| Popis: |
Growth of semiconducting Si~based quantum-confined (QC) nanoparticles (NPs) in non~thermal atmospheric pressure plasmas with potential application in photovoltaic cells is studied in this project. The attractive optoelectronic properties of QC NPs in combination with the advantages of Si-based materials make Si-based QC NPs promising candidates for a range of applications including photovoltaic cells, light emitting devices and biomarkers. Novel radio-frequency microplasma reactors suitable for growth of small NPs with diameter < 10 nm were developed. The work includes extensive materials characterization and specifically TEM analysis of Si, SiC and SiSn NPs. It is demonstrated that the developed plasma reactors are excellent tools for producing QC Si-based NPs with possibility of control over NPs properties; e.g. control over the size and optical properties (i.e. band-gap) of NPs was achieved by changing the precursor concentration. Significant impact of the reactors design on the plasma parameters and also NPs properties such as crystalline/amorphous structure, size and optical properties are observed and analysed. Study of the link between the plasma parameters and NPs properties was possible with the aid of optical emission spectroscopy (OES) of the plasmas. Specifically NPs crystallization has been studied with a theoretical model that describes NPs heating in atmospheric pressure plasmas coupled with the results from OES and NPs characterization. It is found that the growth of crystalline NPs can occur in non-thermal atmospheric pressure plasmas well below the crystallization temperature of Si NPs due to the ion-collision enhanced heating ofNP in this type of plasmas. A noticeable outcome of this work is the development of a plasma reactor for high rate synthesis of NPs in atmospheric pressure plasmas. The reactor design allows scaling-up without any impact on the NPs properties and also it allows deposition of thin film of NPs with potential application in fabrication of solar cell devices. Synthesis of Si and SiC NPs with tunable size and intense photoluminescence has been demonstrated in this reactor. Accurate control over the size of SiC QC NPs in the range of ~ 1-5 nm allowed the study of quantum confinement in these materials; the red shift in the PL peak with increasing size was observed for SiC QC NPs. |
