Two-dimensional (2D) transition metal dichalcogenides (TMDs) offer a platform for nanoscale electronic devices due to their atomically thin geometry and semiconducting band structure. This thesis investigates the fabrication, assembly, and electrical characterization of TMD-based field-effect transistor (FET) devices using MoS2, MoSe2, and WS2 flakes. The primary objective is to evaluate how different transfer method and electrode architecture influence the interface quality of the device inturn having a significant impact on the electrical transport behaviour in 2D semiconductor devices.

In this work, the TMD material was prepared using both bottom-up and top-down approaches. For the transfer of the flakes, two different dry transfer techniques were explored involving the use of either only a PDMS stamp or a PC/PDMS stamps. The Device fabrication itself was performed in Kavli Nanolabs, which provided the cleanroom environment for the process. The whole process of the device fabrication process included several steps including substrate cleaning using fuming nitric acid, organic solvent cleaning, resist coating, photolithography or electron-beam lithography, metal deposition, lift-off, and oxygen plasma cleaning. Three main electrode geometries were fabricated in this work, including two-terminal, four-terminal, and interdigitated structures. The electrical contacts consisted of Ti/Au stacks with thicknesses of 5 nm and 30 nm, respectively, deposited by electron-beam evaporation.
Electrical characterization was conducted at room temperature (∼ 300 K) under vacuum conditions, and these measurements included mainly current-voltage (I-V) and gate-sweep measurements, and four probe measurements (V-I). Across the measured devices, the absolute drain currents ranged from approximately 10−12 A to 10−9 A. For the prepatterned interdigitated device incorporating a 2D MoSe2 flake, the total resistance was calculated to be 2.33 × 1011 Ωand the same device architecture with a nanoscroll device exhibited a resistance of 6.91 × 1011 Ω. For the pre-patterned MoSe2 device, the resistance was measured to be 1.62 GΩ, and it displayed p-type semiconducting behaviour; while the pre-patterned WS2 device exhibited a significantly higher resistance of 1.5 × 1012 Ω and it showed n-type behaviour. The subthreshold swing (SS) and field-effect mobility were also extracted for both these two-electrode prepatterned devices. For the MoSe2 device, the SS was calculated to be 6877.7 mV/dec, with a field-effect mobility of 0.0067 cm2 V−1 s−1. For the WS2 device, the SS was 488.1 mV/dec and the extracted field-effect mobility was 4.1 × 10−4 cm2 V−1 s−1. Finally, resistance measurements were performed on a post-patterned WS2 device, yielding a resistance of 1.65 × 109 Ω. This device exhibited ambipolar semiconducting behaviour, with n-type conduction being dominant. The subthreshold swing for electron transport was calculated to be 10726 mV/dec, and the corresponding field-effect mobility was 0.04 cm2 V−1 s−1. Overall, the results indicated a lower resistance for the post-patterned WS2 device compared to its pre-patterned counterpart, but the results are not comparable since the flake geometry, thickness and quality varied between the pre-patterned and post-patterned devices. However, all gate-sweep measurements demonstrated limited electrostatic modulation, characterized by weak on-off ratios and large subthreshold swing values, which is consistent with suppressed carrier injection. The results indicate that electrical transport in the fabricated devices is dominated by several extrinsic factors, including contact resistance, ambient conditions, interfacial contamination, and measurement constraints, rather than intrinsic TMD channel properties. These require future work and optimization.
Overall this work highlights the challenges associated with fabricating and measuring electrical properties of 2D semiconductor devices and provides practical guidance for improving fabrication workflows, interface engineering, and measurement strategies for future exploration of 1-D TMD-based
electronics.

In an effort to limit global warming to 1.5 °C by the year 2050, the Ultra Low CO₂ Steelmaking (ULCOS) program was launched, from which the HIsarna process was developed by Tata Steel in the Netherlands. This process allows us to refine low-quality iron ore and recycle one of the byproducts of steelmaking, converter slag, as a flux material. These attributes are improvements to the traditional blast furnace and offer a significant reduction in CO₂ emissions. However, research on the interaction between converter slag and low-quality iron ore at such high temperatures is limited. The main purpose of this investigation is to compare the impact of converter slag and limestone on the thermal decomposition of low-quality hematite- and goethite-bearing iron ores, particularly focusing on the conversion degree and the products of decomposition. To achieve this, the thermal decomposition of several combinations of the ores with the fluxes added at fractions ranging from 0 to 50 wt.% was first modelled thermodynamically using FactSage software. Laboratory experimentation was conducted to complement these findings, starting with thermogravimetric analysis, followed by heat treatment in a horizontal tube furnace. It was found that there was an increase in liquid phase fraction and slag content with flux addition, with the effects being more pronounced for limestone than converter slag. Additionally, the conversion degree of hematite reduced from ~10% with 0 wt.% flux to ~6.75% and ~7.60% when limestone and converter slag were added at 25 wt.%, respectively. Such a reduction in the conversion degree was attributed to the entrapment of iron in calcium-rich slag phases. Therefore, converter slag was found to be less detrimental to the thermal decomposition of low-quality iron ores, in comparison to the traditional limestone, at 1500 °C, concluding that the use of converter slag as a flux material in HIsarna is promising.

In response to climate change mitigation and the pursuit of circularity, Tata Steel Netherlands plans to construct an Electric Arc Furnace (EAF) to replace the carbon-based blast furnace. Initially, the EAF will operate with a ratio of 70% Direct Reduced Iron (DRI) and 30% steel scrap, with future intentions to increase scrap input for enhanced circularity. However, the capacity of an EAF to effectively handle significant changes in the scrap ratio remains uncertain. This thesis includes a detailed literature review addressing this gap by exploring the implications of Scrap and DRI, in the EAF operations, covering various fundamentals of the EAF process - raw materials, operating regimes, melting practices, metallurgy, slag engineering, and furnace constructions, with a specific focus on Consteel technology. For optimal EAF operation, fine-tuning slag chemistry is essential to achieve the desired balance of slag basicity, foaming, volume, and ensuring long refractory life of the furnace. Slag composition can vary widely due to multiple process variables including the type of charge mix, charge composition, charge feeding rate, oxygen lancing, carbon injection/addition, fluxing agents, and refractory erosion. These variables cause slag composition and rates to be transient parameters that evolve throughout the heating process, leading to dynamic changes in all related phenomena and outcomes. To accurately capture these effects and realistically simulate EAF operations, especially in the absence of real plant data, a dynamic process model is essential. This thesis investigates the operational implications of varying the Scrap:DRI ratio in an EAF process with continuous raw material charging using the dynamic Effective Equilibrium Reaction Zone (EERZ) model. This model allows for a comprehensive analysis of the transient behavior of slag composition and its impact on EAF performance. This thesis examines three cases of charge mix: 70% DRI with 30% scrap, 50% DRI with 50% scrap, and 30% DRI with 70% scrap. Pilot EAF trial data will be used for the validation of the model. Overall, the thesis aims to provide insights into optimizing Scrap:DRI ratios for sustainable and efficient steelmaking.