Microscopic spectrophotometry applied to quasifractal gold particle clusters

An optical measurement system composed of an optical microscope (Olympus BX60) and an optical multichannel analyzer (EG&G OMA 1460) has been assembled and tested. The optical microscope allows the user to make measurements on a small and well defined area of the sample. The light source, a 100 W halogen lamp, and the diode array detector, result in high sensitivity in the wavelength region of 450-750 nm. The spectral resolution of the instrument is listed as 0.59 nm/channel. The full width at half maximum (FWHM) of the strongest peaks in calibration measurements on a mercury lamp is 5 channels corresponding to 3 nm. Quasifractal clusters of gold particles have been produced with electron beam lithography. The clusters consists of different numbers of particles, giving a cluster size variation from 1.6 (mu) m to 50 (mu) m. The individual gold particles are 50 nm in diameter each. The measurement system has been used to measure both absolute transmittance and the relative transmittance using the uncoated substrate as a reference.

[1]  David A. Weitz,et al.  Colloidal aggregation revisited: New insights based on fractal structure and surface-enhanced Raman scattering , 1985 .

[2]  V. Shalaev.  Nonlinear optics of random media , 1999 .

[3]  R. Botet,et al.  Mean-field approximation of Mie scattering by fractal aggregates of identical spheres. , 1997, Applied optics.

[4]  Marcel Ausloos,et al.  Absorption spectrum of clusters of spheres from the general solution of Maxwell's equations. II. Optical properties of aggregated metal spheres , 1982 .

[5]  F. Aussenegg,et al.  Optical dichroism of lithographically designed silver nanoparticle films. , 1996, Optics letters.

[6]  Kirk A. Fuller,et al.  Light Scattering by Agglomerates: Coupled Electric and Magnetic Dipole Method , 1994 .

[7]  Robert J. Warmack,et al.  Optical absorbance of silver ellipsoidal particles , 1987 .

[8]  G. G. Stokes.  "J." , 1890, The New Yale Book of Quotations.

[9]  Benoit B. Mandelbrot,et al.  Fractal Geometry of Nature , 1984 .

[10]  Gunnar A. Niklasson,et al.  Optical properties of quasifractal metal nanoparticle aggregates , 1999 .

[11]  Ferrell,et al.  Experimental test of the Mie theory for microlithographically produced silver spheres. , 1987, Physical review. B, Condensed matter.

[12]  Harold G. Craighead,et al.  Optical response and fabrication of regular arrays of ultrasmall gold particles , 1985 .

[13]  R. W. Christy,et al.  Optical Constants of the Noble Metals , 1972 .

[14]  Nikolai G. Khlebtsov,et al.  Optics of Fractal Clusters in the Anomalous Diffraction Approximation , 1993 .

[15]  P. Barber,et al.  Quadrupole mode in the extinction and elastic-scattering spectra of gold microstructures. , 1987, Optics letters.

[16]  M. V. Berry,et al.  Optics of Fractal Clusters Such as Smoke , 1986 .