Advanced synthesis of single-walled carbon nanotube films by aerosol CVD method for electro-optical applications
Single-walled carbon nanotubes (SWCNTs) are a unique family of materials emerging towards high performance applications in electronics and optoelectronics. However, despite significant progress over the last 25 years, the problem of SWCNT production with tailored characteristics, the absence of the growth models and postsynthesis methods to improve specific SWCNT properties are still the main barriers towards a wide range of applications. The methods of the SWCNT synthesis, data processing and SWCNT treatment developed are still not fully optimized. In the current thesis, the abovementioned problems were addressed with the following demonstration of advanced applications of SWNT films: A new reactor for the aerosol CVD growth of SWNTs equipped with spark discharge generator of catalyst nanoparticles was developed. The design proposed resulted in a robust apparatus when compared with the ferrocene CVD reactor. The stability and scalability of the SWCNT synthesis are the main benefits of the spark discharge generator. An advanced control of diameter distribution, defectiveness, and the yield for the first time was achieved through the use of artificial neural networks (ANN). This allowed us to achieve precise control towards mutual relation between the reactor parameters and key SWCNT characteristics. The methodology proposed can help with adjusting the diameter distribution, yield and quality of SWCNTs with prediction error of 4%, 14%,23% respectively for very limited data set. A novel technique for the post-synthesis improvement of electro-optical characteristics of SWCNT films by a laser treatment was proposed. In this process by a short pulse laser irradiation, the transparency of SWCNT increases without any changes in conductivity presumably due to the oxidation of the catalyst particles. We improved transparency by 4% and decreased equivalent sheet resistance by 21%. All developed techniques and methods contributed to the synthesis of SWCNT with defined characteristics open a new possibility for their applications. Thesis work includes three different electro-optical devices with advanced performance: i) a bolometer based on freestanding SWCNT film showing response time of 2.6 ms at room temperature 1mbar (several times faster than the corresponding industrially applied devices); ii) an SWCNT-based heating element of fiber Bragg grid for smooth tuning of the resonant wavelength and a stable laser signal; iii) a saturable absorber based on SWCNT films showing femtosecond pulse generation a low degradation rate.
|Tila||Julkaistu - 2019|
|OKM-julkaisutyyppi||G5 Tohtorinväitöskirja (artikkeli)|