Modeling and Experimental Investigations of Nanostructured Ag Thin Films Produced by Oblique-Angle Deposition and Its SERS Performance

Datai Hui,Shigeng Song,Zhentao Wu,Changlong Cai,Xiao Meng,Des Gibson,Da Zhang,Jian Song,Yingbu Duan,Bo Lu,Shun Zhou,Hayrigul Tursun

doi:10.3390/coatings11040458

Abstract

The growth mechanism of nanocolumnar silver thin film deposited on a smooth silicon substrate using electron beam evaporation process at an oblique angle was simulated with the Kinetic Monte Carlo method. Following the simulated silver nanostructured thin film, a further computational simulation was done using COMSOL for surface-enhanced Raman scattering effects. The simulation results were compared against corresponding experimental results, which demonstrated high agreement between simulation results and experimental data. It was found that as the incident deposition angle increased, the density of the Ag thin film significantly decreased and the surface roughness increased. When the incident deposition angle was at 75° and 85°, the resulting nanocolumnar structure was significantly tilted. For Ag thin films deposited at all investigated angles, surface-enhanced Raman scattering effects were observed. Particularly, the Ag nanocolumns deposited at 85° showed remarkable Surface-enhanced Raman Scattering effects. This was seen in both COMSOL simulations and experimental results: Enhancement factors were 2 × 107 in COMSOL simulation and 3.3 × 105 in the experiment.

Highlights

The Oblique-Angle Deposition (OAD) method is a thin-film deposition method that can be used to obtain a thin-film nanostructure or a specific thin-film surface morphology [1]
The systematic investigation on the time evolution of nanostructured Ag films deposited using the OAD method at various oblique angles on smooth Si substrate was simulated at the atomic scale using NASCAM software (NASCAM (4.6.2)), which is based on the Kinetic Monte Carlo (KMC) method [13,14,15]
The growth mechanism of nanocolumnar Ag thin film deposited on a smooth Si substrate using electron beam evaporation process at an oblique angle was simulated with

Summary

Introduction

The Oblique-Angle Deposition (OAD) method is a thin-film deposition method that can be used to obtain a thin-film nanostructure or a specific thin-film surface morphology [1]. The porous, nanostructured film is sculptural and has anisotropy, controllable refractive index, and other useful characteristics, which can be widely used for SurfaceEnhanced Raman Scattering (SERS), phase retarders, biosensors, optoelectronic crystal devices, virus/bacteria/toxin detections [5,6,7], optical fiber probes [8], and ultrathin-layer chromatography plates [9]. Among these applications, the SERS [10] sensor is one of the more typical applications of these nanostructured films deposited using OAD method. Simulation results were compared to and verified by a corresponding experiment

Nanostructure Simulation Using the KMC Method

SERS Performance Simulation Model

Characterization

Comparison of SERS Performance Simulation Results and Experimental Results

Conclusions