Ag inverse opals were fabricated by electrodeposition of silver into opal matrices vioids. The matrices were made of polystyrene microspheres of 440 nm diameter deposited on two types of surfaces (Fig. 1). Ag films were electrochemically deposited onto the surface of ITO or Ag/ITO/glass substrates. The process was carried out in a three-electrode cell and potentiostat-galvanostat Elins P-45X at room temperature using iodous and rhodanic electrolytes. The reference electrode was an aqueous Ag/AgCl/KCl(s), a platinum plate of 2 cm2 surface was applied as a counter electrode. The working and counter electrodes have been placed parallel to each other and separated by a distance of 2 cm.
The samples with a different thickness h of 220–540 nm were prepared, and the amount of the precipitated metal was estimated using Faraday law from the deposition charge.
As principal reagents sodium thiosulphate 5-aqueous (Chimmed, “p. a.”, GOST 27068-86), potassium chloride (Rushim, “pur.”, GOST 4234-77), potassium metabisulphite (98,38%) (Rushim, “pur.”), ethanol 95% (“Medhimprom”), silver nitrate (Carl Roth, “puriss.”), potassium iodide (Chimmed, “pur.”, GOST 4232-74), ammonium rhodanide (Reachem, “pur.”) and distilled water were applied. Four kinds of electrolytes were prepared for silver electrochemical deposition:
-
H2O: 6 g/l Ag; 72 g/l NH4SCN (rhodanic electrolyte)
-
H2O: 4 g/l Ag; 214.5 g/l KI (iodous electrolyte)
-
H2O: 4 g/l Ag; 87.5 g/l Na2S2O3 (thiosulphate electrolyte)
-
H2O: 3 g/l Ag; 261 g/l Na2SO3 (sulphitic electrolyte)
The overall reaction for the deposition of silver is
[AgLx] + e→ Ag + xL. (1)
where L = SCN−, I−, S2O3−, SO3− for rhodanic, iodous, thiosulphate, sulphitic electrolytes, respectively.
Diameter of the polysterene miscospheres used for matrices formation are of 440 ± 20 nm according to scanning electron microscopy (SEM) data. For the template formation Au/ITO/glass substrates have been applied as working electrodes [16]. The colloidal crystal growth was carried out according to procedure reported recently in Ref. [16, 17]. After the electroplating process the matrix was removed chemically.
Surface morphology of Ag invert opals was examined using a Leo Supra 50 VP scanning electron microscope or a Carl Zeiss NVision 40 scanning electron microscope (SEM). Both microscopes are equipped with EDX Oxford Instruments attachments for the local chemical analysis.
Phase composition of Ag films surface was determined by X-ray diffraction analysis using Rigaku D/MAX-2500 PC diffractometer equipped with rotating Cu anode. Measurements have been performed for 2θ in range of 0° − 80° with a step scan of 0.02°.
X-ray photoelectron spectroscopy and energy dispersive X-ray analysis were performed to detect impurities on the surface of the samples and more precisely. X-ray photoelectron spectra were collected using Axis Ultra DLD spectrometer (Kratos Analytical). EDX analysis was carried out using Leo Supra 50 VP scanning electron microscope with EDX Oxford Instruments attachments.
Optical properties of silver inverse opals were investigated by reflection spectroscopy. The spectra were collected using a UV-vis spectrometer Lambda 950 (PerkinElmer). Measurements have been performed in a spectral range of 250–1000 nm with a step scan of 1 nm. Reflectance spectra were collected for the inverse opals with incidence angles of 8°, 30°, 45°, 64°.