Investigation of Silver Nano Structures

• Main Authors: Man-Yu, Lin, 林滿玉
• Other Authors: L. J. Chen
• Format: Others
• Language: en_US
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/43538726543664996786

碩士 === 國立清華大學 === 材料科學工程學系 === 91 === The formation of silver metal nanodots including Ag@HT, Ag@DT and Ag@ODT nanodots has been investigated. By using a liquid-liquid two-phase method, the size of Ag@DT nanodots is close to 4 nm. The size of Ag@ODT nanodots is smaller with wider distribution. The size and size distribution of Ag@HT nanodots are even larger and wider, respectively. Two-dimensional ordered superlattices of the nanodots were formed on carbon films coated on transmission electron microscopy (TEM) copper grids by evaporating a drop of the dispersion in toluene. To fabricate self-assembled metal nanodots, some specifications must be met. First, the quantity of alkanethiol (0.15 ml of dodecanethiol) is important because it permits the non-aggregation of dots and the arrangement in ordered arrays. When Br was substituted by S, the organization in self-assembled arrays is improved. The link between dots is stronger with S so that the prevention of aggregation of nanodots is more effective. Second, the organic solvent (toluene) is selected to realize the rapid drying of the nanodots solution on the substrate. The drying must not be too fast or too slow because the evaporation rate determines the quality of the ordered structures. The silver nanodots were investigated by UV-visible absorption spectroscopy and TEM. A shift of the maximum absorption peak position of the UV-visible spectra occurred for different dot sizes. The results indicated that large thiol-capped silver nanodots led to a red shift in UV-visible absorption spectroscopy; small thiol-capped silver nanodots resulted in a blue shift. The TEM images show consistent results with that of the UV-visible spectra. In addition, the UV-visible spectra of the Ag@DT nanodot colloids obtained show that the system is more monodisperse than those of the Ag@HT and Ag@ODT nanodot colloids, and can remain stable for several weeks. Thermogravimetric analyses were carried out for Ag@HT, Ag@DT and Ag@ODT nanodots. The mass decrease started at about 140, 180, and 225℃ for Ag@HT, Ag@DT and Ag@ODT nanodots, respectively. The results indicate that the outer- shell with longer chain (as octadecyl-thiol) is thermally more stable than that of shorter chain (as hexyl-thiol). For Ag nanodots, grating peaks have been observed in the X-ray diffraction spectra. This behavior appears for multi-layer characterized by linear structures. Moreover, the first peak of diffraction can be used to estimate the distance between layers. Hexagonal networks were formed on carbon films and on Si(001). Solutions containing different concentrations of nanodots were developed to form networks. Good suspension capability, an appropriate concentration of silver nanodots and moisture content are essential to form superior networks. A simple method was used to synthesize silver disks. The rods and disks were found to form and grow to several micro-meters. The rods tend to orient with respect to each other by 60° or 120° if the rods are long enough (at least 500 nm). In addition, for silver disks to form, it seems advantageous to mix with DI water. Replacing ethanol with DI water altogether appears to improve the shapes of silver-disk. Furthermore, the reaction time is shorter than that of solvent with just ethanol.