Exploring ultrafast terahertz dynamics for efficient transmission and emission applications

• Main Author: Ali Abdelaziem Abdelgaied Abdelrahman
• Other Authors: Liu Zheng
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2024
• Subjects: Engineering; Physics; Materials
• Online Access: https://hdl.handle.net/10356/174614
• Institution: Nanyang Technological University

Terahertz (THz) spectroscopy is a powerful and versatile tool for material characterization and a growing field of research. The THz frequency range, which extends from 0.1-30 THz, provides a unique window into the properties of various materials and their interactions with electromagnetic radiation. THz spectroscopy is gaining popularity in various fields, including material science, biology, chemistry, and physics, due to its non-invasive nature that enables the examination of the intrinsic properties of materials, including their structural, vibrational, and electronic states. The non-ionizing nature of THz radiation also makes it particularly useful for studying sensitive biological samples and delicate materials. Thanks to recent technological advancements, THz spectroscopy is now capable of providing real-time measurements with a high spatial and temporal resolution, which makes it a valuable tool for exploring new scientific phenomena and developing practical applications. However, despite its potential, the THz gap, characterized by a lack of compact, low-cost, and high-performance sources and detectors, still prevents its full exploration and utilization. This limits the practical applications of THz technology. Research efforts are ongoing to develop innovative solutions that can overcome these limitations and bridge the THz gap. Advances in areas such as photonics, electronics, and materials science hold promise for the development of efficient and effective THz sources and detectors, which will enable discoveries and applications in this field. To address the THz gap, this project focuses on investigating the optical properties in the THz band for a diverse range of material systems, including polyvinylidene fluoride (PVDF) polymer foam, two-dimensional (2D) chromium dichalcogenide (CrS2) thin films, and strontium iridate oxide (SrIrO3). The first phase of the project involves the preparation and characterization of PVDF using an efficient sugar template method. Impedance spectroscopy in conjunction with time domain THz spectroscopy (THz-TDS) was used to study the PVDF foam at low frequencies from 1 kHz to high frequencies in the THz range. The properties of PVDF were extracted from the THz calculation together with simulation by the Maxwell Garnett model, both indicated that PVDF foam is an efficient material system for transmitting THz. The second phase of the project deals with the preparation and characterization of CrS2 material as single crystal thin films using chemical vapor deposition (CVD). THz-TDS was applied to extract the dielectric properties and static THz conductivity in the range of 0.3-3 THz. The theoretical THz model in combination with the thin film approximation indicated that the conductivity of CrS2 is in the range of semiconducting materials, suggesting it is a good thin film material for THz transmission and could be useful for THz sensing and modulation applications in the future. In the third phase, an efficient THz emitting source was established using SrIrO3 interfaced with ferromagnetic materials such as cobalt (Co) and nickel ferrite (NiFe). The preparation of SrIrO3 using pulsed laser deposition (PLD) and the detailed device fabrication process were outlined. Additionally, the static and photoconductivity of the SrIrO3 system were studied using TDS and optical pump probe THz (OPTP), revealing interesting behavior from this material system. Finally, THz spectroscopy has been proven to be a powerful tool for efficient material characterization in a non-contact manner for a wide range of materials systems, regardless of their type. The results showed that PVDF is an efficient material for transmitting THz, CrS2 is a semiconducting material system that can be used as a THz transmitter, and SrIrO3 has been introduced as a room-temperature THz source and has the potential to replace conventional THz sources with minimum requirements.