ACS Nano

Publisher: American Chemical Society, American Chemical Society

Description

  • Impact factor
    12.03
  • 5-year impact
    12.52
  • Cited half-life
    2.40
  • Immediacy index
    1.94
  • Eigenfactor
    0.20
  • Article influence
    4.01
  • Other titles
    ACS nano (Online), ACS nano, American Chemical Society nano
  • ISSN
    1936-086X
  • OCLC
    85374429
  • Material type
    Document, Periodical, Internet resource
  • Document type
    Internet Resource, Computer File, Journal / Magazine / Newspaper

Publisher details

American Chemical Society

  • Pre-print
    • Author cannot archive a pre-print version
  • Restrictions
    • Must obtain written permission from Editor
    • Must not violate ACS ethical Guidelines
  • Post-print
    • Author cannot archive a post-print version
  • Restrictions
    • If mandated by funding agency or employer/ institution
    • Must obtain written permission from Editor confirming posting does not conflict prior publication policies
    • If mandated to deposit before 12 months, must obtain waiver from Institution/ Agency or use AuthorChoice
    • 12 months
  • Conditions
    • On website or repositories
    • Non-Commercial
    • Must be accompanied by set statement (see policy)
    • Must link to publisher version
    • If mandated sooner than 12 months, must obtain waiver from Editors or use AuthorChoice
    • Publisher's version/PDF may be used, but only via AuthorChoice option
  • Classification
    ​ white

Publications in this journal

  • [Show abstract] [Hide abstract]
    ABSTRACT: Redox cycling in nanometer-wide thin-layer cells holds great promise in ultrasensitive voltammetric detection and in probing fast heterogeneous electron-transfer kinetics. Quantitative understanding of the influence of the nanometer gap distance on the redox processes in the thin-layer cells is of crucial importance for reliable data analysis. We present theoretical considera-tion on the voltammetric behaviors associated with redox cycling of electroactive molecules between two electrodes sepa-rated by nanometer widths. Emphasis is placed on the weakness of the commonly used Butler-Volmer theory and the clas-sic Marcus-Hush theory in describing the electrochemical heterogeneous electron-transfer kinetics at potentials significantly removed from the formal potential of redox moieties and, in addition, the effect of the electric-double-layer on the electron-transfer kinetics and mass transport dynamics of charged redox species. The steady-state voltammetric responses, obtained by using the Butler-Volmer and Marcus-Hush models, and that predicted by the more realistic ET kinetics formulism which is based on the alignments of the density of states between the electrode continuum and the Gaussian distribution of redox agents, and by inclusion of the electric-double-layer effect, are compared through systematic finite element simulations. The effect of the gap width between the electrodes, the standard rate constant and reorganization energy for the electron-transfer reactions, and the charges of the redox moieties are considered. On the basis of the simulation results, the reliability of the conventional voltammetric analysis based on the Butler-Volmer kinetic model and diffusion transport equations is discussed for nanometer-wide thin-layer cells.
    ACS Nano 09/2014;
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    ABSTRACT: Rough surface and poor stability of ultra-thin Ag films limit its applications in nanophotonic and optoelectronic devices. Here, we report an approach for fabricating ultra-smooth and thermally-stable Ag-based thin films on SiO2/Si substrates by Al-doping. The effect of Al-doping on the surface morphology and stability of ultrathin Ag films at room temperature and elevated temperature was investigated. The 15 nm Al-doped Ag films with Al atomic concentration of 4 % have a root-mean-square (RMS) roughness as low as 0.4 nm. The smooth surface morphology is maintained even after 300 °C annealing in N2. Al-doping enhances the nuclei density of films. Moreover, a capping layer spontaneously formed over the Al-doped Ag films restrains the surface diffusion and mass transportation of Ag atoms. Therefore, Al-doping endues ultrathin Ag films with highly-stable and ultra-smooth surface morphology.
    ACS Nano 09/2014;
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    ABSTRACT: Several hundred grams of Janus nanoparticles (d ≈ 40 nm) were synthesized as compatibilizers for blending of technologically relevant polymers, PPE and SAN, on industry-scale extruders. The Janus nanoparticles (JPs) demonstrate superior compatibilization capabilities compared to the corresponding triblock terpolymer, attributed combined intrinsic properties of amphiphilicity and the Pickering effect. Straightforward mixing and extrusion protocols achieve multiscale blend morphologies containing perfect "raspberry-like" structures of JPs-covered PPE phases in a SAN matrix. The JPs densely pack at the blend interface providing the necessary steric repulsion to suppress droplet coagulation during processing. We determine the efficiency of JP-compatibilization by droplet size evaluation and find the smallest average droplet size of d ≈ 300 nm at 10wt.-% of added compatibilizer, whereas at 2wt.-%, use of JPs is most economically with reasonable small droplets with narrow dispersity. In case of excess JPs, they form a double layer at the blend interface altering rheological properties of the system caused by a droplet network formation. The large-scale synthesis of JPs, the low required weight fractions and their exceptional stability against extensive shear and temperature profiles during industrial extrusion process render JPs promising next generation compatibilizers.
    ACS Nano 09/2014;
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    ABSTRACT: Core(Fe)-shell(Au) nanoparticles are obtained by solid-state dewetting of thin Fe/Au bilayer films deposited on a sapphire substrate. The core-shell morphology is achieved by employing the equilibrium segregation phenomenon, where Au atoms form a homogeneous thin shell on the surfaces of an Fe nanoparticle and at its interface with the substrate, reducing the total interfacial energy of the system. The obtained nanoparticles are single crystalline (structurally perfect), thermally stable and of high purity. Their size may be tuned by changing the initial film thickness. We demonstrate that the nanoparticles can subsequently be stripped from the substrate, and/or be modified by attaching thiol-containing organic molecules for use in various nanotechnology-related applications. The method presented herein may easily be extended to other metal combinations, especially those relevant for catalysis, thus helping to reduce precious-metal (e.g. Au, Pt, Rh) content in the catalyst.
    ACS Nano 09/2014;
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    ABSTRACT: We investigate the impact of the coupling symmetry and chemical nature of organic-inorganic interfaces on thermoelectric transport in Cu2-xSe nanocrystal thin films. By coupling ligand exchange techniques with layer-by-layer assembly methods, we are able to systematically vary nanocrystal-organic linker interfaces, demonstrating how the functionality of the polar head group and the coupling symmetry of the organic linkers can change the power factor (S(2)σ) by nearly two orders of magnitude. Remarkably, we observe that ligand coupling symmetry has a profound effect on thermoelectric transport in these hybrid materials. We shed light on these results using a simplified model for inter-particle charge transport via tunneling through the frontier orbital of a bound ligand. Our analysis indicates that ligand coupling symmetry and binding mechanisms correlates with enhanced conductivity approaching 2000 S/cm, and we employ this concept to demonstrate amongst the highest power factors measured for quantum-dot based thermoelectric inorganic-organic composite materials of ~30 µW/m•K(2).
    ACS Nano 09/2014;
  • [Show abstract] [Hide abstract]
    ABSTRACT: A significant barrier to the therapeutic use of stem cells is poor cell retention in vivo. Here, we evaluate the therapeutic potential and long-term engraftment of cardiomyocytes (CMs) derived from mouse embryonic stem cells (mESCs) encapsulated in an injectable nanomatrix gel consisting of peptide amphiphiles incorporating cell adhesive ligand Arg-Gly-Asp-Ser (PA-RGDS) in experimental myocardial infarction (MI). We cultured rat neonatal CMs in PA-RGDS for 7 days and found that more than 90% of the CMs survived. Next, we intramyocardially injected mouse CM cell line HL-1 CMs with or without PA-RGDS into uninjured hearts. Histologic examination and flow cytometry analysis of digested heart tissues showed approximately 3-fold higher engraftment in the mice which received CMs with PA-RGDS compared to those without PA-RGDS. We further investigated the therapeutic effects and long-term engraftment of mESC-CMs with PA-RGDS on MI in comparison with PBS control, CM-only, and PA-RGDS only. Echocardiography demonstrated that the CM-only and CM+PA-RGDS groups showed higher cardiac function at week 2 compared to other groups. However, from 3 weeks, higher cardiac function was only maintained in the CM+PA-RGDS group; this was sustained for 12 weeks. Confocal microscopic examination of the cardiac tissues harvested at 14 weeks demonstrated sustained engraftment and integration of mESC-CMs into host myocardium in CM+PA-RGDS group only. This study for the first time demonstrated that PA-RGDS encapsulation can enhance survival of mESC-derived CMs and improve cardiac function post-MI. This nanomatrix gel-mediated stem cell therapy can be an option for treating MI.
    ACS Nano 09/2014;
  • [Show abstract] [Hide abstract]
    ABSTRACT: The well-known photochemical and thermal methods for silver nanoplate synthesis have been generally regarded as two parallel processes without strong connections. Here we report a surprising finding that both visible light and ambient O2, which are critically important in the photochemical process, also play determining roles in the thermal synthesis. By designing a series of control experiments, we reveal that the typical thermal synthesis is essentially a modified photochemical synthesis coupled with the unique redox properties of H2O2. Light irradiation and dissolved O2 are found to be essential for initiating the formation of nanoplates, but the continued growth of nanoplates is supported by the oxidative etching and subsequent reduction due to H2O2. O2 resulting from the catalytic decomposition of H2O2 etches small nanoparticles to produce Ag+ ions, which are then reduced back to Ag0 by anions of H2O2 to support the growth of nanoplate seeds. The involvement of H2O2 in the reaction significantly speeds up the nanoplate formation process. These findings not only greatly improve our understanding of the unique functions of H2O2 in the thermal synthesis, but also bridge the two well established synthesis processes with a unified mechanism, and significantly enhance the reproducibility of the thermal synthesis of Ag nanoplates by identifying the critical importance of ambient light and O2.
    ACS Nano 09/2014;
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    ABSTRACT: Plasmonic nanoantennas exhibit various resonant modes with distinct properties. Upon resonant excitation, plasmonic gold nanoantennas can generate strong two-photon photoluminescence (TPPL). The TPPL from gold is broadband and depolarized, and may serve as an ideal local source for the investigation of antenna eigenmodes. In this work, TPPL spectra of three arrays of single-crystalline gold nanoantennas are comprehensively investigated. We carefully compare the TPPL spectra with dark-field scattering spectra and numerically simulated spectra. We show the modulation effect of the transverse resonant mode and the nonfundamental longitudinal mode on the TPPL spectrum. We also demonstrate suppression of TPPL due to the subradiant antibonding modes and study the influence of antenna resonant modes on the overall TPPL yield. Our work provides direct experimental evidence on nanoantenna-mediated near-to-far-field energy coupling and gains insight into the emission spectrum of the TPPL from gold nanoantennas.
    ACS Nano 09/2014;
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    ABSTRACT: We study surface photovoltage decays on sub-millisecond timescales in organic solar cells using intensity-modulated Scanning Kelvin Probe Microscopy (SKPM). Using polymer/fullerene (poly[N-9''-hepta-decanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)]/[6,6]-phenyl C71-butyric acid methyl ester, PCDTBT/PC71BM) bulk heterojunction devices as a test case, we show that the decay lifetimes measured by SKPM depend on the intensity of the background illumination. We propose that this intensity dependence is related to the well-known carrier-density-dependent recombination kinetics in organic bulk heterojunction materials. We perform transient photovoltage (TPV) and charge extraction (CE) measurements on the PCDTBT/PC71BM blends to extract the carrier-density dependence of the recombination lifetime in our samples, and we find that the device TPV and CE data are in good agreement with the intensity and frequency dependence observed via SKPM. Finally, we demonstrate the capability of intensity-modulated SKPM to probe local recombination rates due to buried interfaces in organic photovoltaics (OPVs). We measure the differences in photovoltage decay lifetimes over regions of an OPV cell fabricated on an indium tin oxide electrode patterned with two different phosphonic acids monolayers known to affect carrier lifetime.
    ACS Nano 09/2014;
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    ABSTRACT: Interaction of charge carriers with the surface of semiconductor nanocrystals plays an integral role in determining the ultimate fate of the excited state. The surface contains a dynamic ensemble of trap states that can localize excited charges, preventing radiative recombination and reducing fluorescence quantum yields. Here we report quasi-type-II band alignment in graded alloy CdSxSe1-x nanocrystals revealed by femtosecond fluorescence upconversion spectroscopy. Graded alloy CdSxSe1-x quantum dots are a compositionally inhomogeneous nano-heterostructure designed to decouple the exciton from the nanocrystal surface. The large valence band offset between the CdSe-rich core and CdS-rich shell separates the excited hole from the surface by confining it to the core of the nanocrystal. The small conduction band offset, however, allows the electron to delocalize throughout the entire nanocrystal and maintain overlap with the surface. Indeed, the ultrafast charge carrier dynamics reveal that the fast 1-3 ps hole trapping process is fully eliminated with increasing sulfur composition and the decay constant for electron trapping (~20-25 ps) shows a slight increase. These findings demonstrate progress towards highly efficient nanocrystal fluorophores that are independent of their surface chemistry to ultimately enable their incorporation into a diverse range of applications without experiencing adverse effects arising from dissimilar environments.
    ACS Nano 09/2014;
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    ABSTRACT: Essentially all experimental investigations of swimming micro- and nanorobots have focused on swimming in homogeneous Newtonian liquids. In this issue of ACS Nano, Schamel et al. investigate the actuation of "nanopropellers" in a viscoelastic biological gel that illustrates the importance of the size of the nanostructure relative to the gel mesh size. In this Perspective, we shed further light on the swimming performance of larger microrobots swimming in heterogeneous liquids. One of the interesting results of our work is that earlier findings on the swimming performance of motile bacteria in heterogeneous liquids agree, in principle, with our results. We also discuss future research directions that should be pursued in this fascinating interdisciplinary field.
    ACS Nano 09/2014;
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    ABSTRACT: The excellent charge transport properties of graphene suggest a wide range of application in analog electronics. While most practical devices will require that graphene be bonded to a substrate, such bonding generally degrades these transport properties. In contrast, when graphene is transferred to Ge(001) its conductivity is extremely high and the charge carrier mobility derived from the relevant transport measurements is, under some circumstances, higher than that of freestanding, edge-supported graphene. We measure a mobility of ~5x10^5 cm^2/ Vs at 20 K, and ~10^3 cm^2/Vs at 300 K. These values are close to the theoretical limit for doped graphene. Carrier densities in the graphene are as high as 10^14 cm^-2 at 300 K.
    ACS Nano 09/2014;
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    ABSTRACT: Small organic semiconducting molecules assembling into supramolecular J- and H- aggregates have attracted much attention due to outstanding optoelectronic properties. However, their easy and reproducible fabrication is not yet sufficiently developed for industrial applications, except for silver halide photography. Here we present a method based on aggregate precipitation during the phase separation and dewetting of the evaporating dye precursor solution. The smaller the precursor droplets, the more pronounced the J-aggregation. The aggregates cause the films to resonantly scatter incoming light. Because the dye aggregate extinction resonances have narrowest bandwidths, a wavelength selectivity is observed that exceeds the selectivity of localized surface plasmon resonances. The aggregation mechanism can be easily applied to periodically structured substrates, making the method appealing for photonic applications. We demonstrate this point with a 2D grating, where the narrow absorption range of the aggregates leads to wavelength specific (one color only) scattering.
    ACS Nano 09/2014;
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    ABSTRACT: The origins of performance enhancement in hybrid plasmonic organic photovoltaic devices are often embroiled in a complex interaction of light scattering, localized surface plasmon resonances, exciton-plasmon energy transfer and even non-plasmonic effects. To clearly deconvolve the plasmonic contributions from a single nanostructure, we herein investigate the influence of a single silver nanowire (NW) on the charge carriers in bulk heterojunction polymer solar cells using spatially-resolved optical spectroscopy, and correlate to electrical device characterization. Polarization-dependent photocurrent enhancements with a maximum of ~36% over the reference are observed when the transverse mode of the plasmonic excitations in the Ag NW is activated. The ensuing higher absorbance and light scattering induced by the electronic motion perpendicular to the NW long axis lead to increased exciton and polaron densities instead of direct surface plasmon-exciton energy transfer. Finite-difference time-domain simulations also validate these findings. Importantly, our study at the single nanostructure level explores the fundamental limits of plasmonic enhancement achievable in organic solar cells with a single plasmonic nanostructure.
    ACS Nano 09/2014;
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    ABSTRACT: Here we demonstrate significant improvements in the performance of supercapacitor electrodes based on 2D MnO2 nanosheets by the addition of carbon nanotubes. Electrodes based on MnO2 nanosheets do not display high areal capacitance because the electrical properties of such films are poor, limiting the transport of charge between redox sites and the external circuit. In addition, the mechanical strength is low, limiting the achievable electrode thickness, even in the presence of binders. By adding carbon nanotubes to the MnO2-based electrodes, we have increased the conductivity by up to eight orders of magnitude in line with percolation theory. The nanotube network facilitates charge transport, resulting in large increases in capacitance, especially at high rates around 1 V/s. The increase in MnO2 specific capacitance scaled with nanotube content in a manner fully consistent with percolation theory. Importantly, the mechanical robustness was significantly enhanced, allowing the fabrication of electrodes that were 10 times thicker than could be achieved in MnO2-only films. This resulted in composite films with areal capacitances up to 40 times higher than could be achieved with MnO2-only electrodes.
    ACS Nano 09/2014;
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    ABSTRACT: The rise of solution-processed electronics, together with their processing methods and materials, provides unique opportunities to achieve low-cost and low-temperature roll-to-roll printing of non-Si based devices. Here, we demonstrate a wafer-scale direct light patterned, fully transparent, all-solution-processed, and layer-by-layer-integrated electronic device. The deep ultraviolet irradiation of specially designed metal oxide gel films can generate fine-patterned shapes ~3 μm, which easily manifest their intrinsic properties at low temperature annealing. This direct light patterning can be easily applied to the 4˝ wafer scale and diverse pattern shapes, and provides feasibility for integrated circuit applications through the penetration of deep ultraviolet on the quartz mask. With this approach, we successfully fabricate all-oxide based high-performance transparent thin-film transistors on flexible polymer substrates.
    ACS Nano 09/2014;
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    ABSTRACT: The structurally tunable two-dimensional (2D) arrays of nanoscale objects are important for modulating functional responses of thin films. We demonstrate that such tunable and ordered nanoparticles (NP) arrays can be assembled at the charged air-water interface from nanoparticles coated with polyelectrolyte chains, DNA. The electrostatic attraction between the negatively charged non-hybridizing DNA-coated gold NPs and a positively charged lipid layer at the interface facilitates the formation of a 2D hexagonally closed packed (HCP) nanoparticle lattice. We observed about fourfold change of the monolayer nanoparticle density by varying the ionic strength of the subphase. The tunable NP arrays retain their structure reasonably when transferred to a solid support. The influence of particle's DNA corona and lipid layer composition on the salt-induced in-plane and normal structural evolution of NP arrays were studied in detail using a combination of synchrotron-based in-situ surface scattering methods, grazing incidence x-ray scattering (GISAXS) and x-ray reflectivity (XRR). Comparative analysis of the interparticle distances as function of ionic strength reveals the difference between the studied 2D nanoparticle arrays and analogous bulk polyelectrolyte star polymers systems, typically described by Daoud-Cotton model and power law scaling. The observed behavior of the 2D nanoparticle array manifests a non-uniform deformation of the nanoparticle DNA corona due to its electrostatically induced confinement at the lipid interface. The presented study provides insight on the interfacial properties of the NP with charged soft shells.
    ACS Nano 09/2014;
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    ABSTRACT: Antisense oligonucleotides can be employed as a potential approach to effectively treat cancer. However, the inherent instability and inefficient systemic delivery methods for antisense therapeutics remain major challenges to their clinical application. Here, we present a polymerized oligonucleotides (ODNs) that self-assemble during their formation through an enzymatic elongation method (rolling circle replication) to generate a composite nucleic acid/magnesium pyrophosphate sponge-like microstructure, or DNA microsponge, yielding high molecular weight nucleic acid product. In addition, this densely-packed ODN microsponge structure can be further condensed to generate polyelectrolyte complexes with a favorable size for cellular uptake by displacing magnesium pyrophosphate crystals from the microsponge structure. Additional layers are applied to generate a blood-stable and multifunctional nanoparticle via the Layer-by-Layer (LbL) assembly technique. By taking advantage of DNA nanotechnology and LbL assembly, functionalized DNA nanostructures were utilized to provide extremely high numbers of repeated ODN copies for efficient antisense therapy. Moreover, we show that this formulation significantly improves nucleic acid drug/carrier stability during in vivo biodistribution. These polymeric ODN systems can be designed to serve as a potent means of delivering stable and large quantities of ODN therapeutics systemically for cancer treatment to tumor cells at significantly lower toxicity than traditional synthetic vectors, thus enabling a therapeutic window suitable for clinical translation.
    ACS Nano 09/2014;
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    ABSTRACT: A three-dimensional nanoporous Ni(OH)2 thin-film was hydrothermally converted from an anodically formed porous layer of nickel fluoride/oxide. The nanoporous Ni(OH)2 thin-films can be used as additive-free electrodes for energy storage. The nanoporous layer delivers a high capacitance of 1765 F g(-1) under three electrode testing. After assembly with porous activated carbon in asymmetric supercapacitor configurations, the devices deliver superior supercapacitive performances with capacitances of 192 F g(-1), energy densities of 68 Wh kg(-1) and power density of 44 kW kg(-1). The wide working potential window (up to 1.6 V in 6 M aq KOH) and stable cyclability (~ 90% capacitance retention over 10000 cycles) make the thin-film ideal for practical supercapacitor devices.
    ACS Nano 09/2014;
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    ABSTRACT: In this work we use Raman spectroscopy as a non-destructive and rapid technique for probing the Van der Waals (VdW) forces acting between two atomically thin crystals, where one is a transition metal dichalcogenide (TMDC). In this work, MoS2 is used as a Raman probe: we show that its two Raman active phonon modes can provide information on the interaction between the two crystals. In particular, the in-plane vibration (E2g) provides information on the in-plane strain, while the out-of-plane mode (A1g) gives evidence for the quality of the interfacial contact. We show that a VdW contact with MoS2 is characterized by a blue shift of +2 cm-1 of the A1g peak. In the case of a MoS2 /graphene heterostructure, the VdW contact is also characterized by a shift of +14 cm-1 of the 2D peak of graphene. Our approach offers a very simple, non-destructive and fast method to characterize the quality of the interface of heterostructures containing atomically thick TMDCs crystals.
    ACS Nano 09/2014;

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