Stimuli-responsive and on-chip nanomembrane micro-rolls for enhanced macroscopic visual hydrogen detection

Abstract

Nanomembrane rolling offers advanced three-dimensional (3D) mesostructures in electronics, optics, and biomedical applications. We demonstrate a high-density and on-chip array of rolled-up nanomembrane actuators with stimuli-responsive function based on the volume expansion of palladium in hydrogen milieu. The uniform stimuli-responsive behavior of high-density nanomembrane rolls leads to huge macroscopic visual detection with more than 50% transmittance change under optimization of micropattern design. The reversible shape changing between rolled and flat (unrolled) statuses can be well explained on the basis of the elastic mechanical model. The strain change in the palladium layer during hydrogen absorption and desorption produces a marked change in the diameter of nanomembrane rolls. We found that a functional palladium layer established an external compressive strain after hydrogen stimuli and thus also reduced the rolls' diameters. The large area of the nanomembrane roll array performs excellent nonelectrical hydrogen detection, with response and recovery speeds within seconds. Our work suggests a new strategy to integrate high-density 3D mesoscale architectures into functional devices and systems.

Fig. 1. Configuration and stimuli-responsive performance of high-density stimuli-responsive NRs.

(A) SEM images depicting the structure of NRs. Scale bar, 50 μm. (B) Optical image depicting the successful fabrication of NRs with high density. Scale bar, 500 μm. (C) Photograph of 5.5-mm × 5.5-mm array of NRs on a glass substrate. The light gray part is NRs, whereas the dark gray part is the planar nanomembrane as a contrast. Scale bar, 4 mm. (D) Scheme depicting the configuration of NR. The inset is the cross-section TEM image of the deposited trilayer nanomembrane system consisting of Ti, Cr, and Pd from the bottom up. Scale bar, 25 nm. (E) Scheme depicting stimuli-responsive behavior of NR. The NRs change from tubular structure into planar status with hydrogen stimuli. (F and G) Optical images depicting the NR array responding to hydrogen stimuli. Scale bars, 100 μm. (H and I) Visual images depicting the NR array responding to hydrogen stimuli. Scale bars, 2 mm.

Fig. 2. Area ratio change of NRs related to L/λ for different pattern designs and arrangements.

The area ratio is defined as the ratio of the transparent area to the total area. L is the diameter of the circle pattern and semicircle part of the Janus pattern. λ is periodicity. Lines are the calculated results, as shown in the right panels. Black line, circle patterns in square arrangement; red line, Janus patterns in rectangular arrangement; blue line, Janus patterns in hexagonal arrangement. Insets of optical images depict successful fabrication of large arrays of NRs with patterns corresponding to the dots in the diagram. Scale bars, 100 μm.

Fig. 3. Diameter-decreasing behavior of NR after hydrogen stimuli.

(A) SEM images depicting the decreased diameter of NR after different concentration hydrogen stimuli. Scale bar, 25 μm. (B) Diameter of NRs related to the Pd internal strain change after hydrogen stimuli. The experimental results were plotted in the diagram according to the diameter after hydrogen stimuli of different concentrations.

Fig. 4. Stimuli-responsive behavior of single NR.

(A) Diagram depicting NR change with and without 2% hydrogen stimuli. Insets are the optical images of the hydrogen stimuli-responsive behavior. Scale bar, 25 μm. (B) Analytical calculation of NR diameter related to the internal strain. The insets show FEM simulation results of NRs with predefined strain (inset a) and increased strain in the Pd layer after hydrogen injection (lesser strain in inset b and higher strain in inset c). Color reflects the distribution of displacement (Δs).

Fig. 5. Detection property of a high-density NR array as hydrogen detectors.

(A) Transmittance spectra of high-density NRs before (original), during (H₂ in), and after hydrogen stimuli (H₂ out). The testing sample is with the 50-nm Pd layer. Inset a is the scheme of the testing system for transmittance measurement of NRs. Insets b and c are the real images depicting the visual change of FUDAN characters composed of high-density NRs without (b) and with (c) hydrogen stimuli. Scale bars, 2 mm. (B) Time-dependent transmittance spectra of high-density NRs with different Pd layer thicknesses and different concentration hydrogen stimuli.