Browsing by Author "See, Erich M."

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    Multi-photon patterning of photoactive o-nitrobenzyl ligands bound to gold surfaces
    Magill, Brenden A.; Guo, Xi; Peck, Cheryl L.; Reyes, Roberto L.; See, Erich M.; Santos, Webster L.; Robinson, Hans D. (Royal Society of Chemistry, 2019-01-01)
    We quantitatively investigate lithographic patterning of a thiol-anchored self-assembled monolayer (SAM) of photocleavable o-nitrobenzyl ligands on gold through a multi-photon absorption process at 1.7 eV (730 nm wavelength). The photocleaving rate increases faster than the square of the incident light intensity, indicating a process more complex than simple two-photon absorption. We tentatively ascribe this observation to two-photon absorption that triggers the formation of a long-lived intermediate aci-nitro species whose decomposition yield is partially determined either by absorption of additional photons or by a local temperature that is elevated by the incident light. At the highest light intensities, thermal processes compete with photoactivation and lead to damage of the SAM. The threshold is high enough that this destructive process can largely be avoided, even while power densities are kept sufficiently large that complete photoactivation takes place on time scales of tens of seconds to a few minutes. This means that this type of ligand can be activated at visible and near infrared wavelengths where plasmonic resonances can easily be engineered in metal nanostructures, even though their single-photon reactivity at these wavelengths is negligible. This will allow selective functionalization of plasmon hotspots, which in addition to high resolution lithographic applications would be of benefit to applications such as Surface Enhanced Raman Spectroscopy and plasmonic photocatalysis as well as directed bottom-up nanoassembly.
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    Plasmon Directed Chemical Reactivity and Nanoparticle Self-Assembly
    See, Erich M. (Virginia Tech, 2017-04-25)
    Nanotechnology has advanced to the point that nanoparticles can now be fabricated in a broad variety of shapes from a wide range of materials, each with their own properties and uses. As the list of manufacturable particles continues to grow, a new frontier presents itself: assembling these existing nanoparticles into more complicated nanoscale structures. The primary objective of this thesis is to demonstrate and characterize one such method of nanoscale construction, the plasmonically directed self-assembly of gold nanospheres onto both silver nanospheroids and gold nanorods. At the heart of this research is a the use of a photocleavable ligand (1-(6-Nitrobenzo[d][1,3]dioxol-5-yl)ethyl(4-(1,2-Dithiolan-3-yl)butyl) carbamate), which is capable of forming a photoreactive self-assembly monolayer (SAM) on gold and silver surfaces. After photoactivation, this SAM becomes positively charged at low pH, allowing it to electrostatically bind with negatively charged gold nanospheres (or other negatively charged nanoparticles). In this thesis, I describe both a secondary photoreaction that this ligand is capable post-photocleavage, which removes the ligand's ability to bind to negatively charged gold nanospheres, allowing for, among other assembly methods, reverse photopatterning. I further show that this photocleavable ligand can be used in conjunction with gold nanospheres to create aligned, metal structures on silver nanospheroid surface by exposure to linearly polarized UV light. Similarly, I also demonstrate how the ligand can be used to preferentially bind gold nanospheres to the ends of gold nanorods with the use of ultrafast femtosecond pulsed 750 nm laser light, making use of multi-photon absorption. Both methods of self-assembly, as well as the secondary photoreaction, are dependent on the plasmonics of the metal nanoparticles. This thesis also goes into the backgrounds of plasmonics, plasmonically mediated catalysis, self-assembly, and photocleavable chemicals.