Chemical Vapor Deposition of Ruthenium Dioxide Nanorods and Its Field Emission Properties
| Autor: | Chih-Sung Hsieh, 謝志松 |
|---|---|
| Rok vydání: | 2004 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 92 The preparation of RuO2 nanorods via chemical vapor deposition CVD route, its surface composition analysis by X-ray photoelectron spectroscopy XPS, its structural analysis using scanning and transmission electron microscopy SEM and TEM, and its field emission properties with and without annealing, are the research subjects of this master thesis. The CVD preparation of RuO2 nanorods has been carried out in a cold-wall reactor using precursor Ru(C11H19O2)2(C8H12)2. The nanorods of variable length and diameter 22-100 nm can be grown in flowing oxygen at substrate temperature 440-520C and 2-4 mbar. The individual RuO2 rod resembles an obelisk with an off-center tip. The orientation of nanorods on the Si(100) substrate sputtered with transition metals is chaotic, on the other hand, the RuO2 nanorods on the LiNbO3(100) and LiTaO3(012) substrate are aligned vertically and tiltedly. The alignment on single crystal surface implies a delicate crystallographic relation between RuO2 lattice and the substrate lattice. Regardless of the alignment, all the RuO2 nanorods are grown in the [001] direction. The field emission properties of RuO2 nanorods are measured on the specimens of copper-sputtered Si(100) wafer. In general, the threshold field strength Ethr and the turn-on field strength Eto decrease with emission time then reach stable values after a transient period. These stable field strengths are higher if the average nanorod diameter is large. For those specimens being thermal annealed, not only the values of Ethr and Eto both decrease but also the slopes of F-N plots decrease significantly. Meanwhile, the transient period of annealed specimens is shortened. It is inferred that certain oxygen containing species on the RuO2 nanorods desorbed during the initial emission period, and the desorption will be accelerated for annealed specimens. Another piece of evidence for desorption is that we will experience the transient period again if the field-emissioned sample has been exposed to ambient atmosphere, and no transient period will be experienced if the field-emissioned sample is kept under the high vacuum condition. The intrinsic values of Ethr and Eto for RuO2 nanorods seem to be 5.5 V/m and 11.0 V/m, since these two values are measured for those annealed specimens after the transient period. Unfortunately, the stability of 400 and 500C annealed specimens also slightly decline. The degeneration of 500C annealed specimens is more than that of 400C annealed specimens. The transient period of field emission is suspected to originate from the oxygen-containing species on the RuO2 nanorods identified by the XPS analysis. This unknown species is measured up to 18% excess oxygen in the surface composition of as-prepared nanorods. It can be completely removed after argon ion sputtering for 1 minute. If the sample has been stored for 53 days, the surface excess oxygen can be even more, 27%. The 0.6% weight loss in the thermal event at 287C measured by thermal analysis also seems to be related to the desoption of this unknown species. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
| Externí odkaz: |
|