Nanofilm resonators are attractive devices for numerous unique applications due to their ultra-compact size and remarkable mechanical sensing characteristics.
Study: Highly Sensitive Hydrogen Sensor Based on an Optical Driven Nanofilm Resonator. Image Credit: peterschreiber.media/Shutterstock.com
A recent study published in the journal ACS Applied Materials & Interfaces concentrates on developing an optomechanical nanofilm resonator for trace hydrogen sensing using palladium (Pd) and gold (Au) decorated graphene on a fiber end surface.
What are Nanoelectromechanical Systems (NEMS)?
Nanoelectromechanical systems (NEMS) are nanoscale electronics that combine electric and mechanical functionalities. They are composed of miniature electromechanical devices such as actuators, lasers, detectors, pumps, resonators, and rotors.
Nanoelectromechanical systems electronically activate the mechanical states of nanoresonators and show significant potential in sensing applications. Because nanomechanical resonators have a tiny spring constant and a relatively low mass, even extremely mild forces that act on them or minuscule weights attached to their surface may significantly modify their dynamics.
As a result, these devices may be used to detect stresses with extreme accuracy, which has a wide range of industrial applications, such as gas leak identification.
Advantages of Optical Actuation for Sensing Applications
Unlike electronic drives, optical actuation explicitly forces the physical motion of film resonators by using a modified constant laser or pulsing laser rather than adding conducting layer to the resonating surface.
Furthermore, the optical-driven approach allows for the selective activation or repression of specific mechanical states in nanofilm resonators. Some slightly elevated mechanical modes are sensitive to weak forces and can provide good detection applications.
Given the benefits listed above, optical actuation is being extensively employed in the study of nanostructured materials' mechanical characteristics, asymmetric vibration of resonators, microscope imaging, and the fabrication of very sensitive bolometers.
Nanofilm Sensors for Gas Detection
Nanofilm devices' selectivity and precision are critical for gas sensing. A previous study suggested an electrostatically powered composite sheet for toxic gas sensing. The results revealed that analyte sorption had a considerable influence on the compressive stress of the composite sheet, resulting in a shift in the resonance frequency.
Gas identification may be accomplished using all-optical measurements of the mechanical vibration of graphene nanofilm. By monitoring the vibrations of a film with nanoparticle perforations below the resonant frequencies, the pressure relaxing time of various gases may be directly quantified.
Using adsorption-induced resonant frequency shifts of nanofilms as the transmission process can facilitate the development of very accurate gas sensors. The penetration rate of the gas to be examined may change the pressure relaxation time, allowing the identification of a particular gas. The use of sensitive substances may also achieve a remarkable accuracy of gas sensors.
Due to its high sensitivity, palladium (Pd) is among the most widely utilized moderators in hydrogen sensing. Pd-decorated hydrogen detectors respond considerably less to gases such as oxygen, carbon monoxide, water vapors, ethanol, and methanol than hydrogen.
Highlights of the Current Study
As hydrogen is combustible, electronic sensors for detecting hydrogen risk local explosions generated by electric sparking. Due to its chemical resistance and lack of electric arcing, an all-optical detector is a considerably safer and much more capable alternative for hydrogen detection.
In this study, for trace hydrogen analysis, the researchers created an all-optical optoelectronic hydrogen detector on an incorporated optical fiber substrate. A small capillary segment was cut with a single-mode fiber (SMF), the end facet of which was activated by a graphene-gold-palladium multilayer nanofilm electromechanical resonator.
Key Findings of the Research and Future Outlook
When exposed to hydrogen in the hydrogen sensing studies, the Pd film could reversibly change lattice growth into a metal hydride, resulting in lower resonant frequency. By monitoring the change in resonant frequency, the hydrogen content could be determined.
The Au-Pd modified sensor created has great sensitivity, good reproducibility, and a low detection limit (LOD). Furthermore, the sensor construction is extremely repeatable, which opens the door to practical trace gas sensing applications.
In a broader sense, this study lays the framework for combining NEMS with fiber-optic devices to produce high-performance sensing devices. This novel technique is expected to be used in a wide variety of fields, from gas sensing to optomechanical sensing.
Luo, J. et al. (2022). Highly Sensitive Hydrogen Sensor Based on an Optical Driven Nanofilm Resonator. ACS Applied Materials & Interfaces. Available at: https://pubs.acs.org/doi/10.1021/acsami.2c04105