Dataset for "Nanoplastics Detected in Commercial Sea Salt"

Data collection method:

Finite-Difference Time-Domain (FDTD) simulations were performed in Lumerical revealing the electric field distribution on the surface of the Au-AAO-50 SERS substrate. The model SERS substrate was created in Autodesk Inventor based on SEM and AFM of the surface and mapped to Lumerical for simulation. A bicentric hexagonal pattern of holes was generated with side length 500 nm and hole diameter 250 nm. The edges of the orifices were sloped forming a conical cut out based on the AFM. The result of this resembled that of an array of countersunk holes with a chamfer angle of 84° and a diameter of 345 nm at the surface. The AAO was modeled using the built in wavelength dependent material model in the Lumerical database as in refs 41, 42. A 50 nm layer of Au was superimposed onto the surface of the AAO substrate and modelled using a Johnson and Christy material model (based on ref.43) to simulate the substrates used in experiments reported here. Three other metallic layers were modelled for comparison, Ag (Palik 0 - 2 µm material model; ref. 44), Al, and Cu (both CRC material models; ref. 45). The three-dimensional domain space encompassed 2 µm × 1.732 µm of the surface (x and y directions) of the substrate and a depth of 2 µm (z direction). 3 µm of void space was placed above the substrate surface. The boundaries of the domain were periodic in the x and y direction and perfectly matched layers in the z direction which enabled the reduction of the simulation domain without compromising the validity of the simulation. The mesh resolution was approximately 2% of the hole diameter giving high fidelity results. A Bloch plane wave source with amplitude 1 V/m was introduced from 2 µm above the SERS substrate model leaving an additional (but crucial) 1 µm of space between the source and the upper boundary. The source was a Fourier transform limited pulse of light with approximately Gaussian spectral profile centered at 785 nm with a wavelength span of 300 nm. The duration of the pulse was approximately 4.2 fs. The plane wave was linearly polarised parallel to the x-axis of the FDTD domain. A frequency domain field and power monitor were placed in the x-y plane 1 nm above the surface of the SERS substrate to extract the electric field distribution on the surface of the sample.