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We propose an optical approach for analyzing the formation of the conductive layer during organic thin film growth. The relationship between the properties of multi-layer film, such as thickness and optical coefficients, and the corresponding differential reflectance spectrum (DRS) is derived as math formula based on the effective medium approximation. With the deduced formula, the thickness of the deposited film, for example, electron transport layer in this paper, can be estimated according to the measured DRS data. But, in fact, the fitting error always exists. It is, on the other hand, a useful evidence to indicate the actual situation of the thin film. A concept of the normalized fitting error (NFE) is offered here to equivalently assess the fitting results of all DRS data in the growth process. The curve of NFE versus time is proposed to analyze the growth revolution of the thin film and reveal the inner physical mechanism. In order to demonstrate the performance of the proposed method, an organic field effect transistor (OFET) with a bottom-gate structure is fabricated and pentacene organic thin film is deposited by vacuum thermal evaporation, as an electron transport layer, on the top of the transistor, i. e., an insulator substrate of Si/SiO2. The reflected optical spectrum and the current between the drain and the source of the OFET device are investigated in real time in the growth process. It has been reported that pentacene has three kinds of crystal structures and their optical properties differ from each other. The actual phase of the pentacene film in our experiment is discussed at first. The fitting results show that the pentacene layer exists mainly in thin film phase here. Then, the thickness of SiO2 layer is determined to be 296 nm, which is close to the design value of 300 nm. With those parameters, a four-layer model is used to calculate the thickness of the organic film. The thickness data indicate that the film appears to be linearly growing and the growth rate is 0.2 nm/min. Next, the NFE is plot as a function of time. In this plot, the curve of the NFE increases quickly at the beginning of the growth and reaches to a positive peak at 70 min. After that, the NFE decreases and then keeps constant for a while. When the measured current-time curve is added into this plot, one finds that the increase of the current happens at the same time with the peak of the NFE. It implies that the NFE is related to the structure change of the organic film and thus linked indirectly to the electronic property. The peak of the NFE, to a certain extent, reveals the completeness of the organic conductive layer. As a result, the presented optical approach is valuable for analyzing the electronic status of the organic thin film, especially if the electronic test cannot be performed.
[1] Klauk H 2010 Chem. Soc. Rev. 39 2643
[2] Kumar B, Kaushik B K, Negi Y S 2014 Polym. Rev. 54 33
[3] Khana H U, Jangb J, Kimb J, Knolla W 2011 Biosens. Bioelectron. 26 4217
[4] Kim S H, Hong K, Xie W, Lee K H, Zhang S, Lodge T P, Frisbie C D 2013 Adv. Mater. 25 1822
[5] Shin G, Yoon C H, Bae M Y, Kim Y C, Hong S K, Rogers J A, Ha J S 2011 Small 7 1181
[6] Schon J H, Kloc Ch 2001 Appl. Phys. Lett. 78 3538
[7] Park S P, Kim S S 2002 Appl. Phys. Lett. 80 2872
[8] Shehu A, Quiroga S D, D'Angelo P, Albonetti C, Borgatti F, Murgia M, Scorzoni A, Stoliar P, Biscarini F 2010 Phys. Rev. Lett. 104 246602
[9] Yang D, Zhang L, Yang S Y, Zou B S 2015 Acta Phys. Sin. 64 108503 (in Chinese)[杨丹, 张丽, 杨盛谊, 邹炳锁2015物理学报64 108503]
[10] Hu W P 2011 Organic Field Effect Transistor (Beijing:Science Press) pp181-188(in Chinese)[胡文平2011有机场效应晶体管(北京:科学出版社)第181–188页]
[11] Li H Q, Yu J S, Huang W, Shi W, Huang J 2014 Chin. Phys. B 23 038505
[12] Jiang L, Dong H L, Meng Q, Li H X, He M, Wei Z M, He Y D, Hu W P 2011 Adv. Mater. 23 2059
[13] Sun Q J, Xu Z, Zhao S L, Zhang F J, Gao L Y 2011 Chin. Phys. B 20 017306
[14] Forker R, Gruenewald M, Fritz T 2012 Annual Reports Section C (Physical Chemistry) 108 34
[15] Xu J J, Hu C G, Chen X J, Zhang L, Fu X, Hu X T 2015 Acta Phys. Sin. 64 230701 (in Chinese)[徐佳佳, 胡春光, 陈雪娇, 张雷, 傅星, 胡小唐2015物理学报64 230701]
[16] Zhang L 2014 Ph. D. Dissertation (Tianjin:Tianjin University) (in Chinese)[张雷2014博士学位论文(天津:天津大学)]
[17] Borenszten Y 2005 Phys. Status Solidi A 202 1313
[18] Heavens O S 1955 Optical Properties of Thin Solid Films (New York:Dover) pp1-288
[19] Azzam R M A, Bashara N M (translated by Liang M J, Yin S B, Zhang F C, Wang G Y 1986 Ellipsometry and Polarized Light (Beijing:Science Press) pp179-190(in Chinese)[阿查姆R M, 巴夏拉N M著(梁民基, 尹树百, 张福初, 王广阳译) 1986椭圆偏振测量术和偏振光(北京:科学出版社)第179–190页]
[20] Reese C, Bao Z N 2007 Mater. Today 10 20
[21] Philipp H R 1998 Handbook of Optical Constants of Solids (Vol. 1) (San Diego:Academic Press) pp719-763
[22] Auslender M, Hava S 1998 Handbook of Optical Constants of Solids (Vol. 3) (San Diego:Academic Press) pp155-186
[23] Yoshidaa H, Inaba K, Sato N 2007 Appl. Phys. Lett. 90 181930
[24] Faltermeier D, Gompf B, Dressel M, Tripathi A K, Pflaum J 2006 Phy. Rev. B 74 125416
[25] Ruiz R, Choudhary D, Nickel B, Toccoli T, Chang K, Mayer A C, Clancy P, Blakely J M, Headrick R L, Iannotta S, Malliaras G G 2004 Chem. Mater. 16 4497
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[1] Klauk H 2010 Chem. Soc. Rev. 39 2643
[2] Kumar B, Kaushik B K, Negi Y S 2014 Polym. Rev. 54 33
[3] Khana H U, Jangb J, Kimb J, Knolla W 2011 Biosens. Bioelectron. 26 4217
[4] Kim S H, Hong K, Xie W, Lee K H, Zhang S, Lodge T P, Frisbie C D 2013 Adv. Mater. 25 1822
[5] Shin G, Yoon C H, Bae M Y, Kim Y C, Hong S K, Rogers J A, Ha J S 2011 Small 7 1181
[6] Schon J H, Kloc Ch 2001 Appl. Phys. Lett. 78 3538
[7] Park S P, Kim S S 2002 Appl. Phys. Lett. 80 2872
[8] Shehu A, Quiroga S D, D'Angelo P, Albonetti C, Borgatti F, Murgia M, Scorzoni A, Stoliar P, Biscarini F 2010 Phys. Rev. Lett. 104 246602
[9] Yang D, Zhang L, Yang S Y, Zou B S 2015 Acta Phys. Sin. 64 108503 (in Chinese)[杨丹, 张丽, 杨盛谊, 邹炳锁2015物理学报64 108503]
[10] Hu W P 2011 Organic Field Effect Transistor (Beijing:Science Press) pp181-188(in Chinese)[胡文平2011有机场效应晶体管(北京:科学出版社)第181–188页]
[11] Li H Q, Yu J S, Huang W, Shi W, Huang J 2014 Chin. Phys. B 23 038505
[12] Jiang L, Dong H L, Meng Q, Li H X, He M, Wei Z M, He Y D, Hu W P 2011 Adv. Mater. 23 2059
[13] Sun Q J, Xu Z, Zhao S L, Zhang F J, Gao L Y 2011 Chin. Phys. B 20 017306
[14] Forker R, Gruenewald M, Fritz T 2012 Annual Reports Section C (Physical Chemistry) 108 34
[15] Xu J J, Hu C G, Chen X J, Zhang L, Fu X, Hu X T 2015 Acta Phys. Sin. 64 230701 (in Chinese)[徐佳佳, 胡春光, 陈雪娇, 张雷, 傅星, 胡小唐2015物理学报64 230701]
[16] Zhang L 2014 Ph. D. Dissertation (Tianjin:Tianjin University) (in Chinese)[张雷2014博士学位论文(天津:天津大学)]
[17] Borenszten Y 2005 Phys. Status Solidi A 202 1313
[18] Heavens O S 1955 Optical Properties of Thin Solid Films (New York:Dover) pp1-288
[19] Azzam R M A, Bashara N M (translated by Liang M J, Yin S B, Zhang F C, Wang G Y 1986 Ellipsometry and Polarized Light (Beijing:Science Press) pp179-190(in Chinese)[阿查姆R M, 巴夏拉N M著(梁民基, 尹树百, 张福初, 王广阳译) 1986椭圆偏振测量术和偏振光(北京:科学出版社)第179–190页]
[20] Reese C, Bao Z N 2007 Mater. Today 10 20
[21] Philipp H R 1998 Handbook of Optical Constants of Solids (Vol. 1) (San Diego:Academic Press) pp719-763
[22] Auslender M, Hava S 1998 Handbook of Optical Constants of Solids (Vol. 3) (San Diego:Academic Press) pp155-186
[23] Yoshidaa H, Inaba K, Sato N 2007 Appl. Phys. Lett. 90 181930
[24] Faltermeier D, Gompf B, Dressel M, Tripathi A K, Pflaum J 2006 Phy. Rev. B 74 125416
[25] Ruiz R, Choudhary D, Nickel B, Toccoli T, Chang K, Mayer A C, Clancy P, Blakely J M, Headrick R L, Iannotta S, Malliaras G G 2004 Chem. Mater. 16 4497
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