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Prototypical single-molecule transistors with supramolecular gates: varying dipole orientation
Synthetic Metals 146 (2004) 269–272
Prototypical single-molecule transistors with supramolecular gates: varying dipole orientation F. J¨ackela , Z. Wangb , M.D. Watsonb,c , K. M¨ullenb,1 , J.P. Rabea,∗ a
Department of Physics, Humboldt University Berlin, Newtonstraße 15, 12489 Berlin, Germany b Max-Planck-Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany c Department of Chemistry, University of Kentucky, Lexington KY 40506-0055, USA Available online 3 October 2004
Abstract Recently, we presented a prototypical three-terminal device, in which the current through a hybrid-molecular diode, whose current voltage characteristic is determined by a single molecule in the junction of a scanning tunneling microscope, is modified by nanometer-sized charge transfer complexes covalently linked to the molecule in the gap [Phys. Rev. Lett. 92 (2004) 188303]. Since the complexes are formed by electron acceptors covalently bound to the molecule in the gap, and electron donors coming from the ambient fluid, this set-up represents a chemical-field-effect transistor based on a single molecule with a nanometer-sized gate. The gating effect was explained by an interface dipole model. Here, we present first tests of this model addressing the orientation of the electrical dipoles. By using amino- and carboxylic acid functionalized molecules in the hybrid-molecular diode we study the effect of dipoles being perpendicular, instead of parallel, to the transistor channel direction and find agreement with the model. © 2004 Elsevier B.V. All rights reserved.
1. Introduction During the last years much attention has been paid to the experimental as well as theoretical study of electron transport properties of single molecules [2,3]. This was mainly motivated by the proposal of Aviram and Ratner for a rectifier based on a single molecule [4] and led to the vision of molecular electronics. Hybrid-molecular diodes whose current voltage characteristics are determined by a single molecule in a well-controlled gap have been demonstrated using mechanically controlled break junctions [5], scanning tunneling microscopes (STM) [6–8] and nano-fabricated pores [9]. Also three-terminal devices, i.e. field-effect transistors, based on single molecules [10,11] and carbon nanotubes [12,13] have been made. However, these implementations used meso- or macroscopic electrodes which were not readily scalable to nanoscale dimensions. Recently, we showed ∗
Corresponding author. Tel.: +49 30 2093 7788/7621; fax: +49 30 2093 7632. E-mail addresses: [email protected] (K. M¨ullen), [email protected] (J.P. Rabe). 1 Co-corresponding author. Fax: +49 6131 379 350. 0379-6779/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.synthmet.2004.08.030
in a mono-molecular approach that the current voltage characteristic of a hybrid-molecular diode, made from a hexaperi-hexabenzocoronene (HBC) in an STM-junction, can be changed by bringing charge transfer complexes of organic molecules close (∼2 nm) to the molecule in the gap [1]. Thus, the gate in this prototypical transistor is of truly molecular scale, relying on the orientation of electrical dipole moments of the complexes mainly parallel to the channel direction. Here, after a short summary of the key results reported in [1], we present first experiments testing the suggested model. In particular, we varied the orientation of the electrical dipoles from parallel to mainly perpendicular to the channel direction by employing HBCs carrying amino and carboxylic acid functions. Within the experimental accuracy, we find agreement with the predictions of our model.
2. Experimental Fig. 1 displays the molecules under study namely three electron rich hexa-peri-hexabenzocoronenes (HBCs) bearing in the periphery (1) six-electron acceptors (anthraquinones,
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Fig. 1. Chemical formulae of the molecules investigated. Hexa-peri-hexabenzocoronenes (HBCs) bearing six anthraquinone (AQ) functions 1, an amino group 2 and a carboxylic acid group 3, respectively, and 9,10-dimethoxyanthracene (DMA) 4.
AQs), (2) one amino group and five branched alkyl chains or (3) one carboxylic acid function terminated short alkyl chain, as well as the electron donor 9,10-dimethoxyanthracene 4 (DMA). The synthesis, self-assembly and ensemble properties of these materials are described elsewhere [14,15]. Scanning tunneling microscopy (STM) and spectroscopy (STS) were performed at the solid–liquid interface [16] between an almost saturated solution of the molecules under study in 1,2,4-trichlorobenzene and the basal plane of freshly cleaved highly oriented pyrolytic graphite (HOPG) using a home-built beetle-type STM interfaced with a commercial controller (Omicron). STM tips were mechanically cut from a 0.25 mm thick Pt/Ir (80%/20%) wire. The lattice of the underlying HOPG substrate could be routinely visualized at low tunneling junction impedance which allowed for an insitu calibration of the piezo-scanner. STS measurements were performed by positioning the tip above the region of interest and running a voltage ramp with 100 equidistant values between −1.5 and +1.5 V with the feedback loop switched off. For acceptance of spectroscopic data, stable imaging and no lateral shift between images of different scan direction was demanded. Finally, current voltage-characteristics (I–Vs) for a number of molecules were averaged.
3. Results and discussion Fig. 2a shows a high-resolution image of a highly oriented monolayer formed from a mixed solution of 1 and 4 with a tenfold molar excess of 4. The bright circular features can be attributed to the conjugated cores of the HBCs in 1 while the smaller less bright spots are assigned to charge transfer
complexes between 4 and the AQ moieties in 1 [1]. I–Vs measured through HBC-cores in domains where such charge transfer complexes are coadsorbed differ significantly from those where no complexes are present as shown in Fig. 3a. In particular, increased tunneling probability at positive sample bias is observed when the complexes are present. However, it should be noted that the two curves were not necessarily measured with the same tip-sample-separation since this distance is controlled by the settings of the feedback loop before switching it off (−1.4 V and 500 pA in the present case). Thus, all I–Vs must exhibit a current of 500 pA at −1.4 V.We recently explained the observed increase in tunneling current at positive bias [1] by the formation of an interface dipole, originating from the oriented dipoles of the charge transfer complexes, which shifts the molecular frontier orbitals with respect to the Fermi level of HOPG and therefore changes the tunneling probabilities at given biases. The relative shift of the molecular frontier orbitals and the Fermi level of HOPG could be estimated within this model to be ∼120 meV which is in quantitative agreement with the model, using calculations for the dipole moment of the charge transfer complexes between AQ and DMA. In the model of the interface dipole only the components of the dipole moments perpendicular to the substrate surface contribute to the interface dipole. Consequently, a strong dependence of the effect on the orientation of the dipoles should be expected. In particular, no changes in tunneling probabilities should be observed for the dipoles being parallel to the substrate surface. We therefore focused on compounds 2 and 3, HBCs decorated with amino and carboxylic acid groups respectively, which should be able to form complexes involving a proton transfer from the acid to the amino group [17]. Due to the tendency of alkyl chains to
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271
Fig. 2. STM current images of (a) mixture of 1 and 4; clearly visible are the HBC cores (bright circular spots) and the charge transfer complexes between AQ and DMA (smaller spots on zig-zag-row); (b) 2 exhibiting hexagonal arrangement, (c) 3 exhibiting hexagonally packed domains and areas with a dimer structure and (d) 2 + 3 forming the same structures as 3. Tunneling parameters were (a) sample bias Ut = −1.2 V and average tunneling current It = 270 pA (b) Ut = −1.0 V and It = 100 pA (c) Ut = −1.2 V and It = 100 pA and (d) Ut = −0.8 V and It = 50 pA.
physisorb with their long axis parallel to the basal plane of graphite [16] the major component of the resulting dipole is expected to be oriented parallel to the substrate surface. Fig. 2b–d display STM current images of highly ordered monolayers formed from solutions of 2, 3 and equimolar mixtures of 2 and 3 (further referred to as 2 + 3), respectively. In all three cases the bright circular features, corresponding to high tunneling probability, can be assigned to the conjugated HBC-cores since the energy difference between their frontier orbitals and the Fermi level of HOPG is rather small [18]. The amine functionalized HBC 2 arranges in a hexagonal pattern with a lateral spacing of (1.85 ± 0.07) nm. The unit cell does not offer enough space for a single molecule to lie completely flat on the surface. Indeed the sterically demanding methyl branching at the ␥-position of the alkylsubstituents forces the rest of the side-chains to bend up and to be solubilized in the supernatant solution [19]. For compound 3, additionally to the hexagonal packing induced by the branched side chains, we observe a dimer arrangement with the length of the unit cell vectors being a = (4.26 ± 0.18) nm, b = (1,81 ± 0.09) nm, and an angle of (63.7 ± 1.8)◦ between them. This arrangement was shown to be induced by hydrogen bonds between the acid groups [15]. For the mixtures 2 + 3, the same two-dimensional structures as for neat 3 are found. Since the arrangements for 2 + 3 and 3 are indistinguishable within our experimental accuracy, we have no
direct proof at the moment that the desired complex between carboxylic acid and amino groups are formed. However, it has been shown by means of IR-spectroscopy that HBCs bearing one carboxylic acid group can form stochiometric complexes with the amino groups in poly(ethylene oxide)-block-poly(llysine) [17]. In particular, this complex formation is able to compete with the hydrogen bond formation between the acid groups. Since IR-spectroscopy of thin films for the present system is subject of ongoing work we assume that at least in a number of domains the desired complexes have been formed. We therefore measured current voltage characteristics through HBCs in the different arrangements in 2, 3 and 2 + 3. Fig. 3b displays I–Vs measured through the HBC cores of 2, 3 and 2 + 3. Within the experimental error, no significant differences can be detected. In all cases, a rectifying behavior is observed with larger currents at negative sample bias. This behavior was previously observed for alkylated HBCs [6] and has been shown to be related to resonantly enhanced tunneling through the highest occupied molecular orbital (HOMO) of the molecule [20]. For the mixtures 2 + 3, also I–Vs through HBCs in different domains could not be distinguished. This finding is consistent with the model of the interface dipole since electrical dipoles oriented parallel to the surface should not give rise to an interface dipole. Consequently, no effect on the current voltage characteristics should be observed.
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and carboxylic acid groups, which was shown for related systems, needs further clarification. This is subject of ongoing work.
Acknowledgements This work was supported by the Volkswagenstiftung, the European Union (MAC-MES), the German Ministry for Science and Technology and the German Science Foundation.
References
Fig. 3. (a) I–Vs through HBC-cores in mixtures of 1 and 4 measured in domains where charge transfer complexes between 4 and the AQ-moieties in 1 are coadsorbed (full circles) and in domains where no complexes are present (open triangles). (b) I–Vs through HBC-cores in monolayers of 2 (open triangles), 3 (open squares) and 2 + 3 (full triangles). Tunneling parameters before switching off the feedback loop were sample bias Us = −1.4 V and average tunneling current It = 500 pA.
4. Conclusions In this contribution, we presented first tests of the interface dipole model recently suggested for the gating effect observed in prototypical single-molecule chemical-field-effect transistors with nanometer-sized gates [1]. In particular we varied the orientation of the electrical dipoles from parallel to perpendicular with respect to the transistor channel direction by employing hexa-peri-hexabenzocoronenes bearing amino and carboxylic acid functions. Within the experimental accuracy no effect on the current voltage characteristics through HBC-cores was observed as predicted by the model. However, the formation of the desired complex between amino
[1] F. J¨ackel, M.D. Watson, K. M¨ullen, J.P. Rabe, Phys. Rev. Lett. 92 (2004) 188303. [2] C. Joachim, J.K. Gimzewski, A. Aviram, Nature 408 (2000) 541. [3] A. Nitzan, M.A. Ratner, Science 300 (2003) 1384. [4] A. Aviram, M.A. Ratner, Chem. Phys. Lett. 29 (1974) 277. [5] C. Kergueris, J.-P. Bourgoin, S. Palacin, D. Esteve, C. Urbina, M. Magoga, C. Joachim, Phys. Rev. B 59 (1999) 12505. [6] A. Stabel, P. Herwig, K. M¨ullen, J.P. Rabe, Angew. Chem. Int. Ed. 34 (1995) 303. [7] A. Dhirani, P.-H. Lin, P. Guyot-Sionnest, R.W. Zehner, L.R. Sita, J. Chem. Phys. 106 (1997) 5249. [8] R.M. Metzger, Acc. Chem. Res. 32 (1999) 950. [9] C. Zhou, M.R. Desphande, M.A. Reed, L. Jones II, J.M. Tour, Appl. Phys. Lett. 71 (1997) 611. [10] H. Park, J. Park, A.K.L. Lim, E.H. Anderson, A.P. Alivisatos, P.L. McEuen, Nature 407 (2000) 57. [11] W. Liang, M.P. Shores, M. Bockrath, J.R. Long, H. Park, Nature 417 (2002) 725. [12] S. Tans, A.R.M. Verschueren, C. Dekker, Nature 393 (1998) 49. [13] J.A. Misewich, R. Martel, P. Avouris, J.C. Tsang, S. Heinze, J. Tersoff, Science 300 (2003) 783. [14] P. Samori, X. Yin, N. Tchebotareva, Z. Wang, T. Pakula, F. J¨ackel, M.D. Watson, A. Venturini, K. M¨ullen, J.P. Rabe, J. Am. Chem. Soc. 126 (2004) 3567. [15] D. Wasserfallen, I. Fischbach, N. Chebotareva, M. Kastler, W. Pisula, F. J¨ackel, M.D. Watson, I. Schnell, J.P. Rabe, H.W. Spiess, K. M¨ullen, Submitted. [16] J.P. Rabe, S. Buchholz, Science 253 (1991) 424. [17] A.F. Th¨unemann, S. Kubowicz, C. Burger, M.D. Watson, N. Tchebotareva, K. M¨ullen, J. Am. Chem. Soc. 125 (2003) 352. [18] R. Lazzaroni, A. Calderone, J.L. Br´edas, J.P. Rabe, J. Chem. Phys. 107 (1997) 99. [19] P. Samor´ı, A. Fechtenk¨otter, F. J¨ackel, T. B¨ohme, K. M¨ullen, J.P. Rabe, J. Am. Chem. Soc. 123 (2001) 11462. [20] F. J¨ackel, Z. Wang, M.D. Watson, K. M¨ullen, J.P. Rabe, Chem. Phys. Lett. 387 (2004) 372.
Prototypical single-molecule transistors with supramolecular gates: varying dipole orientation F. J¨ackela , Z. Wangb , M.D. Watsonb,c , K. M¨ullenb,1 , J.P. Rabea,∗ a
Department of Physics, Humboldt University Berlin, Newtonstraße 15, 12489 Berlin, Germany b Max-Planck-Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany c Department of Chemistry, University of Kentucky, Lexington KY 40506-0055, USA Available online 3 October 2004
Abstract Recently, we presented a prototypical three-terminal device, in which the current through a hybrid-molecular diode, whose current voltage characteristic is determined by a single molecule in the junction of a scanning tunneling microscope, is modified by nanometer-sized charge transfer complexes covalently linked to the molecule in the gap [Phys. Rev. Lett. 92 (2004) 188303]. Since the complexes are formed by electron acceptors covalently bound to the molecule in the gap, and electron donors coming from the ambient fluid, this set-up represents a chemical-field-effect transistor based on a single molecule with a nanometer-sized gate. The gating effect was explained by an interface dipole model. Here, we present first tests of this model addressing the orientation of the electrical dipoles. By using amino- and carboxylic acid functionalized molecules in the hybrid-molecular diode we study the effect of dipoles being perpendicular, instead of parallel, to the transistor channel direction and find agreement with the model. © 2004 Elsevier B.V. All rights reserved.
1. Introduction During the last years much attention has been paid to the experimental as well as theoretical study of electron transport properties of single molecules [2,3]. This was mainly motivated by the proposal of Aviram and Ratner for a rectifier based on a single molecule [4] and led to the vision of molecular electronics. Hybrid-molecular diodes whose current voltage characteristics are determined by a single molecule in a well-controlled gap have been demonstrated using mechanically controlled break junctions [5], scanning tunneling microscopes (STM) [6–8] and nano-fabricated pores [9]. Also three-terminal devices, i.e. field-effect transistors, based on single molecules [10,11] and carbon nanotubes [12,13] have been made. However, these implementations used meso- or macroscopic electrodes which were not readily scalable to nanoscale dimensions. Recently, we showed ∗
Corresponding author. Tel.: +49 30 2093 7788/7621; fax: +49 30 2093 7632. E-mail addresses: [email protected] (K. M¨ullen), [email protected] (J.P. Rabe). 1 Co-corresponding author. Fax: +49 6131 379 350. 0379-6779/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.synthmet.2004.08.030
in a mono-molecular approach that the current voltage characteristic of a hybrid-molecular diode, made from a hexaperi-hexabenzocoronene (HBC) in an STM-junction, can be changed by bringing charge transfer complexes of organic molecules close (∼2 nm) to the molecule in the gap [1]. Thus, the gate in this prototypical transistor is of truly molecular scale, relying on the orientation of electrical dipole moments of the complexes mainly parallel to the channel direction. Here, after a short summary of the key results reported in [1], we present first experiments testing the suggested model. In particular, we varied the orientation of the electrical dipoles from parallel to mainly perpendicular to the channel direction by employing HBCs carrying amino and carboxylic acid functions. Within the experimental accuracy, we find agreement with the predictions of our model.
2. Experimental Fig. 1 displays the molecules under study namely three electron rich hexa-peri-hexabenzocoronenes (HBCs) bearing in the periphery (1) six-electron acceptors (anthraquinones,
270
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Fig. 1. Chemical formulae of the molecules investigated. Hexa-peri-hexabenzocoronenes (HBCs) bearing six anthraquinone (AQ) functions 1, an amino group 2 and a carboxylic acid group 3, respectively, and 9,10-dimethoxyanthracene (DMA) 4.
AQs), (2) one amino group and five branched alkyl chains or (3) one carboxylic acid function terminated short alkyl chain, as well as the electron donor 9,10-dimethoxyanthracene 4 (DMA). The synthesis, self-assembly and ensemble properties of these materials are described elsewhere [14,15]. Scanning tunneling microscopy (STM) and spectroscopy (STS) were performed at the solid–liquid interface [16] between an almost saturated solution of the molecules under study in 1,2,4-trichlorobenzene and the basal plane of freshly cleaved highly oriented pyrolytic graphite (HOPG) using a home-built beetle-type STM interfaced with a commercial controller (Omicron). STM tips were mechanically cut from a 0.25 mm thick Pt/Ir (80%/20%) wire. The lattice of the underlying HOPG substrate could be routinely visualized at low tunneling junction impedance which allowed for an insitu calibration of the piezo-scanner. STS measurements were performed by positioning the tip above the region of interest and running a voltage ramp with 100 equidistant values between −1.5 and +1.5 V with the feedback loop switched off. For acceptance of spectroscopic data, stable imaging and no lateral shift between images of different scan direction was demanded. Finally, current voltage-characteristics (I–Vs) for a number of molecules were averaged.
3. Results and discussion Fig. 2a shows a high-resolution image of a highly oriented monolayer formed from a mixed solution of 1 and 4 with a tenfold molar excess of 4. The bright circular features can be attributed to the conjugated cores of the HBCs in 1 while the smaller less bright spots are assigned to charge transfer
complexes between 4 and the AQ moieties in 1 [1]. I–Vs measured through HBC-cores in domains where such charge transfer complexes are coadsorbed differ significantly from those where no complexes are present as shown in Fig. 3a. In particular, increased tunneling probability at positive sample bias is observed when the complexes are present. However, it should be noted that the two curves were not necessarily measured with the same tip-sample-separation since this distance is controlled by the settings of the feedback loop before switching it off (−1.4 V and 500 pA in the present case). Thus, all I–Vs must exhibit a current of 500 pA at −1.4 V.We recently explained the observed increase in tunneling current at positive bias [1] by the formation of an interface dipole, originating from the oriented dipoles of the charge transfer complexes, which shifts the molecular frontier orbitals with respect to the Fermi level of HOPG and therefore changes the tunneling probabilities at given biases. The relative shift of the molecular frontier orbitals and the Fermi level of HOPG could be estimated within this model to be ∼120 meV which is in quantitative agreement with the model, using calculations for the dipole moment of the charge transfer complexes between AQ and DMA. In the model of the interface dipole only the components of the dipole moments perpendicular to the substrate surface contribute to the interface dipole. Consequently, a strong dependence of the effect on the orientation of the dipoles should be expected. In particular, no changes in tunneling probabilities should be observed for the dipoles being parallel to the substrate surface. We therefore focused on compounds 2 and 3, HBCs decorated with amino and carboxylic acid groups respectively, which should be able to form complexes involving a proton transfer from the acid to the amino group [17]. Due to the tendency of alkyl chains to
F. J¨ackel et al. / Synthetic Metals 146 (2004) 269–272
271
Fig. 2. STM current images of (a) mixture of 1 and 4; clearly visible are the HBC cores (bright circular spots) and the charge transfer complexes between AQ and DMA (smaller spots on zig-zag-row); (b) 2 exhibiting hexagonal arrangement, (c) 3 exhibiting hexagonally packed domains and areas with a dimer structure and (d) 2 + 3 forming the same structures as 3. Tunneling parameters were (a) sample bias Ut = −1.2 V and average tunneling current It = 270 pA (b) Ut = −1.0 V and It = 100 pA (c) Ut = −1.2 V and It = 100 pA and (d) Ut = −0.8 V and It = 50 pA.
physisorb with their long axis parallel to the basal plane of graphite [16] the major component of the resulting dipole is expected to be oriented parallel to the substrate surface. Fig. 2b–d display STM current images of highly ordered monolayers formed from solutions of 2, 3 and equimolar mixtures of 2 and 3 (further referred to as 2 + 3), respectively. In all three cases the bright circular features, corresponding to high tunneling probability, can be assigned to the conjugated HBC-cores since the energy difference between their frontier orbitals and the Fermi level of HOPG is rather small [18]. The amine functionalized HBC 2 arranges in a hexagonal pattern with a lateral spacing of (1.85 ± 0.07) nm. The unit cell does not offer enough space for a single molecule to lie completely flat on the surface. Indeed the sterically demanding methyl branching at the ␥-position of the alkylsubstituents forces the rest of the side-chains to bend up and to be solubilized in the supernatant solution [19]. For compound 3, additionally to the hexagonal packing induced by the branched side chains, we observe a dimer arrangement with the length of the unit cell vectors being a = (4.26 ± 0.18) nm, b = (1,81 ± 0.09) nm, and an angle of (63.7 ± 1.8)◦ between them. This arrangement was shown to be induced by hydrogen bonds between the acid groups [15]. For the mixtures 2 + 3, the same two-dimensional structures as for neat 3 are found. Since the arrangements for 2 + 3 and 3 are indistinguishable within our experimental accuracy, we have no
direct proof at the moment that the desired complex between carboxylic acid and amino groups are formed. However, it has been shown by means of IR-spectroscopy that HBCs bearing one carboxylic acid group can form stochiometric complexes with the amino groups in poly(ethylene oxide)-block-poly(llysine) [17]. In particular, this complex formation is able to compete with the hydrogen bond formation between the acid groups. Since IR-spectroscopy of thin films for the present system is subject of ongoing work we assume that at least in a number of domains the desired complexes have been formed. We therefore measured current voltage characteristics through HBCs in the different arrangements in 2, 3 and 2 + 3. Fig. 3b displays I–Vs measured through the HBC cores of 2, 3 and 2 + 3. Within the experimental error, no significant differences can be detected. In all cases, a rectifying behavior is observed with larger currents at negative sample bias. This behavior was previously observed for alkylated HBCs [6] and has been shown to be related to resonantly enhanced tunneling through the highest occupied molecular orbital (HOMO) of the molecule [20]. For the mixtures 2 + 3, also I–Vs through HBCs in different domains could not be distinguished. This finding is consistent with the model of the interface dipole since electrical dipoles oriented parallel to the surface should not give rise to an interface dipole. Consequently, no effect on the current voltage characteristics should be observed.
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F. J¨ackel et al. / Synthetic Metals 146 (2004) 269–272
and carboxylic acid groups, which was shown for related systems, needs further clarification. This is subject of ongoing work.
Acknowledgements This work was supported by the Volkswagenstiftung, the European Union (MAC-MES), the German Ministry for Science and Technology and the German Science Foundation.
References
Fig. 3. (a) I–Vs through HBC-cores in mixtures of 1 and 4 measured in domains where charge transfer complexes between 4 and the AQ-moieties in 1 are coadsorbed (full circles) and in domains where no complexes are present (open triangles). (b) I–Vs through HBC-cores in monolayers of 2 (open triangles), 3 (open squares) and 2 + 3 (full triangles). Tunneling parameters before switching off the feedback loop were sample bias Us = −1.4 V and average tunneling current It = 500 pA.
4. Conclusions In this contribution, we presented first tests of the interface dipole model recently suggested for the gating effect observed in prototypical single-molecule chemical-field-effect transistors with nanometer-sized gates [1]. In particular we varied the orientation of the electrical dipoles from parallel to perpendicular with respect to the transistor channel direction by employing hexa-peri-hexabenzocoronenes bearing amino and carboxylic acid functions. Within the experimental accuracy no effect on the current voltage characteristics through HBC-cores was observed as predicted by the model. However, the formation of the desired complex between amino
[1] F. J¨ackel, M.D. Watson, K. M¨ullen, J.P. Rabe, Phys. Rev. Lett. 92 (2004) 188303. [2] C. Joachim, J.K. Gimzewski, A. Aviram, Nature 408 (2000) 541. [3] A. Nitzan, M.A. Ratner, Science 300 (2003) 1384. [4] A. Aviram, M.A. Ratner, Chem. Phys. Lett. 29 (1974) 277. [5] C. Kergueris, J.-P. Bourgoin, S. Palacin, D. Esteve, C. Urbina, M. Magoga, C. Joachim, Phys. Rev. B 59 (1999) 12505. [6] A. Stabel, P. Herwig, K. M¨ullen, J.P. Rabe, Angew. Chem. Int. Ed. 34 (1995) 303. [7] A. Dhirani, P.-H. Lin, P. Guyot-Sionnest, R.W. Zehner, L.R. Sita, J. Chem. Phys. 106 (1997) 5249. [8] R.M. Metzger, Acc. Chem. Res. 32 (1999) 950. [9] C. Zhou, M.R. Desphande, M.A. Reed, L. Jones II, J.M. Tour, Appl. Phys. Lett. 71 (1997) 611. [10] H. Park, J. Park, A.K.L. Lim, E.H. Anderson, A.P. Alivisatos, P.L. McEuen, Nature 407 (2000) 57. [11] W. Liang, M.P. Shores, M. Bockrath, J.R. Long, H. Park, Nature 417 (2002) 725. [12] S. Tans, A.R.M. Verschueren, C. Dekker, Nature 393 (1998) 49. [13] J.A. Misewich, R. Martel, P. Avouris, J.C. Tsang, S. Heinze, J. Tersoff, Science 300 (2003) 783. [14] P. Samori, X. Yin, N. Tchebotareva, Z. Wang, T. Pakula, F. J¨ackel, M.D. Watson, A. Venturini, K. M¨ullen, J.P. Rabe, J. Am. Chem. Soc. 126 (2004) 3567. [15] D. Wasserfallen, I. Fischbach, N. Chebotareva, M. Kastler, W. Pisula, F. J¨ackel, M.D. Watson, I. Schnell, J.P. Rabe, H.W. Spiess, K. M¨ullen, Submitted. [16] J.P. Rabe, S. Buchholz, Science 253 (1991) 424. [17] A.F. Th¨unemann, S. Kubowicz, C. Burger, M.D. Watson, N. Tchebotareva, K. M¨ullen, J. Am. Chem. Soc. 125 (2003) 352. [18] R. Lazzaroni, A. Calderone, J.L. Br´edas, J.P. Rabe, J. Chem. Phys. 107 (1997) 99. [19] P. Samor´ı, A. Fechtenk¨otter, F. J¨ackel, T. B¨ohme, K. M¨ullen, J.P. Rabe, J. Am. Chem. Soc. 123 (2001) 11462. [20] F. J¨ackel, Z. Wang, M.D. Watson, K. M¨ullen, J.P. Rabe, Chem. Phys. Lett. 387 (2004) 372.