Low Temperature Growth, Characterization and Resistive Switching Behavior of Silica Nanowires

학위논문 (박사)-- 서울대학교 대학원 : 재료공학부, 2014. 2. 김형준.Silica nanowires have been the subject of intense study owing to their unique properties of blue light emission and easy surface functionalization. Vapor-liquid-solid (VLS), solid-liquid-solid, and solution-liquid-solid mechanisms have been used to explain the growth characteristics of these silica nanowires. However, these techniques require relatively high growth temperatures up to ~ 1000 oC and long growth durations of several hours or even days to grow micrometer-long nanowires. Moreover, addition of metal catalysts, which is essential for initiating the synthesis of silica nanowires, could potentially pose a concern of metal contamination. The high growth temperature and metal contamination by the catalysts limits their applications to extended areas, such as display devices and bioelectronics. In this paper silica nanowires were synthesized by employing inherent directionality of chemical vapor reaction between bis(ethylmethylamino)silane (H2Si[N(C2H5)(CH3)]2) precursor and water without a metal catalyst at room temperature. The difference in the oxidation reactivity between Si-H and Si-N bonds with water leads to the formation of silica nanowires. The mean diameter and length of the silica nanowires grown for 10 min were ~ 60-80 nm and ~ 1.9 μm, respectively. Transmission electron microscopy revealed that the obtained nanowires had the concave tip, differing from other silica nanowires produced by a conventional vapor-liquid-solid method, and were amorphous. The reverse cone shape at the distal tip of nanowire is due to initial growth starting around the perimeter of the nuclei. Energy dispersive X-ray spectroscopy, Fourier transform infrared, and X-ray photoelectron spectroscopy results indicated that the nanowires have a close composition to stoichiometric SiO2. But a comparison of normalized XPS peaks with thermal oxide indicates that the oxygen is deficient due to many disorders, in this case disorders are Si-H bonds and H2O molecules in the interior of silica nanowires. Unipolar resistive switching behavior in silica nanowires was firstly reported. The switching is stable extended cycling, the minimum ratios of HRS to LRS are maintained over 300 times of switching.1. Introduction 1 1.1 Overview 1 1.2 Silica nanowires 4 1.2.1 Growth techniques and mechanisms of silica nanowire synthesis 4 1.2.2 Properties of silica nanowires 7 1.3 Resistive switching random access memory (ReRAM) 17 1.3.1 Materials for ReRAM application 17 1.3.2 Classification of resistive switching phenomenon 17 1.3.3 Resistive switching mechanisms 20 1.3.4 Electronic conduction mechanism in metal-insulator-metal (MIM) structure 26 1.3.5 Resistive switching behavior in silica 41 2. Experiments and analyses 44 2.1 Apparatus of CVD system for the growth of silica nanowires 44 2.2 Analysis methods 46 2.3 Switching methods for electrical characterization 47 2.4 surface treatments 48 2.5. O3 and UV treatment effects on structural changes of silica nanowires 49 3. Results and discussion 54 3.1 Synthesis of silica nanowires & growth mechanism 54 3.2 Experimental verification of a new mechanism 60 3.2.1 The difference in the oxidation reactivities 60 3.2.2 Nucleation of silica nanowires 61 3.2.3 Distal tip shape of silica nanowires 63 3.2.4 One-dimensional growth of silica nanowires 64 3.2.5 Lateral growth of silica nanowires 66 3.3 Characterization of silica nanowires 79 3.3.2 Chemical structure of silica nanowires 79 3.3.3 Electrical properties of silica nanowires 86 4. Conclusion 99 5. Bibliography 101 List of publications 111 Abstract (in Korean) 122Docto