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Rapid growth of thin and flexible organic semiconductor single crystal Anthracene by solution growth technique for device fabrication
Author's Accepted Manuscript
Rapid growth of thin and flexible organic semiconductor single crystal anthracene by solution growth technique for device fabrication K. Thirupugalmani, G. Shanmugam, V. Kannan, S. Brahadeeswaran
www.elsevier.com/locate/jcrysgro
PII: DOI: Reference:
S0022-0248(14)00818-5 http://dx.doi.org/10.1016/j.jcrysgro.2014.12.009 CRYS22573
To appear in:
Journal of Crystal Growth
Received date: 22 September 2014 Revised date: 9 December 2014 Accepted date: 10 December 2014 Cite this article as: K. Thirupugalmani, G. Shanmugam, V. Kannan, S. Brahadeeswaran, Rapid growth of thin and flexible organic semiconductor single crystal anthracene by solution growth technique for device fabrication, Journal of Crystal Growth, http://dx.doi.org/10.1016/j.jcrysgro.2014.12.009 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Abstract Growth of thin and flexible organic semiconductor crystal Anthracene (AN) has been achieved in a very short duration. This simple, yet an effective approach was serendipitously found to yield high quality crystal with typical dimensions of 22 x 23 x 0.15-0.50 mm3 within a duration of about 30 minutes whereas a conventional method could take about 7 to 10 days to achieve similar dimensions. Further, these crystals were seen swirling and settling down slowly at the bottom of the growth flask. These factors were favorably utilized to place the Anthracene crystals firmly on prefabricated flexible substrates when they were kept in different heights within the solutions. This systematic approach also facilitated the fabrication of organic field effect transistor (OFET) and the results obtained were encouraging.
Key words: A1. Supersaturated solutions, A1. Single crystal growth, A2. Solution growth, B1. Organic compounds, B2. Anthracene, B3. Organic Field Effect Transistors
1
Rapid Growth of Thin and Flexible Organic Semiconductor Single Crystal Anthracene by Solution Growth Technique for Device Fabrication
K. Thirupugalmania, G. Shanmugamb, V. Kannanc, S. Brahadeeswarana*
a
Crystal Research laboratory, Department of Physics, Bharathidasan Institute of Technology,
Anna University, Tiruchirappalli 620024, India, bSSM Institute of Engineering and Technology, Dindigul 624002, India,
c
Department of Physics, M. A. M. School of Engineering,
Tiruchirappalli 621105, India
*Corresponding author. S. Brahadeeswaran Department of Physics Bharathidasan Institute of Technology Anna University Tiruchirappalli-620024 Tamilnadu, India E-mail address: [email protected] (S. Brahadeeswaran). Tel.: +91 0944 2317 559; fax: +91 0431 2407 999.
2
Abstract Growth of thin and flexible organic semiconductor crystal Anthracene (AN) has been achieved in a very short duration. This simple, yet an effective approach was serendipitously found to yield high quality crystal with typical dimensions of 22 x 23 x 0.15-0.50 mm3 within a duration of about 30 minutes whereas a conventional method could take about 7 to 10 days to achieve similar dimensions. Further, these crystals were seen swirling and settling down slowly at the bottom of the growth flask. These factors were favorably utilized to place the Anthracene crystals firmly on prefabricated flexible substrates when they were kept in different heights within the solutions. This systematic approach also facilitated the fabrication of organic field effect transistor (OFET) and the results obtained were encouraging.
Key words: A1. Supersaturated solutions, A1. Single crystal growth, A2. Solution growth, B1. Organic compounds, B2. Anthracene, B3. Organic Field Effect Transistors
3
1. Introduction Organic semiconductor single crystals (OSCs) are of great interest due to their potential applications in large-area and flexible electronic systems such as organic light emitting diodes (OLEDs), organic field effect transistors (OFETs) as they exhibit well defined molecular structure, long range order, high chemical purity and absence of grain boundary [1-3]. For the past few decades, reliable methods such as physical vapour transport (PVT) and solution growth technique have been employed to grow high quality and flexible organic semiconductor single crystal [2, 4-6]. The organic semiconductor crystal integrated as a part of the device through one of the processes called stamping [7], which requires extreme care as the organic crystals are soft and fragile. However, placing the OSC on a prefabricated flexible substrate during the growth could be a challenging task but, if achieved, would be a desirable approach.
While studying the effect of various solvents on the growth of Anthracene (AN) crystals, we serendipitously found that a specific solvent facilitated growth of thin and flexible crystals thus enhancing the possibility of placing them directly on the pre-fabricated substrates if they were already immersed in such solutions. The present communication provides the details on various solvents explored for the growth of AN crystals, the role of specific solvent to grow them in a rapid manner and the characterization studies performed on the thus grown AN crystals to analyze their crystalline orientation, surface features and OFET properties.
2. Experimental The parent material AN was commercially purchased (Merck, AR Grade >99%). The growth experiments were performed in a growth chamber, which is capable of controlling the 4
temperature with an accuracy of ± 0.01 ˚C. The saturated solutions of AN were prepared using solvents such as carbon tetrachloride (CCl4), xylene, carbon disulfide (CS2) and chloroform at 30 ˚C and the temperature was raised further upto 35 ˚C and the solutions were kept at this temperature for about 10 minutes. These solutions were subjected to cooling with the cooling rates of 0.02 ˚C/h (slow cooling) and 45 ˚C/h (rapid cooling). The growth was performed at dark environment to avoid oxidization by photoirradiation. A typical cooling program adapted for the rapid cooling is shown in Fig. 1 (a). An X-Pert Pro PANalytical X-Ray diffractometer with CuKa (λ = 1.5418Å) was used to confirm the crystalline phase of AN powder and the orientation of platy crystals of AN. The surface morphology of the AN crystal was evaluated by Atomic Force Microscope (Park system XE-100). The current–voltage (I–V) characteristics were measured at room temperature (303 K) using a Keithley SCS4200 semiconductor characterization system. The substrate for Organic Field Effect Transistor (OFET) was fabricated using Indium Tin Oxide (ITO) coated poly ethelene tetrathene (PET) (Gate) over which poly (methyl methacrylate) (PMMA) (dielectric medium) was deposited by spin coating technique with a width of about 120 nm. Silver was then coated as a top electrode using thermal evaporation method with the channel length (L = 50 µm), channel width (W = 250 µm) and thickness (t = 14 µm). The fabricated device was entirely covered with (Polydimethylsiloxane) (PDMS) to protect from air and it was gently pressed by mechanical means to improve the electrical contact.
3. Results and Discussion While the slow cooling of solutions prepared with various solvents yielded crystals of differing qualities (Fig. S1) within a duration of 7 to 9 days, the rapid cooling did not yield any 5
crystal except, surprisingly, for one solvent, CS2. The solution prepared with the CS2 solvent exhibited the tendency for rapid nucleation and growth within the duration of about 30 minutes [8]. A video component attached (Supplementary Video 1) depicts the occurrence of nucleation, growth of crystals, which, subsequently, swirl and settle down slowly at the bottom of the flask. Subsequently, a systematic approach was adapted to study the growth of AN crystals using the CS2 solvent. This solution was cooled at the rate of about 45 ˚C/h and the spontaneously nucleated AN crystals were grown until they reach sufficient size. The crystals thus grown were separated from the solution and dried. Fig. 1(b) shows a typical AN crystal grown within a duration of about 30 minutes. The digital photograph of thin and mechanically flexible AN single crystal were shown (Fig. S2).
In order to facilitate the growth of AN crystals directly on the flexible substrate, initial attempts were made to place the fabricated flat ITO substrate with an area of 1 x 1 cm2 at the bottom of the flask (position P1 (a) in Fig. 1 (c)). In this process it was observed that the substrate had many AN crystals settled firmly but randomly placed. Subsequently, a flexible substrate which was bent using a nylon thread was also placed at the bottom (position P1 (b)). After the growth was completed it was observed that the multi-nucleated AN crystals were placed firmly and again randomly on this bent substrate too. In order to avoid the growth of multi-crystals and to explore the possibility of growing a few independent AN crystals on the substrate, the substrates were raised to about 3 cm (flat (position P2 (a)) and bent (position P2 (b)) in two separate flasks, so that the crystals obtained by nucleations occurred between the levels just under the surface of the solution and that of the fabricated substrate could only be placed on the latter. This approach, expectedly, facilitated the placement of one or two AN 6
crystals firmly on the substrate (Fig. 1(c)) and thus enhanced the possibility of fabricating the device in-situ.
Prior to commencing the measurements of OFET properties of the fabricated AN crystal, their orientation and surface quality were ascertained using powder XRD and AFM analysis respectively. The XRD pattern of AN single crystal is shown in Fig. 2(a). The sharp diffraction peaks indicated that the AN single crystal possessed well developed (001) plane. Figure 2(b) shows the AFM image of AN single crystal recorded for the area of 5x5 µm2. From the figure it could be seen that the scanned area exhibited considerable flatness and the surface roughness (rms) was measured to be about 0.11 nm. Subsequently, the surface roughness of rapid grown AN was compared with those obtained for AN crystals grown by melt technique and solution growth method using different solvents [9, 10] (Table 1). From the Table it could be observed that the rapid grown AN crystal possessed enhanced surface quality. This could be attributed to the short growth duration where in the possibilities of entrapment of impurities in the solution could have been considerably reduced.
The Figs. 3(a) and 3(b) shows the schematic of a single crystal AN based FET and OFET device fabricated AN single crystal respectively. The results of ISD – VSD characteristics of the OFET fabricated using the AN crystal on flat substrate measured at 303 K are shown in Fig. 3(c). The inset of Fig. 3(c) shows the ISD versus Vg at VSD = 50 V for the same FET structure at 303 K. The exponent was observed to be weakly gate dependent and an increase in the gate voltage (Vg) decreases the ISD slightly. The calculated on/off ratio Vg = -30 V (on) and Vg = 10 V (off) between the source –drain current at VSD = 50 V should be ≈ 2 X 105 at 303 K with the 7
capacitance of Ci ≈ 6.4 nF/Cm2. The room temperature threshold voltage (Vth) was about ≈ 12 V. The leakage current was less than 2.2 nA. From the transconductance characteristics, the field effect mobility is obtained by the formula
The OFET mobility was measured to be about 0.0016 cm2/Vs at 303 K for the voltage Vg ~ -40 V. The measurements of OFET fabricated on flexible substrate are being carried out and the results will be reported elsewhere.
4. Conclusions Thin and flexible AN single crystals were grown in a short duration using CS2 solvent. The OFET was successfully fabricated by depositing AN single crystals on prefabricated flat and flexible substrate during the growth. The charge carrier transport of rapid grown AN single crystal was studied by means of field-effect-transistor. The attempt reported here could facilitate direct growth of other efficient organic semiconductor crystals on prefabricated flat and flexible substrates.
Acknowledgement This work is supported by the Department of Science and Technology (DST), New Delhi, India, through the SERC Fast Track Young Scientist Scheme (SR/FTP/PS-53/2007 Dt. 22-0808) and its financial support is hereby gratefully acknowledged. The authors thank Dr. M. Sivakumar, Department of Chemistry, Bharathidasan Institute of Technology, Anna University, Tiruchirappalli, India for the help with AFM measurement.
8
Reference [1] X. Li, Y. Xu, F. Li, Y. Ma, Org. Electron. 13 (2012) 762. [2] A. L. Briseno, R. J. Tseng, M. M. Ling, E. H. L. Falcao, Y. Yang, F. Wudl, Z. Bao, Adv. Mater. 18 (2006) 2320. [3] A. N. Aleshin, J. Y. Lee, S. W. Chu, J. S. Kim, Y. W. Park, J. Appl. Phys. 84 (2004) 5383. [4] S. F. Nelson, Y. Y. Lin, D. J. Gundlach, T. N. Jackson, Appl. Phys. Lett. 72 (1998) 1854. [5] R. H. Friend, R. W. Gymer, A. B. Holmes, J. H. Burroughes, Nature 397 (1999) 121. [6] C.W. Tang, S. A. VanSlyke, C. H. Chen, J. Appl. Phys. 65 (1989) 3610. [7] V. C. Sundar, J. Zaumseil, V. Podzorov, E. Menard, R. L. Willett, T. Someya, M. E. Gershenson, J. A. Rogers, Science 303 (2004) 1644. [8] S. Brahadeeswaran, K. Thirupugalmani, G. Shanmugam, Rapid Growth of Thin and Flexible Organic Semiconductor Single Crystals Using Modified Solution Technique, Indian Patent, 584/CHE/2012 (Filed). [9] I. H. Hong, K. J. Tan, M. Toh, H. Jiang, K. Zhang, C. Kloc, Journal of Crystal Growth 363 (2013) 61. [10] H. Li, D. Zhang, L. Duan, G. Dong, L. Wang, Y. Qiu, Jpn. J. Appl. Phys. 46 (2007) 7789.
9
Table. 1 Surface roughness (rms) of Anthracene in various solvents Technique
Ra(rms)
Reference
Melt
2.44 nm
[10]
Carbon Tetrachloride
0.50 nm
[11]
Benzene
1.25 nm
[11]
Acetone
0.46 nm
[11]
Carbon disulfide
0.11 nm
This work
Solution
Figure caption Fig. 1. Anthracene single crystal grown from Rapid technique: (a) Temperature program for rapid solution technique, (b) Digital photograph of as grown AN single crystal and (c) Digital Photographs of AN single crystal deposition on flexible substrate at different stage along with the schematic representation of the substrate positions (see text for detailed information). Fig. 2. (a) XRD pattern of (001) plane of AN single crystal and (b) AFM image of 5 × 5 µm2 area of AN single crystal Fig. 3. (a) Schematic representation of AN based OFET, (b) OFET device fabricated AN single crystal and (c) I-V characteristics of AN based OFET (Inset shows the ISD Vs Vg at 303 K).
10
Fig. 1
b
a
c
Fig. 1. Anthracene single crystal grown from Rapid technique: (a) Temperature program for rapid solution technique, (b) Digital photograph of as grown AN single crystal and (c) Digital Photographs of AN single crystal deposition on flexible substrate at different stage along with the schematic representation of the substrate positions (see text for detailed information).
11
Fig. 2 a
b
Fig. 2. (a) XRD pattern of (001) plane of AN single crystal and (b) AFM image of 5 × 5 µm2 area of AN single crystal
12
Fig. 3
b
a
c
Fig. 3. (a) Schematic representation of AN based OFET, (b) OFET device fabricated AN single crystal and (c) I-V characteristics of AN based OFET (Inset shows the ISD Vs Vg at 303 K).
13
Highlights: •
Thin and flexible AN single crystals were grown by rapid technique in 30 minutes.
•
The AN crystals exhibited considerable flatness and surface roughness was about 0.11 nm.
•
The fabrication of OFET on prefabricated substrate was achieved.
14
Rapid growth of thin and flexible organic semiconductor single crystal anthracene by solution growth technique for device fabrication K. Thirupugalmani, G. Shanmugam, V. Kannan, S. Brahadeeswaran
www.elsevier.com/locate/jcrysgro
PII: DOI: Reference:
S0022-0248(14)00818-5 http://dx.doi.org/10.1016/j.jcrysgro.2014.12.009 CRYS22573
To appear in:
Journal of Crystal Growth
Received date: 22 September 2014 Revised date: 9 December 2014 Accepted date: 10 December 2014 Cite this article as: K. Thirupugalmani, G. Shanmugam, V. Kannan, S. Brahadeeswaran, Rapid growth of thin and flexible organic semiconductor single crystal anthracene by solution growth technique for device fabrication, Journal of Crystal Growth, http://dx.doi.org/10.1016/j.jcrysgro.2014.12.009 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Abstract Growth of thin and flexible organic semiconductor crystal Anthracene (AN) has been achieved in a very short duration. This simple, yet an effective approach was serendipitously found to yield high quality crystal with typical dimensions of 22 x 23 x 0.15-0.50 mm3 within a duration of about 30 minutes whereas a conventional method could take about 7 to 10 days to achieve similar dimensions. Further, these crystals were seen swirling and settling down slowly at the bottom of the growth flask. These factors were favorably utilized to place the Anthracene crystals firmly on prefabricated flexible substrates when they were kept in different heights within the solutions. This systematic approach also facilitated the fabrication of organic field effect transistor (OFET) and the results obtained were encouraging.
Key words: A1. Supersaturated solutions, A1. Single crystal growth, A2. Solution growth, B1. Organic compounds, B2. Anthracene, B3. Organic Field Effect Transistors
1
Rapid Growth of Thin and Flexible Organic Semiconductor Single Crystal Anthracene by Solution Growth Technique for Device Fabrication
K. Thirupugalmania, G. Shanmugamb, V. Kannanc, S. Brahadeeswarana*
a
Crystal Research laboratory, Department of Physics, Bharathidasan Institute of Technology,
Anna University, Tiruchirappalli 620024, India, bSSM Institute of Engineering and Technology, Dindigul 624002, India,
c
Department of Physics, M. A. M. School of Engineering,
Tiruchirappalli 621105, India
*Corresponding author. S. Brahadeeswaran Department of Physics Bharathidasan Institute of Technology Anna University Tiruchirappalli-620024 Tamilnadu, India E-mail address: [email protected] (S. Brahadeeswaran). Tel.: +91 0944 2317 559; fax: +91 0431 2407 999.
2
Abstract Growth of thin and flexible organic semiconductor crystal Anthracene (AN) has been achieved in a very short duration. This simple, yet an effective approach was serendipitously found to yield high quality crystal with typical dimensions of 22 x 23 x 0.15-0.50 mm3 within a duration of about 30 minutes whereas a conventional method could take about 7 to 10 days to achieve similar dimensions. Further, these crystals were seen swirling and settling down slowly at the bottom of the growth flask. These factors were favorably utilized to place the Anthracene crystals firmly on prefabricated flexible substrates when they were kept in different heights within the solutions. This systematic approach also facilitated the fabrication of organic field effect transistor (OFET) and the results obtained were encouraging.
Key words: A1. Supersaturated solutions, A1. Single crystal growth, A2. Solution growth, B1. Organic compounds, B2. Anthracene, B3. Organic Field Effect Transistors
3
1. Introduction Organic semiconductor single crystals (OSCs) are of great interest due to their potential applications in large-area and flexible electronic systems such as organic light emitting diodes (OLEDs), organic field effect transistors (OFETs) as they exhibit well defined molecular structure, long range order, high chemical purity and absence of grain boundary [1-3]. For the past few decades, reliable methods such as physical vapour transport (PVT) and solution growth technique have been employed to grow high quality and flexible organic semiconductor single crystal [2, 4-6]. The organic semiconductor crystal integrated as a part of the device through one of the processes called stamping [7], which requires extreme care as the organic crystals are soft and fragile. However, placing the OSC on a prefabricated flexible substrate during the growth could be a challenging task but, if achieved, would be a desirable approach.
While studying the effect of various solvents on the growth of Anthracene (AN) crystals, we serendipitously found that a specific solvent facilitated growth of thin and flexible crystals thus enhancing the possibility of placing them directly on the pre-fabricated substrates if they were already immersed in such solutions. The present communication provides the details on various solvents explored for the growth of AN crystals, the role of specific solvent to grow them in a rapid manner and the characterization studies performed on the thus grown AN crystals to analyze their crystalline orientation, surface features and OFET properties.
2. Experimental The parent material AN was commercially purchased (Merck, AR Grade >99%). The growth experiments were performed in a growth chamber, which is capable of controlling the 4
temperature with an accuracy of ± 0.01 ˚C. The saturated solutions of AN were prepared using solvents such as carbon tetrachloride (CCl4), xylene, carbon disulfide (CS2) and chloroform at 30 ˚C and the temperature was raised further upto 35 ˚C and the solutions were kept at this temperature for about 10 minutes. These solutions were subjected to cooling with the cooling rates of 0.02 ˚C/h (slow cooling) and 45 ˚C/h (rapid cooling). The growth was performed at dark environment to avoid oxidization by photoirradiation. A typical cooling program adapted for the rapid cooling is shown in Fig. 1 (a). An X-Pert Pro PANalytical X-Ray diffractometer with CuKa (λ = 1.5418Å) was used to confirm the crystalline phase of AN powder and the orientation of platy crystals of AN. The surface morphology of the AN crystal was evaluated by Atomic Force Microscope (Park system XE-100). The current–voltage (I–V) characteristics were measured at room temperature (303 K) using a Keithley SCS4200 semiconductor characterization system. The substrate for Organic Field Effect Transistor (OFET) was fabricated using Indium Tin Oxide (ITO) coated poly ethelene tetrathene (PET) (Gate) over which poly (methyl methacrylate) (PMMA) (dielectric medium) was deposited by spin coating technique with a width of about 120 nm. Silver was then coated as a top electrode using thermal evaporation method with the channel length (L = 50 µm), channel width (W = 250 µm) and thickness (t = 14 µm). The fabricated device was entirely covered with (Polydimethylsiloxane) (PDMS) to protect from air and it was gently pressed by mechanical means to improve the electrical contact.
3. Results and Discussion While the slow cooling of solutions prepared with various solvents yielded crystals of differing qualities (Fig. S1) within a duration of 7 to 9 days, the rapid cooling did not yield any 5
crystal except, surprisingly, for one solvent, CS2. The solution prepared with the CS2 solvent exhibited the tendency for rapid nucleation and growth within the duration of about 30 minutes [8]. A video component attached (Supplementary Video 1) depicts the occurrence of nucleation, growth of crystals, which, subsequently, swirl and settle down slowly at the bottom of the flask. Subsequently, a systematic approach was adapted to study the growth of AN crystals using the CS2 solvent. This solution was cooled at the rate of about 45 ˚C/h and the spontaneously nucleated AN crystals were grown until they reach sufficient size. The crystals thus grown were separated from the solution and dried. Fig. 1(b) shows a typical AN crystal grown within a duration of about 30 minutes. The digital photograph of thin and mechanically flexible AN single crystal were shown (Fig. S2).
In order to facilitate the growth of AN crystals directly on the flexible substrate, initial attempts were made to place the fabricated flat ITO substrate with an area of 1 x 1 cm2 at the bottom of the flask (position P1 (a) in Fig. 1 (c)). In this process it was observed that the substrate had many AN crystals settled firmly but randomly placed. Subsequently, a flexible substrate which was bent using a nylon thread was also placed at the bottom (position P1 (b)). After the growth was completed it was observed that the multi-nucleated AN crystals were placed firmly and again randomly on this bent substrate too. In order to avoid the growth of multi-crystals and to explore the possibility of growing a few independent AN crystals on the substrate, the substrates were raised to about 3 cm (flat (position P2 (a)) and bent (position P2 (b)) in two separate flasks, so that the crystals obtained by nucleations occurred between the levels just under the surface of the solution and that of the fabricated substrate could only be placed on the latter. This approach, expectedly, facilitated the placement of one or two AN 6
crystals firmly on the substrate (Fig. 1(c)) and thus enhanced the possibility of fabricating the device in-situ.
Prior to commencing the measurements of OFET properties of the fabricated AN crystal, their orientation and surface quality were ascertained using powder XRD and AFM analysis respectively. The XRD pattern of AN single crystal is shown in Fig. 2(a). The sharp diffraction peaks indicated that the AN single crystal possessed well developed (001) plane. Figure 2(b) shows the AFM image of AN single crystal recorded for the area of 5x5 µm2. From the figure it could be seen that the scanned area exhibited considerable flatness and the surface roughness (rms) was measured to be about 0.11 nm. Subsequently, the surface roughness of rapid grown AN was compared with those obtained for AN crystals grown by melt technique and solution growth method using different solvents [9, 10] (Table 1). From the Table it could be observed that the rapid grown AN crystal possessed enhanced surface quality. This could be attributed to the short growth duration where in the possibilities of entrapment of impurities in the solution could have been considerably reduced.
The Figs. 3(a) and 3(b) shows the schematic of a single crystal AN based FET and OFET device fabricated AN single crystal respectively. The results of ISD – VSD characteristics of the OFET fabricated using the AN crystal on flat substrate measured at 303 K are shown in Fig. 3(c). The inset of Fig. 3(c) shows the ISD versus Vg at VSD = 50 V for the same FET structure at 303 K. The exponent was observed to be weakly gate dependent and an increase in the gate voltage (Vg) decreases the ISD slightly. The calculated on/off ratio Vg = -30 V (on) and Vg = 10 V (off) between the source –drain current at VSD = 50 V should be ≈ 2 X 105 at 303 K with the 7
capacitance of Ci ≈ 6.4 nF/Cm2. The room temperature threshold voltage (Vth) was about ≈ 12 V. The leakage current was less than 2.2 nA. From the transconductance characteristics, the field effect mobility is obtained by the formula
The OFET mobility was measured to be about 0.0016 cm2/Vs at 303 K for the voltage Vg ~ -40 V. The measurements of OFET fabricated on flexible substrate are being carried out and the results will be reported elsewhere.
4. Conclusions Thin and flexible AN single crystals were grown in a short duration using CS2 solvent. The OFET was successfully fabricated by depositing AN single crystals on prefabricated flat and flexible substrate during the growth. The charge carrier transport of rapid grown AN single crystal was studied by means of field-effect-transistor. The attempt reported here could facilitate direct growth of other efficient organic semiconductor crystals on prefabricated flat and flexible substrates.
Acknowledgement This work is supported by the Department of Science and Technology (DST), New Delhi, India, through the SERC Fast Track Young Scientist Scheme (SR/FTP/PS-53/2007 Dt. 22-0808) and its financial support is hereby gratefully acknowledged. The authors thank Dr. M. Sivakumar, Department of Chemistry, Bharathidasan Institute of Technology, Anna University, Tiruchirappalli, India for the help with AFM measurement.
8
Reference [1] X. Li, Y. Xu, F. Li, Y. Ma, Org. Electron. 13 (2012) 762. [2] A. L. Briseno, R. J. Tseng, M. M. Ling, E. H. L. Falcao, Y. Yang, F. Wudl, Z. Bao, Adv. Mater. 18 (2006) 2320. [3] A. N. Aleshin, J. Y. Lee, S. W. Chu, J. S. Kim, Y. W. Park, J. Appl. Phys. 84 (2004) 5383. [4] S. F. Nelson, Y. Y. Lin, D. J. Gundlach, T. N. Jackson, Appl. Phys. Lett. 72 (1998) 1854. [5] R. H. Friend, R. W. Gymer, A. B. Holmes, J. H. Burroughes, Nature 397 (1999) 121. [6] C.W. Tang, S. A. VanSlyke, C. H. Chen, J. Appl. Phys. 65 (1989) 3610. [7] V. C. Sundar, J. Zaumseil, V. Podzorov, E. Menard, R. L. Willett, T. Someya, M. E. Gershenson, J. A. Rogers, Science 303 (2004) 1644. [8] S. Brahadeeswaran, K. Thirupugalmani, G. Shanmugam, Rapid Growth of Thin and Flexible Organic Semiconductor Single Crystals Using Modified Solution Technique, Indian Patent, 584/CHE/2012 (Filed). [9] I. H. Hong, K. J. Tan, M. Toh, H. Jiang, K. Zhang, C. Kloc, Journal of Crystal Growth 363 (2013) 61. [10] H. Li, D. Zhang, L. Duan, G. Dong, L. Wang, Y. Qiu, Jpn. J. Appl. Phys. 46 (2007) 7789.
9
Table. 1 Surface roughness (rms) of Anthracene in various solvents Technique
Ra(rms)
Reference
Melt
2.44 nm
[10]
Carbon Tetrachloride
0.50 nm
[11]
Benzene
1.25 nm
[11]
Acetone
0.46 nm
[11]
Carbon disulfide
0.11 nm
This work
Solution
Figure caption Fig. 1. Anthracene single crystal grown from Rapid technique: (a) Temperature program for rapid solution technique, (b) Digital photograph of as grown AN single crystal and (c) Digital Photographs of AN single crystal deposition on flexible substrate at different stage along with the schematic representation of the substrate positions (see text for detailed information). Fig. 2. (a) XRD pattern of (001) plane of AN single crystal and (b) AFM image of 5 × 5 µm2 area of AN single crystal Fig. 3. (a) Schematic representation of AN based OFET, (b) OFET device fabricated AN single crystal and (c) I-V characteristics of AN based OFET (Inset shows the ISD Vs Vg at 303 K).
10
Fig. 1
b
a
c
Fig. 1. Anthracene single crystal grown from Rapid technique: (a) Temperature program for rapid solution technique, (b) Digital photograph of as grown AN single crystal and (c) Digital Photographs of AN single crystal deposition on flexible substrate at different stage along with the schematic representation of the substrate positions (see text for detailed information).
11
Fig. 2 a
b
Fig. 2. (a) XRD pattern of (001) plane of AN single crystal and (b) AFM image of 5 × 5 µm2 area of AN single crystal
12
Fig. 3
b
a
c
Fig. 3. (a) Schematic representation of AN based OFET, (b) OFET device fabricated AN single crystal and (c) I-V characteristics of AN based OFET (Inset shows the ISD Vs Vg at 303 K).
13
Highlights: •
Thin and flexible AN single crystals were grown by rapid technique in 30 minutes.
•
The AN crystals exhibited considerable flatness and surface roughness was about 0.11 nm.
•
The fabrication of OFET on prefabricated substrate was achieved.
14