个人简介
B.Sc, 1999, University of Groningen, the Netherlands, M.Sc. 2002, University of Groningen, the Netherlands, Ph. D. with distinction cum laude (top 5%), 2006, University of Twente, the Netherlands. Postdoctoral fellow, 2007-2010, Harvard University, USA.
研究领域
Introduction
Molecular electronics originally promised that molecule(s) bridging two or more electrodes would generate electronic function, and overcome the scaling limits of conventional semiconductor technology. So far, there have been no commercially successful electronic devices employing small molecules as the active element. The main reason for the lack of success of such devices in everyday life is that simple, reliable fabrication techniques are lacking. Most fabrication techniques involve the direct deposition of metal top-contacts on self-assembled monolayers (SAMs) on bottom-electrodes. During the deposition process of the top-contact, the incoming metal atoms and small clusters can react with, or (partially) penetrate, the SAMs. Other methods have been reported that use other approaches to introduce top-contacts, but these methods suffer from other inherent limitations. Consequently, physical-organic studies relating chemical structure to the mechanisms of charge transport across SAM-based junctions are lacking. Indeed, many phenomena reported for molecular junctions were caused by properties independent on the chemical structures inside the junctions due, for instance, metal filaments, or the presence of layers of metal oxides.
Goals
(1)
To study the mechanisms of charge transport across nanostructures.
The mechanisms of charge transport across nano-scale objects are very different from their macro-scale counter parts. Consequently, understanding the mechanisms of charge transport in organic or organometallic tunneling junctions is fundamental to the broad subject of charge transport in organic/organometallic matter, and is a prerequisite for defining the potential (if any) of these junctions to provide new or improved function in devices.
(2)
To study the mechanisms of charge transport across nanostructures.
The mechanisms of charge transport across nano-scale objects are very different from their macro-scale counter parts. Consequently, understanding the mechanisms of charge transport in organic or organometallic tunneling junctions is fundamental to the broad subject of charge transport in organic/organometallic matter, and is a prerequisite for defining the potential (if any) of these junctions to provide new or improved function in devices.
(3)
The design, characterization, and self-assembly of new molecular and supramolecular organic-inorganic hybrid structures.
Exploiting the possibilities of self-assembly and supramolecular chemistry in bottom-up nanofabrication is a promising strategy to obtain devices that are organized at the molecular level. One of the key issues is the controlled immobilization of molecules, or other structures such as nanoparticles, at surfaces leading to well-defined and stable nanostructures. The advantage of supramolecular chemistry, relative to chemi- or physisorption, or covalent chemistry, is that the binding kinetics and thermodynamics can be precisely controlled. Additionally, supramolecular interactions can also respond to external stimuli to give control over adsorption and desorption processes. Although, single supramolecular interactions are in general relatively weak, multivalent interactions increases the stability of supramolecular assemblies dramatically.
Approaches
Device Fabrication
To avoid the problems associated with direct metal deposition onto SAMs, Whitesides et al. developed techniques to contact SAMs on Au or Ag bottom-electrodes with liquid metal top-electrodes, i.e., Hg or eutectic gallium indium (EGaIn, mp. 15.7 ºC). EGaIn has three characteristics that makes it an attractive material to form top-contacts with. EGaIn is i) a low-toxicity material and is commercially available, ii) electrically conductive (the resistivity and work function are similar to that of Ag), and iii) moldable, that is, EGaIn can be molded, unlike Hg, into non-spherical shapes.
Figure 1 shows that cone-shaped tips of EGaIn suspended from a syringe can be fabricated by simply pulling out a syringe of a drop of EGaIn. In a second step, this tip of EGaIn can be used to contact a metal substrate with a SAM to complete the tunneling junction. The whole process takes about 60 s. These junctions are stable for hours, give high yields of working devices (70-90%), and are useful to collect large numbers of data obtained from large numbers of junctions. Typically, to collect 100 - 1000 current-voltage curves from 40 - 50 junctions prepared with SAMs formed on 5 - 10 substrates takes one day.
Figure 1: A series of photographs of the formation of a conical tip of EGaIn. From left to right: A micromanipulator 1) brings a drop of EGaIn suspended from the needle of a syringe into contact with the bare, reflective surface of an Ag film, and 2) raises the syringe until the EGaIn separates into a conical tip (which remains attached to the needle of the syringe) and a drop on the Ag surface. The pictures are sequential and show the formation of a single tip; the time spanned by this sequence is less than 5s.
Figure 2: A and B) Optical micrographs of the arrays of metal-SAM//EGaIn junctions. A micro-channel in PDMS is aligned perpendicularly to the Ag electrodes. Filling the channel with EGaIn, by applying vacuum at the outlet while a drop of EGaIn is present at the inlet, completes the fabrication of the SAM-based junctions. C) An idealized schematic representation of a junction with a SAM of SC11Fc. In reality, these junctions will have defects due to surface roughness of the electrodes, defects in the SAM, etc.
New Physics: Organometallic Molecular Rectification
Tunneling junctions with SAMs of S(CH2)11Fc (Fc = ferrocene) rectified current, that is, they acted like diodes and only passed current in one direction of bias, but junctions with SAM of S(CH2)n-1CH3 (n = 12, 14, 16, or 18) did not rectify (Fig. 3). Thus, these junctions are molecular rectifiers with a rectification ratio (|J(-1.0 V)|/|J(1.0 V)| where |J(V)| is the absolute value of current density as a function of voltage, V) of 128 (determined using 997 J(V)-curves) with a log-standard deviation of 3.3, and with a yield of 87% in working junctions. The rectification is caused by the molecules inside the junctions and not by any other asymmetries of the junctions.
These devices make it possible to conduct temperature dependent measurements and to perform detailed physical-organic studies. These studies revealed that the observed large rectification ratios (> 1.0 x 102) originate from a change in the mechanism of charge transport from tunneling to hopping in only one direction of bias (Fig. 3). Theoretical studies, however, claimed that molecules can not rectify with rectification ratios larger than ~20. In addition, in 1974 Aviram and Ratner proposed molecular rectifiers for the first time, and, since then, a large number of attempts have been made to fabricate devices with these proposed molecular rectifiers. To date, it could not be shown unambiguously that the rectification in those studies (often with rectification ratios less than 10) was molecular in origin, statistically significantly different from 1 (no rectification), and/or followed the mechanism as proposed by Aviram and Ratner. Thus, these SAM-based tunneling junctions resolved the longstanding question whether molecules can rectify currents with large rectification ratios, and that the Aviram-Ratner mechanism is not necessary to achieve rectification.
Figure 3: A) Average traces of the absolute value of the current density, |J|, plotted vs. applied voltage for all AgTS-SC11Fc//Ga2O3/EGaIn junctions (53 junctions, 977 traces), and AgTS-SC11//Ga2O3/EGaIn junctions (23 junctions, 415 traces); B) Histograms of R for ATSS-SC11Fc//Ga2O3/EGaIn junctions (53 junctions and 997 traces, R = J(-1V)/J(+1V)), and AgTS-SC10CH3//Ga2O3/EGaIn junctions (23 junctions and 415 traces); C) four J(V) curves of a AgTS-SC13CH3//EGaIn junction measured at four different temperatures (T = 110, 190, 250, and 293 K) in vacuum (1 x 10-6 bar). The J(V) curves do not depend on the temperature which is consistent with tunneling as the mechanism of charge transport; D) three J(V) curves of a AgTS-SC11Fc//EGaIn junction measured at three different temperatures in vacuum (1 x 10-6 bar). The J(V) curves only change at negative bias, that is, the value of J decreases with decreasing temperature, but not at positive bias. This decrease in current density with decreasing temperature indicates that hopping dominates the mechanism of charge transport only at negative bias, while tunneling dominates at positive bias.
Supramolecular platforms
A supramolecular platform is ideal to construct self-assembled monolayers with well-defined structures organized at the molecular level. This supramolecular platform is a well-characterized, hexagonally packed SAM of heptathioether-functionalized b-cyclodextrin (bCD) on AuTS developed by Reinhoudt et al. The bCD host molecules can form host-guest interactions with small organic molecules. These host-guest interactions, however, are weak, but multiple interactions, that is multivalent interactions, between the host surface and guest molecules result in stable supramolecular assemblies.
Dendrimers serve as a very suitable class of polyfunctional guest molecules for the reason that the number of end groups can be exactly controlled and are located at the periphery of the molecule. The host-guest interactions between the functional termini of the dendrimers and the supramolecular platform are specific, the binding kinetics and thermodynamics can be controlled. This approach allows for optimal manipulation over positioning and structure of the molecules, resulting in well-defined supramolecular structures. This strategy makes it possible to perform studies of charge transport across SAMs as a function of chemical composition of the SAM and to prove that the electrical characteristics are molecular in origin.
Figure 4 shows the supramolecular tunneling junctions with top-electrodes of EGaIn with dendrimers with three different terminal functionalities: i) Fc (redox-active), ii) bi-ferrocene (BFc) (redox-active), and iii) adamantyl (Ad) (redox-inactive). This Figure also shows that junctions with dendrimers with Fc termini rectify currents, while those fabricated without dendrimers, or with redox-inactive adamantyl functionalities, do not rectify. Thus, the rectification is induced by the Fc and BFc moieties and is not due to any other asymmetries in the junction. This demonstrates the potential of a supramolecular platform, to immobilize dendrimers of various functionalities, in order to control the rectification in a molecular electronic junction.
Figure 4. Left:Schematic representation of the junctions: the molecular structure of the core of the PPI (polypropylene imine) dendrimer, with the red sphere representing the functional groups R at the periphery of the dendrimer(R = ferrocene, biferrocene, or adamantyl) and the bleu cups representing the bCD SAM. Right: semi-log plot of the average absolute current density vs. voltage (|J| vs. V): junctions with dendrimers with R = BFc or Fc rectify, while junctions lacking the dendrimers, i.e., only the bCD SAM, or with R = Ad do not rectify.
Awards
Received the Rubicon fellowship (The Netherlands Organization for Scientific Research, NWO) for talented young researches for a two-year overseas post-doc position (2007).
Received the Overijssel PhD Award 2007 for the best PhD thesis of the province of Overijssel in 2007 (Enschede, The Netherlands).
Received the NRF research fellowship (2010).
近期论文
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Dong, Z.; Chu, H.; Zhu, D.; Du, W.; Akimov, Y. A.; Goh, W. P.; Wang, T.; Goh, K. E. J.; Troadec, C.; Nijhuis, C. A.; Yang, J.K.W. Electrically-Excited Surface Plasmon Polaritons with Directionality Control, ACS Photonics 2015, Accepted, DOI: 10.1021/ph5004303
Nurbawono, A.; Liu, S.; Nijhuis, C. A.; Zhang, C. Odd–Even Effects in Charge Transport through Self-Assembled Monolayer of Alkanethiolates, J. Phys. Chem. C 2015, Accepted, DOI: 10.1021/jp5116146
Li, Y.; Nerngchamnong, N.; Cao, L.; Hamoudi, H.; Del Barco, E.; Roemer, M.; Sriramula, R.; Thompson, D.; Nijhuis, C. A. Controlling the Direction of Rectification in a Molecular Diode, Nat. Commun. 2015, 6, Article number: 6324, DOI: 10.1038/ncomms6461.
Jiang, L.; Suchand Sangeeth, C. S.; Wan, A.; Vilan, A.; Nijhuis, C. A. Defect Scaling with Contact Area in EGaIn-Based Junctions: Impact on Quality, Joule Heating, and Apparent Injection Current, J. Phys. Chem. C 2015, 119, 960–969.
Wong, C. P. Y.; Koek, T. J. H.; Liu, Y. P.; Loh, K. P.; Goh, K. E. J.; Troadec, C.; Nijhuis, C. A. Electronically Transparent Graphene Barriers against Unwanted Doping of Silicon, ACS Appl. Mater. Inter. 2014, 6, 20464–20472.
Nerngchamnong, N.; Wu, H.; Sotthewes, K.; Yuan, L.; Cao, L.; Roemer, M.; Lu, J.; Loh, K. P.; Troadec, C.; Zandvliet, H.; Nijhuis, C. A. The Supramolecular Structure of Self-Assembled Monolayers of Ferrocenyl Terminated n-Alkanethiolates on Gold Surfaces, Langmuir 2014, 30, 13447–13455.
Liu, Y.; Yuan, L.; Yang, M.; Zheng, Y.; Nai, C. T.; Gao, L.; Nerngchamnong, N.; Li, L. J.; Suchand Sangeeth, C. S.; Feng, Y. P.; Nijhuis, C. A. and Loh, K. P. Giant Enhancement in Vertical Conductivity of Stacked CVD Graphene sheets by Self-assembled Molecular Layers, Nat. Commun. 2014, 5, Article number: 5461, DOI: 10.1038/ncomms6461.
Suchand Sangeeth, C. S.; Wan, A.; Nijhuis, C. A. The Equivalent Circuits of a Self-Assembled Monolayer Based Tunnel Junction Determined by Impedance Spectroscopy, J. Am. Chem. Soc. 2014, 136, 11134-11144.
Wimbush, K. S.; Fratila, R. M.; Wang, D. D.; Qi, D. C.; Cao, L.; Yuan, L.; Yakovlev, N.; Loh. K. P.; Reinhoudt, D. N.; Velders, A. H.; Nijhuis, C. A. Bias Induced Transition from an Ohmic to a Non-Ohmic Interface in Supramolecular Tunneling Junctions with Ga2O3/EGaIn Top Electrodes, Nanoscale 2014, 19, 11246-11258.
Bosman, M.; Zhang, L.; Duan, H.; Tan, S. F.; Nijhuis, C. A.; Qiu, C. W.; Yang, J. K. W. Encapsulated Annealing: Enhancing the Plasmon Quality Factor in Lithographically–Defined Nanostructures, Sci. Rep. 2014, 4, 5537.
Roemer, M.; Nijhuis, C. A. Syntheses and Purification of the Versatile Synthons Iodoferrocene and 1,1`-Diiodoferrocene, Dalton Trans. 2014, 43, 11815-11818.
Yuan, L.; jiang, L.; Thompson, D.; Nijhuis, C. A. On the Remarkable Role of Surface Topography of the Bottom-Electrodes in Blocking Leakage Currents in Molecular Diodes, J. Am. Chem. Soc. 2014, 136, 6554-6557.
Tan, S. F.; Wu, L.; Yang, J. K. W.; Bai, P.; Bosman, M.; Nijhuis, C. A. Quantum Plasmon Resonances Controlled by Molecular Tunnel Junctions,Science, 2014, 343, 1496-1499.
Wan, A.; Jiang, L.; Suchand Sangeeth, C. S.; Nijhuis, C. A. Reversible Soft Top-Contacts to Yield Molecular Junctions with Precise and Reproducible Electrical Characteristics, Adv. Funct. Mater, 2014, 24, 4442-4456.
Yuan, L.; Jiang, L.; Zhang, B.; Nijhuis, C. A. The Tunneling Decay Coefficient in Molecular Tunneling Junctions Depends on the Topography of the Bottom-Electrodes, Angew. Chem. Int. Ed. 2014, 53, 3377-3381.
Jiang, L.; Yuan, L.; Cao, L.; Nijhuis, C. A. Controlling Leakage Currents: The Role of the Binding Group and Purity of the Precursors for Self-Assembled Monolayers in the Performance of Molecular Diodes, J. Am. Chem. Soc. 2014,136, 1982-1991.
Bosman, M.; Ye, E.; Tan, S. F.; Nijhuis, C. A.; Yang, J. K. W.; Marty, R.; Mlayah, A.; Arbouet, A.; Girard, C.; Han, M. Y. Surface plasmon damping quantified with an electron nanoprobe Sci. Rep. 2013, 3, 1312.
Mahony S. O.; Dwyer, C. O.; Nijhuis, C. A.; Gree, J. C.; Quinn, A. J.; Thompson, D. Nanoscale dynamics and protein adhesivity of alkylamine self-assembled monolayers on graphene Langmuir 2013, 29, 7271-7282.
Nerngchanmnong, N.; Yuan, L.; Qi, D. C.; Jiang, L.; Thompson, D.; Nijhuis, C. A. The role of van der Waals forces in the performance of molecular diodes Nat. Nanotechnol. 2013, 8, 113-118.
Reus, W. F.; Nijhuis, C. A.; Barber, J.; Thuo, M. N.; Tricard, S.; Kim, C.; Whitesides, G. M. Statistical Tools for Analyzing Measurements of Charge Transport J. Phys. Chem.C 2012, 116, 6714-6733.
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