low-cost and portable monitors are demanded. It also constitutes a unique technique for the fundamental study of single filter-fiber behavior. We present the direct measurement of diffusive nanoparticle collection on a single filter-fiber qualitatively confirming Langmuir's model from 1942.

Micro- and Nanotechnology Sensors, Systems, and Applications V, 2013

Airborne nanoparticles can cause severe harm when inhaled. Therefore, small and cheap portable ai... more Airborne nanoparticles can cause severe harm when inhaled. Therefore, small and cheap portable airborne nanoparticle monitors are highly demanded by authorities and the nanoparticle producing industry. We propose to use nanomechanical resonators to build the next generation cheap and portable airborne nanoparticle sensors. Recently, nanomechanical mass spectrometry was established. One of the biggest challenges of nanomechanical sensors is the low efficiency of diffusion-based sampling. We developed an inertial-based sampling method that enables the efficient sampling of airborne nanoparticles on a nanomechanical sensor operating directly in air. We measured a sampling rate of over 1000 particles per second, for 28 nm silica nanoparticles with a concentration of 380000 #/cm 3 , collected on a 500 nm wide nanomechanical string resonator. We show that it is possible to reach a saturated sampling regime in which 100% of all nanoparticles are captured that are flowing in the projection of the nanostring. We further show that it is possible to detect single airborne nanoparticles by detecting 50 nm Au particles with a 250 nm wide string resonator. Our resonators are currently operating in the first bending mode. Mass spectrometry of airborne nanoparticles requires the simultaneous operation in the first and second mode, which can be implemented in the transduction scheme of the resonator. The presented results lay the cornerstone for the realization of a portable airborne nanoparticle mass spectrometer. Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/11/2013 Terms of Use: http://spiedl.org/terms Proc. of SPIE Vol. 8725 872525-2 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/11/2013 Terms of Use: http://spiedl.org/terms Proc. of SPIE Vol. 8725 872525-7 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/11/2013 Terms of Use: http://spiedl.org/terms

2013 Conference on Lasers & Electro-Optics Europe & International Quantum Electronics Conference CLEO EUROPE/IQEC, 2013

Polymer coated ceramic cantilevers are highly sensitive to temperature changes, due to the large ... more Polymer coated ceramic cantilevers are highly sensitive to temperature changes, due to the large difference in coefficient of thermal expansion of the two materials. Silicon rich nitride (SRN) cantilevers coated with SU-8 for temperature sensing were fabricated and tested. The devices were coated with SU-8 through spin coating before they were released to obtain bimorph cantilevers. Deflection versus temperature measurements were carried out in ambient and nitrogen atmosphere. In ambient atmosphere, two different effects were observed as the temperature was cycled between 20 and 50°C; (i) shrinkage of SU-8 with increasing temperature, due to evaporation of absorbed moisture and (ii) thermal expansion of SRN and SU-8. Separately, these two effects generate bending in opposite direction. The observed overall bending was seen to be a combination of both. In nitrogen atmosphere, the cantilevers showed a unidirectional deflection versus temperature characteristic. Transverse bending of the cantilevers resulted in an increased rigidity of the cantilevers which could explain the $50% lower temperature response compared to the theoretical values.

ABSTRACT We present an extensive study shedding light on the role of surface and bulk losses in m... more ABSTRACT We present an extensive study shedding light on the role of surface and bulk losses in micromechanical resonators. We fabricate thin silicon nitride membranes of different sizes and we coat them with different thicknesses of metal. We later characterize the 81 lowest out-of-plane flexural vibrational modes to achieve a total of more than 3000 experimental points that allow us to quantify the contribution of surface and volume intrinsic (material related) losses in MEMS resonators. We conclude that the losses in the interface between silicon nitride and aluminum is a very important contributor to the overall energy loss.

ABSTRACT Plasmonic nanostructures (hotspots) are key components e.g. in plasmon-enhanced spectros... more ABSTRACT Plasmonic nanostructures (hotspots) are key components e.g. in plasmon-enhanced spectroscopy, plasmonic solar cells, or as nano heat sources. The characterization of single hotspots is still challenging due to a lack of experimental tools. We present the direct photothermal probing and mapping of single plasmonic nanoslits via the thermally induced detuning of nanomechanical string resonators. A maximum relative frequency detuning of 0.5 % was measured for a single plasmonic nanoslit for a perpendicularly polarized laser with a power of 1350 nW. Finally, we show the photothermal scan over a nanoslit array.

The resonance frequency of strings is highly sensitive to temperature. In this work we have inves... more The resonance frequency of strings is highly sensitive to temperature. In this work we have investigated the applicability of micro string resonators as temperature sensors. The resonance frequency of strings is a function of the tensile stress which is coupled to temperature by the thermal expansion of the string and the frame clamping it. The sensitivity improves when the length and pre-stress are reduced and the difference in thermal expansion, Young's modulus and resonant mode are increased. At low tensile stress, the sensitivity becomes highly dependent on temperature. The investigation was done with silicon rich silicon nitride (SiNx), nickel (Ni) and aluminum (Al) micro strings. Aluminum strings show a relative sensitivity of up to 15 1 %/ºC, which is more than 100 times higher than values reported by other groups for similar devices. Sub-millisecond time constants can be achieved due to the low thermal mass of the strings. A temperature resolution of 2.5×10 -4 ºC has been achieved with silicon nitride strings. The theoretical limit for the temperature resolution of 8×10 -8 ºC has not been reached yet and requires further improvement of the sensor.

Micromechanical photothermal infrared spectroscopy is a promising technique, where absorption-rel... more Micromechanical photothermal infrared spectroscopy is a promising technique, where absorption-related heating is detected by frequency detuning of microstring resonators. We present photothermal infrared spectroscopy with mechanical string resonators providing rapid identification of femtogram-scale airborne samples. Airborne sample material is directly collected on the microstring with an efficient nondiffusion limited sampling method based on inertial impaction. Resonance frequency shifts, proportional to the absorbed heat in the microstring, are recorded as monochromatic IR light is scanned over the mid-infrared range. As a proof-of-concept, we sample and analyze polyvinylpyrrolidone (PVP) and the IR spectrum measured by photothermal spectroscopy matches the reference IR spectrum measured by an FTIR spectrometer. We further identify the organic surface coating of airborne TiO2 nanoparticles with a total mass of 4 pg. With an estimated detection limit of 44 fg, the presented sensor demonstrates a new paradigm in ultrasensitive vibrational spectroscopy for identification of airborne species.

Physical characterization of viscous samples is crucial in chemical, pharma and petroleum industr... more Physical characterization of viscous samples is crucial in chemical, pharma and petroleum industry. For example, in the refining industry of petroleum, water percentage is verified by measuring the density of a sample. In this article we present a suspended microchannel resonator (SMR) which uses 5 pL of a fluid sample and measures its density with a resolution of 0.01 kg/m 3 and a sensitivity of 16 Hz/kg/m 3 . The resonator can also simultaneously measure viscosity of the solutions with an accuracy of 0.025 mPa s. The SMR is part of a system which contains packaging and tubing to deliver samples to the resonator. The system can easily handle multiple viscous fluids to measure their densities and viscosities. The SMR is transparent, facilitating visual inspection of the microchannel content.

Integration of promising technologies that can enhance sensitivity, selectivity, and throughput i... more Integration of promising technologies that can enhance sensitivity, selectivity, and throughput into micro total analysis systems (μTAS) are important in making them useful in precise screening of reaction byproducts in analytical chemistry, cellular biology and pharmaceutical industries. But unfortunately so far a method to precisely determine molecular signatures of reagents is missing in μTAS. We have developed a technique whereby molecular signatures of 50 pL of liquid reagents confined within a bimetallic microchannel cantilever can be obtained. This is achieved using wavelength dependent mechanical bending of the cantilever under infrared (IR) radiation. This technique also allows simultaneous physical characterization of the liquid reagent using variations in resonance frequency. It is useful in lab-on-a-chip devices and has a myriad of applications in drug screening, bioreactor monitoring, and petrochemical analysis.

CLEO: 2014, 2014

ABSTRACT We experimentally demonstrate, for the first time, quadratic measurement of Brownian mec... more ABSTRACT We experimentally demonstrate, for the first time, quadratic measurement of Brownian mechanical motion in an optomechanical system. We use this nonlinear measurement to conditionally prepare classical non-Gaussian states of motion of a micro-mechanical oscillator.

Nanomechanical resonators have an unprecedented mass sensitivity sufficient to detect single mole... more Nanomechanical resonators have an unprecedented mass sensitivity sufficient to detect single molecules, viruses or nanoparticles. The challenge with nanomechanical mass sensors is the direction of nano-sized samples onto the resonator. In this work we present an efficient inertial sampling technique and gravimetric detection of airborne nanoparticles with a nanomechanical resonant filter-fiber. By increasing the nanoparticle momentum the dominant collection mechanism changes from diffusion to more efficient inertial impaction. In doing so we reach a single filter-fiber collection efficiency of 65 6 31% for 28 nm silica nanoparticles. Finally, we show the detection of single 100 nm silver nanoparticles. The presented method is suitable for environmental or security applications where low-cost and portable monitors are demanded. It also constitutes a unique technique for the fundamental study of single filter-fiber behavior. We present the direct measurement of diffusive nanoparticle collection on a single filter-fiber qualitatively confirming Langmuir's model from 1942.