Nano-engineering of Group IV Nanocrystals by Atmospheric Pressure Plasma

Abstract

Group IV nanocrystals (NCs) such as silicon carbide (SiC), tin and silicon-tin (Si-Sn) promise great potentials in next generation energy conversion and storage devices such as photovoltaics and microsupercapacitors/batteries. The integration of group IV NCs in energy related devices would require tuning the properties of these NCs through novel synthesis approaches other than the conventionally available methods like wet-chemistry. In this thesis, SiC, Sn and Si-Sn NCs are synthesized through atmospheric pressure plasma. The development of different plasma reactor configurations provided an opportunity to engineer the properties of group IV NCs through tuning their sizes and/or compositions.

The major outcome of this work is to effectively engineer the optical and band structural properties of SiC and Si-Sn NCs through atmospheric pressure plasma. SiC NCs with three different sizes of 1.5 nm to 5.3 nm range was studied. The enhancement in photoluminescence from SiC NCs compared to bulk SiC has been presented. For the first time, a complete experimental investigation of the role of quantum confinement on the absolute band edges of SiC NCs thereby extracting the complete energy band diagram is presented. The energy band diagram reflects the designing criterion for integrating SiC NCs in photovoltaics as transporting layers or in water splitting/purification as a catalyst. Furthermore, the successful synthesis of Si-Sn NCs with simultaneously tuning their sizes and compositions in the atmospheric pressure plasma have been demonstrated in this work. The most interesting aspect of this study was that the concentration of Sn NCs was found to be increasing with decreasing the size of Si-Sn NCs as controlled through the plasma process. The interplay of quantum confinement and compositional effects in Si-Sn NCs resulted in lower bandgap for smaller Si-Sn NCs and larger bandgap for larger Si-Sn NCs.

In addition, tuning size of Sn NCs were also accomplished through atmospheric pressure plasma that resulted in the stability of different phases at different sizes. At larger size (6 nm) tetragonal structure of Sn was observed whereas at diamond cubic structure was found to in 1.5 nm Sn NCs. The plasma synthesized Sn NCs further showed enhanced electrochemical properties suitable for microsupercapacitors.

Date of Award	8 May 2018
Original language	English
Sponsors	Marie Curie & RAPID
Supervisor	Paul Maguire (Supervisor) & Davide Mariotti (Supervisor)