Lithuanian Journal of Physics article / Lietuvos fizikos žurnalo straipsnis

A PHYSICAL MECHANISM OF SENSITIVITY ENHANCEMENT OF ORGANIC X-RAY DETECTORS WITH TUNGSTEN NANOPARTICLES
Andrius Poškus, Rokas Dobužinskas, Mindaugas Viliūnas, and Kęstutis Arlauskas
Institute of Chemical Physics, Faculty of Physics, Vilnius University, Saulėtekio 3, 10257 Vilnius, Lithuania
Email: rokas.dobuzinskas@ff.vu.lt

Received 19 November 2019; revised 22 January 2020; accepted 23 January 2020

A simple theoretical model explaining the increase of X-ray sensitivity caused by adding tungsten nanoparticles into thin layers of organic materials is proposed. The mentioned increase of sensitivity is caused by quenched electron multiplication due to secondary electron emission from tungsten particles. After some simplifying assumptions, an expression of the electron multiplication factor K is derived for the case when tungsten atoms are uniformly mixed with the matrix material. The main assumption of the model is the existence of a threshold energy E_min of the order of 0.1 eV, below which the recombination of charge carriers prevents them from being accelerated by the electric field to energies sufficient for impact ionization. It is shown that this assumption makes the increase of K and photocurrent with increasing electric field much slower than the exponential increase commonly associated with an electron avalanche, and K may even start to decrease when the electric field strength exceeds a certain value. Another factor, which has an adverse effect on the X-ray sensitivity, is the ionization energy loss of photoelectrons inside metallic nanoparticles. The results of Monte Carlo simulations show that in the case of spherical tungsten particles with 0.8 μm diameter, the latter phenomenon may cause an additional decrease of the sensitivity by as much as 75%. In order to reduce this effect, the size of nanoparticles should be reduced, or, alternatively, most of the photoelectrons should be generated in the organic matrix rather than inside the nanoparticles.

Keywords: hybrid organic-inorganic X-ray sensors, physical mechanism, Monte Carlo simulation
PACS: 73.61.-r

ORGANINIŲ RENTGENO SPINDULIUOTĖS DETEKTORIŲ JAUTRUMO PADIDINIMO SU VOLFRAMO NANODALELĖMIS FIZINIS MECHANIZMAS
Andrius Poškus, Rokas Dobužinskas, Mindaugas Viliūnas, Kęstutis Arlauskas

Vilniaus universiteto Cheminės fizikos institutas, Vilnius, Lietuva

Pateiktas paprastas teorinis modelis, paaiškinantis padidėjusį rentgeno spindulių jautrį įterpus volframo nanodalelių į plonus organinių medžiagų sluoksnius. Jautrio padidėjimą lemia elektronų dauginimas dėl antrinės elektronų emisijos iš volframo dalelių. Atlikus keletą supaprastinančių prielaidų, išvedama elektronų dauginimo faktoriaus K išraiška tuo atveju, kai volframo atomai yra tolygiai pasiskirstę matricos medžiagoje. Pagrindinė modelio prielaida yra 0,1 eV eilės energijos slenkstinė vertė Emin, žemiau kurios krūvininkų rekombinacija neleidžia jiems elektriniame lauke pagreitėti iki energijų, pakankamų smūginei jonizacijai. Įrodyta, kad, galiojant šiai prielaidai, K ir rentgeno spinduliuotės sukurtos srovės padidėjimas stiprėjant elektriniam laukui yra daug lėtesnis nei eksponentinis (įprastai susijęs su elektronų griūtimi), ir K gali netgi pradėti mažėti, kai elektrinio lauko stipris viršija tam tikrą vertę. Kitas veiksnys, darantis neigiamą įtaką rentgeno spindulių jautriui, yra fotoelektronų jonizaciniai energijos nuostoliai volframo nanodalelėse. Monte Karlo modeliavimo rezultatai rodo, kad esant 0,8 μm skersmens sferinėms volframo dalelėms dėl pastarojo reiškinio jautris gali papildomai sumažėti 75 %. Norint sumažinti šį poveikį reikėtų sumažinti nanodalelių dydį arba didžioji dalis fotoelektronų turėtų būti generuojami ne nanodalelėse, o organinėje matricoje.

References / Nuorodos

[1] H. Mescher, E. Hamann, and U. Lemmer, Simulation and design of folded perovskite X-ray detectors, Sci. Rep. 9, 5231 (2019),
https://doi.org/10.1038/s41598-019-41440-6
[2] L. Li, X. Liu, H. Zhang, B. Zhang, W. Jie, P.J. Sellin, C. Hu, G. Zeng, and Y. Xu, Enhanced X-ray sensitivity of MAPbBr₃ detector by tailoring the interface-states density, ACS Appl. Mater. Interfaces 11, 7522 (2019),
https://doi.org/10.1021/acsami.8b18598
[3] U. Lemmer and H. Mescher, Novel hybrid organic-inorganic perovskite detector designs based on multilayered device architectures: simulation and design, Proc. SPIE 10948, 109480W (2019),
https://doi.org/10.1117/12.2511739
[4] K.D.G.I. Jayawardena, H.M. Thirimanne, S.F. Tedde, J.E. Huerdler, A.J. Parnell, R.M.I. Bandara, C.A. Mills, and S.R.P. Silva, Millimeter-scale unipolar transport in high sensitivity organic-inorganic semiconductor X-ray detectors, ACS Nano 13, 6973 (2019),
https://doi.org/10.1021/acsnano.9b01916
[5] A. Ciavatti, L. Basiricò, I. Fratelli, S. Lai, P. Cosseddu, A. Bonfiglio, J.E. Anthony, and B. Fraboni, Boosting direct X‐ray detection in organic thin films by small molecules tailoring, Adv. Funct. Mater. 29, 1806119 (2019),
https://doi.org/10.1002/adfm.201806119
[6] J. Oliveira, P.M. Martins, V. Correia, L. Hilliou, D. Petrovykh, and S. Lanceros-Mendez, Water based scintillator ink for printed X-ray radiation detectors, Polym. Test. 69, 26 (2018),
https://doi.org/10.1016/j.polymertesting.2018.04.042
[7] H.S. Gill, B. Elshahat, A. Kokil, L. Li, R. Mosurkal, P. Zygmanski, E. Sajo, and J. Kumar, Flexible perovskite-based X-ray detectors for dose monitoring in medical imaging applications, Phys. Med. 5, 20 (2018),
https://doi.org/10.1016/j.phmed.2018.04.001
[8] R. Dobužinskas, A. Poškus, and K. Arlauskas, X-ray sensitivity of small organic molecule and zinc cadmium sulfide mixture layers deposited using thermal melting technique, Org. Electron. 18, 37 (2015),
https://doi.org/10.1016/j.orgel.2015.01.004
[9] A. Intaniwet, C.A. Mills, M. Shkunov, H. Thiem, J.L. Keddie, and P.J. Sellin, Characterization of thick film poly(triarylamine) semiconductor diodes for direct X-ray detection, J. Appl. Phys. 106, 064513 (2009),
https://doi.org/10.1063/1.3225909
[10] B. Elshahat, H.S. Gill, I. Filipyev, S. Shrestha, J. Hesser, J. Kumar, A. Karellas, P. Zygmanski, and E. Sajo, Technical Note: Nanometric organic photovoltaic thin film detectors for dose monitoring in diagnostic x-ray imaging, Med. Phys. 42, 4027 (2015),
https://doi.org/10.1118/1.4922202
[11] L. Basiricò, A. Ciavatti, T. Cramer, P. Cosseddu, A. Bonfiglio, and B. Fraboni, Direct X-ray photoconversion in flexible organic thin film devices operated below 1 V, Nat. Commun. 7, 13063 (2016),
https://doi.org/10.1038/ncomms13063
[12] C.W. Han and Y.H. Tak, in: Flat Panel Display Manufacturing (John Wiley & Sons, Ltd, 2018) pp. 143–158,
https://doi.org/10.1002/9781119161387.ch8_02
[13] H.-W. Chen, J.-H. Lee, B.-Y. Lin, S. Chen, and S.-T. Wu, Liquid crystal display and organic light-emitting diode display: present status and future perspectives, Light Sci. Appl. 7, 17168 (2018),
https://doi.org/10.1038/lsa.2017.168
[14] H. Vartanian and J. Jurikson-Rhodes, Mobile Device with a Flexible Organic Light Emitting Diode (OLED) Multi-touch Display, U.S. Patent Application US20170337858A1 (2017),
[U. S. Patent Application]
[15] N.S. Sariciftci, From organic electronics to bio-organic electronics, Nonlinear Opt. Quantum Opt. 50(1–3), 137 (2019),
https://www.oldcitypublishing.com/journals/nloqo-home/nloqo-issue-contents/nloqo-volume-50-number-1-3-2019/nloqo-50-1-3-p-137-144/
[16] X. Cai, B. Gao, X.-L. Li, Y. Cao, and S.-J. Su, Singlet-triplet splitting energy management via acceptor substitution: complanation molecular design for deep-blue thermally activated delayed fluorescence emitters and organic light-emitting diodes application, Adv. Funct. Mater. 26, 8042 (2016),
https://doi.org/10.1002/adfm.201603520
[17] J. Park, S. Lee, and H.H. Lee, High-mobility polymer thin-film transistors fabricated by solvent-assisted drop-casting, Org. Electron. 7, 256 (2006),
https://doi.org/10.1016/j.orgel.2006.03.008
[18] H. Yang and P. Jiang, Large-scale colloidal self-assembly by doctor blade coating, Langmuir 26, 13173 (2010),
https://doi.org/10.1021/la101721v
[19] Y. Yuan, G. Giri, A.L. Ayzner, A.P. Zoombelt, S.C.B. Mannsfeld, J. Chen, D. Nordlund, M.F. Toney, J. Huang, and Z. Bao, Ultra-high mobility transparent organic thin film transistors grown by an off-centre spin-coating method, Nat. Commun. 5, 3005 (2014),
https://doi.org/10.1038/ncomms4005
[20] Roll-to-Roll Manufacturing: Process Elements and Recent Advances, eds. J. Greener, G.H. Pearson, and M. Cakmak (Wiley, Hoboken, NJ, 2018),
https://www.wiley.com/en-lt/Roll+to+Roll+Manufacturing:+Process+Elements+and+Recent+Advances-p-9781119162209
[21] S. Logothetidis and A. Laskarakis, in: Solution-Processable Components for Organic Electronic Devices, eds. J. Ulanski, B. Luszczynska, and K. Matyjaszewski (Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany, 2019) pp. 627–653,
https://doi.org/10.1002/9783527813872.ch12
[22] F. Pastorelli, T.M. Schmidt, M. Hösel, R.R. Søndergaard, M. Jørgensen, and F.C. Krebs, The organic power transistor: roll-to-roll manufacture, thermal behavior, and power handling when driving printed electronics, Adv. Eng. Mater. 18, 51 (2016),
https://doi.org/10.1002/adem.201500348
[23] D. Yu, D. Beckelmann, M. Opsölder, B. Schäfer, K. Moh, R. Hensel, P.W. De Oliveira, and E. Arzt, Roll-to-roll manufacturing of micropatterned adhesives by template compression, Materials 12, 97 (2019),
https://doi.org/10.3390/ma12010097
[24] H. Wang, Z. Zeng, P. Xu, L. Li, G. Zeng, R. Xiao, Z. Tang, D. Huang, L. Tang, C. Lai, et al., Recent progress in covalent organic framework thin films: fabrications, applications and perspectives, Chem. Soc. Rev. 48, 488 (2019),
https://doi.org/10.1039/C8CS00376A
[25] C.S. Kim, S. Lee, E.D. Gomez, J.E. Anthony, and Y.-L. Loo, Solvent-dependent electrical characteristics and stability of organic thin-film transistors with drop cast bis(triisopropylsilylethynyl) pentacene, Appl. Phys. Lett. 93, 103302 (2008),
https://doi.org/10.1063/1.2979691
[26] R. Dobužinskas, A. Poškus, M. Viliūnas, V. Jankauskas, M. Daškevičienė, V. Getautis, and K. Arlauskas, Melt spin coating for X‐ray‐sensitive hybrid organic-inorganic layers of small carbazolyl‐containing molecules blended with tungsten, Phys. Status Solidi A 216(23), 1900635 (2019),
https://doi.org/10.1002/pssa.201900635
[27] Y. Zhao, X. Zhao, M. Roders, A. Gumyusenge, A.L. Ayzner, and J. Mei, Melt-processing of complementary semiconducting polymer blends for high performance organic transistors, Adv. Mater. 29, 1605056 (2017),
https://doi.org/10.1002/adma.201605056
[28] D.B. Mitzi, C.D. Dimitrakopoulos, J. Rosner, D.R. Medeiros, Z. Xu, and C. Noyan, Hybrid field-effect transistor based on a low-temperature melt-processed channel layer, Adv. Mater. 14, 1772 (2002),
https://doi.org/10.1002/1521-4095(20021203)14:23<1772::AID-ADMA1772>3.0.CO;2-Y
[29] S. Kasap, J.B. Frey, G. Belev, O. Tousignant, H. Mani, J. Greenspan, L. Laperriere, O. Bubon, A. Reznik, D. DeCrescenzo, K.S. Karim, and J.A. Rowlands, Amorphous and polycrystalline photoconductors for direct conversion flat panel X-ray image sensors, Sensors 11, 5112 (2011),
https://doi.org/10.3390/s110505112
[30] A. Intaniwet, C.A. Mills, M. Shkunov, P.J. Sellin, and J.L. Keddie, Heavy metallic oxide nanoparticles for enhanced sensitivity in semiconducting polymer X-ray detectors, Nanotechnology 23, 235502 (2012),
https://doi.org/10.1088/0957-4484/23/23/235502
[31] Y. Wang, X. Liu, X. Li, F. Zhai, S. Yan, N. Liu, Z. Chai, Y. Xu, X. Ouyang, and S. Wang, Direct radiation detection by a semiconductive metalorganic framework, J. Am. Chem. Soc. 141, 8030 (2019),
https://doi.org/10.1021/jacs.9b01270
[32] Y.C. Kim, K.H. Kim, D.-Y. Son, D.-N. Jeong, J.-Y. Seo, Y.S. Choi, I.T. Han, S.Y. Lee, and N.-G. Park, Printable organometallic perovskite enables large-area, low-dose X-ray imaging, Nature 550, 87 (2017),
https://doi.org/10.1038/nature24032
[33] C.A. Mills, H. Al-Otaibi, A. Intaniwet, M. Shkunov, S. Pani, J.L. Keddie, and P.J. Sellin, Enhanced X-ray detection sensitivity in semiconducting polymer diodes containing metallic nanoparticles, J. Phys. Appl. Phys. 46, 275102 (2013),
https://doi.org/10.1088/0022-3727/46/27/275102
[34] M. Daskeviciene, V. Getautis, J.V. Grazulevicius, A. Stanisauskaite, J. Antulis, V. Gaidelis, V. Jankauskas, and J. Sidaravicius, Crosslinkable carbazolyl-containing molecular glasses for electrophotography, J. Imaging Sci. Technol. 46(5), 467 (2002),
https://www.ingentaconnect.com/content/ist/jist/2002/00000046/00000005/art00010
[35] W.D. Schubert and E. Lassner, Production and characterization of hydrogen-reduced submicron tungsten powders - Part 1: State of the art in research, production and characterization of raw materials and tungsten powders, Int. J. Refract. Met. Hard Mater. 10, 133 (1991),
https://doi.org/10.1016/0263-4368(91)90017-I
[36] S. Kutkevicius, A. Stanisauskaite, V. Getautis, A. Railaite, and S. Uss, Synthesis of carbazole containing organic photosemiconductors using dimercapto compounds, J. Prakt. Chem., 337, 315 (1995),
https://doi.org/10.1002/prac.19953370165
[37] J. Heller, D. Lyman, and W. Hewett, The synthesis and polymerization studies of some higher homologues of 9-vinylcarbazole, Makromol. Chem. 73, 48–59 (1964),
https://doi.org/10.1002/macp.1964.020730104
[38] Average Energy Required to Produce an Ion Pair, Report, ICRU-31 (Washington DC, 1979),
https://icru.org/home/reports/average-energy-required-to-produce-an-ion-pair-report-31
[39] S.T. Perkins, D.E. Cullen, and S.M. Seltzer, Tables and Graphs of Electron-Interaction Cross Sections from 10 eV to 100 GeV Derived from the LLNL Evaluated Electron Data Library (EEDL), Z = 1–100, Technical Report, UCRL-50400-Vol. 31, 5691165 (1991),
https://doi.org/10.2172/5691165
[40] Y.-K. Kim, K.K. Irikura, M.E. Rudd, M.A. Ali, P.M. Stone, et. al., Electron-Impact Cross Section for Ionization and Excitation, NIST Standard Reference Database 107 (National Institute of Standards and Technology, 1997),
https://dx.doi.org/10.18434/T4KK5C
[41] D.E. Cullen, J.H. Hubbell, and L. Kissel, EPDL97: The Evaluated Photo Data Library '97 Version, Report, UCRL-50400-Vol. 6-Rev. 5, 295438 (1997),
https://doi.org/10.2172/295438
[42] S.T. Perkins, D.E. Cullen, M.H. Chen, J. Rathkopf, J. Scofield, and J.H. Hubbell, Tables and Graphs of Atomic Subshell and Relaxation Data Derived from the LLNL Evaluated Atomic Data Library (EADL), Z = 1–100, Report, UCRL-50400-Vol. 30, 10121422 (1991),
https://doi.org/10.2172/10121422
[43] A. Poškus, Monte Carlo estimation of average energy required to produce an ion pair in noble gases by electrons with energies from 1 keV to 100 MeV, J. Nucl. Sci. Technol. 52, 675 (2015),
https://doi.org/10.1080/00223131.2014.974710