Gold Nanomesh Electrodes: Flexible, Transparent, and Highly Conductive for Advanced Electronics

Abstract

Achieving a high‑performance flexible electrode demands a careful balance between optical transmittance and electrical conductivity. In this study, we demonstrate that gold nanomesh (AuNM) electrodes fabricated via versatile nanosphere lithography (NSL) achieve this balance by limiting the AuNM thickness to no more than 40 nm—approximately the mean free path of electrons in gold. Under these conditions, the electrodes reach up to 89 % transmittance at 550 nm while maintaining a sheet resistance of 104.5 Ω/□. Flexibility tests reveal that AuNM meshes tolerate significantly higher tensile strains than bulk gold films, with narrower inter‑aperture wire widths providing superior strain accommodation. Finite‑element simulations corroborate the experimental results, confirming the reliability of the NSL process for large‑area, flexible, transparent electrodes.

Introduction

Flexible transparent electrodes are central to next‑generation wearables, displays, and biosensors. Conventional materials such as indium tin oxide (ITO) and fluorine‑doped tin oxide (FTO) suffer from brittleness and high manufacturing costs, while conductive polymers exhibit poor environmental stability. Metal nanomeshes, particularly those made of noble metals like gold (Au) and platinum (Pt), offer long‑term chemical stability and excellent electrical performance. However, optimizing the trade‑off between transmittance and conductivity remains a challenge because these properties are inversely related. In this work, we employ NSL to produce AuNM electrodes with hexagonal, periodic nanostructures, systematically varying wire width and thickness to identify the optimal design for flexible, transparent applications.

Methods and Experiments

Fabrication via Nanosphere Lithography

NSL leverages a monolayer of polystyrene (PS) spheres to template nanostructures over wafer‑scale areas. The process proceeds as follows:

• Deposit a close‑packed PS monolayer (initial diameter 1 µm) onto a 500‑µm PET substrate. Reduce sphere diameter by reactive ion etching (O₂/CHF₃) to create gaps.
• Deposit a 2 nm Ti buffer layer followed by 20 nm Au via electron‑beam evaporation; Au fills the gaps, forming the nanomesh.
• Remove PS spheres with adhesive tape and sonication, leaving the AuNM on PET.

SEM (Nova NanoSEM 450) confirms the hexagonal array and uniform wire widths. A custom strain‑tension setup (Fig. 1b) connects the AuNM to LEDs with silver paste and copper tape, demonstrating optical transparency and electrical continuity under bending.

a AuNM fabrication flow. b Demonstration of transmittance and conductivity under strain.

Sample Library

Six AuNM variants were fabricated with inter‑aperture wire widths (w) ranging from 100 nm to 175 nm (w₁ = 100 nm, w₂ = 115 nm, …, w₆ = 175 nm). All samples share a 20 nm Au thickness and a PET substrate.

SEM images of the six AuNM samples and corresponding numerical models.

Simulation Protocol

Finite‑element analysis (FEA) using periodic boundary conditions models a unit cell of AuNM on PET. Circularly polarized light at 550 nm is used to compute transmittance with an integrating sphere. Material properties are drawn from published experimental data. Mechanical simulations apply 1.5 × 10⁹ N/m² compressive stress along the Y‑direction to assess strain‑dependent resistance.

Results and Discussions

Optical and Electrical Performance

Figure 3 compares measured and simulated transmittance and sheet resistance versus wire width. As wire width increases, both transmittance and resistance decrease linearly in simulation, while experimental values exhibit slight deviations due to surface roughness and defects. The smallest wire width (100 nm) yields the highest transmittance (89 %) but the highest resistance (104.5 Ω/□). The widest wire (175 nm) achieves the lowest resistance (16.5 Ω/□) at the cost of reduced transmittance (65 %). These results confirm the NSL process reliably reproduces the designed nanostructure.

Transmittance and sheet resistance versus inter‑aperture wire width at 550 nm (20 nm thickness).

Thickness‑Dependent Trade‑Off

Simulations (Fig. 4) reveal that increasing AuNM thickness reduces sheet resistance sharply up to ~40 nm, beyond which gains plateau due to the electron mean free path in Au. Transmittance decreases only modestly with thickness, demonstrating that a 40 nm upper limit preserves optical performance while optimizing conductivity.

Transmittance and sheet resistance versus AuNM thickness (W5 = 160 nm) at 550 nm.

Mechanical Flexibility

Strain‑tension experiments (Fig. 5) show bulk Au films exhibit a dramatic rise in resistance beyond 1.9 % strain, while AuNM electrodes maintain initial resistance up to ~2.1 % strain. Narrower wire widths provide better strain tolerance, as the mesh can reorient and deform without breaking. Finite‑element stress maps confirm that stress concentrates at the mesh center, but the mesh structure mitigates failure.

Resistance ratio (R/R₀) versus strain for AuNM and bulk Au films. Insets show mesh deformation during bending.

Long‑Term Bending Stability

Repeated bending cycles (5–400 cycles, 5–15 mm radius) indicate negligible change in sheet resistance, underscoring the robustness of AuNM electrodes for flexible device operation.

Sheet resistance versus bending cycles for AuNM (W5 = 160 nm, 20 nm thick).

Conclusions

We have established a scalable, low‑cost route to fabricate gold nanomesh electrodes with:

• High optical transparency (up to 89 %) and low sheet resistance (≤104 Ω/□) by limiting thickness to 40 nm.
• Superior mechanical flexibility, sustaining >2 % strain without electrical failure.
• Excellent long‑term durability over hundreds of bending cycles.

These properties position AuNM electrodes as a compelling candidate for flexible electronics, including biosensors, displays, and optoelectronic devices.

Abbreviations

AuNM

Gold nanomesh

FEA

Finite element analysis

NSL

Nanosphere lithography

PET

Polyethylene terephthalate

PS

Polystyrene spheres

SEM

Scanning electron microscope