利用氧化鋅奈米柱/氧化銀薄膜之核殼異質結構提升光催化活性

Photocatalytic Enhancement in ZnO-Ag2O Core-shell NanorodHeterostructure

蔡虹驛(Hung-Yi Tsai)

指導教授 ： 吳振名

國立清華大學/工學院/材料科學工程學系/碩士(2014年)

https://doi.org/10.6843/NTHU.2014.00358

摘要

本實驗使用反應式濺鍍(reactive sputtering)，以金屬銀為靶材，將氧氣與氬氣混合通入腔體，成功濺鍍出Ag2O，所獲得的最佳參數為氧分壓25 %、基板溫度170 °C、濺鍍功率50 w及工作壓力5 mTorr。所獲得的氧化銀薄膜為多晶相，在(111)面上有優選結晶方向，能隙值為2.42 eV。
增加濺鍍時氧分壓比例，會使沉降出的薄膜其銀離子價數增加，從Ag(1+)、Ag(2+)到Ag(3+)，從XPS來看3d5/2的訊號峰值有逐漸下降的趨勢(367.6 eV→367.2 eV→366.8 eV)，XRD的分析也可以輔佐印證。氧分壓超過一極值後，會使”再濺鍍”的效應加強，導致薄膜品質下降；升高基板溫度，可以使薄膜中高價數銀離子之氧化物減少，歸因於這些氧化物在高溫的狀態下的熱穩定性不佳。
將Ag2O濺鍍至ZnO奈米柱體上，形成一核殼的異質結構。從能帶關係、吸收光譜與PL光譜可以印證，此異質結構為p-n型的半導體接合，能帶關係的改變可以減少載子對再複合的機率，同時也加強對太陽光的吸收效果。在光催化全光譜系統中，此異質結構對RhB染料的降解效果與純的ZnO奈米柱相比有較高的反應速率(Ka分別0.75 h-1與0.44 h-1)，單純照射可見光的部分此異質結構亦有降解效率(Ka=0.19)，可以確認Ag2O對此系統在光催化方面確實有所幫助。

關鍵字

氧化銀 ； 氧化鋅 ； 光催化

並列摘要

Ag2O thin film, which possessed 2.42eV optical band gap, were deposited on glass and silicon substrates by RF magnetron sputtering using silver target under 25% oxygen flow ratios, 170°C substrate temperature, 50W sputtering power and 5 mTorr working pressure.
The influence of oxygen flow ratio and substrate temperature on the structural, morphological, electrical, and optical properties of deposited Ag2O films was investigated. Increasing oxygen partial pressure during sputtering decreases the crystallinity of Ag2O due to oxidation of large portion of the metal target and re-sputtering effect. X-ray diffraction and X-ray photoelectron spectroscopy indicates that sputtering with higher oxygen partial pressure prefers to deposit silver oxide film with higher oxidation state, and sputtering at higher substrate temperature tend to demonstrate silver oxide film with lower oxidation state.
Reactive-sputtered Ag2O was deposited on ZnO nanowires which were hydrothermally grown on conductive Zn0.99Ga0.01O film/ Si substrate. Absorption in the visible-NIR range of the ZnO-Ag2O core-shell heterostructure is investigated. Photodegradation of organic pollutants in aqueous solution is a promising application for this ZnO-Ag2O core-shell heterostructure, which exhibit a photodegradation rate 1.7 times higher than that recorded for the bare ZNA under sun irradiation.

並列關鍵字

silver oxide ； zinc oxide ； photocatalytist

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