Surface chemistry : a non-negligible parameter in determining optical properties of small colloidal metal nanoparticles.

Journal Article · Sat Jan 01 04:00:00 EST 2011 · Phys. Chem. Chem. Phys.

DOI:https://doi.org/10.1039/c1cp20265k· OSTI ID:1020675

Sun, Y; Gray, S K; Peng, S ^[1]

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1. Center for Nanoscale Materials

Surface chemistry can become pronounced in determining the optical properties of colloidal metal nanoparticles as the nanoparticles become so small (diameters <20 nm) that the surface atoms, which can undergo chemical interactions with the environment, represent a significant fraction of the total number of atoms although this effect is often ignored. For instance, formation of chemical bonds between surface atoms of small metal nanoparticles and capping molecules that help stabilize the nanoparticles can reduce the density of conduction band electrons in the surface layer of metal atoms. This reduced electron density consequently influences the frequency-dependent dielectric constant of the metal atoms in the surface layer and, for sufficiently high surface to volume ratios, the overall surface plasmon resonance (SPR) absorption spectrum. The important role of surface chemistry is highlighted here by carefully analyzing the classical Mie theory and a multi-layer model is presented to produce more accurate predictions by considering the chemically reduced density of conduction band electrons in the outer shell of metal atoms in nanoparticles. Calculated absorption spectra of small Ag nanoparticles quantitatively agree with the experimental results for our monodispersed Ag nanoparticles synthesized via a well-defined chemical reduction process, revealing an exceptional size-dependence of absorption peak positions: the peaks first blue-shift followed by a turnover and a dramatic red-shift as the particle size decreases. A comprehensive understanding of the relationship between surface chemistry and optical properties is beneficial to exploit new applications of small colloidal metal nanoparticles, such as colorimetric sensing, electrochromic devices, and surface enhanced spectroscopies.

• Research Organization: Argonne National Laboratory (ANL)
• Sponsoring Organization: SC
• DOE Contract Number: AC02-06CH11357
• OSTI ID: 1020675
• Report Number(s): ANL/CNM/JA-69279
• Journal Information: Phys. Chem. Chem. Phys., Journal Name: Phys. Chem. Chem. Phys. Journal Issue: 25 ; 2011 Vol. 13; ISSN 1463-9076
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
ABSORPTION
ABSORPTION SPECTRA
ATOMS
CHEMICAL BONDS
CHEMISTRY
ELECTRON DENSITY
ELECTRONS
OPTICAL PROPERTIES
PARTICLE SIZE
PERMITTIVITY
PLASMONS
RED SHIFT
RESONANCE