Nanocluster ionization energies and work function of aluminum, and their temperature dependence

Ionization threshold energies of Al(n) (n = 32-95) nanoclusters are determined by laser ionization of free neutral metal clusters thermalized to several temperatures in the range from 65 K to 230 K. The photoion yield curves of cold clusters follow a quadratic energy dependence above threshold, in a...

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Bibliographic Details
Published in:The Journal of chemical physics 2015-10, Vol.143 (16), p.164313-164313
Main Authors: Halder, Avik, Kresin, Vitaly V
Format: Article
Language:English
Subjects:
ALUMINIUM
Aluminum
CONTAMINATION
Data acquisition
ENERGY DEPENDENCE
EXTRAPOLATION
INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY
IONIZATION
Metal clusters
Nanoclusters
NANOSCIENCE AND NANOTECHNOLOGY
NANOSTRUCTURES
Photoelectric emission
PHOTOEMISSION
Physics
POLYCRYSTALS
SURFACES
TEMPERATURE DEPENDENCE
THERMAL EXPANSION
THRESHOLD ENERGY
WORK FUNCTIONS
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Summary:Ionization threshold energies of Al(n) (n = 32-95) nanoclusters are determined by laser ionization of free neutral metal clusters thermalized to several temperatures in the range from 65 K to 230 K. The photoion yield curves of cold clusters follow a quadratic energy dependence above threshold, in agreement with the Fowler law of surface photoemission. Accurate data collection and analysis procedures make it possible to resolve very small (few parts in a thousand) temperature-induced shifts in the ionization energies. Extrapolation of the data to the bulk limit enables a determination of the thermal shift of the polycrystalline metal work function, found to be in excellent agreement with theoretical prediction based on the influence of thermal expansion. Small clusters display somewhat larger thermal shifts, reflecting their greater susceptibility to thermal expansion. Ionization studies of free size-resolved nanoclusters facilitate understanding of the interplay of surface, electronic, and lattice properties under contamination-free conditions.
ISSN:0021-9606
1089-7690
DOI:10.1063/1.4934761