Rectification of STM Current to Graphite Covered with Phthalocyanine Molecules

Pomerantz, M.; Aviram, Ari; McCorkle, R. A.; Li, L.; Schrott, A. G.

doi:10.1126/science.255.5048.1115

Cited by 116 publications

(81 citation statements)

References 20 publications

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“…This asymmetric current flow is consistent with the polarity dependence in STM imaging. The asymmetry in I-V characteristics is quantified with an asymmetry ratio (R), which is defined by ԽI(ϪV)Խ͞ԽI(V)Խ (15). At the bias voltages of ϩ1.2 and Ϫ1.2 V, where the STM images in Fig.…”

Section: Resultsmentioning

confidence: 99%

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A fullerene molecular tip can detect localized and rectified electron tunneling within a single fullerene–porphyrin pair

Nishino

Ito

Umezawa

2005

Proc. Natl. Acad. Sci. U.S.A.

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A fullerene molecular tip was used to detect electron tunneling from a single porphyrin molecule. Electron tunneling was found to occur locally from an electron-donating moiety of the porphyrin to the fullerene through charge-transfer interaction between them. In addition, electron tunneling within the single fullereneporphyrin pair exhibited rectifying behavior in which electrons can be driven only at the direction from the porphyrin to the fullerene. It is demonstrated that localized electron tunneling enables us to spatially visualize the frontier orbital of the porphyrin involved in electron tunneling. In addition, rectification demonstrates that the fullerene-porphyrin pair constitutes a molecular rectifier. We believe that molecular tips bring insight into intermolecular electron transmission toward realization of molecular electronics as shown here. molecular electronics ͉ nanoscience ͉ scanning tunneling microscopy E lectron transmission through single molecules is currently an interdisciplinary subject of substantial interest (1) because of molecular-scale electronic device research (2, 3). It is desired to measure the molecular conduction on a single molecule rather than on an ensemble of molecules to eliminate a cooperative transport (4) and avoid averaging out the conduction through the molecules in different conformations (5). Recently, there have been significant advances in knowledge of electron transmission through a single molecule (4). However, few works have been reported on electron transmission through a single molecule to an adjacent single molecule on a nanoscale.Scanning tunneling microscopy (STM) has been an essential tool in nanosciences (6). We have studied the construction of molecular tips for STM. The molecular tip is prepared by chemical modification of an underlying metal tip, and the outermost single adsorbate probes electron tunneling to or from a sample molecule. Importantly, the tunneling current increases when sample and tip molecules form metal coordination or hydrogen-bond interactions that provide overlap of their electronic wave functions. The current increase is ascribed to facilitated tunneling through overlapped wave functions. We have demonstrated that this phenomenon can be used for selective observation of chemical species to overcome poor chemical selectivity in conventional STM (7-13). Because the overlap of electronic wave functions is important for the facilitation of electron tunneling, these results suggest that intermolecular electron tunneling can also be facilitated through a charge-transfer interaction as well as metal coordination and hydrogen-bond interactions.Here, we report on the detection of intermolecular electron tunneling within a single fullerene-porphyrin molecular pair. Electron tunneling was found to occur locally from an electrondonating moiety of the porphyrin to the fullerene through charge-transfer interaction between them, but not in the opposite direction. It was shown that localized tunneling can be applied to visualize the frontier orb...

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Section: Resultsmentioning

confidence: 99%

“…Rectification was reported in a hybrid molecular electronic device where copper phthalocyanine (CuPc) molecules were chemically attached to an oxidized HOPG surface (15). This rectification was explained by resonant tunneling through the peak in the density of states of HOPG͞ CuPc originated by the molecular adsorption.…”

Section: Resultsmentioning

confidence: 99%

A fullerene molecular tip can detect localized and rectified electron tunneling within a single fullerene–porphyrin pair

Nishino

Ito

Umezawa

2005

Proc. Natl. Acad. Sci. U.S.A.

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“…Several molecular rectifying systems have been synthesized in the past decade using Langmuir-Blodgett molecular assembly [2][3][4][5][6]. Attempts to provide experimental proof of molecular rectification were complicated by difficulty in establishing reproducible electrical contacts between metallic electrodes and a single molecule which resulted in uncontrollable interface rectification effects [7].…”

Section: Introductionmentioning

confidence: 99%

Rectification Mechanism in Diblock Oligomer Molecular Diodes

et al. 2006

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We investigated a mechanism of rectification in di-block oligomer diode molecules that have recently been synthesized and showed a pronounced asymmetry in the measured I-V spectrum. The observed rectification effect is due to the resonant nature of electron transfer in the system and localization properties of bound state wave functions of resonant states of the tunneling electron interacting with asymmetric molecule in an electric field. The asymmetry of the tunneling wave function is enhanced or weakened depending on the polarity of applied bias. The conceptually new theoretical approach, the Green's function theory of sub-barrier scattering, is able to provide a physically transparent explanation of this rectification effect based on the concept of the bound state spectrum of a tunneling electron. The theory predicts the characteristic features of the I-V spectrum in qualitative agreement with experiment.In their pioneering paper [1] Aviram and Ratner proposed the idea of a molecular rectifier that contains donor and acceptor π-conjugated segments separated by an insulating σ-bonded segment of molecular wire. Several molecular rectifying systems have been synthesized in the past decade using Langmuir-Blodgett molecular assembly [2][3][4][5][6]. Attempts to provide experimental proof of molecular rectification were complicated by difficulty in establishing reproducible electrical contacts between metallic electrodes and a single molecule which resulted in uncontrollable interface rectification effects [7].Recently, a new class of diode molecules has been synthesized based on di-block oligomer molecules [8,9]. These molecules consisting of thiophene and thiazole structural units, have shown a pronounced rectification effect as a result of built-in chemical asymmetry. Importantly, it was unambiguously shown that the rectification effect is an intrinsic property of di-block oligomer molecules, and not due to the molecule-electrode interfacial interactions. In addition, by synthesizing diode molecules with different terminal thiol groups, it has become possible to assemble the diode molecules between gold electrodes with pre-defined rectification direction [10].In this letter we explain the mechanism of rectification in di-block oligomer diode molecules. We demonstrate that the observed asymmetry of current-voltage characteristics is the result of the resonant character of electron transport in molecular diodes and spatial asymmetry of the wave-function of a tunneling electron interacting with asymmetric molecule in an applied electric field. The asymmetry of the tunneling wave function is enhanced or weakened depending on the polarity of applied bias.

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“…This resembles a pattern for copper phthalocyanin where, however, molecular resolution was not achieved. 10 The HOMO is within the bias voltage energy ''tip'' and likely to open resonance or multiphonon ET channels but several close-lying electronic energy levels seem to contribute.…”

Section: Approaches Toward Molecular Rectifying Systemsmentioning

confidence: 99%

“…[5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] Different classes of organic molecules have constituted the tunnel junction, displaying strong features of rectification, switching, [11][12][13][14][15][16][17][18][19][20][21][22] or pulselike behavior ͑negative differential resistance͒, 16 -19 cf. Sec.…”

Section: Introductionmentioning

confidence: 99%

Mechanisms of molecular electronic rectification through electronic levels with strong vibrational coupling

Кузнецов

Ulstrup

2002

The Journal of Chemical Physics

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We present a new view and an analytical formalism of electron flow through a donor-acceptor molecule inserted between a pair of metal electrodes. The donor and acceptor levels are strongly coupled to an environmental nuclear continuum. The formalism applies to molecular donoracceptor systems both in vacuum or air, and in aqueous solution under electrochemical potential control. Multifarious patterns of rectified electron flow from the negatively to the positively biased electrode arise. The electronic interaction between the donor and acceptor fragments, mutually and with the electrodes, can be weak, corresponding to the fully diabatic limit. The rectification process then reduces to a sequence of vibrationally relaxed single-electron transfer steps. In the limits where the interactions are strong, denoted as the partially and fully adiabatic limits, the character of the rectification process is different, and electron flow proceeds coherently, without vibrational relaxation. In still another class of mechanisms the electronic level broadening of either donor or acceptor from the adjacent electrode is so strong that it is comparable to the vibrational broadening. The process then reduces to a three-level transition similar to STM of large redox molecules. Recent data for rectification in hexadecyl-quinolinium tricyanodimethanide monolayers by Metzger and co-workers ͓J. Am. Chem. Soc. 119, 10455 ͑1997͒; Acc. Chem. Res. 32, 950 ͑1999͔͒, are discussed in terms of the reported views and formalism.

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Rectification of STM Current to Graphite Covered with Phthalocyanine Molecules

Cited by 116 publications

References 20 publications

A fullerene molecular tip can detect localized and rectified electron tunneling within a single fullerene–porphyrin pair

A fullerene molecular tip can detect localized and rectified electron tunneling within a single fullerene–porphyrin pair

Rectification Mechanism in Diblock Oligomer Molecular Diodes

Mechanisms of molecular electronic rectification through electronic levels with strong vibrational coupling

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