Browsing by Author "González, M."

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Open Access
Dynamics of NEMS resonators across dissipation limits
(AIP Publishing LLC, 2022-07-12) Ti, C.; McDaniel, J. G.; Liem, A.; Gress, H.; Ma, M.; Kyoung, S.; Svitelskiy, O.; Yanik, C.; Kaya, I. I.; Hanay, M. S.; González, M.; Ekinci, K. L.
The oscillatory dynamics of nanoelectromechanical systems (NEMS) is at the heart of many emerging applications in nanotechnology. For common NEMS, such as beams and strings, the oscillatory dynamics is formulated using a dissipationless wave equation derived from elasticity. Under a harmonic ansatz, the wave equation gives an undamped free vibration equation; solving this equation with the proper boundary conditions provides the undamped eigenfunctions with the familiar standing wave patterns. Any harmonically driven solution is expressible in terms of these undamped eigenfunctions. Here, we show that this formalism becomes inconvenient as dissipation increases. To this end, we experimentally map out the position- and frequency-dependent oscillatory motion of a NEMS string resonator driven linearly by a non-symmetric force at one end at different dissipation limits. At low dissipation (high Q factor), we observe sharp resonances with standing wave patterns that closely match the eigenfunctions of an undamped string. With a slight increase in dissipation, the standing wave patterns become lost, and waves begin to propagate along the nanostructure. At large dissipation (low Q factor), these propagating waves become strongly attenuated and display little, if any, resemblance to the undamped string eigenfunctions. A more efficient and intuitive description of the oscillatory dynamics of a NEMS resonator can be obtained by superposition of waves propagating along the nanostructure.
Open Access
Frequency-dependent piezoresistive effect in top-down fabricated gold nanoresistors
(American Chemical Society, 2021-08-11) Arı, A. B.; Karakan, M. Ç.; Yanık, C.; Kaya, İ. İ.; Hanay, Mehmet Selim; Svitelskiy, O.; González, M.; Seren, H.; Ekinci, K. L.
Piezoresistive strain gauges allow for electronic readout of mechanical deformations with high fidelity. As piezoresistive strain gauges are aggressively being scaled down for applications in nanotechnology, it has become critical to investigate their physical attributes at different limits. Here, we describe an experimental approach for studying the piezoresistive gauge factor of a gold thin-film nanoresistor as a function of frequency. The nanoresistor is fabricated lithographically near the anchor of a nanomechanical doubly clamped beam resonator. As the resonator is driven to resonance in one of its normal modes, the nanoresistor is exposed to frequency-dependent strains of ε ≲ 10–5 in the 4–36 MHz range. We calibrate the strain using optical interferometry and measure the resistance changes using a radio frequency mix-down technique. The piezoresistive gauge factor γ of our lithographic gold nanoresistors is γ ≈ 3.6 at 4 MHz, in agreement with comparable macroscopic thin metal film resistors in previous works. However, our γ values increase monotonically with frequency and reach γ ≈ 15 at 36 MHz. We discuss possible physics that may give rise to this unexpected frequency dependence.
Open Access
Multimode brownian dynamics of a nanomechanical resonator in a viscous fluid
(American Physical Society, 2023-10-24) Gress, H.; Barbish, J.; Yanik, C.; Kaya, I.I.; Erdoğan, Ramazan Tufan; Hanay, Mehmet Selim; González, M.; Svitelskiy, O.; Paul, M.R.; Ekinci, K.L.
Brownian motion imposes a hard limit on the overall precision of a nanomechanical measurement. Here, we present a combined experimental and theoretical study of the Brownian dynamics of a quintessential nanomechanical system, a doubly clamped nanomechanical beam resonator, in a viscous fluid. Our theoretical approach is based on the fluctuation-dissipation theorem of statistical mechanics: we determine the dissipation from fluid dynamics; we incorporate this dissipation into the proper elastic equation to obtain the equation of motion; and the fluctuation-dissipation theorem then directly provides an analytical expression for the position-dependent power spectral density (PSD) of the displacement fluctuations of the beam. We compare our theory to experiments on nanomechanical beams immersed in air and water and obtain excellent agreement. Within our experimental parameter range, the Brownian-force noise driving the nanomechanical beam has a colored PSD due to the "memory"of the fluid; the force noise remains mode independent and uncorrelated in space. These conclusions are not only of interest for nanomechanical sensing but also provide insight into the fluctuations of elastic systems at any length scale.