arXiv subjects

Silvan Schmid

Publications and source records attributed to Silvan Schmid.

At least 37 records · Page 2Linked to original sources

arXiv2023

Towards practical mass spectrometry with nanomechanical pillar resonators by surface acoustic wave transduction

Nanoelectromechanical systems (NEMS) have proven outstanding performance in the detection of small masses down to single proton sensitivity. To obtain a high enough throughput for the application in practical mass spectrometry, NEMS resonators have to be arranged in two-dimensional (2D) arrays. However, all state-of-the-art electromechanical transduction methods rely on electrical lines placed close to the mechanical resonators, which drastically restricts the density of 2D resonator arrays. An exception is the transduction by surface acoustic waves (SAWs), which has so far only been shown for the transduction of single nanomechanical pillar resonators. Here, we demonstrate the transduction of pillar pairs by surface acoustic waves. The pillars have a diameter of 700 nm and show a mass responsivity of -588$\pm$98 ng$^{-1}$. The distances between the pillar pairs are 70 nm and 14.3 $μ$m. SAW transduction enabled us to measure both pillars of each pair with electrical lines no closer than 300 $μ$m, illustrating the potential of SAWs to transduce dense arrays of pillar resonators, a crucial step towards practical mass spectrometry with NEMS.

physics.app-ph↗

arXiv2023

Transduction of single nanomechanical pillar resonators by scattering of surface acoustic waves

One of the challenges of nanoelectromechanical systems (NEMS) is the effective transduction of the tiny resonators. Vertical structures, such as nanomechanical pillar resonators, which are exploited in a wide range of fields, such as optomechanics, acoustic metamaterials, and nanomechanical sensing, are particularly challenging to transduce. Existing electromechanical transduction methods are ill-suited as they complicate the pillars' fabrication process, put constraints on the pillars' material, and do not enable a transduction of freestanding pillars. Here, we present an electromechanical transduction method for single nanomechanical pillar resonators based on surface acoustic waves (SAWs). We demonstrate the transduction of freestanding nanomechanical platinum-carbon pillars in the first-order bending and compression mode. Since the principle of the transduction method is based on resonant scattering of a SAW by a nanomechanical resonator, our transduction method is independent of the pillar's material and not limited to pillar-shaped geometries. It represents a general method to transduce vertical mechanical resonators with nanoscale lateral dimensions.

physics.app-ph↗

arXiv2023

Nanomechanical absorption spectroscopy of 2D materials with femtowatt sensitivity

Nanomechanical spectroscopy (NMS) is a recently developed approach to determine optical absorption spectra of nanoscale materials via mechanical measurements. It is based on measuring changes in the resonance frequency of a membrane resonator vs. the photon energy of incoming light. This method is a direct measurement of absorption, which has practical advantages compared to common optical spectroscopy approaches. In the case of two-dimensional (2D) materials, NMS overcomes limitations inherent to conventional optical methods, such as the complications associated with measurements at high magnetic fields and low temperatures. In this work, we develop a protocol for NMS of 2D materials that yields two orders of magnitude improved sensitivity compared to previous approaches, while being simpler to use. To this end, we use electrical sample actuation, which simplifies the experiment and provides a reliable calibration for greater accuracy. Additionally, the use of low-stress silicon nitride membranes as our substrate reduces the noise-equivalent power to $NEP = 890 fW/\sqrt{Hz}$, comparable to commercial semiconductor photodetectors. We use our approach to spectroscopically characterize a two-dimensional transition metal dichalcogenide (WS$_2$), a layered magnetic semiconductor (CrPS$_4$), and a plasmonic supercrystal consisting of gold nanoparticles.

cond-mat.mes-hall↗

arXiv2022

Thermal IR detection with nanoelectromechanical silicon nitride trampoline resonators

Nanoelectromechanical (NEMS) resonators are promising uncooled thermal infrared (IR) detectors to overcome existing sensitivity limits. Here, we investigated nanoelectromechanical trampoline resonators made of silicon nitride (SiN) as thermal IR detectors. Trampolines have an enhanced responsivity of more than two orders of magnitude compared to state-of-the-art SiN drums. The characterized NEMS trampoline IR detectors yield a sensitivity in terms of noise equivalent power (NEP) of 7pW/$\sqrt{Hz}$ and a thermal response time as low as 4 ms. The detector area features an impedance-matched metal thin-film absorber with a spectrally flat absorption of 50% over the entire mid-IR spectral range from 1$μm$ to 25$μm$.

physics.app-ph↗

arXiv2021

Design Considerations of Gold Nanoantenna Dimers for Plasmomechanical Transduction

Internal optical forces emerging from plasmonic interactions in gold nanodisc, nanocube and nanobar dimers were studied by finite element method. A direct correlation between the electric-field enhancement and optical forces was found by observing largest magnitude of optical forces in nanocube dimers. Moreover, further amplification of optical forces was achieved by employing optical power of the excitation source. The strength of optical forces was observed to be governed by the magnitude of polarisation density on the nanoparticles, which can be varied by modifying the nanoparticle geometry and source wavelength. This study allows us to recognise that nanoparticle geometry along with the inter-dimer distance are the most prominent design considerations for optimising optical forces in plasmonic dimers. The findings facilitate the realisation of all optical modulation in a plasmomechanical nanopillar system, which has promising applications in ultra-sensitive nanomechanical sensing and building reconfigurable metamaterials.

physics.app-ph↗

arXiv2021

Surface acoustic wave coupling between micromechanical resonators

The coupling of micro- or nanomechanical resonators via a shared substrate is intensively exploited to built systems for fundamental studies and practical applications. So far, the focus has been on devices operating in the kHz regime with a spring-like coupling. At resonance frequencies above several 10 MHz, wave propagation in the solid substrate becomes relevant. The resonators act as sources for surface acoustic waves (SAWs) and it is unknown how this effects the coupling between them. Here, we present a model for MHz frequency resonators interacting by SAWs and derive the eigenfrequencies and quality factors of a pair of resonators for the symmetric and antisymmetric mode. Our results are in agreement with finite element method (FEM) simulations and show that in contrast to the well-known strain-induced spring-like coupling, the coupling via SAWs is not only dispersive but also dissipative. This can be exploited to realize high quality phonon cavities, an alternative to acoustic radiation shielding by, e.g. phononic crystals.

physics.app-ph↗

arXiv2020

Analysis of carbon content in direct-write plasmonic Au structures by nanomechanical scanning absorption microscopy

The determination of the chemical content is crucial for the quality control in high-precision device fabrication and advanced process development. For reliable chemical composition characterization, certain interaction volume of the target material is necessary for conventional techniques such as energy-dispersive X-ray spectroscopy (EDX) and electron energy loss spectroscopy (EELS). This remains however a challenge for nanostructures. We hereby propose an alternative technique for measuring chemical composition of nanostructures with limited volume. By measuring the differences in the optical absorption of the nanostructure due to the differences in the chemical composition with the resonance frequency detuning of a nanomechanical resonator as well as the assistance of the analytical optical modelling, we demonstrate the possibility of characterizing the carbon content in the direct-write focused electron beam induced deposition (FEBID) gold nanostructures.

physics.optics↗

arXiv2020

Frequency fluctuations in nanomechanical silicon nitride string resonators

High quality factor ($Q$) nanomechanical resonators have received a lot of attention for sensor applications with unprecedented sensitivity. Despite the large interest, few investigations into the frequency stability of high-$Q$ resonators have been reported. Such resonators are characterized by a linewidth significantly smaller than typically employed measurement bandwidths, which is the opposite regime to what is normally considered for sensors. Here, the frequency stability of high-$Q$ silicon nitride string resonators is investigated both in open-loop and closed-loop configurations. The stability is here characterized using the Allan deviation. For open-loop tracking, it is found that the Allan deviation gets separated into two regimes, one limited by the thermomechanical noise of the resonator and the other by the detection noise of the optical transduction system. The point of transition between the two regimes is the resonator response time, which can be shown to have a linear dependence on $Q$. Laser power fluctuations from the optical readout is found to present a fundamental limit to the frequency stability. Finally, for closed-loop measurements, the response time is shown to no longer be intrinsically limited but instead given by the bandwidth of the closed-loop tracking system. Computed Allan deviations based on theory are given as well and found to agree well with the measurements. These results are of importance for the understanding of fundamental limitations of high-$Q$ resonators and their application as high performance sensors.

cond-mat.mes-hall↗

arXiv2020

Thermal transport and frequency response of localized modes on low-stress nanomechanical silicon nitride drums featuring a phononic bandgap structure

Development of broadband thermal sensors for the detection of, among others, radiation, single nanoparticles, or single molecules is of great interest. In recent years, photothermal spectroscopy based on the shift of the resonance frequency of stressed nanomechanical resonators has been successfully demonstrated. Here, we show the application of soft-clamped phononic crystal membranes made of silicon nitride as thermal sensors. It is experimentally demonstrated how a quasi-bandgap remains even at very low tensile stress, in agreement with finite element method simulations. An increase of the relative responsivity of the fundamental defect mode is found when compared to that of uniform square membranes of equal size, with enhancement factors as large as an order of magnitude. We then show phononic crystals engineered inside nanomechanical trampolines, which results in additional reduction of the tensile stress and increased thermal isolation, resulting in further enhancement of the responsivity. Finally, defect mode and bandgap tuning is shown by laser heating of the defect to the point where the fundamental defect mode completely leaves the bandgap.

physics.app-ph↗

arXiv2020

Towards nanoelectromechanical photothermal localization microscopy

Single-molecule microscopy has become an indispensable tool for biochemical analysis. The capability of characterizing distinct properties of individual molecules without averaging has provided us with a different perspective for the existing scientific issues and phenomena. Recently, the super-resolution fluorescence microscopy techniques have overcome the optical diffraction limit by the localization of molecule positions. However, the labelling process can potentially modify the intermolecular dynamics. Based on the highly-sensitive nanomechanical photothermal microscopy reported previously, we propose optimizations on this label-free microscopy technique towards localization microscopy. A localization precision of 3 $\unicode{x212B}$ is achieved with gold nanoparticles, and the detection of polarization-dependent absorption is demonstrated, which opens the door for further improvement with polarization modulation imaging.

physics.app-ph↗

arXiv2020

Thermal radiation dominated heat transfer in nanomechanical silicon nitride drum resonators

Nanomechanical silicon nitride (SiN) drum resonators are currently employed in various fields of applications that arise from their unprecedented frequency response to physical quantities. In the present study, we investigate the thermal transport in nanomechanical SiN drum resonators by analytical modelling, computational simulations, and experiments for a better understanding of the underlying heat transfer mechanism causing the thermal frequency response. Our analysis indicates that radiative heat loss is a non-negligible heat transfer mechanism in nanomechanical SiN resonators limiting their thermal responsivity and response time. This finding is important for optimal resonator designs for thermal sensing applications as well as cavity optomechanics.

physics.app-ph↗

arXiv2020

A nanoelectromechanical position-sensitive detector with picometer resolution

Sub-nanometer displacement detection lays the solid foundation for critical applications in modern metrology. In-plane displacement sensing, however, is mainly dominated by the detection of differential photocurrent signals from photodiodes, with resolution in the nanometer range. Here, we present an integrated in-plane displacement sensor based on a nanoelectromechanical trampoline resonator. With a position resolution of 4 $pm/Hz^{1/2}$ for a low laser power of 85 $μ$W and a repeatability of 2 nm after 5 cycles of operation as well as good long-term stability, this new detection principle provides a reliable alternative for overcoming the current position detection limit in a wide variety of research and application fields.

physics.app-ph↗

arXiv2019

Spectrally Broadband Electro-Optic Modulation with Nanoelectromechanical String Resonators

In this paper, we present an electro-optical modulator made of two parallel nanoelectromechanical silicon nitride string resonators. These strings are covered with electrically connected gold electrodes and actuated either by Lorentz or electrostatic forces. The in-plane string vibrations modulate thewidth of the gap between the strings. The gold electrodes on both sides of the gap act as a mobile mirror that modulate the laser light that is focused in the middle of this gap. These electro-optical modulators can achieve an optical modulation depth of almost 100% for a driving voltage lower than 1 mV at a frequency of 314 kHz. The frequency range is determined by the string resonance frequency, which can take values of the order of a few hundred kilohertz to several megahertz. The strings are driven in the strongly nonlinear regime, which allows a frequency tuning of several kilohertz without significant effect on the optical modulation depth.

physics.app-ph↗

arXiv2019

Ultrathin 2 nm gold as ideal impedance-matched absorber for infrared light

Thermal detectors are a cornerstone of infrared (IR) and terahertz (THz) technology due to their broad spectral range. These detectors call for suitable broad spectral absorbers with minimalthermal mass. Often this is realized by plasmonic absorbers, which ensure a high absorptivity butonly for a narrow spectral band. Alternativly, a common approach is based on impedance-matching the sheet resistance of a thin metallic film to half the free-space impedance. Thereby, it is possible to achieve a wavelength-independent absorptivity of up to 50 %, depending on the dielectric properties of the underlying substrate. However, existing absorber films typicallyrequire a thickness of the order of tens of nanometers, such as titanium nitride (14 nm), whichcan significantly deteriorate the response of a thermal transducers. Here, we present the application of ultrathin gold (2 nm) on top of a 1.2 nm copper oxide seed layer as an effective IR absorber. An almost wavelength-independent and long-time stable absorptivity of 47(3) %, ranging from 2 $μ$m to 20 $μ$m, could be obtained and is further discussed. The presented gold thin-film represents analmost ideal impedance-matched IR absorber that allows a significant improvement of state-of-the-art thermal detector technology.

physics.optics↗

arXiv2019

Influence of clamp-widening on the quality factor of nanomechanical silicon nitride resonators

Nanomechanical resonators based on strained silicon nitride (Si$_3$N$_4$) have received a large amount of attention in fields such as sensing and quantum optomechanics due to their exceptionally high quality factors ($Q$s). Room-temperature $Q$s approaching 1 billion are now in reach by means of phononic crystals (soft-clamping) and strain engineering. Despite great progress in enhancing $Q$s, difficulties in fabrication of soft-clamped samples limits their implementation into actual devices. An alternative means of achieving ultra-high $Q$s was shown using trampoline resonators with engineered clamps, which serves to localize the stress to the center of the resonator, while minimizing stress at the clamping. The effectiveness of this approach has since come into question from recent studies employing string resonators with clamp-tapering. Here, we investigate this idea using nanomechanical string resonators with engineered clampings similar to those presented for trampolines. Importantly, the effect of orienting the strings diagonally or perpendicularly with respect to the silicon frame is investigated. It is found that increasing the clamp width for diagonal strings slightly increases the $Q$s of the fundamental out-of-plane mode at small radii, while perpendicular strings only deteriorate with increasing clamp width. Measured $Q$s agree well with finite element method simulations even for higher-order resonances. The small increase cannot account for previously reported $Q$s of trampoline resonators. Instead, we propose the effect to be intrinsic and related to surface and radiation losses.

physics.app-ph↗

arXiv2017

Single-molecule optical absorption imaging by nanomechanical photothermal sensing at room temperature

Absorption microscopy is a powerful technique, enabling the detection of single non- fluorescent molecules at room temperature. So far, the molecular absorption has been probed optically via the attenuation of a probing laser. The sensitivity of optical probing is not only restricted by background scattering, but it is fundamentally limited by laser shot noise. Here, we present nanomechanical photothermal microscopy, which overcomes the scattering and shot noise limit by detecting the sample absorption directly with a temperature sensitive substrate. We use nanomechanical silicon nitride drums, whose resonant frequency detunes with local heating. Individual Au nanoparticles with diameters from 10 nm - 200 nm and single molecules (Atto 633) are scanned with a 305 μW heating laser with a peak irradiance of 330 μW/μm2. Using stress-optimized drums, we achieve a sensitivity of 45 fW/sqrt(Hz), which results in a signal-to-noise ratio of >60 for a single molecule. Our method has important consequences for a wide range of applications, such as imaging, absorption analysis and spectrochemical analysis of non-fluorescent samples.

physics.app-ph↗

arXiv2017

Effect of oxygen plasma on nanomechanical silicon nitride resonators

Precise control of tensile stress and intrinsic damping is crucial for the optimal design of nanomechanical systems for sensor applications and quantum optomechanics in particular. In this letter we study the in uence of oxygen plasma on the tensile stress and intrinsic damping of nanomechanical silicon nitride resonators. Oxygen plasma treatments are common steps in micro and nanofabrication. We show that oxygen plasma of only a few minutes oxidizes the silicon nitride surface, creating several nanometer thick silicon dioxide layers with a compressive stress of 1.30(16)GPa. Such oxide layers can cause a reduction of the e ective tensile stress of a 50 nm thick stoichiometric silicon nitride membrane by almost 50%. Additionally, intrinsic damping linearly increases with the silicon dioxide lm thickness. An oxide layer of 1.5nm grown in just 10s in a 50W oxygen plasma almost doubled the intrinsic damping. The oxide surface layer can be e ciently removed in bu ered HF.

cond-mat.mes-hall↗

arXiv2014

Evidence of surface loss as ubiquitous limiting damping mechanism in SiN micro- and nanomechanical resonators

Silicon nitride (SiN) micro- and nanomechanical resonators have attracted a lot of attention in various research fields due to their exceptionally high quality factors ($Q$s). Despite their popularity, the origin of the limiting loss mechanisms in these structures has remained controversial. In this paper we propose an analytical model combining acoustic radiation loss with intrinsic loss. The model accurately predicts the resulting mode-dependent $Q$s of a low-stress silicon-rich and a high-stress stoichiometric SiN membrane. The large acoustic mismatch of the low-stress membrane to the substrate seems to minimize radiation loss and $Q$s of higher modes ($n \wedge m \geq 3$) are limited by intrinsic losses. The study of these intrinsic losses in low-stress membranes with varying lengths $L$ and thicknesses $h$ reveals an inverse linear dependence of the intrinsic loss with $h$ for thin resonators independent of $L$. This finding was confirmed by comparing the intrinsic dissipation of arbitrary (membranes, strings, and cantilevers) SiN resonators extracted from literature, suggesting surface loss as ubiquitous damping mechanism in thin SiN resonators with $Q_{surf} = β\cdot h$ and $β= 6\times10^{10} \pm4\times 10^{10}$~m$^{-1}$. Based on the intrinsic loss the maximal achievable $Q$s and $Q\cdot f$ products for SiN membranes and strings are outlined.

cond-mat.mes-hall↗