Ultrafast Depolarization of Transient Absorption as a Probe of Plasmonicity of Optical Transitions in Ag Nanoclusters (original) (raw)
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The Journal of Physical Chemistry B, 2005
The formation of Ag nanoparticles by electrochemical techniques has been investigated through a timeresolved UV-vis spectroscopy study. The formation of Ag 4 2+ clusters is suggested as the main precursors to the particle formation. The mechanism also considers the electrodeposition which occurs as a parallel process in the electrochemical particle formation. Experiments at different current densities show that the electrodeposition is more important at low current densities. From the fittings of the change of the plasmon (λ ≈ 430 nm) and the cluster (λ) 250 nm) bands to the proposed mechanism, the kinetic constants of the formation and disappearance of the Ag 4 2+ cluster are derived. The kinetic fittings also allowed an estimation of the Ag 4 2+ cluster extinction coefficient (250) 1.0 × 10 4 M-1 cm-1). It is observed that the plasmon bandwidth (fwhm) follows the theoretical predicted 1/R law only for particles with sizes d J 3 nm, but the law is broken for the smallest particles (d < 2.5 nm). The break is associated with the existence of singleelectron (SE) transitions which are activated by the plasmon decay for the smallest nanoparticles. From the broken 1/R law, a limit relaxation time of about 4 fs is derived for the plasmon deactivation. Below this limit, the plasmon seems to decay mainly through a nonradiative channel with the formation of electron-hole (e-h) pairs. By comparison of the 1/R broken law with other literature results, it is concluded that large interactions of the Ag nanoparticles with the used capping molecule (tetrabutylammonium acetate) facilitate the e-h plasmon deactivation.
Femtosecond Multicolor Transient Absorption Spectroscopy of Colloidal Silver Nanoparticles
Time-resolved femtosecond multicolor absorption spectroscopy of silver nanoparticle (NP) colloids with particle diameter in range of 10–30 nm is presented. The amplified femtosecond excitation of the surface plasmon resonance band resulted in transient absorption spectra reflecting the electron-phonon relaxation dynamics, which takes place on the early picosecond time scale. The monitored band with enhanced absorption in the 490–540 nm spectral range exhibited red-shift with increasing pump fluency from 0.4 mJ/cm 2 to the 1.5 mJ/cm 2 level. The growth of the relaxation time with increasing pump fluency reveals the temperature dependent relaxation dynamics caused by the nanometer sized electron confinement in the case of silver. This effect was confirmed also by identification of the relaxation time dependence on the particle diameter at constant pump fluency. The complex experimental results revealed nonlinearities both in the laser excitation and electron relaxation processes.
The Journal of Physical Chemistry C, 2007
Time and frequency resolved transient absorption measurements yield two-dimensional images that map the dynamical correlation between the center and width of the scattering function. Global analysis of such data allows unique diagnostics of the mechanics underlying the time evolution. We specialize in the case of surface plasmon resonances of optically driven nanoparticles. We present a catalog of 2D maps that can be used to fingerprint physically meaningful cases, and we provide two experimental examples to illustrate the diagnostic value of the maps and their utility in extracting the various time constants at play. In silver nanorods, the experiment shows a π/2 phase shift between the oscillations of the center and the width of the plasmon resonance. Inspection of the maps allows the assignment that the center of the plasmon resonance tracks the strain in shape-oscillations, while the width tracks the strain rate. This finding is the basis of the novel mechanism of plasmon damping due to electron scattering from the electrophoretic potential generated by the motion of the interfacial double layer in colloidal nanoparticles. Measurements in gold nanoparticles show over-damped oscillations, which obscure the phase correlation between the center and width of the plasmon. The damping is dominated by inhomogeneous dephasing, and the time dependence of the width, which follows the temperature of the nanoparticles, and is diagnostic of the interband transition contribution to the plasmon resonance.
Chemical Physics Letters, 2002
The ultrafast electron dynamics of chemically prepared gold nanoclusters with a 28 atom gold core surrounded by 16 glutathione molecules were investigated. After excitation with femtosecond laser pulses these clusters show an induced transient absorption in the visible from 2.58 to 1.65 eV (480-750 nm) with a maximum around 2.07 eV (600 nm). The excited state relaxation shows a biexponential decay with a subpicosecond and a longer nanosecond decay time independent of the laser pump power. These results are different from those observed previously for larger gold nanoparticles, which suggests that the Au 28 -glutathione system shows molecular properties. Ó
Picosecond Characteristics on Transient Absorption Spectra of Silver Nanoparticles
Transient absorption spectroscopy with femtosecond time resolution of colloidal silver nanoparticles with diameters of 10 – 100 nm was accomplished. The experimental study was performed by 400 nm pumpbroadband probe apparatus in spectral area of 450 – 600 nm at 1 mJ/cm2 excitation intensity level. The obtained picosecond relaxation times depend on particle size. The revealed electron dynamics has the main responsibility for linear absorption during the excitation process. The effect of excitation intensity remained unambiguous. The extracted relaxation times suggest the dominancy of the electron-phonon scattering during the absorption recovery and its spectral dependence. Additional role of electron-electron scattering requires further more advanced study.
SN Applied Sciences
Bimetallic nanoclusters (NCs) have attracted extensive attention in present research due to the synergic effect of the two kinds of metal atoms and their valuable applications. The broad range of applications of these noble metal NCs and their molecular nature instigated understanding their property of luminescence and the underlying ultrafast dynamics. With a view to enlighten the weakly known changes in excited state dynamics of luminescent noble metal alloy NCs, protein protected bimetallic alloy gold-silver NCs (Au-Ag NCs) with different molar ratios were synthesized and characterized. The results show that a particular optimum molar ratio of the two metal atoms gives maximum luminescence to the NCs. The findings from transient absorption spectroscopy and excited state decay analysis consolidated the results and provided detailed description in this direction. Various applications, such as optical energy harvesting, bio-medical imaging and photocatalysis, would find ample flexibility on knowing the characteristics of the alloy metal NCs that might lead to relevant modulations in their properties. The present study is intended to develop the concept of ultrafast dynamics in noble metal alloy NCs.
Investigation of the ultrafast dephasing time of gold nanoparticles using incoherent light
Chemical Physics Letters, 1995
Measurement of the phase relaxation time and nonlinear susceptibilit~¢ of gold nanoparticles is demonstrated, using incoherent light. The diameters of the gold particles ranged from 50 to 400 A. Experiments were performed in the vicinity of the surface plasmon resonance frequency and the resonantly enhanced susceptibility was found to be approximately 10-16 m 2 V-2 The dephasing time was determined to be of the order of, or faster than, 20 fs.
Ultrafast light-induced dichroism in silver nanoparticles
Physical Review B, 2004
Ultrafast light-induced dichroism in silver nanoparticles is studied. Two differently prepared colloids are examined: one sample has a broad distribution of sizes and shapes of silver nanoparticles, while the second sample, which is processed by laser ablation, presents a more uniform size and shape distribution (greater fraction of spherical particles). The experiments are performed with a femtosecond laser in a two-color, polarization-resolved, pump-probe setup. For the pristine colloid the signal amplitudes for the parallel and perpendicular polarizations present different behaviors as a function of the probe photon energy, which is not observed for the laser ablated samples. The temporal response of the samples is also different, with the laser ablated samples presenting faster electronic cooling rates. A model describing the induced dichroism that takes into account the shape of the colloid particles is presented. The effects of the size distribution are also discussed.
The Journal of Physical Chemistry B, 1997
The electronic dynamics of gold nanocrystals, passivated by a monolayer of alkylthiol(ate) groups, were studied by transient spectroscopy after excitation with subpicosecond laser pulses. Three solution-phase gold samples with average particle size of 1.9, 2.6, and 3.2 nm with size distribution less than 10% were used. The photoexcitation in the intraband (surface plasmon region) leads to the heating of the conduction electron gas and its subsequent thermalization through electron-electron and electron-phonon interaction. The results are analyzed in terms of the contribution of the equilibrated "hot" electrons to the surface plasmon resonance of gold. A different spectral response was observed for different sizes of gold nanoparticles. The results were compared to the dynamics of the large (30 nm diameter) gold nanocrystals colloidal solution. The size-dependent spectral changes are attributed to the reduction of the density of states for small nanoparticles. The observed variation in the kinetics of the cooling process in gold nanoparticles with changing the laser intensity is attributed to the temperature dependence of the heat capacity of the electron gas.
Femtosecond Nanoplasmonic Dephasing of Individual Silver Nanoparticles and Small Clusters
The Journal of Physical Chemistry Letters, 2015
We present experimental measurements of localized surface plasmon emission from individual silver nanoparticles and small clusters via accurately delayed femtosecond laser pulses. Fourier transform analysis of the nanoplasmonic coherence oscillations reveals different frequency components and dephasing rates for each nanoparticle. We find three different types of behavior: single exponential decay, beating between two frequencies, and beating among three or more frequencies. Our results provide insight into inhomogeneous and homogeneous broadening mechanisms in nanoplasmonic spectroscopy that depend on morphology and nearby neighbors. In addition, we find the optical response of certain pairs of nanoparticles to be at least an order of magnitude more intense than the response of single particles.