本研究探討氧含量調控對二維二硫化錫 (SnS2) 薄膜之合成特性以及其在多功能感測元件應用上之電性表現。不同於傳統直接合成法，本研究採用一氧化錫 (SnO) 作為前驅物，於藍寶石基板上利用射頻磁控濺鍍前驅物層，隨後經化學氣相沉積 (CVD) 進行硫化處理，成功製備二維二硫化錫薄膜，並進行材料分析以評估薄膜之製造品質與詳細特性。此外，亦針對二硫化錫相關感測元件之製作與電性特徵進行深入研究。
實驗首要目標為製備穩定且可控的二硫化錫薄膜。在實驗流程中，首先利用射頻濺鍍機在藍寶石基板上鍍上一氧化錫薄膜，接著於高溫爐管中通入硫化氫 (H2S) 進行硫化反應。薄膜品質的關鍵在於前驅物一氧化錫的品質與厚度，因此鍍率控制為首要考量。為了精確控制一氧化錫的厚度，實驗中採用低濺鍍功率與工作壓力，並維持每次濺鍍之偏壓恆定，以確保薄膜成長之一致性。藉由控制沉積時間，本研究成功在藍寶石基板上生長出不同厚度之二維二硫化錫薄膜。此外，還比較了射頻濺鍍時調控通氧比例 (0%、10%與20%) 沉積之薄膜，以研究前驅物以不同通氧量濺鍍對後續硫化參數的影響。
為深入分析材料特性，本研究透過X光繞射 (XRD) 與拉曼光譜 (Raman) 確認晶體結構；利用原子力顯微鏡 (AFM) 分析表面形貌與粗糙度；並藉由能量散射X光光譜 (EDS)、 X射線光電子能譜 (XPS) 與光致發光儀 (PL) 探討其元素組成比例、表面鍵結狀態與能隙特性。此外，穿透式電子顯微鏡 (TEM) 結果證實薄膜為層狀原子厚度之超薄結構。分析結果顯示，我們已成功製備出厚度精確可控之二硫化錫薄膜。
拉曼光譜分析顯示，相較於通氧 10% 與 20% 之條件，於無通氧 (0%) 環境下製備之二硫化錫薄膜具備最佳的結晶品質與穩定性，其特徵峰更為銳利。從研究結果可以推論，氧含量的增加會提升氧與硫原子置換過程中的活化能，進而提高硫化反應之閾值溫度。因此，後續感測元件之製備均採用無通氧條件。
在多功能感測元件應用方面，本研究全面評估了光電感測、氣體感測與液態 pH 酸鹼值感測之效能。在光電感測特性方面，5 nm塊材元件在 550 nm 單色光照射下展現出最穩定的光電流調控，其響應度最高可達8.1 A/W，並進一步透過光開關切換測試驗證其動態響應表現；相較之下，二至五層之超薄元件則因受限於較大的接觸阻抗與界面散射效應，導致光電流信號不明顯。
在氣體感測與液態 pH 酸鹼值感測應用方面，三層二硫化錫元件均展現出本研究中最為卓越的優化感測效能。在二氧化氮 (NO2) 氣體感測測試中，三層元件於 25°C 室溫環境下展現出高達 100.1% 的優異氣敏響應，且經氨氣(NH3)、一氧化碳(CO)、二氧化硫 (SO2) 及乙醇之交叉靈敏度測試，元件對干擾氣體均無明顯響應，證實對二氧化氮具備高度選擇性；而在液態 pH 酸鹼值感測應用中，三層元件同樣表現最佳，其靈敏度高達 91.2 μA/pH，且線性度 (Linearity) 達到 0.98369 之極高水準。
此雙重卓越的性能窗口證實了二維二硫化錫在氣相與液相感測中，存在一個共有的「黃金切入點 (Sweet Spot)」。此厚度依賴趨勢源於核心物理機制的完美權衡：超薄的二層元件易受凡得瓦間隙效應與界面缺陷干擾，導致接面接觸阻抗過大而引發信號不穩定；較厚的配置 (四、五層及塊材) 則會因過剩載子引發強烈的內部靜電屏蔽，形成未受調控的平行分流路徑並嚴重稀釋響應。相較之下，三層薄膜之物理厚度 (~2 nm) 與材料的德拜長度 (Debye length, t ~ 2λD) 達成完美匹配，既足夠厚以克服界面接觸阻障，又足夠薄以使化學閘極電場徹底穿隧整個通道，實現高效的全通道靜電調控 (full-channel electrostatic modulation)，從而賦予元件最佳的感測靈敏度。本研究成功構建之高穩定、高靈敏氧調控二硫化錫感測平台，在未來次世代多功能感測技術整合上具有深遠的應用潛力。

This study investigates the effect of oxygen modulation on the synthesis characteristics of two-dimensional (2D) tin disulfide (SnS2) thin films and their electrical performance in multifunctional sensing devices. Moving away from traditional direct synthesis, a novel two-step approach was developed: tin monoxide (SnO) precursor layers were first deposited on sapphire substrates via radio-frequency (RF) magnetron sputtering, followed by controlled sulfurization using Chemical Vapor Deposition (CVD) with hydrogen sulfide (H2S).
Material characterization techniques, including X-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM), photoluminescence (PL), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM), confirmed the successful fabrication of ultrathin SnS2 films with precisely controlled thicknesses.
Raman analysis revealed that SnS2 films synthesized under oxygen-free (0% O2) precursor conditions exhibited superior crystalline quality and sharper characteristic peaks compared to those with 10% and 20% oxygen flow. The incorporation of oxygen into the precursor lattice increases the activation energy for the sulfur-oxygen displacement reaction, thereby raising the sulfurization threshold temperature. Consequently, 0% O2 conditions were adopted for functional device fabrication.
Regarding multifunctional sensing device applications, this study comprehensively evaluated the performance of photoelectric sensing, gas sensing, and liquid-phase pH sensing. In photodetector characterization, the 5 nm bulk device exhibited the most stable photocurrent modulation under 550 nm monochromatic illumination, achieving a peak responsivity of 8.1 A/W, with its dynamic response behavior further validated through optical on-off switching tests. Conversely, the ultrathin devices (2 to 5 layers) suffered from negligible photocurrent signals due to the constraints of higher contact resistance at the metal interfaces and interface scattering effects.
For gas-sensing and liquid-phase pH sensing applications, the 3-layer SnS2 device consistently delivered the optimized sensing efficacy in this work. In nitrogen dioxide (NO2) gas-sensing examinations, the 3-layer device delivered an outstanding room-temperature response of 100.1% at 25°C toward NO2, with exceptional specificity against interfering gases (NH3, CO, SO2, and ethanol) as verified by cross-sensitivity tests. Concurrently, in liquid-phase pH sensing, the 3-layer device manifested a peerless sensitivity of 91.2 μA/pH and an outstanding linearity of 0.98369.
This dual exceptional performance window reveals a universal "Sweet Spot" for 2D SnS2 chemical and biological sensors, dictated by a synergistic trade-off in thickness-dependent physics. While ultra-thin 2-layer devices suffer from signal instability caused by the van der Waals gap effect and interface defects that lead to excessive contact barriers, thicker configurations (4-layer, 5-layer, and bulk) introduce robust internal electrostatic screening due to excess carriers, creating unmodulated parallel shunting paths that severely dilute the sensor response. Uniquely, the 3-layer architecture (~2 nm) perfectly matches the characteristic Debye length of the material (Debye length, t ~ 2λD). This optimal thickness balances the trade-off by being thick enough to overcome interfacial contact resistance, yet thin enough to enable the surface chemical gating field to thoroughly penetrate the channel for efficient full-channel electrostatic modulation, thereby yielding the optimized sensitivity across both sensing paradigms. The highly stable and sensitive oxygen-modulated SnS2 sensing platform successfully constructed in this study holds profound potential for next-generation multifunctional smart sensing integration.

[1] Novoselov, K. S., et al. "Electric Field Effect in Atomically Thin Carbon Films" Science. 306.5696 (2004): 666-669
[2] Li, Junfeng, et al. "Two-dimensional transition metal MXene-based gas sensors: A review." Chinese Chemical Letters 35.1 (2024): 108286.
[3] Tang, Yanting, Yunong Zhao, and Huan Liu. "Room-temperature semiconductor gas sensors: challenges and opportunities." ACS sensors 7.12 (2022): 3582-3597.
[4] Chakraborty, Nabamita, et al. "Wide-Bandgap 2D SnS2-Based All-Optical Photonic Devices with Strong Nonlinear Optical Response due to Spatial Self-Phase Modulation." ACS Applied Optical Materials 2.7 (2024): 1454-1465.
[5] Zhang, Jian, et al. "A review on two-dimensional materials for chemiresistive-and FET-type gas sensors." Physical Chemistry Chemical Physics 23.29 (2021): 15420-15439.
[6] Zhou, Tengfei, et al. "Enhanced sodium-ion battery performance by structural phase transition from two-dimensional hexagonal-SnS2 to orthorhombic-SnS." ACS nano 8.8 (2014): 8323-8333.
[7] Voznyi, A., et al. "Structural and electrical properties of SnS2 thin films." Materials Chemistry and Physics 173 (2016): 52-61.
[8] Guo, Chenfei, et al. "Two-dimensional SnS2 single crystal for sensitive NO2 detection at room temperature." Microsystems & Nanoengineering 11.1 (2025): 246.
[9] Sun, Qing, et al. "Structural engineering of SnS2 encapsulated in carbon nanoboxes for high‐performance sodium/potassium‐ion batteries anodes." Small 16.45 (2020): 2005023.
[10] Kota, Sumanjali, et al. "Synthesis and characterization of SnS2 nanoparticles for enhanced photocatalytic and electrochemical sensing applications." Tetrahedron Green Chem 5 (2025): 100067.
[11] Jannat, Azmira, et al. "Exciton-driven chemical sensors based on excitation-dependent photoluminescent two-dimensional SnS." ACS applied materials & interfaces 11.45 (2019): 42462-42468.
[12] Mattinen, Miika, et al. "Low‐temperature wafer‐scale deposition of continuous 2D SnS2 films." Small 14.21 (2018): 1800547.
[13] Li-Yang Chang, Investigation of Indium Gallium Oxide Thin Film Fabricated by RF Sputtering System and Their Applications, Master D.Thesis, NCKU. (2017)
[14] A. VAN DER ZIEL, Noise in solid state devices and circuits, WileyInterscience. (1986).
[15] Reynolds, D. C., et al. "Neutral-donor–bound-exciton complexes in ZnO crystals." Physical Review B 57.19 (1998): 12151.
[16] Matt Hughes, What is E-Beam Evaporation?, SEMICORE. (2016).
[17] Gandhewar, Vivek R., Satish V. Bansod, and Atul B. Borade. "Induction furnace–a review." International Journal of Engineering and Technology 3.4 (2011): 277-284.
[18] Lyon, L. Andrew, et al. "Raman spectroscopy." Analytical Chemistry 70.12 (1998): 341-362.
[19] Mulvaney, Shawn P., and Christine D. Keating. "Raman spectroscopy." Analytical Chemistry 72.12 (2000): 145-158.
[20] Rostron, Paul, Safa Gaber, and Dina Gaber. "Raman spectroscopy, review." laser 21 (2016): 24.
[21] Das, Ruchita S., and Y. K. Agrawal. "Raman spectroscopy: Recent advancements, techniques and applications." Vibrational spectroscopy 57.2 (2011): 163-176.
[22] CHANG, C. Y. (ed.). Solutions Manual to Accompany Ulsi Technology. McGraw-Hill, 1996.
[23] Stevie, Fred A., and Carrie L. Donley. "Introduction to x-ray photoelectron spectroscopy." Journal of Vacuum Science & Technology A 38.6 (2020).
[24] Andrade, Joseph D. "X-ray photoelectron spectroscopy (XPS)." Surface and interfacial aspects of biomedical polymers: volume 1 surface chemistry and physics (1985): 105-195.
[25] Li, Qinghe, et al. "Photoluminescence (PL) spectroscopy." Springer Handbook of Advanced Catalyst Characterization. Cham: Springer International Publishing, 2023. 295-321.
[26] Aoki, Takeshi. "Photoluminescence." Optical Properties of Materials and Their Applications (2019): 157-202.
[27] Gravrand, O., et al. "Shockley–Read–Hall Lifetime Study and Implication in HgCdTe Photodiodes for IR Detection: Gravrand, Rothman, Delacourt, Boulard, Lobre, Ballet, Santailler, Cervera, Brellier, Péré-Laperne, Destefanis, and Kerlain." Journal of Electronic Materials 47.10 (2018): 5680-5690.
[28] Gonda, S., et al. "Real-time, interferometrically measuring atomic force microscope for direct calibration of standards." Review of scientific instruments 70.8 (1999): 3362-3368.
[29] Shindo, Daisuke, and Tetsuo Oikawa. "Energy dispersive x-ray spectroscopy." Analytical electron microscopy for materials science. Tokyo: Springer Japan, 2002. 81-102.
[30] Schneider, Reinhard. "Energy‐Dispersive X‐Ray Spectroscopy (EDXS)." Surface and Thin Film Analysis: A Compendium of Principles, Instrumentation, and Applications (2011): 293-310.
[31] Kannan, M. "Transmission electron microscope—Principle, components and applications." A textbook on fundamentals and applications of nanotechnology (2018): 93-102.
[32] Guo, Daoyou, et al. "Fabrication of β-Ga2O3 thin films and solar-blind photodetectors by laser MBE technology." Optical Materials Express 4.5 (2014): 1067-1076.
[33] Hu, Xin, et al. "High‐performance flexible broadband photodetector based on organolead halide perovskite." Advanced Functional Materials 24.46 (2014): 7373-7380.
[34] Uddin, ASM Iftekhar, Duy-Thach Phan, and Gwiy-Sang Chung. "Low temperature acetylene gas sensor based on Ag nanoparticles-loaded ZnO-reduced graphene oxide hybrid." Sensors and Actuators B: Chemical 207 (2015): 362-369.
[35] Takata, Masasuke, DAISUKE TSUBONE, and HIROAKI YANAGIDA. "Dependence of electrical conductivity of ZnO on degree of sintering." Journal of the American Ceramic Society 59.1‐2 (1976): 4-8.
[36] Saruhan, Bilge, Roussin Lontio Fomekong, and Svitlana Nahirniak. "Influences of semiconductor metal oxide properties on gas sensing characteristics." Frontiers in Sensors 2 (2021): 657931.
[37] Navale, Sachin, et al. "Effect of Ag addition on the gas-sensing properties of nanostructured resistive-based gas sensors: an overview." Sensors 21.19 (2021): 6454.
[38] 王俊傑. 離子感測場效應電晶體與微流體晶片平面化封裝技術及其於酸鹼與流速感測之應用. 2014. PhD Thesis. 撰者.
[39] 呂奕鋒. "射頻磁控濺鍍 p 型氧化亞錫薄膜及場效電晶體特性之研究." 臺灣大學光電工程學研究所學位論文 (2013): 1-71.
[40] Chatmaneerungcharoen, Bhobnibhit, et al. "Synthesis of in-plane oriented tin sulfides by organosulfur-mediated sulfurization of ultrathin SnO2 films." Chemistry of Materials 34.13 (2022): 5842-5851.
[41] Kadleıková, M., J. Breza, and M. Veselý. "Raman spectra of synthetic sapphire." Microelectronics journal 32.12 (2001): 955-958.
[42] Choi, Hyeongsu, et al. "Fabrication of high crystalline SnS and SnS2 thin films, and their switching device characteristics." Nanotechnology 29.21 (2018): 215201.
[43] Zhou, Xing, et al. "Large‐size growth of ultrathin SnS2 nanosheets and high performance for phototransistors." Advanced Functional Materials 26.24 (2016): 4405-4413.
[44] Qin, Ziyu, et al. "Enhanced room-temperature NH3 gas sensing by 2D SnS2 with sulfur vacancies synthesized by chemical exfoliation." Sensors and Actuators B: Chemical 262 (2018): 771-779.
[45] Lippens, P. E., M. El Khalifi, and M. Womes. "Electronic structures of SnS and SnS2." physica status solidi (b) 254.2 (2017): 1600194.
[46] Rangappa, A. Putta, et al. "Highly efficient hydrogen generation in water using 1D CdS nanorods integrated with 2D SnS2 nanosheets under solar light irradiation." Applied Surface Science 508 (2020): 144803.
[47] Chastain, Jill, and Roger C. King Jr. "Handbook of X-ray photoelectron spectroscopy." Perkin-Elmer Corporation 40.221 (1992): 25.
[48] Stranick, Michael A., and Anthony Moskwa. "SnO by XPS." Surface Science Spectra 2.1 (1993): 45-49.
[49] Pourfath, Mahdi, and Tibor Grasser. "Device-scaling constraints imposed by the van der Waals gap formed in two-dimensional materials." Science (2026): eaeb2271.
[50] John, John Wellington, et al. "Probing charge traps at the 2D semiconductor/dielectric interface." Nanoscale 15.42 (2023): 16818-16835.
[51] Prakash, Chandra, et al. "Recent developments on 2D-materials for gas sensing application." Journal of Physics: Condensed Matter 37.19 (2025): 193004.
[52] Bo, Renheng, et al. "Low-voltage high-performance UV photodetectors: an interplay between grain boundaries and debye length." ACS applied materials & interfaces 9.3 (2017): 2606-2615.
[53] Zhai, Tianyou, et al. "Recent developments in one‐dimensional inorganic nanostructures for photodetectors." Advanced Functional Materials 20.24 (2010): 4233-4248.
[54] Bechhofer, Adina R., et al. "The 2D Debye length: An analytical study of weak charge screening in 2D semiconductors." Journal of Applied Physics 129.2 (2021).
[55] Liu, Jianqiao, et al. "Effect of depletion layer width on electrical properties of semiconductive thin film gas sensor: a numerical study based on the gradient-distributed oxygen vacancy model." Applied Physics A 122.3 (2016): 146.
[56] Wang, Yuan, et al. "Screening effect of graphite and bilayer graphene on excitons in MoSe2 1-layer." 2D Materials 4.1 (2017): 015021.
[57] Lu, Jiabing, Zesheng Lv, and Hao Jiang. "AlGaN solar-blind phototransistor capable of directly detecting sub-fW signals: self-depletion and photorecovery of full-channel 2DEG enabled by a quasi-pseudomorphic structure." Photonics Research 11.7 (2023): 1217-1226.
[58] Lu, Jiabing, et al. "Ultrasensitive and high-speed AlGaN/AlN solar-blind ultraviolet photodetector: A full-channel-self-depleted phototransistor by a virtual photogate." Photonics Research 10.9 (2022): 2229-2238.