Browsing by Author "Hosseini Jebeli, Seyyed Ali"

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    Absorption Localization in Plasmonic Heterostructures
    (2018-04-16) Hosseini Jebeli, Seyyed Ali; Link, Stephan
    Plasmonic nanoparticles have found many applications in different areas such as nanoelectronics, energy harvesting and conversion, and photothermal therapy due to their strong interaction with light. The light absorption of homogenous plasmonic structures is mostly uniform and cannot be engineered easily. In this work, the absorption localization in heterogeneous structures is presented using different materials in the same structure as well as the same material in heterodimer structures composed of rods of different sizes. Pt decorated gold nanorods are found to have significant heat localization in the Pt particles due to their stronger light absorption than gold. The localization of absorption in the Pt is confirmed by performing correlated photoluminescence and scattering measurements as well as FDTD simulations. Additionally, gold nanorods of different sizes are coupled together to form a heterodimer. In this work, the results of changing the gap size between the nanorods are presented. This alters the amount of coupling between nanorods which allows control over the absorption intensity of each particle. Further, we find that the absorption hot spots can be switched in these structures by changing the excitation wavelength. Significant absorption localization is observed in both cases which demonstrates the great potential of plasmonic heterostructures for manipulating light-matter interactions.
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    Imaging and Control of Heat Generation at the Nanoscale Using Plasmonic Structures
    (2021-08-12) Hosseini Jebeli, Seyyed Ali; Link, Stephan
    Plasmonic nanostructures appear in a variety of applications and devices thanks to their spectral tunability, hot carrier generation, enhanced emission, and their ability to confine electromagnetic fields at volumes smaller than the diffraction limit of light. Despite their utilization and the vast knowledge about the electromagnetic properties of plasmonic structures, their thermal properties are not investigated experimentally in detail. Specifically, the ability of plasmonic structures to heat small volumes at nanometer scale using visible and infrared light is not fully quantified while there have been some applications for it such as heat assisted magnetic recording. In this work, I present the first realization of heat generation control at nanoscale using the wavelength and the polarization of the excitation beam along with demonstration of the thermal effects on the photothermal microscopy images of longitudinally coupled nanorod dimers. My results show that thermal hot spots can be switched over distances smaller than 100 nm using the wavelength and polarization of light and the relative temperatures can be controlled using plasmon hybridization of the nanorods by adjusting the gap size between them. I further analyze the limits of imaging temperature profiles by designing and imaging nanorod trimers that are smaller than the diffraction limit of our pump and probe lasers. The trimers have three normal modes with different thermal profiles and resonant wavelengths. I show that these modes are sensitive to beam position and a focused laser beam can excite different combinations of these modes at each wavelength based on its position relative to each nanorod. The preferential excitation of these modes by the laser beam results in a wavelength dependent temperature profile which affects the asymmetry of the point spread function in a photothermal microscopy image. These findings pave the way towards designing more efficient and localized nanoheaters which have applications in nanofabrication, targeted therapy, and chemical reactions in a small volume.
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    Single-Particle Hyperspectral Imaging Reveals Kinetics of Silver Ion Leaching from Alloy Nanoparticles
    (American Chemical Society, 2021) Al-Zubeidi, Alexander; Stein, Frederic; Flatebo, Charlotte; Rehbock, Christoph; Hosseini Jebeli, Seyyed Ali; Landes, Christy F.; Barcikowski, Stephan; Link, Stephan; Smalley-Curl Institute
    Gold–silver alloy nanoparticles are interesting for multiple applications, including heterogeneous catalysis, optical sensing, and antimicrobial properties. The inert element gold acts as a stabilizer for silver to prevent particle corrosion, or conversely, to control the release kinetics of antimicrobial silver ions for long-term efficiency at minimum cytotoxicity. However, little is known about the kinetics of silver ion leaching from bimetallic nanoparticles and how it is correlated with silver content, especially not on a single-particle level. To characterize the kinetics of silver ion release from gold–silver alloy nanoparticles, we employed a combination of electron microscopy and single-particle hyperspectral imaging with an acquisition speed fast enough to capture the irreversible silver ion leaching. Single-particle leaching profiles revealed a reduction in silver ion leaching rate due to the alloying with gold as well as two leaching stages, with a large heterogeneity in rate constants. We modeled the initial leaching stage as a shrinking-particle with a rate constant that exponentially depends on the silver content. The second, slower leaching stage is controlled by the electrochemical oxidation potential of the alloy being steadily increased by the change in relative gold content and diffusion of silver atoms through the lattice. Interestingly, individual nanoparticles with similar sizes and compositions exhibited completely different silver ion leaching yields. Most nanoparticles released silver completely, but 25% of them appeared to arrest leaching. Additionally, nanoparticles became slightly porous. Alloy nanoparticles, produced by scalable laser ablation in liquid, together with kinetic studies of silver ion leaching, provide an approach to design the durability or bioactivity of alloy nanoparticles.