Dacheng Wei

Fudan University, Shanghai, Shanghai Shi, China

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Publications (34)354.26 Total impact

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    ABSTRACT: Nitrogen doping is one of the most promising routes to modulate the electronic characteristic of graphene. Plasma-enhanced chemical vapor depostion (PECVD) enables low-temperature graphene growth. However, PECVD growth of nitrogen doped graphene (NG) usually requires metal-catalysts, and to the best of our knowledge, only amorphous carbon-nitrogen films have been produced on dielectric surfaces by metal-free PECVD. Here, a critical factor for metal-free PECVD growth of NG is reported, which allows high quality NG crystals to be grown directly on dielectrics like SiO2/Si, Al2O3, h-BN, mica at 435 °C without a catalyst. Thus, the processes needed for loading the samples on dielectrics and n-type doping are realized in a simple PECVD, which would be of significance for future graphene electronics due to its compatibility with the current microelectronic processes.
    Full-text · Article · Jan 2015 · ACS Nano
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    ABSTRACT: We report significant changes of optical conductivity in single layer graphene induced by mild oxygen plasma exposure, and explore the interplay between carrier doping, disorder, and many-body interactions from their signatures in the absorption spectrum. The first distinctive effect is the reduction of the excitonic binding energy that can be extracted from the renormalized saddle point resonance at 4.64 eV. Secondly, the real part of the frequency-dependent conductivity is nearly completely suppressed below an exposure-dependent threshold in the near infrared range. The clear step-like suppression follows the Pauli blocking behaviour expected for doped monolayer graphene. The nearly zero residual conductivity at frequencies below 2Ef can be interpreted as arising from the weakening of the electronic self-energy. Our data shows that mild oxygen exposure can be used to controlably dope graphene without introducing the strong physical and chemical changes that are common in other approaches to oxidized graphene, allowing a controllable manipulation of the optical properties of graphene.
    Full-text · Article · Feb 2014 · Physical Review B
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    ABSTRACT: An Ort und Stelle: Moderates Ätzen durch ein Wasserstoffplasma während der plasmaverstärkten chemischen Dampfabscheidung schafft einen Gleichgewichtszustand beim Kantenwachstum von Graphen, sodass hexagonale Graphen-Einkristalle oder kontinuierliche Graphenfilme bei 400 °C ohne Katalysator auf dielektrischen Substraten erzeugt werden können (siehe Bild). Das resultierende Graphen ist von hoher Qualität und kann unter Vermeidung problematischer Transferprozesse direkt in Funktionssystemen verwendet werden.
    Full-text · Article · Dec 2013 · Angewandte Chemie International Edition
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    ABSTRACT: Graphene is often regarded as one of the most promising candidates for future nanoelectronics. As an indispensable component in graphene-based electronics, the formation of junctions with other materials not only provides utility functions and reliable connexions, but can also improve or alter the properties of pristine graphene, opening up possibilities for new applications. Here we demonstrate an intramolecular junction produced by the controllable unzipping of single-walled carbon nanotubes, which combines a graphene nanoribbon and single-walled carbon nanotube in a one-dimensional nanostructure. This junction shows a strong gate-dependent rectifying behaviour. As applications, we demonstrate the use of the junction in prototype directionally dependent field-effect transistors, logic gates and high-performance photodetectors, indicating its potential in future graphene-based electronics and optoelectronics.
    Full-text · Article · Jan 2013 · Nature Communications
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    ABSTRACT: Graphene has attracted much interest in both academia and industry. The challenge of making it semiconducting is crucial for applications in electronic devices. A promising approach is to reduce its physical size down to the nanometer scale. Here, we present the surface-assisted bottom-up fabrication of atomically precise armchair graphene nanoribbons (AGNRs) with predefined widths, namely 7-, 14- and 21-AGNRs, on Ag(111) as well as their spatially resolved width-dependent electronic structures. STM/STS measurements reveal their associated electron scattering patterns and the energy gaps over 1 eV. The mechanism to form such AGNRs is addressed based on the observed intermediate products. Our results provide new insights into the local properties of AGNRs, and have implications for the understanding of their electrical properties and potential applications.
    Full-text · Article · Dec 2012 · Scientific Reports
  • Dacheng Wei · Bin Wu · Yunlong Guo · Gui Yu · Yunqi Liu
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    ABSTRACT: Because of its atomic thickness, excellent properties, and widespread applications, graphene is regarded as one of the most promising candidate materials for nanoelectronics. The wider use of graphene will require processes that produce this material in a controllable manner. In this Account, we focus on our recent studies of the controllable chemical vapor deposition (CVD) growth of graphene, especially few-layer graphene (FLG), and the applications of this material in electronic devices. CVD provides various means of control over the morphologies of the produced graph ene. We studied several variables that can affect the CVD growth of graphene, including the catalyst, gas flow rate, growth time, and growth temperature and successfully achieved the controlled growth of hexagonal graphene crystals. Moreover, we developed several modified CVD methods for the controlled growth of FLGs. Patterned CVD produced FLGs with desired shapes in required areas. By introducing dopant precursor in the CVD process, we produced substitutionally doped FLGs, avoiding the typically complicated post-treatment processes for graphene doping. We developed a template CVD method to produce FLG ribbons with controllable morphologies on a large scale. An oxidation-activated surface facilitated the CVD growth of polycrystalline graphene without the use of a metal catalyst or a complicated postgrowth transfer process. In devices, CVD offers a controllable means to modulate the electronic properties of the graphene samples and to improve device performance. Using CVD-grown hexagonal graphene crystals as the channel materials in field-effect transistors (FETs), we improved carrier mobility. Substitutional doping of graphene in CVD opened a band gap for efficient FET operation and modulated the Fermi energy level for n-type or p-type features. The similarity between the chemical structure of graphene and organic semiconductors suggests potential applications of graphene in organic devices. We used patterned CVD FLGs as the bottom electrodes in pentacene FETs. The strong π-π interactions between graphene and pentacene produced an excellent interface with low contact resistance and a reduced injection barrier, which dramatically enhances the device performance. We also fabricated reversible nanoelectromechanical (NEM) switches and a logic gate using the FLG ribbons produced using our template CVD method. In summary, CVD provides a controllable means to produce graphene samples with both large area and high quality. We developed several modified CVD methods to produce FLG samples with controlled shape, location, edge, layer, dopant, and growth substrate. As a result, we can modulate the properties of FLGs, which provides materials that could be used in FETs, OFETs, and NEM devices. Despite remarkable advances in this field, further exploration is required to produce consistent, homogeneous graphene samples with single layer, single crystal, and large area for graphene-based electronics.
    No preview · Article · Jul 2012 · Accounts of Chemical Research
  • Dacheng Wei · Yunqi Liu
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    ABSTRACT: Graphene, a two-dimensional material, is regarded as one of the most promising candidates for future nanoelectronics due to its atomic thickness, excellent properties and widespread applications. As the first step to investigate its properties and finally to realize the practical applications, graphene must be synthesized in a controllable manner. Thus, controllable synthesis is of great significance, and received more and more attention recently. This Progress Report highlights recent advances in controllable synthesis of graphene, clarifies the problems, and prospects the future development in this field. The applications of the controllable synthesis are also discussed.
    No preview · Article · Aug 2010 · Advanced Materials
  • Dacheng Wei · Yunqi Liu

    No preview · Article · Aug 2010 · Advanced Materials
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    ABSTRACT: A general and useful method has been developed to evaluate the metallic-to-semiconducting (M/S) ratio for separated single-walled carbon nanotubes (SWNTs). By virtue of measuring UV−vis−NIR spectra of a variety of solutions with different ratios of metallic-rich to semiconducting-rich SWNTs, the commercial IsoNanotubes samples as well as metallic-rich HiPCO SWNTs (HiPCO-M) separated by an Agarose gel method have been evaluated. Values of 99.5% metallic contents for IsoNanotubes-M, 98.9% semiconducting contents for IsoNanotubes-S, and 1.24 for the absorption coefficient of IsoNanotubes, whereas 80.4% metallic contents for HiPCO-M and 1.05 for the absorption coefficient of HiPCO SWNTs were obtained. This method does not need pure metallic (M-) or semiconducting (S-) SWNTs as references. Furthermore, we found that this method can also be applied to evaluate the M/S ratio for any SWNT samples.
    No preview · Article · Jul 2010 · The Journal of Physical Chemistry C
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    ABSTRACT: Molecular electronics are considered one of the most promising ways to meet the challenge of micro-electronics facing its scaling down pathway. Molecular devices, especially molecular scale field-effect transistors (MSFET), are key building blocks for molecular electronics. Three major hurdles to device fabrication are yet to be overcome: electrode pairs must be fabricated with a controllable gap size commensurate with the functional molecule size of interest; the molecules of interest must be arranged between the electrodes with precise location and orientation control; and stable, conducting contacts must be made between the molecules and the electrodes. We have combined “top-down” and “bottom-up” approaches to solve these problems. Using photolithography and molecular lithography with self-assembled mono/multiple molecule layer(s) as a resist, we fabricated electrode structures with a controllable molecular-scale gap between source and drain electrodes and a third terminal of a buried gate. For our device, we synthesized a thiolated phthalocyanine derivative molecule, {di-[1-(S-acetylthio)-4-ethynylphenyl]-di-(tert-butyl)phthalocyanato}copper(II), with acetylthio groups on both ends, conjugated with ethynylphenylgroups. The synthesized end-thiolated molecules were assembled between the tailored molecular gap of the as-fabricated FET electrode structures in solution via Au–S bonding, forming stable contacts between the electrodes and the molecules, and a 3 terminal MSFET device was formed. Electrical measurements show that the device has characteristics of a typical FET device. The field-effect mobility of the as-fabricated MS-FET is 0.16 cm2 V−1 s−1.
    Full-text · Article · Mar 2010 · Journal of Materials Chemistry
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    ABSTRACT: One-dimensional (1D) nanostructures of the wide band gap semiconductors are promising building blocks for photoelectric nanodevices. However, some problems like strong 1D confinement largely hamper their applications. To avoid these problems, here, we provide another 1D configuration, in which an inner-wire coaxial Schottky junction exists, thus effectively avoiding the recombination of the photoexcited carriers. As an example, we produce ZnS/carbon nanotube nanocables with uniform morphologies by a two-step vapor deposition method and find that they have good conductance, obvious light response, and ohmic contacts with electrodes, avoiding the limitations of both the pristine nanomaterials. We believe that this configuration would be valuable for applying the 1D nanomaterials in photoelectronics.
    No preview · Article · Dec 2009 · Chemistry of Materials
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    ABSTRACT: Single-walled carbon nanotubes (SWNTs) are a promising material for future nanotechnology. However, their applications are still limited in success because of the co-existence of metallic SWNTs and semiconducting SWNTs produced samples. Here, electrochemical etching, which shows both diameter and electrical selectivity, is demonstrated to remove SWNTs. With the aid of a back-gate electric field, selective removal of metallic SWNTs is realized, resulting in high-performance SWNT field-effect transistors with pure semiconducting SWNT channels. Moreover, electrochemical etching is realized on a selective area. These findings would be valuable for research and the application of SWNTs in electrochemistry and in electronic devices.
    No preview · Article · Nov 2009 · Advanced Functional Materials
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    ABSTRACT: Ultrahigh-transmittance conducting films (UHTCFs) of single-walled carbon-nanotubes (SWNTs) are prepared by combined direct-synthesis and solution-based methods. Perfect two-dimensional SWNT TCFs (P2DTCFs) act as “bones” and SWNT bundles as “muscles” that fill in the uncovered areas (see picture). The sheet resistance of the film reaches 625Ω sq−1 with a transparency of 94.7%
    No preview · Article · Nov 2009 · Small
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    ABSTRACT: A method for the non-destructive purification of single-walled carbon nanotubes (SWNTs) using classical coordination chemistry to remove the metal catalyst has been developed. In preliminary tests, the conductivity of films based on the resulting SWNTs was markedly better than that of films prepared from SWNTs purified by treatment with oxidizing acid solutions. The transparent and conducting SWNT films have potential applications in optoelectronic devices.
    Preview · Article · Nov 2009 · Nano Research
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    ABSTRACT: Controllable and scalable production is of great importance for the application of graphene; however, to date, it is still a great challenge and a major obstacle which hampers its practical applications. Here, we develop a template chemical vapor deposition method for scalable synthesis of few-layer graphene ribbons (FLGRs) with controlled morphologies. The FLGRs have a good conductivity and are ideal for use in nanoelectromechanics (NEM). As an application, we fabricate a reversible NEM switch and a logic gate by using the FLGRs. This work realizes both controllable and scalable synthesis of graphene, provides an application of graphene in NEM switches, and would be valuable for both the scientific studies and the practical applications of graphene.
    No preview · Article · Aug 2009 · Journal of the American Chemical Society
  • Dacheng Wei · Yunqi Liu · Yu Wang · Hongliang Zhang · Liping Huang · Gui Yu
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    ABSTRACT: To realize graphene-based electronics, various types of graphene are required; thus, modulation of its electrical properties is of great importance. Theoretic studies show that intentional doping is a promising route for this goal, and the doped graphene might promise fascinating properties and widespread applications. However, there is no experimental example and electrical testing of the substitutionally doped graphene up to date. Here, we synthesize the N-doped graphene by a chemical vapor deposition (CVD) method. We find that most of them are few-layer graphene, although single-layer graphene can be occasionally detected. As doping accompanies with the recombination of carbon atoms into graphene in the CVD process, N atoms can be substitutionally doped into the graphene lattice, which is hard to realize by other synthetic methods. Electrical measurements show that the N-doped graphene exhibits an n-type behavior, indicating substitutional doping can effectively modulate the electrical properties of graphene. Our finding provides a new experimental instance of graphene and would promote the research and applications of graphene.
    No preview · Article · Apr 2009 · Nano Letters
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    ABSTRACT: A facile, scalable, and low-cost gas-treatment method for selectively etching semiconductor single-walled carbon nanotubes (SWNTs) is developed. Using SO3 gas as the etchant at a temperature of 400 °C, semiconductor SWNTs can be selectively and efficiently removed, and after this gas treatment samples enriched with metallic SWNTs can be obtained.
    No preview · Article · Feb 2009 · Advanced Materials
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    ABSTRACT: A multistep purification method was adopted to remove the residual octylphenol ethoxylate (Triton X-100) surfactants, resulting in a decreased sheet resistance of single walled carbon nanotubes (SWCNT) films. Results indicate that the sheet resistance of the bare SWNT film, with 78% transparency, accounts for 46% of the total resistance. It is also seen that L-SWNT films present the lowest sheet resistances, while those of H-SWNT films show the highest. The SWNTs or nanotube bundles are isolated from one another and therefore do not form a conducting channel. It is found that when the transparency of a L-SWNT film drops to 91%, its sheet resistance is reduced to 424Ωsq-1. The SWNT are found to be an alternative to ITO as the sheet resistance of ITO with 80% transparency is less than 100Ωsq -1 on glass and 100-300Ωsq-1 on PET.
    No preview · Article · Dec 2008 · Advanced Materials
  • Dacheng Wei · Yunqi Liu
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    No preview · Article · Oct 2008 · ChemInform
  • Chong-an Di · Dacheng Wei · Gui Yu · Yunqi Liu · Yunlong Guo · Daoben Zhu
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    ABSTRACT: A study was conducted to demonstrate a novel method for preparing and patterning graphene layers on a SiO2/Si substrate and demonstrate that they can be used as an electrode material suitable for low-cost electronics. The study shows the fabrication of high performance organic field-effect transistors (OFET) based on low-cost graphene source/drain (S/D) electrodes. The graphene formation process results in large metal clusters and increases roughness of the electrode, which does not decrease the device performance of OFETs. The graphene electrodes also show excellent electrode/organic interface contact and low injection barrier. The results of the study thereby demonstrate a novel way to improve electrode/organic contact and provide effective approach to achieving high-performance low-cost OFETs.
    No preview · Article · Sep 2008 · Advanced Materials

Publication Stats

2k Citations
354.26 Total Impact Points

Institutions

  • 2015
    • Fudan University
      • Department of Macromolecular Science
      Shanghai, Shanghai Shi, China
  • 2012-2014
    • National University of Singapore
      • Department of Physics
      Tumasik, Singapore
  • 2006-2012
    • Chinese Academy of Sciences
      • • Institute of Chemistry
      • • Graduate School
      • • Key Laboratory of Organic Solids
      Peping, Beijing, China
  • 2009
    • Technical Institute of Physics and Chemistry
      Peping, Beijing, China