Porous silicon nanowire arrays fabrication through one-step metal-assisted chemical etching
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摘要: 通過采用一步納米金屬顆粒輔助化學刻蝕法(MACE)成功制備了多孔硅納米線, 并主要研究了硅片摻雜濃度、氧化劑AgNO3濃度以及HF濃度對硅納米線陣列形貌結構的影響規律. 研究結果表明: 較高的摻雜濃度更有利于刻蝕反應的發生和硅納米線陣列的形成, 這是由于高摻雜濃度在硅片表面引入了更多的雜質和缺陷, 同時高摻雜濃度的硅片與溶液界面形成的肖特基勢壘更低, 更容易氧化溶解形成硅納米線陣列; 在一步金屬輔助化學刻蝕法制備多孔硅納米線陣列的過程中, 溶液中AgNO3濃度對于其刻蝕形貌和結構起到主要作用, AgNO3濃度過低或過高時, 硅片表面會形成腐蝕凹坑或坍塌的納米線簇, AgNO3濃度為0.02 mol·L-1時, 硅納米線會生長變長, 最終形成多孔硅納米線陣列. 隨著硅納米線的增長, 納米線之間的毛細應力會使得一些納米線頂部出現團聚現象; 且當HF溶液濃度超過4.6 mol·L-1時, 隨著HF酸濃度的增加, 硅納米線的長度隨之增加. 同時, 硅納米線的頂部有多孔結構生成, 且硅納米線的孔隙率隨HF濃度的增加而增多, 這是由于納米線頂部大量的Ag+隨機形核, 導致硅納米線側向腐蝕的結果. 最后, 根據實驗現象提出相應模型對多孔硅納米線的形成過程進行了解釋, 歸因于銀離子的沉積和硅基底的氧化溶解.Abstract: One-step metal-assisted chemical etching (MACE) was used to fabricate porous silicon nanowire arrays. Also, the effects of doping level, AgNO3 concentration, and HF concentration on the morphology and structure of porous silicon nanowire were investigated. The results show that the higher doping level is beneficial for etching the silicon wafer and forming silicon nanowire arrays. This is because the higher doping level introduces more impurities and defects on the surface of the silicon wafer, and at the same time, the Schottky barrier between the silicon wafer with the higher doping level and the solution is lower. Thus, the silicon wafer is easier to oxidate to form nanowire arrays. The AgNO3 concentration plays a critical role in the fabrication of the porous silicon nanowire arrays during the one-step MACE process. If AgNO3 concentration is too low or too high, corrosion pits and collapsed clusters of nanowires could form on the surface of the silicon wafer. When AgNO3 concentration was 0.02 mol·L-1, silicon nanowires grew and became longer, eventually forming a porous array of silicon nanowire. In the meantime, as silicon nanowires grew, capillary stress between nanowires caused agglomeration at the top of some nanowires. Furthermore, when HF solution concentration exceeded 4.6 mol·L-1, the length of silicon nanowire increased with increasing HF concentration. Furthermore, a porous structure was formed on top the silicon nanowire, and the porosity of the silicon nanowires increased with increasing HF concentration. This was due to a large number of Ag+ random nucleations at the top of the nanowires, and lateral etching of the silicon nanowires occurred. In the end, the formation process of the porous silicon nanowires is explained by a model based on the experimental phenomena. It is attributed to the deposition of silver ions and the oxidation of dissolved silicon substrates.
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圖 1 不同電阻率硅納米線的截面掃描電鏡圖. (a)10~20 Ω·cm；(b)0.3~0.8 Ω·cm；(c~d)0.01~0.09 Ω·cm
Figure 1. Cross-sectional SEM images of SiNWs with different resistivitie: (a)10-20 Ω·cm; (b)0.3-0.8 Ω·cm; (c-d)0.01-0.09 Ω·cm
圖 2 不同AgNO3濃度下獲得的硅納米線的掃描電鏡圖. (a~b)0.003 mol·L-1；(c~d)0.02 mol·L-1；(e~f)0.4 mol·L-1
Figure 2. SEM images of SiNWs prepared under different AgNO3 concentrations: (a-b)0.003 mol·L-1; (c-d)0.02 mol·L-1; (e-f)0.4 mol·L-1
圖 3 不同HF濃度下獲得的硅納米線的截面掃描電鏡圖. (a~b)4.6 mol·L-1；(c~d)9.2 mol·L-1
Figure 3. Cross-sectional SEM images of SiNWs prepared under different HF concentrations: (a-b) 4.6 mol·L-1; (c-d) 9.2 mol·L-1
圖 4 單根多孔硅納米線透射電鏡圖和納米銀顆粒高分辨透射電子顯微鏡圖(腐蝕時間：60 min；AgNO3濃度：0.02 mol·L-1；HF酸濃度：9.2 mol·L-1)
Figure 4. TEM and HRTEM images of single SiNW and silver nano-particles(etching time: 60 min; AgNO3 concentration: 0.02 mol·L-1; HF concentration: 9.2 mol·L-1)
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圖 5 采用HF/AgNO3體系一步金屬輔助化學刻蝕制備多孔硅納米線的形成機理
Figure 5. Formation mechanism of porous SiNWs through one-step metal-assisted chemical etching in HF/AgNO3 solution
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