Langmuir 2008, 24, 9825-9831
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Patterning of Conducting Polymers Using Charged Self-Assembled Monolayers Mi-Hee Jung and Hyoyoung Lee* National CreatiVe Research InitiatiVe, Center for Smart Molecular Memory, IT ConVergence Technology Research DiVision, IT ConVergence and Components Laboratory, Electronics and Telecommunications Research Institute (ETRI), 161 Gajeong-dong, Yuseong-gu, Daejeon 305-350 South Korea ReceiVed May 7, 2008. ReVised Manuscript ReceiVed June 12, 2008 We introduce a new approach to pattern conducting polymers by combining oppositely charged conducting polymers on charged self-assembled monolayers (SAMs). The polymer resist pattern behaves as a physical barrier, preventing the formation of SAMs. The patterning processes were carried out using commercially available conducting polymers: a negatively charged PEDOT/PSS (poly(3,4-ethylene-dioxythiophene)/poly(4-stylenesulphonic acid)) and a positively charged polypyrrole (PPy). A bifunctional NH2 (positively charged) or COOH (negatively charged) terminated alkane thiol or silane was directly self-assembled on a substrate (Au or SiO2). A suspension of the conducting polymers (PEDOT/PSS and PPy) was then spin-coated on the top surface of the SAMs and allowed to adsorb on the oppositely charged SAMs via an electrostatic driving force. After lift-off of the polymer resist, i.e., poly(methyl methacrylate, PMMA), using acetone, the conducting polymers remained on the charged SAMs surface. Optical microscopy, Auger electron spectroscopy, and atomic force microscopy reveal that the prepared nanolines have low line edge roughness and high line width resolution. Thus, conducting polymer patterns with high resolution could be produced by simply employing charged bifunctional SAMs. It is anticipated that this versatile new method can be applied to device fabrication processes of various nano- and microelectronics.
1. Introduction Conductive polymers offer several advantages over metals and conventional inorganic semiconductors, including facile processing and ease of adjustment of the conductivity by changing the dopant and the doping level. They have potential applications in the fabrication of organic light-emitting diodes (LEDs), chemical and biological sensors, polymer, organic, and molecular electronic devices, and mechanical actuators and transducers. For possible applications, particularly organic electronics including flexible devices, the patterning of conducting polymers with feature size ranging from less than 100 nm to 100 µm is important. Considerable efforts have been directed toward patterning conducting polymers such as PEDOT/PSS (poly(3,4-ethylenedioxythiophene)/poly(4-stylenesulphonic acid)) and polypyrrole via a variety of techniques, for example, soft lithography,1–4 inkjet printing,5,6 photochemical patterning by photolithography,7–11 dip pen lithography,12,13 and nanoimprint lithography.14–16 * Author to whom correspondence should be addressed. E-mail:
[email protected]. Phone: +82-42-860-1165. Fax: +82-42-860-3932. (1) Granlund, T.; Nyberg, T.; Roman, L. S.; Svensson, M.; Ingana¨s, O. AdV. Mater. 2000, 12, 269–273. (2) Beh, W. S.; Kim, I. T.; Qin, D.; Xia, Y.; Whitesides, G. M. AdV. Mater. 1999, 11, 1038–1041. (3) Parashkov, R.; Becker, E.; Riedl, T.; Johannes, H. H.; Kowalsky, W. AdV. Mater. 2005, 17, 1523–1527. (4) Dawen, L.; Guo, L. J. Appl. Phys. Lett. 2006, 88, 063513. (5) Jang, J.; Ha, J.; Cho, J. AdV. Mater. 2007, 19, 1772–1775. (6) Yoshioka, Y.; Jabbour, G. E. AdV. Mater. 2006, 18, 1307–1312. (7) Renak, M. L.; Bazan, G. C.; Roitman, D. AdV. Mater. 1997, 9, 392–395. (8) Schanze, K. S.; Bergstedt, T. S.; Hauser, B. T. AdV. Mater. 1996, 8, 531– 534. (9) Venugopal, G.; Quan, X.; Johnson, G. E.; Houlihan, F. M.; Chin, E.; Nalamasu, O. Chem. Mater. 1995, 7, 271–276. (10) Lowe, J.; Holdcroft, S. Macromolecules 1995, 28, 4608–4616. (11) Drury, C. J.; Mutsaers, C. M. J.; Hart, C. M.; Matters, M.; de Leeuw, D. M. Appl. Phys. Lett. 1998, 73, 108–110. (12) Lim, J.-H.; Mirkin, C. A. AdV. Mater. 2002, 14, 1474–1477. (13) Maynor, B. W.; Filocamo, S. F.; Grinstaff, M. W.; Liu, J. J. Am. Chem. Soc. 2002, 124, 522–523. (14) Behl, M.; Seekamp, J.; Zankovych, S.; Torres, C. M. S.; Zentel, R.; Ahopelto, J. AdV. Mater. 2002, 14, 588–591.
Among the various methods, one of the simplest methods for patterning metal lines with high fidelity and fine geometries is a lift-off technique combined with lithographic processes, which allows for the direct use of commercially available conducting polymers. To date, however, this approach has proved incompatible with conducting polymer patterning owing to poor adhesion between the polymers and substrate. In an effort to improve the adhesion of the conducting polymer film on the surface of the substrate, Dong et al. employed a copolymer. The adhesion of the copolymer was tuned by adjusting the fraction of the two comprising monomers, pyrrole and pysilane. However, as pyrrole was added to the copolymer to increase the conductivity of the film, the adhesion decreased.17 Liang et al. described direct patterning of conjugated polymers on solid substrates by microcontact printing. They prepared an amine-containing poly(p-phenylene vinylene) and then printed onto the surface with self-assembled monolayers (SAMs) terminated with carboxylic anhydrides to form an amide bond between the amine and carboxylic anhydride. The covalent bonding of the conducting polymer films to substrates can prevent delamination. However, the film conductivity was very low due to the very thin film thickness.18 Im et al. demonstrated a one-step process for directly grafting conducting polymers onto flexible polymer substrates containing aromatic groups. They did not use linkers such as silane or thiol functional groups but relied on covalent bonding between the conducting polymer film and an aromatic moiety of the polymer substrate that was activated with Friedel-Craft catalysts.19 (15) Makela, T.; Haatainen, T.; Ahopelto, J.; Isotalo, H. J. Vac. Sci. Technol., B 2001, 19, 487–489. (16) Reano, R. M.; Kong, Y. P.; Low, H. Y.; Tan, L.; Wang, F.; Pang, S. W.; Yee, A. F. J. Vac. Sci. Technol., B 2004, 22, 3294–3299. (17) Dong, B.; Zhong, D. Y.; Chi, L. F.; Fuchs, H. AdV. Mater. 2005, 17, 2736–2741. (18) Liang, Z.; Li, K.; Wang, Q. Langmuir 2003, 19, 5555–5558. (19) Im, S. G.; Yoo, P. J.; Hammond, P. T.; Gleason, K. K. AdV. Mater. 2007, 19, 2863–2867.
10.1021/la8014207 CCC: $40.75 2008 American Chemical Society Published on Web 07/29/2008
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Scheme 1. Schematic Illustration of Conducting Polymer Patterning on Bifunctional SAMsa
a Conducting polymer patterns on SAMs formed at the uncovered regions of the polymer resist template, followed by polymer removal: (a) PPy patterning process on MHDA SAM; (b) PEDOT/PSS patterning process on APTS SAM.
However, the patterning process using Friedel-Craft catalysts is limited to substrates having aromatic groups. In the present work, we introduce a new and simple conducting polymer patterning approach that employs bifunctional groups of SAMs. Positively or negatively charged SAMs are used as an anchoring group and can combine with negatively or positively charged conducting polymers through an electrostatic interaction. This leads to greatly improved adhesion between the polymers and the SAMs attached on the substrate. With the use of an in situ process entailing a lift-off step, the feature size of the conducting polymer was as small as 300 nm in width. The patterning of the conducting polymers using the bifunctional group of SAMs yielded polymer films that showed greater adherence to the substrate while retaining sufficiently high conductivity for use as submicrometer-sized electrodes. To the best of our knowledge, this is the first report on the direct use of commercially available PEDOT/PSS and polypyrrol (PPy) without pretreatment in the fabrication of nanosized electrodes via patterning of conducting polymers.
2. Experimental Section 2.1. Compounds. 16-Mercaptohexadecanoic acid (MHDA), 3-aminopropyltriethoxysilane (APTS), and PPy (doped 5 wt % solution in water) were purchased from Aldrich. Poly(methyl methacrylate) (PMMA) (weight-average molecular weight, MW 495 kDa, A6) and poly(3,4-ethylene-dioxythiophene) stabilized with poly(4-stylenesulphonic acid) (PEDOT/PSS, 1:2.5) were purchased from Microchem and Baytron P Co., respectively. All chemicals were used without further purification. Silicon wafers with a 300 nm
thermally oxidized SiO2 layer were purchased from Siltron Inc. (Republic of Korea). 2.2. Electron Beam Lithography. To pattern the conducting polymers on the substrates (Au or SiO2), Au substrates were prepared by evaporating a 5 nm thick Ti layer followed by deposition of a 20 nm Au layer on silicon oxide substrates under a high-vacuum condition (∼2 × 10-7 Torr). For the e-beam writing, an e-beam resist, PMMA, was spun on the Au and SiO2 substrate, respectively, to give a total thickness of about 300 nm. The e-beam resists coated on the substrates were patterned subsequently at 100 kV with line doses between 800 and 1200 µC/ cm2, and the samples were then developed with 1:3 methyl isobutyl ketone/2-propanol (MIBK/IPA) for 3 min. After polymer patterns were created by electron beam lithography (EBL), the residual layer was removed by O2 plasma. The quality of the polymer pattern was checked by Ti lift-off. 2.3. Nanoimprint Lithography. The imprint processes were performed using an IMPRIO 100 (Moleculr Imprint Inc., MII). We spin-coated a planarization layer of PMMA (950K, A2) to a thickness of 65 nm on the Au and SiO2 substrates, respectively. The first layer, PMMA, of the double resists serves not only as a plenary layer but also a residual layer after the imprint process. Hence, we treat the PMMA surface with oxygen plasma to decrease the thickness of PMMA to 25 nm. The treatment of the PMMA surface with oxygen plasma also changed it to a hydrophilic surface, resulting in increased adhesion force between the PMMA surface and the second later, a Si-containing resin. A Si-containing acrylate-based monomer mixture supplied by MII was dispensed on the PMMA surface in a dropon-demand manner using a jet-type dispenser. The quartz mold was lowered to a resin-dispensed surface until the resin completely filled the mold geometry. After the resist was cured via exposure to UV (λ ) 365 nm) light, the mold was separated from the cured resist.
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Figure 1. Optical microscopy images of PEDOT/PSS: (a) 50 µm and (b) 2 µm PEDOT/PSS patterns formed on positively charged amino alkyl SAM/SiO2/Si. AFM images: (c) Two-dimensional (2D) and (d) three-dimensional (3D) PEDOT/PSS morphologies of (b).
Figure 2. Auger elements, S and Si, maps collected at the PEDOT/PSS region on SiO2 with separate scans in sequence, (a and c) showing higher S than Si counts in the PEDOT/PSS region (light area) in the case of the sulfur element scanning and (b and d) showing less Si (gray area) in terms of the silicon element scanning within the same substrate region. (c and d) Line scans for S and Si (S at 156.50 eV), respectively.
Finally, the PMMA residual layer in the compressed area was removed via anisotropic reactive ion etching, thereby exposing the substrate surface.
2.4. Patterning Process of the Conducting Polymers. The patterned PMMA on the silicon oxide surfaces was immersed in 1 mM APTS silane dissolved in ethanol, whereas the patterned PMMA
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Figure 3. Optical microscopy images of PPy: (a) 50 µm and (b) 2 µm PPy patterns formed on negatively charged carboxylate alkyl SAM/Au. AFM images: (c) 2D and (d) 3D of (b).
Figure 4. Optical microscopy images after ultrasonification agitation for 30 min during the lift-off process: (a) PPy patterned on Au without SAM and (b) PPy patterned on MHDA SAM.
on Au was immersed in 1 mM MHDA in ethanol for 18 h. The PEDOT/PSS was diluted to a 2:1 ratio of PEDOT/PSS to ethylene glycol. The PPy doped with 5 wt % in water was further diluted to a 1:3 ratio of PPy to water for the patterning process. PEDOT/PSS and PPy were spin-coated on the surface of the APTS and MHDA SAMs at 2500 rpm for 25 s, respectively. To remove the residual solvents, the conducting polymers coated on the substrate were baked on a hot plate at 90 °C for 1 h. The substrates were immersed into acetone, a polymer remover, for 10 min in an ultrasonic bath to detach the polymer resist, PMMA, resulting in the formation of nanolines of the conducting polymers. 2.5. Surface Analysis of the Patterned Conducting Polymers. Auger electron spectroscopy (AES) can be used for the investigation of surface composition. For the AES experiments, an Auger LEG 500 electron gun was operated at a voltage of 10 keV. The beam current was adjusted to give the best sensitivity and, at the same
time, avoid detector saturation. The samples were oriented perpendicular to the electron beam, whereas the ion beam incidence angle was 28° with respect to the normal sample. The AES data were acquired in integrated mode N(E) with a primary beam energy of 3 keV and a sample current of 33 nA. UV-vis spectra were obtained with a U-3501 UV-vis-NIR spectrophotometer (Hitachi, Japan). Scanning electron microscopy (SEM) images were obtained with a field emission scanning electron microscope (FEI, model: Sirion, Netherlands). Atomic force microscopy (AFM) measurements were carried out on a Multimode XE-100 instrument (PSIA Inc.) operating in noncontact mode with silicon cantilevers (resonance frequency in a range of 204-259 kHz, an integrated Si tip with a typical radius of 10 nm curvature). The sheet resistances of the films were measured by a four-point probe method. Optical microscopic images were collected using a Nikon Eclipse ME600L microscope with a chargecoupled device (CCD) camera system.
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Figure 5. ATM images of PEDOT/PSS nanolines on APTS SAM of SiO2/Si substrates: (a) 2D and (b) 3D image. The width of the nanoline is about 500 nm with a separation of 350 nm, and the height is 50 nm.
3. Results and Discussion We used PEDOT/PSS20,21 and PPy,22 respectively, as a conducting polymer for the fabrication of nanosized organic electrodes. Parts a and b of Scheme 1 illustrate the patterning process of the conducting polymers. First, polymer resist templates were created by EBL or nanoimprinting on PMMA on silicon oxide or Au substrates (PMMA/SiO2 or PMMA/Au), followed by a removal of a residual layer. Second, the patterned wafer was modified using a SAM technique by placing the wafer into a SAM solution. A positively charged APTS was chosen to electrostatically attach the negatively charged PEDOT/PSS, and a negatively charged MHDA SAM was chosen to anchor the positively charged PPy, as shown in Scheme 1, parts a and b, respectively. The conducting polymer was deposited via spincoating on the SAM-modified substrates. Adhesion between the functional groups of the SAMs and the conducting polymers was enhanced via selective electrostatic force. The polymer resist templates were maintained so as to serve a physical barrier for the conducting polymer deposition. After spin-coating the conducting polymer, the polymer resist and the conducting polymer located on top of the resist were removed to yield conducting polymer patterns on the SiO2 and Au substrates, respectively. Conducting polymers on the substrate could be patterned directly using positively or negatively charged SAMs. Figure 1 shows optical microscopy and AFM images of 50 µm and 2 µm PEDOT/PSS patterns on the APTS/SiO2/Si surface. As noted earlier, the APTS SAM was chosen to form a positively charged surface on the silicon substrate to be combined with negatively charged sulfonate groups of the PSS in aqueous solution. After the silicon was modified with the APTS SAMs, protonation was performed by rinsing the silicon with a 2-(Nmorpholino)-ethanesulfonic acid (MES) buffer (pH 5.6) solution, thereby resulting in an -NH2 of aminoalkylsilane monolayer positively charged surface. PEDOT/PSS diluted a 2:1 ratio of PEDOT/PSS to ethylene glycol was then spin-coated onto the SAM. Ethylene glycol is known to increase the chain mobility of polymers, resulting in enhanced conductivity. It also prevents the spin-coated PEDOT/PSS film from completely drying out and facilitates adhesion to the substrate during the lift-off (20) Groenendaal, L.; Jonas, F.; Freitag, D.; Pielartzik, H.; Reynolds, J. R. AdV. Mater. 2000, 12, 481–494. (21) Jonsson, S. K. M.; Birgerson, J.; Crispin, X.; Greczynski, G.; Osikowicz, W.; Denier van der Gon, A. W.; Salaneck, W. R.; Fahlman, M. Synth. Met. 2003, 139, 1. (22) Alan, G. M. Angew. Chem., Int. Ed. 2001, 40, 2581–2590.
process.23 The samples were then left to stand at 90 °C for 1 h in order to allow the solvent to completely evaporate. Finally, the samples were washed with acetone and then ultrasonicated to remove the PMMA used as a polymer resist. The conducting polymer pattern remained strongly fixed on the APTS SAM of the silicon oxide surface even during the lift-off process, whereas the conducting polymer pattern produced without SAM treatment was easily detached. We assume that the PMMA removal solvent, i.e., acetone, used in the lift-off process does not readily infiltrate the interface between the PEDOT/PSS and the APTS SAMs attached on the surface of the SiO2. However, solvent penetrates the interface between the PEDOT/PSS and the surface of SiO2 that is not treated SAMs. Strong electrostatic binding between the NH3+ groups of the APTS SAMs and the SO3-Na+ or SO3-H+ groups of PEDOT/PSS lends PEDOT/PSS greater adhesion to the substrate, making it harder to detach.5 Thus, it is concluded that spin-coating of PEDOT/PSS onto the patterned APTS SAM surface and subsequent annealing result in preferential absorption of the conducting polymer onto the APTS-covered regions and, thereby, the formation of well-defined patterns that mimic the APTS pattern. The film thickness of the conducting polymer was controlled by the conducting polymer concentration and spinning rate. With regard to the deposition of organic materials using spin-coating technique, Chiarelli et al. investigated multilayered polyelectrolyte films that are spin-assembled by dropping a solution onto a spinning substrate and showed the relationship between the spin rate and multilayered thickness.24 In the present experiment, we found that the feature size of the conducting polymer was dependent on the polymer resist template. To confirm the adsorption of PEDOT/PSS onto the APTS SAMs, AES was performed on a patterned test structure, as shown in Figure 2. Auger sulfur and silicon maps of the PEDOT/ PSS patterned on the SiO2 substrate were separately collected in sequence within the same substrate region. Parts a and c of Figure 2 show higher S than Si counts at the PEDOT/PSS region (light area) in the case of sulfur element scanning, whereas in the case of silicon element scanning, less Si (gray area) is counted, as depicted in Figure 2, parts b and d. Sulfur was detected in the PEDOT/PSS region, whereas it was not detected on the SiO2 (23) Kim, W. H.; Makinen, A. J.; Nikolov, N.; Shashidhar, R.; Kim, H.; Kafafi, Z. H. Appl. Phys. Lett. 2002, 80, 3844–3846. (24) Chiarelli, P. A.; Johal, M. S.; Casson, J. L.; Roberts, J. B.; Robinson, J. M.; Wang, H. L. AdV. Mater. 2001, 13, 1167–1171.
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Figure 6. Topographic AFM images (noncontact mode) of PPy nanolines on MHDA SAM on Au substrates and cross-sectional profile of the PPy patterns: line widths of (a) 500 and (b) 300 nm.
surface, which means that the lines (PEDOT/PSS) and space (SiO2) mainly consist of sulfur and silicon, respectively. By comparing the AES spectra, we can demonstrate that the PEDOT/ PSS pattern was maintained during the lift-off process, thus confirming that the polymer patterns are stabilized by the electrostatic interaction between the charged polymer chains and the oppositely charged functionalized SAM surfaces. Parts a and b of Figure 3 show optical microscopy images of PPy attached on MHDA SAMs on a gold electrode, as described in Scheme 1b, after subsequent removal of the polymer resist. The doped PPy conducting polymer has positively charged backbones, whereas the MHDA patterned surface has a negatively charged -COOH functional group.25 In a similar manner to the patterning of PEDOT/PSS, depicted in Scheme 1a, the electrostatic interaction between the positively charged PPy and the negatively charged MHDA self-assembled on the Au substrate is the primary driving force in the patterning of the PPy. Without the MHDA SAMs, we could not obtain PPy conducting polymer patterns due to a weak interaction with the unmodified hydrophobic Au surface. AFM was used in tapping mode to obtain images of the polymer patterns. Parts c and d of Figure 3 show AFM images of the PPy conducting polymer attached to an MHDA SAM pattern. The heights of the polymer pattern were determined to be approximately 100 nm. With regard to patterning of a PPy conducting polymer, Gorman et al. and Sayre and Collard et al. reported on the deposition of PPy on a SAM-covered region with selective deposition on Au.26,27 However, the adhesion was sufficiently weak that the PPy could be easily stripped from gold and transferred to another surface by contact adhesion. (25) Clark, S. L.; Hammond, P. T. Langmuir 2000, 16, 10206–10214. (26) Gorman, C. B.; Biebuyck, H. A.; Whitesides, G. M. Chem. Mater. 1995, 7, 526–529. (27) Sayre, C. N.; Collard, D. M. Langmuir 1997, 13, 714–722.
The present approach differs from previously reported methods in that no bias is required and patterns can be formed by simply using oppositely charged SAMs. Furthermore, the adhesion to the substrate is sufficiently strong. Figure 4 shows that the resulting PPy on SAM patterns exhibits excellent stability on the Au surface, as confirmed by ultrasonification methods, whereas the PPy patterns easily peel off from the Au substrate due to the weak interaction of the unmodified surface. After successfully patterning conducting polymers of PEDOT/ PSS and PPy, we examined the chemical and electrical properties of the conducting polymers with UV-vis spectroscopy5,28,29 and four-point probe measurements. The optical absorption and sheet resistance of the solvent-treated polymer films are not affected in the lift-off process and are identical to those of the untreated polymer films. Although the PEDOT/PSS was treated by acetone, its intrinsic conducting property is not changed, because the majority of the PEDOT/PSS retains its doping level. Therefore, we assume that other effects may be related to the change of electrical properties in the PEDOT/PSS rather than to the removal solvent.21,30 AFM was carried out in contact mode to image the polymer nanolines. The nanolines of the PEDOT/PSS were fabricated from a polymer resist pattern on the SiO2 surface. In the case of PEDOT/PSS, the width and height of the polymer lines were influenced by the size of the primary particles.31 The AFM images presented in Figure 5 show that the PEDOT/PSS nanolines are composed of aggregated polymer chains. We can estimate the (28) Hohnholz, D.; Okuzaki, H.; MacDiarmid, A. G. AdV. Funct. Mater. 2005, 15, 51–56. (29) Dietrich, M.; Heinze, J.; Heywang, G.; Jonas, F. J. Electroanal. Chem. 1994, 369, 87–92. (30) Kim, J. Y.; Jung, J. H.; Lee, D. E.; Joo, J. Synth. Met. 2002, 126, 311–316. (31) Smith, R. R.; Smith, A. P.; Stricker, J. T.; Taylor, B. E.; Durstock, M. F. Macromolecules 2006, 39, 6071–6074.
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conductivity of the nanolines on the assumption that no anisotropy has been generated when the defects between the nanolines are negligible and there is basically no polymer between the nanolines. The conductivity is calculated to be 2/(Rsurf/∆h) ≈ 0.2 S/cm, where ∆h (≈50 nm) is the height of the nanolines and Rsurf is the surface resistance.32 Figure 6 shows AFM images of PPy nanolines on Au. The height of the nanolines is ≈50 nm; the width of the nanolines is ≈500 nm with a spacing of 400 nm in Figure 6a, and the width of the nanolines is ≈300 nm with a spacing of 300 nm in Figure 6b, respectively. The cross-sectional images (right images) show the profiles of the lines and the height. The PPy nanolines are smoother than those of the PEDOT/PSS, reflecting the particle size differences between the PPy polymer solution and the aqueous dispersed PEDOT/PSS, whose conducting PEDOT is embedded in the insulating PSS chains, resulting in a grainlike structure on the substrate.
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in a soluble state can be easily adsorbed on the oppositely charged self-assembled surface due to electrostatic interaction. PEDOT/ PSS negatively charged by sulfonate groups of PSS can easily combine with the quarternary amine functional groups of the SAMs. The conductivity of the PEDOT/PSS is 0.2 S/cm. In addition, PPy having a positively charged backbone structure can be strongly adsorbed on the negatively charged SAMs. Once the conducting polymer pattern was formed on the SAMs surface, the patterned conducting polymer surface was very stable, even during the lift-off process, as confirmed with an ultrasonic agitation method. Thus, we can produce highly resolved conducting polymer patterns by simply utilizing the charged SAMs without changing the intrinsic conducting properties of commercially available conducting polymers. This simple, easily accessible, and economical method offers a number of desirable features such as high resolution, a large range of accessible chemical functions, large surface area, and potential application in flexible conducting electrodes with higher throughput.
4. Conclusions A conducting polymer patterning process was directly performed on SAM surfaces. The charged conducting polymers (32) Zhang, F.; Nyberg, T.; Inganas, O. Nano Lett. 2002, 2, 1373–1377.
Acknowledgment. This work was supported by the Creative Research Initiatives (Project title: Smart Molecular Memory) of MOST/KOSEF. LA8014207
