The back-action damping of mechanical motion by electromagnetic radiation is typically overwhelmed by internal loss channels unless demanding experimental ingredients such as superconducting resonators, high-quality optical cavities, or large magnetic fields are employed. Here we demonstrate the first room temperature, cavity-free, all-electric device where back-action damping exceeds internal loss, enabled by a mechanically compliant parallel-plate capacitor with a nanoscale plate separation and an aspect ratio exceeding 1,000. The device has 4 orders of magnitude lower insertion loss than a comparable commercial quartz crystal and achieves a position imprecision rivaling optical interferometers. With the help of a back-action isolation scheme, we observe radiative cooling of mechanical motion by a remote cryogenic load. This work provides a technologically accessible route to high-precision sensing, transduction, and signal processing.

Strong optomechanical coupling – a regime where mechanical motion is damped by environmental radiation – has traditionally required demanding experimental ingredients such as superconducting resonators, high-quality optical cavities, or large magnetic fields. Here we demonstrate a room temperature, cavity-free, all-electric device reaching this regime at radio frequencies, enabled by a mechanically compliant parallel-plate capacitor with a nanoscale plate separation and an aspect ratio exceeding 1,000. The device has four orders of magnitude lower insertion loss than a comparable commercial quartz crystal, and achieves a position imprecision rivaling an optical interferometer. With the help of a back-action isolation scheme, we observe radiative cooling of mechanical motion by a remote cryogenic load. This work provides a technologically accessible route to high-precision sensing, transduction, and signal processing.

We present a novel method for the quantitative analysis of mixtures of semivolatile chemical compounds. For the first time, thermal desorption is integrated directly with nanoelectromechanical infrared spectroscopy (NEMS-IR-TD). In this new technique, an analyte mixture is deposited via nebulization on the surface of a NEMS sensor and subsequently desorbed using heating under vacuum. The desorption process is monitored in situ via infrared spectroscopy and thermogravimetric analysis. The resulting spectro-temporal maps allow for selective identification and analysis of the mixture. In addition, the corresponding thermogravimetric data allow for analysis of the desorption dynamics of the mixture components. As a demonstration, caffeine and theobromine were selectively identified and quantified from a mixture with a detection limit of less than 6 pg (about 30 fmol). With its exceptional sensitivity, NEMS-IR-TD allows for the analysis of low abundance and complex analytes with potential applications ranging from environmental sensing to life sciences.

Nanoelectromechanical (NEMS) resonators are promising uncooled thermal infrared (IR) detectors to overcome existing sensitivity limits. Here, we investigated NEMS 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 7 pW/ $\sqrt {\text {Hz}}$ 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 to 25 $\mu \text{m}$ .

Nanomechanical resonators can serve as high performance detectors and have potential to be widely used in the industry for a variety of applications. Most nanomechanical sensing applications rely on detecting changes of resonance frequency. In commonly used frequency tracking schemes, the resonator is driven at or close to its resonance frequency. Closed-loop systems can continually check whether the resonator is at resonance and accordingly adjust the frequency of the driving signal. In this work, we study three resonance frequency tracking schemes, a feedback-free (FF), a self-sustaining oscillator (SSO), and a phase-locked loop oscillator (PLLO) scheme. We improve and extend the theoretical models for the FF and the SSO tracking schemes, and test the models experimentally with a nanoelectromechanical system (NEMS) resonator. We employ a SSO architecture with a pulsed positive feedback topology and compare it to the commonly used PLLO and FF schemes. We show that all tracking schemes are theoretically equivalent and that they all are subject to the same speed versus accuracy trade-off characteristics. In order to verify the theoretical models, we present experimental steady-state measurements for all tracking schemes. Frequency stability is characterized by computing the Allan deviation. We obtain almost perfect correspondence between the theoretical models and the experimental measurements. These results show that the choice of the tracking scheme is dictated by cost, robustness and usability in practice as opposed to fundamental theoretical differences in performance.

Near-infrared detection is widely used for nondestructive and non-contact inspections in various areas, including thermography, environmental and chemical analysis as well as food and medical diagnoses. Common room temperature bolometer-type infrared sensors are based on architectures in the mu m range, limiting miniaturization for future highly integrated 'More than Moore' concepts. In this work, we present a first principle study on a highly scalable and CMOS compatible bolometer-type detector utilizing Ge nanowires as the thermal sensitive element. For this approach, we implemented the Ge nanowires on top of a low thermal conducting and highly absorptive membrane as a near infrared (IR) sensor element. We adopted a freestanding membrane coated with an impedance matched platinum absorber demonstrating wavelength independent absorptivity of 50% in the near to mid IR regime. The electrical characteristics of the device were measured depending on temperature and biasing conditions. A strong dependence of the resistance on the temperature was shown with a maximum temperature coefficient of resistance of -0.07 K-1 at T = 100 K. Heat transport simulations using COMSOL were used to optimize the responsivity and temporal response, which are in good agreement with the experimental results. Further, lock-in measurements were used to benchmark the bolometer device at room temperature with respect to detectivity and noise equivalent power. Finally, we demonstrated that by operating the bolometer with a network of parallel nanowires, both detectivity and noise equivalent power can be effectively improved.

We demonstrate an advanced approach for quantitative spectral analysis of volatile chemical compounds with nanoelectromechanical infrared spectroscopy. We present high resolution infrared spectra of caffeine with a sensitivity of 7 pg obtained with SiN trampoline resonators.

During the past decade, so-called nanoelectromechanical photothermal infrared spectroscopy (NEMS-IR) has demonstrated exceptional sensitivities for the analysis of airborne particles up to chemical compounds. Here, we present an advanced approach for quantitative spectral analysis of volatile chemical compounds based on NEMS-IR spectroscopy. We present high resolution infrared spectra of caffeine with a sensitivity of 21 pg obtained with silicon nitride trampoline 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 modeling, computational simulations, and experiments for a better understanding of the underlying heat transfer mechanism causing the thermal frequency response. Our analysis shows 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.

Thermal detectors are a cornerstone of infrared and terahertz technology due to their broad spectral range. These detectors call for efficient absorbers with a broad spectral response and minimal thermal mass. A common approach is based on impedance-matching the sheet resistance of a thin metallic film to half the free-space impedance. Thereby, one can achieve a wavelength-independent absorptivity of up to 50%. However, existing absorber films typically require a thickness of the order of tens of nanometers, which can significantly deteriorate the response of a thermal transducer. Here, we present the application of ultrathin gold (2 nm) on top of a surfactant layer of oxidized copper as an effective infrared absorber. An almost wavelength-independent and long-time stable absorptivity of 47(3)%, ranging from 2 μm to 20 μm, can be obtained. The presented absorber allows for a significant improvement of infrared/terahertz technologies in general and thermal detectors in particular.

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 demon-strated. 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-band-gap remains even at very low ten-sile 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 engi-neered 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 band-gap tuning is shown by laser heating of the defect to the point where the fundamental defect mode completely leaves the band gap.

The sensitive detection of infrared (IR) radiation is a essential task in today's modern world. The sensitivity of the state-of-the-art uncooled thermal infrared detectors is still several orders of magnitude above the fundamental photon noise limit. Thermal detectors based on temperature sensitive micro- and nanomechanical resonators are a promising approach to obtain improved thermal IR detectors. Here, we present an uncooled infrared detector based on a 1 mm×1 mm large nanoelectromechanical drum resonator made of 50 nm thick low-stress silicon nitride (SiN). The detector features a titanium nitride absorber with an absorptivity of ∼30% over the entire mid-IR range. The detector drum is driven at its resonance frequency by means of a phase-locked loop. Absorbed IR radiation results in an observable detuning of the drum's oscillation frequency. We measured an Allan deviation of σA = 5.5 × 10−7 at room temperature at a noise bandwidth of 25 Hz. With a responsivity of R = 343 W−1 this results in a sensitivity defined as noise equivalent power (NEP) of NEP = 320 pW/rtHz for an IR beam at a wavelength of 9.5 µm. For this measurement, the IR beam focus spot diameter was equal to the drum size. The drum's responsivity improves by a factor of ten for a focal spot size smaller than ∼ 100 μm. For smaller spots the responsivity remains constant. Based on this analysis we predict a sensitivity of ∼ 30 pW/rtHz for an IR spot size smaller than 100 μm. The detector can be improved further by e.g. optimizing the tensile pre-stress to a lower value or by improving the absorptivity.

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 influence 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 for 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 in the effective tensile stress of a 50 nm thick stoichiometric silicon nitride membrane by almost 50%. Additionally, intrinsic damping linearly increases with the silicon dioxide film thickness. An oxide layer of 1.5 nm grown in just 10 s in a 50 W oxygen plasma almost doubled the intrinsic damping. The oxide surface layer can be efficiently removed in buffered hydrofluoric acid.