Method to Fabricate Polymer Nanostructures and a Polymer Nanosensor manufactured therefrom

Field of the Invention

The invention relates to conducting polymers nanowires and nanosensors made therefrom.

Background to the Invention

Conducting polymers have attracted considerable attention owing to the unique combination of their electronic, optical, magnetic and mechanical properties (lightweight, easily processable, highly flexible), see for example the reviews of H. Shirakawa, Angew. Chem. Int. Ed. 2001, 40, 2574-2580, A. G. MacDiarmid, Angew. Chem. Int. Ed. 2001, 40, 2581-2590 and A. J. Heeger, Angew. Chem. Int. Ed. 2001, 40, 2591-2611

The anticipated application areas of conducting polymers range from microelectronics, electro-optics and optical electronics to sensors and actuators as has been reported in the publications of J. H. Burroughes, D. D. C. Bradley, A. R. Brown, R. N. Marks, K. Mackay, R. H. Friend, P. L. Burns, A. B. Holmes, Nature 1990, 347, 539-541, M. Angelopoulos, IBM J. RES. & DEV. 2001, 45, 57-75 and E. W. H. Jager, E. Smela, O. Inganas, Science 2000, 290, 1540-1545.

In recent years, a significant portion of these studies has been devoted to the fabrication of all- polymer devices (as is taught by D. Voss, Nature, 2000, 407, 442-444). All-polymer devices have been demonstrated to possess properties that may rival those of inorganic devices while still retaining their low cost, flexibility and disposable nature (see H. Sirringhaus, N. Tessler,

R. H. Friend, Science, 1998, 280, 1741-1744). Although they are still at the prototype stage, different kinds of devices, such as field effect transistors (FET) (see F. Gamier, R. Hajlaoui, A. Yassar, P. Srivastava, Science, 1994, 265, 1684-1686, Z. Bao, Y. Feng, A. Dodabalapur, V. R. Raju, A. J. Lovinger, Chem. Mater. 1997, 9, 1299-1301 and M. Halik, H. Klauk, U. Zschieschang, T. Kriem, G. Schmid, W. Radlik, K. Wussow, Appl. Phys. Lett. 2002, 57, 289- 291), charge storage devices (Y. Gofer, H. Sarker, J. G. Killian, T. O. Poehler, P. C. Searson, Appl Phys. Lett. 1997, 71, 1582-1584), integrated circuits (C. J. Drury, C. M. J. Mutsaers, C. M. Hart, M. Matters, D. M. de Leeuw, Appl. Phys. Lett. 1998, 73, 108-110, H. Sirringhaus, T. Kawase, R. H. Friend, T. Shimoda, M. Inbasekaran, W. Wu, E. P. Woo, Science, 2000, 290, 2123-2126 and G. H. Gelinck, T. C. T. Geuns, D. M. de Leeuw, Appl Phys. Lett. 2000, 77, 1487-1489) and optoelectronic devices (A. Dodabalapur, Z. Bao, A. Makhija, J. G. Laquindanum, V. R. Raju, Y, Feng, H. E. Katz, J. Rogers, Appl Phys. Lett. 1998, 73, 142-144 and P. K. H. Ho, D. S. Thomas, R. H. Friend, N. Tessler, Science, 1999, 285, 233-236) have been demonstrated.

The emerging field of nanosensors offers the prospect of high sensitivity and rapid detection of the analyte (K. C. Persaud, S. M. Khaffaf, J. S. Payne, A. M. Pisanelli, D. H. Lee, H. G. Byun, Sen. Actuators. B 1996, 35-36, 267-273, M. H. Yun, N. V. Myung, R. P. Vasquez, C. Lee, E. Menke, R. M. Penner, Nano Lett. 2004, 4, 419-422, K. Ramanathan, M. A. Bangar, M. H. Yun, W. Chen, A. Mulchandani, N. V. Myung, Nano Lett. 2004, 4, 1237-1239 and D. T. McQuade, A. E. Pullen, T. M. Swager, Chem. Rev. 2000, 100, 2537-257 '4). For instance, Craighead et al. , Nano left. 2004, 4, 671-675, have reported a polyaniline nanowire chemical sensor 30 times more sensitive than the traditional film-based sensors to ammonium gas. Huang et al., J. Am. Chem. Soc. 2003, 125, 314-315, reported a nanofiber film sensor that responds much faster than the conventional film sensor to HCl gas. Apart from the detection of chemical vapors, the improved sensing behavior is also observed for detecting biological

molecules, such as glucose ⁽ E. S. Forzani, H. Q, Zhang, L. A. Nagahara, I. Amlani, R. Tsui, N. J. Tao, Nano Lett. 2004, 4, 1785-1788) and biotin (K. Ramanathan, M. A. Bangar, M. H. Yun, W. Chen, N. V. Myung, A. Mulchandani, J. Am. Chem. Soc. 2005, 127, 496-497).

A sensor which uses an immobilized affinity component capable of interacting with an analyte species and associated with a conducting polymer is known from US Patent No. 6,300,123 (Vadgama et al, assigned to the Victoria University of Manchester). In this patent, a conducting polymer of poly (3-methylthiophene) or poly(pyrrole)bridges two gold electrodes. The affinity component is immobilized with the conducting polymer layer.

Another sensor using conductor polymer compositions is known from US patent application number US 2004/0040841.

This prior art all has in common that an all-polymer concept has currently not yet been applied to nanosensors. This is possibly due to the limitation in the resolution and integration of the conducting polymer lines.

The term "nanosensor", "nanowire" and "nanoscale" as used in this patent application imply that at least one dimension of the object has a size which is in the "nanoregion", i.e. less than around 100 nm.

There are basically two approaches to the construction of nanoscale conducting polymeric structures: the synthesis and post assembly method (see, for examples, Y. Huang, X. F. Duan, Q. Q. Wei, C. M. Lieber, Science, 2001, 291, 630-633, P. A. Smith, C. D. Nordquist, T. N. Jackson, T. S. Mayer, B. R. Martin, J. Mbindyo, T. E. Mallouk, Appl. Phys. Lett. 2000, 77, 1399-1401) or the microfabrication method (taught in J. Y. Bai, C. M. Snively, W. N.

Delgass, J. Lauterbach, Adv. Mater. 2002, 14, 1546-1549, F. Shi, B. Dong, D. L. Qiu, J. Q.

Sun, T. Wu, X. Zhang, Adv. Mater. 2002, 14, 805-809, Y. N. Xia, G. M. Whitesides, Angew.

Chem. Int. Ed. 1998, 37, 550-575, C. B. Gorman, H. A. Biebuyck, G. M. Whitesides, Chem.

Mater. 1995, 7, 526-529, Z. Y. Huang, P. C. Wang, A. G. MacDiarmid, Y. N. Xia, G. M. Whitesides, Langmuir 1997, 13, 6480-6484, K. M. Vaeth, R. J. Jackman, A. J. Black, G. M.

Whitesides, K. F. Jensen, Langmuir 2000, 16, 8495-8500, B. W. Maynor, S. F. Filocamo, M.

W. Grinstaff, J. Liu, J. Am. Soc. Chem. 2002, 124, 522-523, J. H. Lim, C. A. Mirkin, Adv.

Mater. 2002, 14, 1474-1477 and M. Su, M. Aslam, L. Fu, N. Q. Wu, V. P. Dravidλ/jp/. Phys.

Lett. 2004, 84, 4200-4202 (photolithography, soft lithography, etc). In the former approach, the sub 100 nm structures can be readily obtained by either template synthesis (taught in Z.

H.Cai, C. R. Martin, J. Am. Chem. Soc. 1989, Ul, 4138-4139, W. B. Liang, C. R. Martin, J.

Am. Chem. Soc. 1990, 112, 9666-9668, C. R. Martin, Science 1994, 266, 1961-1966) or electrospinning (taught in D. H. Reneker, I. Chun, Nanotechnology, 1996, 7, 216-223, D. H.

Reneker, A. L. Yarin, H. Fong, S. Koombhongse, J. Appl. Phys. 2000, 87, 4531-4547, 1. D. Norris, M. M. Shaker, F. K. Ko, A. G. MacDiarmid, Synth. Met. 2000, 114, 109-114, A. G.

MacDiarmid, W. E. Jones, I. D. Norris, J. Gao, A. T. Johnson, N. J. Pinto, J. Hone, B. Han, F.

K. Ko, H. Okuzaki, M. Llaguno, Synth. Met. 2001, 119, 27-30, D. Li, Y. L. Wang, Y. N. Xia,

Nano Lett. 2003, 3, 1167-1171, D. Li, Y. N. Xia, Nano Lett. 2004, 4, 933-938). However, manipulation and positioning of these synthesized nano-objects with respect to the microelectrodes is rather difficult and not precise. In the latter case, the microfabrication techniques provide conducting polymer microstructures, but these techniques possess significant limitation for patterning structures of sub 100 nm dimensions.

Summary of the Invention

It is therefore an object of the invention to provide a method of fabrication which overcomes the above limitations.

It is furthermore an object of the invention to fabricate a polymer nanosensor with a resolution of less than 100 nm,

In the present work, fabrication of an all-polymer nanosensor by a copolymer strategy with a resolution less than 100 nm is described. Copolymerization of a conducting polymer with another components is known to be an effective way to improve the solubility and processability of conducting polymers (as has been show in several papers: J. R. Reynolds, P.

A. Poropatic, R. L. Toyooka, Macromolecules 1987, 20, 958-961, D. Stanke, M. L.

Hallensleben, L. Toppare, Synth. Met. 1995, 72, 89-94, D. Stanke, M. L. Hallensleben, L.

Toppare, Synth Met. 1995, 72, 167-171, D. Stanke, M. L. Hallensleben, L. Toppare, Synth.

Met. 1995, 73, 261-266, F. Fusalba, D. Belanger, J. Phys. Chem. B 1999, 103, 9044-9054, C. J. Xia, X. W. Fan, M. Park, R. C. Advincula, Lcmgmuir, 2001, 17, 7893-7898, and P.

Taranekar, X. W. Fan, R. Advincula, Langmuir, 2002, 18, 7943-7952.

By adjusting the fraction of the two monomers in the resulting copolymer, the properties of the conducting polymer such as conductivity and adhesion, can also be tuned. Adhesion has been demonstrated to be quintessential for the microfabrication techniques that involve lift off processes, e.g. the deposition of metals (see S. Y. Chou, P. R. Krauss, P. J. Renstrom, Appl. Phys. Lett. 1995, 67, 3114-3116, S. Y. Chou, P. R. Krauss, P. J. Renstrom, Science 1996, 272, 85-87and S. Y. Chou, P. R. Krauss, P. J. Renstrom, J. Vac. Sci. Technol B 1996, 14, 4129- 4133). Conducting polymers are usually not amenable to the lift off process because their films do not adhere to the substrate. As a result, they can be easily peeled off from the substrate to give freestanding films. Various methods have been established in order to

improve the adhesion of conducting polymer films, e.g. surface anchoring (R. A. Simon, A. J. Ricco, M. S. Wrighton, J. Am. Chem. Soc. 1982, 104, 2031-2034, R. J. Willicut, R. L. McCarley, J. Am. Chem. Soc. 1994, 116, 10823-10824, and C. O. Noble, R. L. McCarley, J. Am. Chem. Soc. 2000, 122, 6518-6519), addition of additives (E. L. Kupila, J. Kankare, Synth. Met. 1995, 74, 241-249) etc. By utilizing both silane groups and a surfactant as glue molecules, the fabrication of sub-micron polypyrrole wires through a lift off process was reported (B. Dong, M. Krutschke, X. Zhang, L. F. Chi, H. Fuchs, Small 2005, 1, 520-524). However, due to the lack of control over the film thickness during deposition, this method is not suitable for high resolution (< 100 nm) fabrication.

Description of the Figures

Fig. 1 shows a schematic representation of the fabrication process.

Fig. 2 shows the molecular formula of the copolymer. Fig. 3a shows an AFM image of an 80 nm wide polypyrrole wire (size: 11 μmxl 1 μm).

Fig. 3b shows optical images of six pairs of polypyrrole microelectrode shaped structures

(size: 475 μm><390 μm).

Fig. 3c shows an enlarged AFM image of the area inside the black box of Figure 3b, showing one 100 nm wide polypyrrole wire that bridges the end of two polypyrrole microelectrodes (size: 9 μm ^χ lθ μm).

Fig. 4a shows the I-V characteristics of a 100 nm all-polypyrrole nanodevice as shown in

Figure 3c.

Fig. 4b show a real time response of this 100 nm nanowire sensor (Figure 3c) to a 240 ppm

NH ₃ stream (40 s on / 40 s off). Fig. 4c shows the sensitivity dependence on the width of the wire between the electrodes (at constant thickness).

Fig. 5a shows optical images of five pairs of polyaniline microelectrode shaped structures on silicon substrate with 100 nm SiO ₂ layer (size: 350 μm*200 μm).

Fig. 5a inset shows an AFM image of one all-polyaniline device containing 200 nm wire, size: 3.5 μm ^χ 3.5 μm). Fig. 5b shows the I-V characteristics of the structure shown in Figure 5a inset.

Detailed Description of the Invention

The present invention is based on using a copolymer strategy to control the thickness, adhesive and electrical properties of conducting polymer by incorporating a surface active monomer into the main chains of the conducting polymer, thus make the conducting polymer suitable for the fabrication of devices exclusively based on conducting polymers with a sub 100 nm resolution through a lift off process. Due to the generality of the copolymerization process, the method is applicable to a wide range of species of conducting polymers. Two different types of all-polymer nanostructures consisting exclusively of polypyrrole or polyaniline are fabricated and their use as nanosensors are demonstrated. The invention is not limited to these types of conducting polymers but could also be used by other polymers, such as light-emitting polymers.

Fig. 1 depicts the fabrication process comprising three steps. In the first step, a resist layer 10 is deposited on the surface of a substrate 20 and a resist pattern 30 is defined on the photoresist using e-beam lithography as is known in the art. In the second step, a copolymer film 40 thinner than the resist layer 10 is deposited by oxidizing pyrrole (or aniline) and N-(3- trimethoxysilylpropyl)pyrrole (abbreviated as py-silane) with iron chloride. Finally, the resist layer 10 is lifted off in acetone by sonication.

Figure 2 depicts the structure of the copolymers used for the copolymer film 40. In order to realize the successful fabrication of conducting polymer structures by the lift off process and the further application as sensors, conductivity and adhesion as well as their combination are the parameters that should be taken into account. In this work, the two-point measurement method and the adhesion tape test (as taught in Z. Y. Huang, P. C. Wang, A. G. MacDiarmid, Y. N. Xia, G. M. Whitesides, Langmuir 1997, 13, 6480-6484) was respectively used to estimate the electrical and adhesive properties of the copolymer film 40, respectively. Taking polypyrrole as an example, the introduction of py-silane has a significant influence on the properties of polypyrrole as is shown in Table 1.

Table 1. Influence of copolymer composition on the properties of the resulting polypyrrole film.

Pyrrole: Film Film Withstand py-silane conductivity thickness adhesion

(v%:v%) (S/cm) (nm) tape test

(yes/no)

100:0 32±5 60±10 no

91:9 20±4 50±10 yes

73:27 5.5±1.5 40±10 yes

55:45 0.45±0.2 34±10 yes

36:64 0.013±0.005 26±10 yes

22:78 2.6 ^χ l0- ⁵ ±l ^χ l0- ⁵ 17±10 yes

0:100 ^O ^"6 <10 yes

Notably, copolymers that contain only a small amount of py-silane (9% volume percent) can successfully withstand the adhesion tape test whereas pure polypyrrole cannot. Moreover, upon increasing the fraction of py-silane, the electrical conductivity and film thickness of the copolymer film 40 decreases (as described in J. R. Reynolds, P. A. Poropatic, R. L. Toyooka, Macromoϊecules 1987, 20, 958-961, D. Stanke, M. L. Hallensleben, L. Toppare, Synth. Met. 1995, 72, 89-94, D. Stanke, M. L. Hallensleben, L. Toppare, Synth. Met. 1995, 72, 167-171, D. Stanke, M. L. Hallensleben, L. Toppare, Synth. Met. 1995, 73, 261-266 F. Fusalba, D.

Belanger, J. Phys. Chem. B 1999, 103, 9044-9054 C. J. Xia, X. W. Fan, M. Park, R. C. Advincula, Langmuir, 2001, 17, 7893-7898 P. Taranekar, X. W. Fan, R. Advincula, Langmuir, 2002, 18, 7943-7952) The thickness of the copolymer film 40 can be well controlled by the deposition time (as is shown in Z. Y. Huang, P. C. Wang, A. G. MacDiarmid, Y. N. Xia, G. M. Whitesides, Langmuir 1997, 13, 6480-6484), thus the copolymer film 40 can be kept thinner than the resist layer 10, thereby facilitating the lift off process. In order to obtain a strongly adherent copolymer film 40 that retained as high an electrical conductivity as possible, depositions were carried out at a pyrrole to py-silane volume ratio of 91 :9 unless mentioned otherwise. Under these conditions, the actual copolymer composition is estimated to be roughly 97:3 (pyrrole to py-silane) based on XPS measurements (Table 2). See also J. R. Reynolds, P. A. Poropatic, R. L. Toyooka, Macromolecules 1987, 20, 958-961, D. Stanke, M. L. Hallensleben, L. Toppare, Synth. Met. 1995, 72, 89-94, D. Stanke, M. L. Hallensleben, L. Toppare, Synth. Met. 1995, 72, 167-171, D. Stanke, M. L. Hallensleben, L. Toppare, Synth Met. 1995, 73, 261-266, F. Fusalba, D. Belanger, J. Phys. Chem. B 1999, 103, 9044-9054, C. J. Xia, X. W. Fan, M. Park, R. C. Advincula, Langmuir, 2001, 17, 7893-7898, P. Taranekar, X. W. Fan, R. Advincula, Langmuir, 2002, 18, 7943-7952.

Table 2. Binding energies and relative contribution of different elements present in the copolymer deposited at a pyrrole to py-silane ratio of 91 :9 as determined by XPS.

Binding Contribution Assignment energy(ev) ^(0/ -

C CIIss 2 28844..9922 78.6 C Cll 2 28844..7755 C-C

C2 2 288O6..88J3 C-O/C-N

C C33 2 28888..4455 C=O

N NIIss 3 39999..8888 13.5 N N Nlll 3 3 3999777...666555 C=N

N2 399.74 N-H, Pyrrole

N3 400.76 C-N ⁺

Ols 531 .85 7.4

Si2p 101 .97 0.4

Simon et al., J Am. Chem. Soc. 1982, 104, 2031-2034, have previously reported that a py- silane modified electrode with a small coverage of < 5*10 ^"9 mol/cm ² can dramatically improve the adhesion of the electrochemically deposited polypyrrole overlayer. The results are thus in agreement with the observation of Simon et al, that is, the existence of a small amount of py-silane is sufficient to promote adhesion of the polypyrrole film. The appearance of a C=O peak and a C-N ⁺ peak in the previously reported high resolution CIs and NIs XPS spectra (as shown in Table 2), can be ascribed to over-oxidation phenomena and doped structures, respectively (F. Fusalba, D. Belanger, J. Phys. Chem. B 1999, 103, 9044-9054, C. J. Xia, X. W. Fan, M. Park, R. C. Advincula, Langmuir, 2001, 17, 7893-7898, P. Taranekar, X. W. Fan, R. Advincula, Langmuir, 2002, 18, 7943-7952).

The invention provides a method of fabrication of conducting polymers structures with a resolution of less than 100 nm. For example, using the invention an 80 nm wide, 11 μm long polypyrrole nanowire was produced on a silicon substrate with a 100 nm SiO ₂ layer (as shown in Figure 3a).. Other substrates can be used which include, but are not limited to, glass, and other OH functional group terminated plastic surfaces. The structure of the polypryrrole wire is initially defined on the resist by e-beam lithography. Since an inexpensive technique to pattern the resist at a sub 100 nm scale has already been established (e.g. nanoimprinting - see S. Y. Chou, P. R. Krauss, P. J. Renstrom, Appl. Phys. Lett. 1995, 67, 3114-3116, S. Y. Chou, P. R. Krauss, P. J. Renstrom, Science 1996, 272, 85-87 and S. Y. Chou, P. R. Krauss, P. J.

Renstrom, J. Vac. ScL Technol. B 1996, 14, 4129-4133), the method of the invention opens an opportunity for large scale patterning of conducting polymer nanostructures in a single step, which may be useful in many different application fields.

Precise manipulation and placement of the nanostructures at desired locations and their integration with larger scale systems has long been a challenge and has set a serious hindrance for the further development of nanoelectronics (see, for example, Y. Huang, X. F. Duan, Q. Q. Wei, C. M. Lieber, Science, 2001, 291, 630-633 and P. A. Smith, C. D. Nordquist, T. N. Jackson, T. S. Mayer, B. R. Martin, J. Mbindyo, T. E. Mallouk, Appl. Phys. Lett. 2000, 77, 1399-1401). Exploiting advantages of the method of the invention, the nanowires can be integrated in between the conducting polymer microelectrodes in one deposition step. This facilitates, in particular, the fabrication of an all-polymer nanosensor. Fig. 3b shows an optical image of six pairs of polypyrrole microelectrodes on a silicon substrate with a 100 nm SiO ₂ layer (structures defined by e-beam lithography). The polypyrrole wires situated in between the polypyrrole microelectrodes are not visible at the magnification of Fig. 3b. The overall electrodes consist of homogeneous, closely packed, globular shaped polypyrrole structures (see, for example, Figure 3c, electrode part). It has been reported by T. Silk, Q. Hong, J. Tamm, R. G. Compton, Synth. Met. 1998, 93, 59-64, that the surface morphology of polypyrrole films is globular at film thicknesses below 1000 nm and is independent of the dopant. Since the thicknesses of polypyrrole structures fabricated using the inventive method are all well below 100 nm (see Table 1), the measured morphology of this polypyrrole nanodevice (Figure 3c) is consistent with the observations in the literature. The densely packed, defect free nature of this polypyrrole film indicates that it can serve as a suitable substitute for metals as the electrode material (see, for example, M. Angelopoulos, IBM J. RES. & DEV. 2001, 45, 57-75). All six pairs of electrodes were successfully connected with the polypyrrole nanowires, proving the reliability of this strategy. In Figure 3c one of the six junctions, consisting of one single polypyrrole nanowire (100 nm wide, 1.25 μm long) bridging the ends of two polypyrrole microelectrodes, is shown.

To demonstrate the functionality of the structure, a current vs. potential study was carried out. A linear dependence of the current on the applied potential was observed (as is shown in Fig. 4a), confirming the ohmic behavior of the material. The sensing performance of the device was evaluated by exposing it to a 240 ppm NH ₃ stream. The detection of NH ₃ in air is of interest from an environmental point of view because of the high toxicity of this gas. The sensing principle is based on the fact that the electron-donating molecule (in this case NH ₃ ) can reduce the charge carrier concentration of polypyrrole (a p-type conducting polymer or electron acceptor) and decrease its conductivity (see J. P. Blanc, N. Derouiche, A. El Hadri, J. P. Germain, C. Maleysson, H. Robert, Sen. Actuators. B 1990, 1, 130-133 and J. Janata, M. Josowicz, D. M. DeVaney, Anal. Chem. 1994, 66, 207R-228R). The device shown in Fig. 3c exhibits a reversible response upon the addition of NH ₃ with a sensitivity (defined as R/Ro-1, where Ro is the initial resistance, while R is the resistance after exposure to NH ₃ ) of 0.8 (Fig. 4b), which is of the same order of magnitude as reported for polypyrrole-based sensors (as discussed in H. Nagase, K. Wakabayashi, T. Imanaka, Sen. Actuators. B 1993, 14, 596-597 and M. Brie, R. Turcu, C. Neamtu, S. Pruneanu, Sen. Actuators. B 1996, 37, 119-122).

This value can be further improved by the introduction of other anionic dopants (see H. Nagase, K. Wakabayashi, T. Imanaka, Sen. Actuators. B 1993, 14, 596-597 and M. Brie, R. Turcu, C. Neamtu, S. Pruneanu, Sen. Actuators. B 1996, 37, 119-122). The sensitivity of this all-polymer nanosensor was compared with a polypyrrole nanowire sensor with metal electrode contact and no difference was observed. This indicates that the nanowire is the key element that determines the sensitivity. By increasing the width of the wire from nanometer regime to micrometer (e.g. 2 μm in width) or even into a bulk film, a decrease in sensitivity was observed (see Fig. 4c), proving the superiority of the nanoscale device. This is likely to be due to the high surface area to volume ratio of the nanowire. A conductivity enhancement trend was also observed with decreased wire width which is in agreement with the results

reported in literature (Z. H.Cai, C. R. Martin, J. Am. Chem. Soc. 1989, 111, 4138-4139, W. B. Liang, C. R. Martin, J. Am. Chem. Soc. 1990, 112, 9666-9668, C. R. Martin, Science 1994, 266, 1961-1966).

This method of the invention can be readily extended from polypyrrole to other systems. Fig. 5 shows an example of the all-polymer nanodevices consisting exclusively of polyaniline and the corresponding I-V characteristic of one 200 run all-polyaniline nanodevice. Since the copolymerization is highly applicable to a wide range of monomers such as pyrrole, thiophene, aniline and their substituted derivatives, one could easily obtain conductive nanostrucrures comprising different components with this method, making it useful in fabricating all-polymer nanosensor arrays and other organic nanoelectronic devices.

Although the fabricating all-polymer nanosensor was demonstrated on silicon surface, the concept can be easily extended to other surfaces such as glass and OH functional group terminated plastic surfaces, , which can chemically bind with silian molecule.

Examples

Materials and fabrication methods: Iron chloride (FeCl ₃ , 97%), pyrrole and aniline were purchased from Sigma-Aldrich. N-(3- trimethoxysilylpropyl)pyrrole was purchased from ABCR GmbH. Poly (methyl methacrylate) (PMMA), 950K and 5OK, was purchased from All Resist GmbH. All chemicals were used without further purification. The silicon wafers with a 100 nm thermally oxidized SiO ₂ layer were purchased from Si-mat Company.

One example of a polypyrrole copolymer deposition process is as follows: 0.72 g (or 0.08 g) FeCl ₃ was dissolved in 7 ml purified water. Another solution containing 300 μl pyrrole, 30 μl py-silane, 2 ml isopropanol (absent in those cases where 0.08 g FeCl ₃ was used) and 12 ml purified water was added to initiate polymerization at room temperature (21 ⁰ C). The substrate was patterned with the resist was placed vertically into the resulting solution for 10 min in order to deposit the copolymer films. The deposition process of polyaniline copolymer resembles the above one: 0.72 g FeCl ₃ was dissolved in 7 ml purified water. Another solution containing 1 ml aniline, 30 μl py-silane, and 7 ml purified water was added to initiate polymerization (21 ⁰ C). The substrate with the patterned resist was immersed into this solution for 1 h to deposit polyaniline copolymer.

It should be noted that substituted analogues of pyrrole and aniline (such as poly (substituted) pyrrole or poly-pyrrole-aniline) can also be used in the co-polymer deposition process. Furthermore, it is noted that thiophene (and analogues) could also be used

Instruments and characterization:

E-beam lithography was performed by a LEO VP 1530 field emission scanning electron microscope (SEM) with a Raith Elphy Plus lithography attachment system. Atomic Force Microscopy (AFM) measurements were carried out on a Multimode Nanoscope IHa instrument (Digital Instrument) operating in tapping mode with silicon cantilevers (resonance frequency in the range of 280-340 kHz). Electrical measurements were performed with a Keithley 6430 sub-femtoamp remote Source Meter. X-ray Photoelectron Spectroscopy (XPS) measurements were carried out using a VG ESCALAB 250 imaging XPS spectrometer. The samples deposited on gold were irradiated with monochromatic Al Ka X-rays (15 kV, 150 W, 500 μm spot size). The real time gas-sensing experiment was carried out by exposing the conducting polymer wire or film to a 240 ppm NH ₃ stream applied with a flow rate of 4.4 L/h

via a gas tubing source held at a fixed distance of 0.5 cm above the sample. The resistance change was monitored and recorded while supplying a constant potential of 100 mV.

Reference Numbers