Atomic layer deposition of hafnium oxide on porous silicon to form a template for athermal SERS-active substrates

In present work, two types of substrates for the surface enhanced Raman scattering (SERS) spectroscopy based on silver-coated porous silicon (por-Si) and HfO x /por-Si are engineered. The por-Si samples are formed by electrochemical etching the monocrystalline silicon and have a mean pore diameter of 850 nm and a porous layer thickness of 5 µm. Deposition of the hafnium oxide film on the por-Si surface is performed by atomic layer technique, while the SERS-active silver particles are grown by the chemical “silver mirror” method. The HfO x -free substrates demonstrate better SERS-activity but result in changes of the analyte molecule (Ellman’s reagent) spectra, which is supposed to associate with their thermal degradation. Oppositely, the Ag/HfO x /por-Si samples provide sufficient and stable enough SERS-activity during at least 1-min SERS-measurements. We assume the observed stability of the analyte on the substrates containing HfO x can be caused by the faster heat dissipation from the laser spot due to more uniform and conformal silver coating than that on HfO x -free sample. The conformal deposition of silver is provided by passivation of the por-Si surface with auxiliary HfO x layer. An analytical enhancement factor for the Ag/HfO x /por-Si substrate equals to 2·10 3 . Therefore, the SERS-active substrate containing HfO x provided athermal effect on analyte.