Thickness tailored synthesis of two dimensional materials and tuning their intrinsic properties: fundamentals to application
Creators: name: KURIAKOSE, Sruthi
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 401605
subject: Functional materials

description: Traditional semiconductor based devices like any electronic and opto-electronic gadgets use conventional semiconductor materials like silicon. As silicon is reaching its physical limits of operation, according to Moore's law, new materials and technologies are required to shrink the size of future smart electronic devices. This calls for exploration of new materials to fulfil the current and future demands of devices. The research on two dimensional (2D) materials to take over the conventional 3D materials like silicon has been increasing dramatically especially after the discovery of graphene. The key factor to choose 2D materials is their band gap tunability with respect to their thicknesses due to quantum confinement. This property makes them an exciting prospect for deployment in a variety of novel applications in electronic, optoelectronic photonic devices and sensors. 

This thesis focuses on thickness tailored synthesis of elemental 2D materials and tuning their intrinsic properties by modulating their band gap enabling their use in novel electronic and optoelectronic devices. Among the elemental 2D materials, Black phosphorus (BP) and Antimonene (Sb) have emerged as an exciting class of materials for their wide tuneable band gap suitable for electrical and opto-electronic applications. The biggest challenge of BP is, its environmental stability issues which are being addressed by current research activities. The challenge for Sb is that the experimental investigations are of recent origin, even though theoretical studies are available. As the traditional mechanical exfoliation is less amenable due to its structural morphology limitations, various synthesis techniques are being explored. In this thesis, firstly, the context of the mechanisms governing the atmospheric instability of BP and the major developments in effectively countering the problem is critically reviewed to understand manoeuvrability of the material. This is followed by tuning of the band gap of BP which is presented in two techniques: plasma assisted thinning and doping. BP is synthesized with a tailored thinning process using two different gases to achieve a desired thickness. A comparison of the two thinning processes are made by studying the effects of thinning on their electrical and opto-electronic properties- pre and post thinning. In the second technique, the asexfoliated multilayer BP is doped chemically to tune their band gap to achieve a strong photoluminescence, opening the application base of BP in opto-electronics.

Secondly, the charge carrier injection of BP and a chosen set of contact materials in a vertical configuration are studied to understand the charge carrier injection through different contact materials. This work adds an important piece of knowledge to the fundamental studies of choosing the contact material with the optimal barrier height at the interface of BP. This enables designing electrical and opto-electronic devices based on the multilayer BP, in particular, for devices designed in a stacked configuration.

Lastly, the research gap in the synthesis techniques of Sb is identified by reviewing the techniques reported in the literature. The research gap is addressed by using a physical vapour deposition technique for the growth of a large aspect ratio growth of ß-phase and few layerantimonene nanosheets using a physical vapor deposition synthesis directly on SiO2/Si substrates, a widely used complementary metal-oxide-semiconductor (CMOS)-compatible substrate. This reduces fabrication complexity by enabling direct device fabrication, which broadens the applicability of FL-Sb.

This thesis presents fundamental studies of the elemental 2D materials namely, BP and Sb using novel thickness tailored synthesis and band gap tuning techniques in the nanotechnology domain. These novel scalable and low cost synthesis methods lays a platform for future investigations into the synthesis and applications of the elemental two dimensional materials.