Time‑Resolved Corrosion Dynamics of Single‑Crystalline Silver Triangular Nanoparticles

Introduction

Metal nanoparticles exhibit strong light–matter interactions through localized surface plasmon resonances (LSPR), enabling applications in sensing, optical labeling, color printing, and catalysis [1]. While gold remains the preferred plasmonic material due to its chemical stability, silver offers superior optical performance with lower intrinsic damping, yet it is more prone to tarnishing and oxidation [2]. Understanding silver’s corrosion pathways at the single‑particle level is therefore essential for expanding its practical use.

Previous studies have largely focused on bulk electrodes or silver films, rarely addressing isolated nanostructures [3]. Here, we investigate the chemical stability of single‑crystalline silver triangular nanoparticles (TrNPs), tracking morphological and optical changes over time to elucidate the mechanisms that compromise their plasmonic performance.

Materials and Methods

Synthesis and Immobilization of Silver Triangles

Silver triangles (80–100 nm edge × 8 nm height) were synthesized via a two‑step colloidal route using a microfluidic seed‑growth system [4]. The resulting particles exhibit an LSPR centered at ~710 nm. Solutions were stored in darkness under argon at 4 °C. For deposition, 1 % pre‑hydrolyzed 3‑aminopropyl‑triethoxysilane (APTES) was applied to glass substrates with chromium alignment marks, followed by a 10‑min incubation of diluted particle solution, washing, and drying. Samples were immediately transferred to the characterization stage.

Characterization of the Morphology and Optical Properties

AFM imaging was performed in tapping mode with silicon tips (Tap300) on a Nanoscope IIIa. Morphological data were analyzed using Gwyddion and custom MATLAB scripts. Transmission electron microscopy (HR‑TEM, JEOL JEM‑3010) confirmed monocrystallinity. Single‑particle scattering spectra were recorded with a Zeiss AxioImager Z1 and a SpectraPro SP2300i spectrometer; spectra were normalized to lamp intensity and background.

Electromagnetic Simulation

Finite‑element calculations (COMSOL Multiphysics RF module) modeled the TrNP as an equilateral prism with rounded edges. The dielectric function of silver was taken from Johnson and Christy [5]. Scattering spectra were obtained by integrating the power flux through a surrounding spherical domain.

Results and Discussion

Morphological Evolution During Corrosion

AFM images immediately after deposition confirm a flat, 8 nm‑high triangular geometry (Fig. 1). After 24 h in air, the particles retain their triangular silhouette but display pronounced protrusions (~20 nm) at the tips and edges (Fig. 2). Dark‑field microscopy shows a drastic reduction in scattering intensity and a color shift from red (~710 nm) to green/blue, indicating LSPR damping.

Time‑Resolved Corrosion Dynamics

Sequential AFM scans over 10.1 h reveal a largely static period (first 8 h) followed by a rapid protrusion growth within ~1 h, reaching ~20 nm. Subsequent scans show no further change (Fig. 3). We quantified the process using a corrosion parameter CPn(t) based on the ratio of maximum to average particle height. Twelve particles were monitored across three independent experiments, yielding a consistent sigmoidal trend (Fig. 3b). The majority of particles initiate corrosion within 1 h, though some exhibit extended onset times.

Crystallographic Basis for Tip‑Specific Corrosion

According to the model by Aherne [6], silver triangles consist of two low‑defect fcc layers ({111}) and a central hcp layer rich in defects. The hcp layer is thermodynamically less stable, promoting atom diffusion at the particle tips where it is exposed. Corrosion therefore initiates at these sites, leading to isotropic protrusion growth until the hcp layer can no longer supply silver atoms.

Optical Consequences of Protrusion Formation

Single‑particle spectra before and after 20 h of exposure (Fig. 4a) show complete suppression of the LSPR peak following protrusion growth. Finite‑element simulations of a silver sphere protrusion on the tip reproduce this damping, even for the smallest protrusion size, confirming that the corroded material (Ag₂O, Ag₂S, or Ag₂CO₃) strongly absorbs the localized field.

Conclusion

We demonstrate that monocrystalline silver triangles corrode anisotropically in ambient air, with tip‑initiated protrusions forming within hours and destroying the LSPR. The observed behavior aligns with a defect‑rich hcp layer model and underscores the importance of protecting the particle tips to preserve plasmonic functionality. These insights pave the way for designing more stable silver nanostructures and for tailoring silver‑based catalysts with enhanced surface reactivity.

Availability of Data and Materials

The datasets generated during this study are available from the corresponding author upon reasonable request.

Abbreviations

APTES

1 % pre‑hydrolyzed 3‑aminopropyl‑triethoxysilane

EDS

Energy‑dispersive X‑ray spectroscopy

fcc

Face‑centered cubic structure

hcp

Hexagonal closed‑packed structure

LSPR

Localized surface plasmon resonances

SEM

Scanning electron microscopy

SERS

Surface‑enhanced Raman spectroscopy

TEM

Transmission electron microscopy

TrNPs

Triangular‑shaped nanoparticles