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VO2表面氧缺陷的存在对VO2材料具有显著的电子掺杂效应, 极大地影响材料的本征电子结构和相变性质. 通过2, 3, 5, 6-四氟-7, 7', 8, 8'-四氰二甲基对苯醌(F4TCNQ)分子表面吸附反应, 可以有效消除表面氧缺陷及其电子掺杂效应. 利用同步辐射光电子能谱和X射线吸收谱原位研究了修复过程中电子结构的变化以及界面的化学反应, 发现这种方式使得VO2薄膜样品氩刻后得到的V3+失去电子成功地被氧化成原先的V4+, 同时F4TCNQ分子吸附引起电子由衬底向分子层转移, 界面形成带负电荷的分子离子物种. 受电化学性质的制约, F4TCNQ分子吸附反应修复氧缺陷较氧气氛退火更安全有效, 不会引起表面过度氧化形成V2O5.Oxygen-defect vacancies that routinely exist in wet production of VO2 material or on the surface of VO2 single crystal after surface treatment have significant influence on the metal-insulator phase transition features mainly due to their enhanced effect of doping on V 3d electronic structure. The removal of the surface oxygen defects is highly desired for investigating the VO2 intrinsic electronic properties. In this work, we propose a charge transfer doping method by using strong electric affinity molecule tetrafluorotetracyanoquinodimethane (F4TCNQ) adsorption rather than the normal thermal annealing in oxygen atmosphere to heal the surface oxygen defects of VO2 crystalline film. The healing effect is probed by the electronic structure evolution at the F4TCNQ/VO2 interface. The VO2 crystalline film is grown by an oxygen plasma assisted molecular beam epitaxy method on an Al2O3(0001) substrate. Surface oxygen defects on VO2 film are produced after a mild sputtering with an ionic energy of 1 keV and a thermal annealing in vacuum at 100 ℃. The influence of F4TCNQ molecule adsorption on the electronic structure of the sputtered VO2 film is studied by using in-situ synchrotron-based photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). XPS and XAS results demonstrate convincingly that V3+ species of sputtered VO2 are oxidized into the V4+ and simultaneously negative molecular ions form at F4TCNQ/VO2 interface resulting from the electron transfer from VO2 to the F4TCNQ layer. The preferred adsorption on surface defects and the strong electron withdrawing function of F4TCNQ molecules may account for the effective elimination of the electron doping effect of oxygen defects on VO2 surface. This charge transfer effect at interface recovers the electronic properties of VO2. Compared with thermal annealing in oxygen environment, the healing of oxygen defects by the molecular adsorption can prevent the surface from over oxidating VO2 into V2O5, which opens a new route to surface defect healing.
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Keywords:
- VO2 /
- oxygen defects /
- F4TCNQ molecule /
- synchrotron radiation
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[2] Yang Z, Ko C, Ramanathan S 2011 Annu. Rev. Mater. Res. 41 337
[3] Park J H, Coy M J, Kasirga S, Huang C, Fei Z, Hunter S, Cobden H D 2013 Nature 500 431
[4] Zhou J, Gao Y, Zhang Z, Luo H, Cao C, Chen Z, Dai L, Liu X 2013 Sci. Rep. 3 3029
[5] Driscoll T, Kim H T, Chae B G, Kim B J, Lee Y W, Jokerst D M, Palit S, Smith D R, Ventra M D, Basov D N 2009 Science 325 1518
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[21] Gao W, Kahn A 2001 Appl. Phys. Lett. 79 4040
[22] Chen W, Qi D C, Gao X Y, Wee A T S 2009 Prog. Surf. Sci. 84 279
[23] Silversmit G, Depla D, Poelman H, Marin G B, Gryse R D 2004 J. Electron. Spectrosc. Relat. Phenom. 135 167
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[25] Zimmermann R, Claessen R, Reinert F, Steiner P, Hufner S 1998 J. Phys.: Condens. Matter 10 5697
[26] Groot F M F, Fuggle J C, Thole B T, Sawatzky G A 1990 Phys. Rev. B 42 5459
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[28] Groot F M F, Grioni M, Fuggle J C, Ghijsen J, Petersen H 1989 Phys. Rev. B 40 5715
[29] Ruzmetov D, Sanjaya D, Ramanathan S 2007 Phys. Rev. B 75 195102
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[31] Fraxedas J, Lee Y J, Jimnez I, Gago R, Nieminen R M, Ordejon P, Canadell E 2003 Phys. Rev. B 68 195115
[32] Tseng T C, Urban C, Wang Y, Otero R, Tait S, Alcami M, Ecija D, Trelka M, Gallego J M, Lin N, Konuma M, Starke U, Nefedow A, Langner A, Woll C, Herranz M A, Martin F, Martin N, Kern K, Miranda R 2010 Nature. Chem. 2 374
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[34] Koch N, Duhm S, Rabe J P, Vollmer A, Johnson R L 2005 Phys. Rev. Lett. 95 237601
[35] Tian X Q, Xu J B, Wang X M 2010 J. Phys. Chem. B 114 11377
[36] Le T H, Nafady A, Qu X H, Matin L L, Bond A M 2011 Anal. Chem. 83 6731
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[1] Morin F J 1959 Phys. Rev. Lett. 3 34
[2] Yang Z, Ko C, Ramanathan S 2011 Annu. Rev. Mater. Res. 41 337
[3] Park J H, Coy M J, Kasirga S, Huang C, Fei Z, Hunter S, Cobden H D 2013 Nature 500 431
[4] Zhou J, Gao Y, Zhang Z, Luo H, Cao C, Chen Z, Dai L, Liu X 2013 Sci. Rep. 3 3029
[5] Driscoll T, Kim H T, Chae B G, Kim B J, Lee Y W, Jokerst D M, Palit S, Smith D R, Ventra M D, Basov D N 2009 Science 325 1518
[6] Stefanovich G, Pergament A, Stefanovich D 2000 J. Phys. : Condens. Matter 12 8837
[7] Strelcov E, Lilach Y, Kolmakov A 2009 Nano Lett. 9 2322
[8] Surnev S, Ramsey M G, Netzer F P 2003 Prog. Surf. Sci. 73 117
[9] Wu Y F, Fan L L, Liu Q H, Chen S, Huang W F, Chen F H, Liao G M, Zou C W, Wu Z Y 2015 Sci. Rep. 5 9328
[10] Kim H T, Chae B G, Youn D H, Kim G, Kang K Y, Lee S J, Kim K, Lim Y S 2005 Appl. Phys. Lett. 86 242101
[11] Zhou H J, Cao X, Jiang M, Bao S H, Jin P 2014 Laser Photon. Rev. 8 617
[12] Zhou H J, Li J H, Xin Y C, Cao X, Bao S H, Jin P 2015 J. Mater. Chem. C 3 5089
[13] Mendialdua J, Casanova R, Barbaux Y 1995 J. Electron. Spectrosc. Relat. Phenom. 71 249
[14] Yang T H, Nori S, Zhou H, Narayan J 2009 Appl. Phys. Lett. 95 102506
[15] Gupta A, Narayan J, Dutta T 2010 Appl. Phys. Lett. 97 151912
[16] Tashman J W, Lee J H, Paik H, Moyer A W, Misra R, Mundy J A, Spila T, Merz T A, Schubert J, Muller D A, Schiffer P, Schlom D G 2014 Appl. Phys. Lett. 104 063104
[17] Fan L L, Chen S, Wu Y F, Chen F H, Chu W S, Chen X, Zou C W, Wu Z Y 2013 Appl. Phys. Let. 103 131914
[18] Tan X G, Yao T, Long R, Sun Z H, Feng Y J, Cheng H, Yuan X, Zhang W Q, Liu Q H, Wu C Z, Xie Y, Wei S Q 2012 Sci. Rep. 2 466
[19] Tsai K Y, Chin T S, Shieh H P D 2003 Jpn. J. Appl. Phys. 42 4480
[20] Yu S, Ahmadi S, Sun C H, Palmgren P, Hennies F, Zuleta M, Gthelid M 2010 J. Phys. Chem. C 114 2315
[21] Gao W, Kahn A 2001 Appl. Phys. Lett. 79 4040
[22] Chen W, Qi D C, Gao X Y, Wee A T S 2009 Prog. Surf. Sci. 84 279
[23] Silversmit G, Depla D, Poelman H, Marin G B, Gryse R D 2004 J. Electron. Spectrosc. Relat. Phenom. 135 167
[24] Okimura K, Suzuki Y 2011 Jpn. J. Appl. Phys. 50 065803
[25] Zimmermann R, Claessen R, Reinert F, Steiner P, Hufner S 1998 J. Phys.: Condens. Matter 10 5697
[26] Groot F M F, Fuggle J C, Thole B T, Sawatzky G A 1990 Phys. Rev. B 42 5459
[27] Soriano L, Abbate M, Fuggle J C, Jimenez M A, Sanz J M, Mythen C, Padmore H A 1993 Solid State Commun. 87 699
[28] Groot F M F, Grioni M, Fuggle J C, Ghijsen J, Petersen H 1989 Phys. Rev. B 40 5715
[29] Ruzmetov D, Sanjaya D, Ramanathan S 2007 Phys. Rev. B 75 195102
[30] Haverkort M W, Hu Z, Tanaka A, Reichelt W, Streltsov V, Korotin M A, Anisimov V I, Hsieh H H, Lin H J, Chen C T, Khomskii D I, Tjeng L H 2005 Phys. Rev. Lett. 95 196404
[31] Fraxedas J, Lee Y J, Jimnez I, Gago R, Nieminen R M, Ordejon P, Canadell E 2003 Phys. Rev. B 68 195115
[32] Tseng T C, Urban C, Wang Y, Otero R, Tait S, Alcami M, Ecija D, Trelka M, Gallego J M, Lin N, Konuma M, Starke U, Nefedow A, Langner A, Woll C, Herranz M A, Martin F, Martin N, Kern K, Miranda R 2010 Nature. Chem. 2 374
[33] Qi D, Chen W, Gao X Y, Wang L, Chen S, Loh P K, Wee T S W 2007 J. Am. Chem. Soc. 129 8084
[34] Koch N, Duhm S, Rabe J P, Vollmer A, Johnson R L 2005 Phys. Rev. Lett. 95 237601
[35] Tian X Q, Xu J B, Wang X M 2010 J. Phys. Chem. B 114 11377
[36] Le T H, Nafady A, Qu X H, Matin L L, Bond A M 2011 Anal. Chem. 83 6731
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