The spectra for the same samples before gold deposition are also shown for comparison purposes. The spectra are divided Selleckchem CRT0066101 in the UV-visible region (left) and in the near-IR region (right) to improve the visibility of the oscillations, as their frequency is higher in the UV-visible region. With the deposition of gold, the FI of the samples increases significantly while the number of oscillations remains constant and only a small blue shift of the
oscillations can be realized. The increase in FI is due to the increase in refractive index contrast between the NAA film and the deposited gold layer. However, for increasing NAA film porosity, the FI of the gold-coated samples decreases in the same way as it happened for the as-produced samples. Another remarkable feature of the spectra in the UV-visible range is that the maximum measured reflectance decreases for increasing t PW. In this region, gold has its click here stronger absorption at 500 nm, making the reflectivity of light decrease . This decrease is stronger for the samples with 20 nm of deposited gold. Figure 3 Reflectance spectra of samples with different t PW before gold deposition and after sputtering 10- and 20-nm
gold on NAA. Solid black line represents samples without gold. Dashed blue line represents samples with 10 nm sputtered gold. Red symbols joined with red lines represent samples with 20 nm of gold. Plots on the left correspond to the UV–vis spectral region, while plots on the right correspond to the near-IR spectral region. (a, b) t PW = 0 min, (c, d) t PW = 6 min,
(e, f) t PW = 12 min, and (g, h) t PW = 18 min. In the near-IR range, the spectra show bigger differences: the reflectance for the samples with 10 nm of gold show Oxymatrine symmetric oscillations with respect to the reflectance minima, while for 20 nm of gold, the oscillations are asymmetric. Furthermore, the position of the minima is clearly blue shifted in the samples with 20 nm of gold with respect to the samples without and with 10 nm of gold. It is important to remark that this asymmetry and blue shift decrease with increasing t PW and that for the two lower porosities (corresponding to t PW = 0 min and t PW = 6 min), this asymmetry Selleck mTOR inhibitor results in narrow valleys with small width and a well-defined minimum wavelength that can be useful in the detection of spectral shifts. If the FI between the samples with 10 and 20 nm of deposited gold is compared, it can be concluded that the relation of the FI with the gold thickness is strongly dependent on the porosity of the NAA film: for the lower porosities, the FI for the 10 nm gold-coated samples is bigger, but this trend is reversed as the porosity increases.