Nanoscale physics
Synthesizing gold nanostructures free of stabilizer on a modified MoS2 substrate
Borodinova T.I.*1, Styopkin V.I.2, Vasko A.A.2, Cherepanov V.V.2, 
Marchenko А.A.2
1F. D. Ovcharenko Institute of Biocolloid Chemistry, NAS of Ukraine, Vernadsky Ave. 42, Kyiv-03680, Ukraine. 
E-mail: borodinova@ua.fm
2Institute of Physics of the NAS of Ukraine, avenu Nauki 46, Kyiv-03028, Ukraine.

Tunability of plasmonic nanoparticles through a cheap chemical procedure has strongly excited nanomatter research in recent years due to its possibility of application in photochemistry and sensing fields. The size and shape of nanoparticles (NPs) of noble metals can be controlled with using different surfactants. The polyvinylpyrrolidone (PVP) is the most widespread non-ionic surfactant for these purposes.
In the case of using Au NPs in sensors technology such as surface-enhanced Raman spectroscopy (SERS) the layer of surfactant creates a physical barrier for the free access of analyte molecules to a surface of the metal particle. Removing these layer from the surface by different methods (intense UV irradiation in the ozone atmosphere, the heat treatment in O2/He/N2, washing in acetone/ethanol, replacing by a thiol layer) inevitably cause damage of NPs facets. Thus, at nowadays the problem of cleanliness of the NPs surface remains not fully resolved.
We demonstrate another approach to solve above mentioned problem. In our study the flat gold nanoprisms (GNPRs) are chosen as test objects. Usually, in the synthesis of GNPRs, the PVP concentration in the growth solution is significant, which leads to the formation of a sufficiently thick PVP coating of the NPs surface. Main idea is to improve the technology of PVP layering. We propose not to remove the PVP layer from the surface of these GNPRs, but to change the conditions for their synthesis in way providing the minimal involving of PVP in the process. To obtain NPRs with a clean (not contaminated PVP) surface on the molybdenum disulfide (MoS2) substrate the changes in the proposed synthesis are next: (i) a PVP layer is preliminary adsorbed on the MoS2; (ii) the synthesis of GNPRs is carried out on MoS2/PVP surface in growth solution containing no PVP.