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Free keywords:
biomolecules; clusters; electrospray ionization; epitaxy; mass spectrometry
Abstract:
An ion beam source using electrospray ionization is presented for
non-destructive vacuum deposition of mass-selected large organic
molecules and inorganic clusters. Electrospray ionization is used to
create an ion beam from a solution containing the nanoparticles or
molecules to be deposited. To form and guide the ion beam, radio
frequency and electrostatic ion optics are utilized. The kinetic energy
distribution of the particles is measured to control the beam formation
and the landing process. The particle mass-to-charge ratio is analyzed
by in situ time-of-flight mass spectrometry. To demonstrate the
performance of the setup, deposition experiments with gold nanoclusters
and bovine serum albumin proteins on graphite surfaces were performed
and analyzed by ex situ atomic force microscopy. The small gold
clusters are found to form three-dimensional agglomerations at the
surface, preferentially decorating the step edges. In contrast, bovine
serum albumin creates two-dimensional fractal nanostructures on the
substrate terraces due to strong intermolecular interactions.
