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 HfOx/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 HfOx-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/HfOx/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 HfOx can be caused by the faster heat dissipation from the laser spot due to more uniform and conformal silver coating than that on HfOx-free sample. The conformal deposition of silver is provided by passivation of the por-Si surface with auxiliary HfOx layer. An analytical enhancement factor for the Ag/HfOx/por-Si substrate equals to 2·103. Therefore, the SERS-active substrate containing HfOx provided athermal effect on analyte. [ABSTRACT FROM AUTHOR]