GeTe, Sb2Te3 나노소재의 합성 및 분석

다국어 초록 (Multilingual Abstract)

This is general introductory chapter and highlights a brief account on the chemistry of GeTe and Sb2Te3 nanomaterials and its applications. Here, we have described the various processes of GeTe and Sb2Te3 and its uses in PRAM. The concluding part of this chapter gives a brief account on the works that has been done by different groups in the field of GeTe and Sb2Te3 nanomaterials.

다국어 초록 (Multilingual Abstract)

Solution based synthetic routes are attractive strategies for synthesizing GeTe materials, because they have the potential to impart morphology control on the crystallites and permit liquid-based processing of films and patterned structures. A facile liquid phase method for the synthesis of crystalline and amorphous GeTe nanoparticles (NPs) using germanium chloride dioxane and elemental tellurium dispersed in tri-n-octylphosphine (TOP) in the presence of olylamine (OLA) which acts as reducinging agent as well as solvent and using germanium chloride dioxane and (Et3Si)2Te in the presence TOPO as solvent without the use of any reducing agent is reported. As synthesized, the crystalline GeTe NPs possess rhombohedral symmetry with cube-shaped morphologies. Amorphous GeTe particles prepared at smaller reaction time (2 mins and 5 mins) are nearly spherical in morphology and display amorphous -to- crystalline phase transition with increasing reaction time. Subsequent experiments suggested that the morphology of the GeTe product had a strong dependence on the reaction temperatures. The SEM image of NPs obtained by germanium chloride dioxane and (Et3Si)2Te reveals that with increase in reaction time (2, 5, 10, 15, 30 and 60 min), size of the NPs increases and shape becomes uniform. We assume that the amorphous-to-crystalline transition in GeTe NPs is probably kinetically impeded by the surface restructuring that happens in NPs during their growth in order to minimize the surface energy. The GeTe crystallites are characterized by XRD, SEM, EDS (including element mapping), DSC, XPS and TEM.

다국어 초록 (Multilingual Abstract)

Syntheses of single crystalline nanomaterials are of special importance because of their thermoelectric properties. Herein, we report the first example of the generation of Sb2Te3 nanoflowers from a solution based method at very low temperature (100°C). A simple and convenient germanium assisted low temperature liquid phase synthesis of Sb2Te3 3D flowerlike architectures with diameters of 300-500 nanometers which consisted of the aggregated flakes is described. TEM results showed the flakes were built up from many nanocrystals with around 5 nm diameters. Subsequent experiments performed without the use of germanium source gives only platelike architectures of irregular size and shapes. The results obtained from SEM and TEM suggest that the morphology of the as synthesized nanoflowers is completely based on reaction time and use of germanium source. The morphologies and composition of the as-prepared Sb2Te3 nanoflowers have been characterized by powder XRD, scanning electron microscope (SEM), transmission electron microscope (TEM), high-resolution transmission electron microscope (HRTEM), Differential scanning calorimetry (DSC) energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The atomic ratio of the Sb to Te is very close to 2:3 stoichiometry. A possible mechanism is also proposed for the formation of these flowerlike nanostructures.

목차 (Table of Contents)

• Abstract I
• Chapter1 1
• 1.1. What is Semiconductor Memory? 2
• 1.2. Types of Semiconductor memory 3
• 1.2.1. Volatile memory 3
• 1.2.1.1. DRAM (Dynamic random access memory) 4
• 1.2.1.2. SRAM (Static random access memory) 4
• 1.2.2. Non-Volatile memory 4
• 1.2.2.1. Flash memory 5
• 1.2.2.2. FeRAM (Ferroelectric Random Access Memory) 5
• 1.2.2.3. RRAM (Resistive random-access memory) 6
• 1.2.2.4. PRAM (Phase change random-access memory) 6
• 1.3. Principle of PRAM 9
• 1.4. How to make PRAM materials? 11
• 1.4.1 ALD(Atomic layer deposition) Mechanism 11
• 1.4.2 VLS(Vapor-Liquid-Solid) Mechanism 14
• 1.4.3 Self-Catalytic VLS 18
• 1.4.4 VLS Vapor Phase Methods 19
• 1.5 Reported Articles Related to Synthesis of GeTe and Sb2Te3 Nanomaterials 21
• 1.6 References 22
• CHAPTER 2 30
• 2.1. Introduction 31
• 2.2. Experimental 33
• 2.2.1. Materials 33
• 2.2.2. Characterization 33
• 2.2.3. Synthesis of GeTe nanocrystals 34
• 2.2.3.1. Synthesis of GeTe nanocrystals using Germanium chloride dioxane and TOP-Te 34
• 2.2.3.2. Synthesis of GeTe nanocrystals using Germanium chloride dioxane and (Et3Si)2Te 35
• 2.3. Results and Discussion 36
• 2.4. Conclusions 49
• 2.5. References 50
• CHAPTER 3 52
• 3.1. Introduction 53
• 3.2. Experimental 55
• 3.2.1. Materials 55
• 3.2.2. Characterization 55
• 3.2.3. Synthesis of Sb2Te3 Nanoflowers 55
• 3.2.3.1. Synthesis of Sb2Te3 nanocrystals using Germanium chloride dioxane, Antimony(III)chloride and TOP-Te 55
• 3.3. Results and Discussion 58
• 3.4. Conclusions 67
• 3.5. References 68