Chemically non-perturbing SERS detection of a catalytic reaction with black silicon

• Published in: Nanoscale 2018-01, Vol.10 (20), p.9780-9787
• Main Authors: Mitsai, E, Kuchmizhak, A, Pustovalov, E, Sergeev, A, Mironenko, A, Bratskaya, S, Linklater, D P, Balčytis, A, Ivanova, E, Juodkazis, S
• Format: Article
• Language: English
• Subjects: Catalytic converters; Conversion coating; Copper converters; Copper oxides; Dielectrics; Finite difference method; Finite difference time domain method; Low concentrations; Mass production; Molecular chains; Nanoparticles; Plasma etching; Raman spectra; Recyclability; Resonators; Silicon substrates; Silver
• ISSN: 2040-3364; 2040-3372
• DOI: 10.1039/c8nr02123f

All-dielectric resonant micro- and nano-structures made of high-index dielectrics have recently emerged as a promising surface-enhanced Raman scattering (SERS) platform which can complement or potentially replace the metal-based counterparts in routine sensing measurements. These unique structures combine the highly-tunable optical response and high field enhancement with the non-invasiveness, i.e. chemically non-perturbing the analyte, simple chemical modification and recyclability. Meanwhile, commercially competitive fabrication technologies for mass production of such structures are still missing. Here, we attest a chemically inert black silicon (b-Si) substrate consisting of randomly-arranged spiky Mie resonators for a true non-invasive (chemically non-perturbing) SERS identification of the molecular fingerprints at low concentrations. Based on the comparative in situ SERS tracking of the para-aminothiophenol (PATP)-to-4,4'-dimercaptoazobenzene (DMAB) catalytic conversion on the bare and metal-coated b-Si, we justify the applicability of the metal-free b-Si for ultra-sensitive non-invasive SERS detection at a concentration level as low as 10-6 M. We performed supporting finite-difference time-domain (FDTD) calculations to reveal the electromagnetic enhancement provided by an isolated spiky Si resonator in the visible spectral range. Additional comparative SERS studies of the PATP-to-DMAB conversion performed with a chemically active bare black copper oxide (b-CuO) substrate as well as SERS detection of the slow daylight-driven PATP-to-DMAB catalytic conversion in the aqueous methanol solution loaded with colloidal silver nanoparticles (Ag NPs) confirm the non-invasive SERS performance of the all-dielectric crystalline b-Si substrate. A proposed SERS substrate can be fabricated using the easy-to-implement scalable technology of plasma etching amenable on substrate areas over 10 × 10 cm2 making such inexpensive all-dielectric substrates promising for routine SERS applications, where the non-invasiveness is of high importance.