Photoacoustic and terahertz techniques applied to biophotonics and photonic devices in studies in 2D materials

Abstract

Nowadays, technological advancements demand smaller, faster, and more efficient devices. This makes nanomaterials essential, as they offer innovative solutions by enhancing performance at the nanoscale and driving the development of new materials. Their applications

span a wide range of fields, from next-generation transistors and flexible electronics to high- efficiency solar cells and advanced drug delivery systems. However, one of the major

challenges in working with nanomaterials is their characterization, which requires contactless and non-destructive techniques. The electronic, structural, and optical properties of these materials are crucial for the future of materials science. This thesis, divided into five chapters, presents results obtained using two powerful techniques for characterizing different types of two-dimensional (2D) materials: photoacoustics (PA) and terahertz (THz) spectroscopy. Both methods are widely employed in imaging and material analysis. Following the introduction in Chapter 1, Chapter 2 provides a brief review of absorption and refraction, serving as a simple reminder. Chapter 3 is dedicated to photoacoustics, explaining the underlying phenomena, relevant equations, and applications. Photoacoustic microscopy (PAM) is introduced, and results obtained in the laboratory using this setup are presented for four different types of

nanoparticles: titanium nitride (TiN), gold nanoparticles (nanospheres and nanorods), erbium- ytterbium (Er3+–Yb3+) co-doped nanoparticles, and an iron oxide (Fe3O4) nanocomposite

(Fe3O4@βCD-PHY). All images acquired using PAM demonstrated excellent resolution and contrast. Moreover, the diversity in optical and electronic properties among the samples confirms the versatility and effectiveness of photoacoustic microscopy. Chapter 4 explores terahertz experiments, particularly Terahertz Time-Domain Spectroscopy (THz-TDS). It presents the theory behind the generation and detection of THz radiation, along with applications within this low-frequency range of the electromagnetic spectrum. Results include the characterization of 2D transition metal dichalcogenides (TMDs) and the design of a continuously tunable filter for THz telecommunication systems. Finally, Chapter 5 outlines future work to be carried out in upcoming THz experiments. Through these chapters, this work aims to contribute to the rapidly advancing field of nanomaterial characterization.