Optical thickness, change

The developed sensor was used for ultrathin-film measurement. The reflection spectrum was shifted during the deposition of thin films (e.g., self-assembly of polyelectrolyte layers) onto the sensor end. The reflection between the thin film and the fiber endface was neglected because of their similar refractive indices. As the film increased its thickness, the length of the fiber cavity changed. The amount of change was estimated by the phase shift of the interferogram. The device could also be used as an immunosensor in which the optical thickness changes were used to... 

As mentioned previously, photoisomerization of azobenzenes leads to refractive index or optical thickness changes that can be probed by means of evanescent wave optics. 

If this change in optical thickness is followed on line (during irradiation) by recording the reflected intensity at a fixed angle of incidence (e.g., 6 = 45°, cf, Fig. 9, top) a kinetic analysis of the optical thickness changes can give information about the reaction rates, the equilibrium changes, the... 

Figure 9. Top PSP resonance of the bare Ag substrate (dosed circles) after coating with a self-assembled monolayer the azo-silane (open circles) the inset shows the thickness of Ag, SiO,, and the SAM. Bottom Optical thickness change as obtained by recording the reflected intensity of the same sample at a fixed angle of incidence (6 = 45°, cf. top) while irradiating the moments of turning the irradiation light on and off are indicated by arrows.

After this calibration step (the effective absorption coefficient is determined from a known wall thickness change and the corresponding variation of the optical film density) the evaluation of local wall thickness changes Aw (corresponding to De,o) from the nominal wall thickness w o , (corresponding to Dnom) can be done according to ... 

Profile Plot This window display the data (grey values, optical densities or wall thickness changes in mm after calibration) along the line shown in the image window. 

The preparation of the reflecting silver layers for MBI deserves special attention, since it affects the optical properties of the mirrors. Another important issue is the optical phase change [ ] at the mica/silver interface, which is responsible for a wavelength-dependent shift of all FECOs. The phase change is a fimction of silver layer thickness, T, especially for T < 40 mn [54]. The roughness of the silver layers can also have an effect on the resolution of the distance measurement [59, 60]. 

Platinum was added to Nation before Incorporating CdS In order to avoid the reduction of CdS during the platlnlzatlon process. Nation (DuPont 117, 0.018 cm thick) films were soaked In Pt(NH2)2l2 (0.1 mM) solution for 4 hr. The amount of the Pt complex Incorporated was determined by measuring the optical absorption change In the liquid phase. The films were subsequently reduced with NaBH (0.1 M) solution for one day to produce Pt metal dispersed throughout the polymer film. The amount of Pt was found to be about 0.02 mg cm 2. 

Figure 4. Reflectometric interference spectroscopy (RIFS) caused by constructive and destructive superposition of two partial beams being reflected at the two interfaces of a thin layer (300 nm - some pm), shift of the interference spectrum caused by a change in the optical thickness.

Figure 5. Binding curves time-resolved measurement of the change in optical thickness during association. The second part of the figure shows the regeneration which returns the signal hack to the baseline.

Fig. 9.6 The calculated effective index change in the silicon PWEF waveguide of Fig. 9.3 induced by adsorbed films of constant optical thickness (a) Dopt 0.4 nm and (b) Dopt 0.1 nm for film thickness between 0.5 and 16 nm. As the film thickness changes, the refractive index is adjusted so that the optical thickness remains constant. For comparison, the graphs also show 8iVeff and the corresponding SPR angle shift A6 for an SPR experiment...

Therefore Z)opt provides a convenient single parameter that can be used to estimate the response of guided modes to very thin adsorbed layers. To assess and compare surface sensitivity, in this chapter, we will use the differential change of mode effective index with the optical thickness ... 

The measured intensity modulation can then be used to recover the original optical phase change Aphase shift, shown in Fig. 9.14b, is directly proportional to the density of molecules on the surface, as long as the film thickness is much less than the evanescent field penetration depth of <5 162 nm. 

The interferometry trace shows the change in the optical thickness of the polymer film with respect to time. Both the completion of the polymer film dissolution and the DR can be determined. 

There are two fundamental assumptions in the use of absorbance subtraction. First, the absorbance and shape of a band does not change with the optical thickness. This assumption is tested with every subtraction and if the residual absorbance after a subtraction has a different shape than the original absorbance bands, then this assumption is violated and the procedure or samples should be reexamined for the appearance of effects producing nonlinear results. A number of these effects will be discussed below. Secondly, one also assumes that the absorbance of a mixture is the stun of the absorbances of the components, that is, that the components do not interact with each other differently at different relative concentrations, such interactions will lead to frequency shifts and band shape changes 7S>, but rarely are such effects observed in solids. Care must be exercised, however, since wedging and orientation can produce nonlinear effects in solids. 

Morrissey 53) used transmission infrared spectroscopy to study protein adsorption onto silica particles in a heavy water (DzO) buffer. By observing the shift in the amide I absorption band, he could deduce the fraction of protein carbonyl groups involved in bonding to the silica surface. He found that bovine IgG had a bound fraction of 0.20 at low bulk solution concentrations, but only about 0.02 at high solution concentrations. However, neither prothrombin nor bovine serum albumin exhibited a change in bound fraction with concentration. Parallel experiments with flat silica plates using ellipsometry showed that the IgG-adsorbed layers had an optical thickness of 140 A and a surface concentration of 1.7 mg/m2 at low bulk solution concentration — in concentrated solutions the surface amount was 3.4 mg/m2 with a thickness of 320 A (Fig. 17). 

In this chapter two different kinds of phase materials are presented the first is a chiral diamide selector bonded to a polysiloxane matrix the other selector system is a calix[4]arene with chiral residues which is attached to a polysiloxane backbone (Sect. 2.4). These systems were used in direct optical methods based on a change in the refractive index or the optical thickness of a transparent polymeric layer. 

RIfS was used to characterise changes in the optical thickness A(nd) of a polymeric sensitive layer. RIfS is based on interference effects in thin transparent films. By interaction of analyte molecules with the sensitive layer, a swelling takes place and so the interference pattern is changed [21],... 

These three methods are compared since each of them provides complemantary information. SE offers the possibility to determine absolute values of the refractive index n and physical layer thickness d by fitting a simulation to measured quantities for adequate layer systems. SPR is highly sensitive towards changes in the refractive index. RIfS presents itself as a straightforward method for the determination of changes in the optical thickness (n d). 

In the RIflS-method, one part of the radiation is reflected at the interface of a thin layer, whereas the other penetrates the layer and is there reflected at the other interface. These two partial reflected beams become superimposed and form an interference pattern resulting in constructive or destructive interference. This interference pattern depends also on the optical thickness of the layer, which is given by the product of refractive index and the physical thickness of the layer. By a parabolic fit, the shift of an extremum is evaluated and the change in the optical thickness is given as result. 

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