| 摘要: | 本實驗以99.98%鋅箔為工作電極，304不鏽鋼為對應電極，Ag/AgCl為參考電極，使用電化學定電位方式在添加硝酸鋅的氫氧化鈉溶液中製備氧化鋅奈米結構。 首先，使用三極式恆電位儀(273A)在含0.00 M, 0.15 M, 0.20 M, 0.25 M, 0.50 M Zn(NO3)2和0.20M NaNO3之2M NaOH鹼性溶液中以拋光鋅箔進行陽極動態極化實驗，其開路電位大約分佈在-1.20V(v.s SHE)附近，並隨著鋅離子濃度增加而增加，在-0.87V左右會有一電流急速下降至極小值，所對應之電位隨添加的硝酸鋅越多而下降，此電位為活化區與鈍態區之界線。由動態極化結果，選擇電位(-0.5V、-0.7V、-0.9V、-1.1V)，在添加0.00 M, 0.15 M, 0.20 M, 0.25 M Zn(NO3)2的2M NaOH鹼性溶液中各進行一小時定電位處理做為比較；由FESEM結果可知，於活化區電位-0.9V與-1.1V進行定電位處理，所得到之形貌為片狀奈米氧化鋅多晶結構，在硝酸鋅濃度0.15M~0.25M下並無太大之差異；於鈍態區電位-0.5V與-0.7V進行定電位處理所得到之形貌為線狀奈米結構(長度約250nm，直徑約25nm)，並且隨著硝酸鋅濃度增加而形貌越明顯，0.25M為較佳之參數；由X光能譜散佈分析儀(EDS)結果可知試片表面結構物的組成，氧和鋅的比例接近1:1；由化學分析能譜儀(ESCA)結果可知分別為Zn(2p1/2)波峰值1045.1 eV與Zn(2p3/2)波峰值1021.9 eV，此兩個鍵結能皆為為氧化鋅(Zn-O)鍵結，並無其他峰值存在；由X光繞射分析(XRD)可得知為hexagonal wurtzite ZnO結構，且以(002)的峰值為優選方向；由光致螢光光譜分析(PL) 結果可知在紫外光區380nm(~3.26eV)有一最高峰值，此峰值屬於氧化鋅本質發光性質，其餘激發光波長則為缺陷所造成。 An attempt was made in his work to fabricate nano structure zinc oxides on zinc foil (10 mm x 10 mm x 0.62 mm) from the alkaline solution containing zinc ions by electrochemical method. In this system, zinc was the working electrode, stainless steel (ss) 304 was the counter electrode and Ag/AgCl was the reference electrode. After polishing to obtain mirror surface, the zinc foil was potentiodynamically polarized in 2M NaOH solution containing 0.00 M, 0.15M, 0.20M, 0.25M Zn(NO3)2 and 0.20M NaNO3, from the potentials at which the open circuit potentials (OCPs) minus 0.250V to 2.00V(vs. SHE) by the aid of Potentiostat 273A, with the scan rate at 1mV/s. The open circuit potential is at about -1.20V (vs. SHE), and it increases with the concentration of zinc ions. Electrolysis at -0.87V, the current will decrease to the lowest value so that it is a critical potential to have an abrupt change in current density. This potential is the boundary between active region and passive region. According to the polarization diagram, we conducted potentiostatic electrolysis at -0.5V, -0.7V, -0.9V, and -1.1V, respectively. And examined the morphology of the deposits with field-emission scanning electron microscope (FESEM), we found that the deposits fabricated at -0.5V and -0.7V are in nano single crystalline wires of ZnO (250 nm in length and 25 nm in diameter), and there is no clear difference when Zn(NO3)2 at 0.15M~0.25M. However, those fabricate at -0.9V and -1.1V are in polycrystalline nano sheets (200 nm in diameter and 25 nm in thickness) , and 0.25M Zn(NO3)2 has better morphology. Analysis by Energy-dispersive X-ray spectroscopy (EDX), we found that these two different structures have almost the same composition with the ratio between zinc and oxygen about 1:1. Analysis by X-ray photoelectron spectroscopy (XPS), we confirmed the composition of ZnO in which the peak Zn(2p3/2) at 1021.9 eV belonging to zinc oxide. X-ray diffraction (XRD) measurement demonstrated the crystal is a wurtzite of hexagonal with a texture of (002). Analysis by Photoluminescence (PL), we found that these two different structures have a peak at 380nm, and this peak belong to ZnO intrinsic peak. The other peak is due to impurities and defects. |
