本論文旨在探討以水熱法製備氧化鎢(WOx)與氧化鎳(NiOx)奈米結構及其於酸鹼值感測器之應用。首先，利用水熱成長(HTG)方式於平面的鎢箔與矽(Si)基板上分別成長WO3與NiO奈米片(nanosheets, NSs)作為感測電極(sensing electrodes, SEs)，並結合商用MOSFET以製備pH-EGFET感測器；研究過程中，除分析HTG WO3與NiO NSs的晶體結構以及探討不同HTG製程於SEs所形成的表面積(surface area, SA)對pH感測特性之影響外，同時亦使用濺鍍法所沉積WO3與NiO薄膜之SEs作為比較。其次，為進一步使HTG NiO NSs所製備的Si基板增加SA，於濕式蝕刻製備具粗化Si基板，增加SEs表面吸附酸鹼離子之能力，以進一步增進pH-EGFET感測器的靈敏度。

本論文內容歸納如下: 第一部分為探討HTG溫度之WO3 NSs形貌，並分析其不同SA之SEs感測特性；研究結果顯示，WO3 NSs (90 °C) SEs具有高靈敏度(63.37 mV/pH)、低遲滯(4.79 mV)與低飄移(0.37 mV/h)的特性。其次為探討所獲得超能斯特(super-Nernstian)效應(>59.16 mV/pH)現象及原因，應可歸因於本研究最適化WO3 NSs SA可提高表面離子吸附與NSs邊緣之局部電場增強效應所造成。

第二部分為探討於HTG時間之NiO NSs形貌；最適化HTG NiO NSs (9 h)之SA較濺鍍沉積平面之NiO薄膜高約6.28倍，其SEs感測靈敏度為54.24 mV/pH較平面(47.44 mV/pH)增加14.33%。並具有低遲滯5.27 mV與低飄移0.46 mV/h的特性。

第三部分為探討利用濕式蝕刻製備出角錐、奈米線與角錐奈米線之Si基板表面粗化結構，與研究粗化基板之SA與pH感測靈敏度關係。於利用HTG製備NiO NSs於粗化Si基板上，本研究進一步製備出多重粗化之SEs基板。實驗結果顯示，於採用最適化蝕刻參數之Si基板，角錐奈米線之SA較角錐與奈米線者，分別增加121.65% 與173.30%，其靈敏度(54.77 mV/pH)則分別增加8.84%與12.83%。其次，最適化HTG參數製備出NiO NSs於粗化基板上，NiO NSs角錐奈米線靈敏度(56.60 mV/pH)較角錐與奈米線基板，分別增進0.10%與2.95%。此研究證實HTG NiO NSs多重粗化之SEs基板，可進一步增加SEs表面離子吸附能力與提高感測靈敏度。
最後，對HTG製備之WO3 NSs與NiO NSs及NiO NSs於三種不同粗化Si基板SEs結構之酸鹼值感測器做一總結。本研究所提於提升SEs表面之粗化結構，實驗證實確可有效提升酸鹼離子感測能力，預期將對未來酸鹼值感測器應用極有助益。

The present dissertation aims at the fabrication of WOx and NiOx nanostructures using hydrothermal growth (HTG) method and their applications on pH sensors. Using W foil and Si substrates, pH sensing electrodes (SEs) based on WO3 and NiO nanosheets (NSs) were prepared by a HTG method. Extended-gate field-effect transistor (pH-EGFET) configuration with a commercial n-MOSFET was employed for the pH sensing measurement. In this study, both the material analysis of WO3 and NiO NSs and the influence of different HTG parameters on surface area (SA) of the SEs on the pH sensitivity were investigated. Detailed comparisons with that of the pH SEs with sputtered WO3 and NiO films were also examined. In addition, to further increase the surface area (SA) of the pH SEs, the HTG of NiO NSs on wet-etched roughened Si substrates were also studied.

In chapter 3, WO3 NSs synthesized samples were prepared at different HTG temperatures (50–110 ℃) and the effect of surface morphology on SA were analyzed. It reveals that WO3 NSs synthesized at 90 ℃ shows the largest SA and the highest sensing response of 63.37 mV/pH with a low hysteresis voltage of 4.79 mV and drift rate of 0.37 mV/h. The super-Nernstian response (>59.16 mV/pH) could be attributed to the enhanced surface ion adsorption sites of the NS structure and the occurrence of local electric field enhancement over sharp edges and corners of the WO3 NSs.

The preparation and sensing performance of pH sensors based on HTG NiO NSs with different synthesized times (3–15 h) were presented in chapter 4. Experimental results show that the 9 h SEs exhibit a much better response of 54.24 mV/pH, which is about 14.33% enhancement as compared that one of the NiO film SEs (47.44 mV/pH). An improvement in SAG of around 6.28 as compared with that of the NiO film SEs and a low hysteresis voltage of 5.27 mV and the long-term drift rate of 0.46 mV/h were obtained.

In chapter 5, the fabrication of three types of roughened Si substrates using wet chemical etching to enhanced SA of SEs was presented. HTG of NiO NSs on the roughened Si substrates to maximize the SA and sensitivity of the SEs are demonstrated. To further increase SA of the KOH-roughened Si substrate, Si nanowires (NWs) through adding AgNO3 in the KOH etching solution on the pyramids of the SEs were also prepared. It shows an SA enhancement of 121.65% and 173.30% as compared with that of the pyramid Si and Si NWs prepared on plane Si substrates, respectively. The high sensing response of 54.77 mV/pH based on the proposed SEs with Si NWs on KOH-etched Si substrates was obtained, which is about 8.84% and 12.83% enhancement in pH sensitivity as compared with that of using Si pyramid and Si NWs prepared on plane Si substrates. The pH SEs with a multiple surface roughening using HTG NiO NSs on Si NWs on KOH-etched Si substrates was also proposed. Experimental results indicated that the HTG NiO NSs on pyramid Si NWs shows an enhancement in pH sensitivity (56.60 mV/pH) of about 0.10% and 2.95% as compared with that of the HTG NiO NSs on the pyramid Si and Si NWs on roughened Si substrates and the hysteresis voltage and drift of 6.71 mV and 1.79 mV/h were obtained.

Finally, in chapter 6, the conclusions of the present dissertation in employing surface roughening schemes to enhanced SA of SEs, including HTG of WO3 and NiO NSs on the plane substrates and multiple surface roughening using HTG NiO NSs on the roughened Si substrates are presented. The improvement in pH sensing performance through the enhanced SA of several SEs summarized.

Suggestions for further enhancing SA on the roughened Si substrate and further improving the pH sensing response are proposed. It is expected that the proposed surface roughening schemes with HTG methods and wet chemical etching processes proposed in this study could be an efficient means for pH sensing applications.

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