基於鈀奈米結構的氫氣感測器及具矯頑力增進的鐵鈀垂直磁紀錄介質之研究

Development of Pd nanostructure based hydrogen gas sensors and coercivity-enhanced FePd-based perpendicular magnetic recording media

阮德昭(Duc-Chau Nguyen)

指導教授 ： 李志浩 ； 張嘉升

國立清華大學/原子科學院/工程與系統科學系/博士(2018年)

摘要

本論文分別探討Pd薄膜的奈米尺度的織構對於氫氣感測器的影響以及Fe/Pd多層薄膜的矯頑力改善對於垂直磁紀錄的影響。第一部分說明奈米結構的氫氣感測器是如何成長島狀結構的Pd薄膜在MgO(001)基板上並且闡述間隙關閉機制對於其影響，我們運用直流磁濺鍍的方法在攝氏550度的基板溫度環境下沉積100 nm的Pd薄膜使其擁有(002)的優選取向。隨著稀土元素釓(Gd)或鋱(Tb)的參雜量的增加，成長出的晶粒大小以及表面型態產生了顯著的變化，對於提高氫氣偵測中濃度變化的敏感度提供了一個研究面向。藉由比對樣品間的變化了解，間隙關閉機制使得我們提供氫氣環境給所有的氫氣感測器時其電阻值都出現明顯的下降。第二部分的研究聚焦在FePd合金薄膜中垂直矯頑力高於900 Oe的研究成果以了解垂直磁紀錄媒介的可能。我們用磁濺鍍的方式在MgO (001)基板上層積[Fe(2 nm)/Pd(2 nm)]×30的多層膜結構，並且在攝氏700度的基板溫度下退火1小時以及10小時，藉此得到了不按化學當量比例組成的FePd薄膜。結果顯示，隨著退火時間的增加，具有(001)優選取向的FePd薄膜除了呈現出晶粒大小以及表面粗糙度的增加之外也有增強結晶度以及降低微觀應變的表現，我們觀察到其薄膜的垂直矯頑力顯著的增加到1.5 kOe以及觀察到Pd失去其4d軌域的電子，最後再由分析X光吸收光譜中FePd四方晶系中Fe的散射相來了解薄膜微結構的細節。此篇論文也提供一個方法藉由從延伸X光吸收光譜精細結構中提取出的正方性比率結合薄膜的化學當量比例的偏差來決定吸收光譜中長程序化的參數。

關鍵字

鈀奈米結構 ； 氫感測器 ； 鐵鈀 ； 磁垂直紀錄

並列摘要

This thesis work presents the development of the nano-scale textures of Pd films and coercivity enhancement of Fe/Pd multilayer thin films for hydrogen gas sensing and perpendicular magnetic recording, respectively. Firstly, the simple preparation of the self-assembled network of palladium islands on MgO(001) substrate and the exploration of the gap closing mechanism in these nanostructured hydrogen sensors are reported. Pd films of 100 nm in thickness, deposited at 550 ˚C using the DC magnetron sputtering technique, possess the (002) preferred orientation that it still retains while doping with rare-earth metals such as Gd or Tb. However, the grain size and surface morphology of the Pd films change markedly with the addition of dopants, offering a route for tailoring the film toward higher sensitivity and scalable responses to changes in H2 concentrations. All the sensors show the decreased resistance in the presence of H2, the behavior attributed to the physical gap closing mechanism. Sensing performances of the samples are also compared. Secondly, the research focus was also on the attainment of perpendicular coercivity higher than 900 Oe in an FePd alloy thin film for realization of the perpendicular magnetic recording media. The off-stoichiometric FePd films were prepared through the multilayer growth of [Fe(2 nm)/Pd(2 nm)]×30 on MgO(001) substrates by magnetron sputtering, followed by the post-annealing at 700 ˚C for 1 h and 10 h. The results show that, with increasing annealing time, the FePd thin films are predominantly (001)-oriented with progressive increase of the grain size and surface roughness, as well as the improved crystallinity and reduced micro-strain. Accordingly, the perpendicular coercivity is significantly increased to the value of 1.5 kOe, and Pd loses its 4d electrons upon alloying. Furthermore, analysis of X-ray absorption data elucidates some structural details of the Fe scattering phase in addition to the dominant tetragonal FePd phase. Additionally, the thesis also presents a way of determining the long-range order parameter for the FePd alloy thin film, using combined information of tetragonality ratio extracted from extended x-ray absorption fine-structure spectroscopy and the stoichiometric deviation of the thin film.

並列關鍵字

Pd nanostructure ； Hydrogen gas sensors ； FePd ； Perpendicular magnetic recording

參考文獻

References

[1] A. Pundt, “Hydrogen in nano-sized metals,” Adv. Eng. Mater. 6 (2004) 11–21.

[2] J. Villatoro, D. Monzón-Hernández, “Fast detection of hydrogen with nano fiber tapers coated with ultra thin palladium layers,” Opt. Express 13 (2005) 5087–5092.

[3] Z. Zhao, M. A. Carpenter, H. Xia, D. Welch, “All-optical hydrogen sensor based on a high alloy content palladium thin film,” Sens. Actuators B Chem. 113 (2006) 532–538.

[4] T. Hubert, L. Boon-Brett, G. Black, U. Banach, “Hydrogen sensors – a review,” Sens. Actuators B Chem. 157 (2011) 329–352.