Cation Exchange in Single Nanowires

• Applicant: Professor Dr. Alf Mews, since 5/2017
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2017 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 325949791

Cation exchange reactions are typically very slow in macroscopic solids and are therefore often not favorable. Nanostructures, however, have very large surface to volume ratios, which enable cation exchange to progress many orders of magnitude faster than in the corresponding bulk materials. Cation exchange reactions have therefore become a very popular and efficient rout for modifying the material composition of nanostructures. However, currently relatively little is known about the kinetics of cation exchange reactions in individual nanostructures. In macroscopic solids and in ensembles of nanoparticles, cation exchange reactions appear to proceed continuously. However, in these scenarios cation exchange reactions are averaged over a multitude of domains, defects, and crystal facets. Reaction kinetics could therefore be markedly different at the single nanostructure level.The goal of our project is to control and analyze cation exchange reactions in individual nanowires in situ by means of optical and electronic measurements. As model systems we will study the well-known reactions from CdSe to Ag2Se and from CdS to Ag2S. Synthesizing and contacting single nanowires are already well established procedures in our labs. We will extend our method for in situ electrical monitoring of cation exchange on nanowire ensembles to single nanowires and to include optical measurement techniques.We plan to investigate the following questions: a) How does the electrical conductivity, fluorescence, and optical absorption change at the single nanowire level during cation exchange, and which conclusions can be drawn with respect to reaction kinetics? b) How precisely can the electronic and optical properties of individual nanowires be controlled through cation exchange? c) How homogeneous is cation exchange from CdSe to Ag2Se in single nanowires? d) Does the appearance of striped phases during the cation exchange reaction from CdS to Ag2S in nanowires have corresponding signatures in the electrical conductivity? In addition to being of basic interest in materials science, our results could find applications in semiconductor doping, battery electrodes, and in chemical sensors.

• DFG Programme: Research Grants
• Co-Investigator: Dr. August Dorn