## 1 Introduction  
Raman spectroscopy has long been established as a powerful analytic tool for the detection of compounds and chemical bonds, as well as analysis of the vibrational and structural properties of a given material. Owing to its non-destructive nature, it is a very attractive method for various applications, including medicine, environmental monitoring, substance regulation and geology [1]. Although very informative, the normal Raman signal of any given analyte is weak and can easily become obscured by fluorescence and even just the background noise. There are multiple ways to remedy this issue, and surface-enhanced Raman spectroscopy (SERS) is one of the most efficient techniques which allows to enhance the intensity of the Raman signal by several orders of magnitude [2]. Two main effects are considered to be responsible for the enhancement of the signal, namely, local electromagnetic (EM) field enhancement and chemical enhancement [3]. Chemical enhancement involves charge transfer between the analyte and substrate molecules, thus enhancing the Raman signal. The main contributor to the enhancement effect, however, is the EM field enhancement which is attributed to surface plasmon resonance (SPR) observed in metallic structures. In addition, by creating nanoscale feature sizes, which are what is often used for SERS applications, these SPRs become localised and, by fine-tuning various structural parameters and configurations, it is possible to obtain a considerable EM field enhancement which in turn creates a large Raman signal amplification. In the best cases, SERS is a method capable of detecting single molecules.  
The most widely used SERS substrates contain silver or gold nanoparticles. These metal nanoparticles have unique plasmonic properties that enable the amplification of Raman signals [4]. The size, shape, and surface chemistry of the nanoparticles can be tailored to enhance their SERS activity [5; 6]. In recent years, researchers have also developed more complex nanostructures, such as nanorods, nanostars, nanocubes, nanocages, and even fractal structures, which exhibit unique plasmonic properties and offer improved SERS sensitivity [7; 8; 9]. In addition to the experimental development of SERS substrates, researchers have also used theoretical and computational models to understand the factors that contribute to SERS enhancement and to design new SERS substrates with improved performance. The electromagnetic theory of SERS enhancement is based on the interaction between incident electromagnetic radiation and the plasmonic resonance of the SERS substrate. This theory explains how the plasmonic properties of metallic nanostructures can amplify the Raman signal of analytes. Computational models such as finite-difference time-domain (FDTD) and finite element method (FEM) simulations have been used to reveal the plasmonic properties of metallic nanostructures and predict their SERS performance [10; 11; 12].  
In this work, an analysis of SERS performance for commercially available substrates is conducted. Raman spectra are presented for different concentrations of the analyte Rhodamine B and SEM images are obtained, showing in detail the structures of these substrates. We hypothesise in the context of this research that more chaotic structures lead to better overall Raman enhancement due to the increased likelihood of small interstructural distances. FEM modelling is also carried out in a novel approach, where the real nanostructures are approximated and modelled inside _COMSOL_, and the relevant results are used to support our observations.