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Preparation of Se-doped polyaniline emeraldine base films
Synthetic Metals 139 (2003) 321–325
Preparation of Se-doped polyaniline emeraldine base films Edward Bormashenko a,∗ , Roman Pogreb a , Semion Sutovski a , Alexander Shulzinger a , Avigdor Sheshnev a , Alexander Gladkikh b a
The Laboratory of Polymer and Composite Materials, The Research Institute, The College of Judea and Samaria, Ariel 44837, Israel b Wolfson Applied Materials Research Center, Tel Aviv University, Tel Aviv 69978, Israel Received 7 September 2002; received in revised form 24 February 2003; accepted 19 March 2003
Abstract Our letter focuses on the preparation of polyaniline emeraldine base films doped with selenium. PANI EB and Se were dissolved in dimethylsulfoxide. Thin films of selenium-doped PANI EB were obtained by spin-coating of Si and ZnSe substrates with a PANI EB + Se solution in DMSO. We studied the distribution of the selenium in the PANI EB films using time-of-flight secondary ion mass spectrometry (TOF-SIMS). The IR spectra of these thin films were obtained with an FT-IR spectrometer. © 2003 Elsevier Science B.V. All rights reserved. Keywords: Polyaniline; Selenium; Dimethylsufoxide; Doping; TOF-SIMS; Infrared; Spectrum
1. Introduction Polymers containing selenium have promising properties as organic superconductors [1,2]. For example, tetraselensulfalene and other selenium-containing organic compounds have displayed metal-to-semiconductor (insulator) transition at low temperatures. PANI derivatives doped with selenium may be of interest both from the point of view of understanding the fundamental processes, and with a view to possible applications such as preparing of quantum dots of semiconductors dispersed within PANI matrix [3,4]. However, selenium-containing PANI EB has not been prepared previously. The essentials of doping of PANI and PANI derivatives were explained by Heeger [6], McDiarmida and Epstein [5]. The study of doping PANI with non-organic dopants such as palladium and platinum compounds is still in intensive progress [7,8]. Dopants such as TiO2 , FeCl4, vanadium, tungsten and molybdic-containing acids have also been studied [9,10]. The IR spectra of PANI derivatives have been thoroughly investigated. IR spectroscopy has been used to analyze the effect of doping PANI [8,11–15]. The infrared spectrum of selenium was studied by Stephens [16]. The infrared spectra of selenium-containing organic compounds ∗ Corresponding author. Tel.: +972-3-906-61-34; fax: +972-3-936-68-73. E-mail address: [email protected] (E. Bormashenko).
were investigated recently [17]. It was shown by Gal and Hodes [18] that Se demonstrates solubility in DMSO. This fact allows the preparation of Se-doped PANI EB films.
2. Experimental The polyaniline emeraldine base and dimethylsulfoxide were supplied by Sigma–Aldrich. ZnSe plates were supplied by Eksma Ltd. (parameters of the plates: transmission band 0.6–22 m, refractive index in the band 8–13 m, n = 2.417–2.385). Se in the form of irregularly shaped pellets with a diameter of 2–3 mm (purity > 99.995%) was supplied by Sigma–Aldrich. First 0.1% solution of PANI EB in DMSO were prepared, then Se pellets were added to the solution and stirred under t = 60 ◦ C for 24 h. The Se was present in excess in the solution; Gal and Hodes noted that dissolved Se concentration in DMSO equals 5 mM [16]. Se is distinguished by its toxic properties and DMSO is readily absorbed through the skin, so care should be taken when working with this solution. Then Si and ZnSe substrates were coated with the obtained solutions by the spin-casting process and exposed to vacuum evaporation. The absorbance spectra of coated with PANI EB and Se-doped PANI EB ZnSe substrates in the middle and far IR bands (400–7500 cm−1 ) were established using a Bruker Vector 22 FT-IR spectrometer. Coated Si
0379-6779/$ – see front matter © 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0379-6779(03)00182-6
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E. Bormashenko et al. / Synthetic Metals 139 (2003) 321–325
Fig. 1. The part of the mass spectrum obtained on the PANI EB film containing Se (upper graph) and representing all isotopes of Se (74 Se, 78 Se, 80 Se, 82 Se). The lower graph is enlarged image of 80 Se mass peak (most intensive).
76 Se, 77 Se,
Fig. 2. Shallow depth profile of the Se-doped PANI EB film deposited onto Si substrate. The part of the profile (from 25 to 50 s of sputter time) was used for calculation of the surface concentration of Se in the sample, which was estimated as 5 × 1011 atoms/cm2 .
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323
substrates were studied by time-of-flight secondary ion mass spectrometry (TOF-SIMS), using a TRIFT-2 mass spectrometer produced by Physical Electronics Co.
3. Results and discussion Si substrates were coated with the prepared solution of PANI EB and Se in DMSO (films with a thickness of 100–400 nm were obtained) and studied by TOF-SIMS, which indicated the presence of Se in PANI EB films (see Figs. 1–3). Concentration of selenium in the film was estimated with the use of shallow depth profiling data (Fig. 2). The part of the profile corresponding to a very near surface region in Si substrate was chosen and RSF (relative sensitivity factor) for Si matrix was applied to calculate the Se concentration on the Si surface as 5 × 1011 atoms/cm2 . Surface mapping (Fig. 3) of the samples revealed that Se forms clusters with an average dimension of ∼10 m. In addition to such relatively large-sized clusters TOF-SIMS mapping indicated the presence of small-sized submicron dots of Se distributed uniformly in the films (Fig. 3), which may be of great interest with a view to selenium quantum
Fig. 3. TOF-SIMS image in Se negative ions of the Se-doped PANI EB films (light shapes—clusters of Se, dispersed in PANI EB matrix).
Fig. 4. Optical bench used for controlling vacuum evaporation of Se-doped PANI EB films.
dots study. Concentration of selenium in clusters is one order of the magnitude higher than the average concentration of selenium in the PANI EB films. The concentration of Se in obtained PANI EB films was relatively small (estimated roughly as 1–10 ppm), so significant changes in the IR spectra could not be anticipated. Nevertheless, we studied the IR spectra of the Se-doped PANI EB films. ZnSe substrates were spin-coated with a SE + PANI EB solution in DMSO and exposed to vacuum evaporation. Evaporation of the solvent from the Se-doped PANI EB films on ZnSe substrates was carried out under vacuum on an optical bench. This allowed us to monitor evaporation of the solvent from the films with IR spectroscopy. The bench is described in Fig. 4. Absorption spectra of the PANI EB coating were taken when vacuumed using a FT-IR spectrometer Bruker Vector 22. Evaporation of the solvent was accompanied by changes in the absorption spectra. The termination of such change is indicative of the net removal of the solvent from the PANI EB film. We showed that IR spectra in the mid-infrared region of pure PANI EB and Se-doped PANI EB are identical (see Fig. 5). We did not observe splitting or displacement of PANI EB peaks described by Quillard et al. [15]. This fact can be explained easily: selenium and selenium-containing organic compounds demonstrate absorption in far-infrared band only [16,17]. Se–Se stretching mode is characterized by absorption at 285 cm−1 , and Se–C stretching vibration demonstrates absorption at 452 cm−1 . We observed a new peak at 872 cm−1 in the Se-doped PANI EB films, that we assign to be inherent (see Fig. 6). Pure PANI EB does not demonstrate absorption at this frequency. It is suggested that the 872 cm−1 frequency is an overtone of Se–Se stretching vibration, which has its main absorption peak at 285 cm−1 . Exhaustive information about IR absorption spectra and chemical structure of the Se-doped PANI films could be obtained using spectrometric equipment, which provides spectral data in far IR band (400–200 cm−1 ). We are currently investigating the far-infrared region of the IR spectra of Se-doped PANI EB films.
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Fig. 5. Infrared absorbance spectrum (absorbance, a.u. vs. wavenumber) in 1100–1600 cm−1 of (1) PANI emeraldine base and (2) Se-doped PANI emeraldine base.
Fig. 6. Infrared absorbance spectrum (absorbance, a.u. vs. wavenumber) in 800–900 cm−1 of (1) PANI emeraldine base and (2) Se-doped PANI emeraldine base.
4. Conclusions PANI EB films doped with Se were prepared. The distribution of the dopant in the PANI EB films was studied using time-of-flight secondary ion mass spectrometry. The IR spectra of the SE-doped PANI EB films were investigated with FT-IR spectroscopy.
Acknowledgements This work was supported by the Israel Ministry of Science, Culture and Sport (Project No. 1461-2-00) and the
Israel Ministry of Absorption. The authors are thankful to Professor Alexander Voronel for his generous support of our experimental activity and fruitful discussions.
References [1] L. Balicas, K. Behnia, W. Kang, P. Auban-Senzier, E. Canadell, D. Jerome, M. Ribault, J.M. Fabre, Adv. Mater. 6 (10) (1994) 762. [2] T. Jigami, K. Takimiya, Y. Aso, T. Otsubo, Synth. Met. 102 (1999) 1714. [3] K. Wundke, S. Potting, J. Auxier, A. Shulzgen, N. Peyghambarian, N.F. Borrelli, Appl. Phys. Lett. 76 (1) (2000) 10.
E. Bormashenko et al. / Synthetic Metals 139 (2003) 321–325 [4] A.A. Lipovski, E.V. Kolobkova, A. Olkhovets, V.D. Petrikov, F. Wise, Physica E 5 (3) (1999) 157. [5] A.G. McDiarmida, J.M. Epstein, Synth. Met. 69 (1995) 85. [6] A.J. Heeger, Synth. Met. 125 (2002) 23. [7] J.W. Sobczak, A.E. Sobczak, A. Kosiskia, A. Biliskia, J. Alloys Compd. 328 (1–2) (2001) 132. [8] A. Drelinkievicz, M. Hasik, M. Choczyski, Mater. Res. Bull. 33 (15) (1998) 739. [9] S.J. Su, N. Kuramoto, Synth. Met. 114 (2000) 147. [10] J. Wang, M.X. Wan, Synth. Met. 101 (1999) 846. [11] J. Gong, Z.M. Su, Z.M. Dai, R.S. Wang, L.Y. Qu, Synth. Met. 101 (1999) 751.
325
[12] M. Wan, S. Li, J. Li, Solid State Commun. 97 (6) (1996) 527. [13] A. Dhanabalan, S.S. Twalar, A.Q. Contractor, N.P. Kumar, S.N. Narang, S.S. Major, K.P. Muthe, J.C. Vyas, J. Mater. Sci. Lett. 18 (8) (1999) 63. [14] M.C. Bernard, T.B. Vu, S. Cordoba-de-Torresi, A. Hugot-Le-Goff, Proc. SPIE 3145 (1997) 376. [15] S. Quillard, G. Louarn, S. Lefrant, A.G. Macdiarmid, Phys. Rev. B 50 (17) (1994) 12496. [16] R.B. Stephens, J. Appl. Phys. 49 (12) (1978) 5855. [17] Z.V. Popovic, V.A. Ivanov, O.P. Khoung, T. Nakamura, G. Saito, V.V. Moshchalkov, Synth. Met. 124 (2001) 421. [18] D. Gal, G. Hodes, J. Electrochem. Soc. 147 (5) (2000) 1825.
Preparation of Se-doped polyaniline emeraldine base films Edward Bormashenko a,∗ , Roman Pogreb a , Semion Sutovski a , Alexander Shulzinger a , Avigdor Sheshnev a , Alexander Gladkikh b a
The Laboratory of Polymer and Composite Materials, The Research Institute, The College of Judea and Samaria, Ariel 44837, Israel b Wolfson Applied Materials Research Center, Tel Aviv University, Tel Aviv 69978, Israel Received 7 September 2002; received in revised form 24 February 2003; accepted 19 March 2003
Abstract Our letter focuses on the preparation of polyaniline emeraldine base films doped with selenium. PANI EB and Se were dissolved in dimethylsulfoxide. Thin films of selenium-doped PANI EB were obtained by spin-coating of Si and ZnSe substrates with a PANI EB + Se solution in DMSO. We studied the distribution of the selenium in the PANI EB films using time-of-flight secondary ion mass spectrometry (TOF-SIMS). The IR spectra of these thin films were obtained with an FT-IR spectrometer. © 2003 Elsevier Science B.V. All rights reserved. Keywords: Polyaniline; Selenium; Dimethylsufoxide; Doping; TOF-SIMS; Infrared; Spectrum
1. Introduction Polymers containing selenium have promising properties as organic superconductors [1,2]. For example, tetraselensulfalene and other selenium-containing organic compounds have displayed metal-to-semiconductor (insulator) transition at low temperatures. PANI derivatives doped with selenium may be of interest both from the point of view of understanding the fundamental processes, and with a view to possible applications such as preparing of quantum dots of semiconductors dispersed within PANI matrix [3,4]. However, selenium-containing PANI EB has not been prepared previously. The essentials of doping of PANI and PANI derivatives were explained by Heeger [6], McDiarmida and Epstein [5]. The study of doping PANI with non-organic dopants such as palladium and platinum compounds is still in intensive progress [7,8]. Dopants such as TiO2 , FeCl4, vanadium, tungsten and molybdic-containing acids have also been studied [9,10]. The IR spectra of PANI derivatives have been thoroughly investigated. IR spectroscopy has been used to analyze the effect of doping PANI [8,11–15]. The infrared spectrum of selenium was studied by Stephens [16]. The infrared spectra of selenium-containing organic compounds ∗ Corresponding author. Tel.: +972-3-906-61-34; fax: +972-3-936-68-73. E-mail address: [email protected] (E. Bormashenko).
were investigated recently [17]. It was shown by Gal and Hodes [18] that Se demonstrates solubility in DMSO. This fact allows the preparation of Se-doped PANI EB films.
2. Experimental The polyaniline emeraldine base and dimethylsulfoxide were supplied by Sigma–Aldrich. ZnSe plates were supplied by Eksma Ltd. (parameters of the plates: transmission band 0.6–22 m, refractive index in the band 8–13 m, n = 2.417–2.385). Se in the form of irregularly shaped pellets with a diameter of 2–3 mm (purity > 99.995%) was supplied by Sigma–Aldrich. First 0.1% solution of PANI EB in DMSO were prepared, then Se pellets were added to the solution and stirred under t = 60 ◦ C for 24 h. The Se was present in excess in the solution; Gal and Hodes noted that dissolved Se concentration in DMSO equals 5 mM [16]. Se is distinguished by its toxic properties and DMSO is readily absorbed through the skin, so care should be taken when working with this solution. Then Si and ZnSe substrates were coated with the obtained solutions by the spin-casting process and exposed to vacuum evaporation. The absorbance spectra of coated with PANI EB and Se-doped PANI EB ZnSe substrates in the middle and far IR bands (400–7500 cm−1 ) were established using a Bruker Vector 22 FT-IR spectrometer. Coated Si
0379-6779/$ – see front matter © 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0379-6779(03)00182-6
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E. Bormashenko et al. / Synthetic Metals 139 (2003) 321–325
Fig. 1. The part of the mass spectrum obtained on the PANI EB film containing Se (upper graph) and representing all isotopes of Se (74 Se, 78 Se, 80 Se, 82 Se). The lower graph is enlarged image of 80 Se mass peak (most intensive).
76 Se, 77 Se,
Fig. 2. Shallow depth profile of the Se-doped PANI EB film deposited onto Si substrate. The part of the profile (from 25 to 50 s of sputter time) was used for calculation of the surface concentration of Se in the sample, which was estimated as 5 × 1011 atoms/cm2 .
E. Bormashenko et al. / Synthetic Metals 139 (2003) 321–325
323
substrates were studied by time-of-flight secondary ion mass spectrometry (TOF-SIMS), using a TRIFT-2 mass spectrometer produced by Physical Electronics Co.
3. Results and discussion Si substrates were coated with the prepared solution of PANI EB and Se in DMSO (films with a thickness of 100–400 nm were obtained) and studied by TOF-SIMS, which indicated the presence of Se in PANI EB films (see Figs. 1–3). Concentration of selenium in the film was estimated with the use of shallow depth profiling data (Fig. 2). The part of the profile corresponding to a very near surface region in Si substrate was chosen and RSF (relative sensitivity factor) for Si matrix was applied to calculate the Se concentration on the Si surface as 5 × 1011 atoms/cm2 . Surface mapping (Fig. 3) of the samples revealed that Se forms clusters with an average dimension of ∼10 m. In addition to such relatively large-sized clusters TOF-SIMS mapping indicated the presence of small-sized submicron dots of Se distributed uniformly in the films (Fig. 3), which may be of great interest with a view to selenium quantum
Fig. 3. TOF-SIMS image in Se negative ions of the Se-doped PANI EB films (light shapes—clusters of Se, dispersed in PANI EB matrix).
Fig. 4. Optical bench used for controlling vacuum evaporation of Se-doped PANI EB films.
dots study. Concentration of selenium in clusters is one order of the magnitude higher than the average concentration of selenium in the PANI EB films. The concentration of Se in obtained PANI EB films was relatively small (estimated roughly as 1–10 ppm), so significant changes in the IR spectra could not be anticipated. Nevertheless, we studied the IR spectra of the Se-doped PANI EB films. ZnSe substrates were spin-coated with a SE + PANI EB solution in DMSO and exposed to vacuum evaporation. Evaporation of the solvent from the Se-doped PANI EB films on ZnSe substrates was carried out under vacuum on an optical bench. This allowed us to monitor evaporation of the solvent from the films with IR spectroscopy. The bench is described in Fig. 4. Absorption spectra of the PANI EB coating were taken when vacuumed using a FT-IR spectrometer Bruker Vector 22. Evaporation of the solvent was accompanied by changes in the absorption spectra. The termination of such change is indicative of the net removal of the solvent from the PANI EB film. We showed that IR spectra in the mid-infrared region of pure PANI EB and Se-doped PANI EB are identical (see Fig. 5). We did not observe splitting or displacement of PANI EB peaks described by Quillard et al. [15]. This fact can be explained easily: selenium and selenium-containing organic compounds demonstrate absorption in far-infrared band only [16,17]. Se–Se stretching mode is characterized by absorption at 285 cm−1 , and Se–C stretching vibration demonstrates absorption at 452 cm−1 . We observed a new peak at 872 cm−1 in the Se-doped PANI EB films, that we assign to be inherent (see Fig. 6). Pure PANI EB does not demonstrate absorption at this frequency. It is suggested that the 872 cm−1 frequency is an overtone of Se–Se stretching vibration, which has its main absorption peak at 285 cm−1 . Exhaustive information about IR absorption spectra and chemical structure of the Se-doped PANI films could be obtained using spectrometric equipment, which provides spectral data in far IR band (400–200 cm−1 ). We are currently investigating the far-infrared region of the IR spectra of Se-doped PANI EB films.
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E. Bormashenko et al. / Synthetic Metals 139 (2003) 321–325
Fig. 5. Infrared absorbance spectrum (absorbance, a.u. vs. wavenumber) in 1100–1600 cm−1 of (1) PANI emeraldine base and (2) Se-doped PANI emeraldine base.
Fig. 6. Infrared absorbance spectrum (absorbance, a.u. vs. wavenumber) in 800–900 cm−1 of (1) PANI emeraldine base and (2) Se-doped PANI emeraldine base.
4. Conclusions PANI EB films doped with Se were prepared. The distribution of the dopant in the PANI EB films was studied using time-of-flight secondary ion mass spectrometry. The IR spectra of the SE-doped PANI EB films were investigated with FT-IR spectroscopy.
Acknowledgements This work was supported by the Israel Ministry of Science, Culture and Sport (Project No. 1461-2-00) and the
Israel Ministry of Absorption. The authors are thankful to Professor Alexander Voronel for his generous support of our experimental activity and fruitful discussions.
References [1] L. Balicas, K. Behnia, W. Kang, P. Auban-Senzier, E. Canadell, D. Jerome, M. Ribault, J.M. Fabre, Adv. Mater. 6 (10) (1994) 762. [2] T. Jigami, K. Takimiya, Y. Aso, T. Otsubo, Synth. Met. 102 (1999) 1714. [3] K. Wundke, S. Potting, J. Auxier, A. Shulzgen, N. Peyghambarian, N.F. Borrelli, Appl. Phys. Lett. 76 (1) (2000) 10.
E. Bormashenko et al. / Synthetic Metals 139 (2003) 321–325 [4] A.A. Lipovski, E.V. Kolobkova, A. Olkhovets, V.D. Petrikov, F. Wise, Physica E 5 (3) (1999) 157. [5] A.G. McDiarmida, J.M. Epstein, Synth. Met. 69 (1995) 85. [6] A.J. Heeger, Synth. Met. 125 (2002) 23. [7] J.W. Sobczak, A.E. Sobczak, A. Kosiskia, A. Biliskia, J. Alloys Compd. 328 (1–2) (2001) 132. [8] A. Drelinkievicz, M. Hasik, M. Choczyski, Mater. Res. Bull. 33 (15) (1998) 739. [9] S.J. Su, N. Kuramoto, Synth. Met. 114 (2000) 147. [10] J. Wang, M.X. Wan, Synth. Met. 101 (1999) 846. [11] J. Gong, Z.M. Su, Z.M. Dai, R.S. Wang, L.Y. Qu, Synth. Met. 101 (1999) 751.
325
[12] M. Wan, S. Li, J. Li, Solid State Commun. 97 (6) (1996) 527. [13] A. Dhanabalan, S.S. Twalar, A.Q. Contractor, N.P. Kumar, S.N. Narang, S.S. Major, K.P. Muthe, J.C. Vyas, J. Mater. Sci. Lett. 18 (8) (1999) 63. [14] M.C. Bernard, T.B. Vu, S. Cordoba-de-Torresi, A. Hugot-Le-Goff, Proc. SPIE 3145 (1997) 376. [15] S. Quillard, G. Louarn, S. Lefrant, A.G. Macdiarmid, Phys. Rev. B 50 (17) (1994) 12496. [16] R.B. Stephens, J. Appl. Phys. 49 (12) (1978) 5855. [17] Z.V. Popovic, V.A. Ivanov, O.P. Khoung, T. Nakamura, G. Saito, V.V. Moshchalkov, Synth. Met. 124 (2001) 421. [18] D. Gal, G. Hodes, J. Electrochem. Soc. 147 (5) (2000) 1825.