Finally, the sample was spin-coated at 500 rpm for Momelotinib 6 min (spin coater: Laurell Technologies Corporation, North Wales, PA, USA; model: WS-400B-6NPP/LITE). The polyNIPAM microspheres were fixed to the surface by silanization. For this purpose, the samples were treated with APTES vapor for 30 min and afterwards baked at 80°C for 1 h. Results and discussion In Figure 1a,b, SEM images of a bare pSi film as well as a pSi film covered with polyNIPAM microspheres, taken at high magnification, are displayed. SEM images

taken at low magnification can be found in Additional file 1: Figure S1. High-magnification SEM images reveal that both porous layers have open pores. The polyNIPAM spheres appear as black circles and form a quasi-hexagonally non-close packed array on top of the pSi layer, whose geometrical arrangement was analyzed with the software package ImageJ. Of the porous surface, 42 ± 3% was covered with hydrogel spheres with a diameter of 837 ± 17 nm and a center to center distance of 1,032 ± 175 nm. The chosen fabrication parameters for the pSi film resulted in a pSi layer thickness of 1,503 ± 334 nm, determined from cross-sectional SEM images, and a porosity of 65 ± 9%, obtained by using the spectroscopic liquid infiltration

method (SLIM) [22]. Figure 1 SEM images of the investigated structures. (a) pSi monolayer and (b) pSi monolayer with a non-close packed array of polyNIPAM microspheres on top. Scale bars, 500 nm. In order to study the influence

of selleck compound the polyNIPAM microspheres on the optical properties of the pSi layer, interferometric Quisinostat chemical structure reflectance spectra of porous silicon films with and without polyNIPAM spheres were taken at normal incidence. The fringe patterns, observed in the reflectance spectra, result from the interference of reflected light rays at the boundaries of the pSi film, and the position of the fringe maxima can be calculated using the Fabry-Pérot equation: (1) where m is an integer, λ is the wavelength of the incident light, n is the effective refractive index of the pSi film, and L is its thickness. By applying a fast Fourier Erastin transform to the reflectance spectra, the effective optical thicknesses (EOTs, 2 nL) of the porous structures can be directly extracted from the position of the resulting single peak in the frequency spectrum. Changes in the position and amplitude of the FFT peak provide information on the effective refractive index of the pSi layer and the appearance of the involved interfaces, respectively. Hence, a variation in the EOT documents the infiltration of the surrounding medium into the porous layer, and an increase or decrease of the FFT peak indicates variations in the appearance of the porous silicon interfaces, including refractive index contrast and light scattering. This method is referred to as reflective interferometric Fourier transform spectroscopy (RIFTS) [17].