以鉛為介面活性劑電鍍製備Ni/Cu(111)薄膜研究

本實驗主要以鉛作為介面活性劑，藉以改變鎳在銅(111)上的成長模式以及薄膜磁特性。實驗中以電化學方式電鍍薄膜，以銅(111)為工作電極、銀/氯化銀為參考電極、白金為相對電極，實驗都在室溫下進行。將銅(111)置於 1 mM HCl + 1 mM NiCl2 水溶液中，利用循環伏安法（CV） step by step 的掃描方式，可以找出鎳成對的吸附、剝離峰電位分別為 E = -950 mV（←）和E = -480 mV（→），藉由控制循環伏安法停留在鎳的吸附電位並改變停留時間，以在銅(111)上鍍上不同厚度的鎳。在滴加少量氯化鉛溶液後，因為鉛的沉積電位在鎳之前，故可以優先沉積在銅(111)上，並與隨後沉積的鎳交換位置，藉由介面活性劑的特性以達到改善鎳成長模式的機制。在電鍍薄膜後，透過掃描穿隧式顯微鏡（STM）觀察鎳鍍在銅上的形貌大致可區分為兩類，第一類是三維島狀成長，可能是鎳銅合金的形貌；第二類是成塊堆疊的形貌，經掃描剝除電位後，仍可看到底層較難剝除的特殊結構，此亦和鎳銅合金有關。配合循環伏安法中需要多次掃描鎳的剝除電位區段才能將鎳的訊號退除，和磁光柯爾效應儀（MOKE）中磁滯訊號變化不同的現象，證實有鎳銅合金的產生。而從磁光柯爾效應儀掃描出的磁滯曲線隨層數的變化中，可觀察到不論有無加鉛，鎳在銅上的沉積皆有磁性易軸由平行膜面轉變到垂直膜面，再回到平行膜面的方向—即自旋重新排列轉變（SRT）的現象發生。最後比較有無加鉛的差異：利用掃描穿隧式顯微鏡的掃描圖計算粗糙度值，加入鉛之後的粗糙度值明顯下降，表示表面趨於平整；而從磁滯曲線中計算矯頑場與方正度，數值也比未加入鉛時高。這些證據都顯示鉛確實具有介面活性劑的功效，能有效改善鎳在銅上的成長模式，同時使該薄膜展現較佳的磁特性。

關鍵字

介面活性劑；鎳；銅(111) ；循環伏安法；掃描穿隧式顯微鏡；磁光柯爾效應儀；鎳銅合金；自旋重新排列轉變

並列摘要

The properties of electrodeposited Ni thin films on Cu(111) modulated using Pb surfactant are investigated by employing cyclic voltammetry (CV), electrochemical scanning tunneling microscope (EC-STM) and magneto-optic Kerr effect (MOKE). From the CV measurements of Cu(111) in 1 mM HCl + 1 mM NiCl2 solution, a cathodic current commencing at -950 mV and an anodic peak between -480 and -200 mV were observed due to the adsorption and desorption of Ni, respectively. For Ni on Cu(111), two types of the morphologies have been observed. The three-dimensional island growth was observed due to the formation of CuNi alloy. The second type is stacked like block which is formed after CV stripping for many times. The formation of CuNi alloy has been confirmed by the multiple striping off to get Ni-free surface and changing sign of the magneto-optic signals. From MOKE measurements, spin reorientation transitions are observed. After dropping a little PbCl2 solution, Pb atoms tend to firstly adsorb onto Cu(111) surface and then exchange with the subsequently deposited Ni atoms. The exchange process enhances the smoothness of the surface morphology as compared with the films grown without Pb. From MOKE measurements, the squareness of the hysteresis loops is close to unity after adding Pb atoms. These evidences suggest that Pb performs the role of a surfactant to improve the smoothness of the grown films.

並列關鍵字

surfactant ； Ni ； Cu(111) ； cyclic voltammetry ； scanning tunneling microscope ； magneto-optic Kerr effect ； CuNi alloy ； spin reorientation transition

參考文獻

[ 7 ] K. M. Poduska and S. Morin，Rev. Sci. Instrum.，74，11，4723-4727（2003）

[17] Adzic. R. R.，in Advances in Electrochemistry and Electrochemical Engineering，13，159（1984）

[24] Potentials of Common Reference Electrodes，http://www.consultrsr.com/resources/ref/refpotls.htm#mse

[26] R. Eisberg, and R. Resnik，Quantum Physics of Atoms, Molecules, Solids, Nuclei, and Particles，2nd edit，Wiley，New York（1985）

[28] K. Besocke，Surf. Sci.，181，145（1987）

國際替代計量

以鉛為介面活性劑電鍍製備Ni/Cu(111)薄膜研究

主題瀏覽