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Li T, Bandari VK, Schmidt OG. Molecular Electronics: Creating and Bridging Molecular Junctions and Promoting Its Commercialization. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2023; 35:e2209088. [PMID: 36512432 DOI: 10.1002/adma.202209088] [Citation(s) in RCA: 14] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/02/2022] [Revised: 11/28/2022] [Indexed: 06/02/2023]
Abstract
Molecular electronics is driven by the dream of expanding Moore's law to the molecular level for next-generation electronics through incorporating individual or ensemble molecules into electronic circuits. For nearly 50 years, numerous efforts have been made to explore the intrinsic properties of molecules and develop diverse fascinating molecular electronic devices with the desired functionalities. The flourishing of molecular electronics is inseparable from the development of various elegant methodologies for creating nanogap electrodes and bridging the nanogap with molecules. This review first focuses on the techniques for making lateral and vertical nanogap electrodes by breaking, narrowing, and fixed modes, and highlights their capabilities, applications, merits, and shortcomings. After summarizing the approaches of growing single molecules or molecular layers on the electrodes, the methods of constructing a complete molecular circuit are comprehensively grouped into three categories: 1) directly bridging one-molecule-electrode component with another electrode, 2) physically bridging two-molecule-electrode components, and 3) chemically bridging two-molecule-electrode components. Finally, the current state of molecular circuit integration and commercialization is discussed and perspectives are provided, hoping to encourage the community to accelerate the realization of fully scalable molecular electronics for a new era of integrated microsystems and applications.
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Affiliation(s)
- Tianming Li
- Research Center for Materials, Architectures and Integration of Nanomembranes (MAIN), Chemnitz University of Technology, 09126, Chemnitz, Germany
- Material Systems for Nanoelectronics, Chemnitz University of Technology, 09111, Chemnitz, Germany
| | - Vineeth Kumar Bandari
- Research Center for Materials, Architectures and Integration of Nanomembranes (MAIN), Chemnitz University of Technology, 09126, Chemnitz, Germany
- Material Systems for Nanoelectronics, Chemnitz University of Technology, 09111, Chemnitz, Germany
| | - Oliver G Schmidt
- Research Center for Materials, Architectures and Integration of Nanomembranes (MAIN), Chemnitz University of Technology, 09126, Chemnitz, Germany
- Material Systems for Nanoelectronics, Chemnitz University of Technology, 09111, Chemnitz, Germany
- Nanophysics, Dresden University of Technology, 01069, Dresden, Germany
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2
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Abstract
The field of molecular electronics has grown rapidly since its experimental realization in the late 1990s, with thousands of publications on how molecules can act as circuit components and the possibility of extending microelectronic miniaturization. Our research group developed molecular junctions (MJs) using conducting carbon electrodes and covalent bonding, which provide excellent temperature tolerance and operational lifetimes. A carbon-based MJ based on quantum mechanical tunneling for electronic music represents the world's first commercial application of molecular electronics, with >3000 units currently in consumer hands. The all-carbon MJ consisting of aromatic molecules and oligomers between vapor-deposited carbon electrodes exploits covalent, C-C bonding which avoids the electromigration problem of metal contacts. The high bias and temperature stability as well as partial transparency of the all-carbon MJ permit a wide range of experiments to determine charge transport mechanisms and observe photoeffects to both characterize and stimulate operating MJs. As shown in the Conspectus figure, our group has reported a variety of electronic functions, many of which do not have analogs in conventional semiconductors. Much of the described research is oriented toward the rational design of electronic functions, in which electronic characteristics are determined by molecular structure.In addition to the fabrication of molecular electronic devices with sufficient stability and operating life for practical applications, our approach was directed at two principal questions: how do electrons move through molecules that are components of an electronic circuit, and what can we do with molecules that we cannot do with existing semiconductor technology? The central component is the molecular junction consisting of a 1-20+ nm layer of covalently bonded oligomers between two electrodes of conducting, mainly sp2-hybridized carbon. In addition to describing the unique junction structure and fabrication methods, this Account summarizes the valuable insights available from photons used both as probes of device structure and dynamics and as prods to stimulate resonant transport through molecular orbitals.Short-range (<5 nm) transport by tunneling and its properties are discussed separately from the longer-range transport (5-60 nm) which bridges the gap between tunneling and transport in widely studied organic semiconductors. Most molecular electronic studies deal with the <5 nm thickness range, where coherent tunneling is generally accepted as the dominant transport mechanism. However, the rational design of devices in this range by changing molecular structure is frustrated by electronic interactions with the conducting contacts, resulting in weak structural effects on electronic behavior. When the molecular layer thickness exceeds 5 nm, transport characteristics change completely since molecular orbitals become the conduits for transport. Incident photons can stimulate transport, with the observed photocurrent tracking the absorption spectrum of the molecular layer. Low-temperature, activationless transport of photogenerated carriers is possible for up to at least 60 nm, with characteristics completely distinct from coherent tunneling and from the hopping mechanisms proposed for organic semiconductors. The Account closes with examples of phenomena and applications enabled by molecular electronics which may augment conventional microelectronics with chemical functions such as redox charge storage, orbital transport, and energy-selective photodetection.
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Affiliation(s)
- Richard L McCreery
- Department of Chemistry, University of Alberta, 11227 Saskatchewan Drive, Edmonton, Alberta T6G 2G2, Canada
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3
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Tyagi P, Brown H, Grizzle A, D'Angelo C, Dahal BR. Molecular coupling competing with defects within insulator of the magnetic tunnel junction-based molecular spintronics devices. Sci Rep 2021; 11:17128. [PMID: 34429460 PMCID: PMC8384883 DOI: 10.1038/s41598-021-96477-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2021] [Accepted: 08/04/2021] [Indexed: 11/24/2022] Open
Abstract
Nearly 70 years old dream of incorporating molecule as the device element is still challenged by competing defects in almost every experimentally tested molecular device approach. This paper focuses on the magnetic tunnel junction (MTJ) based molecular spintronics device (MTJMSD) method. An MTJMSD utilizes a tunnel barrier to ensure a robust and mass-producible physical gap between two ferromagnetic electrodes. MTJMSD approach may benefit from MTJ's industrial practices; however, the MTJMSD approach still needs to overcome additional challenges arising from the inclusion of magnetic molecules in conjunction with competing defects. Molecular device channels are covalently bonded between two ferromagnets across the insulating barrier. An insulating barrier may possess a variety of potential defects arising during the fabrication or operational phase. This paper describes an experimental and theoretical study of molecular coupling between ferromagnets in the presence of the competing coupling via an insulating tunnel barrier. We discuss the experimental observations of hillocks and pinhole-type defects producing inter-layer coupling that compete with molecular device elements. We performed theoretical simulations to encompass a wide range of competition between molecules and defects. Monte Carlo Simulation (MCS) was used for investigating the defect-induced inter-layer coupling on MTJMSD. Our research may help understand and design molecular spintronics devices utilizing various insulating spacers such as aluminum oxide (AlOx) and magnesium oxide (MgO) on a wide range of metal electrodes. This paper intends to provide practical insights for researchers intending to investigate the molecular device properties via the MTJMSD approach and do not have a background in magnetic tunnel junction fabrication.
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Affiliation(s)
- Pawan Tyagi
- Center for Nanotechnology Research and Education, Mechanical Engineering, University of the District of Columbia, Washington, DC, 20008, USA.
| | - Hayden Brown
- Center for Nanotechnology Research and Education, Mechanical Engineering, University of the District of Columbia, Washington, DC, 20008, USA
| | - Andrew Grizzle
- Center for Nanotechnology Research and Education, Mechanical Engineering, University of the District of Columbia, Washington, DC, 20008, USA
| | - Christopher D'Angelo
- Center for Nanotechnology Research and Education, Mechanical Engineering, University of the District of Columbia, Washington, DC, 20008, USA
| | - Bishnu R Dahal
- Center for Nanotechnology Research and Education, Mechanical Engineering, University of the District of Columbia, Washington, DC, 20008, USA
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4
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Kudas Z, Atmaca U, Saruhan T, Celik M, Ekinci D. Electrocatalytic Reduction of Oxygen at Glassy Carbon Electrodes Coated with Diazonium‐derived Porphyrin/Metalloporphyrin Films. ELECTROANAL 2020. [DOI: 10.1002/elan.201900707] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Affiliation(s)
- Zuleyha Kudas
- Department of Chemistry, Faculty of SciencesAtatürk University 25240 Erzurum Turkey
| | - Ufuk Atmaca
- Department of Food Processing, Oltu Vocational CollegeAtatürk University 25240 Erzurum Turkey
| | - Tuba Saruhan
- Department of Chemistry, Faculty of SciencesAtatürk University 25240 Erzurum Turkey
| | - Murat Celik
- Department of Chemistry, Faculty of SciencesAtatürk University 25240 Erzurum Turkey
| | - Duygu Ekinci
- Department of Chemistry, Faculty of SciencesAtatürk University 25240 Erzurum Turkey
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Parrino F, De Pasquale C, Palmisano L. Influence of Surface-Related Phenomena on Mechanism, Selectivity, and Conversion of TiO 2 -Induced Photocatalytic Reactions. CHEMSUSCHEM 2019; 12:589-602. [PMID: 30387918 DOI: 10.1002/cssc.201801898] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/19/2018] [Revised: 09/28/2018] [Indexed: 06/08/2023]
Abstract
Heterogeneous photocatalysis is the result of an inextricable connection of several factors differently contributing to the overall process. Photon absorption is the "sine qua non" condition for the reaction to occur. In fact, photons can be considered as immaterial reactants, and all of the phenomena related to the interaction of light-matter play a prominent role. However, other factors contribute in a concerted way to address the reaction, so that the relative contribution of each of them is often difficult to evaluate. In this framework, the present paper highlights some aspects of the interaction of TiO2 surface-adsorbate species that could be underestimated and their influence on the conversion, selectivity, and mechanisms of photocatalytic reactions. To this aim, some paradigmatic examples on the adsorption of water and organics on TiO2 are reported.
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Affiliation(s)
- Francesco Parrino
- Dipartimento di Scienze Agrarie, Alimentari e Forestali, Università degli Studi di Palermo, viale delle Scienze 8, 90128, Palermo, Italy
- Dipartimento di Energia, Ingegneria dell'informazione e Modelli Matematici (DEIM), Università degli Studi di Palermo, viale delle Scienze Ed. 6, 90128, Palermo, Italy
- Dipartimento di Ingegneria Industriale (DII), Università di Trento, via Sommarive 9, 38123, Trento, Italy
| | - Claudio De Pasquale
- Dipartimento di Scienze Agrarie, Alimentari e Forestali, Università degli Studi di Palermo, viale delle Scienze 8, 90128, Palermo, Italy
| | - Leonardo Palmisano
- Dipartimento di Energia, Ingegneria dell'informazione e Modelli Matematici (DEIM), Università degli Studi di Palermo, viale delle Scienze Ed. 6, 90128, Palermo, Italy
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Wang L, Zhu L, Li L, Cao D. Tetraphenylethene-functionalized diketopyrrolopyrrole solid state emissive molecules: enhanced emission in the solid state and as a fluorescent probe for cyanide detection. RSC Adv 2016. [DOI: 10.1039/c6ra10073b] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Tetraphenylethene-functionalized diketopyrrolopyrrole solid state red-emissive molecules (DPP1andDPP2) with enhanced emission in the solid state have been developed.
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Affiliation(s)
- Lingyun Wang
- School of Chemistry and Chemical Engineering
- State Key Laboratory of Luminescent Materials and Devices
- South China University of Technology
- Guangzhou
- China
| | - Linhui Zhu
- School of Chemistry and Chemical Engineering
- State Key Laboratory of Luminescent Materials and Devices
- South China University of Technology
- Guangzhou
- China
| | - Lin Li
- School of Food Science and Engineering
- South China University of Technology
- Guangzhou
- China
| | - Derong Cao
- School of Chemistry and Chemical Engineering
- State Key Laboratory of Luminescent Materials and Devices
- South China University of Technology
- Guangzhou
- China
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7
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Oyama M, Ozawa H, Nagashima T, Haga MA, Ishida T. Effects of Fe cations in ruthenium-complex multilayers fabricated by a layer-by-layer method. Phys Chem Chem Phys 2016; 18:9005-12. [DOI: 10.1039/c5cp07970e] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Molecular multilayers were fabricated using a Ru complex containing Fe cations on an indium tin oxide surface to control the properties of the Ru-complex multilayers such as the multilayer orientation and the electron transport.
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Affiliation(s)
- Makiko Oyama
- Nanomaterials Research Institute (NMRI)
- Department of Materials and Chemistry
- National Institute of Advanced Industrial Science and Technology (AIST)
- Tsukuba
- Japan
| | - Hiroaki Ozawa
- Department of Applied Chemistry
- Faculty of Science and Engineering
- Chuo University
- Bunkyo-ku
- Japan
| | - Takumi Nagashima
- Department of Applied Chemistry
- Faculty of Science and Engineering
- Chuo University
- Bunkyo-ku
- Japan
| | - Masa-aki Haga
- Department of Applied Chemistry
- Faculty of Science and Engineering
- Chuo University
- Bunkyo-ku
- Japan
| | - Takao Ishida
- Nanomaterials Research Institute (NMRI)
- Department of Materials and Chemistry
- National Institute of Advanced Industrial Science and Technology (AIST)
- Tsukuba
- Japan
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8
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Fereiro JA, Kondratenko M, Bergren AJ, McCreery RL. Internal Photoemission in Molecular Junctions: Parameters for Interfacial Barrier Determinations. J Am Chem Soc 2015; 137:1296-304. [DOI: 10.1021/ja511592s] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Affiliation(s)
- Jerry A. Fereiro
- Department
of Chemistry, University of Alberta, 11227 Saskatchewan Drive Northwest, Edmonton, Alberta T6G 2G2, Canada
| | - Mykola Kondratenko
- Department
of Chemistry, University of Alberta, 11227 Saskatchewan Drive Northwest, Edmonton, Alberta T6G 2G2, Canada
- National
Institute for Nanotechnology, National Research Council Canada, 11421
Saskatchewan Drive, Edmonton, Alberta T6G 2M9, Canada
| | - Adam Johan Bergren
- National
Institute for Nanotechnology, National Research Council Canada, 11421
Saskatchewan Drive, Edmonton, Alberta T6G 2M9, Canada
| | - Richard L. McCreery
- Department
of Chemistry, University of Alberta, 11227 Saskatchewan Drive Northwest, Edmonton, Alberta T6G 2G2, Canada
- National
Institute for Nanotechnology, National Research Council Canada, 11421
Saskatchewan Drive, Edmonton, Alberta T6G 2M9, Canada
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9
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Amdursky N, Marchak D, Sepunaru L, Pecht I, Sheves M, Cahen D. Electronic transport via proteins. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2014; 26:7142-61. [PMID: 25256438 DOI: 10.1002/adma.201402304] [Citation(s) in RCA: 130] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/22/2014] [Revised: 08/07/2014] [Indexed: 05/25/2023]
Abstract
A central vision in molecular electronics is the creation of devices with functional molecular components that may provide unique properties. Proteins are attractive candidates for this purpose, as they have specific physical (optical, electrical) and chemical (selective binding, self-assembly) functions and offer a myriad of possibilities for (bio-)chemical modification. This Progress Report focuses on proteins as potential building components for future bioelectronic devices as they are quite efficient electronic conductors, compared with saturated organic molecules. The report addresses several questions: how general is this behavior; how does protein conduction compare with that of saturated and conjugated molecules; and what mechanisms enable efficient conduction across these large molecules? To answer these questions results of nanometer-scale and macroscopic electronic transport measurements across a range of organic molecules and proteins are compiled and analyzed, from single/few molecules to large molecular ensembles, and the influence of measurement methods on the results is considered. Generalizing, it is found that proteins conduct better than saturated molecules, and somewhat poorer than conjugated molecules. Significantly, the presence of cofactors (redox-active or conjugated) in the protein enhances their conduction, but without an obvious advantage for natural electron transfer proteins. Most likely, the conduction mechanisms are hopping (at higher temperatures) and tunneling (below ca. 150-200 K).
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Affiliation(s)
- Nadav Amdursky
- Dept. of Materials & Interfaces, Weizmann Institute of Science, Rehovot, 76305, Israel
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10
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Shen XY, Wang YJ, Zhang H, Qin A, Sun JZ, Tang BZ. Conjugates of tetraphenylethene and diketopyrrolopyrrole: tuning the emission properties with phenyl bridges. Chem Commun (Camb) 2014; 50:8747-50. [DOI: 10.1039/c4cc03024a] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Bridging DPP (ACQ-gen) and TPE (AIE-gen) with phenyls derived TPE–ph–DPP conjugates displaying enhanced and red-shifted emission in the solid state.
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Affiliation(s)
- Xiao Yuan Shen
- MOE Key Laboratory of Macromolecule Synthesis and Functionalization
- Department of Polymer Science and Engineering
- Zhejiang University
- Hangzhou 310027, China
| | - Yi Jia Wang
- MOE Key Laboratory of Macromolecule Synthesis and Functionalization
- Department of Polymer Science and Engineering
- Zhejiang University
- Hangzhou 310027, China
| | - Haoke Zhang
- MOE Key Laboratory of Macromolecule Synthesis and Functionalization
- Department of Polymer Science and Engineering
- Zhejiang University
- Hangzhou 310027, China
| | - Anjun Qin
- MOE Key Laboratory of Macromolecule Synthesis and Functionalization
- Department of Polymer Science and Engineering
- Zhejiang University
- Hangzhou 310027, China
- Guangdong Innovative Research Team
| | - Jing Zhi Sun
- MOE Key Laboratory of Macromolecule Synthesis and Functionalization
- Department of Polymer Science and Engineering
- Zhejiang University
- Hangzhou 310027, China
| | - Ben Zhong Tang
- MOE Key Laboratory of Macromolecule Synthesis and Functionalization
- Department of Polymer Science and Engineering
- Zhejiang University
- Hangzhou 310027, China
- Guangdong Innovative Research Team
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Xiang D, Jeong H, Lee T, Mayer D. Mechanically controllable break junctions for molecular electronics. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2013; 25:4845-67. [PMID: 23913697 DOI: 10.1002/adma.201301589] [Citation(s) in RCA: 105] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2013] [Indexed: 05/13/2023]
Abstract
A mechanically controllable break junction (MCBJ) represents a fundamental technique for the investigation of molecular electronic junctions, especially for the study of the electronic properties of single molecules. With unique advantages, the MCBJ technique has provided substantial insight into charge transport processes in molecules. In this review, the techniques for sample fabrication, operation and the various applications of MCBJs are introduced and the history, challenges and future of MCBJs are discussed.
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Affiliation(s)
- Dong Xiang
- Department of Physics and Astronomy, Seoul National University, Gwanak-ro, Gwanak-gu, Seoul 151-747, Korea
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12
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McCreery RL, Yan H, Bergren AJ. A critical perspective on molecular electronic junctions: there is plenty of room in the middle. Phys Chem Chem Phys 2013; 15:1065-81. [DOI: 10.1039/c2cp43516k] [Citation(s) in RCA: 124] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
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13
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Thuo MM, Reus WF, Simeone FC, Kim C, Schulz MD, Yoon HJ, Whitesides GM. Replacing −CH2CH2– with −CONH– Does Not Significantly Change Rates of Charge Transport through AgTS-SAM//Ga2O3/EGaIn Junctions. J Am Chem Soc 2012; 134:10876-84. [DOI: 10.1021/ja301778s] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Affiliation(s)
- Martin M. Thuo
- Department
of Chemistry and
Chemical Biology, Harvard University, 12
Oxford Street, Cambridge, Massachusetts 02138, United States
| | - William F. Reus
- Department
of Chemistry and
Chemical Biology, Harvard University, 12
Oxford Street, Cambridge, Massachusetts 02138, United States
| | - Felice C. Simeone
- Department
of Chemistry and
Chemical Biology, Harvard University, 12
Oxford Street, Cambridge, Massachusetts 02138, United States
| | - Choongik Kim
- Department
of Chemistry and
Chemical Biology, Harvard University, 12
Oxford Street, Cambridge, Massachusetts 02138, United States
| | - Michael D. Schulz
- Department
of Chemistry and
Chemical Biology, Harvard University, 12
Oxford Street, Cambridge, Massachusetts 02138, United States
| | - Hyo Jae Yoon
- Department
of Chemistry and
Chemical Biology, Harvard University, 12
Oxford Street, Cambridge, Massachusetts 02138, United States
| | - George M. Whitesides
- Department
of Chemistry and
Chemical Biology, Harvard University, 12
Oxford Street, Cambridge, Massachusetts 02138, United States
- Kavli Institute for Bionano Science & Technology, School of Engineering and Applied Sciences, Harvard University, Pierce Hall, 29 Oxford Street, Cambridge, Massachusetts 02138, United States
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14
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Charge transport in molecular electronic junctions: compression of the molecular tunnel barrier in the strong coupling regime. Proc Natl Acad Sci U S A 2012; 109:11498-503. [PMID: 22660930 DOI: 10.1073/pnas.1201557109] [Citation(s) in RCA: 99] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Molecular junctions are essentially modified electrodes familiar to electrochemists where the electrolyte is replaced by a conducting "contact." It is generally hypothesized that changing molecular structure will alter system energy levels leading to a change in the transport barrier. Here, we show the conductance of seven different aromatic molecules covalently bonded to carbon implies a modest range (< 0.5 eV) in the observed transport barrier despite widely different free molecule HOMO energies (> 2 eV range). These results are explained by considering the effect of bonding the molecule to the substrate. Upon bonding, electronic inductive effects modulate the energy levels of the system resulting in compression of the tunneling barrier. Modification of the molecule with donating or withdrawing groups modulate the molecular orbital energies and the contact energy level resulting in a leveling effect that compresses the tunneling barrier into a range much smaller than expected. Whereas the value of the tunneling barrier can be varied by using a different class of molecules (alkanes), using only aromatic structures results in a similar equilibrium value for the tunnel barrier for different structures resulting from partial charge transfer between the molecular layer and the substrate. Thus, the system does not obey the Schottky-Mott limit, and the interaction between the molecular layer and the substrate acts to influence the energy level alignment. These results indicate that the entire system must be considered to determine the impact of a variety of electronic factors that act to determine the tunnel barrier.
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15
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Terada KI, Nakamura H, Kanaizuka K, Haga MA, Asai Y, Ishida T. Long-range electron transport of ruthenium-centered multilayer films via a stepping-stone mechanism. ACS NANO 2012; 6:1988-1999. [PMID: 22324341 DOI: 10.1021/nn300126m] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We studied electron transport of Ru complex multilayer films, whose structure resembles redox-active complex films known in the literature to have long-range electron transport abilities. Hydrogen bond formation in terms of pH control was used to induce spontaneous growth of a Ru complex multilayer. We made a cross-check between electrochemical measurements and I-V measurements using PEDOT:PSS to eliminate the risk of pinhole contributions to the mechanism and have found small β values of 0.012-0.021 Å(-1). Our Ru complex layers exhibit long-range electron transport but with low conductance. On the basis of the results of our theoretical-experimental collaboration, we propose a modified tunneling mechanism named the "stepping-stone mechanism", where the alignment of site potentials forms a narrow band around E(F), making resonant tunneling possible. Our observations may support Tuccito et al.'s proposed mechanism.
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Affiliation(s)
- Kei-ichi Terada
- Nanosystem Research Institute (NRI), National Institute of Advanced Industrial Science and Technology (AIST), 1-2-1 Namiki, Tsukuba, Ibaraki 305-8564, Japan
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16
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Paczesny J, Sozański K, Żywociński A, Hołyst R, Glettner B, Kieffer R, Tschierske C, Nikiforov K, Pociecha D, Górecka E. Spontaneous self-assembly of partially fluorinated bolaamphiphiles into ordered layered structures. Phys Chem Chem Phys 2012; 14:14365-73. [DOI: 10.1039/c2cp41970j] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
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17
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Shpaisman H, Seitz O, Yaffe O, Roodenko K, Scheres L, Zuilhof H, Chabal YJ, Sueyoshi T, Kera S, Ueno N, Vilan A, Cahen D. Structure Matters: Correlating temperature dependent electrical transport through alkyl monolayers with vibrational and photoelectron spectroscopies. Chem Sci 2012. [DOI: 10.1039/c1sc00639h] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
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18
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Martin P, Della Rocca ML, Anthore A, Lafarge P, Lacroix JC. Organic electrodes based on grafted oligothiophene units in ultrathin, large-area molecular junctions. J Am Chem Soc 2011; 134:154-7. [PMID: 22148633 DOI: 10.1021/ja209914d] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Molecular junctions were fabricated with the combined use of electrochemistry and conventional CMOS tools. They consist of a 5-10 nm thick layer of oligo(1-(2-bisthienyl)benzene) between two gold electrodes. The layer was grafted onto the bottom electrode using diazonium electroreduction, which yields a stable and robust gold-oligomer interface. The top contact was obtained by direct electron-beam evaporation on the molecular layers through masks defined by electron-beam lithography. Transport mechanisms across such easily p-dopable layers were investigated by analysis of current density-voltage (J-V) curves. Application of a tunneling model led to a transport parameter (thickness of ~2.4 nm) that was not consistent with the molecular thickness measured using AFM (~7 nm). Furthermore, for these layers with thicknesses of 5-10 nm, asymmetric J-V curves were observed, with current flowing more easily when the grafted electrode was positively polarized. In addition, J-V experiments at two temperatures (4 and 300 K) showed that thermal activation occurs for such polarization but is not observed when the bias is reversed. These results indicate that simple tunneling cannot describe the charge transport in these junctions. Finally, analysis of the experimental results in term of "organic electrode" and redox chemistry in the material is discussed.
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Affiliation(s)
- Pascal Martin
- Université Paris Diderot, Sorbonne Paris Cité, ITODYS, UMR 7086 CNRS, 15 rue J-A de Baïf, 75205 Paris Cedex 13, France
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19
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Mccreery RL. The merger of electrochemistry and molecular electronics. CHEM REC 2011; 12:149-63. [DOI: 10.1002/tcr.201100006] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2011] [Indexed: 01/30/2023]
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20
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Yan H, Bergren AJ, McCreery RL. All-Carbon Molecular Tunnel Junctions. J Am Chem Soc 2011; 133:19168-77. [DOI: 10.1021/ja206619a] [Citation(s) in RCA: 84] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Haijun Yan
- National Institute for Nanotechnology, National Research Council Canada, Edmonton, Alberta, Canada
| | - Adam Johan Bergren
- National Institute for Nanotechnology, National Research Council Canada, Edmonton, Alberta, Canada
| | - Richard L. McCreery
- National Institute for Nanotechnology, National Research Council Canada, Edmonton, Alberta, Canada
- Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada
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Nitoń P, Żywociński A, Paczesny J, Fiałkowski M, Hołyst R, Glettner B, Kieffer R, Tschierske C, Pociecha D, Górecka E. Aggregation and Layering Transitions in Thin Films of X-, T-, and Anchor-Shaped Bolaamphiphiles at the Air-Water Interface. Chemistry 2011; 17:5861-73. [DOI: 10.1002/chem.201003671] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2010] [Indexed: 12/19/2022]
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22
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Thuo MM, Reus WF, Nijhuis CA, Barber JR, Kim C, Schulz MD, Whitesides GM. Odd−Even Effects in Charge Transport across Self-Assembled Monolayers. J Am Chem Soc 2011; 133:2962-75. [DOI: 10.1021/ja1090436] [Citation(s) in RCA: 164] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Martin M. Thuo
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138, United States
| | - William F. Reus
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138, United States
| | - Christian A. Nijhuis
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543
| | - Jabulani R. Barber
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138, United States
| | - Choongik Kim
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138, United States
| | - Michael D. Schulz
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138, United States
| | - George M. Whitesides
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138, United States
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Bergren AJ, McCreery RL. Analytical chemistry in molecular electronics. ANNUAL REVIEW OF ANALYTICAL CHEMISTRY (PALO ALTO, CALIF.) 2011; 4:173-195. [PMID: 21370986 DOI: 10.1146/annurev-anchem-061010-113847] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
This review discusses the analytical characterization of molecular electronic devices and structures relevant thereto. In particular, we outline the methods for probing molecular junctions, which contain an ensemble of molecules between two contacts. We discuss the analytical methods that aid in the fabrication and characterization of molecular junctions, beginning with the confirmation of the placement of a molecular layer on a conductive or semiconductive substrate. We emphasize methods that provide information about the molecular layer in the junction and outline techniques to ensure molecular layer integrity after the complete fabrication of a device. In addition, we discuss the analytical information derived during the actual device operation.
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Affiliation(s)
- Adam Johan Bergren
- National Institute for Nanotechnology, National Research Council Canada, Edmonton, Alberta T6G 2M9, Canada.
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Macyk W, Szaciłowski K, Stochel G, Buchalska M, Kuncewicz J, Łabuz P. Titanium(IV) complexes as direct TiO2 photosensitizers. Coord Chem Rev 2010. [DOI: 10.1016/j.ccr.2009.12.037] [Citation(s) in RCA: 126] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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26
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Adaligil E, Slowinski K. Electron tunneling through monolayers of alkanethiols self-assembled on a hanging mercury drop electrode in the presence of aliphatic alcohols. J Electroanal Chem (Lausanne) 2010. [DOI: 10.1016/j.jelechem.2010.02.018] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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27
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Yeşildağ A, Ekinci D. Covalent attachment of pyridine-type molecules to glassy carbon surfaces by electrochemical reduction of in situ generated diazonium salts. Formation of ruthenium complexes on ligand-modified surfaces. Electrochim Acta 2010. [DOI: 10.1016/j.electacta.2010.06.020] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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28
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Adaligil E, Shon YS, Slowinski K. Effect of headgroup on electrical conductivity of self-assembled monolayers on mercury: n-alkanethiols versus n-alkaneselenols. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2010; 26:1570-1573. [PMID: 20000324 DOI: 10.1021/la904180u] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
The relative efficiencies of electron tunneling across self-assembled monolayers (SAMs) of n-alkanethiols and n-alkaneselenols, CH(3)-(CH(2))(n)-XH, where n = 8, 9, 11, and X = S or Se, deposited on mercury electrodes were measured via electroreduction of Ru(NH(3))(6)(3+) in aqueous solutions. Electron tunneling rates across the monolayer films decay exponentially with the monolayer thickness with a tunneling coefficient, beta = 1.1 +/- 0.1 per CH(2) irrespective of the identity of the -XH headgroup. Electron tunneling rates across n-alkanethiol monolayers are ca. 4-fold larger than the rates measured across n-alkaneselenol monolayers containing the same number of carbon atoms, signifying the importance of headgroup/metal contact resistance in electron transfer through SAMs on mercury.
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Affiliation(s)
- Emel Adaligil
- Department of Chemistry and Biochemistry, California State University, Long Beach, 1250 Bellflower Boulevard, Long Beach, California 90840, USA
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29
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McCreery RL, Bergren AJ. Progress with molecular electronic junctions: meeting experimental challenges in design and fabrication. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2009; 21:4303-4322. [PMID: 26042937 DOI: 10.1002/adma.200802850] [Citation(s) in RCA: 225] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/25/2008] [Revised: 01/26/2009] [Indexed: 05/28/2023]
Abstract
Molecular electronics seeks to incorporate molecular components as functional elements in electronic devices. There are numerous strategies reported to date for the fabrication, design, and characterization of such devices, but a broadly accepted example showing structure-dependent conductance behavior has not yet emerged. This progress report focuses on experimental methods for making both single-molecule and ensemble molecular junctions, and highlights key results from these efforts. Based on some general objectives of the field, particular experiments are presented to show progress in several important areas, and also to define those areas that still need attention. Some of the variable behavior of ostensibly similar junctions reported in the literature is attributable to differences in the way the junctions are fabricated. These differences are due, in part, to the multitude of methods for supporting the molecular layer on the substrate, including methods that utilize physical adsorption and covalent bonds, and to the numerous strategies for making top contacts. After discussing recent experimental progress in molecular electronics, an assessment of the current state of the field is presented, along with a proposed road map that can be used to assess progress in the future.
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Affiliation(s)
- Richard L McCreery
- Department of Chemistry, University of Alberta Edmonton, AB T6G 2G2 (Canada).
- National Institute for Nanotechnology, National Research Council Canada Edmonton, AB T6G 2M9 (Canada).
| | - Adam Johan Bergren
- National Institute for Nanotechnology, National Research Council Canada Edmonton, AB T6G 2M9 (Canada)
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McCreery RL. Electron Transport and Redox Reactions in Molecular Electronic Junctions. Chemphyschem 2009; 10:2387-91. [DOI: 10.1002/cphc.200900416] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Coll M, Miller LH, Richter LJ, Hines DR, Jurchescu OD, Gergel-Hackett N, Richter CA, Hacker CA. Formation of Silicon-Based Molecular Electronic Structures Using Flip-Chip Lamination. J Am Chem Soc 2009; 131:12451-7. [PMID: 19670858 DOI: 10.1021/ja901646j] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Mariona Coll
- Semiconductor Electronics Division, Electronics Electrical Engineering Laboratory and Surface and Microanalysis Science Division, Chemical Science and Technology Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, and Physics Department and Laboratory for Physical Sciences, University of Maryland, College Park, Maryland 20740
| | - Lauren H. Miller
- Semiconductor Electronics Division, Electronics Electrical Engineering Laboratory and Surface and Microanalysis Science Division, Chemical Science and Technology Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, and Physics Department and Laboratory for Physical Sciences, University of Maryland, College Park, Maryland 20740
| | - Lee J. Richter
- Semiconductor Electronics Division, Electronics Electrical Engineering Laboratory and Surface and Microanalysis Science Division, Chemical Science and Technology Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, and Physics Department and Laboratory for Physical Sciences, University of Maryland, College Park, Maryland 20740
| | - Daniel R. Hines
- Semiconductor Electronics Division, Electronics Electrical Engineering Laboratory and Surface and Microanalysis Science Division, Chemical Science and Technology Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, and Physics Department and Laboratory for Physical Sciences, University of Maryland, College Park, Maryland 20740
| | - Oana D. Jurchescu
- Semiconductor Electronics Division, Electronics Electrical Engineering Laboratory and Surface and Microanalysis Science Division, Chemical Science and Technology Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, and Physics Department and Laboratory for Physical Sciences, University of Maryland, College Park, Maryland 20740
| | - Nadine Gergel-Hackett
- Semiconductor Electronics Division, Electronics Electrical Engineering Laboratory and Surface and Microanalysis Science Division, Chemical Science and Technology Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, and Physics Department and Laboratory for Physical Sciences, University of Maryland, College Park, Maryland 20740
| | - Curt A. Richter
- Semiconductor Electronics Division, Electronics Electrical Engineering Laboratory and Surface and Microanalysis Science Division, Chemical Science and Technology Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, and Physics Department and Laboratory for Physical Sciences, University of Maryland, College Park, Maryland 20740
| | - Christina A. Hacker
- Semiconductor Electronics Division, Electronics Electrical Engineering Laboratory and Surface and Microanalysis Science Division, Chemical Science and Technology Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, and Physics Department and Laboratory for Physical Sciences, University of Maryland, College Park, Maryland 20740
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32
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DiBenedetto SA, Facchetti A, Ratner MA, Marks TJ. Charge Conduction and Breakdown Mechanisms in Self-Assembled Nanodielectrics. J Am Chem Soc 2009; 131:7158-68. [DOI: 10.1021/ja9013166] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Affiliation(s)
- Sara A. DiBenedetto
- Department of Chemistry and the Materials Research Center, Northwestern University, Evanston, Illinois 60208-3113
| | - Antonio Facchetti
- Department of Chemistry and the Materials Research Center, Northwestern University, Evanston, Illinois 60208-3113
| | - Mark A. Ratner
- Department of Chemistry and the Materials Research Center, Northwestern University, Evanston, Illinois 60208-3113
| | - Tobin J. Marks
- Department of Chemistry and the Materials Research Center, Northwestern University, Evanston, Illinois 60208-3113
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Bergren AJ, Harris KD, Deng F, McCreery RL. Molecular electronics using diazonium-derived adlayers on carbon with Cu top contacts: critical analysis of metal oxides and filaments. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2008; 20:374117. [PMID: 21694424 DOI: 10.1088/0953-8984/20/37/374117] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Evaporation of Cu metal onto thin (less than 5 nm) molecular layers bonded to conductive carbon substrates results in electronic junctions with an ensemble of molecules sandwiched between two conductors. The resulting devices have previously been characterized through analysis of current density-voltage (j-V) curves for several different molecular layers and as a function of layer thickness. The approach represents an 'ensemble' rather than 'single molecule' technique, in which the electronic response represents that of a large number of molecules (10(6)-10(12)) in parallel as well as the conducting contacts contained in the molecular junction. In this paper, we extend a more detailed investigation of two critical issues: the possibility of conduction by metal filaments, and the potential role of top contact oxidation contributing to the electronic properties of the junctions. The results show that the conductance of the junctions can be modulated by changes in the deposition environment, but that the changes are not related to Cu oxide in the top contact. Based on these results, we propose that the conditions during top contact deposition change the way in which the molecules contact the metal, leading to differences in the effective junction area. Finally, through systematic studies using variation of the temperature, we show that metal filament conduction is distinct from that observed for the molecular junctions and that if the current observed experimentally passed through nanoscopic metal filaments the Joule heating would lead to rapid melting. For a series of junctions with structurally related aromatic molecules (including biphenyl, nitrobiphenyl, fluorene, and nitroazobenzene), the electron transfer mechanism is briefly investigated using area-independent analysis methods. It is shown that field emission and/or transport through bands formed by the molecular layer is likely, based on the weak temperature dependence of junction conductance.
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Affiliation(s)
- Adam Johan Bergren
- National Institute for Nanotechnology, National Research Council Canada, Edmonton, Alberta, Canada
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34
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Khoshroo M, Rostami AA, Yeganegi S. Cyclic voltammetric and computational study of a 4-bromophenyl monolayer on a glassy carbon electrode. MONATSHEFTE FUR CHEMIE 2008. [DOI: 10.1007/s00706-007-0851-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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35
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Tian H, Bergren AJ, McCreery RL. Ultraviolet-visible spectroelectrochemistry of chemisorbed molecular layers on optically transparent carbon electrodes. APPLIED SPECTROSCOPY 2007; 61:1246-53. [PMID: 18028705 DOI: 10.1366/000370207782597094] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
Pyrolysis of diluted commercial photoresist spun onto quartz slides yields optically transparent graphitic films. Transparent carbon electrodes approximately 6 nm thick can be reproducibly prepared, with a maximum absorbance in the ultraviolet-visible (UV-vis) range of 0.25 at 270 nm. These electrodes are sufficiently conductive for electrochemistry, enabling modification of the surface via diazonium ion reduction and spectroelectrochemistry. Good quality ultraviolet-visible absorption spectra of covalently bonded molecular layers of nitroazobenzene, nitrobiphenyl, and azobenzene, with thicknesses of 1.4-4 nm, were obtained after subtracting the spectrum of the unmodified substrate. The spectra of all three molecules immobilized on the carbon surface showed red shifts of the absorption maxima relative to a solution of free molecules, indicating substantial electronic interactions between chemisorbed molecules and the Pi system of the substrate and/or intermolecular coupling. Spectroelectrochemical measurements show that reduction of free and chemisorbed molecules produce new absorption features in the 500-800 nm range; these spectral changes are partially reversible upon repeated potential cycling. Finally, density functional calculations correlate the new bands to the formation of anion radical or "methide" species that have more extensive electron delocalization than the parent molecules. The results from this work are useful for linking structural transformations in molecular layers "buried" under conductive top contacts in a type of molecular junction to changes in the electronic properties of the junction.
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Affiliation(s)
- Hong Tian
- Department of Chemistry, The Ohio State University, 100 W 18th Avenue, Columbus, OH 43210, USA
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36
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Weiss EA, Kriebel JK, Rampi MA, Whitesides GM. The study of charge transport through organic thin films: mechanism, tools and applications. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2007; 365:1509-37. [PMID: 17430810 DOI: 10.1098/rsta.2007.2029] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
In this paper, we discuss the current state of organic and molecular-scale electronics, some experimental methods used to characterize charge transport through molecular junctions and some theoretical models (superexchange and barrier tunnelling models) used to explain experimental results. Junctions incorporating self-assembled monolayers of organic molecules - and, in particular, junctions with mercury-drop electrodes - are described in detail, as are the issues of irreproducibility associated with such junctions (due, in part, to defects at the metal-molecule interface).
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Affiliation(s)
- Emily A Weiss
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, MA 02138, USA
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37
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Tyagi P, Li D, Holmes SM, Hinds BJ. Molecular Electrodes at the Exposed Edge of Metal/Insulator/Metal Trilayer Structures. J Am Chem Soc 2007; 129:4929-38. [PMID: 17391029 DOI: 10.1021/ja065789d] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Producing reliable electrical contacts of molecular dimensions has been a critical challenge in the field of molecule-based electronics. Conventional thin film deposition and photolithography techniques have been utilized to construct novel nanometer-sized electrodes on the exposed vertical plane on the edge of a thin film multilayer structure (metal/insulator/metal). Via thiol surface attachment to metal leads, an array of paramagnetic, cyanide-bridged octametal complexes, [(pzTp)FeIII(CN)3]4[NiII(L)]4[O3SCF3]4 (1) [(pzTp) = tetra(pyrazol-1-yl)borate; L = 1-S(acetyl)tris(pyrazolyl)decane], were covalently linked onto the electrodes forming a dominant conduction pathway. A series of molecule-based devices were fabricated using Ni, NiFe, Ta, and Au as metal electrodes separated by insulating Al2O3 spacers, followed by treatment with 1. A series of control experiments were also performed to demonstrate that the conduction path was through tethered metal clusters. The molecular current was analyzed via the Simmons tunnel model, and calculations are consistent with electron tunneling through the alkane ethers to the central metal core. With a Ni/Al2O3/Au molecular electrode, the tether binding was found to be reversible to the top Au layer, allowing for a new class of chemical detection based on the steric bulk of coordinating analytes to disconnect the molecular current path. Simple and economical photolithography/liftoff/self-assembly fabrication techniques afford robust molecular junctions with high reproducibility (>90%) and long operational lifetimes (>1 year).
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Affiliation(s)
- Pawan Tyagi
- Department of Chemical and Materials Engineering and Center for Nanoscale Science and Engineering, University of Kentucky, Lexington, Kentucky 40506-0046, USA
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38
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Chu C, Na JS, Parsons GN. Conductivity in Alkylamine/Gold and Alkanethiol/Gold Molecular Junctions Measured in Molecule/Nanoparticle/Molecule Bridges and Conducting Probe Structures. J Am Chem Soc 2007; 129:2287-96. [PMID: 17279744 DOI: 10.1021/ja064968s] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Charge transport through alkane monolayers on gold is measured as a function of molecule length in a controlled ambient using a metal/molecule/nanoparticle bridge structure and compared for both thiol and amine molecular end groups. The current through molecules with an amine/gold junction is observed to be more than a factor of 10 larger than that measured in similar molecules with thiol/gold linkages. Conducting probe atomic force microscopy is also used to characterize the same monolayer systems, and the results are quantitatively consistent with those found in the nanoparticle bridge geometry. Scaling of the current with contact area is used to estimate that approximately 100 molecules are probed in the nanoparticle bridge geometry. For both molecular end groups, the room-temperature conductivity at low bias as a function of molecule length shows a reasonable fit to models of coherent nonresonant charge tunneling. The different conductivity is ascribed to differences in charge transfer and wave function mixing at the metal/molecule contact, including possible effects of amine group oxidation and molecular conformation. For the amine/Au contact, the nitrogen lone pair interaction with the gold results in a hybrid wave function directed along the molecule bond axis, whereas the thiol/Au contact leads to a more localized wave function.
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Affiliation(s)
- Changwoong Chu
- Department of Chemical & Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina 27695, USA
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Na JS, Ayres J, Chandra KL, Chu C, Gorman CB, Parsons GN. Conduction mechanisms and stability of single molecule nanoparticle/molecule/nanoparticle junctions. NANOTECHNOLOGY 2007; 18:035203. [PMID: 19636113 DOI: 10.1088/0957-4484/18/3/035203] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Nanoparticle/molecule/nanoparticle dimer assemblies have been successfully trapped by dielectrophoresis across nanogap electrodes, enabling temperature dependent charge transport measurements through an oligomeric phenylene ethynylene molecule, and transition from direct tunnelling to Fowler-Nordheim tunnelling is observed at approximately 1.5 V. Samples formed by dielectrophoresis show better contact stability than those formed by receding meniscus. The junction shows stable operation over several weeks in a vacuum, but current increases with time upon exposure to air, possibly due to the adsorbed water molecules near the molecule/gold nanoparticle contacts.
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Affiliation(s)
- Jeong-Seok Na
- Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC 27695, USA
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40
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Anariba F, Viswanathan U, Bocian DF, McCreery RL. Determination of the Structure and Orientation of Organic Molecules Tethered to Flat Graphitic Carbon by ATR-FT-IR and Raman Spectroscopy. Anal Chem 2006; 78:3104-12. [PMID: 16643000 DOI: 10.1021/ac052042h] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Mono- and multilayers of nitroazobenzene (NAB), azobenzene (AB), nitrobiphenyl (NBP), biphenyl (BP), and fluorene (FL) were covalently bonded to flat pyrolyzed photoresist films (PPF) by electrochemical reduction of their diazonium derivatives. The structure and orientation of the molecular layers were probed with ATR-FT-IR and Raman spectroscopy. A hemispherical germanium ATR element used with p-polarized light at 65 degrees incidence angle yielded high signal/noise IR spectra for monolayer coverage of molecules on PPF. The IR spectra are dominated by in-plane vibrational modes in the 1000-2000-cm(-1) spectral range but also exhibit weaker out-of-plane deformations in the 650-1000-cm(-1) region. The average tilt angle with respect to the surface normal for the various molecules varied from 31.0 +/- 4.5 degrees for NAB to 44.2 +/- 5.4 degrees for FL with AB, NBP, and BP exhibiting intermediate adsorption geometries. Raman intensity ratios of NAB and AB for p- and s-polarized incident light support the conclusion that the chemisorbed molecules are in a predominantly upright orientation. The results unequivocally indicate that molecules electroreduced from their diazonium precursors are not chemisorbed flat on the PPF surface, but rather at an angle, similar to the behavior of Au/thiol self-assembled monolayers, Langmuir-Blodgett films, and porphyrin molecules chemisorbed thermally on silicon and PPF from alkyne and alkene precursors.
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Affiliation(s)
- Franklin Anariba
- Department of Chemistry, University of California, Riverside, California 92521, USA
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Study of Nitroazobenzene Films Covalently Attached at the Surface of Carbon that Exhibit Conductance Switching. E-JOURNAL OF SURFACE SCIENCE AND NANOTECHNOLOGY 2006. [DOI: 10.1380/ejssnt.2006.419] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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42
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McCreery RL, Wu J, Kalakodimi RP. Electron transport and redox reactions in carbon-based molecular electronic junctions. Phys Chem Chem Phys 2006; 8:2572-90. [PMID: 16738711 DOI: 10.1039/b601163m] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
A unique molecular junction design is described, consisting of a molecular mono- or multilayer oriented between a conducting carbon substrate and a metallic top contact. The sp2 hybridized graphitic carbon substrate (pyrolyzed photoresist film, PPF) is flat on the scale of the molecular dimensions, and the molecular layer is bonded to the substrate via diazonium ion reduction to yield a strong, conjugated C-C bond. Molecular junctions were completed by electron-beam deposition of copper, titanium oxide, or aluminium oxide followed by a final conducting layer of gold. Vibrational spectroscopy and XPS of completed junctions showed minimal damage to the molecular layer by metal deposition, although some electron transfer to the molecular layer resulted in partial reduction in some cases. Device yield was high (>80%), and the standard deviations of junction electronic properties such as low voltage resistance were typically in the range of 10-20%. The resistance of PPF/molecule/Cu/Au junctions exhibited a strong dependence on the structure and thickness of the molecular layer, ranging from 0.13 ohms cm2 for a nitrobiphenyl monolayer, to 4.46 ohms cm2 for a biphenyl monolayer, and 160 ohms cm2 for a 4.3 nm thick nitrobiphenyl multilayer. Junctions containing titanium or aluminium oxide had dramatically lower conductance than their PPF/molecule/Cu counterparts, with aluminium oxide junctions exhibiting essentially insulating behavior. However, in situ Raman spectroscopy of PPF/nitroazobenzene/AlO(x)/Au junctions with partially transparent metal contacts revealed that redox reactions occurred under bias, with nitroazobenzene (NAB) reduction occurring when the PPF was biased negative relative to the Au. Similar redox reactions were observed in PPF/NAB/TiO(x)/Au molecular junctions, but they were accompanied by major effects on electronic behavior, such as rectification and persistent conductance switching. Such switching was evident following polarization of PPF/molecule/TiO2/Au junctions by positive or negative potential pulses, and the resulting conductance changes persisted for several minutes at room temperature. The "memory" effect implied by these observations is attributed to a combination of the molecular layer and the TiO2 properties, namely metastable "trapping" of electrons in the TiO2 when the Au is negatively biased.
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Affiliation(s)
- Richard L McCreery
- Department of Chemistry, The Ohio State University, 100 W 18th Avenue, Columbus, OH 43210, USA.
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43
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McCreery RL, Viswanathan U, Kalakodimi RP, Nowak AM. Carbon/molecule/metal molecular electronic junctions: the importance of “contacts”. Faraday Discuss 2006; 131:33-43; discussion 91-109. [PMID: 16512363 DOI: 10.1039/b505684p] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Molecular electronic junctions fabricated by covalent bonding onto a graphitic carbon substrate were examined with Raman spectroscopy and characterized electronically. The molecular layer was a 4.5 nm thick multilayer of nitroazobenzene (NAB), and the top contact material was varied to investigate its effect on junction behavior. A 3.0 nm thick layer of copper, TiO2, or Al(III) oxide (AlO(x)) was deposited on top of the NAB layer, followed by a 7.0 nm thick layer of gold. Copper "contacts" yielded molecular junctions with low resistance and showed a strong dependence on molecular structure. Carbon/ NAB/AlO(x)/Au junctions exhibited high resistance, with current densities three orders of magnitude less than those for analogous Cu junctions. However, Raman spectroscopy revealed that the NAB layer was reduced when the carbon substrate was biased negative, to a product resembling that resulting from electrochemical reduction of NAB. Carbon/ NAB/TiO2/Au junctions showed rectifying J/V behavior, with high conductivity to electrons able to enter the TiO2 conduction band. Substitution of azobenzene for nitroazobenzene yielded junctions with similar spectroscopic and electronic behavior to NAB, indicating that the nitro group is not essential for rectification. The results are interpreted in terms of the energy levels of the molecule relative to those of TiO2. The combination of a covalently bonded molecular layer and a semiconducting oxide yields unusual electronic properties in a carbon/molecule/semiconductor/Au molecular junction.
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Affiliation(s)
- Richard L McCreery
- Department of Chemistry, Ohio State University, Columbus, OH 43210, USA.
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York RL, Nacionales D, Slowinski K. Electrical resistivity of monolayers and bilayers of alkanethiols in tunnel junction with gate electrode. Chem Phys 2005. [DOI: 10.1016/j.chemphys.2005.05.001] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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Brooksby PA, Downard AJ, Yu SSC. Effect of applied potential on arylmethyl films oxidatively grafted to carbon surfaces. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2005; 21:11304-11. [PMID: 16285804 DOI: 10.1021/la051964c] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Arylmethyl films have been grafted to glassy carbon surfaces and to pyrolyzed photoresist films (PPFs) by electrochemical oxidation of 1-naphthylmethylcarboxylate and 4-methoxybenzylcarboxylate. Atomic force microscopy (AFM) and electrochemistry were used to characterize the as-prepared films and to monitor changes induced by post-preparation treatments. Film thickness was measured by depth profiling using an AFM tip to remove film from the PPF surface. Surface coverage of electroactive modifiers was estimated from cyclic voltammetry, and monitoring the response of a solution-based redox probe at grafted surfaces gave a qualitative indication of changes in film properties. For preparation of the films, the maximum film thickness increased with the potential applied during grafting, and all films were of multilayer thickness. The apparent rate of electron transfer for the Fe(CN)(6)3-/Fe(CN)(6)4- couple was very low at as-prepared films. After film-grafted electrodes were transferred to pure acetonitrile-electrolyte solution and subjected to negative potential excursions, the response of the Fe(CN)(6)3-/Fe(CN)(6)4- couple changed and was consistent with faster electron-transfer kinetics, the film thickness decreased and the surface roughness increased substantially. Applying a positive potential to the treated film reversed changes in film thickness, but the voltammetric response of the Fe(CN)(6)3-/Fe(CN)(6)4- couple remained kinetically fast. After as-prepared films were subjected to positive applied potentials in acetonitrile-electrolyte solution, the apparent rate of electron transfer for the Fe(CN)(6)3-/Fe(CN)(6)4- couple remained very slow and the measured film thickness was the same or greater than that before treatment at positive potentials. Mechanisms are considered to explain the observed effects of applied potential on film characteristics.
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Affiliation(s)
- Paula A Brooksby
- MacDiarmid Institute for Advanced Materials and Nanotechnology, Department of Chemistry, University of Canterbury, Private Bag 4800, Christchurch, New Zealand
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Ssenyange S, Anariba F, Bocian DF, McCreery RL. Covalent bonding of alkene and alkyne reagents to graphitic carbon surfaces. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2005; 21:11105-12. [PMID: 16285778 DOI: 10.1021/la0516173] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Various aromatic and aliphatic alkynes and one alkene were covalently bonded to sp(2)-hybridized carbon surfaces by heat treatment in an argon atmosphere. X-ray photoelectron spectroscopy, Raman, and FTIR spectra of the modified surfaces showed that the molecules were intact after the 400 degrees C heat treatment but that the alkyne group had reacted with the surface to form a covalent bond. Alkynes with ferrocene and porphyrin centers exhibited chemically reversible voltammetric waves that could be cycled many times. Atomic force microscopy of the modified surfaces indicated a thickness of the molecular layer consistent with monolayer coverage, and surface coverage determined by voltammetry was also in the monolayer range. Raman spectroscopy of the porphyrin monolayers formed from a porphyrin alkyne showed no evidence for dimer formation, although multilayer formation may occur at undetected levels. FTIR spectra of the porphyrin-modified carbon surfaces were well-defined, similar to the parent molecule, and indicative of an average tilt angle between the porphyrin plane and the surface normal of 37 degrees . The bond between the molecular monolayer and the carbon surface was quite stable, withstanding sonication in tetrahydrofuran, mild aqueous acid and base, and repeated voltammetric cycling in propylene carbonate electrolyte. Heat treatment of alkynes and alkenes appears to be a generally useful method for modifying carbon surfaces, which can be applied to both aromatic and aliphatic molecules.
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Affiliation(s)
- Solomon Ssenyange
- Department of Chemistry, The Ohio State University, Columbus, Ohio 43210, USA
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Weiss EA, Tauber MJ, Kelley RF, Ahrens MJ, Ratner MA, Wasielewski MR. Conformationally Gated Switching between Superexchange and Hopping within Oligo-p-phenylene-Based Molecular Wires. J Am Chem Soc 2005; 127:11842-50. [PMID: 16104763 DOI: 10.1021/ja052901j] [Citation(s) in RCA: 153] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
We observe well-defined regions of superexchange and thermally activated hopping in the temperature dependence of charge recombination (CR) in a series of donor-bridge-acceptor (D-B-A) systems, where D = phenothiazine (PTZ), B = p-phenylene (Ph(n)), n = 1-4, and A = perylene-3,4:9,10-bis(dicarboximide) (PDI). A fit to the thermally activated CR rates of the n = 3 and n = 4 compounds yields activation barriers of 1290 and 2030 cm(-1), respectively, which match closely with theoretically predicted and experimentally observed barriers for the planarization of terphenyl and quaterphenyl. Negative activation of CR in the temperature regions dominated by superexchange charge transport is the result of a fast conformational equilibrium that increasingly depopulates the reactive state for CR as temperature is increased. The temperature dependence of the effective donor-acceptor superexchange coupling, V(DA), measured using magnetic field effects on the efficiency of the charge recombination process, shows that CR occurs out of the conformation with lower V(DA) via the energetically favored triplet pathway.
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Affiliation(s)
- Emily A Weiss
- Center for Nanofabrication and Molecular Self-Assembly and Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113, USA
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Anariba F, Steach JK, McCreery RL. Strong Effects of Molecular Structure on Electron Transport in Carbon/Molecule/Copper Electronic Junctions. J Phys Chem B 2005; 109:11163-72. [PMID: 16852362 DOI: 10.1021/jp051093f] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Carbon/molecule/copper molecular electronic junctions were fabricated by metal deposition of copper onto films of various thicknesses of fluorene (FL), biphenyl (BP), and nitrobiphenyl (NBP) covalently bonded to flat, graphitic carbon. A "crossed-wire" junction configuration provided high device yield and good junction reproducibility. Current/voltage characteristics were investigated for 69 junctions with various molecular structures and thicknesses and at several temperatures. The current/voltage curves for all cases studied were nearly symmetric, scan rate independent, repeatable at least thousands of cycles and exhibited negligible hysteresis. Junction conductance was strongly dependent on the dihedral angle between phenyl rings and on the nature of the molecule/copper "contact". Junctions made with NBP showed a decrease in conductivity of a factor of 1300 when the molecular layer thickness increased from 1.6 to 4.5 nm. The slope of ln(i) vs layer thickness for both BP and NBP was weakly dependent on applied voltage and ranged from 0.16 to 0.24 A(-1). These attenuation factors are similar to those observed for similar molecular layers on modified electrodes used to study electrochemical kinetics. All junctions studied showed weak temperature dependence in the range of approximately 325 to 214 K, implying activation barriers in the range of 0.06 to 0.15 eV. The carbon/molecule/copper junction structure provides a robust, reproducible platform for investigations of the dependence of electron transport in molecular junctions on both molecular structure and temperature. Furthermore, the results indicate that junction conductance is a strong function of molecular structure, rather than some artifact resulting from junction fabrication.
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Affiliation(s)
- Franklin Anariba
- Department of Chemistry, The Ohio State University, 100 West 18th Avenue, Columbus, Ohio 43210, USA
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Calvente JJ, López-Pérez G, Ramírez P, Fernández H, Zón MA, Mulder WH, Andreu R. Experimental Study of the Interplay between Long-Range Electron Transfer and Redox Probe Permeation at Self-Assembled Monolayers: Evidence for Potential-Induced Ion Gating. J Am Chem Soc 2005; 127:6476-86. [PMID: 15853356 DOI: 10.1021/ja050265j] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Evidence for the competition between long-range electron transfer across self-assembled monolayers (SAMs) and incorporation of the redox probe into the film is reported for the electroreduction of Ru(NH(3)) at hydroxyl- and carboxylic-acid-terminated SAMs on a mercury electrode, by using electrochemical techniques that operate at distinct time scales. Two limiting voltammetric behaviors are observed, consistent with a diffusion control of the redox process at mercaptophenol-coated electrodes and a kinetically controlled electron transfer reaction in the presence of neutral HS-(CH(2))(10)-COOH and HS-(CH(2))(n)()-CH(2)OH (n = 3, 5, and 10) SAMs. The monolayer thickness dependence of the standard heterogeneous electron transfer rate constant shows that the electron transfer plane for the reduction of Ru(NH(3)) at hydroxyl-terminated SAMs is located outside the film | solution interface at short times. However, long time scale experiments provide evidence for the occurrence of potential-induced gating of the adsorbed structure in some of the monolayers studied, which takes the form of a chronoamperometric spike. Redox probe permeation is shown to be a kinetically slow process, whose activation strongly depends on redox probe concentration, applied potential, and chemical composition of the intervening medium. The obtained results reveal that self-assembled monolayers made of mercaptobutanol and mercaptophenol preserve their electronic barrier properties up to the reductive desorption potential of a fully grown SAM, whereas those of mercaptohexanol, mercaptoundecanol, and mercaptoundecanoic acid undergo an order/disorder transition below a critical potential, which facilitates the approach of the redox probe toward the electrode surface.
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Affiliation(s)
- Juan José Calvente
- Departamento de Quimica Fisica, Facultad de Quimica, Universidad de Sevilla, 41012, Sevilla, Spain
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Brooksby PA, Downard AJ. Multilayer Nitroazobenzene Films Covalently Attached to Carbon. An AFM and Electrochemical Study. J Phys Chem B 2005; 109:8791-8. [PMID: 16852044 DOI: 10.1021/jp046095z] [Citation(s) in RCA: 120] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Nitroazobenzene films have been grafted to pyrolyzed photoresist films by electrochemical reduction of the corresponding diazonium salt in acetonitrile solution. Two component films were also prepared by electrochemically grafting methylbenzene layers to preformed NAB films. Voltammetric investigation of the films in aqueous acid medium and the measurement of film thickness using atomic force microscopy (AFM) lead to new insights into film structure. In aqueous acid solution, the azobenzene groups have no detectable electroactivity and not all nitro groups in the films can be reduced. These findings point to a compact film structure in which proton diffusion is limited. There may also be spatial inhibition of the conformational changes that accompany azobenzene reduction. For increasingly thick NAB films, the peak for reduction of the nitro groups moves to more negative potentials and the peaks become more asymmetric in shape. These changes are interpreted in terms of the dielectric properties and the rate of proton diffusion in the films. Film thickness was measured by ploughing through the film with an AFM tip. When an NAB film prepared in acetonitrile solution is reduced in aqueous acid, the film thickness decreases by more than 50%. The changes can be partially reversed by treatment in acetonitrile-electrolyte solution and hence are attributed to ion-solvent induced swelling and shrinking. Thus, the large decrease in thickness detected by AFM after treatment of the film in aqueous acid is consistent with the compact film structure revealed by electrochemistry.
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Affiliation(s)
- Paula A Brooksby
- MacDiarmid Institute for Advanced Materials and Nanotechnology, Department of Chemistry, University of Canterbury, Private Bag 4800, Christchurch, New Zealand
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