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利用紫外光电子能谱、X射线光电子能谱以及原子力显微镜系统研究了2,7-二辛基[1] 苯并噻吩并[3,2-b]苯并噻吩(C8-BTBT)生长在单晶Ni(100)上的能级结构随着薄膜厚度的演化以及薄膜的生长方式. 发现第一层C8-BTBT平躺生长且与Ni基底发生了化学吸附反应. 从第二层起分子直立生长且呈现岛状生长模式. 这种平躺至直立的分子取向转变, 导致薄膜的能级结构在第一层与第二层间发生阶梯式的变化, 真空能级与最高占据能级同步下降. 此后能带结构随着薄膜厚度的增加逐渐向下弯曲, 功函数随着膜厚的增加而减小. 同时还发现由于直立生长的C8-BTBT其层间电导率较差导致实验中的能级未能收敛. 实验结果提示对基于Ni和C8-BTBT的自旋器件需要插入缓冲层并尽可能减少C8-BTBT的层数.Combining ultraviolet photoemission spectroscopy (UPS), X-ray photoemission spectroscopy and atomic force microscopy (AFM), we perform a systematic investigation on the correlation of energy level alignment, film growth and molecular orientation of 2, 7-dioctyl[1]benzothieno-[3, 2-b][1]benzothiophene (C8-BTBT) on Ni(100). The molecules lie down at the first layer and are partly devulcanized by the substrate. Chemical adsorption of reaction products of sulfur atoms on the Ni substrate and the evaporation of the hydrocarbon products into vacuum make the C/S ratio as low as 11.5 : 1 in the XPS of the initially deposited C8-BTBT film of 1-4 thickness, far less than the stoichiometric of 15 : 1. With the thickness increasing from 4 to 8 , there are sharp downward shifts of Evac, HOMO and core levels of C 1s, S 2p, and a sharp increase of C/S ratio, which can be ascribed to the change of molecular orientations from lying down at 4 to standing up at 8 . From 8 onward, the C/S ratio increases steadily till it reaches 15 : 1. The energy levels show relatively less changes when the thickness increases from 8 to 32 . When the thickness increases over 32 , the energy band starts bending downward apparently because of the charging effect during the photoelectron emission processes. The poor conductivity along the standing alkyl chain of C8-is the main cause for the charging. The standing up configurations of the C8-BTBT molecules are confirmed by the AFM investigation in which the heights of the upper layers of C8-BTBT are around 30 , close to the length of the long c-axis. AFM image also indicates that the molecules tend to grow into islands for larger thickness, which is consistent with the slower decrease of the (I/I0) of Ni 2p3/2 with the C8-BTBT film thickness. Our results suggest that a buffer layer be inserted between Ni and C8-BTBT and the thickness of the C8-BTBT film be controlled as thin as possible in related devices.
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Keywords:
- interface reaction /
- molecule orientation /
- band bending /
- electronic structure
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[24] Laquindanum J G, Katz H E, Lovinger A J, Dodabalapur A 1996 Chem. Mater. 8 2542
[25] Resel R 2003 Thin Solid Films 433 1
[26] Sirringhaus H, Brown P J, Friend R H, Nielsen M M, Bechgaard K, Langeveld-Voss B M W, Spiering A J H, Janssen R A J, Meijer E W, Herwig P, de Leeuw D M 1999 Nature 401 685
[27] Sundar V C, Zaumseil J, Podzorov V, Menard E, Willett R L, Someya T, Gershenson M E, Rogers J A 2004 Science 303 1644
[28] Tian X Y, Zhao S L, Xu Z, Yao J F, Zhang J F, Jia Q J, Chen Y, Fan X, Gong W 2011 Acta Phys. Sin. 60 027201 (in Chinese) [田雪雁, 赵谡玲, 徐征, 姚江峰, 张福俊, 贾全杰, 陈雨, 樊星, 龚伟 2011 60 027201]
[29] Yamane H, Yabuuchi Y, Fukagawa H, Kera S, Okudaira K K, Ueno N 2006 J. Appl. Phys. 99 093705
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[31] Richardson N V, Campuzano J C 1981 Vacuum 31 449
[32] Schoofs G R, Preston R E, Benziger J B 1985 Langmuir 1 313
[33] Huang H, Chen W, Chen S, Qi D C, Gao X Y 2009 Appl. Phys. Lett. 94 163304
[34] Huntley D R, Mullins D R, Wingeier M P 1996 J. Phys. Chem. 100 19620
[35] Xie F Z, Hu H R, Hua M Q, Yan S R, Fan K N, Lei H, Tan D L, Bao X H, Zong B N, Zhang X X 2006 Chem. J. Chinese Universities 27 1729 (in Chinese) [谢福中, 胡华荣, 华明桥, 闫世润, 范康年, 雷浩, 谭大力, 包信和, 宗保宁, 张晓昕 2006 高等学校化学学报 27 1729]
[36] Chen W, Huang H, Chen S, Chen L, Zhang H L, Gao X Y, Wee A T S 2007 Appl. Phys. Lett. 91 114102
[37] Wang C G, Turinske A J, Gao Y L 2013 Appl. Phys. B 113 361
[38] Le Q T, Forsythe E W, Nuesch F, Rothberg L J, Yan L, Gao Y L 2000 Thin Solid Films 363 42
[39] Razafitrimo H, Ettedgui E, Guo L H, McLendon G L, Gao Y L 1995 Appl. Phys. Lett. 67 2621
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[1] Shi F F 1996 J. Macro. Sci. C 36 795
[2] Zhou Y S, Peng J, Wang E B, Zhang L J 1998 Transition Metal Chemistry 23 125
[3] Klauk H, Zschieschang U, Pflaum J, Halik M 2007 Nature 445 745
[4] Sanvito S 2011 Chem. Soc. Rev 40 3336
[5] Someya T, Pal B, Huang J, Katz H E 2008 Mrs Bull. 33 690
[6] Burroughes J H, Bradley D D C, Brown A R, Maeks R N, Mackay K, Friend R H, Burns P L, Holmes A B 1990 Nature 347 539
[7] Tang C W, Vanslyke S A 1987 Appl. Phys. Lett. 51 913
[8] Yang F, Shtein M, Forrest S R 2005 Nat. Mater. 4 37
[9] Facchetti A 2007 Mater. Today 10 28
[10] Gelinck G H, Huitema H E A, van Veenendaal E, Cantatore E, Schrijnemakers L, van der Putten J B P H, Geuns T C T, Beenhakkers M, Giesbers J B, Huisman B H, Meijer E J, Benito E M, Touwslager F J, Marsman A W, van Rens B J E, De Leeuw D M 2004 Nat. Mater. 3 106
[11] Baude P F, Ender D A, Haase M A, Kelley T W, Muyres D V, Theiss S D 2003 Appl. Phys. Lett. 82 3964
[12] Someya T, Kato Y, Sekitani T, Iba S, Noguchi Y, Murase Y, Kawaguchi H, Sakurai T 2005 PNAS 102 12321
[13] Kuribara K, Wang H, Uchiyama N, Fukuda K, Yokota T, Zschieschang U, Jaye C, Fischer D, Klauk H, Yamamoto T, Takimiya K, Ikeda M, Kuwabara H, Sekitani T, Loo Y L, Someya T 2012 Nat. Commun. 3 723
[14] Berggren M, Dahlfors A R 2007 Adv. Mater. 19 3201
[15] Koezuka H, Tsumura A, Ando T 1987 Synthetic Metals 18 699
[16] Takeya J, Yamagishi M, Tominari Y, Hirahara R, Nakazawa Y, Nishikawa T, Kawase T, Shimoda T, Ogawa S 2007 Appl. Phys. Lett. 90 102120
[17] Yuan Y B, Giri G, Ayzner A L, Zoombelt A P, Mannsfeld S C B, Chen J H, Nordlund D, Toney M F, Huang J S, Bao Z N 2014 Nat. Commun. 5 3005
[18] Sinha S, Wang C H, Mukherjee M, Yang Y W 2014 J. Phys. D 47 245103
[19] Ding H J, Gao Y L 2008 Phys. Rev. B 78 075311
[20] McCulloch L, Heeney M, Chabinyc M L, DeLongchamp D, Kline R J, Coelle M, Duffy W, Fischer D, Gundlach D, Hamadani B, Hamilton R, Richter L, Salleo A, Shkunov M, Sporrowe D, Tierney S, Zhong W 2009 Adv. Mater. 21 1091
[21] Virkar A A, Mannsfeld S, Bao Z A, Stingelin N 2010 Adv. Mater. 22 3857
[22] Chen W, Huang H, Chen S, Gao X Y, Wee A T S 2008 J. Phys. Chem. C 112 5036
[23] Kobayashi H, Kobayashi N, Hosoi S, Koshitani N, Murakami D, Shirasawa R, Kudo Y, Hobara D, Tokita Y, Itabashi M 2013 J. Chem. Phys. 139 014707
[24] Laquindanum J G, Katz H E, Lovinger A J, Dodabalapur A 1996 Chem. Mater. 8 2542
[25] Resel R 2003 Thin Solid Films 433 1
[26] Sirringhaus H, Brown P J, Friend R H, Nielsen M M, Bechgaard K, Langeveld-Voss B M W, Spiering A J H, Janssen R A J, Meijer E W, Herwig P, de Leeuw D M 1999 Nature 401 685
[27] Sundar V C, Zaumseil J, Podzorov V, Menard E, Willett R L, Someya T, Gershenson M E, Rogers J A 2004 Science 303 1644
[28] Tian X Y, Zhao S L, Xu Z, Yao J F, Zhang J F, Jia Q J, Chen Y, Fan X, Gong W 2011 Acta Phys. Sin. 60 027201 (in Chinese) [田雪雁, 赵谡玲, 徐征, 姚江峰, 张福俊, 贾全杰, 陈雨, 樊星, 龚伟 2011 60 027201]
[29] Yamane H, Yabuuchi Y, Fukagawa H, Kera S, Okudaira K K, Ueno N 2006 J. Appl. Phys. 99 093705
[30] Cao N T, Zhang L, Lv L, Xie H P, Huang H, Niu D M, Gao Y L 2014 Acta Phys. Sin. 63 167903 (in Chinese) [曹宁通, 张雷, 吕路, 谢海鹏, 黄寒, 牛冬梅, 高永立 2014 63 167903]
[31] Richardson N V, Campuzano J C 1981 Vacuum 31 449
[32] Schoofs G R, Preston R E, Benziger J B 1985 Langmuir 1 313
[33] Huang H, Chen W, Chen S, Qi D C, Gao X Y 2009 Appl. Phys. Lett. 94 163304
[34] Huntley D R, Mullins D R, Wingeier M P 1996 J. Phys. Chem. 100 19620
[35] Xie F Z, Hu H R, Hua M Q, Yan S R, Fan K N, Lei H, Tan D L, Bao X H, Zong B N, Zhang X X 2006 Chem. J. Chinese Universities 27 1729 (in Chinese) [谢福中, 胡华荣, 华明桥, 闫世润, 范康年, 雷浩, 谭大力, 包信和, 宗保宁, 张晓昕 2006 高等学校化学学报 27 1729]
[36] Chen W, Huang H, Chen S, Chen L, Zhang H L, Gao X Y, Wee A T S 2007 Appl. Phys. Lett. 91 114102
[37] Wang C G, Turinske A J, Gao Y L 2013 Appl. Phys. B 113 361
[38] Le Q T, Forsythe E W, Nuesch F, Rothberg L J, Yan L, Gao Y L 2000 Thin Solid Films 363 42
[39] Razafitrimo H, Ettedgui E, Guo L H, McLendon G L, Gao Y L 1995 Appl. Phys. Lett. 67 2621
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