https://doi.org/10.1140/epjd/e2007-00117-6
The colours of nanometric gold
Optical response functions of selected gold-cluster thiolates
School of Chemistry & Biochemistry, Georgia Institute of Technology, Atlanta, GA, 30332-0400, USA
Corresponding author: a whetten@chemistry.gatech.edu
Received:
25
August
2006
Revised:
2
October
2006
Published online:
24
May
2007
A set of broad-range NIR-vis-UV optical absorption spectra, measured for selected gold-cluster thiolate compounds (GCTs, containing ~20 to 300 Au atoms), is consistently displayed and then analyzed within the dielectric-functions approach. The size-evolution toward `bulk' (Au diameter >3-nm) optical response is thereby clearly demonstrated. The emergence of apparent energy gaps, Eon, for onset of optical absorption, as well as other fine-structure, is consistent with that of a well-quantized metallic electronic structure for the compounds' cores: the onset-band's location Eon and intensity are attributed semiclassically to a circulation-frequency resonance of the Fermi-level electrons. With decreasing cluster-size, an increasing fraction of the integrated (sum-rule) intensity is `missing' from the <4 eV region. This might be explained by the outermost layer consisting of Au(I)thiolate complexes.
PACS: 73.22.-f – Electronic structure of nanoscale materials: clusters, nanoparticles, nanotubes, and nanocrystals / 73.22.Lp – Collective excitations / 36.40.Vz – Optical properties of clusters / 78.20.Ci – Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2007
