基於懸浮/支撐式架構之石墨烯–液體界面於多種液體環境中的實驗探究

Abstract

隨著全球化學感測器市場規模持續擴大，液相感測的應用需求亦日益增加。石墨烯因具備高比表面積與優異的導電性，被視為提升感測器性能的理想材料。現今多數感測器優化策略仰賴表面功能化處理以增強感測靈敏度與選擇性。然而，功能化對感測性能的影響多停留於經驗層面，對其具體作用機制的探討仍相對不足。另一方面，石墨烯作為單原子層材料，其表面行為高度受基底影響，包括基底的潤濕性、表面電位及吸附能力等因素。這些基底效應在液相環境中尤為顯著，當目標分析物為帶電離子或極性分子時，界面行為將變得更為複雜，進一步影響感測機制與最終性能表現。 為釐清石墨烯於液相環境中受基底與表面功能化影響之感測行為，本研究聚焦於其在不同離子價態與極性分子條件下的界面反應機制。我們提出兩個以狄拉克點遲滯為基礎的核心界面模型，分別為濃度依賴電荷模型與有效吸附能模型，並透過石墨烯場效應電晶體之電性量測，系統比較不同裝置結構（懸浮式與支撐式）、基板表面性質（親水與疏水）以及表面功能化狀態（功能化與非功能化）界面結構對離子感測行為的調控。同時，進一步將該模型拓展至極性有機溶劑的檢測系統，以驗證其在複雜液相環境中的適用性。透過本研究，期望釐清界面潤濕性、靜電場穩定性與功能化導入對吸附行為與電性響應的調控機制，並為液相石墨烯感測器之優化設計提供理論基礎與實驗支持。 實驗結果顯示，親水性的氧化物基底能形成穩定且均勻的靜電場，有效降低離子脫水能障，使其更容易接近感測通道，將檢測極限分別改善至 0.1 nM（鉀離子）與 0.04 nM（鎂離子）。此外，我們也探討了脫水能與吸附能的耦合效應，並於無閘極偏壓條件下觀察離子在界面上的分佈特性，結果顯示一價與二價離子在疏水界面上呈現明顯差異的吸附行為。 功能化的作用亦受到基底效應的調控。在懸浮式器件中，功能化促進了二價離子的吸附，明顯改善了檢測極限；然而在支撐式器件中，表面偶極子的無序排列與遮罩效應抑制了離子累積，不利於感測極限的改善。 進一步拓展至極性有機分子檢測，我們發現氧化物支撐式器件的靈敏度較懸浮結構提升約1.5倍，並展現出更穩定的遲滯行為。結合二維氫鍵網絡與集體偶極耦合模型可推知，親水性基底會破壞界面原有的水合平衡，促進極性分子與石墨烯間的范德華作用，進而提升整體感測表現。 綜合而言，本研究建立了一套系統化的界面感測機制分析方法，並透過不同裝置設計驗證基底潤濕性與功能化對離子與分子辨識性能的調控效果。此結果為未來發展高靈敏、高選擇性且具穩定性的石墨烯感測器提供了設計原則與應用指引，適用於環境監測、生醫檢測等多種液相感測場景。

With the continuous expansion of the global chemical sensor market, the demand for liquid-phase sensing applications is steadily increasing. As a two-dimensional material with high surface area and excellent conductivity, graphene shows great potential in enhancing sensor performance. Currently, most sensor optimization strategies rely on surface functionalization to improve sensing performance. However, the impact of functionalization remains largely empirical, and the underlying mechanisms by which it unfluences sensing performance are still not well understood. In addition, as a single-atom-thick material, graphene behavior is highly influenced by its supporting substrate. Factors such as substrate wettability, surface potential, and molecular adsorption significantly affect interfacial interactions. These effects are more pronounced in liquid environments, especially in the presence of charged ions or polar molecules, which further complicate interfacial interactions and impact sensing efficiency. To clarify graphene sensing behavior in liquid environments influenced by substrate and surface functionalization, this study investigates interfacial mechanisms in ionic and polar organic solutions. We propose two models based on Dirac point hysteresis: the concentration-dependent charge model and the effective adsorption energy model. Using electrical measurements of graphene field-effect transistors (GFETs), we systematically compare how device configurations (suspended vs. supported), substrate properties (hydrophilic vs. hydrophobic), and surface states (functionalized vs. unfunctionalized) affect ionic sensing. These models are further extended to polar organic solvents to assess their applicability in complex systems. This work elucidates how wettability, electrostatic stability, and functionalization regulate adsorption and electrical response, offering theoretical and experimental guidance for optimizing liquid-phase graphene sensors. Experimental results show that hydrophilic oxide substrates form stable and uniform electrostatic fields, effectively lowering ion dehydration barriers and enabling easier access to the sensing channel, thereby improving detection limits to 0.1 nM for K⁺ and 0.04 nM for Mg²⁺. We also explored the coupling between dehydration and adsorption energies. Under zero gate bias, ion distributions showed distinct adsorption differences between monovalent and divalent ions on hydrophobic surfaces. The effect of functionalization is also modulated by substrate effects. In suspended devices, functionalization promotes the adsorption of divalent ions and clearly improves the detection limit. In supported devices, the disordered arrangement of surface dipoles and the shielding effects suppress ion accumulation, which degrades detection limits. This approach was further extended to polar organic molecule detection. Oxide-supported devices exhibited ~1.5× higher sensitivity and more stable hysteresis than suspended ones. A combined model of 2D hydrogen-bond networks and collective dipole coupling suggests that hydrophilic substrates disrupt interfacial hydration and strengthen van der Waals interactions between graphene and polar molecules, improving sensing performance. In summary, this work provides a systematic framework for interfacial sensing analysis. Through device-level comparisons, we demonstrate how substrate wettability and surface functionalization influence ion and molecule recognition. These findings offer design principles for developing high-performance graphene sensors for liquid-phase applications such as environmental monitoring and biomedical diagnostics.