演講者 : 黃子恩（Huang Tzu-En） 博士候選人 PhD Candidate (物理系)

演講地點 : 理學教學新大樓物理系 5F 36567會議室

演講時間 : 2026 / 09 / 16 15:00

自從石墨烯被發現以來，二維材料因其原子級的厚度結構與獨特的物理特性受到了廣泛的關注。在過渡金屬二硫屬化物家族中（transition metal dichalcogenides, TMDs），二硫化鉬（MoS 2 ）尤其受到重視。單層 MoS 2 具有約 1.8 eV 的直接能隙、高電流開關比、成熟的製程技術以及優異的光學性質，為此，MoS 2 成為了下一世代光學與電子感測應用中極具潛力的材料。然而，MoS 2 極高的表面積與體積比也使得該材料的物理性質對於周遭環境和接觸材料的表面狀態高度敏感。
Since the discovery of graphene, two-dimensional (2D) materials have attracted considerable attention because of their atomically thin structures and unique physical properties. Among the family of transition metal dichalcogenides (TMDs), molybdenum disulfide (MoS 2 ) has received particular interest. Owing to its direct bandgap of approximately 1.8 eV in the monolayer limit, high current on/off ratio, relatively mature fabrication processes, and excellent optical properties, MoS 2 has emerged as a promising candidate for next-generation optical and electronic sensors. However, its extremely large surface-to-volume ratio also makes its physical properties highly sensitive to the surrounding environment and to the surface conditions of contacting materials.
在材料與元件製備過程中，界面載子陷阱以及表面原子空缺，例如硫空缺，往往難以避免。這些缺陷可能降低所製備元件的載子傳輸特性。例如，在氣體感測的應用中，表面原子空缺可能促進氣體分子在材料表面的化學吸附，導致感測訊號無法完全回復，進而限制其定量分析能力。在光感測器中，界面陷阱不僅會增加暗電流，也可能誘發光致電場（optically induced field, OIF），進一步影響光電流的大小與方向。此外，過去研究常忽略閘極材料在光電流生成過程中的貢獻；在弱光照的條件下，此效應尤為重要，因為閘極材料的貢獻可能反而主導整體光響應。除了感測應用之外，如何準確評估 MoS 2 的表面物理狀態仍是一項重要挑戰。雖然表面分子摻雜提供了一種有效調控表面性質的方法，但應變往往也會同時被引入，進而干擾或污染光致發光（photoluminescence, PL）訊號的解析。
During the fabrication of materials and devices, interfacial carrier traps and surface atomic vacancies, such as sulfur vacancies, are often unavoidable. These imperfections can degrade the carrier-transport properties of the resulting devices. For example, in gas-sensing applications, surface atomic vacancies may promote chemical adsorption on the material surface, leading to incomplete recovery of the sensing signal and limiting quantitative analysis. In optical sensors, interfacial traps can not only increase the dark current but also induce an optically induced field (OIF), which further influences both the magnitude and direction of the photocurrent. In addition, previous studies have often overlooked the role of the gate material in photocurrent generation. This effect may become particularly important under weak illumination, where the contribution from the gate material can dominate the photoresponse. Beyond sensing applications, accurately evaluating the surface physical condition of MoS 2 remains an important challenge. Although surface molecular doping provides an effective approach for modulating surface properties, strain is often introduced simultaneously, which can interfere with and obscure the interpretation of photoluminescence (PL) signals.
為了應對上述挑戰，本研究針對單層 MoS 2 中複雜的界面現象進行一系列基礎研究，旨在將不同界面效應加以解耦。在氣體感測應用方面，本研究提出雙陷阱模型與表面調制方法，藉此恢復訊號可逆性，並實現可重複且可定量的氣體感測。在光電元件方面，本研究表徵光致電場（OIF），並揭示閘極材料在弱光照條件下所扮演的主動角色，其可作為主要的光載子來源。最後，本研究證明角度解析二次諧波(angle-resolved second-harmonic generation, SHG）是一種強而有力且非破壞性的探測方法，可用於區分電荷轉移所誘發的摻雜效應與晶格應變，同時提供傳統光譜技術無法解析的應變鬆弛方向資訊。整體而言，這些研究結果建立了一套完整的架構，可用於理解並控制MoS 2 界面，以推動下一世代感測與光電應用的發展。
To address these challenges, this work presents a series of fundamental studies aimed at decoupling complex interfacial phenomena in monolayer MoS 2 . For gas- sensing applications, we introduce a two-trap model and a surface modulation
method, thereby restoring signal reversibility and enabling repeatable, quantitative gas sensing. In optoelectronic devices, we characterize the OIF and reveal the active role of the gate material, which can serve as the dominant source of photocarriers under weak illumination. Finally, we demonstrate that angle-resolved second-harmonic generation (SHG) provides a powerful, non-destructive probe for distinguishing charge-transfer-induced doping from lattice strain, while also offering directional information on strain relaxation that cannot be resolved by conventional spectroscopy. Together, these findings establish a comprehensive framework for understanding, controlling, and engineering MoS 2 interfaces for next-generation sensing and optoelectronic applications.
關鍵字：二維材料、過渡金屬二硫屬化物、單層二硫化鉬、場效電晶體、界面工程、電荷捕捉、氣體感測、表面調制、光電元件、光致電場、負光電流、表面分子摻雜、角度解析二次諧波產生、密度泛函理論計算
Keywords: Two-dimensional materials, Transition metal dichalcogenides, Monolayer MoS 2 , Field effect transistors, Interface engineering, Charge trapping, Gas sensing, Surface modulation, Optoelectronic devices, Optically induced field, Negative photocurrent, Surface molecular doping, Angle-resolved SHG, DFT calculation