Organic electronics on natural cotton fibres

Organic Electronics 12 (2011) 2033–2039

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Organic electronics on natural cotton fibres Giorgio Mattana a,b, Piero Cosseddu a,b, Beatrice Fraboni c, George G. Malliaras d, Juan P. Hinestroza e, Annalisa Bonfiglio a,b,⇑ a

Dipartimento di Ingegneria Elettrica ed Elettronica, Università di Cagliari, Piazza d’Armi, 09123 Piazza D’Armi, Cagliari, Italy CNR Institute of Nanoscience, Via Campi 213/A, 41126 Modena, Italy c Dipartimento di Fisica, Alma Mater Studiorum – Università di Bologna, Viale Berti Pichat 6/2, 40127 Bologna, Italy d Centre Microélectronique de Provence, Ecole Nationale Supérieure des Mines de Saint Etienne, 880 route de Mimet, 13541 Gardanne, France e Cornell University, Dept. of Fiber Science and Apparel Design, Martha Van Rensselaer Hall 242, Ithaca, NY 14853-4401, USA b

a r t i c l e

i n f o

Article history: Received 2 March 2011 Received in revised form 31 August 2011 Accepted 1 September 2011 Available online 13 September 2011 Keywords: OECT OFET E-textiles Cotton fibres Conductive fibres

a b s t r a c t Nanoscale modification of natural cotton fibres with conformal coatings of gold nanoparticles, deposition of thin layers of the conductive polymer poly(3,4-ethylenedioxithiophene) (PEDOT) and a combination of these two processes were employed to increase conductivity of plain cotton yarns. This innovative approach was especially designed to fabricate two classes of devices: passive devices such as resistors obtained from electrically conductive cotton yarns, and two types of active devices, namely organic electrochemical transistors (OECTs) and organic field effect transistors (OFETs). The detailed electrical and mechanical analysis we performed on treated cotton yarns revealed that they can be used as conductors still maintaining a good flexibility. This study opens an avenue for real integration between organic electronics and traditional textile technology and materials. Ó 2011 Elsevier B.V. All rights reserved.

1. Introduction The concept of ‘‘wearable electronics’’ has emerged in the last 15 years, as a direct consequence of the intensive miniaturization of silicon technology [1]. While in the early years this expression was used in a literal sense to indicate the insertion of small electronic equipment into textile substrates, its meaning has slowly become broader and nowadays it includes any electronic device directly realized in a textile form [2]. A first, simple example of wearable electronics was the fabrication of resistive yarns which were used as electrodes in a system designed to detect electrocardiogram signals (ECG) [3]. More recently, the first example of organic textile active device, namely a field effect transistor [4,5], has also been presented. A transistor in textile form is a real step forward because it paves the way to the possibil-

⇑ Corresponding author. Tel.: +39 070 675 5764; fax: +39 070 675 5782. E-mail address: [email protected] (A. Bonfiglio). 1566-1199/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.orgel.2011.09.001

ity of realizing more complex devices and functions, including the fabrication of whole textile-based circuits. In addition, the inclusion of some kind of chemical receptors in the transistor structure may open an avenue for the realization of chemo- and bio-sensors. This fact is important for several reasons: first of all because it allows to overcome problems intrinsically related to the fusion of two very different technologies, like textile and electronics, enabling low cost integration of electronic functions on a normal textile platform; secondly, but not less relevant, because it allows to exploit the topological richness offered by textiles (for instance the ability of obtaining 3D structures, the possibility of combining different yarns in a unique structure, etc.). These possibilities are strategically related to the ability of obtaining yarns that, besides having the required electronic properties, also maintain the mechanical and processing features of a normal fibre. Among the materials utilized for textiles and apparel production, cotton (natural cellulose) is indeed the most commonly used material, because of its process easiness, relative cheapness, good mechanical properties and

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wearability comfort [6]; the aim of many research groups has therefore become the development of a specific treatment on cotton yarns with the purpose of obtaining conductive fibres while preserving cotton’s unique set of physical and comfort properties. Several different methods for the realization of conductive cellulose fibres have already been described in the literature [7–14]. These procedures may be roughly grouped into two different categories. On one hand, cotton’s conductivity was increased by incorporating metal particles onto cotton modified with polymer brushes [7] or carbon nanotubes (CNTs) [8] into cellulose yarns. With these techniques, very high values of conductance per length unit (up to 1 S cm 1) were achieved. The majority of reported works on conductive cotton, however, have focused on grafting conductive polymers (CPs) onto cellulose fibres by in-situ, liquid-phase polymerization [9–13] or simple soaking the cellulosic substrates in polymeric aqueous solutions [14]. The most commonly used CPs are p-conjugated polymers including polythiophenes (such as PEDOT) [9,12,14], polypyrrole [10,13] and polyaniline [11]. Incorporation of CPs into cotton fibres has shown to raise the conductance per length unit of the native fibre from 10 12 to 10 1 S cm 1. Surprisingly enough, even though it has been shown that the incorporation of metallic (e.g. Au, Ag, Pt) nanoparticles (NPs) into CPs films may result in the formation of highly conductive layers, characterized by conductivities several orders of magnitude greater than the values obtained for the CPs alone [15,16], the deposition of such composites on cotton substrates has not yet been attempted. In this paper, we present a novel technique in which conductive Au NPs are deposited onto the cotton surface and subsequently interconnected with a layer of conductive polymer. The electrical properties of these samples are compared to those of yarns on which only Au NPs or only a CP layer was deposited, in order to evaluate the effect on the electrical behaviour of the combination of the two deposition processes. We will show that the deposition of a metal NPs/CP composite on plain cotton yarns determines a dramatic increase of its conductivity so that treated yarns may be used as electrical connectors in order to bias or to interconnect electronic devices, behaving thus as relatively low resistance resistors. Moreover, to demonstrate practically the possibility of using cotton fibres to fabricate organic textiles circuits, two different kinds of transistors have been realized. The first device is based on the concept of OECT, first developed in planar form [17] and also realized in form of yarn based on a nylon fibre [18] and more recently on silk [19]. An OECT is made up of two electrodes, source and drain, connected by an active layer called channel realized using a conductive polymer which can be electrochemically doped/de-doped [20]. The channel conductivity is modulated by applying a voltage on a third electrode, the gate, immersed in an electrolyte solution in contact with the channel. The gate voltage drives the electrolyte cations into the channel where they cause its de-doping and, as a con-

sequence, a decrease of the current flowing between the source and drain terminals. Channel de-doping is a reversible process: when the gate voltage is brought back to zero, the channel conductivity increases again. The second example of active device realized on a cotton yarn is based on the concept of organic field effect transistor (OFET). In this case, the conductivity of the channel, made of a semiconductor deposited between two metal contacts (source and drain), is modulated by the voltage applied to a gate electrode, capacitively coupled with the device channel [21]. The transistor current is modulated by varying the voltage on the gate. To realize a yarnshaped OFET, a multilayered structure based on a conductive yarn (that acts as the gate of the device) is used. This cylindrical structure is able to act as a transistor, according to a model that takes into account its geometrical characteristics [22] giving rise to results very similar to those obtained with planar structures. 2. Materials and methods 2.1. Preparation of Au NPs/PEDOT:tos coated conductive cotton yarns The procedure for the deposition of Au nanoparticles on cellulosic substrates has been already reported in previous publications [23]. After conformally coating cotton yarns with high packing surface density of Au NPs, a thin layer of tosylatedoped PEDOT (PEDOT:tos) was deposited on the yarns by means of a vapour phase polymerization (VPP) process. Such a procedure has already been described in detail in the literature [24,25] for the deposition of thin PEDOT:tos films on planar substrates. In our case, we prepared a solution of 125:25:1 wt% of isopropanol:Fe(III)–tosylate:pyridine in which the yarns were soaked for 10 min and then dried on a hot plate at 80 °C for 3 min. After polymerization of EDOT monomer into PEDOT, the samples were dried in an oven at 50 °C for 30 min. Then they were rinsed into ethanol for 10 min and finally dried in a vacuum oven at room temperature for 12 h. This procedure is described in the cartoon presented in the Supplementary data. Conductive cotton fibres were used as source, drain and gate electrodes in the assembly of cotton-made electrochemical transistors (see Section 2.6). 2.2. Preparation of PEDOT:poly(styrenesulphonate) coated semiconductive yarns The cotton yarns were soaked in an aqueous dispersion of PEDOT:poly(styrenesulphonate) (PEDOT:PSS) (CLEVIOS™ PH 500, H.C. Starck, used as received) for 48 h at 6 °C. Samples were then baked on a hotplate at 145 °C for 60 min. After baking, samples were soaked in ethylene glycol (EG) (anhydrous, 99.8%, Sigma–Aldrich, used as received) for 3 min at room temperature. Then they were baked on a hotplate at 145 °C for 60 min. Such semiconductive yarns were used for the realization of the channel of organic electrochemical transistors.

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Fig. 1. Organic transistors realized on a cotton fibre. (a) Scheme of an OECT on cotton yarns seen both from the above (left) and from a lateral perspective (right). (b) Actual picture of the transistor. (c) Scheme showing the structure of an OFET fabricated on a cotton yarn.

2.3. Microscopic and spectroscopic analysis of conductive cotton yarns Short pieces (1 cm) of conductive cotton yarns were immersed into small blocks of epoxy resin and baked at 80 °C for 24 h in order to achieve the complete solidification of the resin. Such blocks were then sectioned by means of a microtome (Dupont Sorvall MT500 Ultramicrotome) obtaining slices with a thickness of approximately 90 nm. The samples slices were placed onto a copper microgrid and analysed with a Tecnai FEI F20 TEM STEM microscope. This instrument is also equipped with a Gatan tridium spectrometer for electron energy loss spectroscopic analysis, so that on the samples treated with both Au NPs and PEDOT:tos an energy-dispersive X-ray spectrum (EDX) was acquired. 2.4. Electrical characterization of conductive cotton yarns Resistance per unit length was measured using a four probe method, performed using a couple of Keithley 2636 SYSTEM Source Meters. More in detail, a current of 10 lA was injected by means of a couple of electrodes (outer electrodes) connected to the yarn and placed at a distance of 2 cm. Another couple of electrodes (inner electrodes) was inserted between the external electrodes, connected to the yarn and placed at a distance of 1 cm in order to measure the voltage drop resulting from the current passage; resistance was measured as the ratio between this potential drop and the current injected. For each yarn type, 10 samples were acquired.

2.5. Mechanical characterization of conductive cotton yarns Conductive cotton fibres were characterized by means of stress–strain measurements performed using a TA Instruments DMA Q800 Dynamic Mechanical Thermal Analysis (DMTA) equipment. The samples measured were 4 cm long, the stress applied varied from 0 to 18 N with steps of 0.3 N. Percentage elongation was measured with respect to the sample’s original length.

2.6. Cotton-based organic electrochemical transistors assembly First, a 250 mM solution of KCl in deionized water was prepared. Bacto™ Agar (DIFCO Microbiology) was employed as gelling agent (3.75% in weight). The solution was heated up at 90 °C and vigorously stirred for 60 min. To improve solidification, the gel was stored at 6 °C for 24 h before being used. The gel is used in the OECT assembly to realize the ionic bridge between the gate and the channel. A piece of semiconductive yarn (1 cm, prepared as described in Section 2.2) was inserted into the centre of a small parallelepiped of electrolyte gel (approximately: 6 mm3) with the help of a needle. Two conductive yarns (2 cm long, prepared as described in Section 2.1) were fixed at the end of the semiconductive yarn with a simple knot and then connected to the power supply by means of a couple of micrograbbers (Fig. 1a and b). Another conductive yarn was fixed on the top of the electrolyte gel block and used as the gate electrode.

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2.7. Cotton-based organic field effect transistors assembly The core of the organic field effect transistors (OFET) is a yarn treated with PEDOT:PSS/EG (prepared as described in Section 2.2), which acts as the gate electrode of the final device. The gate dielectric layer was realized by depositing a thin film of poly(chloro-p-xylylene) (usually known as Parylene C) with a nominal thickness of 1.5 lm on the entire yarn surface through a chemical vapour deposition (CVD) process performed using a PDS 2010 LABCOTER deposition system. Such a dielectric film was obtained starting from 3.3 g of dichloro-[2,2]-paracyclophane (dimer), vapourized at 175 °C at a pressure of around 1 mmHg. The dimer vapours are then pyrolized at 690 °C at a pressure of around 0.5 mmHg to form the gaseous monomer which is eventually deposited at room temperature at a pressure of around 0.1 mmHg on the substrate surface, where polymerization of monomers occurs. After that, a thin pentacene (nominal thickness 50 nm) film was deposited by thermal evaporation at pressure below 2  10 5 mbar, at a constant rate of ca. 4 Å min 1. Source and drain electrodes have been realized by depositing two drops of conductive silver paint on the previously realized structure. The silver paint drops have been placed by means of a very sharp needle, in this way, a typical channel length of approximately 200 ± 50 lm have been obtained, whereas the channel width is usually given by the average semicircumference of the employed yarn (Fig. 1c). 2.8. Electrical characterization of OECTs and OFETs Each transistor was characterized by acquiring the Ids– Vds curves. The source electrode was grounded while the voltage applied to the drain was: – Varied from 0.5 to 0.5 V with steps of 0.01 V (forward curve) and then again from 0.5 to 0.5 V with steps of 0.01 V (backward curve) for OECTs. – Varied from 0 V to 60 V with steps of 1 V for OFETs. During the acquisition of each curve, the gate voltage was fixed at a specific value and then increased in correspondence with the acquisition of the next curve (gate voltage range: 0  0.4 V, step width: 0.1 V for OECTs; 20  100 V, step width 20 V for OFETs). OECT samples were also characterized by the acquisition of drain current vs. time curve. In this case, drain voltage was kept constant at 0.5 V while gate voltage varied abruptly from 0 to 0.4 V (square wave) every 60 s. 3. Results and discussion Fig. 2 shows a example of the use of the described conductive cotton yarn for connecting a LED to a battery. It is noteworthy that the flexibility of this yarn (made according to the procedure described in Section 2.1) is such that the connection is made through a simple knot. The described yarn treatment in fact modifies the yarn conductivity without significantly compromising its mechanical features.

Fig. 2. Light emitting diode (LED) biased by means of conductive cotton yarns.

To investigate the modifications induced in the conductive yarn structure, transmission electron microscopy (TEM) analysis of the cross section of the treated yarns was performed and the obtained results are shown in Fig. 3. Gold nanoparticles clearly appear as an external coating (Fig. 3a). Conversely, it was found that PEDOT:tos is not confined to the yarn’s external surface but penetrates among the yarn inner fibres in a very irregular way (Fig. 3b). For this reason, it was not possible to obtain a precise measurement of the samples’ cross-sectional conductive area. Fig. 3d shows an energy-dispersive X-ray spectroscopy (EDX) spectrum of a sample treated with both Au NPs and PEDOT:tos (cross section shown in Fig. 3c). EDX was performed to identify the chemical composition of the materials deposited on the cotton yarn surface: the spectrum confirmed the presence of both Au NPs (Au peaks) and PEDOT:tos (S peaks, caused by the sulphur atoms contained into the thiophene rings). The sharp Cu peak which appears in the spectrum is due to the copper grid on which the samples slices were placed during the analysis. All conductive cotton samples were electrically characterized with a four-point probe method in order to eliminate possible contributions of contact resistances. The following types of samples were compared: Type 1: Cotton yarns as received; Type 2: Cotton yarns covered with Au NPs; Type 3: Cotton yarns covered with PEDOT:tos; Type 4: Cotton yarns covered with Au NPs and subsequently covered with a layer of PEDOT:tos. Since, as previously mentioned, a precise determination of the samples cross section was not possible, the electrical performance of the different fibres has been compared in terms of resistance per unit length. The mean values of the electrical resistance of all samples types are summarized in the first column of Table 1: the most conductive samples were type 4. The unmodified cotton specimens show a resistance of (3.1 ± 0.9)  108 X cm 1; the deposition of nanoparticles onto the cotton fibres does not seem significantly influence the resistance value, which remains of the same order of magnitude. However, when PEDOT:tos layers are deposited over plain cotton yarns, the resistance value of the modified fibre is reduced by three orders of magnitude.

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Fig. 3. Transmission electron microscope (TEM) analysis of the cross section of the conductive cotton fibres. (a) Cross section of a cationic cotton fibre uniformly coated with Au nanoparticles. (b) (Bright Field TEM image) Cross section of a fibre coated with PEDOT:tos. (c) (Dark Field TEM image) Cross section of a fibre treated with Au nanoparticles and a conductive polymer layer (PEDOT:tos). The rectangle in the conductive layer indicates the area in which the EDX spectrum (see inset d) was acquired. (d) EDX analysis performed on the area shown in (c).

Table 1 Electrical and mechanical data of the conductive cotton yarns. Yarn type 1. 2. 3. 4.

Plain cotton Cotton + Au NPs Cotton + PEDOT:tos Cotton + Au NPs + PEDOT:tos

Resistance per unit length (X cm

1

)

8

(3.1 ± 0.9)  10 (1.1 ± 0.1)  108 (186.8 ± 0.2)  103 (24.7 ± 0.3)  103

An unexpected further reduction of one order of magnitude in resistance is then achieved when PEDOT:tos is deposited on NPs coated cotton fibres, which clearly proves a Au NPs-enhanced conductivity phenomenon. These experimental results demonstrate that a natural cotton fibre can be made conductive by a conformal coating with thin layers of a conductive polymer, hence increasing the conductance by about three orders of magnitude. More importantly, when the PEDOT:tos layers are deposited on a Au NPs previously treated substrate, a further increase, up to four orders of magnitude, in conductance is observed. Further investigations are being performed to establish the exact nature of the electrical transport mechanism in the treated fibres and the synergistic role of the Au NPs. Such treated yarns were then mechanically characterized by measuring static stress vs. strain curves. Three mechanical parameters were acquired: Young’s modulus, stress at break and elongation before breaking (also called elongation to break, indicated as eb); the mean values of such parameters for the different types of conductive yarns are reported in Table 1 (see Supplementary data for the full

Young’s modulus (MPa)

Stress at break (MPa)

Elongation to break (%)

342 ± 75 140 ± 60 331 ± 82 142 ± 18

10.3 ± 3.3 8.2 ± 1.9 4.0 ± 1.3 4.3 ± 1.0

4.4 ± 1.8 11.0 ± 5.3 2.5 ± 1.0 4.4 ± 0.9

Fig. 4. Stress strain curves on conductive cotton yarns.

statistical analysis). On a typical curve of a yarn treated with Au NPs + PEDOT:tosylate compared to plain cotton, shown in Fig. 4, two main observations can be made: first

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Fig. 5. Electrical characteristics of organic transistors on cotton yarns. (a) Drain current and gate voltage vs. time characteristics of an all cotton-made OECT. (b) Id–Vd curves acquired on a cotton-made OFET.

the maximum elongation before breaking appears to be similar for both samples, thus indicating that the main mechanical property of interest for evaluating the ability of the yarn to be woven or knit are preserved in treated yarns. Secondly, the treated yarn can reach larger strain values before starting to experience elongational stress (represented by the slope of the curve in the initial phase). This unusual effect, that was observed only in NPs-treated samples (with and without PEDOT:tos, see the full statistical analysis of all kinds of yarns in Table 1) may be tentatively attributed to a ‘‘lubricant’’ effect due to the conformal nature of the NPs coating which seems to enable them to slide on one another following the application of the mechanical stimulus (see the inset in Fig. 4). These observations demonstrate that the proposed treatment does not stiffen the cotton yarns that, at the same time, still possess mechanical properties apt for weaving purposes. Finally, active electronic devices have been made starting from natural cotton fibres. As for the transistors characterization, it can be seen from Fig. 1a and b that the OECT structure includes an electrolyte in gel form. Being this based on water, it is strictly necessary that the OECT channel (in this case the yarn) is impermeable to water. Cotton yarns simply soaked in PEDOT:PSS cannot be used as such as the contact with a waterbased electrolyte solution would cause on one hand the dissolution of PEDOT:PSS and on the other hand, the possible absorption of water and the consequent ionic conduction of the yarn through the adsorbed water: in any case, the loss of the transistor action. To avoid this problem, after the deposition of PEDOT:PSS, the samples were treated with ethylene glycol (EG). The effect of this treatment is twofold: on one hand it dramatically decreases PEDOT:PSS solubility in water, on the other EG is also able to increase its conductivity [26,27]. In the SD section, the comparison (in terms of electrical resistance and waterresistance) between yarns soaked in PEDOT:PSS with and without ethylene glycol treatment is presented. Fig. 5a shows the electrical characteristics of the cottonmade OECT. It is noteworthy that source and drain contacts were made by a simple knot between the yarn that acts as the device channel (i.e. the semiconductive yarn obtained with the procedure described in Section 2.2) and two conductive cotton yarns (i.e. the conductive yarns obtained with the procedure described in Section 2.1) used to

connect the device to the source/measure units. This is a very basic example of textile circuit entirely based on cotton yarns. Despite the non optimal ratio between the on and off currents, the transistor effect is clearly achieved. It is noticeable that we have attempted also to obtain an OECT device using the conductive cotton yarn (i.e. the conductive yarn obtained with the procedure described in Section 2.1) but we never obtained a transistor action with this yarn, i.e. its conductivity cannot be modulated by the exchange of ions with the electrolytic solution. This aspect is under further investigation. The structure of the yarn-shaped organic field effect transistor (OFET) is shown in Fig. 1c. The core of the OFETs is a yarn treated with PEDOT:PSS/EG as described above, which acts as the gate electrode of the final device. Even if the PEDOT:PSS/EG yarn nominally behaves as a semiconductor, its resistance per unit length (2  103 X cm 1), is such that at the voltage values used for operating the gate in the OFETs, it may be considered as a conductor. In addition, the contact with any external agent able to modulate its conductivity is prevented in the OFET, as the gate is coated with an insulating layer. Clearly, also conductive cotton yarns based on Au NPs and PEDOT:tos could be used for this function but the yarn treated with PEDOT:PSS was preferred because its external surface is smoother and this feature improves the quality of the dielectric layer deposition. Fig. 5b shows an example of the electrical characteristics of the OFETs. The insulating layer capacitance was measured and found to be 2.17 nF cm 2 (corresponding to an estimated thickness of the insulating layer of 1.5 lm). The OFET mobility mean value (over 20 devices measured) is 1.3 ± 1.0  10 2 cm2 (V 1 s 1) and the threshold voltage is 24 ± 5 V. These values are not too different from those taken from typical curves of planar OFETs with comparable aspect ratios. Relatively high values of the threshold voltage may be attributed to the thickness of the insulating layer.

4. Conclusions In conclusion, we presented an innovative method based on the combination of two deposition processes which can be used in order to obtain conductive yarns starting from common cotton fibres, which are by

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themselves intrinsically insulating. The electrical and mechanical characterization of these fibres showed that these yarns can be successfully used as conductors, in order to bias electronic devices. Cotton was also successfully employed as a basis for realizing two kinds of active devices based respectively on the concept of organic electrochemical transistor and of organic field effect transistor. Our study demonstrates the possibility of realizing a fully textile circuit, including passive and active elements, and paves the way for a future complete integration between electronics and textiles.

[6]

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Acknowledgements [10]

Prof. Ennio Bonetti is gratefully acknowledged for the fruitful discussions about the mechanical measurements conducted on the yarns. G.M. would like to thank Dr. Sang Yang for the fruitful discussions concerning the polarization of OECTs and Alwin Wan for the help with the polymerization of PEDOT:tosylate process. A.B. and G.M. gratefully acknowledge EU Commission for funding the Integrated Project #26987 ‘‘Proetex’’. G.G.M. would like to thank ReynoldsTech for building the tool for vapour deposition of conducting polymers. J.P.H. acknowledges the US Department of Agriculture for partially funding this work under projects NRINCZ09462 and CRIS-Hatch NYC-329433. P.C. acknowledges Regione Autonoma della Sardegna (RAS) for funding his research activity under the PO Sardegna FSE 2007-2013, L.R.7/2007, CRP Prot. No. 1399/207. This work made use of the electron microscopy facility of the Cornell Center for Materials Research (CCMR) with support from the National Science Foundation Materials Research Science and Engineering Centers (MRSEC) program (DMR 0520404). This work was performed in part at the Cornell NanoScale Facility, a member of the National Nanotechnology Infrastructure Network, which is supported by the National Science Foundation (ECS-0335765). Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.orgel.2011. 09.001. References [1] J. Berzowska, Electronic textiles: wearable computers reactive fashion and soft computation, Textile: J Cloth Culture 3 (2005) 58– 75. [2] D. De Rossi, Electronic textiles: a logical step, Nat. Mater. 6 (2007) 328–329. [3] D. De Rossi, F. Carpi, F. Lorussi, A. Mazzoldi, R. Paradiso, E.P. Scilingo, A. Tognetti, Electroactive fabrics and wearable biomonitoring devices, AUTEX Res. J. 3 (2003) 180–185. [4] J.B. Lee, V. Subramanian, Organic transistors on fibre: a first step towards electronic textiles, IEEE Int. Electron Device Meet. Techn. Digest 8 (2003) 1–4. [5] M. Maccioni, E. Orgiu, P. Cosseddu, S. Locci, A. Bonfiglio, Towards the textile transistor: assembly and characterization of an organic field

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