Laser ablation combined with a fast flowtube reactor is employed for the production and isolation of ligand-coated metal clusters and nanomaterials. The source employs high repetition rate laser vaporization with a 400 Hz KrF (248 nm) excimer laser, while cluster growth and passivation with ligands takes place in a flowtube with ligand addition via a vapor or nebulizer spray. Samples are isolated in a low temperature trap and then the resulting clusters are thawed and collected in a solution of excess ligand. These solutions are analyzed with laser desorption or electrospray ionization time-of-flight mass spectrometry. In addition to mass spectrometry, infrared, Raman, UV-VIS absorption and emission, and density functional theory computations are employed to characterize these new cluster materials. Raman measurements rely on surface enhancement induced by silver nanorod array substrates. Vanadium oxide and chromium oxide nanoclusters coated with THF or acetonitrile ligands have been produced in the size range up to 40-50 atoms. Chromium oxide clusters produce ligand-coated Cr4O10 or Cr6O14 clusters under different conditions, using either acetonitrile or water as the ligand. Experiments on aluminum vaporization produce Al3(CH3CN)3, which has vibrationally resolved electronic absorption and fluorescence spectra. Molybdenum oxide nanorods roughly 10 x 100 nm have optical and vibrational spectroscopy similar to those of larger molybdenum oxide particles, but are far more reactive.

Laser synthesis and spectroscopy of ligand-coated nanoclusters and nanomaterials

2019 Fall National Meeting

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