Probing the Electrical Response of Double‑Sided Polymer Surface Nanostructures

Background

Surface‑engineered nanostructures such as nanoparticles, gratings, and nanopillars have become indispensable in enhancing Raman scattering, plasmonic resonance, nonlinear optics, and electrical response [1–5]. Their unique properties stem from the pronounced surface effects that differentiate them from bulk counterparts. Polymer nanostructures, in particular, exhibit exceptional triboelectric behavior due to increased surface roughness and contact area, which amplify electrostatic induction [11–13]. This triboelectric effect can generate substantial electrical charges, enabling applications in nanogenerators, pressure and temperature sensors, and other electronic devices [14–17].

Advances in fabrication techniques—photolithography, NIL, self‑assembly, and interference lithography—have made it possible to create periodic and aperiodic nanostructures with high precision and throughput [18–22]. NIL stands out for its simplicity, cost‑effectiveness, and sub‑nanometer resolution, making it ideal for polymer nanostructure production [23–25]. By tailoring parameters such as diameter, shape, and arrangement, the electrical response of these structures can be finely tuned, underscoring the importance of systematic electrical characterization.

In this work, we present a comprehensive experimental investigation of two classes of double‑sided polymer surface nanostructures—gratings and nanopillar arrays—fabricated via a repeatable NIL approach. The conductive electrodes were deposited using ITO or silver, allowing us to probe the electrical response under controlled mechanical loading. Our goal was to understand how external pressure and structural parameters influence the open‑circuit voltage and short‑circuit current of these devices.

Methods

Samples

We fabricated two types of nanostructured surfaces: a 300 nm‑period grating with 160 nm width, and a nanopillar array with ~300 nm diameter (Fig. 1). Scanning electron microscopy (SEM) images confirm the fidelity of the patterns.

SEM images of the fabricated structures: (a) grating and (b) nanopillar array.

The double‑sided devices were produced by sequential UV‑curable NIL on polydimethylsiloxane (PDMS) and Kapton substrates. An ITO film was electrodeposited between the two patterned sides, yielding a flexible composite structure (Fig. 2). The triboelectric response arises when a mechanical load induces contact, friction, and separation between the polymer surface and an opposing material, generating charges that are subsequently measured via the ITO electrode.

Schematic of the double‑sided polymer nanostructure device.

Measurement Method

Electrical measurements were performed under a controlled load ranging from 0.5 to 50 N at ambient temperature. A linear motor (E1100‑RS‑HC) varied the applied force, while a Keithley 6514 source meter, Stanford SR570 amplifier, and MDO 3014 oscilloscope recorded voltage and current traces. The experimental setup is illustrated in Fig. 3.

Experimental arrangement for applying mechanical load.

Results and Discussion

Figure 4 shows the voltage and current responses of the grating and nanopillar arrays as a function of applied force. Both structures exhibit a clear dependence on load, but the nanopillar arrays display a markedly stronger response. While the grating’s voltage rises slowly, its current increases rapidly with force. In contrast, the nanopillar arrays show simultaneous increases in both voltage and current, reaching a plateau in voltage around 42 N while the current continues to rise—indicating superior electrical performance of the two‑dimensional pillar geometry.

Electrical performance of (a) grating voltage, (b) grating current, (c) nanopillar voltage, and (d) nanopillar current versus applied force.

To probe the influence of pillar arrangement and geometry, we fabricated random, square, and hexagonal nanopillar arrays (Fig. 5). The hexagonal array, with ~400 nm diameter pillars and sub‑50 nm gaps, presents a highly packed, sharp‑tipped configuration reminiscent of nanoscale pyramids.

SEM images: (a) random, (b) square, (c) hexagonal pillars, (d) magnified hexagonal view.

The force‑dependent voltage and current curves (Fig. 6) confirm that the hexagonal arrangement delivers the highest output. At forces below 20 N, random pillars outperform square pillars, but as the load increases, the hexagonal array surpasses both. The enhanced performance is attributed to the increased surface roughness and contact area provided by the sharp tips and narrow gaps, which amplify the triboelectric effect. The voltage curves level off beyond ~35 N, whereas the current continues to rise until ~40 N, suggesting an optimal operating pressure for maximal electrical output without damaging the nanostructures.

Electrical performance of (a) voltage and (b) current for the three pillar arrangements.

These results demonstrate that carefully engineered double‑sided nanostructures can significantly enhance triboelectric output, paving the way for high‑sensitivity pressure sensors and efficient nanogenerators.

Conclusions

We successfully fabricated double‑sided polymer grating and nanopillar arrays using a repeatable NIL approach and characterized their electrical response under mechanical load at room temperature. The voltage and current signals were found to be highly sensitive to force, pillar geometry, and arrangement. Hexagonal nanopillar arrays with ~400 nm diameters and sub‑50 nm features produced the strongest electrical signals, particularly at an applied pressure of ~40 N. These findings establish a clear design guideline for leveraging double‑sided nanostructures in pressure sensing, energy harvesting, and other nano‑optoelectronic applications.

Availability of Data and Materials

All data generated or analyzed during this study are included in this published article and its supplementary information files.

Abbreviations

ITO:

Indium tin oxide

NIL:

Nanoimprint lithography

PDMS:

Polydimethylsiloxane

SEM:

Scanning electron microscopy

SERS:

Surface‑enhanced Raman scattering