Browsing by Author "Lauchner, Adam"

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    Enhancing the photocurrent and photoluminescence of single crystal monolayer MoS2ﾠwith resonant plasmonic nanoshells
    (AIP Publishing LLC., 2014) Sobhani, Ali; Lauchner, Adam; Najmaei, Sina; Ayala-Orozco, Ciceron; Wen, Fangfang; Lou, Jun; Halas, Naomi J.
    Monolayer molybdenum disulfide (MoS2) produced by controlled vapor-phase synthesis is a commercially promising new two-dimensional material for optoelectronics because of its direct bandgap and broad absorption in the visible and ultraviolet regimes. By tuning plasmonic core-shell nanoparticles to the direct bandgap of monolayer MoS2 and depositing them sparsely (<1% coverage) onto the material's surface, we observe a threefold increase in photocurrent and a doubling of photoluminescence signal for both excitonic transitions, amplifying but not altering the intrinsic spectral response.
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    Molecular Plasmonics: Graphene Plasmons in the Picoscale Limit
    (2015-08-20) Lauchner, Adam; Halas, Naomi; Nordlander, Peter; Link, Stephan
    Doped graphene supports surface plasmons in the mid- to far-infrared that are both electrically and spatially tunable. Graphene has been shown to enable greater spatial confinement of the plasmon and fewer losses than typical noble metals. Reduced-dimensional graphene structures, including nanoribbons, nanodisks, and other allotropes including carbon nanotubes exhibit higher frequency plasmons throughout the mid- and near-infrared regimes due to additional electronic confinement of the electrons to smaller length scales. Recent theoretical predictions have suggested that further spatial confinement to dimensions of only a few nanometers (containing only a few hundred atoms) would result in a near-infrared plasmon resonance remarkably sensitive to the addition of single charge carriers. At the extreme limit of quantum confinement, picoscale graphene structures known as Polycyclic Aromatic Hydrocarbons (PAHs) containing only a few dozen atoms should possess a plasmon resonance fully switched on by the addition or removal of a single electron. This thesis reports the experimental realization of plasmon resonances in PAHs with the addition of a single electron to the neutral molecule. Charged PAHs are observed to support intense absorption in the visible regime with geometrical tunability analogous to plasmonic resonances of much larger nanoscale systems. To facilitate charge transfer to and from PAH molecules, a three-electrode electrochemical cell with optical access was designed, where current is passed through a nonaqueous electrolyte solution that contains a known concentration of PAH molecules. In contrast to larger graphene nanostructures, the PAH absorption spectra possess a rich and complex fine structure that we attribute to the coupling between the molecular plasmon and the vibrational modes of the molecules. The natural abundance, low cost, and extremely large variety of PAH molecules available could make extremely large-area active color-switching applications, such as walls, windows or other architectural elements, even vehicles, a practical technology.