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大綱
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摘要
石墨烯因擁有大的比表面積及材料性質，近年來作為氣體感測材料極具發展潛力，但仍有著靈敏度較低及回復時間長等缺點。本研究為改善此缺點，將還原氧化石墨烯及氧化鋅以10：1的比例進行混和以提升氣體感測響應，並使用波長355 nm，脈衝寬度為28 ns之Nd:YVO4奈秒紫外光脈衝雷射針對噴塗於矽晶圓基板之此石墨烯複合材料
(rGO/ZnO=10/1) 進行表面改質。研究發現，當雷射參數設為離焦加工(光斑大小為240 μm)、雷射輸出功率3 W、掃描速度300 mm/s時，即於低雷射能量密度(66.31 mJ/cm2)及高脈衝重疊率(98.75 %)下可在未發生材料剝蝕的情況下有效將片電阻值自原始之2.72×103
Ω/square大幅降低至1.13×103 Ω/square，降幅達58 %且單片加工僅耗時131.2秒。經分析材料經過雷射表面改質前後之拉曼光譜及X光光電子能譜後，可了解到片電阻下降的主因是雷射表面改質過程中移除了還原氧化石墨烯於製程中殘留之含氧官能基團，導致材料缺陷結構減少，導電率則因此上升。X光光電子能譜中亦顯示材料氧碳原子數比自33.73 %下降至12.59 %，由鍵結結構來看，材料之碳原子sp2鍵結比例增加，取代原本之sp3鍵結，使得材料越發貼近完整石墨烯結構。透過氣體感測實驗可知，不同於rGO試片，rGO/ZnO試片在雷射表面改質前便具有氣體感測能力，在5 ppm NO2氣體環境下具有4.2 %之氣體響應，而透過雷射表面改質後氣體響應可提升至6.2 %，另測試不同濃度NO2氣體環境下表面改質後試片之響應，在10 ppm、30 ppm及50 ppm氣體濃度下感測器分別具有11.0 %、14.8 %及23.7
%之氣體響應，且在連續開關NO2氣瓶實驗中顯示此試片具有穩定性，並具備可再現性及長期可靠性。
關鍵字：還原氧化石墨烯、氧化鋅、複合材料、氣體感測、紫外光脈衝雷射、表面改質、二氧化氮、電阻式氣體感測器
Abstract
Due to its large specific surface area and material properties,
graphene has great development potential as a gas sensing material in
recent years. However certain disadvantages such as weak sensitivity and
long recovery time, still exist. To improve the above shortcomings, reduced
graphene oxide decorated with ZnO NPs in a ratio of 10:1 to improve the gas
sensing response was adopted. Furthermore the laser-induced surface
modification of the graphene composite material film (rGO/ZnO=10/1) with
sprayed coating on silicon wafer substrate was conducted via nano-second
pulsed Nd:YVO4 UV laser of 355 nm wavelength and 28 ns pulse width. By
controlling the laser power and scanning speed at 3 W and 100 mm/s with a
defocused beam radius (the spot size of 240 μm), under low laser fluence
(66.31 mJ/cm2) and high pulse overlap (98.75 %), the sheet resistance of
the rGO/ZnO film was effectively reduced from 2.72×103 Ω/square to 1.13×103
Ω/square without significant ablations. The drop of sheet resistance was
seen about 58 % and the process only took 131.2 seconds.
By analyzing Raman spectroscopy and X-ray photoelectron
spectroscopy of the rGO/ZnO film before and after the laser surface
modification, it was found that the main factor to the drop of sheet
resistance was the removal of oxygen-containing functional groups during
the laser surface modification process, which led to the decrease of
defects and the increase of conductivity. X-ray photoelectron spectroscopy
also showed that the O/C atomic ratio in the material has decreased from
33.73 % to 12.59 %, and the main hybridization of carbon changed from sp3
to sp2 accordingly, shown closer to the graphene structure.
In the gas sensing experiment, different from rGO film,
rGO/ZnO film had a basic gas sensing ability before laser surface
modification and had a 4 % gain in response to 5 ppm NO2. After surface
modification, the response can be raised to 6 %. In addition, testing the
response of rGO/ZnO film after surface modification in different
concentrations of NO2, the corresponding response in 10 ppm, 30 ppm, 50 ppm
were 11 %, 15 %, 23 %, respectively. Also high stability, reproducibility,
and long-term reliability of the materials developed were demonstrated.
Keywords:
Reduced graphene oxide,
Zinc oxide, Composite, Gas sensing, Pulsed UV laser, Surface modification, NO2,
Resistive gas sensor.
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