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含铀（U）薄膜在激光惯性约束聚变的实验研究中有重要的用途.研究其在不同气氛下的氧化性能可以为微靶制备、储存及物理实验提供关键的实验数据.通过超高真空磁控溅射技术制备了纯U薄膜及金-铀（Au-U）复合平面膜，将其在大气、高纯氩（Ar）气及超高真空度环境中暴露一段时间后，利用X射线光电子能谱仪结合Ar+束深度剖析技术考察U层中氧（O）元素分布及价态，分析氧化产物及机理.结果显示，初始状态的U薄膜中未检测到O的存在.Au-U复合薄膜中的微观缺陷减弱了Au防护层的屏蔽效果，使其在3周左右时间内严重氧化，产物为U表面致密的氧化膜及缺陷周围的点状腐蚀物，主要成分均为二氧化铀（UO2）.在高纯Ar气中纯U薄膜仅暴露6 h后表面即被严重氧化，生成厚度不均匀的UO2.在超高真空度环境下保存12 h后，纯U薄膜表面也发生明显氧化，生成厚度不足1 nm的UO2.Ar+束对铀氧化物的刻蚀会因择优溅射效应而使UO2被还原成非化学计量的UO2-x，但这种效应受O含量的影响.Uranium film is a main functional component to realize the high efficiency conversion of laser to X-ray in the study on laser inertial confinement fusion. It also has important applications in relevant physics experiments. Due to its active chemical properties, the metal uranium film is extremely difficult to preserve in the atmosphere. A variety of methods may help to avoid the oxidation of uranium film, such as coating protective layer, vacuum or inert atmosphere protection. But under these conditions, the oxidation property of uranium film still needs experimental investigation. In this paper, the oxidation processes of uranium films under different atmospheres are studied by X-ray photoelectron spectroscopy (XPS) and depth profiling. Firstly, uranium films and gold-uranium multilayer films are prepared by ultra-high vacuum magnetron sputtering deposition, and then they are exposed to atmosphere, high purity argon and ultrahigh vacuum for a period of time. Finally, the distributions and valence states of oxygen and uranium elements are investigated by XPS depth profiling. The oxidation mechanism is analyzed according to the oxidation products and the microstructure characteristics of samples. The results show that the oxygen element is undetectable in the initial films. In the Au-U multilayer film, the protective ability of Au layer is greatly weakened by the micro-defects. The defect is not only the micro channel of oxygen entering into the sample directly, but also the origin of the interlaminar cracks at the Au/U interface. In about three weeks, the uranium layer is severely oxidized and large area lamination occurs. The oxidation products consist of a dense oxide thin film on uranium surface and corrosion pitting around the defects, which are mainly UO2. For the pure uranium film, the surface of the film is completely oxidized when it is exposed to high purity argon only for 6 h. The UO2 layers with different thickness values are formed on their surface, which is due to the rapid diffusion of oxygen atoms at the columnar grain boundaries of the film. After the sample is exposed to the ultra-high vacuum for 12 h, UO2 layer with a thickness of less than 1 nm is generated on the surface of the pure uranium film. In the etching of oxide by argon ion beams, the preferential sputtering effect of O is produced, and UO2 is reduced into non-stoichiometric UO2-x. The effect of preferential sputtering is weakened with the decrease of oxide content. When the oxide content is less than 10%, the reduction of UO2 can hardly be detected.
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Keywords:
- deposition /
- uranium film /
- oxidation /
- X-ray photoelectron spectroscopy
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[1] Orzechowski T J, Rosen M D, Kornblum H N, Porter J L, Suter L J, Thiessen A R, Wallace R J 1996 Phys. Rev. Lett. 77 3545
[2] Jones O S, Schein J, Rosen M D, Suter L J, Wallace R J, Dewald E L, Glenzer S H, Campbell K M, Gunther J, Hammel B A, Landen O L, Sorce C M, Olson R E, Rochau G A, Wilkens H L, Kaae J L, Kilkenny J D, Nikroo A, Regan S P 2007 Phys. Plasmas 14 056311
[3] Winer K, Colmenares C A, Smith R L 1986 Surf. Sci. 177 484
[4] Younes C M, Allen G C, Embong Z 2007 Surf. Sci. 601 3207
[5] Shamir N, Tiferet E, Zalkind S, Mintz M H 2006 Surf. Sci. 600 657
[6] McLean W, Colmenares C A, Smith R L, Somorjai G A 1982 Phys. Rev. B 25 8
[7] Ritchie A G 1984 J. Nucl. Mater. 120 143
[8] Wang X L, Fu Y B, Xie R S 1999 At. Energ. Sci. Technol. 33 1 (in Chinese)[汪小琳, 傅依备, 谢仁寿 1999 原子能科学技术 33 1]
[9] Lu L, Bai B, Zou J S, Tang S H. Xiao H 2003 Mater. Mach. Eng. 29 16 (in Chinese)[陆雷, 白彬, 邹觉生, 唐世红, 肖红 2003 机械工程材料 29 16]
[10] Hein N A, Wilkens H L, Nikroo A, Chen H B, Streckert H H, Quan K, Wall J R, Fuller T A, Jackson M R, Giraldez E M, Price S J, Sohn R J, Stadermann M 2013 Fusion Sci. Technol. 63 218
[11] Geng H Y, Song H X, Wu Q 2012 Phys. Rev. B 85 1279
[12] Gouder T, Colmenares C A, Naegele J R 1995 Surf. Sci. 342 299
[13] Yi T M, Xing P F, Du K, Zheng F C, Yang M S, Xie J, Li C Y 2012 Acta Phys. Sin. 61 088103 (in Chinese)[易泰民, 邢丕峰, 杜凯, 郑凤成, 杨蒙生, 谢军, 李朝阳 2012 61 088103]
[14] Mirkarimi P B, Stearns D G 2000 Appl. Phys. Lett. 77 2243
[15] Shan Y G, He H B, Wei C Y, Li S H, Zhou M, Li D W, Zhao Y A 2010 Appl. Opt. 49 4290
[16] Dillard J G, Moera H, Klewe-Nebenius H, Kirch G, Pfennig G, Ache H J 1984 Surf. Sci. 145 62
[17] Winer K, Colmenares C A, Smith R L, Wooten F 1987 Surf. Sci. 183 67
[18] Shan Y G, Liu X F, He H B, Fan Z X 2011 High Power Laser and Particle Beams 23 1421 (in Chinese)[单永光, 刘晓凤, 贺洪波, 范正修 2011 强激光与粒子束 23 1421]
[19] Idriss H 2010 Surf. Sci. Rep. 65 67
[20] Chong S V, Griffiths T R, Idriss H 2000 Surf. Sci. 444 187
[21] Hedhili M N, Yakshinskiy B V, Madey T E 2000 Surf. Sci. 445 512
[22] Allen G C, Tucker P M, Tyler J W 1982 J. Phys. Chem. 86 224
[23] Chary K V R, Seela K K, Sagar G V, Sreedhar B 2004 J. Phys. Chem. B 108 658
[24] Jesus J C, Pereira P, Carrazza J, Zaera F 1996 Surf. Sci. 369 217
[25] Krishna M G, Debauge Y, Bhattacharya A K 1998 Thin Solid Films 312 116
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