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Synthesis, characterization, and ultrafast dynamics of porphyrin- and zinc porphyrin-based nanomaterials are reported. Spherical nanoparticles composed of a group of uniform materials based on orga...

In situ second harmonic generation (SHG) coupled with extinction spectroscopy is used for real-time monitoring of seed-mediated growth dynamics of colloidal citrate-stabilized gold nanoparticles in water. The time-dependent in situ SHG results capture an early stage of the growth process where a large enhancement in the SHG signal is observed, which is attributed to the formation of plasmonic hot spots from a rough and uneven nanoparticle surface. The temporal peak in the SHG signal is followed by a decay that is fit to an exponential function to characterize the size-dependent nanoparticle growth lifetime, which varies from 0.45 to 1.7 min for final nanoparticle sizes of 66 and 94 nm, respectively. This early growth stage also corresponds to a broadening of the plasmon spectra, as monitored using time-dependent in situ extinction spectroscopy. Over the course of the seed-mediated growth reaction, the nanoparticle becomes more thermodynamically stable through surface reconstruction resulting in a smoother...

Organic/inorganic hybrid nanoscale materials possess fascinating optical, electronic, magnetic, and catalytic properties that are promising for a variety of practical applications. Such properties can be dramatically affected by the hierarchical structure and molecular organization in the nanomaterials. Herein, we employed surface-initiated Kumada catalyst-transfer polymerization to prepare hybrid materials consisting of shells of conjugated polymers (CPs)—polythiophene or poly(p-phenylene)—and their block copolymers covalently attached to the surface of silica nanoparticles. Because of the controlled chain-growth mechanism of surface-initiated polymerization, we obtained structurally well-defined CP blocks in the diblock copolymer shells, which produced distinct spectroscopic properties related to the intraparticle excitation energy transfer between the nanoscale polymer shell components, as well as the formation of interfacial exciplex states. The spectroscopic phenomena were further understood via time...

Ultrafast electron diffraction is used to probe the time-resolved dynamics in a few-layer TiSe2 sample. At normal incidence, the suppression of the Bragg diffraction peak intensities following photoexcitation displays strongly biexponential behavior. For tilted samples, changes in the diffraction peak positions reveal coherent acoustic vibrations that are dependent on the sample thickness and that further permit a calculation of the Young’s modulus. The complex room temperature lattice dynamics observed are attributed to strong electron–phonon coupling and electron–lattice equilibration processes, which support a Jahn–Teller origin of the charge density wave behavior in TiSe2. Additionally, the significant role that the related Kohn anomalies may play in the electron transport dynamics and transition mechanism of this material is emphasized. These results demonstrate the importance of strongly coupled electron–phonon dynamics in the relaxation of electronically excited room temperature TiSe2, which is exp...

Ultrafast electron diffraction is employed to spatiotemporally visualize the lattice dynamics of 11 nm-thick single-crystal and 2 nm-thick polycrystalline gold nanofilms. Surprisingly, the electron-phonon coupling rates derived from two temperature simulations of the data reveal a faster interaction between electrons and the lattice in the case of the single-crystal sample. We interpret this unexpected behavior as arising from quantum confinement of the electrons in the 2 nm-thick gold nanofilm, as supported by absorption spectra, an effect that counteracts the expected increase in the electron scattering off surfaces and grain boundaries in the polycrystalline materials.

Photon-induced near-field electron microscopy (PINEM) is a technique to produce and then image evanescent electromagnetic fields on the surfaces of nanostructures. Most previous applications of PINEM have imaged surface plasmon-polariton waves on conducting nanomaterials. Here, the application of PINEM on whole human cancer cells and membrane vesicles isolated from them is reported. We show that photons induce time-, orientation-, and polarization-dependent evanescent fields on the surfaces of A431 cancer cells and isolated membrane vesicles. Furthermore, the addition of a ligand to the major surface receptor on these cells and vesicles (epidermal growth factor receptor, EGFR) reduces the intensity of these fields in both preparations. We propose that in the absence of plasmon waves in biological samples, these evanescent fields reflect the changes in EGFR kinase domain polarization upon ligand binding.

A multiscale hybrid quantum/classical approach using classical electrodynamics and a collection of discrete three-level quantum systems is used to simulate the coupled dynamics and spectra of a malachite green monolayer adsorbed to the surface of a spherical gold nanoparticle (NP). This method utilizes finite difference time domain (FDTD) to describe the plasmonic response of the NP within the main FDTD framework and a three-level quantum description for the molecule via a Maxwell/Liouville framework. To avoid spurious self-excitation, each quantum molecule has its own auxiliary FDTD subregion embedded within the main FDTD grid. The molecular parameters are determined by fitting the experimental extinction spectrum to Lorentzians, yielding the energies, transition dipole moments, and the dephasing lifetimes. This approach can be potentially applied to modeling thousands of molecules on the surface of a plasmonic NP. In this paper, however, we first present results for two molecules with scaled oscillator strengths to reflect the optical response of a full monolayer. There is good agreement with experimental extinction measurements, predicting the plasmon and molecule depletions. Additionally, this model captures the polariton peaks overlapped with a Fano-type resonance profile observed in the experimental extinction measurements. This technique can be generalized to any nanostructure/multichromophore system, where the molecules can be treated with essentially any quantum method.

Atomically-thin materials have drawn great interest due to their exotic properties leading to a variety of promising new applications. However, the out-of-equilibrium dynamics of these materials are still not fully understood. Ultrafast electron diffraction (UED) is a powerful technique for the investigation of the transient structural dynamics of monolayers with unprecedented spatiotemporal resolution. The UED results of WSe2_ monolayers are reported and the suppression of the intensity of the Bragg diffraction spots following laser excitation is attributed to electron-phonon and phonon-phonon scattering. A two-temperature model is used to accurately describe these dynamics due to the low thermal conduction of the monolayer. Furthermore, the reported lifetimes are fit using a single-mode relaxation time approximation.

The synthesis, characterization, and ultrafast spectroscopy of size-selected nanospheres of ruthenium bipyridine–bis(pentafluoroethylsulfonyl)imide ([Ru(bipy)3][BETI]2) in water are reported. These studies represent the first experimental evidence of phonons with nanosecond lifetimes in organometallic nanomaterials. Thermally stable, crystalline nanoparticles of [Ru(bipy)3][BETI]2 are derived from a group of uniform materials based on organic salts (GUMBOS). Excited-state relaxation dynamics are studied using pump–probe time-resolved transient absorption spectroscopy, and the results are compared to corresponding measurements of aqueous Ru(bipy)3Cl2. The nanoGUMBOS show spectral shifts and size-dependent relaxation dynamics for nanoparticle diameters varying from 20 to 100 nm, characterized by excited-state decay dynamics similar to those of the precursor dye at higher pump pulse energies with an additional pathway attributed to intermolecular energy transfer, where all lifetimes increase with increasing ...

The synthesis, characterization, and excited-state dynamics of colloidal gold–silver–gold core–shell–shell nanoparticles are reported. These plasmonic nanoparticles are spherical in shape with uniform shells. The plasmonic extinction peak wavelengths can be controlled over the visible and near-infrared regions by varying the thicknesses of the gold and silver shells. These unique spectroscopic properties make these nanoparticles potential candidates for biologically relevant applications including photothermal cancer therapy and biosensing. The ratio of the gold shell thickness to the overall particle size shows a linear dependence with the position of the plasmon extinction peak wavelength. Temperature measurements after laser irradiation show that the colloidal core–shell–shell nanoparticles have a higher photothermal effect compared to spherical gold nanoparticles and gold nanorods. Transient absorption measurements determine that the phonon–phonon scattering lifetime is considerably faster in the core...

Second harmonic generation is used to investigate the surface charge density of 50 nm colloidal gold nanoparticles in water. The gold nanoparticles are thiolated with mercaptosuccinic acid and are dialyzed in ultrapure water to remove excess salts and reactants. The second harmonic generation signal from the nanoparticle sample is measured as a function of added sodium chloride and magnesium chloride salt concentrations using the χ(3) technique. The experimental results are fit to the Gouy–Chapman model and to numerical solutions to the spherical Poisson–Boltzmann equation that account for the nanoparticle surface curvature, the different salt valences, and ion adsorption to the Stern layer interface. The best fits use the numerical solutions including ion adsorption and determine the initial surface charge density to be (−2.0 ± 0.1) × 10–3 C/m2 at the gold nanoparticle surface, in agreement with electrophoretic mobility measurements. In addition, the sodium ion is observed to adsorb with a higher surface...

Second harmonic generation is used to investigate the adsorption properties of malachite green, brilliant green, and methyl green to the surface of 80 nm colloidal gold nanoparticles capped with mercaptosuccinic acid in water. The experimental results are fit using the modified Langmuir model to obtain the free energies of adsorption and the adsorbate site densities for each cationic triphenylmethane molecular dye. Malachite green is observed to bind more strongly than brilliant green or methyl green to the nanoparticle surface but has a lower adsorbate site density, indicating differences in image-charge effects, adsorbate–adsorbate repulsions, and adsorption tilt angles. Complementary measurements from extinction spectroscopy show plasmonic and molecular resonance coupling leading to the formation of new polaritonic states and Fano-type resonances with corresponding plasmon and molecular spectral depletions as the adsorbate concentration is increased. The changes in the resonance coupling spectra are co...

We study a cobalt phosphate Liesegang pattern from cobalt(II) and phosphate ions in a 1D tube. The system yields a complex, multi-component pattern. Characterization of the different precipitates by FTIR, SEM and XRD reveals that they are cobalt phosphate polymorphs with different degrees of hydration.

Periodic precipitation of sparingly soluble salts yields parallel Liesegang bands in 1D whose spacings obey either one of two known trends. The overwhelming trend is an increase in spacing as we move away from the junction, while some systems display a decrease in spacing as the bands get further away from the interface. The latter trend is much less common and is known as the revert spacing law. Whereas the direct (normal) spacing law is generally well-understood, the revert spacing trend has not been explicitly and distinctly elucidated. In this paper, we propose a mechanism of revert spacing governed by the adsorption of the diffusing CrO4(2−) ions on the formed PbCrO4 Liesegang bands and carry out a set of experiments that support the suggested scenario. It is shown that this adsorption increases as the band number (n) increases in revert spacing systems, while it decreases as n increases in direct spacing systems. It is concluded that this correlation in opposite directions decisively reveals the role of adsorption in the mechanism. The attraction between the CrO4(2−) and Pb(2+) in the gel causes the bands to form gradually closer and closer. Secondary structure (thinner bands formed within the main ones) obtained under some conditions is discussed in view of the light sensitivity of the chromate ion and the stability of the lead chromate sol.

Demand for electricity in the northern Middle East region has experienced considerable growth in the past few decades. However, power sector planning in the countries of this region has been mainly carried out in an independent manner. Electricity trade has been discussed as a means for regional cooperation and a viable option for integrated regional planning. This paper reports on a study to evaluate the potential economic benefits from such an integrated planning approach. A mathematical model is formulated and used with country level technical and economic data with different acceptable levels of trade and for different demand growth scenarios. This demonstrates potential gains from complementarities of peak load and diversity of fuel resources in the studied region. Results obtained for a northern Middle East region consisting of Egypt, Iraq, Jordan, Lebanon and Syria estimate savings of more than 13% in required installed generation capacity in these countries. The savings occur over a 15-year planning horizon when an integrated regional planning approach is followed allowing individual countries to have up to 50% of their peak demand met by other countries in the region. The analytical model developed and applied here can prove to be a valuable tool to decision makers in the region as they study future plans for the energy sector and negotiate their participation in regional interconnection projects.

The synthesis, characterization, ultrafast dynamics, and nonlinear spectroscopy of 30 nm nanospheres of brilliant green-bis(pentafluoroethylsulfonyl)imide ([BG][BETI]) in water are reported. These thermally stable nanoparticles are derived from a group of uniform materials based on organic salts (nanoGUMBOS) that exhibit enhanced near-infrared emission compared with the molecular dye in water. The examination of ultrafast transient absorption spectroscopy results reveals that the overall excited-state relaxation lifetimes of [BG][BETI] nanoGUMBOS are longer than the brilliant green molecular dye in water due to steric hindrance of the torsional degrees of freedom of the phenyl rings around the central carbon. Furthermore, the second harmonic generation signal of [BG][BETI] nanoGUMBOS is enhanced by approximately 7 times and 23 times as compared with colloidal gold nanoparticles of the same size and the brilliant green molecular dye in water, respectively. A very clear third harmonic generation signal is observed from the [BG][BETI] nanoGUMBOS but not from either the molecular dye or the gold nanoparticles. Overall, these results show that [BG][BETI] nanoGUMBOS exhibit altered ultrafast and nonlinear spectroscopy that is beneficial for various applications including nonlinear imaging probes, biomedical imaging, and molecular sensing.

The ultrafast excited-state dynamics of size-dependent TiO2-Au nanocomposites synthesized by reducing gold nanoclusters to the surface of colloidal TiO2 nanoparticles are studied using pump-probe transient absorption spectroscopy with 400 nm excitation pulses. The results show that the relaxation processes of the plasmon depletion band, which are described by electron-phonon and phonon-phonon scattering lifetimes, are independent of the gold nanocluster shell size surrounding the TiO2 nanoparticle core. The dynamics corresponding to interfacial electron transfer between the gold nanoclusters and the TiO2 bandgap are observed to spectrally overlap with the gold interband transition signal, and the electron transfer lifetimes are shown to significantly decrease as the nanocluster shell size increases. Additionally, size-dependent periodic oscillations are observed and are attributed to acoustic phonons of a porous shell composed of aggregated gold nanoclusters around the TiO2 core, with frequencies that decrease and damping times that remain constant as the nanocluster shell size increases. These results are important for the development of improved catalytic nanomaterial applications.