| Summary: | 碩士 === 大同大學 === 機械工程學系(所) === 103 === Indium tin oxide (ITO) is often used as transparent conductive electrode. The applications of this materials are mobile phone, LCD and solar cells. Due to the limit supply of indium and the brittle nature of ITO, the search of alternative has been a hot topic both in industry and academia. Nano-structures like nanotube,or nanowire are popular candidates due to their simple fabrication and inexpensive nature. In this thesis, we investigate the several factors that affect the electrical and optical properties of silver nanowires thin films.
The first issue is the size effect. The results indicate under the same weight, the large diameter silver nanowire has better optical transmission and larger sheet resistance. The reason is for similar weight percentage, large diameter silver nanowires has less area coverage than that in small diameter counterpart. Therefore the less dense coverage and interconnection results in better optical transmission and higher sheet resistance.
Another factor that influence the silver nanowires performance is the substrate wettability. To probe this effect, different plasma power was applied to glass substrate to vary its surface property. The results indicate the effect of wettability on these properties seems depend on size. For smaller diameter (AR 40), the high power plasma surface treatment (more hydrophilic) gives rise to high sheet resistance and high optical transmission. On the other hand, for larger diameter (AR 90), the medium power plasma surface treatment (less hydrophilic) results in low sheet resistance and high optical transmission. This implies different size silver nanowires has distinct response for surface wettability and lead to different electrical and optical properties variation.
Apart from the size and wettability, we also investigate how the dielectrophoresis (DEP) can affect the microstructure in silver nanowires. A microchip used to purify the silver nanowires was fabricated to perform the DEP purification. The results show for smaller diameter silver nanowires (AR 40), DEP has bigger impact in sheet resistance than that in optical transmission. The lower sheet resistance occurs in high frequency which has larger DEP force. However, for larger diameter silver nanowires (AR 90), DEP has profound impact for optical transmission and the lowest sheet resistance does not occur in high frequency. The mechanism for DEP purification is the spread of the bundle nanowires which leads to more uniform distribution of the nanowires.
In conclusion, the sheet resistance and optical transmission in silver nanowires are dependent on size and distribution. The effects of surface treatment and DEP purification are sensitive to nanowire diameter and operation condition. The distribution and the microstructure of the nanowires are keys to understand these phenomena.
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