Porous Nanophotonic Optomechanical Beams for Enhanced Mass Adsorption

Abstract

We have developed a porous silicon nanocantilever for a nano-optomechanical system (NOMS) with a universal sensing surface for enhanced sensitivity. Using electron beam lithography, we selectively applied a V 2 O 5 /HF stain etch to the mechanical elements while protecting the silicon-on-insulator photonic ring resonators. This simple, rapid, and electrodeless approach generates tunable device porosity simultaneously with the mechanical release step. By controlling the porous etchant concentration and etch time, the porous etch depth, resonant frequency, and the adsorption surface area could be precisely manipulated. Using this control, cantilever sensors ranging from nonporous to fully porous were fabricated and tested as gas-phase mass sensors of volatile organic compounds coming from a gas chromatography stream. The fully porous cantilever produced a dramatic 10-fold increase in sensing signal and a 6-fold improvement in limit of detection (LOD) compared to an otherwise identical nonporous cantilever. This signal improvement could be separated into mass responsivity increase and adsorption increase components. Allan deviation measurements indicate that a further 4-fold improvement in LOD could be expected upon speeding up characteristic peak response time from 1 s to 50 ms. These results show promise for performance enhancement in nanomechanical sensors for applications in gas sensing, gas chromatography, and mass spectrometry.

Prompt Electronic Discrimination of Gas Molecules by Self-Heating Temperature Modulation

“…The porosity of the OAD film is enhanced with the increase of the glancing angle and the shadow area. We have prepared three kinds of OAD films under varied glancing angles (65–86°); a high glancing angle of 86° contributes to a high gas response (Figure S4), which probably arises from the large surface area in the presence of abundant nanopores (2–5 nm, Figure S3c), benefiting for gas/oxide charge interaction via offering plenty of adsorption sites . A relatively thick (1400 nm) film with relatively low resistance was employed to ensure a thermally stable self-heating by applying a relatively low bias voltage (<200 V for Keithley 4200; Figure S4) and achieving high response due to the higher carrier concentration or more adsorption active sites.…”

The Recent Progress of MEMS/NEMS Resonators

“…At atmospheric pressure and a temperature of 298 K, the non-porous nanomachine cantilever beam’s resonance frequency is . Under the same conditions, the frequency decreases as the porosity of the nanomachine device increases [ 88 ].…”

Enhancing responsivity and detection limit in tunable nano-electromechanical system resonator mass sensors

“…9) In this regard, modifying the resonator material or structure has also been adopted to enhance the sensing performance. This includes strategies like adjusting the anchor structure for quasi-one-dimensional oscillation with high-quality factors, 10) heating buckled micro-beam resonators for highly selective detection, 11) expanding the analyte adsorption area using porous nanostructures, 12) and surface functionalization with specific sensing materials. 13) These approaches primarily focus on the pre-application stages; once a device is fabricated, opportunities for further improvement or control over the responsivity and detection limit are limited.…”