Song Jin

University of Wisconsin–Madison, Madison, Wisconsin, United States

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Publications (107)1147.95 Total impact

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    ABSTRACT: Porous materials are of particular interest due to their high surface area and rich edge sites, which are favorable for applications such as catalysis. Although there are well-established strategies for synthesizing porous metal oxides (e.g., by annealing the corresponding metal hydroxides), facile and scalable routes to porous metal hydroxides and metal chalcogenides are lacking. Here, we report a simple and general strategy to synthesize porous nanosheets of metal hydroxides by selectively etching layered double hydroxide (LDH) nanoplate precursors that contain amphoteric metal and to further convert them into porous metal chalcogenides by a solution method. Using NiGa LDH as an example, we show that the thin nanoplates with high surface accessibility facilitate the topotactic conversion of NiGa LDH to β-Ni(OH) 2 and further to NiSe 2 with porous texture while preserving the sheet-like morphology. The converted β-Ni(OH) 2 and NiSe 2 are highly active for electrocatalytic oxygen evolution reaction and hydrogen evolution reaction (HER), respectively, which demonstrates the applications of such high surface area porous nanostructures with rich edge sites. Particularly, the porous NiSe 2 nanosheets exhibited excellent catalytic activity toward HER with low onset overpotential, small Tafel slope, and good stability under both acidic and alkaline conditions. Overall electrochemical water splitting experiments using these porous β-Ni(OH) 2 and NiSe 2 nanosheets were further demonstrated. Our work presents a new strategy to prepare porous nanomaterials and to further enhance their catalytic and other applications. ■ INTRODUCTION Porous nanomaterials have found many applications in energy conversion and storage, catalysis, and drug delivery because of their high surface area, rich edge sites, and generally good strain accommodation. 1−3 The common route to fabricate porous nanostructures involves the use of hard templates, such as anodic aluminum oxide, mesoporous silica and carbon, or soft templates such as surfactants. 4,5 Despite the wide adoption, templated syntheses require selective removal of the templates and often suffer from tedious procedures. 5 Alternatively, thermal decomposition of precursor materials (e.g., metal hydroxides) can be an efficient route to introduce pores when water or other volatile species leave the solid precursors, 6−11 but this approach is generally limited to the preparation of metal oxides, while the facile and scalable preparation of other porous nanomaterials, such as metal hydroxides and metal chalcogenides, is more difficult and highly desired. We suggest that layered double hydroxides (LDHs) 12 can serve as versatile precursors for porous nanomaterials of other metal compounds. LDHs are a class of two-dimensional (2D) materials with unique structure consisting of metal hydroxide layers and inorganic/organic gallery anions/molecules. 12−16 The general form ula of LDHs can be expressed as [M II 1−x M III x (OH) 2 ] x+ (A n‑) x/n ·mH 2 O, where M II (M = Mn, Fe, Co, Ni, Cu, Zn, etc.) and M III (M = Al, Ga, Ti, Cr, Fe, Co, etc.) are di-and trivalent metal cations, respectively, and A n− is a charge-balancing anion intercalated between the brucite-like metal hydroxide layers. The easily tailored properties, composition versatility, and low cost of LDHs have led to surging interest in these materials and many applications, such as adsorption, 16,17 photochemistry, 14,18,19 and electrocatalysis. 20−24 Moreover, LDHs can be readily synthesized in aqueous solutions and can serve as versatile precursors to produce a variety of porous (mixed) metal oxides. 8,14 In this work, we describe an off-the-beaten-path strategy by selectively etching nanoplates of LDH precursors that contain amphoteric metals (e.g., Ga, Al) to prepare porous nanosheets of metal hydroxides with layered
    Chemistry of Materials 09/2015; 2015(27):5702-5711. DOI:10.1021/acs.chemmater.5b02177 · 8.54 Impact Factor
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    ABSTRACT: Supplementary information available for this article at http://www.nature.com/ncomms/2015/150420/ncomms7883/suppinfo/ncomms7883_S1.html
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    ABSTRACT: In situ techniques with high temporal, spatial and chemical resolution are key to understand ubiquitous solid-state phase transformations, which are crucial to many technological applications. Hard X-ray spectro-imaging can visualize electrochemically driven phase transformations but demands considerably large samples with strong absorption signal so far. Here we show a conceptually new data analysis method to enable operando visualization of mechanistically relevant weakly absorbing samples at the nanoscale and study electrochemical reaction dynamics of iron fluoride, a promising high-capacity conversion cathode material. In two specially designed samples with distinctive microstructure and porosity, we observe homogeneous phase transformations during both discharge and charge, faster and more complete Li-storage occurring in porous polycrystalline iron fluoride, and further, incomplete charge reaction following a pathway different from conventional belief. These mechanistic insights provide guidelines for designing better conversion cathode materials to realize the promise of high-capacity lithium-ion batteries.
    Nature Communications 04/2015; 6:6883. DOI:10.1038/ncomms7883 · 10.74 Impact Factor
  • Nature Communications 04/2015; 6. · 10.74 Impact Factor
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    ABSTRACT: Supplementary information available for this article at http://www.nature.com/ncomms/2015/150420/ncomms7883/suppinfo/ncomms7883_S1.html
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    ABSTRACT: Magnetic skyrmions are topologically stable whirlpool-like spin textures that offer great promise as information carriers for future ultra-dense memory and logic devices1-4. To enable such applications, particular attention has been focused on the skyrmions properties in highly confined geometry such as one dimensional nanowires5-8. Hitherto it is still experimentally unclear what happens when the width of the nanowire is comparable to that of a single skyrmion. Here we report the experimental demonstration of such scheme, where magnetic field-driven skyrmion cluster (SC) states with small numbers of skyrmions were demonstrated to exist on the cross-sections of ultra-narrow single-crystal MnSi nanowires (NWs) with diameters, comparable to the skyrmion lattice constant (18 nm). In contrast to the skyrmion lattice in bulk MnSi samples, the skyrmion clusters lead to anomalous magnetoresistance (MR) behavior measured under magnetic field parallel to the NW long axis, where quantized jumps in MR are observed and directly associated with the change of the skyrmion number in the cluster, which is supported by Monte Carlo simulations. These jumps show the key difference between the clustering and crystalline states of skyrmions, and lay a solid foundation to realize skyrmion-based memory devices that the number of skyrmions can be counted via conventional electrical measurements.
    Nature Communications 04/2015; 6. DOI:10.1038/ncomms8637 · 10.74 Impact Factor
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    ABSTRACT: A variety of crystals contain quasi-one-dimensional substructures, which yield distinctive electronic, spintronic, optical and thermoelectric properties. There is a lack of understanding of the lattice dynamics that influences the properties of such complex crystals. Here we employ inelastic neutron scatting measurements and density functional theory calculations to show that numerous low-energy optical vibrational modes exist in higher manganese silicides, an example of such crystals. These optical modes, including unusually low-frequency twisting motions of the Si ladders inside the Mn chimneys, provide a large phase space for scattering acoustic phonons. A hybrid phonon and diffuson model is proposed to explain the low and anisotropic thermal conductivity of higher manganese silicides and to evaluate nanostructuring as an approach to further suppress the thermal conductivity and enhance the thermoelectric energy conversion efficiency. This discovery offers new insights into the structure-property relationships of a broad class of materials with quasi-one-dimensional substructures for various applications.
    Nature Communications 04/2015; 6:6723. DOI:10.1038/ncomms7723 · 10.74 Impact Factor
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    ABSTRACT: Understanding crystal growth and improving material quality is important for improving semiconductors for electronic, optoelectronic, and photovoltaic applications. Amidst the surging interest in solar cells based on hybrid organic-inorganic lead halide perovskites and the exciting progress in device performance, improved understanding and better control of the crystal growth of these perovskites could further boost their optoelectronic and photovoltaic performance. Here, we report new insights on the crystal growth of the perovskite materials, especially crystalline nanostructures. Specifically, single crystal nanowires, nanorods, and nanoplates of methylammonium lead halide perovskites (CH3NH3PbI3 and CH3NH3PbBr3) are successfully grown via a dissolution-recrystallization pathway in a solution synthesis from lead iodide (or lead acetate) films coated on substrates. These single crystal nanostructures display strong room-temperature photoluminescence and long carrier lifetime. We also report that a solid-liquid interfacial conversion reaction can create a highly crystalline, nanostructured MAPbI3 film with micrometer grain size and high surface coverage which enables photovoltaic devices with a power conversion efficiency of 10.6%. These results suggest that single-crystal perovskite nanostructures provide improved photophysical properties that are important for fundamental studies and future applications in nanoscale optoelectronic and photonic devices.
    Journal of the American Chemical Society 04/2015; 137(17). DOI:10.1021/jacs.5b02651 · 11.44 Impact Factor
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    ABSTRACT: Layered double hydroxides (LDHs) are a family of two-dimensional (2D) materials with layered crystal structures that have found many applications. Common strategies to synthesize LDHs lead to a wide variety of morphologies, from discrete 2D nanosheets to nanoflowers. Here we report a study of carefully controlled LDH nanoplate syntheses using zinc aluminum (ZnAl) and cobalt aluminum (CoAl) LDHs as examples, and reveal their crystal growth to be driven by screw dislocations. By controlling and maintaining a low precursor supersaturation using a continuous flow reactor, individual LDH nanoplates with well-defined morphologies were synthesized on alumina-coated substrates, instead of the nanoflowers that result from uncontrolled overgrowth. The dislocation-driven growth was further established for LDH nanoplates directly synthesized using the respective metal salt precursors. Atomic force microscopy revealed screw dislocation growth spirals, and under transmission electron microscopy thin CoAl LDH nanoplates displayed complex contrast contours indicative of strong lattice strain caused by dislocations. These results suggest the dislocation-driven mechanism is generally responsible for the growth of 2D LDH nanostructures, and likely other materials with layered crystal structures, which could help the rational synthesis of well-defined 2D nanomaterials with improved properties.
    Nano Letters 04/2015; 15(5). DOI:10.1021/acs.nanolett.5b00758 · 13.59 Impact Factor
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    ABSTRACT: To address the complexity of proteome in mass spectrometry (MS)-based top-down proteomics, multi-dimensional liquid chromatography (MDLC) strategies that can effectively separate proteins with high resolution and automation are highly desirable. Although various MDLC methods that can effectively separate peptides from protein digests exist, very few MDLC strategies, primarily consisting of 2DLC, are available for intact protein separation, which is insufficient to address the proteome complexity. We recently demonstrated that hydrophobic interaction chromatography (HIC) utilizing a MS-compatible salt can provide high-resolution separation of intact proteins for top-down proteomics. Herein, we have developed a novel 3DLC strategy by coupling HIC with ion exchange chromatography (IEC) and reverse phase chromatography (RPC) for intact protein separation. We demonstrated that a 3D (IEC-HIC-RPC) approach greatly outperformed the conventional 2D IEC-RPC approach. For the same IEC fraction (out of 35 fractions) from a crude HEK 293 cell lysate, a total of 640 proteins were identified in the 3D approach (corresponding to 201 non-redundant proteins) as compared to 47 in the 2D approach, whereas simply prolonging the gradients in RPC in the 2D approach only led to minimal improvement in protein separation and identifications. Therefore this novel 3DLC method has great potential for effective separation of intact proteins to achieve deep proteome coverage in top-down proteomics.
    Analytical Chemistry 04/2015; 87(10). DOI:10.1021/acs.analchem.5b00657 · 5.83 Impact Factor
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    ABSTRACT: The remarkable performance of lead halide perovskites in solar cells can be attributed to the long carrier lifetimes and low non-radiative recombination rates, the same physical properties that are ideal for semiconductor lasers. Here, we show room-temperature and wavelength-tunable lasing from single-crystal lead halide perovskite nanowires with very low lasing thresholds (220 nJ cm(-2)) and high quality factors (Q ∼ 3,600). The lasing threshold corresponds to a charge carrier density as low as 1.5 × 10(16) cm(-3). Kinetic analysis based on time-resolved fluorescence reveals little charge carrier trapping in these single-crystal nanowires and gives estimated lasing quantum yields approaching 100%. Such lasing performance, coupled with the facile solution growth of single-crystal nanowires and the broad stoichiometry-dependent tunability of emission colour, makes lead halide perovskites ideal materials for the development of nanophotonics, in parallel with the rapid development in photovoltaics from the same materials.
    Nature Material 04/2015; DOI:10.1038/nmat4271 · 36.43 Impact Factor
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    ABSTRACT: Resurgent interest in iron pyrite (FeS2) as an earth-abundant, non-toxic semiconductor for solar applications has resulted in many attempts to grow phase-pure thin films via chemical vapor deposition (CVD). However, all thin films grown via CVD or sulfidation to date have contained marcasite phase or other iron sulfide impurities. Here, we report the use of metallic cobalt pyrite (cattierite, CoS2) thin films as an ideal substrate leading to the first direct growth of phase-pure iron pyrite thin films via atmospheric pressure CVD. This synthesis was achieved by reacting FeCl3 and di-tert butyl disulfide (TBDS) at 400-450 oC. The products were confirmed as phase-pure iron pyrite using X-ray diffraction (XRD), Raman spectroscopy, and energy dispersive X-ray spectroscopy (EDS). In addition to phase purity, the synthesis produced crystal domains >1 μm and a conformal coating 3-5 μm thick, which are attributed to the <2% lattice mismatch of the isostructural cattierite substrate. The surface was characterized by Ultraviolet and X-ray photoelectron spectroscopy (UPS & XPS) and the electrical properties by electrochemical impedance spectroscopy (EIS) and Mott-Schottky analysis. The direct growth of a phase-pure iron pyrite film on a conductive substrate provides the most convenient configuration so far for potential solar cells.
    Chemistry of Materials 04/2015; 27(8):150408161512006. DOI:10.1021/acs.chemmater.5b00664 · 8.54 Impact Factor
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    ABSTRACT: Skyrmions, novel topologically stable spin vortices, hold promise for next-generation magnetic storage due to their nanoscale domains to enable high information storage density and their low threshold for current-driven motion to enable ultralow energy consumption. One-dimensional (1D) nanowires are ideal hosts for skyrmions since they not only serve as a natural platform for magnetic racetrack memory devices but also can potentially stabilize skyrmions. Here we use the topological Hall effect (THE) to study the phase stability and current-driven dynamics of the skyrmions in MnSi nanowires. The THE was observed in an extended magnetic field-temperature window (15 to 30 K), suggesting stabilization of skyrmion phase in nanowires compared with the bulk (27 to 29.5 K). Furthermore, for the first time, we study skyrmion dynamics in this extended skyrmion phase region and found that under the high current-density of $10^{8}-10^{9} Am^{-2}$ enabled by nanowire geometry, the THE decreases with increasing current densities, which demonstrates the current-driven motion of skyrmions generating the emergent electric field. These results open up the exploration of nanowires as an attractive platform for investigating skyrmion physics in 1D systems and exploiting skyrmions in magnetic storage concepts.
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    ABSTRACT: Analysis of protein phosphorylation remains a significant challenge due to the low abundance of phosphoproteins and the low stoichiometry of phosphorylation, which requires effective enrichment of phosphoproteins. Here we have developed superparamagnetic nanoparticles (NPs) whose surface is functionalized by multivalent ligand molecules that specifically bind to the phosphate groups on any phosphoproteins. These NPs enrich phosphoproteins from complex cell and tissue lysates with high specificity as confirmed by SDS-PAGE analysis with a phosphoprotein-specific stain and mass spectrometry analysis of the enriched phosphoproteins. This method enables universal and effective capture, enrichment, and detection of intact phosphoproteins towards a comprehensive analysis of the phosphoproteome.
    Journal of the American Chemical Society 02/2015; 137(7). DOI:10.1021/ja511833y · 11.44 Impact Factor
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    ABSTRACT: We report the controlled synthesis of NiCo layered double hydroxide (LDH) nanoplates using a newly developed high temperature high pressure hydrothermal continuous flow reactor (HCFR), which enables direct growth onto conductive substrates in high yield, and most importantly better control of the precursor supersaturation and thus nanostructure morphology and size. The solution coordination chemistry of metal-ammonia complexes was utilized to synthesize well-defined NiCo LDH nanoplates directly in a single step without topochemical oxidation. The as-grown NiCo LDH nanoplates exhibit a high catalytic activity toward the oxygen evolution reaction (OER). By chemically exfoliating LDH nanoplates to thinner nanosheets, the catalytic activity can be further enhanced to yield an electrocatalytic current density of 10 mA cm(-2) at an overpotential of 367 mV and a Tafel slope of 40 mV dec(-1). Such enhancement could be due to the increased surface area and more exposed active sites. X-ray photoelectron spectroscopy (XPS) suggests the exfoliation also caused some changes in electronic structure. This work presents general strategies to controllably grow nanostructures of LDH and ternary oxide/hydroxides in general, and to enhance the electrocatalytic performance of layered nanostructures by exfoliation.
    Nano Letters 01/2015; 15(2). DOI:10.1021/nl504872s · 13.59 Impact Factor
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    ABSTRACT: We report amorphous MoSxCly as a high-performance electrocatalyst for both electrochemical and photoelectrochemical hydrogen generation. This novel ternary electrocatalyst is synthesized via chemical vapour deposition at temperatures lower than those typically used to grow crystalline MoS2 nanostructures and structurally characterized. The MoSxCly electrocatalysts exhibit stable and high catalytic activity toward the hydrogen evolution reaction, as evidenced by large cathodic current densities at low overpotentials and low Tafel slopes (ca. 50 mV decade-1). The electrocatalytic performance can be further enhanced through depositing MoSxCly on conducting vertical graphenes. Furthermore, MoSxCly can be directly deposited on p-type silicon photocathodes to enable efficient photoelectrochemical hydrogen evolution.
    Energy & Environmental Science 01/2015; 8(3). DOI:10.1039/C4EE03240C · 20.52 Impact Factor
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    ABSTRACT: Iron pyrite (FeS2) is considered a promising earth-abundant semiconductor for solar energy conversion with the potential to achieve terawatt-scale deployment. However, despite extensive efforts and progress the solar conversion efficiency of iron pyrite remains below 3%, primarily due to a low open circuit voltage (VOC). Here we report a comprehensive investigation on {100}-faceted n-type iron pyrite single crystals to understand its puzzling low VOC. We utilized electrical transport, optical spectroscopy, surface photovoltage, photoelectrochemical measurements in aqueous and acetonitrile electrolytes, UV and X-ray photoelectron spectroscopy, and Kelvin force microscopy to characterize the bulk and surface defect states and their influence on the semiconducting properties and solar conversion efficiency of iron pyrite single crystals. These insights were used to develop a circuit model analysis for the electrochemical impedance spectroscopy that allowed a complete characterization of the bulk and surface defect states and the construction of a detailed band energy diagram for iron pyrite crystals. A holistic evaluation revealed that the high-density of intrinsic surface states cannot satisfactorily explain the low photovoltage; instead the ionization of high-density bulk deep donor states, likely resulting from bulk sulfur vacancies, creates a non-constant charge distribution and a very narrow surface space charge region that limits the total barrier height, thus satisfactorily explains the limited photovoltage and poor photoconversion efficiency of iron pyrite single crystals. These findings lead to suggestions to improve single crystal pyrite and nanocrystalline or polycrystalline pyrite films for successful solar applications.
    Journal of the American Chemical Society 11/2014; 136(49). DOI:10.1021/ja509142w · 11.44 Impact Factor
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    ABSTRACT: Understanding semiconductor surface states is critical for their applications, but fully characterizing surface electrical properties is challenging. Such a challenge is especially crippling for semiconducting iron pyrite (FeS2), whose potential for solar energy conversion has been suggested to be held back by rich surface states. Here, by taking advantage of the high surface-to-bulk ratio in nanostructures and effective electrolyte gating, we develop a general method to fully characterize both the surface inversion and bulk electrical transport properties for the first time through electrolyte-gated Hall measurements of pyrite nanoplate devices. Our study shows that pyrite is n-type in the bulk and p-type near the surface due to strong inversion and yields the concentrations and mobilities of both bulk electrons and surface holes. Further, solutions of the Poisson equation reveal a high-density of surface holes accumulated in a 1.3 nm thick strong inversion layer and an upward band bending of 0.9-1.0 eV. This work presents a general methodology for using transport measurements of nanostructures to study both bulk and surface transport properties of semiconductors. It also suggests that high-density of surface states are present on surface of pyrite, which partially explains the universal p-type conductivity and lack of photovoltage in polycrystalline pyrite.
    Nano Letters 11/2014; 14(12). DOI:10.1021/nl501942w · 13.59 Impact Factor
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    ABSTRACT: Higher manganese silicides (HMS) made of earth-abundant and non-toxic elements are regarded as promising p-type thermoelectric materials because their complex crystal structure results in low lattice thermal conductivity. It is shown here that the already low thermal conductivity of HMS can be reduced further to approach the minimum thermal conductivity via partial substitution of Mn with heavier rhenium (Re) to increase point defect scattering. The solubility limit of Re in the obtained RexMn1-xSi1.8 is determined to be about x = 0.18. Elemental inhomogeneity and the formation of ReSi1.75 inclusions with 50−200 nm size are found within the HMS matrix. It is found that the power factor does not change markedly at low Re content of x ≤ 0.04 before it drops considerably at higher Re contents. Compared to pure HMS, the reduced lattice thermal conductivity in RexMn1-xSi1.8 results in a 25% increase of the peak figure of merit ZT to reach 0.57 ± 0.08 at 800 K for x = 0.04. The suppressed thermal conductivity in the pure RexMn1-xSi1.8 can enable further investigations of the ZT limit of this system by exploring different impurity doping strategies to optimize the carrier concentration and power factor.
    Advanced Energy Materials 10/2014; 4(14). DOI:10.1002/aenm.201400452 · 16.15 Impact Factor
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    ABSTRACT: Many materials have been explored as potential hydrogen evolution reaction (HER) electrocatalysts to generate clean hydrogen fuel via water electrolysis, but none so far compete with the highly efficient and stable (but cost prohibitive) noble metals. Similarly, noble metals often excel as electrocatalytic counter electrode materials in regenerative liquid-junction photoelectrochemical solar cells, such as quantum dot-sensitized solar cells (QDSSCs) that employ the sulfide/polysulfide redox electrolyte as the hole mediator. Here, we systematically investigate thin films of the earth-abundant pyrite-phase transition metal disulfides (FeS2, CoS2, NiS2, and their alloys) as promising alternative electrocatalysts for both the HER and polysulfide reduction. Their electrocatalytic activity toward the HER is correlated to their composition and morphology. The emergent trends in their performance suggest that cobalt plays an important role in facilitating the HER, with CoS2 exhibiting highest overall performance. Additionally, we demonstrate the high activity of the transition metal pyrites toward polysulfide reduction and highlight the particularly high intrinsic activity of NiS2, which could enable improved QDSSC performance. Furthermore, structural disorder introduced by alloying different transition metal pyrites could increase their areal density of active sites for catalysis, leading to enhanced performance.
    The Journal of Physical Chemistry C 09/2014; 118(37):21347-21356. DOI:10.1021/jp506288w · 4.77 Impact Factor