Dacheng Wei

Northeast Institute of Geography and Agroecology, Beijing, Beijing Shi, China

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Publications (27)228.94 Total impact

  • [Show abstract] [Hide abstract]
    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.
    Accounts of Chemical Research 07/2012; · 20.83 Impact Factor
  • 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.
    Advanced Materials 08/2010; 22(30):3225-41. · 14.83 Impact Factor
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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.
    Journal of Physical Chemistry C - J PHYS CHEM C. 01/2010; 114(28):12095-12098.
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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.
    Journal of Materials Chemistry 01/2010; 20(12). · 5.97 Impact Factor
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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.
    Chemistry of Materials - CHEM MATER. 12/2009; 22(2).
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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.
    Advanced Functional Materials 10/2009; 19(22):3618 - 3624. · 10.44 Impact Factor
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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.
    Journal of the American Chemical Society 08/2009; 131(31):11147-54. · 10.68 Impact Factor
  • Small 08/2009; 5(21):2392-6. · 7.82 Impact Factor
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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.
    Nano Letters 04/2009; 9(5):1752-8. · 13.03 Impact Factor
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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.
    Nano Research 01/2009; 2(11):865-871. · 7.39 Impact Factor
  • Advanced Materials 12/2008; 21(7):813 - 816. · 14.83 Impact Factor
  • Advanced Materials 10/2008; 20(23):4442 - 4449. · 14.83 Impact Factor
  • Advanced Materials 07/2008; 20(17):3289 - 3293. · 14.83 Impact Factor
  • Dacheng Wei, Yunqi Liu
    Advanced Materials 07/2008; 20(15):2815 - 2841. · 14.83 Impact Factor
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    ABSTRACT: Molecular electronics is often limited by the lack of a simple method to fabricate nanoelectrodes with controlled gap size. This is partly attributed to the lack of a real time characterization in the fabrication. Here, we report a new method based on an electron induced deposition process operated in scanning electron microscopy that realizes in situ and real time characterization in the nanoelectrode fabrication; thus the gap size can be controlled easily and precisely. It is a clean and nondestructive process for carbon nanotube (CNT) electrodes. The mechanism is detailed. The nanoelectrodes have a pi-conjugated surface due to the deposition of sp(2)-rich amorphous carbon. As an application, DNA molecules are assembled between the CNT electrodes by pi-stacking interaction for current-voltage measurement. Our result provides a feasible route to prepare nanoelectrodes with controlled gap size, and it will be valuable for current efforts in molecular electronics and nanoelectronics.
    Nano Letters 07/2008; 8(6):1625-30. · 13.03 Impact Factor
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    ABSTRACT: We report high performance organic field-effect transistors (OFETs) with the modified Cu bottom-contact electrodes. Efficient modification of the Cu electrodes with nanometer-size copper tetracyanoquinodimethane (Cu-TCNQ) increases the electrode/organic layer contact area and reduces contact resistance. We investigated the effect of the Cu-TCNQ morphology on the device performance. The pentacene-based OFETs with the modified Cu bottom-contact electrodes exhibited high device performance. The field-effect mobility up to 0.31 cm(2)/V s was achieved. To the best of our knowledge, this is the highest device performance for the OFETs with the bottom Cu electrodes ever reported. Consequently, our results provide an effective approach to fabricate high performance and low-cost OFETs.
    Physical Chemistry Chemical Physics 06/2008; 10(17):2302-7. · 4.20 Impact Factor
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    ABSTRACT: Highly photosensitive nanoswitches with a structure of indium tin oxide/organic insulator/metal have been fabricated. Electric current in the photoswitches is sensitive to ultraviolet (UV) radiation, and can be inhibited and recovered by exposing the photoswitch to, or shielding it from, UV radiation, respectively. Photoswitches with a very high on/off ratio exceeding 106, which is the highest ratio recorded for all reported organic photoswitches, have been demonstrated under UV radiation even with a low power density ( ∼ 10−5 W/cm2).
    Applied Physics Letters 01/2008; 92(4):043302-043302-3. · 3.52 Impact Factor
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    ABSTRACT: The pyrolysis of iron(II) phthalocyanine on an Au substrate under an atmosphere of ethanol/argon was found to produce recumbent bamboo-like multi-walled carbon nanotubes. By changing the pattern of the Au bars in the substrate, the configuration of the nanotube could be changed. A possible mechanism for the formation of these patterns is suggested.
    Carbon. 01/2008; 46(2):255-260.
  • Dacheng Wei, Yunqi Liu
    Advanced Materials 01/2008; 20(15). · 14.83 Impact Factor
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    ABSTRACT: A simple acid treatment method was applied to remove the catalyst impurities and other residues contaminated in the vertically aligned carbon nanotube arrays. We demonstrated that acid treatment was an efficient approach for aligned carbon nanotube purification. Scanning electron microscopy and X-ray photoelectron spectroscopy were used to characterize the morphology of the aligned carbon nanotube arrays and to determine the efficiency of the purification. Using hydrochloric acid could efficiently eliminate catalyst impurities and retain the original structures of the aligned carbon nanotube arrays. The method provided a simple, economical, and effective way to purify the aligned carbon nanotubes, and it would promote the applications of vertically aligned carbon nanotube arrays in electronic field.
    ACTA PHYSICO-CHIMICA SINICA 01/2008; 24(6):951-954. · 0.87 Impact Factor

Publication Stats

479 Citations
228.94 Total Impact Points

Institutions

  • 2006–2012
    • Northeast Institute of Geography and Agroecology
      • • Key Laboratory of Organic Solids
      • • Institute of Chemistry
      Beijing, Beijing Shi, China
  • 2007–2010
    • Chinese Academy of Sciences
      • • Institute of Chemistry
      • • Key Laboratory of Organic Solids
      Peping, Beijing, China
  • 2009
    • Technical Institute of Physics and Chemistry
      Peping, Beijing, China