Effect of Electron-Beam Irradiation on Organic Semiconductor and Its

Subscriber access provided by CORNELL UNIVERSITY LIBRARY

Letter

The Effect of Electron Beam Irradiation on Organic Semiconductor and its Application for Transistor-based Dosimeters Jae Joon Kim, Jun Mok Ha, Hyeok Moo Lee, Hamid Saeed Raza, Ji Won Park, and Sung Oh Cho ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b05555 • Publication Date (Web): 11 Jul 2016 Downloaded from http://pubs.acs.org on July 21, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

The Effect of Electron Beam Irradiation on Organic Semiconductor and its Application for Transistor-based Dosimeters Jae Joon Kim,1 Jun Mok Ha, 1 Hyeok Moo Lee,2 Hamid Saeed Raza,3 Ji Won Park,1 and Sung Oh Cho1*

1

Department of Nuclear and Quantum Engineering, Korea Advanced Institute of Science and

Technology (KAIST), Daejeon, 305-701, Republic of Korea 2

Department of Informative Electronic Materials, LG Chemistry Research Park, Daejeon, 305-

738, Republic of Korea 3

Safety Analysis Center (SAC), Pakistan Nuclear Regulatory Authority 42-C, 24th Commercial

Street, Phase-II Ext., DHA, Karachi, 75500, Pakistan. *

Corresponding author. E-mail address: [email protected]

KEYWORDS: Electron beam irradiation, rubrene, organic thin-film transistor, dosimeter, semiconductor doping

ACS Paragon Plus Environment

1


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 22

ABSTRACT

The effects of electron beam irradiation on the organic semiconductor rubrene and its application as a dosimeter was investigated. Through the measurements of photoluminescence and the ultraviolet photoelectron spectroscopy, we found that electron beam irradiation induces n-doping of rubrene. Additionally, we fabricated rubrene thin-film transistors with pristine and irradiated rubrene, and discovered that the decrease of transistor properties are originated from the irradiation of rubrene and the threshold voltages are shifted to the opposite directions as the irradiated layers. Finally, a highly sensitive and air-stable electron-dosimeter was fabricated based on a rubrene transistor.

Organic semiconductors have been widely studied in the last decades because of their promising potential in the field of organic electronics.1,2 To realize these applications, there has been a large amount of research into the understanding and improving organic semiconductors in the aspects of physics, chemistry, materials science, and electronics. However, only limited studies have been conducted on the effect of radiation on organic semiconductors in spite of their novelty and high functionality for various organic materials.3,4 Although the effect of radiation on organic semiconductors has been known to be destructive, there are many of current and potential applications in characterization, patterning, and new synthesis or engineering of organic semiconductors. Thus, the investigations about the mechanism and changing tendencies of organic semiconductor to irradiation are crucial. Additionally, organic electronic devices could be ideal detectors or dosimeters of radiation due to their changed optoelectronic characteristics.5,6


2

Page 3 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Electron beam irradiation is a necessary and promising area of research because of its wide usages and unique advantages. First, most conjugated organic semiconductors can be changed by electron beam irradiation, their band gap can be tuned by electron beam irradiation7,8 Second, electron beam irradiation has been known to crosslink organic semiconductors, like other wellknown organic crosslinking-type polymers.9,10 Using irradiation techniques, device performance increase11 and selective patterning of organic semiconductors12 has been achieved. Specifically, the high resolution of electron beam implies the appropriateness of its application for the nanopatterning of organic semiconductors.13 Third, electron-beam-based measuring techniques are widely used for the investigation of the morphologic, optoelectronic, and crystallographic properties of organic semiconductors. Because accelerated electrons react with the materials during these measurements,14,15 an understanding of the electron-material interactions and degradation conditions of organic semiconductors are necessary for successful characterization. Despite of its importance, there have been only limited studies on the effect of electron beam irradiation on organic semiconductors regarding electronic performances. In addition, the dosimetry of the electron beam is required not only for organic electronics, but also other research fields.16 Though there are several kinds of conventional dosimeters, none of them used relatively inexpensive and highly radiation-sensitive organic semiconductors for the dosimetry of accelerated electrons. In this letter, we irradiated electron beam to poly-crystalline rubrene thin film17,18 under vacuum and

induced

n-doping

of

organic

semiconductor

rubrene.

These

radiation-induced

transformations of semiconducting properties were investigated using photoluminescence (PL) and ultraviolet photoelectron spectroscopy (UPS). In addition, we fabricated thin-film transistors with the irradiated rubrene and observed the changes in electronic performances as a function of


3


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 22

electron dose. A clear dose-performance dependency was identified and differentiated the effect of electron irradiation on the semiconductor and dielectric and we prorose rubrene TFTs as a sensitive and air-stable dosimeter of the electron irradiation.

Figure 1. (a) Pristine PL spectrum and its fit curves. Inset figure is showing polarization direction of rubrene molecule. (b) PL spectra of pristine and irradiated rubrene thin films.

Figure 1 shows the PL spectra of pristine and electron-irradiated rubrene thin-films. The PL spectrum and fit curves of non-irradiated pristine rubrene film of Figure 1a correspond well with the previously reported peak positions of orthorhombic single crystals of rubrene.19,20 The clearly


4

Page 5 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


distinguishable peaks of 567 and 602 nm are typical peaks of orthorhombic single crystal as the M- and L-polarized transition directions of rubrene molecules. Other minor peaks located at 648, 696, and 759 nm are also well matched with previously reported peak positions. These clearly show that our rubrene films were composed of polycrystalline rubrene of orthorhombicrubrene and contained very few defects or non-crystalline regions. In Figure 1b, the PL spectra of electron-irradiated rubrene with different doses are compared. At the doses of 104 to 106 rad, the PL spectra resembled that of the pristine sample; the peak positions and relative intensities of the samples were approximately maintained. Only the peak intensities decreased on account of the partial destruction of the conjugation system and delocalization of electronic states.21 However, above the dose of 106 rad, the relative intensity ratio of the 567 to 602 nm peaks started to decrease. Peak representative of the backbone (602 nm, L-polarized transition) can be distorted by electron beam, and this could be the reason for anisotropic decreases of PL intensities. At the highest dose of 107 rad, the typical peaks of orthorhombic rubrene subsequently disappeared and unknown broad peaks appeared. This newly emerged broad PL peak implies that the heavily irradiated rubrene underwent the diversification of molecular conjugation systems. In addition to the distortion of phenyl rings, changes to the conjugation system and/or irradiation-induced doping of rubrene molecules could be the reason of these spectra changes.22


5


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 22

Figure 2. UPS spectra of pristine and irradiated rubrene thin films deposited on Au film.

The UPS of rubrene thin films before and after electron beam irradiation are shown in Figure 2. The binding energy of UPS was derived from the Fermi level of the pre-deposited Au films. The energy difference of the highest occupied molecular orbital (HOMO) to the Fermi level, ε was found to be 0.6 eV at the pristine and irradiated rubrene of low doses. However, as the dose of the electron beam is increased, the ε value changes from 0.7 eV at the dose of 106 rad to 1.1 eV at the dose of 107 rad. These increase can be explained by the n-doping of the organic semiconductor, as reported in the other articles.23,24 This n-doping highly affects the electronic properties of the p-type semiconductor because the charge injection of hole from electrodes to the semiconductor is highly dependent on their HOMO to fermi level position. Additionally, the intensity decrease and broadening of the HOMO peak appeared when the dose was increased to 107 rad. This result can be interpreted as a change in the conjugation system, as suggested by the PL spectra. Similar broadening and shift of the HOMO peak was observed previously at the research of the UV-irradiated organic semiconductor.25 In the article, UV was irradiated in


6

Page 7 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


vacuum and the intentional n-doping of the semiconductor, CuPc (copper phthalocyanine), was shown.


7


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 22

Figure 3. Typical transfer characteristics of rubrene TFTs (a) irradiated to the SiO2 dielectrics on Si substrates prior to the rubrene deposition and (b) irradiated to the whole devices. The transfer curves were measured at a drain-source voltage of -15 V. (c) The tendencies of on-current changes (red, 3a and blue, 3b) as the electron dose increase. All of on-currents were measured at the gate voltage of -15 V.

The electronic characteristics of rubrene were investigated through the fabrication of TFTs by depositing gold source and drain electrodes on the rubrene-layered SiO2/Si substrate. In operation of a TFT, not only the semiconductor but also the dielectric that affects the device performance. Considering the fact that electron beam can degrade both of the semiconductor and dielectric due to its high penetration depth, the effects of electron beam irradiation must be differentiated as the irradiated layer. Therefore, we compared the layers of semiconductor and dielectric by irradiating before and after the deposition of rubrene on SiO2/Si dielectric/substrate under irradiation. Typical transfer curves of the rubrene TFTs are shown in Figure 3a and 3b. In Figure 3a, the drain currents of rubrene TFTs fabricated from irradiated SiO2/Si substrates and non-irradiated rubrene thin film are shown. Though there were slight decreases in the drain currents as the electron dose increased, the overall charge transfer behaviors were almost maintained. However, in the case of Figure 3b where the electron beam irradiated the whole device, a significant decrease in the drain current is shown as the dose increases. The drain current decrease begins at a dose level of 105 rad, and no field-effect behavior appears at a dose of 107 rad. These electron-beam-induced decreases of the on-currents are clearly compared in Figure 3c.


8

Page 9 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4. Calculated (a) mobilities and (b) threshold voltages (c) subthreshold swings and interface trap densities of rubrene TFTs. Blue color corresponds devices irradiated to the dielectrics and red color corresponds to the devices irradiated entirely.


9


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 22

To investigate and evaluate the radiation-induced performance changes more clearly, the mobilities and threshold voltages after different electron doses were calculated from the transfer curves. The non-irradiated rubrene devices were measured and the average of the mobilities and threshold voltages were measured to 0.84 cm2V-1s-1 and -1.7 V, respectively. The change of mobility as a function of electron beam dose is shown in Figure 4a. In this case, the decrease in mobility was relatively small. Even at the highest dose of 107 rad, the mobility was still 0.45 cm2V-1s-1, maintained more than 50 % of the pristine value. However, in the case of the TFTs irradiated all layers, the mobilities were dramatically decreased. A 50 % drop in mobility was observed at the dose lower than 105 rad and at the highest dose of 107 rad, no charge transportation was observed. These differing mobility trends clearly show that irradiation mainly affects the organic semiconducting layer, not the dielectric. As the electron dose increases, rubrene undergoes a n-doping process, so the charge injection of holes from the Au electrodes to the HOMO level of rubrene becomes more difficult as the energy gap of ε increases. Additionally, the diversified conjugation systems of irradiated rubrene molecules diminish the intramolecular charge transportation. Both of these phenomena play a role in the decreasing mobility after irradiation. In addition to the mobility, different effects of irradiation on the semiconductor and dielectric can be confirmed by investigating changes in the threshold voltage, as shown in Figure 4b. In the case of TFTs with non-irradiated rubrene, the threshold voltage was slightly increased as dose. The threshold voltage was decreased as the dose increases when the entire device was irradiated. These differing behaviors can be explained by the electron-beam-induced doping taking place at the different layers of the TFTs. When only the dielectric is irradiated, electron defects were implanted in the dielectric, and they can act as additional negative gate voltage which can cause


10

Page 11 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


larger accumulation of holes at the channel.26,27 As a result, the threshold voltage shifts in a positive direction. Inversely, the negative shift in threshold voltage on whole-layer-irradiated TFTs can be explained by n-doping of the semiconducting layer28 Though irradiation effects both the semiconducting and dielectric layers, the semiconductor change is much more dominant than the effect on the dielectric. It should be mentioned that addition to the doping, charge trapping can be taken place on the irradiated organic semiconductor. It is shown in Figure 3a and Figure 4c that the subthreshold swing is decreased as the irradiation dose is increased. As shown more specifically in Figure 4c, the calculated density of traps at the semiconductor-dielectric interface is increased as a function of radiation dose and suggests that electrons can induce traps in the bulk semiconductor and at the dielectric interface. Tapping and doping of the semiconductor can cause a threshold voltage shift, but the UPS shift clearly shows that the doping of semiconductor is more dominant than the trapping. With these results, we found that the performance changes clearly corresponded to the dose of electron beam irradiation and thereby, we could estimate the dose of the electron beam from the change of on-current, mobility, and threshold voltage of irradiated rubrene TFTs for the highly sensitive electron irradiation dosimetry. Because the on-current can be measured easily during the electron irradiation, the continuous in-situ measurement of the dose can be realized by fixing the sizes and structure of transistors. Oppositely, the mobility and threshold voltage values are the intrinsic properties of materials only affected by electron beam irradiation so the performance changes of these two values could be valid to any other transistors with different sizes and geometries. Furthermore, we could rule out undesired oxidation effects during and/or after the irradiation process. Because all of our irradiations of electron beam were conducted in a high vacuum, the ionization of oxygen and oxidation-induced p-doping of semiconductors cannot be


11


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 22

placed in our experiments. Add to this, the extremely high stability of crystalline rubrene for oxidation29,30 makes it stable even after many measurements of different conditions. Since the high sensitivity and air stability are essential for real applications, we suggest that our dosimeter as an ideal solution for the electron beam dosimeter. In summary, we have investigated the effect of electron beam irradiation on the organic semiconductor rubrene and applied it as a dosimeter by fabricating rubrene TFTs. Through electron beam irradiation, n-doping of the semiconductor and diversification of the conjugation system appeared in the crystalline films of organic semiconductor rubrene. By comparing TFTs with irradiated and non-irradiated rubrene thin films, we found that electron irradiation to the organic semiconductor is a dominant factor for the changed performances. Consequently, we discovered a clear mechanism of the electron-induced tuning of the semiconducting properties and utilized it as a high-sensitive electron beam dosimeter. We believe that our approach is a promising way to interpret and design electron-beam-based measurements and many applications in organic electronics, such as semiconductor isolation, optical waveguide, the polymerization of semiconductors, and especially the pattering of organic semiconductors.

ASSOCIATED CONTENT Supporting Information Experimental details and methodology to determine the dose of irradiated electron. This material is available free of charge via the Internet at http://pubs.acs.org.


12

Page 13 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


AUTHOR INFORMATION Corresponding Author *E-mail: [email protected].

ACKNOWLEDGMENT This work was supported by the Creative Research Program of the Korea Atomic Energy Research Institute Grant funded by the Korean government.


13


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 22

REFERENCES (1) Forrest, S. R., The Path to Ubiquitous and Low-Cost Organic Electronic Appliances on Plastic. Nature 2004, 428, 911-918. (2) Friend, R. H.; Gymer, R. W.; Holmes, A. B.; Burroughes, J. H.; Marks, R. N.; Taliani, C.; Bradley, D. D. C.; Dos Santos, D. A.; Bredas, J. L.; Logdlund, M.; Salaneck, W. R., Electroluminescence in Conjugated Polymers. Nature 1999, 397, 121-128. (3) Ciavatti, A.; Capria, E.; Fraleoni‐Morgera, A.; Tromba, G.; Dreossi, D.; Sellin, P. J.; Cosseddu, P.; Bonfiglio, A.; Fraboni, B., Toward Low‐Voltage and Bendable X‐Ray Direct Detectors Based on Organic Semiconducting Single Crystals. Adv. Mater. 2015, 27, 7213-7220. (4) Fraboni, B.; Fraleoni-Morgera, A.; Zaitseva, N., Ionizing Radiation Detectors Based on Solution-Grown Organic Single Crystals. Adv. Funct. Mater. 2016, 26, 2276-2291. (5) Raval, H. N.; Tiwari, S. P.; Navan, R. R.; Rao, V. R., Determining Ionizing Radiation Using Sensors Based on Organic Semiconducting Material. Appl. Phys. Lett. 2009, 94, 123304. (6) Suzuki, T.; Miyata, H.; Katsumata, M.; Nakano, S.; Matsuda, K.; Tamura, M., Organic Semiconductors as Real-Time Radiation Detectors. Nucl. Instrum. Methods Phys. Res., Sect. A 2014, 763, 304-307. (7) Lee, H. M.; Kim, Y. N.; Kim, B. H.; Kim, S. O.; Cho, S. O., Fabrication of Luminescent Nanoarchitectures by Electron Irradiation of Polystyrene. Adv. Mater. 2008, 20, 2094-2098. (8) Yoo, S. H.; Kum, J. M.; Cho, S. O., Tuning the Electronic Band Structure of Pcbm by Electron Irradiation. Nanoscale Res. Lett. 2011, 6, 1-7. (9) Kim, J. J.; Lee, H. M.; Park, J. W.; Cho, S. O., Patterning of Rubrene Thin-Film Transistors Based on Electron Irradiation of a Polystyrene Dielectric Layer. J. Mater. Chem. C 2015, 3, 2650-2655.


14

Page 15 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(10) Kim, J. J.; Li, Y.; Lee, E. J.; Cho, S. O., Fabrication of Size-Controllable Hexagonal NonClose-Packed Colloidal Crystals and Binary Colloidal Crystals by Pyrolysis Combined with Plasma− Electron Coirradiation of Polystyrene Colloidal Monolayer. Langmuir 2011, 27, 23342339. (11) Kato, T.; Yasumatsu, M.; Origuchi, C.; Tsutsui, K.; Ueda, Y.; Adachi, C., High Carrier Mobility of 3.8 Cm2 V-1 S-1 in Polydiacetylene Thin Films Polymerized by Electron Beam Irradiation. Appl. Phys. Express 2011, 4, 091601. (12) Gibbons, F. P.; Manickam, M.; Preece, J. A.; Palmer, R. E.; Robinson, A. P., Direct Electron‐Beam Writing of Highly Conductive Wires in Functionalized Fullerene Films. Small 2009, 5, 2750-2755. (13) Ma, S.; Con, C.; Yavuz, M.; Cui, B., Polystyrene Negative Resist for High-Resolution Electron Beam Lithography. Nanoscale Res. Lett. 2011, 6, 1-6. (14) Egerton, R.; Li, P.; Malac, M., Radiation Damage in the Tem and Sem. Micron 2004, 35, 399-409. (15) Egerton, R.; Takeuchi, M., Radiation Damage to Fullerite (C~ 6~ 0) in the Transmission Electron Microscope. Appl. Phys. Lett. 1999, 75. (16) Chao, A., Handbook of Accelerator Physics and Engineering. World scientific: 1999. (17) Lee, H. M.; Kim, J. J.; Choi, J. H.; Cho, S. O., In Situ Patterning of High-Quality Crystalline Rubrene Thin Films for High-Resolution Patterned Organic Field-Effect Transistors. ACS Nano 2011, 5, 8352-8356. (18) Lee, H. M.; Moon, H.; Kim, H.-S.; Kim, Y. N.; Choi, S.-M.; Yoo, S.; Cho, S. O., Abrupt Heating-Induced High-Quality Crystalline Rubrene Thin Films for Organic Thin-Film Transistors. Org. Electron. 2011, 12, 1446-1453.


15


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 22

(19) Ma, L.; Zhang, K.; Kloc, C.; Sun, H.; Soci, C.; Michel-Beyerle, M. E.; Gurzadyan, G. G., Fluorescence from Rubrene Single Crystals: Interplay of Singlet Fission and Energy Trapping. Phys. Rev. B 2013, 87, 201203. (20) Mitrofanov, O.; Kloc, C.; Siegrist, T.; Lang, D. V.; So, W.-Y.; Ramirez, A. P., Role of Synthesis for Oxygen Defect Incorporation in Crystalline Rubrene. Appl. Phys. Lett. 2007, 91, 212106. (21) Ahn, H.; Oblas, D.; Whitten, J., Electron Irradiation of Poly (3-Hexylthiophene) Films. Macromolecules 2004, 37, 3381-3387. (22) Park, H. J.; Kim, M. S.; Kim, J.; Joo, J., Fine Control of Photoluminescence and Optical Waveguiding Characteristics of Organic Rubrene Nanorods Using Focused Electron-Beam Irradiation. J. Phys. Chem. C 2014, 118, 30179-30186. (23) Chan, C. K.; Kahn, A., N-Doping of Pentacene by Decamethylcobaltocene. Appl. Phys. A 2009, 95, 7-13. (24) Cheng, C.-P.; Li, T.; Kuo, C.-H.; Pi, T.-W., Electronic Structures of Pristine and Potassium-Doped Rubrene Thin Films. Org. Electron. 2013, 14, 942-950. (25) Ono, M.; Sueyoshi, T.; Zhang, Y.; Kera, S.; Ueno, N., Vuv Induced Doping of CuPhthalocyanine Thin Films: A Possibility of N-Type Doping. Mol. Cryst. Liq. Cryst. 2006, 455, 251-256. (26) Aitken, J.; Young, D.; Pan, K., Electron Trapping in Electron‐Beam Irradiated Sio2. J. Appl. Phys. 1978, 49, 3386-3391. (27) Badila, M.; Godignon, P.; Millan, J.; Berberich, S.; Brezeanu, G., The Electron Irradiation Effects on Silicon Gate Dioxide Used for Power Mos Devices. Microelectron. Reliab. 2001, 41, 1015-1018.


16

Page 17 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(28) Lüssem, B.; Tietze, M. L.; Kleemann, H.; Hoßbach, C.; Bartha, J. W.; Zakhidov, A.; Leo, K., Doped Organic Transistors Operating in the Inversion and Depletion Regime. Nat Commun 2013, 4. (29) Fumagalli, E.; Raimondo, L.; Silvestri, L.; Moret, M.; Sassella, A.; Campione, M., Oxidation Dynamics of Epitaxial Rubrene Ultrathin Films. Chem. Mater. 2011, 23, 3246-3253. (30) Käfer, D.; Witte, G., Growth of Crystalline Rubrene Films with Enhanced Stability. Phys. Chem. Chem. Phys. 2005, 7, 2850-2853.


17


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 22

Table of Contents


18

Page 19 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 1. (a) Pristine PL spectrum and its divided fit curves. Inset figure is showing polarization direction of rubrene molecule. (b) PL spectra of pristine and irradiated rubrene thin films. 85x121mm (300 x 300 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 2. UPS spectra of pristine and irradiated rubrene thin films deposited on Au film. 85x67mm (300 x 300 DPI)


Page 20 of 22

Page 21 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 3. Typical transfer characteristics of rubrene TFTs (a) irradiated to the SiO2 dielectrics on Si substrates prior to the rubrene deposition and (b) irradiated to the whole devices. The transfer curves were measured at a drain-source voltage of -15 V. (c) The tendencies of on-current changes (red, 3a and blue, 3b) as the electron dose increase. All of on-currents were measured at the gate voltage of -15 V. 85x202mm (300 x 300 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 4. Calculated (a) mobilities and (b) threshold voltages (c) subthreshold swings and interface trap densities of rubrene TFTs. Blue color corresponds devices irradiated to the dielectrics and red color corresponds to the devices irradiated entirely. 85x168mm (300 x 300 DPI)


Page 22 of 22

Effect of Electron-Beam Irradiation on Organic Semiconductor and Its

Recommend Documents