George C. Schatz

Northwestern University, Evanston, Illinois, United States

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Publications (762)3846.18 Total impact

  • Michael B Ross, George C Schatz
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    ABSTRACT: We explore localized surface plasmon resonances in small (5–30 nm radius) aluminum and silver nanoparticles using classical electrodynamics simulations, focusing on radiative (far-field scattering) effects and the unique characteristics of aluminum as a plasmonic material. In Al spheres, higher-order plasmon resonances (e.g. quadrupoles) are significant at smaller sizes (>15 nm) than in Ag spheres. Additionally, although the plasmon width is minimized at a radius of about 15 nm for both materials, the Al plasmon linewidth (~1.4 eV) for the dipole mode is much larger than that observed in Ag (~0.3 eV). The radiative contribution to damping dominates over non-radiative effects for small (5–20 nm) Al spheres (>95%) whereas for similar size Ag spheres damping is almost entirely attributed to the bulk dielectric function (non-radiative). For Al nanorods the linewidths can be narrowed by increasing aspect ratio such that for an aspect ratio of 4.5, the overall Al (0.75 eV) linewidth is reasonably close to that of the same size Ag rod (0.35 eV). This narrowing arises from frequency dispersion in the real part of the Al dielectric function, and is associated with a 65% (1.5 to 0.5 eV) decrease in the radiative contribution to the linewidth for Al. Concurrently, an increase in the non-radiative width occurs as the aspect ratio increases and the plasmon tunes to the red. This demonstrates that anisotropy can be used as a parameter for controlling Al plasmon dephasing where the composition of the plasmon linewidth (radiative or non-radiative) can be tailored with aspect ratio. Overall, these data suggest that localized surface plasmon resonance dephasing mechanisms in Al nanostructures are inherently different from those in the noble metals, which could allow for new applications of plasmonic materials, tunable plasmon lifetimes, and new physics to be observed.
    Journal of Physics D Applied Physics 05/2015; 48(18). DOI:10.1088/0022-3727/48/18/184004 · 2.52 Impact Factor
  • Montacer Dridi, George C. Schatz
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    ABSTRACT: We study the effect of nanoparticle (NP) array spacing on plasmon-enhanced lasing using a computational model that combines classical electrodynamics for arrays of gold NPs interacting with a four-level model of the laser dye photophysics. Parameters of the model are related to a laser system that was recently demonstrated experimentally, but in this work we consider arrays that tune away from the lattice plasmon resonance condition. We show that approximate matching of the lattice plasmon with the red branch of the dye emission spectrum leads to lower laser thresholds and higher intensities than can be achieved with plasmon excitation that does not satisfy the Bragg condition, even for anisotropic NPs. Surprisingly, there is a range of lattice spacings where both purely photonic enhancement of the bulk dye simulated emission and mixed photonic/plasmonic enhancement of emission by dye molecules within 50 nm of the NPs have comparable laser thresholds and intensities above threshold. We also show there is a tradeoff between sharpness of the lattice plasmon and overlap of the lattice mode with the dye emission maximum such that the highest intensity modes are not necessarily those with the highest plasmon enhancement.
    Journal of the Optical Society of America B 05/2015; 32(5). DOI:10.1364/JOSAB.32.000818 · 1.81 Impact Factor
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    ABSTRACT: The nanoscale manipulation of matter allows properties to be created in a material that would be difficult or even impossible to achieve in the bulk state. Progress towards such functional nanoscale architectures requires the development of methods to precisely locate nanoscale objects in three dimensions and for the formation of rigorous structure-function relationships across multiple size regimes (beginning from the nanoscale). Here, we use DNA as a programmable ligand to show that two- and three-dimensional mesoscale superlattice crystals with precisely engineered optical properties can be assembled from the bottom up. The superlattices can transition from exhibiting the properties of the constituent plasmonic nanoparticles to adopting the photonic properties defined by the mesoscale crystal (here a rhombic dodecahedron) by controlling the spacing between the gold nanoparticle building blocks. Furthermore, we develop a generally applicable theoretical framework that illustrates how crystal habit can be a design consideration for controlling far-field extinction and light confinement in plasmonic metamaterial superlattices.
    Nature Nanotechnology 04/2015; DOI:10.1038/nnano.2015.68 · 33.27 Impact Factor
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    ABSTRACT: A novel method for preparing conformal silica-embedded crystalline nanoparticle sheets via DNA programmable assembly provides independent control over nanoparticle size, nanoparticle spacing, and film thickness. The conformal materials retain the nanoparticle crystallinity and spacing after being transferred to flat or highly curved substrates even after being subjected to various mechanical, physical, and chemical stimuli. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    Advanced Materials 04/2015; DOI:10.1002/adma.201500858 · 15.41 Impact Factor
  • SPIENewsroom 04/2015; DOI:10.1117/2.1201503.005823
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    ABSTRACT: DNA-based molecular electronics will require charges to be transported from one site within a 2D or 3D architecture to another. While this has been shown previously in linear, π-stacked DNA sequences, the dynamics and efficiency of charge transport across a DNA three-way junction (3WJ) have yet to be determined. Here, we present an investigation of hole transport and trapping across a DNA-based three-way junction systems by a combination of femtosecond transient absorption spectroscopy and molecular dynamics simulations. Hole transport across the junction is proposed to be gated by conformational fluctuations in the ground state which bring the transiently-populated hole carrier nucleobases into better aligned geometries on the nanosecond timescale, thus modulating the - electronic coupling along the base pair sequence.
    Journal of the American Chemical Society 03/2015; DOI:10.1021/jacs.5b00931 · 11.44 Impact Factor
  • Prashant Kamat, George C Schatz
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    ABSTRACT: The hybridization of free oligonucleotides to densely packed, oriented arrays of DNA modifying the surfaces of spherical nucleic acid (SNA)-gold nanoparticle conjugates occurs with negative cooperativity; i.e., each binding event destabilizes subsequent binding events. DNA hybridization is thus an ever-changing function of the number of strands already hybridized to the particle. Thermodynamic quantification of this behavior reveals a 3 orders of magnitude decrease in the binding constant for the capture of a free oligonucleotide by an SNA conjugate as the fraction of pre-hybridized strands increases from 0 to ∼30%. Increasing the number of pre-hybridized strands imparts an increasing enthalpic penalty to hybridization that makes binding more difficult, while simultaneously decreasing the entropic penalty to hybridization, which makes binding more favorable. Hybridization of free DNA to an SNA is thus governed by both an electrostatic barrier as the SNA accumulates charge with additional binding events and an effect consistent with allostery, where hybridization at certain sites on an SNA modify the binding affinity at a distal site through conformational changes to the remaining single strands. Leveraging these insights allows for the design of conjugates that hybridize free strands with significantly higher efficiencies, some of which approach 100%.
    Journal of the American Chemical Society 03/2015; DOI:10.1021/jacs.5b00670 · 11.44 Impact Factor
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    ABSTRACT: We report that in the red light-absorbing (Pr) state, the bilin chromophore of the Deinococcus radiodurans proteobacterial phytochrome (DrBphP) is hyper-sensitive to X-ray photons used in typical synchrotron X-ray protein crystallography experiments. This caused the otherwise fully protonated chromophore to deprotonate without additional major structural changes. These results have major implications for our understanding of the structural and chemical characteristics of the resting and intermediate states of phytochromes and other photoreceptor proteins.
    Journal of the American Chemical Society 02/2015; DOI:10.1021/ja510923m · 11.44 Impact Factor
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    Journal of Physical Chemistry Letters 01/2015; 6(2):251-255. DOI:10.1021/jz502648y · 6.69 Impact Factor
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    ABSTRACT: Herein, we report the synthesis of structurally uniform gold circular disks as two-dimensional plasmonic nanostructures that complement the well-established one-dimensional rod and three-dimensional shell structures. We show that a Au conproportionation reaction can be used to etch a collection of nonuniform triangular prisms into a uniform circular disk product with thickness and diameter varying <10%. These new particles have broadly tunable plasmon resonances (650-1000 nm) with narrow bandwidths (0.23-0.28 eV) and can be described as "effectively two-dimensional" plasmonic structures, as they do not support a significant transverse mode.
    Nano Letters 01/2015; 15(2). DOI:10.1021/nl5038566 · 12.94 Impact Factor
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    ABSTRACT: Plasmon lasers can support ultrasmall mode confinement and ultrafast dynamics with device feature sizes below the diffraction limit. However, most plasmon-based nanolasers rely on solid gain materials (inorganic semiconducting nanowire or organic dye in a solid matrix) that preclude the possibility of dynamic tuning. Here we report an approach to achieve real-time, tunable lattice plasmon lasing based on arrays of gold nanoparticles and liquid gain materials. Optically pumped arrays of gold nanoparticles surrounded by liquid dye molecules exhibit lasing emission that can be tuned as a function of the dielectric environment. Wavelength-dependent time-resolved experiments show distinct lifetime characteristics below and above the lasing threshold. By integrating gold nanoparticle arrays within microfluidic channels and flowing in liquid gain materials with different refractive indices, we achieve dynamic tuning of the plasmon lasing wavelength. Tunable lattice plasmon lasers offer prospects to enhance and detect weak physical and chemical processes on the nanoscale in real time.
    Nature Communications 01/2015; 6:6939. DOI:10.1038/ncomms7939 · 10.74 Impact Factor
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    ABSTRACT: Three-dimensional dielectric photonic crystals have well-established enhanced light–matter interactions via high Q factors. Their plasmonic counterparts based on arrays of nanoparticles, however, have not been experimentally well explored owing to a lack of available synthetic routes for preparing them. However, such structures should facilitate these interactions based on the small mode volumes associated with plasmonic polarization. Herein we report strong light-plasmon interactions within 3D plasmonic photonic crystals that have lattice constants and nanoparticle diameters that can be independently controlled in the deep subwavelength size regime by using a DNA-programmable assembly technique. The strong coupling within such crystals is probed with backscattering spectra, and the mode splitting (0.10 and 0.24 eV) is defined based on dispersion diagrams. Numerical simulations predict that the crystal photonic modes (Fabry–Perot modes) can be enhanced by coating the crystals with a silver layer, achi
  • Yang Yang, Mark A. Ratner, George C. Schatz
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    ABSTRACT: We have used multiconfigurational (MC) and multireference (MR) methods (CASSCF, CASPT2, and MRCI) to study d-d transitions and other optical excitations for octahedral [M(H2O)6]n+ clusters (M = Ti, V, Mn, Cr, Fe, Co, Ni, Cu) as models of hematite and other transition-metal oxides of interest in solar fuels. For [Fe(H2O)6]3+, all calculations substantially overestimate the d-d transition energies (∼3.0 versus ∼1.5 eV) compared to what has been experimentally assigned. This problem occurs even though theory accurately describes (1) the lowest d-d transition energy in the atomic ion Fe3+ (∼4.4 eV), (2) the t2g-eg splitting (∼1.4 eV) in [Fe(H2O)6]3+, and (3) the ligand-to-metal charge transfer (LMCT) energy in [Fe(H2O)6]3+. Indeed, the results for Fe3+ and the t2g-eg splitting suggest that the lowest d-d excitation energy in the hexa-aqua complex should be ∼3 eV (or slightly below because of Jahn-Teller stabilization), as we find. Possible origins for the d-d discrepancy are examined, including Fe2+ and low-spin Fe3+ impurities. For the [M(H2O)6]n+ clusters not involving Fe(III), our MR calculations show reasonable correlation (mostly within 0.5 eV) with experiments for the d-d transitions, including consistent trends for the intensities of spin-allowed and spin-forbidden transitions. Our calculations also greatly complement experimental data because (1) experimental results for some species are insufficient or even scarce, (2) some of the experimental peaks were not observed directly but were inferred, and (3) the nature or existence of some shoulder peaks and weak peaks is uncertain. Our MR calculations have also been used to study convergence of the results with choice of active space, including the importance of the “double shell” effect in which there are 10 active d orbitals per transition-metal atom rather than 5. The results show that the larger active space does not significantly change the excitation energy, although it lowers the absolute energies for complexes with high 3d occupations. This indicates that reasonable accuracy can be achieved using MR methods in studies of transition-metal oxide clusters using minimal active spaces. This study establishes fundamental principles for the further modeling of larger cluster models of pure and doped hematite and other metal oxides.
    The Journal of Physical Chemistry C 12/2014; 118(50):29196-29208. DOI:10.1021/jp5052672 · 4.84 Impact Factor
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    ABSTRACT: Using on-wire lithography to synthesize well-defined nanorod dimers and trimers, we report a systematic study of the plasmon coupling properties of such materials. By comparing the dimer/trimer structures to discrete nanorods of the same overall length, we demonstrate many similarities between antibonding coupled modes in the dimers/trimers and higher-order resonances in the discrete nanorods. These conclusions are validated with a combination of discrete dipole approximation and finite-difference time-domain calculations and lead to the observation of antibonding modes in symmetric structures by measuring their solution-dispersed extinction spectra. Finally, we probe the effects of asymmetry and gap size on the occurrence of these modes and demonstrate that the delocalized nature of the antibonding modes lead to longer-range coupling compared to the stronger bonding modes.
    Nano Letters 11/2014; DOI:10.1021/nl503207j · 12.94 Impact Factor
  • Journal of Physical Chemistry Letters 10/2014; 5(20):3519. DOI:10.1021/jz502010v · 6.69 Impact Factor
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    ABSTRACT: Here, we examine ultrafast photoluminescence produced from plasma-grown, colloidal silicon nanocrystals as a function of both particle size and lattice crystallinity. In particular, we quantify the decay time and spectral profiles of nominally few-picosecond direct-gap emission previously attributed to phononless electron-hole recombination. We find that the high-energy (400-600 nm, 2-3 eV) photoluminescence component consists of two decay processes with distinct time scales. The fastest photoluminescence exhibits an similar to 30 ps decay constant largely independent of emission energy and particle size. Importantly, nearly identical temporal components and blue spectral features appear for amorphous particles. We thus associate high-energy, rapid emission with an amorphous component in all measured samples, as supported by Raman analysis and molecular dynamics simulation. Based on these observations, we advise that the observed dynamics proceed too slowly to originate from intraband carrier thermalization and instead suggest a nonradiative origin associated with the amorphous component.
    10/2014; 1(10):960-967. DOI:10.1021/ph500145p

Publication Stats

35k Citations
3,846.18 Total Impact Points

Institutions

  • 1977–2015
    • Northwestern University
      • • Department of Chemistry
      • • Nanofabrication and Molecular Self-Assembly Center
      Evanston, Illinois, United States
    • Massachusetts Institute of Technology
      • Department of Chemistry
      Cambridge, MA, United States
  • 2011–2013
    • University of Maryland, College Park
      • Department of Chemistry and Biochemistry
      College Park, MD, United States
  • 1986–2011
    • The University of Manchester
      • School of Chemistry
      Manchester, England, United Kingdom
  • 1980–2009
    • Argonne National Laboratory
      • Center for Nanoscale Materials
      Lemont, Illinois, United States
  • 1992–2008
    • Northwest University
      Evanston, Illinois, United States
  • 2007
    • Max Planck Institute for Biophysical Chemistry
      Göttingen, Lower Saxony, Germany
    • Universität Konstanz
      Constance, Baden-Württemberg, Germany
  • 2006
    • National Cheng Kung University
      • Institute of Electro-Optical Science and Engineering
      臺南市, Taiwan, Taiwan
  • 2005–2006
    • University of South Carolina
      • Chemistry and Biochemistry
      Columbia, SC, United States
    • National Academy of Sciences of Ukraine
      Kievo, Kyiv City, Ukraine
  • 1983–2006
    • Stanford University
      • Department of Chemistry
      Stanford, CA, United States
  • 1993–2004
    • Hungarian Academy of Sciences
      Budapeŝto, Budapest, Hungary
    • NASA
      Вашингтон, West Virginia, United States
  • 1998
    • Hebrew University of Jerusalem
      Yerushalayim, Jerusalem, Israel
  • 1989
    • University of Colorado at Boulder
      Boulder, Colorado, United States
  • 1974–1976
    • California Institute of Technology
      • Arthur Amos Noyes Laboratory of Chemical Physics
      Pasadena, CA, United States