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Chen Y, Bâldea I, Yu Y, Liang Z, Li MD, Koren E, Xie Z. CP-AFM Molecular Tunnel Junctions with Alkyl Backbones Anchored Using Alkynyl and Thiol Groups: Microscopically Different Despite Phenomenological Similarity. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2024; 40:4410-4423. [PMID: 38348971 PMCID: PMC10906003 DOI: 10.1021/acs.langmuir.3c03759] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/05/2023] [Revised: 01/24/2024] [Accepted: 01/24/2024] [Indexed: 02/28/2024]
Abstract
In this paper, we report results on the electronic structure and transport properties of molecular junctions fabricated via conducting probe atomic force microscopy (CP-AFM) using self-assembled monolayers (SAMs) of n-alkyl chains anchored with acetylene groups (CnA; n = 8, 9, 10, and 12) on Ag, Au, and Pt electrodes. We found that the current-voltage (I-V) characteristics of CnA CP-AFM junctions can be very accurately reproduced by the same off-resonant single-level model (orSLM) successfully utilized previously for many other junctions. We demonstrate that important insight into the energy-level alignment can be gained from experimental data of transport (processed via the orSLM) and ultraviolet photoelectron spectroscopy combined with ab initio quantum chemical information based on the many-body outer valence Green's function method. Measured conductance GAg < GAu < GPt is found to follow the same ordering as the metal work function ΦAu < ΦAu < ΦPt, a fact that points toward a transport mediated by an occupied molecular orbital (MO). Still, careful data analysis surprisingly revealed that transport is not dominated by the ubiquitous HOMO but rather by the HOMO-1. This is an important difference from other molecular tunnel junctions with p-type HOMO-mediated conduction investigated in the past, including the alkyl thiols (CnT) to which we refer in view of some similarities. Furthermore, unlike in CnT and other junctions anchored with thiol groups investigated in the past, the AFM tip causes in CnA an additional MO shift, whose independence of size (n) rules out significant image charge effects. Along with the prevalence of the HOMO-1 over the HOMO, the impact of the "second" (tip) electrode on the energy level alignment is another important finding that makes the CnA and CnT junctions different. What ultimately makes CnA unique at the microscopic level is a salient difference never reported previously, namely, that CnA's alkyne functional group gives rise to two energetically close (HOMO and HOMO-1) orbitals. This distinguishes the present CnA from the CnT, whose HOMO stemming from its thiol group is well separated energetically from the other MOs.
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Affiliation(s)
- Yuhong Chen
- Department
of Materials Science and Engineering, Technion-Israel
Institute of Technology, Haifa 3200003, Israel
- Department
of Materials Science and Engineering, Guangdong Provincial Key Laboratory
of Materials and Technologies for Energy Conversion (MATEC), Guangdong Technion-Israel Institute of Technology, 241 Daxue Road, Shantou, Guangdong 515063, China
| | - Ioan Bâldea
- Theoretical
Chemistry, Heidelberg University, Im Neuenheimer Feld 229, D-69120 Heidelberg, Germany
| | - Yongxin Yu
- Department
of Materials Science and Engineering, Guangdong Provincial Key Laboratory
of Materials and Technologies for Energy Conversion (MATEC), Guangdong Technion-Israel Institute of Technology, 241 Daxue Road, Shantou, Guangdong 515063, China
| | - Zining Liang
- Department
of Materials Science and Engineering, Guangdong Provincial Key Laboratory
of Materials and Technologies for Energy Conversion (MATEC), Guangdong Technion-Israel Institute of Technology, 241 Daxue Road, Shantou, Guangdong 515063, China
| | - Ming-De Li
- Department
of Chemistry and Key Laboratory for Preparation and Application of
Ordered Structural Materials of Guangdong Province, Shantou University, Shantou 515063, China
| | - Elad Koren
- Department
of Materials Science and Engineering, Technion-Israel
Institute of Technology, Haifa 3200003, Israel
| | - Zuoti Xie
- Department
of Materials Science and Engineering, Technion-Israel
Institute of Technology, Haifa 3200003, Israel
- Department
of Materials Science and Engineering, Guangdong Provincial Key Laboratory
of Materials and Technologies for Energy Conversion (MATEC), Guangdong Technion-Israel Institute of Technology, 241 Daxue Road, Shantou, Guangdong 515063, China
- Quantum
Science Center of Guangdong-Hong Kong-Macao Greater Bay Area (Guangdong), Shenzhen-Hong Kong International Science and Technology
Park, No. 3 Binglang
Road, Futian District, Shenzhen, Guangdong 518048, China
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2
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Li Z, Yu X. Reply to the 'Comment on "A single level tunneling model for molecular junctions: evaluating the simulation methods"' by I Baldea, Phys. Chem. Chem. Phys., 2024, 26, D2CP05110A (http://D2CP05110A). Phys Chem Chem Phys 2024; 26:7236-7238. [PMID: 38332719 DOI: 10.1039/d3cp05375j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/10/2024]
Abstract
We respond to the recent comment by Dr. Ion Bâldea concerning our work, "A single level tunneling model for molecular junctions: evaluating the simulation methods [E. M. Opodi et al.,Phys. Chem. Chem. Phys., 2022, 24, 11958]". Dr. Bâldea has raised concerns about the applicability map we developed based on the comparison study of the 3 analytical models used in the study of molecular electronics. In our response, we have dissected Dr. Bâldea's critique into four primary points. For each, we have provided comprehensive replies that address and rectify the misinterpretations of our initial study. We'd like to thank Dr. Ion Bâldea for his comments, which have resulted in further clarification of the applicability of the analytical models for the study of molecular electronics.
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Affiliation(s)
- Zheyang Li
- Tianjin Key Laboratory of Molecular Optoelectronic Science, School of Science, Tianjin University, Tianjin 300072, China.
- Key Laboratory of Organic Integrated Circuits, Ministry of Education, Tianjin, 300072, China
| | - Xi Yu
- Tianjin Key Laboratory of Molecular Optoelectronic Science, School of Science, Tianjin University, Tianjin 300072, China.
- Key Laboratory of Organic Integrated Circuits, Ministry of Education, Tianjin, 300072, China
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Bâldea I. Comment on "A single level tunneling model for molecular junctions: evaluating the simulation methods" by E. M. Opodi, X. Song, X. Yu and W. Hu, Phys. Chem. Chem. Phys., 2022, 24, 11958". Phys Chem Chem Phys 2024; 26:7230-7235. [PMID: 38329445 DOI: 10.1039/d2cp05110a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/09/2024]
Abstract
The present Comment demonstrates important flaws of the paper Opodi et al. Phys. Chem. Chem. Phys., 2022, 24, 11958 Their crown result ("applicability map") aims at indicating parameter ranges wherein two approximate methods (called method 2 and 3) apply. My calculations reveal that the applicability map is a factual error. Deviations of I2 from the exact current I1 do not exceed 3% for model parameters where Opodi et al. claimed that method 2 is inapplicable. As for method 3, the parameter range of the applicability map is beyond its scope, as stated in papers cited by Opodi et al. themselves.
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Affiliation(s)
- Ioan Bâldea
- Theoretical Chemistry, Heidelberg University, Im Neuenheimer Feld 229, D-69120 Heidelberg, Germany.
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Bâldea I. Can tunneling current in molecular junctions be so strongly temperature dependent to challenge a hopping mechanism? Analytical formulas answer this question and provide important insight into large area junctions. Phys Chem Chem Phys 2024; 26:6540-6556. [PMID: 38328878 DOI: 10.1039/d3cp05046g] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/09/2024]
Abstract
Analytical equations like Richardson-Dushman's or Shockley's provided a general, if simplified conceptual background, which was widely accepted in conventional electronics and made a fundamental contribution to advances in the field. In the attempt to develop a (highly desirable, but so far missing) counterpart for molecular electronics, in this work, we deduce a general analytical formula for the tunneling current through molecular junctions mediated by a single level that is valid for any bias voltage and temperature. Starting from this expression, which is exact and obviates cumbersome numerical integration, in the low and high temperature limits we also provide analytical formulas expressing the current in terms of elementary functions. They are accurate for broad model parameter ranges relevant for real molecular junctions. Within this theoretical framework we show that: (i) by varying the temperature, the tunneling current can vary by several orders of magnitude, thus debunking the myth that a strong temperature dependence of the current is evidence for a hopping mechanism, (ii) real molecular junctions can undergo a gradual (Sommerfeld-Arrhenius) transition from a weakly temperature dependent to a strongly ("exponential") temperature dependent current that can be tuned by the applied bias, and (iii) important insight into large area molecular junctions with eutectic gallium indium alloy (EGaIn) top electrodes can be gained. E.g., merely based on transport data, we estimate that the current carrying molecules represent only a fraction of f ≈ 4 × 10-4 out of the total number of molecules in a large area Au-S-(CH2)13-CH3/EGaIn junction.
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Affiliation(s)
- Ioan Bâldea
- Theoretical Chemistry, Heidelberg University, Im Neuenheimer Feld 229, D-69120 Heidelberg, Germany.
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Bera S, Fereiro JA, Saxena SK, Chryssikos D, Majhi K, Bendikov T, Sepunaru L, Ehre D, Tornow M, Pecht I, Vilan A, Sheves M, Cahen D. Near-Temperature-Independent Electron Transport Well beyond Expected Quantum Tunneling Range via Bacteriorhodopsin Multilayers. J Am Chem Soc 2023; 145. [PMID: 37933117 PMCID: PMC10655127 DOI: 10.1021/jacs.3c09120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2023] [Revised: 10/19/2023] [Accepted: 10/20/2023] [Indexed: 11/08/2023]
Abstract
A key conundrum of biomolecular electronics is efficient electron transport (ETp) through solid-state junctions up to 10 nm, often without temperature activation. Such behavior challenges known charge transport mechanisms, especially via nonconjugated molecules such as proteins. Single-step, coherent quantum-mechanical tunneling proposed for ETp across small protein, 2-3 nm wide junctions, but it is problematic for larger proteins. Here we exploit the ability of bacteriorhodopsin (bR), a well-studied, 4-5 nm long membrane protein, to assemble into well-defined single and multiple bilayers, from ∼9 to 60 nm thick, to investigate ETp limits as a function of junction width. To ensure sufficient signal/noise, we use large area (∼10-3 cm2) Au-protein-Si junctions. Photoemission spectra indicate a wide energy separation between electrode Fermi and the nearest protein-energy levels, as expected for a polymer of mostly saturated components. Junction currents decreased exponentially with increasing junction width, with uniquely low length-decay constants (0.05-0.5 nm-1). Remarkably, even for the widest junctions, currents are nearly temperature-independent, completely so below 160 K. While, among other things, the lack of temperature-dependence excludes, hopping as a plausible mechanism, coherent quantum-mechanical tunneling over 60 nm is physically implausible. The results may be understood if ETp is limited by injection into one of the contacts, followed by more efficient charge propagation across the protein. Still, the electrostatics of the protein films further limit the number of charge carriers injected into the protein film. How electron transport across dozens of nanometers of protein layers is more efficient than injection defines a riddle, requiring further study.
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Affiliation(s)
- Sudipta Bera
- Department
of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Jerry A. Fereiro
- Department
of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 7610001, Israel
- School
of Chemistry, Indian Institute of Science
Education and Research, Thiruvananthapuram 695551, Kerala, India
| | - Shailendra K. Saxena
- Department
of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 7610001, Israel
- Department
of Physics and Nanotechnology, College of Engineering and Technology, SRM Institute of Science and Technology, Kattankulathur, Chennai 603203, Tamil
Nadu, India
| | - Domenikos Chryssikos
- Molecular
Electronics, Technical University of Munich, 85748 Garching, Germany
- Fraunhofer
Institute for Electronic Microsystems and Solid State Technologies
(EMFT), 80686 München, Germany
| | - Koushik Majhi
- Department
of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Tatyana Bendikov
- Department
of Chemical Research Support, Weizmann Institute
of Science, Rehovot 7610001, Israel
| | - Lior Sepunaru
- Department
of Chemistry and Biochemistry, University
of California, Santa
Barbara, California 93106, United States
| | - David Ehre
- Department
of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Marc Tornow
- Molecular
Electronics, Technical University of Munich, 85748 Garching, Germany
- Fraunhofer
Institute for Electronic Microsystems and Solid State Technologies
(EMFT), 80686 München, Germany
| | - Israel Pecht
- Department
of Immunology and Regenerative Biology, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Ayelet Vilan
- Department
of Chemical and Biological Physics Weizmann
Institute of Science, Rehovot 7610001, Israel
| | - Mordechai Sheves
- Department
of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - David Cahen
- Department
of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 7610001, Israel
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6
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Bâldea I. Can room-temperature data for tunneling molecular junctions be analyzed within a theoretical framework assuming zero temperature? Phys Chem Chem Phys 2023. [PMID: 37439691 DOI: 10.1039/d3cp00740e] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/14/2023]
Abstract
Routinely, experiments on tunneling molecular junctions report values of conductances (GRT) and currents (IRT) measured at room temperature. On the other hand, theoretical approaches based on simplified models provide analytic formulas for the conductance (G0K) and current (I0K) valid at zero temperature. Therefore, interrogating the applicability of the theoretical results deduced in the zero-temperature limit to real experimental situations at room temperature (i.e., GRT ≈ G0K and IRT ≈ I0K) is a relevant aspect. Quantifying the pertaining temperature impact on the transport properties computed within the ubiquitous single-level model with Lorentzian transmission is the specific aim of the present work. Comprehensive results are presented for broad ranges of the relevant parameters (level's energy offset ε0 and width Γa, and applied bias V) that safely cover values characterizing currently fabricated junctions. They demonstrate that the strongest thermal effects occur at biases below resonance (2|ε0| - δε0 - 0.3 ≲ |eV| - 0.3 ≲ 2|ε0|). At fixed V, they affect an ε0-range whose largest width δε0 is about nine times larger than the thermal energy (δε0 ≈ 3πkBT) at Γa → 0. The numerous figures included aim to convey a quick overview on the applicability of the zero-temperature limit to a specific real junction. In quantitative terms, the conditions of applicability are expressed as mathematical inequalities involving elementary functions. They constitute the basis of a proposed interactive data-fitting procedure, which aims to guide experimentalists interested in data processing in a specific case.
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Affiliation(s)
- Ioan Bâldea
- Theoretical Chemistry, Heidelberg University, Im Neuenheimer Feld 229, D-69120 Heidelberg, Germany.
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7
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Nguyen QV, Thi HL, Truong GL. Chemical Conformation Induced Transport Carrier Switching in Molecular Junction based on Carboxylic-Terminated Thiol Molecules. NANO LETTERS 2022; 22:10147-10153. [PMID: 36475760 DOI: 10.1021/acs.nanolett.2c04031] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
The paper demonstrates the effect of the chemical conformation of the -COOH group on the transport characteristic including conductance, rectification, and length effect in molecular junctions (MJs) formed by self-assembled monolayers of carboxylic-terminated thiol molecules. For an alkyl chain shorter than C11, the transport mechanism was attributed to a direct off-resonant tunneling of a hole carrier, located at the Au-S interface, whereas a hopping mechanism was assigned to the alkyl chain longer than the C11 chain located at the -COOH group. The hopping mechanism may be operated by electron transport associated with the breaking of the -OH bonding likely driven by a voltage. Importantly, at the C11 alkyl chain, we observed that the transport carrier operating in MJs could change from a hole carrier into an electron carrier. The result strongly proves that the chemical conformation should be considered in analyzing molecular electronics and provides a basis for the rational design of molecular electronic devices.
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Affiliation(s)
- Quyen Van Nguyen
- Department of Advanced Materials Science and Nanotechnology, University of Science and Technology of Hanoi, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay, Hanoi 11307, Vietnam
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, United States
| | - Huong Le Thi
- Department of Advanced Materials Science and Nanotechnology, University of Science and Technology of Hanoi, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay, Hanoi 11307, Vietnam
| | - Giang Le Truong
- Institute of Chemistry, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay, Hanoi 11307, Vietnam
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8
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Estimating the Number of Molecules in Molecular Junctions Merely Based on the Low Bias Tunneling Conductance at Variable Temperature. Int J Mol Sci 2022; 23:ijms232314985. [PMID: 36499309 PMCID: PMC9737784 DOI: 10.3390/ijms232314985] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2022] [Revised: 11/23/2022] [Accepted: 11/25/2022] [Indexed: 12/05/2022] Open
Abstract
Temperature (T) dependent conductance G=G(T) data measured in molecular junctions are routinely taken as evidence for a two-step hopping mechanism. The present paper emphasizes that this is not necessarily the case. A curve of lnG versus 1/T decreasing almost linearly (Arrhenius-like regime) and eventually switching to a nearly horizontal plateau (Sommerfeld regime), or possessing a slope gradually decreasing with increasing 1/T is fully compatible with a single-step tunneling mechanism. The results for the dependence of G on T presented include both analytical exact and accurate approximate formulas and numerical simulations. These theoretical results are general, also in the sense that they are not limited, e.g., to the (single molecule electromigrated (SET) or large area EGaIn) fabrication platforms, which are chosen for exemplification merely in view of the available experimental data needed for analysis. To be specific, we examine in detail transport measurements for molecular junctions based on ferrocene (Fc). As a particularly important finding, we show how the present analytic formulas for G=G(T) can be utilized to compute the ratio f=Aeff/An between the effective and nominal areas of large area Fc-based junctions with an EGaIn top electrode. Our estimate of f≈0.6×10-4 is comparable with previously reported values based on completely different methods for related large area molecular junctions.
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9
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Gupta N, Karuppannan SK, Pasula RR, Vilan A, Martin J, Xu W, May EM, Pike AR, Astier HPA, Salim T, Lim S, Nijhuis CA. Temperature-Dependent Coherent Tunneling across Graphene-Ferritin Biomolecular Junctions. ACS APPLIED MATERIALS & INTERFACES 2022; 14:44665-44675. [PMID: 36148983 PMCID: PMC9542697 DOI: 10.1021/acsami.2c11263] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/04/2022] [Accepted: 09/08/2022] [Indexed: 06/16/2023]
Abstract
Understanding the mechanisms of charge transport (CT) across biomolecules in solid-state devices is imperative to realize biomolecular electronic devices in a predictive manner. Although it is well-accepted that biomolecule-electrode interactions play an essential role, it is often overlooked. This paper reveals the prominent role of graphene interfaces with Fe-storing proteins in the net CT across their tunnel junctions. Here, ferritin (AfFtn-AA) is adsorbed on the graphene by noncovalent amine-graphene interactions confirmed with Raman spectroscopy. In contrast to junctions with metal electrodes, graphene has a vanishing density of states toward its intrinsic Fermi level ("Dirac point"), which increases away from the Fermi level. Therefore, the amount of charge carriers is highly sensitive to temperature and electrostatic charging (induced doping), as deduced from a detailed analysis of CT as a function of temperature and iron loading. Remarkably, the temperature dependence can be fully explained within the coherent tunneling regime due to excitation of hot carriers. Graphene is not only demonstrated as an alternative platform to study CT across biomolecular tunnel junctions, but it also opens rich possibilities in employing interface electrostatics in tuning CT behavior.
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Affiliation(s)
- Nipun
Kumar Gupta
- Department
of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore
- Centre
for Advanced 2D Materials, National University
of Singapore, 6 Science Drive 2, Singapore 117546, Singapore
| | - Senthil Kumar Karuppannan
- Department
of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore
| | - Rupali Reddy Pasula
- School
of Chemical and Biomedical Engineering, Nanyang Technological University, 70 Nanyang Drive, Singapore 637457, Singapore
| | - Ayelet Vilan
- Department
of Chemical and Biological Physics, Weizmann
Institute of Science, Rehovot 76100, Israel
| | - Jens Martin
- Centre
for Advanced 2D Materials, National University
of Singapore, 6 Science Drive 2, Singapore 117546, Singapore
| | - Wentao Xu
- Centre
for Advanced 2D Materials, National University
of Singapore, 6 Science Drive 2, Singapore 117546, Singapore
| | - Esther Maria May
- Chemistry-School
of Natural and Environmental Sciences, Newcastle
University, Newcastle
upon Tyne NE1 7RU, U.K.
| | - Andrew R. Pike
- School
of
Materials Science and Engineering, Nanyang
Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore
| | - Hippolyte P. A.
G. Astier
- Department
of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore
| | - Teddy Salim
- School
of
Materials Science and Engineering, Nanyang
Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore
| | - Sierin Lim
- School
of Chemical and Biomedical Engineering, Nanyang Technological University, 70 Nanyang Drive, Singapore 637457, Singapore
| | - Christian A. Nijhuis
- Department
of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore
- Centre
for Advanced 2D Materials, National University
of Singapore, 6 Science Drive 2, Singapore 117546, Singapore
- Hybrid
Materials for Opto-Electronics Group, Department of Molecules and
Materials, MESA+ Institute for Nanotechnology and Centre for Brain-Inspired
Nano Systems, Faculty of Science and Technology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
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Bâldea I. Exact Analytic Formula for Conductance Predicting a Tunable Sommerfeld–Arrhenius Thermal Transition within a Single‐Step Tunneling Mechanism in Molecular Junctions Subject to Mechanical Stretching. ADVANCED THEORY AND SIMULATIONS 2022. [DOI: 10.1002/adts.202200158] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Ioan Bâldea
- Theoretical Chemistry Heidelberg University Im Neuenheimer Feld 229 D‐69120 Heidelberg Germany
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11
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Carlotti M, Soni S, Kovalchuk A, Kumar S, Hofmann S, Chiechi RC. Empirical Parameter to Compare Molecule-Electrode Interfaces in Large-Area Molecular Junctions. ACS PHYSICAL CHEMISTRY AU 2022; 2:179-190. [PMID: 35637782 PMCID: PMC9136952 DOI: 10.1021/acsphyschemau.1c00029] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/14/2021] [Revised: 12/20/2021] [Accepted: 12/22/2021] [Indexed: 12/03/2022]
Abstract
![]()
This paper describes
a simple model for comparing the degree of
electronic coupling between molecules and electrodes across different
large-area molecular junctions. The resulting coupling parameter can
be obtained directly from current–voltage data or extracted
from published data without fitting. We demonstrate the generalizability
of this model by comparing over 40 different junctions comprising
different molecules and measured by different laboratories. The results
agree with existing models, reflect differences in mechanisms of charge
transport and rectification, and are predictive in cases where experimental
limitations preclude more sophisticated modeling. We also synthesized
a series of conjugated molecular wires, in which embedded dipoles
are varied systematically and at both molecule–electrode interfaces.
The resulting current–voltage characteristics vary in nonintuitive
ways that are not captured by existing models, but which produce trends
using our simple model, providing insights that are otherwise difficult
or impossible to explain. The utility of our model is its demonstrative
generalizability, which is why simple observables like tunneling decay
coefficients remain so widely used in molecular electronics despite
the existence of much more sophisticated models. Our model is complementary,
giving insights into molecule–electrode coupling across series
of molecules that can guide synthetic chemists in the design of new
molecular motifs, particularly in the context of devices comprising
large-area molecular junctions.
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Affiliation(s)
- Marco Carlotti
- Stratingh Institute for Chemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
| | - Saurabh Soni
- Stratingh Institute for Chemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
| | - Andrii Kovalchuk
- Stratingh Institute for Chemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
| | - Sumit Kumar
- Electrical Engineering Division, Department of Engineering, University of Cambridge, Cambridge CB3 0FA, U.K
| | - Stephan Hofmann
- Electrical Engineering Division, Department of Engineering, University of Cambridge, Cambridge CB3 0FA, U.K
| | - Ryan C Chiechi
- Stratingh Institute for Chemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
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Opodi EM, Song X, Yu X, Hu W. A single level tunneling model for molecular junctions: evaluating the simulation methods. Phys Chem Chem Phys 2022; 24:11958-11966. [PMID: 35531608 DOI: 10.1039/d1cp05807j] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A single level tunneling model has been the most popular model system in both experimental and theoretical studies of molecular junctions. We performed a detailed simulation study on the performance of the single level tunneling model for analyzing the charge transport in molecular junctions. Three different modeling methods, including the numerical integration of the Landauer formula and two approximated analytical formulas that are extensively used for extracting key transport parameters, i.e. the energy offset and the coupling strength between molecules and electrodes from current-voltage (I-V) characteristics were compared and evaluated for their applicability. The simulation of I-V plots shows that the applicability of the two approximated analytical models is dependent on the energy offset and coupling strength. Model analysis based on the three methods performed on experimental data obtained from representative literature papers revealed that the two approximated analytical methods are neither suitable for small coupling strength nor suitable for low energy offset, and they also deviated from the exact results at high bias. These results imply that the transport parameters by the model analysis can be wrong if the models were not correctly applied under their intrinsic constraints, therefore providing wrong physical information about the system. We finally provided an applicability map as a guide for different modeling methods for charge transport studies in molecular devices.
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Affiliation(s)
- Esther Martine Opodi
- Tianjin Key Laboratory of Molecular Optoelectronic Science, School of Science, Tianjin University & Collaborative Innovation Center of Chemical Science and Engineering, Tianjin 300072, China.
| | - Xianneng Song
- Tianjin Key Laboratory of Molecular Optoelectronic Science, School of Science, Tianjin University & Collaborative Innovation Center of Chemical Science and Engineering, Tianjin 300072, China.
| | - Xi Yu
- Tianjin Key Laboratory of Molecular Optoelectronic Science, School of Science, Tianjin University & Collaborative Innovation Center of Chemical Science and Engineering, Tianjin 300072, China.
| | - Wenping Hu
- Tianjin Key Laboratory of Molecular Optoelectronic Science, School of Science, Tianjin University & Collaborative Innovation Center of Chemical Science and Engineering, Tianjin 300072, China.
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Mukhopadhyay A, Liu K, Paulino V, Olivier JH. Modulating the Conduction Band Energies of Si Electrode Interfaces Functionalized with Monolayers of a Bay-Substituted Perylene Bisimide. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2022; 38:4266-4275. [PMID: 35353503 DOI: 10.1021/acs.langmuir.1c03423] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
The confinement of π-conjugated chromophores on silicon (Si) electrode surfaces is a powerful approach to engineer electroresponsive monolayers relevant to microelectronics, electrocatalysis, and information storage and processing. While common strategies to functionalize Si interfaces exploit molecularly dissolved building blocks, only a handful number of studies have leveraged the structure-function relationships of π-aggregates to tune the electronic structures of hybrid monolayers at Si interfaces. Herein, we show that the semiconducting properties of n-type monolayers constructed on Si electrodes are intimately correlated to the initial aggregation state of π-conjugated chromophore precursors derived from bay-substituted perylene bisimide (PBI) units. Specifically, our study unravels that for n-type monolayers engineered using PBI π-aggregates, the cathodic reduction potentials required to inject negative charge carriers into the conduction bands can be stabilized by 295 mV through reversible switching of the maximum anodic potential (MAP) that is applied during the oxidative cycles (+0.5 or +1.5 V vs Ag/AgCl). This redox-assisted stabilization effect is not observed with n-type monolayers derived from molecularly dissolved PBI cores and monolayers featuring a low surface density of the redox-active probes. These findings unequivocally point to the crucial role played by PBI π-aggregates in modulating the conduction band energies of n-type monolayers where a high MAP of +1.5 V enables the formation of electronic trap states that facilitate electron injection when sweeping back to cathodic potentials. Because the structure-function relationships of PBI π-aggregates are shown to modulate the semiconducting properties of hybrid n-type monolayers constructed at Si interfaces, our results hold promising opportunities to develop redox-switchable monolayers for engineering nonvolatile electronic memory devices.
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Affiliation(s)
- Arindam Mukhopadhyay
- Department of Chemistry, University of Miami, Cox Science Center, 1301 Memorial Drive, Coral Gables, Florida 33146, United States
| | - Kaixuan Liu
- Department of Chemistry, University of Miami, Cox Science Center, 1301 Memorial Drive, Coral Gables, Florida 33146, United States
| | - Victor Paulino
- Department of Chemistry, University of Miami, Cox Science Center, 1301 Memorial Drive, Coral Gables, Florida 33146, United States
| | - Jean-Hubert Olivier
- Department of Chemistry, University of Miami, Cox Science Center, 1301 Memorial Drive, Coral Gables, Florida 33146, United States
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14
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Bâldea I. Are Asymmetric SAM‐Induced Work Function Modifications Relevant for Real Molecular Rectifiers? ADVANCED THEORY AND SIMULATIONS 2022. [DOI: 10.1002/adts.202200077] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Ioan Bâldea
- Theoretical Chemistry Heidelberg University Im Neuenheimer Feld 229 Heidelberg D‐69120 Germany
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15
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Mennicken M, Peter SK, Kaulen C, Simon U, Karthäuser S. Impact of device design on the electronic and optoelectronic properties of integrated Ru-terpyridine complexes. BEILSTEIN JOURNAL OF NANOTECHNOLOGY 2022; 13:219-229. [PMID: 35281628 PMCID: PMC8895035 DOI: 10.3762/bjnano.13.16] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/10/2021] [Accepted: 01/28/2022] [Indexed: 06/14/2023]
Abstract
The performance of nanoelectronic and molecular electronic devices relies strongly on the employed functional units and their addressability, which is often a matter of appropriate interfaces and device design. Here, we compare two promising designs to build solid-state electronic devices utilizing the same functional unit. Optically addressable Ru-terpyridine complexes were incorporated in supramolecular wires or employed as ligands of gold nanoparticles and contacted by nanoelectrodes. The resulting small-area nanodevices were thoroughly electrically characterized as a function of temperature and light exposure. Differences in the resulting device conductance could be attributed to the device design and the respective transport mechanism, that is, thermally activated hopping conduction in the case of Ru-terpyridine wire devices or sequential tunneling in nanoparticle-based devices. Furthermore, the conductance switching of nanoparticle-based devices upon 530 nm irradiation was attributed to plasmon-induced metal-to-ligand charge transfer in the Ru-terpyridine complexes used as switching ligands. Finally, our results reveal a superior device performance of nanoparticle-based devices compared to molecular wire devices based on Ru-terpyridine complexes as functional units.
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Affiliation(s)
- Max Mennicken
- Peter Grünberg Institut (PGI-7) and JARA-FIT, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
- RWTH Aachen University, 52062 Aachen, Germany
| | - Sophia Katharina Peter
- Institute of Inorganic Chemistry and JARA-FIT, RWTH Aachen University, 52074 Aachen, Germany
| | - Corinna Kaulen
- Institute of Inorganic Chemistry and JARA-FIT, RWTH Aachen University, 52074 Aachen, Germany
- Faculty of Medical Engineering and Applied Mathematics, FH Aachen, University of Applied Science, 52428 Jülich, Germany
| | - Ulrich Simon
- Institute of Inorganic Chemistry and JARA-FIT, RWTH Aachen University, 52074 Aachen, Germany
| | - Silvia Karthäuser
- Peter Grünberg Institut (PGI-7) and JARA-FIT, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
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16
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Charge Transport Characteristics of Molecular Electronic Junctions Studied by Transition Voltage Spectroscopy. MATERIALS 2022; 15:ma15030774. [PMID: 35160719 PMCID: PMC8836750 DOI: 10.3390/ma15030774] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/23/2021] [Revised: 01/11/2022] [Accepted: 01/18/2022] [Indexed: 11/25/2022]
Abstract
The field of molecular electronics is prompted by tremendous opportunities for using a single-molecule and molecular monolayers as active components in integrated circuits. Until now, a wide range of molecular devices exhibiting characteristic functions, such as diodes, transistors, switches, and memory, have been demonstrated. However, a full understanding of the crucial factors that affect charge transport through molecular electronic junctions should yet be accomplished. Remarkably, recent advances in transition voltage spectroscopy (TVS) elucidate that it can provide key quantities for probing the transport characteristics of the junctions, including, for example, the position of the frontier molecular orbital energy relative to the electrode Fermi level and the strength of the molecule–electrode interactions. These parameters are known to be highly associated with charge transport behaviors in molecular systems and can then be used in the design of molecule-based devices with rationally tuned electronic properties. This article highlights the fundamental principle of TVS and then demonstrates its major applications to study the charge transport properties of molecular electronic junctions.
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17
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Xie Z, Diez Cabanes V, Van Nguyen Q, Rodriguez-Gonzalez S, Norel L, Galangau O, Rigaut S, Cornil J, Frisbie CD. Quantifying Image Charge Effects in Molecular Tunnel Junctions Based on Self-Assembled Monolayers of Substituted Oligophenylene Ethynylene Dithiols. ACS APPLIED MATERIALS & INTERFACES 2021; 13:56404-56412. [PMID: 34783518 DOI: 10.1021/acsami.1c16398] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
A number of factors contribute to orbital energy alignment with respect to the Fermi level in molecular tunnel junctions. Here, we report a combined experimental and theoretical effort to quantify the effect of metal image potentials on the highest occupied molecular orbital to Fermi level offset, εh, for molecular junctions based on self-assembled monolayers (SAMs) of oligophenylene ethynylene dithiols (OPX) on Au. Our experimental approach involves the use of both transport and photoelectron spectroscopy to extract the offsets, εhtrans and εhUPS, respectively. We take the difference in these quantities to be the image potential energy eVimage. In the theoretical approach, we use density functional theory (DFT) to calculate directly eVimage between positive charge on an OPX molecule and the negative image charge in the Au. Both approaches yield eVimage ∼ -0.1 eV per metal contact, meaning that the total image potential energy is ∼-0.2 eV for an assembled junction with two Au contacts. Thus, we find that the total image potential energy is 25-30% of the total offset εh, which means that image charge effects are significant in OPX junctions. Our methods should be generally applicable to understanding image charge effects as a function of molecular size, for example, in a variety of SAM-based junctions.
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Affiliation(s)
- Zuoti Xie
- Department of Materials Science and Engineering, Guangdong Technion-Israel Institute of Technology, Shantou, Guangdong 515063, China
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, United States
| | - Valentin Diez Cabanes
- Laboratory for Chemistry of Novel Materials, University of Mons, Mons B-7000, Belgium
| | - Quyen Van Nguyen
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, United States
| | - Sandra Rodriguez-Gonzalez
- Laboratory for Chemistry of Novel Materials, University of Mons, Mons B-7000, Belgium
- Department of Physical Chemistry, University of Malaga, Campus de Teatinos s/n, Malaga 29071, Spain
| | - Lucie Norel
- Univ Rennes, CNRS, ISCR (Institut des Sciences Chimiques de Rennes)-UMR 6226, Rennes F-3500, France
| | - Olivier Galangau
- Univ Rennes, CNRS, ISCR (Institut des Sciences Chimiques de Rennes)-UMR 6226, Rennes F-3500, France
| | - Stéphane Rigaut
- Univ Rennes, CNRS, ISCR (Institut des Sciences Chimiques de Rennes)-UMR 6226, Rennes F-3500, France
| | - Jérôme Cornil
- Laboratory for Chemistry of Novel Materials, University of Mons, Mons B-7000, Belgium
| | - C Daniel Frisbie
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, United States
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18
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Li J, Mei Y, Ma S, Yang Q, Jiang B, Xin B, Yao T, Wu J. Internal-electric-field induced high efficient type-I heterojunction in photocatalysis-self-Fenton reaction: Enhanced H 2O 2 yield, utilization efficiency and degradation performance. J Colloid Interface Sci 2021; 608:2075-2087. [PMID: 34749154 DOI: 10.1016/j.jcis.2021.10.119] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2021] [Revised: 10/19/2021] [Accepted: 10/20/2021] [Indexed: 11/19/2022]
Abstract
Herein, a type-I phosphorus-doped carbon nitride/oxygen-doped carbon nitride (P-C3N4/O-C3N4) heterojunction was designed for photocatalysis-self-Fenton reaction (photocatalytic H2O2 production and following Fenton reaction). In P-C3N4/O-C3N4, the photoinduced charge carriers were effectively separated with the help of internal-electric-field near the interface, ensuring the high catalytic performance. As a result, the production rate of H2O2 in an air-saturated solution was 179 μM·h-1, about 7.2, 2.5, 2.5 and 2.1 times quicker than that on C3N4, P-C3N4, O-C3N4, and phosphorus and oxygen co-doped C3N4, respectively. By taking advantage of the cascade mode in photocatalysis-self-Fenton reaction, H2O2 utilization efficiency was remarkably improved to 77.7%, about 9.0 times higher than that of traditional homogeneous Fenton reaction. Befitting from the superior yield and utilization efficiency, the degradation performance of P-C3N4/O-C3N4 was undoubtedly superior than other photocatalysts. This work well addressed two bottlenecks in traditional Fenton reaction: source of H2O2 and their low utilization efficiency, and the findings were beneficial to understand the mechanism and advantage of the photocatalysis-self-Fenton system in environmental remediation.
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Affiliation(s)
- Jiaqi Li
- Key Laboratory of Functional Inorganic Material Chemistry, Ministry of Education, School of Chemistry and Materials Science, Heilongjiang University, Harbin, China
| | - Yuqing Mei
- Key Laboratory of Functional Inorganic Material Chemistry, Ministry of Education, School of Chemistry and Materials Science, Heilongjiang University, Harbin, China
| | - Shouchun Ma
- State Key Lab Urban Water Resource and Environment, School of Chemistry and Chemical Engineering, Harbin Institute of Technology, Harbin, China
| | - Qingfeng Yang
- State Key Laboratory of High-efficiency Utilization of Coal and Green Chemical Engineering, College of Chemistry and Chemical Engineering, Ningxia University, Yinchuan, China
| | - Baojiang Jiang
- Key Laboratory of Functional Inorganic Material Chemistry, Ministry of Education, School of Chemistry and Materials Science, Heilongjiang University, Harbin, China
| | - Baifu Xin
- Key Laboratory of Functional Inorganic Material Chemistry, Ministry of Education, School of Chemistry and Materials Science, Heilongjiang University, Harbin, China.
| | - Tongjie Yao
- State Key Lab Urban Water Resource and Environment, School of Chemistry and Chemical Engineering, Harbin Institute of Technology, Harbin, China.
| | - Jie Wu
- Key Laboratory of Functional Inorganic Material Chemistry, Ministry of Education, School of Chemistry and Materials Science, Heilongjiang University, Harbin, China.
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19
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Tian L, Martine E, Yu X, Hu W. Amine-Anchored Aromatic Self-Assembled Monolayer Junction: Structure and Electric Transport Properties. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2021; 37:12223-12233. [PMID: 34606290 DOI: 10.1021/acs.langmuir.1c02194] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
We studied the structure and transport properties of aromatic amine self-assembled monolayers (NH2-SAMs) on an Au surface. The oligophenylene and oligoacene amines with variable lengths can form a densely packed and uniform monolayer under proper assembly conditions. Molecular junctions incorporating an eutectic Ga-In (EGaIn) top electrode were used to characterize the charge transport properties of the amine monolayer. The current density J of the junction decreases exponentially with the molecular length (d), as J = J0 exp(-βd), which is a sign of tunneling transport, with indistinguishable values of J0 and β for NH2-SAMs of oligophenylene and oligoacene, indicating a similar molecule-electrode contact and tunneling barrier for two groups of molecules. Compared with the oligophenylene and oligoacene molecules with thiol (SH) as the anchor group, a similar β value (∼0.35 Å-1) of the aromatic NH2-SAM suggests a similar tunneling barrier, while a lower (by 2 orders of magnitude) injection current J0 is attributed to lower electronic coupling Γ of the amine group with the electrode. These observations are further supported by single-level tunneling model fitting. Our study here demonstrates the NH2-SAMs can work as an effective active layer for molecular junctions, and provide key physical parameters for the charge transport, paving the road for their applications in functional devices.
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Affiliation(s)
- Lixian Tian
- Tianjin Key Laboratory of Molecular Optoelectronic Science, School of Science, Tianjin University & Collaborative Innovation Center of Chemical Science and Engineering, Tianjin 300072, China
| | - Esther Martine
- Tianjin Key Laboratory of Molecular Optoelectronic Science, School of Science, Tianjin University & Collaborative Innovation Center of Chemical Science and Engineering, Tianjin 300072, China
| | - Xi Yu
- Tianjin Key Laboratory of Molecular Optoelectronic Science, School of Science, Tianjin University & Collaborative Innovation Center of Chemical Science and Engineering, Tianjin 300072, China
| | - Wenping Hu
- Tianjin Key Laboratory of Molecular Optoelectronic Science, School of Science, Tianjin University & Collaborative Innovation Center of Chemical Science and Engineering, Tianjin 300072, China
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20
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Xie Z, Bâldea I, Nguyen QV, Frisbie CD. Quantitative analysis of weak current rectification in molecular tunnel junctions subject to mechanical deformation reveals two different rectification mechanisms for oligophenylene thiols versus alkane thiols. NANOSCALE 2021; 13:16755-16768. [PMID: 34604892 DOI: 10.1039/d1nr04410a] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Metal-molecule-metal junctions based on alkane thiol (CnT) and oligophenylene thiol (OPTn) self-assembled monolayers (SAMs) and Au electrodes are expected to exhibit similar electrical asymmetry, as both junctions have one chemisorbed Au-S contact and one physisorbed, van der Waals contact. Asymmetry is quantified by the current rectification ratio RR apparent in the current-voltage (I-V) characteristics. Here we show that RR < 1 for CnT and RR > 1 for OPTn junctions, in contrast to expectation, and further, that RR behaves very differently for CnT and OPTn junctions under mechanical extension using the conducting probe atomic force microscopy (CP-AFM) testbed. The analysis presented in this paper, which leverages results from the previously validated single level model and ab initio quantum chemical calculations, allows us to explain the puzzling experimental findings for CnT and OPTn in terms of different current rectification mechanisms. Specifically, in CnT-based junctions the Stark effect creates the HOMO level shifting necessary for rectification, while for OPTn junctions the level shift arises from position-dependent coupling of the HOMO wavefunction with the junction electrostatic potential profile. On the basis of these mechanisms, our quantum chemical calculations allow quantitative description of the impact of mechanical deformation on the measured current rectification. Additionally, our analysis, matched to experiment, facilitates direct estimation of the impact of intramolecular electrostatic screening on the junction potential profile. Overall, our examination of current rectification in benchmark molecular tunnel junctions illuminates key physical mechanisms at play in single step tunneling through molecules, and demonstrates the quantitative agreement that can be obtained between experiment and theory in these systems.
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Affiliation(s)
- Zuoti Xie
- Department of Materials Science and Engineering, Guangdong Technion-Israel Institute of Technology, Shantou, Guangdong, 515063, China.
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota, 55455, USA.
| | - Ioan Bâldea
- Theoretical Chemistry, Heidelberg University, Im Neuenheimer Feld 229, D-69120 Heidelberg, Germany.
| | - Quyen Van Nguyen
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota, 55455, USA.
| | - C Daniel Frisbie
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota, 55455, USA.
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21
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Zhang Z, Cao L, Chen X, Thompson D, Qi D, Nijhuis CA. Energy-Level Alignment and Orbital-Selective Femtosecond Charge Transfer Dynamics of Redox-Active Molecules on Au, Ag, and Pt Metal Surfaces. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2021; 125:18474-18482. [PMID: 34476044 PMCID: PMC8404196 DOI: 10.1021/acs.jpcc.1c04655] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/27/2021] [Revised: 07/28/2021] [Indexed: 06/13/2023]
Abstract
Charge transfer (CT) dynamics across metal-molecule interfaces has important implications for performance and function of molecular electronic devices. CT times, on the order of femtoseconds, can be precisely measured using synchrotron-based core-hole clock (CHC) spectroscopy, but little is known about the impact on CT times of the metal work function and the bond dipole created by metals and the anchoring group. To address this, here we measure CT dynamics across self-assembled monolayers bound by thiolate anchoring groups to Ag, Au, and Pt. The molecules have a terminal ferrocene (Fc) group connected by varying numbers of methylene units to a diphenylacetylene (DPA) wire. CT times measured using CHC with resonant photoemission spectroscopy (RPES) show that conjugated DPA wires conduct electricity faster than aliphatic carbon wires of a similar length. Shorter methylene connectors exhibit increased conjugation between Fc and DPA, facilitating CT by providing greater orbital mixing. We find nearly 10-fold increase in the CT time on Pt compared to Ag due to a larger bond dipole generated by partial electron transfer from the metal-sulfur bond to the carbon-sulfur bond, which creates an electrostatic field that impedes CT from the molecules. By fitting the RPES signal, we distinguish electrons coming from the Fe center and from cyclopentadienyl (Cp) rings. The latter shows faster CT rates because of the delocalized Cp orbitals. Our study demonstrates the fine tuning of CT rates across junctions by careful engineering of several parts of the molecule and the molecule-metal interface.
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Affiliation(s)
- Ziyu Zhang
- Department
of Chemistry, National University of Singapore, 3 Science Drive, 117543, Singapore
| | - Liang Cao
- Anhui
Province Key Laboratory of Condensed Matter Physics at Extreme Conditions,
High Magnetic Field Laboratory, Chinese
Academy of Sciences, Hefei, Anhui 230031, China
| | - Xue Chen
- Anhui
Province Key Laboratory of Condensed Matter Physics at Extreme Conditions,
High Magnetic Field Laboratory, Chinese
Academy of Sciences, Hefei, Anhui 230031, China
| | - Damien Thompson
- Department
of Physics, Bernal Institute, University
of Limerick, Limerick V94 T9PX, Ireland
| | - Dongchen Qi
- Centre
for Materials Science, School of Chemistry and Physics, Queensland University of Technology, Brisbane, Queensland 4001, Australia
| | - Christian A. Nijhuis
- Department
of Chemistry, National University of Singapore, 3 Science Drive, 117543, Singapore
- Centre
for Advanced 2D Materials, National University
of Singapore, 6 Science Drive 2, Singapore 117546, Singapore
- Hybrid Materials
for Opto-Electronics Group, Department of Molecules and Materials,
MESA+ Institute for Nanotechnology and Center for Brain-Inspired Nano
Systems, Faculty of Science and Technology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
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22
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Han Y, Maglione MS, Diez Cabanes V, Casado-Montenegro J, Yu X, Karuppannan SK, Zhang Z, Crivillers N, Mas-Torrent M, Rovira C, Cornil J, Veciana J, Nijhuis CA. Reversal of the Direction of Rectification Induced by Fermi Level Pinning at Molecule-Electrode Interfaces in Redox-Active Tunneling Junctions. ACS APPLIED MATERIALS & INTERFACES 2020; 12:55044-55055. [PMID: 33237732 DOI: 10.1021/acsami.0c15435] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Control over the energy level alignment in molecular junctions is notoriously difficult, making it challenging to control basic electronic functions such as the direction of rectification. Therefore, alternative approaches to control electronic functions in molecular junctions are needed. This paper describes switching of the direction of rectification by changing the bottom electrode material M = Ag, Au, or Pt in M-S(CH2)11S-BTTF//EGaIn junctions based on self-assembled monolayers incorporating benzotetrathiafulvalene (BTTF) with EGaIn (eutectic alloy of Ga and In) as the top electrode. The stability of the junctions is determined by the choice of the bottom electrode, which, in turn, determines the maximum applied bias window, and the mechanism of rectification is dominated by the energy levels centered on the BTTF units. The energy level alignments of the three junctions are similar because of Fermi level pinning induced by charge transfer at the metal-thiolate interface and by a varying degree of additional charge transfer between BTTF and the metal. Density functional theory calculations show that the amount of electron transfer from M to the lowest unoccupied molecular orbital (LUMO) of BTTF follows the order Ag > Au > Pt. Junctions with Ag electrodes are the least stable and can only withstand an applied bias of ±1.0 V. As a result, no molecular orbitals can fall in the applied bias window, and the junctions do not rectify. The junction stability increases for M = Au, and the highest occupied molecular orbital (HOMO) dominates charge transport at a positive bias resulting in a positive rectification ratio of 83 at ±1.5 V. The junctions are very stable for M = Pt, but now the LUMO dominates charge transport at a negative bias resulting in a negative rectification ratio of 912 at ±2.5 V. Thus, the limitations of Fermi level pinning can be bypassed by a judicious choice of the bottom electrode material, making it possible to access selectively HOMO- or LUMO-based charge transport and, as shown here, associated reversal of rectification.
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Affiliation(s)
- Yingmei Han
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore
| | - Maria Serena Maglione
- Institut de Ciéncia de Materials de Barcelona (ICMAB-CSIC)/CIBER-BBN, Campus de la UAB, Bellaterra 08193, Spain
| | - Valentin Diez Cabanes
- Laboratory for Chemistry of Novel Materials, University of Mons, Place du Parc 20, Mons 7000, Belgium
| | - Javier Casado-Montenegro
- Institut de Ciéncia de Materials de Barcelona (ICMAB-CSIC)/CIBER-BBN, Campus de la UAB, Bellaterra 08193, Spain
| | - Xiaojiang Yu
- Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore 117603, Singapore
| | - Senthil Kumar Karuppannan
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore
| | - Ziyu Zhang
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore
| | - Núria Crivillers
- Institut de Ciéncia de Materials de Barcelona (ICMAB-CSIC)/CIBER-BBN, Campus de la UAB, Bellaterra 08193, Spain
| | - Marta Mas-Torrent
- Institut de Ciéncia de Materials de Barcelona (ICMAB-CSIC)/CIBER-BBN, Campus de la UAB, Bellaterra 08193, Spain
| | - Concepció Rovira
- Institut de Ciéncia de Materials de Barcelona (ICMAB-CSIC)/CIBER-BBN, Campus de la UAB, Bellaterra 08193, Spain
| | - Jérôme Cornil
- Laboratory for Chemistry of Novel Materials, University of Mons, Place du Parc 20, Mons 7000, Belgium
| | - Jaume Veciana
- Institut de Ciéncia de Materials de Barcelona (ICMAB-CSIC)/CIBER-BBN, Campus de la UAB, Bellaterra 08193, Spain
| | - Christian A Nijhuis
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore
- Centre for Advanced 2D Materials and Graphene Research Center, National University of Singapore, 6 Science Drive 2, Singapore 117546, Singapore
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23
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The Potential of X-ray Photoelectron Spectroscopy for Determining Interface Dipoles of Self-Assembled Monolayers. APPLIED SCIENCES-BASEL 2020. [DOI: 10.3390/app10175735] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
In the current manuscript we assess to what extent X-ray photoelectron spectroscopy (XPS) is a suitable tool for probing the dipoles formed at interfaces between self-assembled monolayers and metal substrates. To that aim, we perform dispersion-corrected, slab-type band-structure calculations on a number of biphenyl-based systems bonded to an Au(111) surface via different docking groups. In addition to changing the docking chemistry (and the associated interface dipoles), the impacts of polar tail group substituents and varying dipole densities are also investigated. We find that for densely packed monolayers the shifts of the peak positions of the simulated XP spectra are a direct measure for the interface dipoles. In the absence of polar tail group substituents they also directly correlate with adsorption-induced work function changes. At reduced dipole densities this correlation deteriorates, as work function measurements probe the difference between the Fermi level of the substrate and the electrostatic energy far above the interface, while core level shifts are determined by the local electrostatic energy in the region of the atom from which the photoelectron is excited.
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24
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Xie Z, Bâldea I, Frisbie CD. Energy Level Alignment in Molecular Tunnel Junctions by Transport and Spectroscopy: Self-Consistency for the Case of Alkyl Thiols and Dithiols on Ag, Au, and Pt Electrodes. J Am Chem Soc 2019; 141:18182-18192. [PMID: 31617711 DOI: 10.1021/jacs.9b08905] [Citation(s) in RCA: 42] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We report here an extensive study of transport and electronic structure of molecular junctions based on alkyl thiols (CnT; n = 7, 8, 9, 10, 12) and dithiols (CnDT; n = 8, 9, 10) with various lengths contacted with different metal electrodes (Ag, Au, Pt). The dependence of the low-bias resistance (R) on contact work function indicates that transport is HOMO-assisted (p-type transport). Analysis of the current-voltage (I-V) characteristics for CnT and CnDT tunnel junctions with the analytical single-level model (SLM) provides both the HOMO-Fermi energy offset εhtrans and the average molecule-electrode coupling (Γ) as a function of molecular length (n), electrode work function (Φ), and the number of chemical contacts (one or two). The SLM analysis reveals a strong Fermi level (EF) pinning effect in all the junctions, i.e., εhtrans changes very little with n, Φ, and the number of chemical contacts, but Γ depends strongly on these variables. Significantly, independent measurements of the HOMO-Fermi level offset (εhUPS) by ultraviolet photoelectron spectroscopy (UPS) for CnT and CnDT SAMs agree remarkably well with the transport-estimated εhtrans. This result provides strong evidence for hole transport mediated by localized HOMO states at the Au-thiol interface, and not by the delocalized σ states in the C-C backbones, clarifying a long-standing issue in molecular electronics. Our results also substantiate the application of the single-level model for quantitative, unified understanding of transport in benchmark molecular junctions.
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Affiliation(s)
- Zuoti Xie
- Department of Chemical Engineering and Materials Science , University of Minnesota , Minneapolis , Minnesota 55455 , United States
| | - Ioan Bâldea
- Theoretische Chemie , Universität Heidelberg , INF 229 , D-69120 Heidelberg , Germany
| | - C Daniel Frisbie
- Department of Chemical Engineering and Materials Science , University of Minnesota , Minneapolis , Minnesota 55455 , United States
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Lamport ZA, Broadnax AD, Scharmann B, Bradford RW, DelaCourt A, Meyer N, Li H, Geyer SM, Thonhauser T, Welker ME, Jurchescu OD. Molecular Rectifiers on Silicon: High Performance by Enhancing Top-Electrode/Molecule Coupling. ACS APPLIED MATERIALS & INTERFACES 2019; 11:18564-18570. [PMID: 31050879 DOI: 10.1021/acsami.9b02315] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
One of the simplest molecular-scale electronic devices is the molecular rectifier. In spite of considerable efforts aimed at understanding structure-property relationships in these systems, devices with predictable and stable electronic properties are yet to be developed. Here, we demonstrate highly efficient current rectification in a new class of compounds that form self-assembled monolayers on silicon. We achieve this by exploiting the coupling of the molecules with the top electrode which, in turn, controls the position of the relevant molecular orbitals. The molecules consist of a silane anchoring group and a nitrogen-substituted benzene ring, separated by a propyl group and imine linkage, and result from a simple, robust, and high-yield synthetic procedure. We find that when incorporated in molecular diodes, these compounds can rectify current by as much as 3 orders of magnitude, depending on their structure, with a maximum rectification ratio of 2635 being obtained in ( E)-1-(4-cyanophenyl)- N-(3-(triethoxysilyl) propyl)methanimine (average Ravg = 1683 ± 458, at an applied voltage of 2 V). This performance is on par with that of the best molecular rectifiers obtained on metallic electrodes, but it has the advantage of lower cost and more efficient integration with current silicon technologies. The development of molecular rectifiers on silicon may yield hybrid systems that can expand the use of silicon toward novel functionalities governed by the molecular species grafted onto its surface.
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Xie Z, Bâldea I, Frisbie CD. Determination of Energy-Level Alignment in Molecular Tunnel Junctions by Transport and Spectroscopy: Self-Consistency for the Case of Oligophenylene Thiols and Dithiols on Ag, Au, and Pt Electrodes. J Am Chem Soc 2019; 141:3670-3681. [DOI: 10.1021/jacs.8b13370] [Citation(s) in RCA: 56] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- Zuoti Xie
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, United States
| | - Ioan Bâldea
- Theoretische Chemie, Universität Heidelberg, INF 229, D-69120 Heidelberg, Germany
| | - C. Daniel Frisbie
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, United States
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Kayser B, Fereiro JA, Guo C, Cohen SR, Sheves M, Pecht I, Cahen D. Transistor configuration yields energy level control in protein-based junctions. NANOSCALE 2018; 10:21712-21720. [PMID: 30431054 DOI: 10.1039/c8nr06627b] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
The incorporation of proteins as functional components in electronic junctions has received much interest recently due to their diverse bio-chemical and physical properties. However, information regarding the energies of the frontier orbitals involved in their electron transport (ETp) has remained elusive. Here we employ a new method to quantitatively determine the energy position of the molecular orbital, nearest to the Fermi level (EF) of the electrode, in the electron transfer protein Azurin. The importance of the Cu(ii) redox center of Azurin is demonstrated by measuring gate-controlled conductance switching which is absent if Azurin's copper ions are removed. Comparing different electrode materials, a higher conductance and a lower gate-induced current onset is observed for the material with smaller work function, indicating that ETp via Azurin is LUMO-mediated. We use the difference in work function to calibrate the difference in gate-induced current onset for the two electrode materials, to a specific energy level shift and find that ETp via Azurin is near resonance. Our results provide a basis for mapping and studying the role of energy level positions in (bio)molecular junctions.
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Affiliation(s)
- Ben Kayser
- Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot, 76100, Israel.
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28
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Bâldea I. A sui generis electrode-driven spatial confinement effect responsible for strong twisting enhancement of floppy molecules in closely packed self-assembled monolayers. Phys Chem Chem Phys 2018; 20:23492-23499. [PMID: 30183036 DOI: 10.1039/c8cp04974b] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
At present, it is widely accepted that properties (e.g., molecular conformation) of molecules adsorbed to form self-assembled monolayers (SAMs) on electrodes can be very different from isolated species because of a substantial charge transfer or specific chemical bonding at the interface. Contrary to this view, the theoretical results presented here predict that the strong twisting angle (φ) enhancement of floppy molecules adsorbed to form densely packed SAMs on most common electrodes (Pt, Au, Ag, and Cu) is neither due to charge transfer nor to specific bonding but rather to a sui generis electrode-driven spatial confinement effect that can be quantitatively described within an electrode-free two-dimensional model. We predict a logistic ("Fermi-Dirac") growth pattern of φ as the coverage approaches the value characteristic of a herringbone arrangement, which is twice the value for isolated molecules or low-coverage SAMs.
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Affiliation(s)
- Ioan Bâldea
- Theoretische Chemie, Universität Heidelberg, Im Neuenheimer Feld 229, D-69120 Heidelberg, Germany.
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Yi SG, Park MU, Kim SH, Lee CJ, Kwon J, Lee GH, Yoo KH. Artificial Synaptic Emulators Based on MoS 2 Flash Memory Devices with Double Floating Gates. ACS APPLIED MATERIALS & INTERFACES 2018; 10:31480-31487. [PMID: 30105909 DOI: 10.1021/acsami.8b10203] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
We fabricated MoS2-based flash memory devices by stacking MoS2 and hexagonal boron nitride (hBN) layers on an hBN/Au substrate and demonstrated that these devices can emulate various biological synaptic functions, including potentiation and depression processes, spike-rate-dependent plasticity, and spike-timing dependent plasticity. In particular, compared to a flash memory device prepared on an hBN substrate, the device fabricated on the hBN/Au exhibited considerably more symmetric and linear bidirectional gradual conductance change curves, which may be attributed to the device structure incorporating double floating gate. For the device on the hBN/Au, electron transfers may occur between the floating gate MoS2 and Au, as well as between the floating gate MoS2 and the channel MoS2, allowing for more control over electron tunneling and injection. To test our hypothesis, we also fabricated a MoS2-based flash memory device on an hBN/Pd substrate and found behavior similar to the device fabricated on hBN/Au. Our results demonstrate that flexible synaptic electronics may be implemented using MoS2-based flash memory devices with double floating gates.
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Huang ML, Zhang F, Wang C, Zheng JF, Mao HL, Xie HJ, Shao Y, Zhou XS, Liu JX, Zhuang JL. Side-Group Effect on Electron Transport of Single Molecular Junctions. MICROMACHINES 2018; 9:E234. [PMID: 30424167 PMCID: PMC6187264 DOI: 10.3390/mi9050234] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/23/2018] [Revised: 05/09/2018] [Accepted: 05/10/2018] [Indexed: 11/23/2022]
Abstract
In this article, we have investigated the influence of the nitro side-group on the single molecular conductance of pyridine-based molecules by scanning tunneling microscopy break junction. Single molecular conductance of 4,4'-bipyridine (BPY), 3-nitro-4-(pyridin-4-yl)pyridine (BPY-N), and 3-nitro-4-(3-nitropyridin-4-yl)pyridine (BPY-2N) were measured by contact with Au electrodes. For the BPY molecular junction, two sets of conductance were found with values around 10-3.1 G₀ (high G) and 10-3.7 G₀ (low G). The addition of nitro side-group(s) onto the pyridine ring resulted in lower conductance of 10-3.8 G₀ for BPY-N and 10-3.9 G₀ for BPY-2N, respectively, which can be attributed to the twist angle of two pyridine rings. Moreover, the steric hindrance of nitro group(s) also affects the contacting configuration of electrode-molecule-electrode. As a consequence, only one set of conductance value was observed for BPY-N and BPY-2N. Our work clearly shows the important role of side-groups on the electron transport of single-molecule junctions.
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Affiliation(s)
- Miao-Ling Huang
- Key Laboratory of the Ministry of Education for Advanced Catalysis Materials, College of Chemistry and Life Sciences, Zhejiang Normal University, Jinhua 321004, China.
| | - Fan Zhang
- Key Laboratory of the Ministry of Education for Advanced Catalysis Materials, College of Chemistry and Life Sciences, Zhejiang Normal University, Jinhua 321004, China.
| | - Chen Wang
- Key Lab for Functional Materials Chemistry of Guizhou Province, School of Chemistry and Materials Science, Guizhou Normal University, Guiyang 550001, China.
| | - Ju-Fang Zheng
- Key Laboratory of the Ministry of Education for Advanced Catalysis Materials, College of Chemistry and Life Sciences, Zhejiang Normal University, Jinhua 321004, China.
| | - Hui-Ling Mao
- Key Lab for Functional Materials Chemistry of Guizhou Province, School of Chemistry and Materials Science, Guizhou Normal University, Guiyang 550001, China.
| | - Hu-Jun Xie
- Department of Applied Chemistry, Zhejiang Gongshang University, Hangzhou 310018, China.
| | - Yong Shao
- Key Laboratory of the Ministry of Education for Advanced Catalysis Materials, College of Chemistry and Life Sciences, Zhejiang Normal University, Jinhua 321004, China.
| | - Xiao-Shun Zhou
- Key Laboratory of the Ministry of Education for Advanced Catalysis Materials, College of Chemistry and Life Sciences, Zhejiang Normal University, Jinhua 321004, China.
| | - Jin-Xuan Liu
- State Key Laboratory of Fine Chemicals, Institute of Artificial Photosynthesis, Dalian University of Technology, Dalian 116024, China.
| | - Jin-Liang Zhuang
- Key Lab for Functional Materials Chemistry of Guizhou Province, School of Chemistry and Materials Science, Guizhou Normal University, Guiyang 550001, China.
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