Seminar LMGP - 28/09/2017 - LIU Hongjun

Hongjun LIU, PhD student, Laboratoire des Matériaux et du Génie Physique (LMGP), Université Grenoble Alpes.

Abstract

AgCuO2 is a new appealing metal oxide which is gaining attention from researchers. This is so since it is a p-type semiconductor with a high expected conductivity thanks to its peculiar electronic structure, in which both Ag and Cu atoms are oxidized and the charge is delocalized. Although lots studies have been done in bulk, no proper thin film has been yet synthesized and thus characterized. The ability of depositing AgCuO2 thin films is also key for device fabrication. The objective of my work is thus to develop for the first time a chemical route towards the deposition of AgCuO2 thin films.

There are mainly two challenges to synthesize such a thin film: the high oxidation states present in AgCuO2 and its instability over 200 °C in air. This PhD work reports three routes we have chosen to approach this target. Firstly, we have tried to deposit AgCuO2 in Aerosol Assisted CVD. To achieve that, works about silver/silver oxide films and copper (I) oxide films have been optimized and the results and problems for compound deposition will be presented. Secondly, oxidation of silver-copper alloy films using plasma/electrochemistry to achieve the silver copper oxide compound was tested and the results will be presented and discussed. Lastly, we have also explored the use of the SILAR (Successive Ionic Layer Deposition) technique, which have yielded the first dense and continuous AgCuO2 thin films. Characterization of the films deposited by SILAR has shown that the carrier concentration of AgCuO2 film is around 1017 ~ 1018 and mobility is reaching 40 cm2/ (V.s). The optical bandgap was determined to be around 1~ 1.2 eV. This results are in agreement with theoretical calculations reported in the literature, and thus confirm the potential of AgCuO2 for application in photovoltaics.

Finally, and in parallel to the before mentioned work, we have studied the reaction mechanism of the synthesis of bulk AgCuO2 by hydrothermal reactions, using an in situ hydrothermal cell at the ESRF. The results will be presented and discussed.