Browsing by Author "Zhang, Yue"

Now showing 1 - 4 of 4
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    Charge Transfer Plasmons: Optical Frequency Conductances and Tunable Infrared Resonances
    (American Chemical Society, 2015) Wen, Fangfang; Zhang, Yue; Gottheim, Samuel; King, Nicholas S.; Zhang, Yu; Nordlander, Peter; Halas, Naomi J.; Laboratory for Nanophotonics
    A charge transfer plasmon (CTP) appears when an optical-frequency conductive pathway between two metallic nanoparticles is established, enabling the transfer of charge between nanoparticles when the plasmon is excited. Here we investigate the properties of the CTP in a nanowire-bridged dimer geometry. Varying the junction geometry controls its conductance, which modifies the resonance energies and scattering intensities of the CTP while also altering the other plasmon modes of the nanostructure. Reducing the junction conductance shifts this resonance to substantially lower energies in the near- and mid-infrared regions of the spectrum. The CTP offers both a high-information probe of optical frequency conductances in nanoscale junctions and a new, unique approach to controllably engineering tunable plasmon modes at infrared wavelengths.
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    Interacting Surface Plasmon with Electron Beam and Acoustic Vibration
    (2017-05-04) Zhang, Yue; Nordlander, Peter
    Surface plasmon, collaborative oscillation of conduction band electrons in metal, has attracted research attention very much, due to its potential applications to many fields, such as sensing, photodetector, photocatalysis and imaging. It benefits from easily tunable resonance from ultra-violet (UV) to infrared by many factors like environment, structure size, shape, material and coupling between individual structures. This thesis will cover two parts of surface plasmon: (1) imaging surface plasmon with electron spectroscopies and (2) acoustic vibration excited by surface plasmon. Electron excited plasmon method can achieve high spatial resolution and energy resolution than optical spectroscopy. This makes it a great to image and map surface plasmon. Building corresponding simulation model help us to have deep understanding about how electrons interact with material and excite surface plasmon. Acoustic vibration excited by surface plasmon is also important. After plasmon excited by a femtosecond laser, it will generate hot electron which will further transfer energy to phonon and launch acoustic vibration. This thesis shows how to find a good excitation and probing condition to generate acoustic vibration.
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    Tunable Charge Transfer Plasmon
    (2015-12-03) Zhang, Yue; Nordlander, Peter J.; Hals, Naomi J.; Link, Stephan
    Both bonding dipolar mode (BDP) and charge transfer plasmon (CTP) is observed when two metallic nanoparticles are linked by conductive junction. This thesis investigates optical properties of CTP, and demonstrated that CTP, as a result of charge transfer through conductive junction, is very sensitive to junction geometry and junction conductance. This thesis systematically studied resonance energies, scattering intensities and linewidths of CTPs and BDPs supported by linked pairs of nanoparticles. The most important finding of their spectral dependence on conductance is: decreasing the junction conductance shifts CTP resonance to lower energy to the near-infrared (NIR) or mid-infrared (MIR) spectral region. Therefore, we find a novel approach to control plasmon modes at infrared wavelengths: tune CTP by changing junction properties. At the same time, CTP can be used to measure the electrical transport properties of nanomaterials at optical frequencies when they are placed in the junction.
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    Tuning the acoustic frequency of a gold nanodisk through its adhesion layer
    (Nature Publishing Group, 2015) Chang, Wei-Shun; Wen, Fangfang; Chakraborty, Debadi; Su, Man-Nung; Zhang, Yue; Shuang, Bo; Nordlander, Peter; Sader, John E.; Halas, Naomi J.; Link, Stephan; Laboratory for Nanophotonics
    To fabricate robust metallic nanostructures with top-down patterning methods such as electron-beam lithography, an initial nanometer-scale layer of a second metal is deposited to promote adhesion of the metal of interest. However, how this nanoscale layer affects the mechanical properties of the nanostructure and how adhesion layer thickness controls the binding strength to the substrate are still open questions. Here we use ultrafast laser pulses to impulsively launch acoustic phonons in single gold nanodisks with variable titanium layer thicknesses, and observe an increase in phonon frequencies as a thicker adhesion layer facilitates stronger binding to the glass substrate. In addition to an all-optical interrogation of nanoscale mechanical properties, our results show that the adhesion layer can be used to controllably modify the acoustic phonon modes of a gold nanodisk. This direct coupling between optically excited plasmon modes and phonon modes can be exploited for a variety of emerging optomechanical applications.