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X-WR-CALNAME:Department of Chemistry
X-WR-CALDESC:Department of Chemistry
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UID:MEC-fe40fb944ee700392ed51bfe84dd4e3d@yorku.ca
DTSTART:20230323T173000Z
DTEND:20230323T183000Z
DTSTAMP:20230320T184200Z
CREATED:20230320
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SUMMARY:Seminar Series - Al-Amin Dhirani - UofT St. George
DESCRIPTION:Nanostructures - building blocks for designer materials exhibiting exotic quantum behaviour\n \nAl-Amin Dhirani\nDepartment of Chemistry and Department of Physics, University of Toronto\nLM 254 - Lash Miller Chemical Laboratories, 80 St. George Street, Toronto, ON, M5S 3H6\na.dhirani@utoronto.ca\n \nAbstract:\nA theme of our research is to employ a bottom-up, building block strategy to fabricate nanostructured\nmaterials exploiting the tunability of nanostructures. This approach leads to a possibility of\nnanoengineering materials (NEMs) with desired behaviours and potentially realizing emergent quantum\nphenomena (q-NEMS). In this talk, I will present two examples.\nThe first employes an extension of Langmuir’s method that enables for the first time fabrication of\nmolecularly cross-linked 2-D nanoparticle sheets (X-NS). X-NS are macroscopic (cm – scale laterally),\none nanoparticle thick and highly ordered. Remarkably, X-NS fabricated with gold nanoparticles and\nsemiconducting “molecular wires” linkers (oligophenylene dithiol, HS-(C6H4)n-SH, with 1 ≤ n ≤ 3)\nexbibit conductivity that decreases with increasing molecule length (the opposite trend of tunneling) and\nstrongly enhanced molecular optical absorption compared with that of unlinked molecules in solution.\nModelling and control measurements exclude strong local fields present in X-NS as the cause of the\nenhancement; rather, they point to strong changes to the local complex dielectric constant upon cross-\nlinking, suggesting quantum hybridization at a molecule – band (HMB) level. The tunability of the\nelectrical properties of X-NS via length of molecular wires linkers demonstrates an outstanding goal of\nmolecular electronics to realize molecular circuits whose behaviour is tunable through molecular\nstructure.\nIn the second example, we have shown that self-assembled gold nanostructures (nanoparticle, NP and\nnanoshell, NS) + molecule cross-linkers (butanedithiol, BDT) exhibit multiple hallmark signatures of the\nKondo effect. In this quantum effect, delocalized s- electrons in a metal film hybridize with localized,\nunpaired impurity d-electrons. Such interactions are of intense interest in condensed matter as they play\ncritical roles in exotic quantum effects, including high Tc superconductivity. Remarkably, NP + NS\nfilms, exhibit signatures of the Kondo effect up to > 220 K i.e., > 10-fold higher than in NP films. Based\non these and magnetic measurements, we propose a mechanism whereby varying nanobuilding-blocks\ncan modify underlying electron-electron interactions to such a large degree.\n
URL:https://www.yorku.ca/science/chemistry/events/seminar-series-al-amin-dhirani-uoft-st-george/
LOCATION:PSE 317
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