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ABSTRACT: Based on the phenomenological statistical model of dephasing introduced by Pala and Iannaccone Phys. Rev. B 69, 235304 2004, we perform an analytical and numerical calculation of electron transmission through a one-dimensional 1D scattering chain. With the introduction of random phase fluctuations into the computation of the scattering matrix, dephasing can be treated as a distribution phenomenon. By adopting the scattering matrix method combined with a Monte Carlo averaging procedure, we simulate the transition from a coherent transport to a fully incoherent transport in the 1D scattering chain. We also find the random-phase fluctuations closely related to the phase breaker model introduced by Mello et al.
Phys. Rev. B. ; 61742023(73).
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ABSTRACT: Reduction of graphene oxide at the nanoscale is an attractive approach to graphene-based electronics. Here we use a platinum-coated atomic force microscope tip to locally catalyse the reduction of insulating graphene oxide in the presence of hydrogen. Nanoribbons with widths ranging from 20 to 80 nm and conductivities of >10(4) S m(-1) are successfully generated, and a field effect transistor is produced. The method involves mild operating conditions, and uses arbitrary substrates, atmospheric pressure and low temperatures (≤115 °C).
Nature Communications 11/2012; 3:1194. · 7.40 Impact Factor
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06/2011; , ISBN: 978-953-307-199-2
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ABSTRACT: Chemical enhancement is an important mechanism in surface-enhanced Raman spectroscopy. It is found that mildly reduced graphene oxide (MR-GO) nanosheets can significantly increase the chemical enhancement of the main peaks by up to 1 order of magnitude for adsorbed Rhodamine B (RhB) molecules, in comparison with the mechanically exfoliated graphene. The observed enhancement factors can be as large as ∼10(3) and show clear dependence on the reduction time of graphene oxide, indicating that the chemical enhancement can be steadily controlled by specific chemical groups. With the help of X-ray photoelectron spectra, these chemical species are identified and the origin of the observed large chemical enhancement can thus be revealed. It is shown that the highly electronegative oxygen species, which can introduce a strong local electric field on the adsorbed molecules, are responsible for the large enhancement. In contrast, the local defects generated by the chemical reduction show no positive correlation with the enhancement. Most importantly, the dramatically enhanced Raman spectra of RhB molecules on MR-GO nanosheets reproduce all important spectral fingerprints of the molecule with a negligible frequency shift. Such a unique noninvasive feature, along with the other intrinsic advantages, such as low cost, light weight, easy availability, and flexibility, makes the MR-GO nanosheets very attractive to a variety of practical applications.
ACS Nano 02/2011; 5(2):952-8. · 10.77 Impact Factor
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Berichte der deutschen chemischen Gesellschaft 08/2010; 2010(27):4344 - 4350. · 2.94 Impact Factor
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ABSTRACT: A linker-free connected reduced graphene oxide/CdSe nanoparticle (R-GO/CdSe NP) nanocomposite was produced by directly anchoring CdSe NPs onto R-GO. The morphological and structural characterizations evidence that the single-crystal CdSe NPs with the size of a few tens of nanometers can be efficiently decorated on the R-GO. The photoresponse of this nanocomposite is drastically enhanced compared with that of the pure CdSe NPs, the bare R-GO, and the physically mixed R-GO/CdSe NPs, while the photoluminescence of the CdSe NPs in the composite is much quenched, indicating that the photoinduced carriers generated from the CdSe NPs can be transferred to the R-GO effectively and separately. This ability makes the R-GO/CdSe NP nanocomposite a great promise for wide potential applications in optoelectronics.
ACS Nano 06/2010; 4(6):3033-8. · 10.77 Impact Factor
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ABSTRACT: Vertically well-aligned ZnO nanorod arrays with three kinds of tip morphology-abruptly sharpened, tapered and plane-have been controllably fabricated with wafer size uniformity by vapor phase transport and condensation. Except that the tip morphology is distinctly different, all of these nanorods are single crystalline, growing along their wurtzite 0001 axis, with similar diameters, lengths and densities. The field emission properties of these nanorod arrays are comparatively investigated and are found to be strongly affected by the tip morphology. A nanorod with the abruptly sharpened tip possesses the lowest turn-on and threshold electric fields as well as the highest field enhancement factor. Further analysis reveals that the abruptly sharpened tip morphology can reduce the screening effect more efficiently than the others. These results are very helpful for the design, fabrication and optimization of integrated field emitters using 1D nanostructures as the cathode material.
Nanotechnology 06/2010; 21(22):225707. · 3.98 Impact Factor
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ABSTRACT: Curved ZnO nanowires were deliberately prepared on a Si substrate and the strain effect on their near band edge (NBE) emission was investigated by spatially resolved cathodoluminescence (CL). By moving the electron beam step-by-step across individual curved nanowires and acquiring the CL spectra simultaneously, we found that the NBE emissions from the inner region of the curved nanowires with compressive strain show blueshift, while those from the outer region with tensile strain show redshift. Both the strains have been estimated from the local curvature by a geometrical model and have been further examined by high-resolution transmission electron microscopy. A nearly linear relation between the strain and the peak energy shift in NBE emission was obtained. The result indicates that the optical band gap of ZnO nanowire is quite sensitive to and can be readily modulated by the induced strain via simply curving the nanowire, which has potential applications for designing new optical-electromechanical (OEM) and flexible optoelectronic nanodevices.
Nanotechnology 05/2010; 21(21):215701. · 3.98 Impact Factor
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Advanced Materials 04/2010; 22(17). · 13.88 Impact Factor
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Advanced Materials 03/2010; 22(17):1936-40. · 13.88 Impact Factor
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ABSTRACT: Spatially resolved cathodoluminescence spectra are collected along the scanning positions of the electron beam across an individual hexagonally cross-sectioned ZnO nanowire to probe the surface effect on the deep-level (DL) emissions of the nanowire. A double-peak feature of DL emission intensity is observed in the intensity versus scanning position when the electron beam scans across the nanowire from one edge to the other. This spatial variation in DL intensity can be well-described by a simple core−shell model considering the strong surface effect. By further quasi-quantitative analysis and comparison with experimental results, we obtained an equivalent surface shell thickness of about 5−6 nm. The result unambiguously confirms that the surface effect plays a key role in the DL emission process of the nanowire, which should be carefully considered and cautiously modified for better performance of nanoscale functional materials and devices.
07/2009;
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ABSTRACT: We have developed a simple, yet highly effective and reliable, poly(dimethylsiloxane) (PDMS) transfer method to fabricate highly dense and well-aligned CdS nanowires on silica substrates, following DNA templates. CdS nanoparticles are selectively deposited and confined on DNA strings aligned on a PDMS sheet to form CdS nanowires. The nanowires are then transferred to the substrate with a low occurrence of parasitic CdS nanoparticles. The mapping of elements in the nanowires by scanning Auger electron spectroscopy reveals the dense distribution of Cd and S elements along DNA scaffolds. The width and length of the nanowires can be controlled by adjusting the incubation time on the PDMS sheet. Atomic force microscopy and field emission scanning electron microscopy show that the height and width of the nanowires reach 45 and 77 nm, respectively, after 72 h of growth. The nanowire can continuously stretch over 10 μm after 96 h of incubation. The method is easily replicable, and controllable, which makes it promising for building nanophotoelectronic devices and nanosensors.
04/2009;
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ABSTRACT: Gold nanoparticles (GNPs) and modified GNPs having two kinds of functional molecules, cysteamine (AET) and thioglucose (Glu), are synthesized. Cell uptake and radiation cytotoxicity enhancement in a breast-cancer cell line (MCF-7) versus a nonmalignant breast-cell line (MCF-10A) are studied. Transmission electron microscopy (TEM) results show that cancer cells take up functional Glu-GNPs significantly more than naked GNPs. The TEM results also indicate that AET-capped GNPs are mostly bound to the MCF-7 cell membrane, while Glu-GNPs enter the cells and are distributed in the cytoplasm. After MCF-7 cell uptake of Glu-GNPs, or binding of AET-GNPs, the in vitro cytotoxicity effects are observed at 24, 48, and 72 hours. The results show that these functional GNPs have little or no toxicity to these cells. To validate the enhanced killing effect on cancer cells, various forms of radiation are applied such as 200 kVp X-rays and gamma-rays, to the cells, both with and without functional GNPs. By comparison with irradiation alone, the results show that GNPs significantly enhance cancer killing.
Small 10/2008; 4(9):1537-43. · 8.35 Impact Factor
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ABSTRACT: Since the discovery of WS2 nanotubes in 1992 ( Nature 1992, 360, 444), there have been significant research efforts to synthesize nanotubes and fullerene-like hollow nanoparticles (HNPs) of inorganic materials ( Nat. Nanotechnol. 2006, 1, 103) due to their potential applications as solid lubrications ( J. Mater. Chem. 2005, 15, 1782), chemical sensing ( Adv. Funct. Mater. 2006, 16, 371), drug delivering ( J. Am. Chem. Soc. 2005, 127, 7316), catalysis ( Adv. Mater. 2006, 18, 2561), or quantum harvesting ( Acc. Chem. Res. 2006, 39, 239). Nanotubes can be produced either by rolling up directly from layer compounds ( Nature 2001, 410, 168) or through other mechanisms ( Adv. Mater. 2004, 16, 1497) such as template growth ( Nature 2003, 422, 599) and decomposition ( J. Am. Chem. Soc. 2001, 123, 4841). The Kirkendall effect, a classical phenomenon in metallurgy ( Trans. AIME 1947, 171, 130), was recently exploited to fabricate hollow 0-D nanocrystals ( Science 2004, 304, 711) as well as 1-D nanotubes ( Nat. Mater. 2006, 5, 627). Although the dimension of resulting hollow nanostructures depends on precursors, the hollow nanomaterials can also be organized into various dimensional nanostructures spontaneously or induced by an external field. In this letter, we report, for the first time, the UV-light induced fabrication of the ends-closed 1-D CdCl2 nanotubes from 0-D CdSe solid nanocrystals through the Kirkendall effect and the head-to-end assembled process. Our results demonstrate the possibility to control the dimension (0-D to 1-D) and the configuration (solid to hollow) of nanostructures simultaneously and have implications in fabricating hollow nano-objects from zero-dimensional to multidimensional.
Nano Letters 06/2008; 8(5):1318-22. · 13.20 Impact Factor
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ABSTRACT: The electronic and phase-coherent transport properties of a doped zigzag graphene nanoribbon are studied theoretically in this paper. The I-V curve of the device shows an interesting negative differential resistance (NDR) phenomenon. We found that the NDR is caused by the chiral tunneling of graphene, which is attributed to the symmetry of the eigenstates of individual subbands. This new physics finding is helpful for us to gain more insights about carrier transport in graphene nanoribbons and to design graphene-based nanoelectronic devices.
Applied Physics Letters 04/2008; · 3.84 Impact Factor
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ABSTRACT: In this paper, we focus on a graphene heterojunction device: a Z-shaped graphene nanoribbon, which consists of two armchair leads and a zigzag junction. Based on the Landauer–Büttiker formula and the tight binding model, we found that the rectifying behavior can be achieved by applying an external gate voltage in the heterjunction region. We also found that the rectification effect is independent of junction width and length, it is an intrinsic property of the Z-junction graphene nanoribbon. This platform can be used to design and study functional graphene nanoscale devices.
Applied Physics Letters 04/2008; · 3.84 Impact Factor
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ABSTRACT: We successfully synthesized gold nanoparticles (GNPs) modified with two kinds of functional molecules, Cysteamine (AET) and thio-glucose (Glu). We also studied their cell uptake and radiation cytotoxicity enhancement in the breast and pancreatic cancer cells. Our Transmission Electron Microscopy (TEM) results showed that cancer cells uptake functional Glu-GNPs significantly more than naked GNPs. The TEM results also indicated that AET-capped GNPs were mostly bound to the MCF-7 cell membrane while Glu-GNPs entered the cells and were distributed in the cytoplasm. After the cancer cell uptaking of Glu-GNPs, or binding of AET-GNPs, the in vitro cytotoxicity effects were determined at 24, 48 and 72 hours, respectively. The results showed that these functional GNPs had little or no toxicity to these cells. We applied various forms of irradiation, such as 200 kVp X-rays and gamma-rays, to the target cells, either with or without functional GNPs. By comparison with irradiation alone, our results showed that the GNPs could significantly enhance cancer killing induced by irradiation.
Life Science Systems and Applications Workshop, 2007. LISA 2007. IEEE/NIH; 12/2007
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ABSTRACT: In this study, we developed GNPs with various types of chemical surface features and evaluated how these features led nanoparticles to selectively bind to different target cell sites. Results showed that selective binding was successful in producing high concentrations in target locations. We also explored the potential application of these GNPs to enhance the cancer cell cytotoxicity induced by radiotherapy.
Life Science Systems and Applications Workshop, 2007. LISA 2007. IEEE/NIH; 12/2007
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ABSTRACT: In this paper, the average density of states (ADOS) with a binary alloy disorder in disordered graphene systems are calculated based on the recursion method. We observe an obvious resonant peak caused by interactions with surrounding impurities and an anti-resonance dip in ADOS curves near the Dirac point. We also find that the resonance energy (Er) and the dip position are sensitive to the concentration of disorders (x) and their on-site potentials (v). An linear relation, not only holds when the impurity concentration is low but this relation can be further extended to high impurity concentration regime with certain constraints. We also calculate the ADOS with a finite density of vacancies and compare our results with the previous theoretical results. Comment: 10 pages, 8 figures
11/2007;
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ABSTRACT: The pressure dependence of photoluminescence of wurtzite 5.5 nm CdZnSe alloy quantum dots (QDs) was studied and compared with that of the wurtzite 3.5 nm CdSe QDs. The direct Γ energy gaps of wurtzite QDs were found to increase with the pressure, and the pressure coefficients were gained as 35.4 meV/GPa for CdZnSe and 28.4 meV/GPa for CdSe QDs. The authors attributed the high value of pressure coefficient for CdZnSe alloy QDs to the alloying effect with strengthening the anion-cation s‐s orbital coupling and weakening p‐d orbital coupling in the alloy. The result demonstrates that the alloying process has a dominant role in the electronic state and structure transition under high pressure.
Journal of Applied Physics 09/2007; 102(5):053509-053509-3. · 2.17 Impact Factor
