Abstract
In this paper, we present an improved reflectometric interference spectroscopy (RIfS) sensor principle which is suitable for thin films. The conventional RIfS technique is an appropriate method to detect interfacial interactions at the solid–gas or solid–liquid interface in the case of thin films with a thickness of a few hundred nanometers, but when a significantly lower layer thickness (~100 nm) is required, the method is barely usable. By applying polarized reflected light and monitoring the ratio of the p- and s-polarized components, a characteristic curve can be obtained with one or a few local extreme value(s) with significantly favorable intensity ratios compared to the conventional method. In this work we studied the effect of film thickness, incident angle and the refractive indices of the thin film, the medium and the substrate. As a main result, it was demonstrated that the sensitivity of the PRIfS method is 4–7 times higher than that of the conventional technique near a critical angle. In simulated adsorption experiments, it was determined that the sensitivity of RIfS is around 550 nm/RIU (refractive index unit), while it is 1825 and 3966 nm/RIU for PRIfS in gas and aqueous phase, respectively.
Highlights
The monitoring of molecule adsorption or nanoparticle adhesion on different surfaces is based on the measurement of the surface excess
While the explicit parameters are the film thickness (d), the refraction angle (ε1 ) and the refractive index of the film (n1 ), the implicit parameters are included in the reflection and transmission amplitudes (in conventional and polarized cases, Equations (4)–(6), (8)–(11), respectively), namely the refractive indices of the medium (n0 ), the film (n1 ) and the substrate (n2 )
Simulating an Immobilization Measurement in Aqueous Phase In Subsections 3.1–3.3, we presented the benefits of using polarized reflected light in reflectometric interference spectroscopy measurements and the optimal conditions were discussed
Summary
The monitoring of molecule adsorption or nanoparticle adhesion on different surfaces is based on the measurement of the surface excess. The difference between the RIfS and PRIfS t01 the detector measures the average of all the polarization states in the former case, the ratio of the sThe reflected intensity from the surface of a thin film is described by Equation (7): and p-polarized reflected intensity is measured by using a polarizer in the latter (Equation 14) This difference is illustrated on Figure 2: (A) is a conventional RIfS spectrum, (B) presents the sand p-polarized spectra and their average, whereas (C)interference shows the ratio of thedecorated s- and p-polarized. This equation describes a typical reflectometric spectrum with the components of the spectrum
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