Ionic liquids (ILs) are nowadays a large and widely explored class of ionic compounds that melt below 100 °C. Due to their attractive properties, ILs are now of growing interests in a variety of inorganic materials preparation. However, most studies have put much focus on the description of new synthetic strategies. The chemical reactivity of ILs in the reactions is often neglected. In this dissertation, a series of metal chalcogenides were synthesized using the decompositions of ILs. The role or chemical reactivity of ILs in the reactions was demonstrated in detail. The hierarchical desert-rose-like SrTiO3 particles have been successfully prepared based on an ethylene glycol (EG) mediated one-pot IL-assisted solvothermal synthetic route. The used basic ionic liquid tetrabutylammonium hydroxide (TBAH) serves as an alkaline source and can also replace EG as the sole solvent to synthesize polyhedral SrTiO3, showing “all-in-one” solvent and reactant. A series of metal sulfides, such as Sb2S3, Bi2S3, PbS, CuS, Ag2S, ZnS, and CdS have been obtained from a choline chloride/thioacetamide based deep eutectic solvent (DES, an IL analog solvent) by a simple and general synthetic method. The reaction mainly proceeds in two steps: i) the dispersion of metal salts in the DES and the formation of a metal-DES complex, and ii) the decomposition of the metal-DES complex and formation of the final products. In addition, the chemical reactivity of phosphonium based ILs with selenium and tellurium at above 220 °C was systematically investigated by a series of dissolution experiments, tracking the solute selenium and tellurium species by nuclear magnetic resonance (NMR). NMR results clearly indicate some common decomposition mechanisms for quaternary phosphonium ILs at a relatively high temperature in the presence of selenium or tellurium. The decomposition of the quaternary phosphonium cations should proceed by an elimination of one alkyl substituent via an SN2 reaction, forming the respective trialkylphosphane selenides or tellurides in the presence of selenium or tellurium, which is then responsible for the genuine dissolution of selenium or tellurium. However, in the case of tellurium, the dissolution behavior is much more complicated compared to that of selenium. The coupling of P and Te which indicates a P–Te bond formation is only observed in the NMR spectra when a sufficient amount of tellurium (e.g. Te : IL = 1 : 1) is provided. The existence of a parallel-competitive IL decomposition route besides the SN2 reaction is regarded as the side reaction for the dissolution of tellurium. This may at least partially explain the relatively lower solubility of tellurium in phosphonium based ILs compared to that of selenium.

Ionic liquids (ILs) are nowadays a large and widely explored class of ionic compounds that melt below 100 °C. Due to their attractive properties, ILs are now of growing interests in a variety of inorganic materials preparation. However, most studies have put much focus on the description of new synthetic strategies. The chemical reactivity of ILs in the reactions is often neglected. In this dissertation, a series of metal chalcogenides were synthesized using the decompositions of ILs. The role or chemical reactivity of ILs in the reactions was demonstrated in detail. The hierarchical desert-rose-like SrTiO3 particles have been successfully prepared based on an ethylene glycol (EG) mediated one-pot IL-assisted solvothermal synthetic route. The used basic ionic liquid tetrabutylammonium hydroxide (TBAH) serves as an alkaline source and can also replace EG as the sole solvent to synthesize polyhedral SrTiO3, showing “all-in-one” solvent and reactant. A series of metal sulfides, such as Sb2S3, Bi2S3, PbS, CuS, Ag2S, ZnS, and CdS have been obtained from a choline chloride/thioacetamide based deep eutectic solvent (DES, an IL analog solvent) by a simple and general synthetic method. The reaction mainly proceeds in two steps: i) the dispersion of metal salts in the DES and the formation of a metal-DES complex, and ii) the decomposition of the metal-DES complex and formation of the final products. In addition, the chemical reactivity of phosphonium based ILs with selenium and tellurium at above 220 °C was systematically investigated by a series of dissolution experiments, tracking the solute selenium and tellurium species by nuclear magnetic resonance (NMR). NMR results clearly indicate some common decomposition mechanisms for quaternary phosphonium ILs at a relatively high temperature in the presence of selenium or tellurium. The decomposition of the quaternary phosphonium cations should proceed by an elimination of one alkyl substituent via an SN2 reaction, forming the respective trialkylphosphane selenides or tellurides in the presence of selenium or tellurium, which is then responsible for the genuine dissolution of selenium or tellurium. However, in the case of tellurium, the dissolution behavior is much more complicated compared to that of selenium. The coupling of P and Te which indicates a P–Te bond formation is only observed in the NMR spectra when a sufficient amount of tellurium (e.g. Te : IL = 1 : 1) is provided. The existence of a parallel-competitive IL decomposition route besides the SN2 reaction is regarded as the side reaction for the dissolution of tellurium. This may at least partially explain the relatively lower solubility of tellurium in phosphonium based ILs compared to that of selenium.

This thesis concentrates on advancing the thermal atom layer deposition (ALD) of Sb2Te3 and related multilayered metal chalcogenide thin films. It involves depositing a sub-monolayer of the target compound during each ALD cycle through successive, separated, and self-limiting gas-solid reactions between typically two gaseous reactants. The low deposition temperatures facilitate the creation of unconventional combinations of multilayers in distinct thermodynamic regimes. The well-defined chemical reactions inherent in ALD processes yield layers with ideal stoichiometry, and subsequent heat treatment enhances crystallite size and interface quality. Various methodologies have been explored to manipulate the optical and electrical properties of these thin films, demonstrating the capacity to tune their electrical and thermal transport properties using ALD.:Abstract Table of Contents Acknowledgments 1. Introduction 2. Background and Motivation 2.1. Basic Features of ALD 2.2. ALD of Metal Chalcogenides 2.3. Functional Properties 2.3.1. Photoresponse Effect 2.3.2. Thermoelectric Effect 2.4. State-of-art in Sb2Te3 and Related Multilayers 3. Experimental Techniques 3.1. Thin Films and Devices Preparation 3.2. Transport Property Evaluation 4. Wafer-Scale Growth of Sb2Te3 for Photodetectors 4.1. Microstructure Characterization 4.2. Rectifying Behaviour 4.3. Photoresponse Behaviour 4.4. DFT Calculation 4.5. High Yield Integration 4.6. Conclusion 5. Sb2Te3 with Insulator SbOx Layer 5.1. Microstructure Characterization 5.2. Sb2Te3 with Single-cycle of SbOx 5.3. Sb2Te3 with Multi-cycles of SbOx 5.4. Comparison of TE Performance 5.5. Conclusion 6. Sb2Te3 with Semiconductor Sb2Se3 Layer 6.1. Microstructure Characterization 6.2. Transport Properties 6.3. Thermal Conductivity and zT Values 6.4. Conclusion 7. Conclusion and Outlook Appendix: Wafer-Scale Growth of Sb2Te3 for Photodetectors Bibliography