GaN基光电传感器件的制备及其多功能应用研究

随着社会快速步入智能化、万物互联的新时代，对高集成度、小型化、高性能传感器的需求日益迫切。其中，光电传感器件因其精度高、响应速度快、抗电磁干扰能力优异等优点而受到广泛关注和研究。近年来，研究人员提出采用InGaN/GaN多量子阱结构，结合光电子集成技术，制备出兼具发光与光探测一体化功能的同质GaN光电集成器件，展现了广阔的应用前景。然而，该同质集成器件技术在传感领域的研究仍处于早期阶段，其基础研究匮乏，导致其应用场景主要局限于光通信。为了拓展其在湿度等相关领域的单一及多功能传感应用，对GaN光电器件结构及其适配的集成湿敏材料进行深入研究与优化显得尤为重要，并探究其传感机理。

本论文提出在绿光GaN光电器件上集成人造蛋白石光学湿敏材料薄膜的方案。通过快速破碎微米化工艺和滴涂成膜技术，该薄膜与绿光GaN光电器件实现了低成本、高生物兼容性的有效集成，并能将环境湿度的变化灵敏地转化为光学信号。由此，该湿度传感器件实现了宽湿度检测范围（3.8～90 %RH）、高灵敏度（0.046～0.051 μA/%RH）以及优异的线性传感性能。为验证其实用性，将传感器件安装于口罩上，展示了其对人类呼吸频率的实时监测能力。

本论文利用GaN光电器件的发光与光探测功能一体化特性，通过在蓝光和绿光器件上集成氧化石墨烯（GO）薄膜，实现了对光还原化学反应的实时监测。研究结果表明，随着片上LED发光波长的缩短和光辐照强度的增大， GO的光还原反应速率显著加快。此外，经过光还原处理形成的光还原氧化石墨烯（P-rGO）材料，相较于原始的GO，其光吸收能力得到增强，部分亲水性含氧官能团减少，展示其亲水性的调控。基于在蓝光GaN器件上原位集成的P-rGO薄膜，构建了高性能的湿度传感器件，其检测范围宽达5～95 %RH，响应和恢复时间分别为2.5 s和1.2 s，相较于人造蛋白石湿敏材料，其响应速度得到显著提升，同时验证了该传感器件对人体口鼻呼吸的快速响应能力。

本论文通过开发基于GaN光电器件的湿度和距离传感单元，并实现了二者的集成，从而构建了多功能传感器。其中，湿度传感单元采用蓝光GaN器件与Glucose/P-rGO薄膜的集成设计，展现出宽检测范围（30～95 %RH）、快速响应/恢复时间（11.7 s/3.1 s）以及高灵敏度（0.105 μA/%RH）的传感性能。而距离传感单元则基于绿光GaN基器件构建，其在0.5～3.5 mm的范围内展现出高灵敏度（2.13 μA/mm）、对表面光学性质变化灵敏且响应迅速（响应/恢复时间：60 ms/82 ms）。通过将该集成传感器件固定在人手指上，其高灵敏度和快速响应速度有助对微小湿度和表面光学性质的变化进行实时响应和高效协同工作。在卷积神经网络算法反馈的混淆矩阵中，实现对15种水果高达97%的平均识别准确率。

[1] 宋爱国，赵辉，贾伯年. 传感器技术:(第4版）[M]. 南京: 东南大学出版社, 2021.
[2] McGeehan M A, Karipott S S, Hahn M E, et al. An optoelectronics-based sensor for measuring multi-axial shear stresses[J]. IEEE Sensors Journal, 2021, 21(22): 25641-25648.
[3] Kim R H, Kim D H, Xiao J, et al. Waterproof AlInGaP optoelectronics on stretchable substrates with applications in biomedicine and robotics[J]. Nature Materials, 2010, 9(11): 929-937.
[4] Přibil J, Přibilová A, Frollo I. Comparative measurement of the PPG signal on different human body positions by sensors working in reflection and transmission modes[J]. Engineering Proceedings, 2020, 2(1): 69-76.
[5] Castaneda D, Esparza A, Ghamari M, et al. A review on wearable photoplethysmography sensors and their potential future applications in health care[J]. International Journal of Biosensors & Bioelectronics, 2018, 4(4): 195-214.
[6] Tamura T, Maeda Y, Sekine M, et al. Wearable photoplethysmographic sensors-past and present[J]. Electronics, 2014, 3(2): 282-302.
[7] Kavsaoğlu A R, Polat K, Hariharan M. Non-invasive prediction of hemoglobin level using machine learning techniques with the PPG signal's characteristics features[J]. Applied Soft Computing, 2015, 37: 983-991.
[8] Enderle J, Bronzino J. Introduction to biomedical engineering[M]. Academic Press, 2012.
[9] Yokota T, Zalar P, Kaltenbrunner M, et al. Ultraflexible organic photonic skin[J]. Science Advances, 2016, 2(4): e1501856-1501864.
[10] Khan Y, Han D, Ting J, et al. Organic multi-channel optoelectronic sensors for wearable health monitoring[J]. IEEE Access, 2019, 7: 128114-128124.
[11] Turkey N S, Jeber J N. A flow analysis system integrating an optoelectronic detector for the quantitative determination of active ingredients in pharmaceutical formulations[J]. Microchemical Journal, 2021, 160: 105710-105719.
[12] Flores G, Perdigones F, Aracil C, et al. Microfluidic platform with absorbance sensor for glucose detection[C]//2015 10th Spanish Conference on Electron Devices (CDE). IEEE, 2015: 1-4.
[13] Lochner C M, Khan Y, Pierre A, et al. All-organic optoelectronic sensor for pulse oximetry[J]. Nature Communications, 2014, 5(1): 5745-5752.
[14] Lovecchio N, Costantini F, Parisi E, et al. Integrated optoelectronic device for detection of fluorescent molecules[J]. IEEE Transactions on Biomedical Circuits and Systems, 2018, 12(6): 1337-1344.
[15] Lim C J, Lee S, Kim J H, et al. Wearable, luminescent oxygen sensor for transcutaneous oxygen monitoring[J]. ACS Applied Materials & Interfaces, 2018, 10(48): 41026-41034.
[16] Ding H, Lv G, Cai X, et al. An optoelectronic thermometer based on microscale infrared-to-visible conversion devices[J]. Light: Science & Applications, 2022, 11(1): 130-138.
[17] Sumiya M, Fuke S. Review of polarity determination and control of GaN[J]. Materials Research Society Internet Journal of Nitride Semiconductor Research, 2004, 9: e1.
[18] Speck J S, Chichibu S F. Nonpolar and semipolar group III nitride-based materials[J]. MRS Bulletin, 2009, 34(5): 304-312.
[19] Chen F, Ji X, Lau S P. Recent progress in group III-nitride nanostructures: from materials to applications[J]. Materials Science and Engineering: R: Reports, 2020, 142: 100578-100629.
[20] Pankove J I, Miller E A, Berkeyheiser J E. GaN electroluminescent diodes[C]//1971 International Electron Devices Meeting. IEEE, 1971: 78-78.
[21] Yanagisawa T. Changes in properties of GaN blue light-emitting diodes over time[J]. Electronics Letters, 1986, 22(16): 846-847.
[22] Monroy E, Munoz E, Sánchez F J, et al. High-performance GaN pn junction photodetectors for solar ultraviolet applications[J]. Semiconductor Science and Technology, 1998, 13(9): 1042-1047.
[23] Meneghini M, Trevisanello L R, Meneghesso G, et al. A review on the reliability of GaN-based LEDs[J]. IEEE Transactions on Device and Materials Reliability, 2008, 8(2): 323-331.
[24] Zhang Y, Xu R, Kang Q, et al. Recent advances on GaN-based Micro-LEDs[J]. Micromachines, 2023, 14(5): 991-1010.
[25] Xu R, Kang Q, Zhang Y, et al. Research progress of AlGaN-Based deep ultraviolet light-emitting diodes[J]. Micromachines, 2023, 14(4): 844-854.
[26] Guo J, Ye B, Gu Y, et al. Broadband photodetector for ultraviolet to visible wavelengths based on the BA2PbI4/GaN heterostructure[J]. ACS Applied Materials & Interfaces, 2023,15(48):56014-56021.
[27] Yi C, Chen Y, Kang Z, et al. MXene‐GaN van der waals heterostructures for high-speed self-driven photodetectors and light-emitting diodes[J]. Advanced Electronic Materials, 2021, 7(5): 2000955-2000963.
[28] Janardhanam V, Zummukhozol M, Jyothi I, et al. Self-powered MoS2/n-type GaN heterojunction photodetector with broad spectral response in ultraviolet–visible–near-infrared range[J]. Sensors and Actuators A: Physical, 2023, 360: 114534-114544.
[29] Cai Z, He X, Wang K, et al. Enhancing performance of GaN/Ga2O3 P‐N junction Uvc photodetectors via interdigitated structure[J]. Small Methods, 2023: 2301148-2301157.
[30] Alamoudi H, Xin B, Mitra S, et al. Enhanced solar-blind deep UV photodetectors based on solution-processed p-MnO quantum dots and n-GaN p-n junction-structure[J]. Applied Physics Letters, 2022, 120(12):122102-122110.
[31] Wang D, Liu X, Kang Y, et al. Bidirectional photocurrent in p-n heterojunction nanowires[J]. Nature Electronics, 2021, 4(9): 645-652.
[32] Paul S, Helwig A, Müller G, et al. Opto-chemical sensor system for the detection of H2 and hydrocarbons based on InGaN/GaN nanowires[J]. Sensors and Actuators B: Chemical, 2012, 173: 120-126.
[33] Maier K, Helwig A, Müller G, et al. Detection of oxidising gases using an optochemical sensor system based on GaN/InGaN nanowires[J]. Sensors and Actuators B: Chemical, 2014, 197: 87-94.
[34] Cai Q, You H, Guo H, et al. Progress on AlGaN-based solar-blind ultraviolet photodetectors and focal plane arrays[J]. Light: Science & Applications, 2021, 10(1): 94-125.
[35] Wu G, Du L, Deng C, et al. High-performance self-driven single GaN-Based p-i-n homojunction one-dimensional microwire ultraviolet photodetectors[J]. ACS Applied Electronic Materials, 2022, 4(8): 3807-3814.
[36] Cicek E, McClintock R, Cho C Y, et al. AlxGa1-xN-based back-illuminated solar-blind photodetectors with external quantum efficiency of 89%[J]. Applied Physics Letters, 2013, 103(19):191108-191113.
[37] Reddeppa M, Park B G, Chinh N D, et al. A novel low-temperature resistive NO gas sensor based on InGaN/GaN multi-quantum well-embedded p-i-n GaN nanorods[J]. Dalton Transactions, 2019, 48(4): 1367-1375.
[38] 吕红亮，张玉明，张义门. 化合物半导体器件[M].北京: 电子工业出版社, 2009.
[39] Zhang H, Dai X, Guan N, et al. Flexible photodiodes based on nitride core/shell p-n junction nanowires[J]. ACS Applied Materials & Interfaces, 2016, 8(39): 26198-26206.
[40] Chen Y C, Shih H Y, Chen J Y, et al. An optically detectable CO2 sensor utilizing polyethylenimine and starch functionalized InGaN/GaN multiple quantum wells[J]. Applied Physics Letters, 2013, 103(2):022109-022114.
[41] Yin Y, Chen R, He R, et al. Strain visualization enabled in dual-wavelength InGaN/GaN multiple quantum wells Micro-LEDs by piezo-phototronic effect[J]. Nano Energy, 2023, 109: 108283-108293.
[42] Li K H, Fu W Y, Cheung Y F, et al. Monolithically integrated InGaN/GaN light-emitting diodes, photodetectors, and waveguides on Si substrate[J]. Optica, 2018, 5(5): 564-569.
[43] Li J, Wu J, Chen L, et al. On-chip integration of III-nitride flip-chip light-emitting diodes with photodetectors[J]. Journal of Lightwave Technology, 2021, 39(8): 2603-2608.
[44] Gao X, Liu P, Yin Q, et al. Wireless light energy harvesting and communication in a waterproof GaN optoelectronic system[J]. Communications Engineering, 2022, 1(1): 16-23.
[45] Yin J, Yang H, Luo Y, et al. III-Nitride Microsensors for 360° Angle Detection[J]. IEEE Electron Device Letters, 2022, 43(3): 458-461.
[46] He R, Liu N, Gao Y, et al. Monolithically integrated UVC AlGaN-based multiple quantum wells structure and photonic chips for solar-blind communications[J]. Nano Energy, 2022, 104: 107928-107937.
[47] Chen L, An X, Jing J, et al. Ultracompact chip-scale refractometer based on an InGaN-based monolithic photonic chip[J]. ACS Applied Materials & Interfaces, 2020, 12(44): 49748-49754.
[48] Wang Y, Xu Y, Yang Y, et al. Simultaneous light emission and detection of InGaN/GaN multiple quantum well diodes for in-plane visible light communication[J]. Optics Communications, 2017, 387: 440-445.
[49] Zhang H, Yan J, Ye Z, et al. Monolithic GaN optoelectronic system on a Si substrate[J]. Applied Physics Letters, 2022, 121(18): 181103-181109.
[50] Hou Y, Jing J, Luo Y, et al. A versatile, incubator‐compatible, monolithic GaN photonic chipscope for label-free monitoring of live cell activities[J]. Advanced Science, 2022, 9(17): 2200910-2200921.
[51] Jing J, Hou Y, Luo Y, et al. Chip-scale in situ salinity sensing based on a monolithic optoelectronic chip[J]. ACS Sensors, 2022, 7(3): 849-855.
[52] Gao X, Li T, Wu D, et al. Monolithic integrated MQW-based optoelectronic glucose sensor[J]. Optics Letters, 2023, 48(20): 5367-5370.
[53] Yang H, Luo Y, Lu G, et al. Viscosity sensors based on III-nitride optical devices integrated with droplet sliding channels[J]. IEEE Electron Device Letters, 2022, 43(12): 2169-2172.
[54] Jing J, An X, Luo Y, et al. A compact optical pressure sensor based on a III-nitride photonic chip with nanosphere-embedded PDMS[J]. ACS Applied Electronic Materials, 2021, 3(5): 1982-1987.
[55] An X, Luo Y, Yu B, et al. A chip-scale GaN-based optical pressure sensor with microdome-patterned polydimethylsiloxane (PDMS)[J]. IEEE Electron Device Letters, 2021, 42(10): 1532-1535.
[56] Shi F, Zhang H, Ye Z, et al. Miniature optical fiber curvature sensor via integration with GaN optoelectronics[J]. Communications Engineering, 2022, 1(1): 47-55.
[57] Wang B, Fu K, Fu J, et al. Miniature GaN optoelectronic temperature sensor[J]. Optics Letters, 2023, 48(16): 4209-4212.
[58] Sajid M, Khattak Z J, Rahman K, et al. Progress and future of relative humidity sensors: a review from materials perspective[J]. Bulletin of Materials Science, 2022, 45(4): 238-262.
[59] Li N, Jiang Y, Zhou C, et al. High-performance humidity sensor based on urchin-like composite of Ti3C2 MXene-derived TiO2 nanowires[J]. ACS Applied Materials & Interfaces, 2019, 11(41): 38116-38125.
[60] Dai J, Zhao H, Lin X, et al. Ultrafast response polyelectrolyte humidity sensor for respiration monitoring[J]. ACS Applied Materials & Interfaces, 2019, 11(6): 6483-6490.
[61] Si R, Xie X, Li T, et al. TiO2/NaNbO3 heterojunction for boosted humidity sensing ability[J]. Sensors and Actuators B: Chemical, 2020, 309: 127803-127812.
[62] Lin J, Gao N, Liu J, et al. Superhydrophilic Cu(OH)2 nanowire-based QCM transducer with self-healing ability for humidity detection[J]. Journal of Materials Chemistry A, 2019, 7(15): 9068-9077.
[63] Zheng X, Fan R, Li C, et al. A fast-response and highly linear humidity sensor based on quartz crystal microbalance[J]. Sensors and Actuators B: Chemical, 2019, 283: 659-665.
[64] Zhao Y, Tong R, Chen M Q, et al. Relative humidity sensor based on hollow core fiber filled with GQDs-PVA[J]. Sensors and Actuators B: Chemical, 2019, 284: 96-102.
[65] Aldaba A L, Lopez-Torres D, Elosua C, et al. SnO2-MOF-Fabry-Perot optical sensor for relative humidity measurements[J]. Sensors and Actuators B: Chemical, 2018, 257: 189-199.
[66] Liu Y, Huang H, Wang L, et al. Electrospun CeO2 nanoparticles/PVP nanofibers based high-frequency surface acoustic wave humidity sensor[J]. Sensors and Actuators B: Chemical, 2016, 223: 730-737.
[67] Su Y, Li C, Li M, et al. Surface acoustic wave humidity sensor based on three-dimensional architecture graphene/PVA/SiO2 and its application for respiration monitoring[J]. Sensors and Actuators B: Chemical, 2020, 308: 127693-127704.
[68] Liu Z, Su J, Zhou K, et al. Fully Integrated Patch Based on Lamellar Porous Film Assisted GaN Optopairs for Wireless Intelligent Respiratory Monitoring[J]. Nano Letters, 2023, 23(23): 10674-10681.
[69] Arman Kuzubasoglu B. Recent studies on the humidity sensor: a mini review[J]. ACS Applied Electronic Materials, 2022, 4(10): 4797-4807.
[70] Song P, Wang H. High‐performance polymeric materials through hydrogen‐bond cross‐linking[J]. Advanced Materials, 2020, 32(18): 1901244-1901256.
[71] Liu B, Zhou Y, Chen L, et al. High-performance sensors based on Chinese ink and water-based glue for detection of strain, temperature, and humidity[J]. ACS Sustainable Chemistry & Engineering, 2022, 10(5): 1847-1856.
[72] Zhao G, Huang Y, Mei C, et al. Chiral nematic coatings based on cellulose nanocrystals as a multiplexing platform for humidity sensing and dual anticounterfeiting[J]. Small, 2021, 17(50): 2103936-2103946.
[73] Anichini C, Aliprandi A, Gali S M, et al. Ultrafast and highly sensitive chemically functionalized graphene oxide-based humidity sensors: harnessing device performances via the supramolecular approach[J]. ACS Applied Materials & Interfaces, 2020, 12(39): 44017-44025.
[74] Chaloeipote G, Samarnwong J, Traiwatcharanon P, et al. High-performance resistive humidity sensor based on Ag nanoparticles decorated with graphene quantum dots[J]. Royal Society Open Science, 2021, 8(7): 210407-210418.
[75] Chen Z, Lu C. Humidity sensors: a review of materials and mechanisms[J]. Sensor Letters, 2005, 3(4): 274-295.
[76] Cho S Y, Lee Y, Koh H J, et al. Superior chemical sensing performance of black phosphorus: comparison with MoS2 and graphene[J]. Advanced Materials, 2016, 28(32): 7020-7028.
[77] Yu Y, Chen H, Liu Y, et al. Humidity sensing properties of single Au-decorated boron nitride nanotubes[J]. Electrochemistry Communications, 2013, 30: 29-33.
[78] Zhang Q, Zhang J, Wan S, et al. Stimuli‐responsive 2D materials beyond graphene[J]. Advanced Functional Materials, 2018, 28(45): 1802500-1802519.
[79] Wang Z, Fan X, Li C, et al. Humiditysensing performance of 3DOM WO3 with controllable structural modifcation[J]. ACS Applied Materials & Interfaces, 2018, 10(4):3776-3783.
[80] Qi R, Lin X, Dai J, et al. Humidity sensors based on MCM-41/polypyrrole hybrid film via in-situ polymerization[J]. Sensors and Actuators B: Chemical, 2018, 277: 584-590.
[81] Zhang D, Wang D, Zong X, et al. High-performance QCM humidity sensor based on graphene oxide/tin oxide/polyaniline ternary nanocomposite prepared by in-situ oxidative polymerization method[J]. Sensors and Actuators B: Chemical, 2018, 262: 531-541.
[82] Kang T G, Park J K, Yun G H, et al. A real-time humidity sensor based on a microwave oscillator with conducting polymer PEDOT: PSS film[J]. Sensors and Actuators B: Chemical, 2019, 282: 145-151.
[83] Lin Y, Jiang H, Liang G, et al. The exceptionally high moisture responsiveness of a new conductive-coordination-polymer based chemiresistive sensor[J]. CrystEngComm, 2021, 23(19): 3549-3556.
[84] Huang X, Li B, Wang L, et al. Superhydrophilic, underwater superoleophobic, and highly stretchable humidity and chemical vapor sensors for human breath detection[J]. ACS Applied Materials & Interfaces, 2019, 11(27): 24533-24543.
[85] Kinoshita S, Yoshioka S. Structural colors in nature: the role of regularity and irregularity in the structure[J]. ChemPhysChem, 2005, 6(8): 1442-1459.
[86] Kano S, Jarulertwathana N, Mohd-Noor S, et al. Respiratory monitoring by ultrafast humidity sensors with nanomaterials: A review[J]. Sensors, 2022, 22(3): 1251-1281.
[87] Kou D, Ma W, Zhang S, et al. High-performance and multifunctional colorimetric humidity sensors based on mesoporous photonic crystals and nanogels[J]. ACS Applied Materials & Interfaces, 2018, 10(48): 41645-41654.
[88] Tulliani J M, Inserra B, Ziegler D. Carbon-based materials for humidity sensing: A short review[J]. Micromachines, 2019, 10(4): 232-261.
[89] Wu Y, Huang Q, Nie J, et al. All-carbon based flexible humidity sensor[J]. Journal of Nanoscience and Nanotechnology, 2019, 19(8): 5310-5316.
[90] Lv C, Hu C, Luo J, et al. Recent advances in graphene-based humidity sensors[J]. Nanomaterials, 2019, 9(3): 422-464.
[91] Lee Y, Yoon J, Kim Y, et al. Humidity effects according to the type of carbon nanotubes[J]. IEEE Access, 2020, 9: 6810-6816.
[92] Ghosh S, Ghosh R, Guha P K, et al. Humidity sensor based on high proton conductivity of graphene oxide[J]. IEEE Transactions on Nanotechnology, 2015, 14(5): 931-937.
[93] Songkeaw P, Onlaor K, Thiwawong T, et al. Transparent and flexible humidity sensor based on graphene oxide thin films prepared by electrostatic spray deposition technique[J]. Journal of Materials Science: Materials in Electronics, 2020, 31: 12206-12215.
[94] Zhang D, Tong J, Xia B. Humidity-sensing properties of chemically reduced graphene oxide/polymer nanocomposite film sensor based on layer-by-layer nano self-assembly[J]. Sensors and Actuators B: Chemical, 2014, 197: 66-72.
[95] Park S Y, Kim Y H, Lee S Y, et al. Highly selective and sensitive chemoresistive humidity sensors based on rGO/MoS2 van der Waals composites[J]. Journal of Materials Chemistry A, 2018, 6(12): 5016-5024.
[96] Liu Y, Zhang C, Zhu P. The temperature humidity monitoring system of soil based on wireless sensor networks[C]//2011 International Conference on Electric Information and Control Engineering. IEEE, 2011: 1850-1853.
[97] Imam S A, Choudhary A, Sachan V K. Design issues for wireless sensor networks and smart humidity sensors for precision agriculture: a review[C]//2015 International Conference on Soft Computing Techniques and Implementations (ICSCTI). IEEE, 2015: 181-187.
[98] Blank T A, Eksperiandova L P, Belikov K N. Recent trends of ceramic humidity sensors development: a review[J]. Sensors and Actuators B: Chemical, 2016, 228: 416-442.
[99] Duan Z, Jiang Y, Tai H. Recent advances in humidity sensors for human body related humidity detection[J]. Journal of Materials Chemistry C, 2021, 9(42): 14963-14980.
[100] Güder F, Ainla A, Redston J, et al. Paper‐based electrical respiration sensor[J]. Angewandte Chemie International Edition, 2016, 55(19): 5727-5732.
[101] Li T, Li L, Sun H, et al. Porous ionic membrane based flexible humidity sensor and its multifunctional applications[J]. Advanced Science, 2017, 4(5): 1600404-1600411.
[102] Wang Y, Zhang L, Zhou J, et al. Flexible and transparent cellulose-based ionic film as a humidity sensor[J]. ACS Applied Materials & Interfaces, 2020, 12(6): 7631-7638.
[103] He J, Xiao P, Shi J, et al. High performance humidity fluctuation sensor for wearable devices via a bioinspired atomic-precise tunable graphene-polymer heterogeneous sensing junction[J]. Chemistry of Materials, 2018, 30(13): 4343-4354.
[104] Wan T, Shao B, Ma S, et al. In‐sensor computing: materials, devices, and integration technologies[J]. Advanced Materials, 2023, 35(37): 2203830-2203844.
[105] Majumder B D, Roy J K, Padhee S. Recent advances in multifunctional sensing technology on a perspective of multi-sensor system: a review[J]. IEEE Sensors Journal, 2018, 19(4): 1204-1214.
[106] Xie M, Hisano K, Zhu M, et al. Flexible multifunctional sensors for wearable and robotic applications[J]. Advanced Materials Technologies, 2019, 4(3): 1800626-1800655.
[107] Lin M, Zheng Z, Yang L, et al. A high‐performance, sensitive, wearable multifunctional sensor based on rubber/CNT for human motion and skin temperature detection[J]. Advanced Materials, 2022, 34(1): 2107309-2107322.
[108] Seok Jo H, An S, Kwon H J, et al. Transparent body-attachable multifunctional pressure, thermal, and proximity sensor and heater[J]. Scientific Reports, 2020, 10(1): 2701-2713.
[109] Wang S, Wang X, Wang Q, et al. Flexible optoelectronic multimodal proximity/pressure/temperature sensors with low signal interference[J]. Advanced Materials, 2023, 35(49): 2304701-2304711.
[110] Dai Y, Gao S. A flexible multi-functional smart skin for force, touch position, proximity, and humidity sensing for humanoid robots[J]. IEEE Sensors Journal, 2021, 21(23): 26355-26363.
[111] Yang S, Li C, Wen N, et al. All-fabric-based multifunctional textile sensor for detection and discrimination of humidity, temperature, and strain stimuli[J]. Journal of Materials Chemistry C, 2021, 9(39): 13789-13798.
[112] Zhang Z, Lu T, Yang D, et al. A dual‐function sensor for highly sensitive detection of flame and humidity[J]. Small, 2022, 18(38): 2203334-2203342.
[113] Yamamoto Y, Harada S, Yamamoto D, et al. Printed multifunctional flexible device with an integrated motion sensor for health care monitoring[J]. Science Advances, 2016, 2(11): e1601473-1601481.
[114] Kim T, Lee S, Hong T, et al. Heterogeneous sensing in a multifunctional soft sensor for human-robot interfaces[J]. Science Robotics, 2020, 5(49): eabc6878-6891.
[115] Chen L, Chang X, Wang H, et al. Stretchable and transparent multimodal electronic-skin sensors in detecting strain, temperature, and humidity[J]. Nano Energy, 2022, 96: 107077-107086.
[116] Lu Y, Xu K, Zhang L, et al. Multimodal plant healthcare flexible sensor system[J]. ACS Nano, 2020, 14(9): 10966-10975.
[117] Li C, Yang S, Guo Y, et al. Flexible, multi-functional sensor based on all-carbon sensing medium with low coupling for ultrahigh-performance strain, temperature and humidity sensing[J]. Chemical Engineering Journal, 2021, 426: 130364-130378.
[118] Xu Y, Liu S, Zhang J, et al. Fabrication of micro-cantilever sensor based on clay minerals for humidity detection[J]. Sensors, 2023, 23(15): 6962-6974.
[119] Guo J Y, Shi B, Sun M Y, et al. Application of PI-FBG sensor for humidity measurement in unsaturated soils[J]. Measurement, 2022, 188: 110415-110426.
[120] Su P G, Chen C Y. Humidity sensing and electrical properties of Na-and K-montmorillonite[J]. Sensors and Actuators B: Chemical, 2008, 129(1): 380-385.
[121] Marlow F, Muldarisnur, Sharifi P, et al. Opals: status and prospects[J]. Angewandte Chemie International Edition, 2009, 48(34): 6212-6233.
[122] Renfro N, McClure S F. Dyed purple hydrophane opal[J]. Gems & Gemology, 2011, 47(4):260-270.
[123] Eckert A W. The world of opals[M]. John Wiley & Sons, 1997.
[124] Jia Y, Wang B, Zhang T. A comparative study of different amorphous and paracrystalline silica by NMR and SEM/EDS[J]. Journal of Wuhan University of Technology-Materials Science Edition, 2015, 30(5): 900-907.
[125] Martin R W, Middleton P G, O’donnell K P, et al. Exciton localization and the Stokes’shift in InGaN epilayers[J]. Applied Physics Letters, 1999, 74(2): 263-265.
[126] Bjorkqvist M, Paski J, Salonen J, et al. Studies on hysteresis reduction in thermally carbonized porous silicon humidity sensor[J]. IEEE Sensors Journal, 2006, 6(3): 542-547.
[127] Park E U, Choi B I, Kim J C, et al. Correlation between the sensitivity and the hysteresis of humidity sensors based on graphene oxides[J]. Sensors and Actuators B: Chemical, 2018, 258: 255-262.
[128] Islam T, Saha H. Hysteresis compensation of a porous silicon relative humidity sensor using ANN technique[J]. Sensors and Actuators B: Chemical, 2006, 114(1): 334-343.
[129] Wang X, Ye M. Hysteresis and nonlinearity compensation of relative humidity sensor using support vector machines[J]. Sensors and Actuators B: Chemical, 2008, 129(1): 274-284.
[130] Duan Z, Zhao Q, Wang S, et al. Halloysite nanotubes: natural, environmental-friendly and low-cost nanomaterials for high-performance humidity sensor[J]. Sensors and Actuators B: Chemical, 2020, 317: 128204-128211.
[131] Zhao J, Li N, Yu H, et al. Highly sensitive MoS2 humidity sensors array for noncontact sensation[J]. Advanced Materials, 2017, 29(34): 1702076-1702083.
[132] Si R, Xie X, Li T, et al. TiO2/(K, Na) NbO3 nanocomposite for boosting humidity-sensing performances[J]. ACS Sensors, 2020, 5(5): 1345-1353.
[133] Duan Z, Jiang Y, Yan M, et al. Facile, flexible, cost-saving, and environment-friendly paper-based humidity sensor for multifunctional applications[J]. ACS Applied Materials & Interfaces, 2019, 11(24): 21840-21849.
[134] Dwiputra M A, Fadhila F, Imawan C, et al. The enhanced performance of capacitive-type humidity sensors based on ZnO nanorods/WS2 nanosheets heterostructure[J]. Sensors and Actuators B: Chemical, 2020, 310: 127810-127821.
[135] Gao N, Li H Y, Zhang W, et al. QCM-based humidity sensor and sensing properties employing colloidal SnO2 nanowires[J]. Sensors and Actuators B: Chemical, 2019, 293: 129-135.
[136] Gao R, Lu D, Cheng J, et al. Humidity sensor based on power leakage at resonance wavelengths of a hollow core fiber coated with reduced graphene oxide[J]. Sensors and Actuators B: Chemical, 2016, 222: 618-624.
[137] Darragh P J, Gaskin A J, Sanders J V. Opals[J]. Scientific American, 1976, 234(4): 84-95.
[138] Bartoli F, Wilding L P. Dissolution of biogenic opal as a function of its physical and chemical properties[J]. Soil Science Society of America Journal, 1980, 44(4): 873-878.
[139] Franklin J, Wang Z Y. Refractive index matching: a general method for enhancing the optical clarity of a hydrogel matrix[J]. Chemistry of Materials, 2002, 14(11): 4487-4489.
[140] Ojeda-Mendoza G J, Contreras-Tello H, Rojas-Ochoa L F. Refractive index matching of large polydisperse silica spheres in aqueous suspensions[J]. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2018, 538: 320-326.
[141] Teoman B, Potanin A, Armenante P M. Optimization of optical transparency of personal care products using the refractive index matching method[J]. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2021, 610: 125595-125604.
[142] Tarcan R, Todor-Boer O, Petrovai I, et al. Reduced graphene oxide today[J]. Journal of Materials Chemistry C, 2020, 8(4): 1198-1224.
[143] Ahmad H, Fan M, Hui D. Graphene oxide incorporated functional materials: a review[J]. Composites Part B: Engineering, 2018, 145: 270-280.
[144] Agarwal V, Zetterlund P B. Strategies for reduction of graphene oxide-a comprehensive review[J]. Chemical Engineering Journal, 2021, 405: 127018-127047.
[145] Feng J, Ye Y, Xiao M, et al. Synthetic routes of the reduced graphene oxide[J]. Chemical Papers, 2020, 74: 3767-3783.
[146] Toh S Y, Loh K S, Kamarudin S K, et al. Graphene production via electrochemical reduction of graphene oxide: synthesis and characterisation[J]. Chemical Engineering Journal, 2014, 251: 422-434.
[147] Graf D, Molitor F, Ensslin K, et al. Spatially resolved Raman spectroscopy of single-and few-layer graphene[J]. Nano Letters, 2007, 7(2): 238-242.
[148] Zhang Y L, Guo L, Xia H, et al. Photoreduction of graphene oxides: methods, properties, and applications[J]. Advanced Optical Materials, 2014, 2(1): 10-28.
[149] Mohandoss M, Gupta S S, Nelleri A, et al. Solar mediated reduction of graphene oxide[J]. RSC Advances, 2017, 7(2): 957-963.
[150] Du T, Adeleye A S, Zhang T, et al. Influence of light wavelength on the photoactivity, physicochemical transformation, and fate of graphene oxide in aqueous media[J]. Environmental Science: Nano, 2018, 5(11): 2590-2603.
[151] Gengler R Y N, Badali D S, Zhang D, et al. Revealing the ultrafast process behind the photoreduction of graphene oxide[J]. Nature Communications, 2013, 4(1): 2560.
[152] Zhao Z, Pu R, Wang Z, et al. Identification of ultraviolet photoinduced presolvated electrons in water as the reducing agent in the photoreduction of graphene oxide[J]. The Journal of Physical Chemistry C, 2023, 127(7): 3516-3522.
[153] Thomsen C L, Madsen D, Keiding S R, et al. Two-photon dissociation and ionization of liquid water studied by femtosecond transient absorption spectroscopy[J]. The Journal of Chemical Physics, 1999, 110(7): 3453-3462.
[154] Park S, An J, Jung I, et al. Colloidal suspensions of highly reduced graphene oxide in a wide variety of organic solvents[J]. Nano Letters, 2009, 9(4): 1593-1597.
[155] Liu W, Speranza G. Tuning the oxygen content of reduced graphene oxide and effects on its properties[J]. ACS Omega, 2021, 6(9): 6195-6205.
[156] Guex L G, Sacchi B, Peuvot K F, et al. Experimental review: chemical reduction of graphene oxide (GO) to reduced graphene oxide (rGO) by aqueous chemistry[J]. Nanoscale, 2017, 9(27): 9562-9571.
[157] Basko D M, Piscanec S, Ferrari A C. Electron-electron interactions and doping dependence of the two-phonon Raman intensity in graphene[J]. Physical Review B, 2009, 80(16):165413-165422.
[158] Rabchinskii M K, Shnitov V V, Dideikin A T, et al. Nanoscale perforation of graphene oxide during photoreduction process in the argon atmosphere[J]. The Journal of Physical Chemistry C, 2016, 120(49): 28261-28269.
[159] Ansón-Casaos, Alejandro, et al. The effect of gamma-irradiation on few-layered graphene materials[J]. Applied Surface Science, 2014, 301: 264-272.
[160] Konkena B, Vasudevan S. Understanding aqueous dispersibility of graphene oxide and reduced graphene oxide through pKa measurements[J]. The Journal of Physical Chemistry Letters, 2012, 3(7): 867-872.
[161] Coates J. Interpretation of infrared spectra, a practical approach[J]. 2000.
[162] Li L Y, Dong Y F, Jiang W F, et al. High-performance capacitive humidity sensor based on silicon nanoporous pillar array[J]. Thin Solid Films, 2008, 517(2): 948-951.
[163] Traversa E. Ceramic sensors for humidity detection: the state-of-the-art and future developments[J]. Sensors and Actuators B: Chemical, 1995, 23(2-3): 135-156.
[164] Seiyama T, Yamazoe N, Arai H. Ceramic humidity sensors[J]. Sensors and Actuators, 1983, 4: 85-96.
[165] Niu H, Yue W, Li Y, et al. Ultrafast-response/recovery capacitive humidity sensor based on arc-shaped hollow structure with nanocone arrays for human physiological signals monitoring[J]. Sensors and Actuators B: Chemical, 2021, 334: 129637-129647.
[166] Yap K Z, Lim W Y, Kalkal A, et al. Electrophoretic deposited Mg ion functionalised graphene oxide based ultra-highly sensitive humidity sensor[J]. IEEE Transactions on Instrumentation and Measurement, 2023,72:1-8.
[167] Bi H, Yin K, Xie X, et al. Ultrahigh humidity sensitivity of graphene oxide[J]. Scientific Reports, 2013, 3(1): 2714-2721.
[168] Zou S, Tao L Q, Wang G, et al. Humidity-based human–machine interaction system for healthcare applications[J]. ACS Applied Materials & Interfaces, 2022, 14(10): 12606-12616.
[169] Li S, Zhang Y, Liang X, et al. Humidity-sensitive chemoelectric flexible sensors based on metal-air redox reaction for health management[J]. Nature Communications, 2022, 13(1): 5416-5426.
[170] Xia B, Liu B, Wang N, et al. Polyelectrolyte/graphene oxide nano-film integrated fiber-optic sensors for high-sensitive and rapid-response humidity measurement[J]. ACS Applied Materials & Interfaces, 2022, 14(36): 41379-41388.
[171] Wang S, Yan H, Zheng H, et al. Fast response humidity sensor based on chitosan/graphene oxide/tin dioxide composite[J]. Sensors and Actuators B: Chemical, 2023,392:134070-134079.
[172] Guo L, Jiang H B, Shao R Q, et al. Two-beam-laser interference mediated reduction, patterning and nanostructuring of graphene oxide for the production of a flexible humidity sensing device[J]. Carbon, 2012, 50(4): 1667-1673.
[173] Cai J, Lv C, Aoyagi E, et al. Laser direct writing of a high-performance all-graphene humidity sensor working in a novel sensing mode for portable electronics[J]. ACS Applied Materials & Interfaces, 2018, 10(28): 23987-23996.
[174] Wang X, Xiong Z, Liu Z, et al. Exfoliation at the liquid/air interface to assemble reduced graphene oxide ultrathin films for a flexible noncontact sensing device[J]. Advanced Materials, 2015, 27(8): 1370-1375.
[175] Wu Z, Sun X, Guo X, et al. Development of a rGO-BiVO4 heterojunction humidity sensor with boosted performance[J]. ACS Applied Materials & Interfaces, 2021, 13(23): 27188-27199.
[176] Zhang D, Xu Z, Yang Z, et al. High-performance flexible self-powered tin disulfide nanoflowers/reduced graphene oxide nanohybrid-based humidity sensor driven by triboelectric nanogenerator[J]. Nano Energy, 2020, 67: 104251.
[177] Trung T Q, Duy L T, Ramasundaram S, et al. Transparent, stretchable, and rapid-response humidity sensor for body-attachable wearable electronics[J]. Nano Research, 2017, 10: 2021-2033.
[178] Crebolder J M, Sloan R B. Determining the effects of eyewear fogging on visual task performance[J]. Applied Ergonomics, 2004, 35(4): 371-381.
[179] Gultepe I, Tardif R, Michaelides S C, et al. Fog research: a review of past achievements and future perspectives[J]. Pure and Applied Geophysics, 2007, 164: 1121-1159.
[180] Sorli B, Pascal-Delannoy F, Giani A, et al. Fast humidity sensor for high range 80-95% RH[J]. Sensors and Actuators A: Physical, 2002, 100(1): 24-31.
[181]Pascal-Delannoy F, Sackda A, Giani A, et al. Fast humidity sensor using optoelectronic detection on pulsed Peltier device[J]. Sensors and Actuators A: Physical, 1998, 65(2-3): 165-170.
[182] Liu H, Guo D, Sun F. Object recognition using tactile measurements: kernel sparse coding methods[J]. IEEE Transactions on Instrumentation and Measurement, 2016, 65(3): 656-665.
[183] Li G, Liu S, Wang L, et al. Skin-inspired quadruple tactile sensors integrated on a robot hand enable object recognition[J]. Science Robotics, 2020, 5(49): eabc8134-8145.
[184] Jung P G, Lim G, Kim S, et al. A wearable gesture recognition device for detecting muscular activities based on air-pressure sensors[J]. IEEE Transactions on Industrial Informatics, 2015, 11(2): 485-494.
[185] Navarro S E, Mühlbacher-Karrer S, Alagi H, et al. Proximity perception in human-centered robotics: a survey on sensing systems and applications[J]. IEEE Transactions on Robotics, 2021, 38(3): 1599-1620.
[186] Huang L, Wang S, Zhang K, et al. Research progress of multifunctional flexible proximity sensors[J]. Sensors and Actuators A: Physical, 2023: 114500.
[187] Xu X, Yan B. Bioinspired luminescent HOF-based foam as ultrafast and ultrasensitive pressure and acoustic bimodal sensor for humanmachine interactive object and information recognition[J]. Advanced Materials, 2023: 2303410-2303424.
[188] Rassel S, Xu C, Zhang S, et al. Noninvasive blood glucose detection using a quantum cascade laser[J]. Analyst, 2020, 145(7): 2441-2456.
[189] Lee H K, Chang S I, Yoon E. Dual-mode capacitive proximity sensor for robot application: Implementation of tactile and proximity sensing capability on a single polymer platform using shared electrodes[J]. IEEE Sensors Journal, 2009, 9(12): 1748-1755.
[190] Kedambaimoole V, Kumar N, Shirhatti V, et al. Reduced graphene oxide tattoo as wearable proximity sensor[J]. Advanced Electronic Materials, 2021, 7(4): 2001214-2001231.
[191] Chen C H, Lin C F, Wang K H, et al. High-resolution proximity sensor using flexible semi-transparent organic photo detector[J]. Organic Electronics, 2017, 49: 305-312.
[192] Behera S K, Rath A K, Mahapatra A, et al. Identification, classification & grading of fruits using machine learning & computer intelligence: a review[J]. Journal of Ambient Intelligence and Humanized Computing, 2020: 1-11.
[193] Peng H, Shao Y, Chen K, et al. Research on multi-class fruits recognition based on machine vision and SVM[J]. IFAC-PapersOnLine, 2018, 51(17): 817-821.
[194]Alzubaidi L, Al-Shamma O, Fadhel M A, et al. A deep convolutional neural network model for multi-class fruits classification[C]//Intelligent Systems Design and Applications: 19th International Conference on Intelligent Systems Design and Applications (ISDA 2019),Springer International Publishing, 2021: 90-99.
[195] Gu J, Wang Z, Kuen J, et al. Recent advances in convolutional neural networks[J]. Pattern Recognition, 2018, 77: 354-377.
[196] Li Z, Liu F, Yang W, et al. A survey of convolutional neural networks: analysis, applications, and prospects[J]. IEEE Transactions on Neural Networks and Learning Systems, 2022, 33(12): 6999-7019.