Chongwu Zhou

University of Southern California, Los Ángeles, California, United States

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Publications (215)1237.45 Total impact

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    ABSTRACT: We report the integration of high voltage cathode material LiNi0.5Mn1.5O4 and multiwall carbon nanotube network for the first time, which has led to charge/discharge rate as high as 20C and has also been demonstrated to work as cathode for flexible batteries. The LiNi0.5Mn1.5O4/ multiwall carbon nanotube network is flexible and light-weight since the use of binder, conductive additive and metal current collector is eliminated. Due to the high voltage provided by LiNi0.5Mn1.5O4 particles, the total energy of the battery is significantly enhanced. In addition, with the high conductivity from multiwall carbon nanotube network, the LiNi0.5Mn1.5O4/multiwall carbon nanotube network electrodes can deliver 80% of the 1C capacity even when the charge/discharge current density increased to 20C (1C=140 mA/g). During the high current rate cycling test, no obvious capacity decay is observed after 100 cycles at 10C. Calculation of the polarization resistance Rp reveals that the Rp of the LiNi0.5Mn1.5O4/multiwall carbon nanotube electrodes is less than 25% of that of the conventional electrodes fabricated through slurry-casting on metal current collector. In addition, the power density calculated from LiNi0.5Mn1.5O4/multiwall carbon nanotube electrodes is over two times larger than that provided by the conventional electrodes. The combined effect from high voltage, high current rate performance and reduced weight has led our LiNi0.5Mn1.5O4/multiwall carbon nanotube electrodes to be a promising candidate for high-power lithium ion batteries. Moreover, the features of flexibility and light-weight also demonstrate the potential of applying the LiNi0.5Mn1.5O4 / multiwall carbon nanotube electrodes in new-generation flexible or ultrathin/ultralight electronic devices in the future.
    Nano Energy 03/2015; 12. DOI:10.1016/j.nanoen.2014.11.052 · 10.21 Impact Factor
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    ABSTRACT: Nanostructure field-effect transistor (FET) biosensors have shown great promise for ultra sensitive biomolecular detection. Top-down assembly of these sensors increases scalability and device uniformity but faces fabrication challenges in achieving the small dimensions needed for sensitivity. We report top-down fabricated indium oxide (In2O3) nanoribbon FET biosensors using highly scalable radio frequency (RF) sputtering to create uniform channel thicknesses ranging from 50 nm to 10 nm. We combine this scalable sensing platform with amplification from electronic enzyme-linked immunosorbent assay (ELISA) to achieve high sensitivity to target analytes such as streptavidin and human immunodeficiency virus type 1 (HIV-1) p24 proteins. Our approach circumvents Debye screening in ionic solutions and detects p24 protein at 20 fg/ml (about 250 viruses/ml or about three orders of magnitude lower than commercial ELISA) with a 35% conduction change in human serum. The In2O3 nanoribbon biosensors have 100% device yield and use a simple 2 mask photolithography process. The electrical properties of 50 In2O3 nanoribbon FETs showed good uniformity in on-state current, on/off current ratio, mobility, and threshold voltage. In addition, the sensors show excellent pH sensitivity over a broad range (pH 4 to 9) as well as over the physiological-related pH range (pH 6.8 to 8.2). With the demonstrated sensitivity, scalability and uniformity, the In2O3 nanoribbon sensor platform makes great progress toward clinical testing, such as for early diagnosis of acquired immunodeficiency syndrome (AIDS).
    Nano Letters 01/2015; 15(3). DOI:10.1021/nl5047889 · 12.94 Impact Factor
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    ABSTRACT: The inability to synthesize single-wall carbon nanotubes (SWCNTs) possessing uniform electronic properties and chirality represents the major impediment to their widespread applications. Recently, there is growing interest to explore and synthesize well-defined carbon nanostructures, including fullerenes, short nanotubes, and sidewalls of nanotubes, aiming for controlled synthesis of SWCNTs. One noticeable advantage of such processes is that no metal catalysts are used, and the produced nanotubes will be free of metal contamination. Many of these methods, however, suffer shortcomings of either low yield or poor controllability of nanotube uniformity. Here, we report a brand new approach to achieve high efficiency metal-free growth of nearly pure SWCNT semiconductors, as supported by extensive spectroscopic characterization, electrical transport measurements, and density functional theory calculations. Our strategy combines bottom-up organic chemistry synthesis with vapour phase epitaxy elongation. We identify a strong correlation between the electronic properties of SWCNTs and their diameters in nanotube growth. This study not only provides material platforms for electronic applications of semiconducting SWCNTs, but also contributes to fundamental understanding of the growth mechanism and controlled synthesis of SWCNTs.
    Nano Letters 12/2014; 15(1). DOI:10.1021/nl504066f · 12.94 Impact Factor
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    ABSTRACT: Semiconducting single-wall carbon nanotubes are very promising materials in printed electronics due to their excellent mechanical and electrical property, outstanding printability, and great potential for flexible electronics. Nonetheless, developing scalable and low-cost approaches for manufacturing fully printed high-performance single-wall carbon nanotube thin-film transistors remains a major challenge. Here we report that screen printing, which is a simple, scalable, and cost-effective technique, can be used to produce both rigid and flexible thin-film transistors using separated single-wall carbon nanotubes. Our fully printed top-gated nanotube thin-film transistors on rigid and flexible substrates exhibit decent performance, with mobility up to 7.67 cm(2) V(-1) s(-1), on/off ratio of 10(4) ∼ 10(5), minimal hysteresis, and low operation voltage (<10 V). In addition, outstanding mechanical flexibility of printed nanotube thin-film transistors (bent with radius of curvature down to 3 mm) and driving capability for organic light-emitting diode have been demonstrated. Given the high performance of the fully screen-printed single-wall carbon nanotube thin-film transistors, we believe screen printing stands as a low-cost, scalable, and reliable approach to manufacture high-performance nanotube thin-film transistors for application in display electronics. Moreover, this technique may be used to fabricate thin-film transistors based on other materials for large-area flexible macroelectronics, and low-cost display electronics.
    ACS Nano 12/2014; DOI:10.1021/nn505979j · 12.03 Impact Factor
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    ABSTRACT: Two-dimensional (2D) layered tungsten diselenides (WSe2) material has recently drawn a lot of attention due to its unique optoelectronic properties and ambipolar transport behavior. However, direct chemical vapor deposition (CVD) synthesis of 2D WSe2 is not as straightforward as other 2D materials due to the low reactivity between reactants in WSe2 synthesis. In addition, the growth mechanism of WSe2 in such CVD process remains unclear. Here we report the observation of a screw-dislocation-driven (SDD) spiral growth of 2D WSe2 flakes and pyramid-like structures using a sulfur-assisted CVD method. Few-layer and pyramid-like WSe2 flakes instead of monolayer were synthesized by introducing a small amount of sulfur as a reducer to help the selenization of WO3, which is the precursor of tungsten. Clear observations of steps, helical fringes, and herring-bone contours under atomic force microscope characterization reveal the existence of screw dislocations in the as-grown WSe2. The generation and propagation mechanisms of screw dislocations during the growth of WSe2 were discussed. Back-gated field-effect transistors were made on these 2D WSe2 materials, which show on/off current ratios of 106 and mobility up to 44 cm2/Vs.
    ACS Nano 10/2014; DOI:10.1021/nn504775f · 12.03 Impact Factor
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    ABSTRACT: We report substantial improvements in the photoluminescence (PL) efficiency and Fabry-Perot (FP) resonance of individual GaAs nanowires through surface passivation and local field enhancement, enabling FP peaks to be observed even at room temperature. For bare GaAs nanowires, strong FP resonance peaks can be observed at 4 K, but not at room temperature. However, depositing the nanowires on gold substrates leads to substantial enhancement in the PL intensity (5X) and 3.7X to infinite enhancement of FP peaks. Finite-difference time-domain (FDTD) simulations show that the gold substrate enhances the PL spectra predominately through enhanced absorption (11X) rather than enhanced emission (1.3X), predicting a total PL enhancement of 14X in the absence of non-radiative recombination. Despite the increased intensity of the FP peaks, lower Q factors are observed due to losses associated with the underlying gold substrate. As a means of reducing the non-radiative recombination in these nanowires, the surface states in the nanowires can be passivated by either an ionic liquid (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM TFSI)) or an AlGaAs surface layer to achieve up to 12X enhancement of the photoluminescence intensity and observation of FP peaks at room temperature without a gold substrate.
    Nano Research 08/2014; 7(8):1146-1153. DOI:10.1007/s12274-014-0477-0 · 6.96 Impact Factor
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    ABSTRACT: The objective was to use carbon nanotubes (CNT) coupled with near-infrared radiation (NIR) to induce hyperthermia as a novel non-ionizing radiation treatment for primary brain tumors, glioblastoma multiforme (GBM). In this study, we report the therapeutic potential of hyperthermia-induced thermal ablation using the sequential administration of carbon nanotubes (CNT) and NIR. In vitro studies were performed using glioma tumor cell lines (U251, U87, LN229, T98G). Glioma cells were incubated with CNTs for 24 h followed by exposure to NIR for 10 min. Glioma cells preferentially internalized CNTs, which upon NIR exposure, generated heat, causing necrotic cell death. There were minimal effects to normal cells, which correlate to their minimal uptake of CNTs. Furthermore, this protocol caused cell death to glioma cancer stem cells, and drug-resistant as well as drug-sensitive glioma cells. This sequential hyperthermia therapy was effective in vivo in the rodent tumor model resulting in tumor shrinkage and no recurrence after only one treatment. In conclusion, this sequence of selective CNT administration followed by NIR activation provides a new approach to the treatment of glioma, particularly drug-resistant gliomas.
    Frontiers in Oncology 07/2014; 4:180. DOI:10.3389/fonc.2014.00180
  • Haitian Chen, Yu Cao, Jialu Zhang, Chongwu Zhou
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    ABSTRACT: Carbon nanotubes and metal oxide semiconductors have emerged as important materials for p-type and n-type thin-film transistors, respectively; however, realizing sophisticated macroelectronics operating in complementary mode has been challenging due to the difficulty in making n-type carbon nanotube transistors and p-type metal oxide transistors. Here we report a hybrid integration of p-type carbon nanotube and n-type indium-gallium-zinc-oxide thin-film transistors to achieve large-scale (>1,000 transistors for 501-stage ring oscillators) complementary macroelectronic circuits on both rigid and flexible substrates. This approach of hybrid integration allows us to combine the strength of p-type carbon nanotube and n-type indium-gallium-zinc-oxide thin-film transistors, and offers high device yield and low device variation. Based on this approach, we report the successful demonstration of various logic gates (inverter, NAND and NOR gates), ring oscillators (from 51 stages to 501 stages) and dynamic logic circuits (dynamic inverter, NAND and NOR gates).
    Nature Communications 06/2014; 5:4097. DOI:10.1038/ncomms5097 · 10.74 Impact Factor
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    ABSTRACT: Due to unique structural, optical and electrical properties, solar cells based on semiconductor nanowires are a rapidly-evolving scientific enterprise. Various approaches employing III-V nanowires have emerged, among which GaAs, especially, is under intense research and development. Most reported GaAs nanowire solar cells form p-n junctions in the radial direction; however, nanowires using axial junction may enable the attainment of high open circuit voltage (Voc) and integration into multi-junction solar cells. Here, we report GaAs nanowire solar cells with axial p-i-n junctions that achieve 7.58% efficiency. Simulations show that axial junctions are more tolerant to doping variation than radial junctions and lead to higher Voc under certain conditions. We further study the effect of wire diameter and junction depth using electrical characterization and cathodoluminescence. The results show that large diameter and shallow junctions are essential for high extraction efficiency. Our approach opens up great opportunity for future low-cost, high-efficiency photovoltaics.
    Nano Letters 05/2014; 14(6). DOI:10.1021/nl500704r · 12.94 Impact Factor
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    ABSTRACT: Semiconducting SnO2 nanowires have been used to demonstrate high quality field-effect transistors, optically transparent devices, photodetectors, and gas sensors. However, controllable assembly of rutile SnO2 nanowires is necessary for scalable and practical device applications. Here we demonstrate aligned, planar SnO2 nanowires grown on A-plane, M-plane, and R-plane sapphire substrates. These parallel nanowires can reach 100 μm in length with sufficient density to be patterned photolithographically for field-effect transistors and sensor devices. As proof-of-concept, we show that transistors made this way can achieve on/off current ratios on the order of 10(6), mobilities around 71.68 cm(2)/V∙s, and sufficiently high currents to drive external organic light-emitting diode displays. Furthermore, the aligned SnO2 nanowire devices are shown to be photosensitive to UV light, with the capability to distinguish between 254 nm and 365 nm wavelengths. Their alignment is advantageous for polarized UV light detection; we have measured a polarization ratio of photoconductance (σ) of 0.3. Lastly, we show that the nanowires can detect NO2 at a concentration of 0.2 ppb, making them a scalable, ultra-sensitive gas sensing technology. Aligned SnO2 nanowires offer a straightforward method to fabricate scalable SnO2 nano-devices for a variety of future electronic applications.
    Nano Letters 05/2014; 14(6). DOI:10.1021/nl404289z · 12.94 Impact Factor
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    ABSTRACT: Bottom-up synthesis of graphene nanoribbons (GNRs) is an essential step toward utilizing them in electronic and sensing applications due to their defined edge structure and high uniformity. Recently, structurally perfect GNRs with variable lengths and edge structures were created using various chemical synthesis techniques. Nonetheless, issues like GNR deposition, characterization, electronic properties, and applications are not fully explored. Here we report optimized conditions for deposition, characterization, and device fabrication of individual and thin films of ultra-long chemically synthesized GNRs. Moreover, we have demonstrated exceptional NO2 gas sensitivity of the GNR film devices down to parts per billion (ppb) levels. The results lay the foundation for using chemically synthesized GNRs for future electronic and sensing applications.
    Journal of the American Chemical Society 05/2014; 136(21):7555–7558. DOI:10.1021/ja502764d · 11.44 Impact Factor
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    ABSTRACT: Carbon nanotubes have the potential to spur future development in electronics due to their unequalled electrical properties. In this article, we present a review on carbon nanotube-based circuits in terms of their electrical performance in two major directions: nanoelectronics and macroelectronics. In the nanoelectronics direction, we direct our discussion to the performance of aligned carbon nanotubes for digital circuits and circuits designed for radio-frequency applications. In the macroelectronics direction, we focus our attention on the performance of thin films of carbon nanotube random networks in digital circuits, display applications, and printed electronics. In the last part, we discuss the existing challenges and future directions of nanotube-based nano- and microelectronics.
    Semiconductor Science and Technology 05/2014; 29(7):073001. DOI:10.1088/0268-1242/29/7/073001 · 2.21 Impact Factor
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    ABSTRACT: Lightweight and high-power LiNi0.5Mn1.5O4/carbon nanofiber (CNF) network electrodes are developed as a high-voltage cathode for lithium ion batteries. The LiNi0.5Mn1.5O4/CNF network electrodes are free-standing and can be used as a cathode without using any binder, carbon black, or metal current collector, and hence the total weight of the electrode is highly reduced while keeping the same areal loading of active materials. Compared with conventional electrodes, the LiNi0.5Mn1.5O4/CNF network electrodes can yield up to 55% reduction in total weight and 2.2 times enhancement in the weight percentage of active material in the whole electrode. Moreover, the LiNi0.5Mn1.5O4/carbon nanofiber (CNF) network electrodes showed excellent current rate capability in the large-current test up to 20C (1C = 140 mAh/g), when the conventional electrodes showed almost no capacity at the same condition. Further analysis of polarization resistance confirmed the favorable conductivity from the CNF network compared with the conventional electrode structure. By reducing the weight, increasing the working voltage, and improving the large-current rate capability simultaneously, the LiNi0.5Mn1.5O4/CNF electrode structure can highly enhance the energy/power density of lithium ion batteries and thus holds great potential to be used with ultrathin, ultralight electronic devices as well as electric vehicles and hybrid electric vehicles.
    ACS Nano 04/2014; 8(5). DOI:10.1021/nn500814v · 12.03 Impact Factor
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    ABSTRACT: Trace chemical detection is important for a wide range of practical applications. Recently emerged two-dimensional (2D) crystals offer unique advantages as potential sensing materials with high sensitivity, owing to their very high surface-to-bulk atom ratios and semiconducting properties. Here, we report the first use of Schottky-contacted chemical vapor deposition grown monolayer MoS2 as high-performance room temperature chemical sensors. The Schottky-contacted MoS2 transistors show current changes by 2-3 orders of magnitude upon exposure to very low concentrations of NO2 and NH3. Specifically, the MoS2 sensors show clear detection of NO2 and NH3 down to 20 ppb and 1 ppm, respectively. We attribute the observed high sensitivity to both well-known charger transfer mechanism and, more importantly, the Schottky barrier modulation upon analyte molecule adsorption, the latter of which is made possible by the Schottky contacts in the transistors and is not reported previously for MoS2 sensors. This study shows the potential of 2D semiconductors as high-performance sensors and also benefits the fundamental studies of interfacial phenomena and interactions between chemical species and monolayer 2D semiconductors.
    ACS Nano 04/2014; 8(5). DOI:10.1021/nn5015215 · 12.03 Impact Factor
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    ABSTRACT: The effects of near-interfacial trapping induced by ionizing radiation exposure of aligned single-walled carbon nanotube (SWCNT) arrays are investigated via measurements of gate hysteresis in the transfer characteristics of aligned SWCNT field-effect transistors. Gate hysteresis is attributed to charge injection (i.e., trapping) from the SWCNTs into radiation-induced traps in regions near the SWCNT/dielectric interface. Self-consistent calculations of surface-potential, carrier density, and trapped charge are used to describe hysteresis as a function of ionizing radiation exposure. Hysteresis width (h) and its dependence on gate sweep range are investigated analytically. The effects of non-uniform trap energy distributions on the relationship between hysteresis, gate sweep range, and total ionizing dose are demonstrated with simulations and verified experimentally.
    Journal of Applied Physics 02/2014; 115(5):054506-054506-8. DOI:10.1063/1.4864126 · 2.19 Impact Factor
  • 02/2014; 2(2):133-133. DOI:10.1002/ente.201490002
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    ABSTRACT: Bandgap engineering of graphene is an essential step toward employing graphene in electronic and sensing applications. Recently, graphene nanoribbons (GNRs) were used to create a bandgap in graphene and function as a semiconducting switch. Although GNRs with widths of <10 nm have been achieved, problems like GNR alignment, width control, uniformity, high aspect ratios, and edge roughness must be resolved in order to introduce GNRs as a robust alternative technology. Here we report patterning, characterization, and superior chemical sensing of ultranarrow aligned GNR arrays down to 5 nm width using helium ion beam lithography (HIBL) for the first time. The patterned GNR arrays possess narrow and adjustable widths, high aspect ratios, and relatively high quality. Field-effect transistors were fabricated on such GNR arrays and temperature-dependent transport measurements show the thermally activated carrier transport in the GNR array structure. Furthermore, we have demonstrated exceptional NO2 gas sensitivity of the 5 nm GNR array devices down to parts per billion (ppb) levels. The results show the potential of HIBL fabricated GNRs for the electronic and sensing applications.
    ACS Nano 01/2014; 8(2). DOI:10.1021/nn405759v · 12.03 Impact Factor

Publication Stats

8k Citations
1,237.45 Total Impact Points

Institutions

  • 2001–2015
    • University of Southern California
      • • Department of Chemical Engineering and Materials Science
      • • Department of Electrical Engineering
      • • Division of Cardiovascular Medicine
      Los Ángeles, California, United States
  • 2002–2014
    • University of California, Los Angeles
      • • Department of Materials Science and Engineering
      • • Department of Electrical Engineering
      Los Ángeles, California, United States
  • 2013
    • Michigan State University
      • Department of Electrical and Computer Engineering
      Ист-Лансинг, Michigan, United States
  • 2009–2013
    • Huazhong University of Science and Technology
      • Wuhan National Laboratory for Optoelectronics
      Wuhan, Hubei, China
  • 2012
    • Purdue University
      • Department of Electrical and Computer Engineering Technology (ECET)
      West Lafayette, IN, United States
  • 2010
    • Harvard University
      • Department of Chemistry and Chemical Biology
      Cambridge, MA, United States
  • 2008
    • Kyonggi University
      Sŏul, Seoul, South Korea
  • 2004
    • NASA
      Вашингтон, West Virginia, United States
    • San Jose State University
      • Department of Chemistry
      San José, California, United States
    • Rice University
      • Department of Chemistry
      Houston, Texas, United States