Surface Plasmon Resonance Based Measurement of the Dielectric Function of a Thin Metal Film

Abstract

A spectral method based on surface plasmon resonance (SPR) in air is used to measure the dielectric function of a thin metal film. The method utilizes the spectral dependence of the ratio of the reflectances of p- and s-polarized waves measured in the Kretschmann configuration at different angles of incidence. By processing these dependences in the vicinity of a dip, or equivalently near the resonance wavelength, and using the dispersion characteristics of a metal film according to a proposed physical model, the real and imaginary parts of the dielectric function of the metal can be determined. The corresponding dielectric function of the metal is obtained by a least squares method for such a thickness minimizing the difference between the measured and theoretical dependence of the resonance wavelength on the the angle of incidence. The feasibility of the method is demonstrated in measuring the dielectric function of a gold film of an SPR structure comprising an SF10 glass prism and a gold coated SF10 slide with an adhesion film of chromium. The dielectric function according to the Drude–Lorentz model with two additional Lorentzian terms was determined in a wavelength range from 534 to 908 nm, and the results show that the gold film is composed of homogenous and rough layers with thicknesses 42.8 nm and 2.0 nm, respectively. This method is particularly useful in measuring the thickness and dielectric function of a thin metal film of SPR structures, directly in the Kretschmann configuration.

Phase sensitive measurement of the wavelength dependence of the complex permittivity of a thin gold film using surface plasmon resonance

“…We prefer to consider, as in our previous work [22], the SPR phenomenon for air and to measure the wavelength dependence of the complex permittivity of a thin gold film via adjusting the resonance conditions at different angles of incidence. If the angle between the incident beam and the normal to the prism face (see Fig.…”

“…If the angle between the incident beam and the normal to the prism face (see Fig. 1) is denoted as α, the angle of incidence θ on the base of the equilateral prism is affected by the dispersion of both the prism glass and air, respectively [22].…”

“…The thickness of the chromium film is t Cr =2 nm and the thickness of the gold film is 44.8 nm as specified by producer (Accurion, Germany). The surface morphology analysis has shown that the gold film is composed of homogenous and rough layers with thicknesses t Au =42.8 nm and t eff =2.0 nm, respectively, and that the volume fraction of the gold in the pseudolayer is q=0.5 [22]. To attach the SF10 glass slide with the deposited films to the equilateral prism (SF10 glass), a thin film of index-matching fluid (n D =1.730, Cargille) was used.…”

“…Techniques of SPR-based spectral ellipsometry [19] and reflectometry [20][21][22] are also available. Recently, we proposed and realized a simple and cost-effective method compared to standard approaches like spectral ellipsometry, enabling to measure the wavelength dependence of the complex permittivity of a thin metal film [22]. Unfortunately, because this method is based on measuring the reflectance ratio for p and s polarizations, it is very sensitive to the birefringence properties of a read optical fiber.…”

ZnO for performance enhancement of surface plasmon resonance biosensor: a review

“…The major application of SPR biosensor is for detection of a variety of biomolecules such as lipid [5], peptides [6], receptor [7], nucleic acid [8], protein [9] and antibodies [10]. The SPR technique has not only been used for biosensing purposes but also in characterizing a broad range of material thin films [11]. The most commonly used configuration to excite SPR is by prism coupling through Kretschmann configuration in attenuated total reflection method [12].…”