SURFACE PLASMON RESONANCE AT A SILVER-AIR INTERFACE

HOME THEORY APPARATUS DATA ACQUISITION RESULTS AND CONCLUSIONS

Apparatus

The general experimental setup is shown in the figure below.

A silver film was probed by monochromatic light incident through a prism (index of refraction n) and focused on the silver-air interface. A prism was necessary to increase magnitude of wavevector of light into resonance regime [1].

Resonance transfers energy from the incident light to surface plasmon wave, decreasing the intensity of the reflected beam and allowing measurement of specific angle of resonance Θint [1]. The reflected light was projected onto a piece of paper for imaging of the location of the decrease in intensity.

The film was approximately 40 nm thick and coated on glass coverslip. The coated coverslip was connected via index-matching liquid to the glass prism and oriented so that the top of silver film was exposed to the air; this is known as the Kretschmann configuration and is common to surface plasmon resonance studies. Index-matching liquid prevented any air gaps from forming between the slide and the prism; such gaps would reflect incident light before it reached the interface. The particular prism employed was a N-BK7 (Schott) right angle prism with a wavelength-dependent index of refraction.

The various frequencies of light were obtained by filtering a high intensity white light source with a tunable diffraction grating. The high intensity source was required so that the filtered output would still have a great enough intensity for measurement.

Below is a closer look at the geometry of the exiting beam which was used to calculate the angle at which resonance occurred for a given frequency.

The resonance band at Θplasmon will be a distance b from the center of the beam. Knowing the distances a and c labeled in the figure above, one can use basic trigonometry and Snell's Law to identify the angle of resonance. This allows the connection between measuring the location of a pixel in the projected image and calculating resonance criterion as described in THEORY .

Below are figures of the actual experimental setup with the prism-interface shown on the left and the light source shown on the right. The filtered white light was focused by a lens on the end of a fiber optic cable. This allowed the light to be properly integrated into the main apparatus without the use of mirrors and the like.

Molly Andersen & Jesse Grindstaff

References:

[1] Pluchery O., Vayron R., and Van K., 2011 “Laboratory experiments for exploring the surface plasmon resonance.” Eur. J. Phys. 32 585–99.

[2] Haes A.J. and Van Duyne R.P., 2002 “A Nanoscale Optical Biosensor: Sensitivity and Selectivity of an Approach Based on the Localized Surface Plasmon Resonance Spectroscopy of Triangular Silver Nanoparticles.” J. ACS 124 (35), 10596-10604.

[3] Barnes W.L., Dereux A. and Ebbesen T.W., 2003 “Surface plasmon subwavelength optics.” Nature 424 824-830.

[4] Drescher, D. G., Ramarkrishnan, N. A., and Drescher, M. J., 2009 “Surface plasmon resonance (SPR) analysis of binding interactions of proteins in inner-ear sensory epithelia.” Meth. Mol. Biol. (493) 323-343.

[5] Yang, H.U., D’Archangel, J., Sundheimer, M.L., Tucker, E., Boreman, G.D., Raschke, M.B., 2015 “Optical dielectric function of silver” Physical Review B 91 234137.

[6] Griffiths, D.J. “Introduction to Electrodynamics.” (Pearson Education, Inc.) 4th ed. 2013.

[7] Novotny, L., and Hecht, B. “Principles of nano-optics.” (Cambridge University Press, New York, New York). 2006.