Dottorato in FISICA

Titolo della tesi: Ultraviolet Sensors Based on Carbon Nanostructures as Photocathode

Ultraviolet (UV) photodetectors play a crucial role in a wide range of applications, from environ- mental monitoring and space research to biomedical diagnostics and national security. Traditional UV detectors rely on metal photocathodes, such as gold and cesium-based compounds, which, despite their high efficiency, have inherent limitations such as high cost, bulkiness, and limited tunability. To address these challenges, this thesis investigates the potential of Vertically Aligned Carbon Nanotubes (VACNTs) as an alternative photocathode material for UV sensing applications. A comprehensive study was conducted to understand the fundamental mechanisms governing the photoelectric effect in carbon nanostructures. VACNTs were synthesized using Thermal Chemical Vapor Deposition (CVD) and Plasma-Enhanced CVD (PECVD), and their structural and electronic properties were analyzed. Scanning Electron Microscopy (SEM) and coherency analysis (analysis of alignment) confirmed that thermally grown VACNTs exhibited significant waviness, whereas PECVD-grown VACNTs demonstrated improved vertical alignment. The impact of nanotube alignment on the photoelectric efficiency of VACNTs was systemat- ically evaluated. A key finding of this work is the direct correlation between the alignment of VACNTs and their relative efficiency as a photocathode. The optimized PECVD-grown VACNTs exhibited a relative efficiency close to 1 compared to gold, highlighting their potential as a viable alternative to conventional photocathodes. This result demonstrates that improved alignment en- hances electron emission properties, validating the hypothesis that VACNTs can serve as effective UV photocathodes. Furthermore, this thesis explores additional nanoengineering strategies, such as plasma etching, which could further enhance the performance of VACNT-based UV sensors. The findings of this study open new avenues for the development of next-generation nanostructured UV detectors that are cost-effective, and scalable for industrial applications. Overall, this research provides a significant step toward integrating carbon nanomaterials into optoelectronic devices. By optimizing the growth and alignment of VACNTs, this work contributes to the advancement of high-performance, miniaturized UV sensors, offering a promising alternative to traditional metallic photocathodes. Future research will focus on further improving efficiency, stability, and scalability to enable the widespread adoption of VACNT-based UV detectors across various technological fields.