摘要

本實驗在超高真空的環境中，使用蒸鍍的方式將Co膜成長在Si (111)-7×7表面上，通入高純度之O2來研究曝氧效應對於Co/Si(111)超薄膜之影響，以歐傑電子能譜儀分析其表面成份，以低能量電子繞射儀以及反射式高能量電子繞射儀觀察其表面週期性結構，以表面磁光柯爾效應儀量測其磁性質。

在純Si (111)基板以及CoSi2介面上，O2會有弱物理吸附而不形成化合態；在鍍上Co膜後，O2吸附之效應較強，且吸附效果隨著Co膜厚成正相關。而O2的吸附作用將改變Co/Si(111)超薄膜之表面磁性層的電子組態改變，故MS、MR與其磁滯曲線角型比皆呈現下降之趨勢。此外由於O2的吸附之效應，一方面降低了有效磁性Co的層數，因而降低了HC；另一方面形成了釘紮區域(pinning sites)阻礙磁化的反轉，因而提高HC，而本系統所觀測到HC之變化為此兩種效應互相競爭的結果。

另一方面，以氧壓下鍍Co的方式製作超薄反鐵磁CoO膜於11 ML Co/Si (111)上，其易磁化軸由原本的水平膜面轉變至傾斜出膜面。且經過場冷卻至150 K可發現水平膜面與垂直膜面兩方向皆有交換偏壓的現象產生。於 CoO膜厚為20 ML時，此系統有最大水平膜面交換偏向場為258 Oe，且其阻隔溫度為200 K；而於CoO膜厚為15 ML時，此系統有最大垂直膜面交換偏向場為924 Oe，且其阻隔溫度為164 K。

Abstract

The purpose of this research is to study effect of oxygen exposure and ultrathin antiferromagnetic CoO films on the magnetic properties of ultrathin Co/Si(111)-7×7 surface. All experiments were in-situ performed in an ultrahigh vacuum (UHV) chamber with a base pressure of 2.5×10-10 torr, which was equipped with Auger electron spectroscopy (AES) for surface composition analysis, low-energy electron diffraction (LEED) and reflection high energy electron diffraction (RHEED) for surface structure analysis, and surface magneto-optic Kerr effect (SMOKE) for magnetic properties measurement.
For Si (111)-7×7 surface and CoSi2 interface, it is found that oxygen is weakly adsorbed. As the thickness of Co films increases to above 5 monolayers (ML), pure cobalt islands start to accumulate on the surface and the amount of oxygen on the surface increases with increasing the oxygen exposure time. The adsorbed oxygen influences the electronic density of states of Co and leads to the decrease of saturated and remanent magnetization and poor squareness of demagnetization. The trend of coercivity with oxygen exposure is mainly governed by two competed factors: one is the reduction in the effective ferromagnetic Co films, resulting in the decrease of the coercivity; another is the action of oxygen as pinning sites to impede the magnetization reversal, leading to the enhancement of the coercivity.
On other hand, the method to fabricate the antiferromagnetic CoO film is the evaporation of Co in oxygen atmosphere. As ultrathin CoO film is grown on 11 ML Co/Si(111) films, the direction of easy axis is transformed from in-plane to canted-out-of-plane. Interestingly, both longitudinal and perpendicular exchange bias phenomena are observed for 15 ML CoO/ 11 ML Co/Si(111) films measured at T = 150 K after cooling in a field H = 700 Oe from T = 300 K, and the maximum perpendicular exchange bias field of 924 Oe and the blocking temperature of 164 K are attained for 15 ML CoO, while the maximum longitudinal exchange bias field of 258 Oe and the blocking temperature of 200 K are obtained for 20 ML CoO.

參考資料
[1] Gordon Moore , Electronics Magazine , 114 (1965)
[2] E.Grochowski , Hitachi Global storage Technologies (http://www.hitachigst.com/hdd/technolo/overview/chart02.html)
[3] B.Dieny , V.S.Speriosu et al.,”Grant magnetoresistive in soft ferromagnetic multilayers”, Phys.Rev.B 43,1297 (1991)
[4] C.A.Ross,”Fabrication of patterned media for high density magnetic storage”, Microelectronic Engineering.53,67 (2000)
[5] R.C.O’Handley , Modern Magnetic Materials. John Wiley & Sons inc, (NewYork, 2000)
[6] W.H.Meiklejohn & C.P.Bean , “New Magnetic Anisotropy”, Phys. Rev.102,1413 (1956)
[7] 黃正宏,”鈷/鍺(100)與鈷/銀/鍺（100）薄膜介面磁性性質研究”,東海大學物理所碩士論文(2004)
[8] J.Nogues, J.Sortm, V.Langlais, V.Skumryev, S.Surinach, J.S.Munoz and M.D.Baro,”Exchange bias in nanostructures”, Phys.Report 422,65 (2005)”
[9] J.Nogues and I.K.Schuller,”Exchange bias ”, J.Magn.Magn.Mater. 192,203 (1999)
[10] Don Hoefler,” Electronic News” (1971)
[11] J.S.Tsay and Y.D.Yao, “Magnetic phase diagram of ultrathin Co/Si(111) film studied by surface magneto-optic Kerr effect”, Appl. Phys. Lett. 74,1311 (1999)
[12] 洪育奇, “Co/Si(111)超薄膜的表面結構研究”, 國立中正大學碩士論文(2006).
[13] M.Gruyters and D.Riegel,” Optimized exchange biasing by controlled in situ oxidation” J.Appl.Phys. 88, 6610 (2000).
[14] 張新政,”CoO/Co超薄雙層結構在半導體基底上之磁性研究”,國立臺灣師範大學碩士論文 (2007)
[15] S. N. Piramanayagam, J. P. Wang, C. H. Hee, S. I. Pang, T.C. Chong, Z. S. Shan, and L. Huang, “ Noise reduction mechanisms in laminated antiferromagnetically coupled recording media,” Appl. Phys. Lett. 79, 2423 (2002).
[16] Eric E. Fullerton, D. T. Margulies, M. E. Schabes, M. Carey, B. Gurney, A.Moser, M. Best, G. Zeltzer, K. Rubin, and H. Rosen, M. Doerner,“Antiferromagnetically coupled magnetic media layers for thermally stable high-density recording,” Appl. Phys. Lett. 77, 3806 (2000).
[17] D. T. Margulies, M. E. Schabes, W. McChesney, and E. E. Fullerton, “Interlayercoupling and magnetic reversal of antiferromagnetically coupled media,” Appl.Phys. Lett. 80, 91 (2002).
[18] Manfred E. Schabes, Eric E. Fullerton, and David T. Margulies,“Theory ofAntiferromagnetically Coupled Magnetic Recording Media,” IEEE Trans. Magn.,vol. 37,1432 (2001).
[19] J. Lohau, A. Moser, D. T. Margulies, E. E. Fullerton, and M. E. Schabes,“Dynamic coercivity measurments of atiferromagnetically coupled magneticmedia layers,” Appl. Phys. Lett. 78, 2748 (2002).
[20] 張仁勇,”反鐵磁性耦合磁紀錄媒體中交換耦合現象之研究”國立中央大學碩士論文(2002)
[21] B.D.Cullity, Introduction to Magnetic Materials, Addison Wesley,New York（1972）
[22] J.A.C Bland and B.Heinrick,Ultrathin Magnetic structure (Springer-Verlag, New York)(1994)
[23] C.Kittel, Introduction of Solid State Phys, 7th ed ,John Wiley&Sons inc ,New York (1997)
[24] 王坤池, “超高真空中在Ge(111)面上成長Co超薄膜之退火效應及磁性現象研究”, 國立台灣科技大學機研所碩士論文 (2001).
[25] D. J. Griffiths , Introduction to Electrodynamics (Prentice Hall , New York,1981).
[26] D. L. Mills,” The ferromagnetism of ultrathin films; from two to three dimensions “ , J. Magn. Magn. Mater. 100, 515 (1991).
[27]　M.E.Fisher,” The renormalization group in the theory of critical behavior“ , Rev. Mod. Phys. 46, 597 (1974).
[28] P. Beauvillain, A. Bounouh, C. Chappert, R. Mégy, S. Ould-Mahfoud, J. P. Renard, and P. Veillet,” Effect of submonolayer coverage on magnetic anisotropy of ultrathin cobalt films M/Co/Au(111) with M=Au, Cu, Pd“ , J. Appl. Phys. 76, 6078 (1994).
[29] 蔡志申, 物理雙月刊, 廿五卷五期, 605 (2003)
[30] A. E. Berkowitz and K. Takano, ” Exchange anisotropy — a 　review “, J. Magn. Magn. Mater. 200, 552-570 (1999).
[31]　W. H. Meiklejohn, ” Exchange Anisotropy—A Review“, J. Appl. Phys. 33, 1328 (1962).
[32]　R. Morel, A. Brenac, and C. Portemont, ” Exchange bias and coercivity in oxygen-exposed cobalt clusters” , J. Appl. Phys. 95, 3757 (2004).
[33] D. Mauri, H. C. Seigmann et al, ” Simple model for thin ferromagnetic films exchange coupled to an antiferromagnetic substrate”, J. Appl. Phys. 62, 3047 (1987).
[34]　A. P. Malozemoff, ” Random-field model of exchange anisotropy at rough ferromagnetic-antiferromagnetic interface”, Phys. Rev. B 35, 3679 (1987).
[35]　T. C. Schulthess and W. H. Butler, ” Consequences of Spin-Flop Coupling in Exchange Biased Films”, Phys. Rev. Lett. 81, 4516 (1998).
[36] 薛增泉, 吳全德, 李浩, 薄膜物理 (電子工業出版社,1991).
[37] 蔡篤承, “Ag/Ir(111)和Ag/Co/Ir(111)超薄膜介面物性探討與高真空濺鍍系統和薄膜量測系統之建立”, 東海大學物理所碩士論文 (2004)
[38] M. Prutton, Surface Physics (Oxford University Press , U.K , 1987).
[39]　C. Su, C. S. Tsai, C. E. Lin, K. H. Chen, J. K. Wang and J. C. Lin, ” TPEA device as seismic damper for high-rise buildings”, Surface Science 445, 139 (2000).
[40]　J. B. Pendry, Low Energy Electron Diffraction( Academic Press , London, 1974).
[41] G. Ertl, J. Küppers “Low-Energy Electrons and Surface Chemistry” ,VCH (1985)。
[42] 聶亨芸, “銀中介層對鈷超薄膜在鍺(111)基板上磁性質影響之研究”, 國立清華大學物理所碩士論文 (2002).
[43] 曾騰寬, “在鍺(100)及(111)面上成長超薄鈷膜之磁性研究”國立台灣科技大學機研所碩士論文（2000）。
[44] 呂登復, 實用真空技術 (國興出版,台灣, 1986）
[45] 陳元宗, “於鍺(111)面上成長鈷超薄膜之低溫磁性及高溫熱退火方式研究”, 國立台灣科技大學機研所碩士論文（2003）。
[46] 蘇青森,真空技術精華,五南圖書出版社(2004)
[47] 伍秀菁,汪若文,林美吟,真空技術與應用,行政院國科會精儀中心(2001)
[48] 王坤池, “超高真空中在Ge(111)面上成長Co超薄膜之退火效應及磁性現象研究”, 國立台灣科技大學機研所碩士論文 (2001).
[49] Sputter Ion Source User’s Guide,Omicron,Inc(1997)
[50] 鄭文源, “鈷超薄膜在銥(111)表面上的磁性研究：成長與熱退火效應”, 私立東海大學碩士論文 (2004).
[51] 陳信良, 國立臺灣師範大學物理所碩士論文(1997)
[52] L.E.Davis,N.C.Macdonald,P.W.Palmberg,G.E.Riach,and R.E.Weber,HANDBOOK OF AUGER,2nd ed,Physical Electronics Industries,Inc,Eden Prairie (1976)
[53] 邱彦霖, “氧對於鈷/鍺(111)奈米超級薄膜介面磁性影響研究”, 東海大學碩士論文(2005)
[54] L. E. Davis , “Handbook of Auger Electron Spectroscopy” , (1976).
[55]　D. Briggs and M. P. Seah, Practical Surface Analysis Vol. 1( Wiley,New York, 1990).
[56] 盧志權, 物理雙月刊19卷2期, 221（1997）。
[57] 陳宿惠, “銀/鈷超薄膜在鉑（111）表面的磁性探討”, 國立台灣師範大學物理所碩士論文 (1999)
[58] D. K. Cheng, Field and Wave Electromagnetics , 3rd ed.( 　Addison-Wesley, New York , 1989).
[59] 陳裕善,國立中正大學物理所碩士論文 (2005)
[60]　M. A. Plonus著，婁祥麟譯，應用電磁學（下冊）(乾泰圖書, 台北,1985)
[61] W. Braun, Applied RHEED, Reflection High-Energy Electron Diffraction During Crystal Growth(Springer-Verlag, 1999)
[62] 林正勛,” Using RHEED、LEED and AES to investigate the growing situation and geometric structure of Al2O3 on NiAl(100) and Co on Al2O3/NiAl(100) ”國立中央大學碩士論文 (2005)
[63] Dr.John A.Carlisle,"Reflection High-Energy Electron Diffraction" , (springer, 1999)
[64] 馮學正,”Ge(100)表面上成長 CoO/Co超薄膜之磁性研究”, 天主教輔仁大學物理系碩士論文 (2006)
[65] V.Skumryev , S.Stoyanov , Y.Zhang , G.Hadjkpanayis , D.Givord & J.Nogues, ” Beating the superparamagnetic limit with exchange bias”, Nature .423 ,850(2003)
[66] N.kihara , F.Kohno &Y.Ishigaki , IEEE Trans . Consum. Electron. , 22 , 26 ( 1976)
[67] J.S.Tsay , Y.D.Yao , Y.Liou ,”Magnetic phase diagram study of ultrathin Co /Si(111) films ”, Surf. Sci. 454 , 856(2000)
[68] M.L.Williams and R.L.Comstock , AIP Conference Proceedings , no.5,738(1971)
[69] H.W.Chang , J.S.Tsay , Y.C.Hung ,”Magnetic properties and microstructure of ultrathin Co/Si(111) films” Jour. Appl .Phys. 101,09D124 (2007)
[70] 張志高, “橫向式高密度記錄媒體的原理與極限” , 中華民國磁性技術協會會訊 , 第26期 , p11(2000)
[71] 楊正旭, “超高真空中在矽晶片上成長鈷超薄膜之真空內量測磁性研究” , 輔仁大學物理學研究所碩士論文 (1999)
[72] J.S.Tsay ,T.Y.Fu , M.H.Lin, et al. “Microscopic interfacial structure and magnetic properties ultrathin Co/ Si(111) films” . Appl.Phys.Lett. 88,102506 (2006)
[73] M.T.Johnson , P.J.H.Bloemen , F.J.Aden Broeder, and J.Jde Vrist , Rep.Prog.Phys.59,1409(1996)
[74] Z.Q.Qiu and S.D.Bader , J.Magn.Magn.Mater .200,664(1999)
[75] Z.Q.Qiu ,J.Pearson , and S.D.Bader , Phys.Rev.B 45 ,7211 (1992)
[76] J. Zak, E. R. Moog, C. Liu, S. D. Bader ,“Additivity of the Kerr effect in thin-film magnetic systems” .Jour. Magn.Mag. Mater. Volume 88 , L261-L266(1990,)
[77] J.S.Tsay ,H.W.Chang et al, “Effect of oxygen exposure on the magnetic properties of ultrathin Co / Ge(111) films” .Journ.Magn.Magn.Mater.304 ,168-170 (2006)
[78] E. C. Stoner and E. P. Wohlfarth, Proc. R. Soc. London, Ser. A240,
599 (1948)
[79] J. L. Vossen and W. Kern,Thin film processe, Part II, Academ.ic
Press, 1978.