Abstract
The formation conditions of gold nanofilms on silicon (Si) substrate by galvanic replacement in a dimethyl sulfoxide (DMSO) solvent and their subsequent use for the fabrication of Si nanostructures by metal-assisted chemical etching (MACE) method were under study. It was found that the average size and number of Au nanoparticles increase with an increase in the reducible metal ion concentration from 2 to 8 mM HAuCl4 in DMSO, whereas the distribution of Au nanoparticles in height remains low for all concentrations of the reducible metal. In the temperature range 40 - 70°C, a different morphology of the deposited Au nanofilms observed. In particular, at 40 °C, the film is porous mainly homogeneous, whereas at a temperature of 50°C the film is rougher. The subsequent rise in temperature from 60°C to 70°C results in the formation of Au nanofilm with a discontinuous morphology. It was established that regardless of the morphology of deposited Au nanofilms, the Si nanostructures maintain a vertical orientation to the plane of the Si substrate during MACE-etching. The produced Si nanostructures were 1.5 - 2.5 μm in height and their average diameter ranged from 100 to 300 nm.
Highlights
Nanoparticles of gold (AuNPs) are known to be a promising material in terms of their application in biomedicine as biosensors [1,2,3], biomarkers [4, 5], and for bioimaging [6, 7], drug delivery [8, 9] etc
The average size and number of Au nanoparticles increase with an increase in the reducible metal ion concentration from 2 to 8 mM HAuCl4 in dimethyl sulfoxide (DMSO)
Considering that the electromotive force of the process is ΔE0 = 2.62 V, the reduction rate of Au on the silicon surface will be higher than in case of using metals with low values of the standard electrode potential such as Ag, Pd, Ru, Cu, Ni etc. Another important factor influencing the morphology of Si surface covered with Au nanoparticles which have been deposited by galvanic replacement method is the temperature
Summary
Nanoparticles of gold (AuNPs) are known to be a promising material in terms of their application in biomedicine as biosensors [1,2,3], biomarkers [4, 5], and for bioimaging [6, 7], drug delivery [8, 9] etc. The deposition method and the control of morphology of deposited gold nanoparticles and nanofilms are known to be urgent tasks [15]. Widely studied physico-chemical methods of deposition are carried out mainly in aqueous solutions, in which besides the main process of metal reduction, there are side processes, in particular the release of hydrogen in the cathode regions and the decomposition of the substrate on which the particles or films are deposited. This issue complicates controlled formation of metal nanoparticles, which is a necessary condition for surface modification. Utilizing the galvanic repalcement in the medium of organic aprotic solvents, e.g. DMSO can prevent the occurrence of these disadvantages, as it was shown in [15, 16]
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