Internal-reflection element advantages

The concept of ATR at the interface of two media is described in 1.4.10° and Section 1.8.3. In situ ATR measurements of ultrathin films started in the mid-1960s with studies of the adsorption of a stearic acid monolayer from D2O onto Ge [448], and chemical [449] and electrochemical [450] oxidation of Ge, where a Ge multiple internal reflection element (MIRE) acts as both the substrate and the electrode. Later, coated ATR [60, 451-454] and MO ATR with the SEIRA effect [455] were introduced in in situ experiments. The principal advantage of the ATR geometry is that the corresponding in situ cells are free from diffusion effects (the volume of solution phase in contact with the IRE is arbitrary), which is useful when studying time-dependent phenomena (Section 4.9.1). 

Metals. A thin metal electrode deposited on the IRE, as for transmission measurements, is called an OTE, while the whole IRE-OTE-sample layer system is referred to as an extended internal reflection element (EIRE). Metal coatings provide the shortest penetration depths (up to a few nanometers). Another important advantage of the OTE is the enhancement of IR absorption of species in the... 

Kellar et al [108] have demonstrated the potential of NIR internal reflection spectroscopy (NIR-IRS) with reactive internal reflection elements for in situ monitoring of surfactant adsorption. An advantage of the NIR-IRS technique over the mid-IR analogue is that a wider range of materials are transparent in the NIR region. As a result, broader ranges of substrates are available for NIR-IRS than for IR-IRS. 

The setup for internal reflection spectroscopy is shown in Kg. 3. The electrode consists of a germanium reflection element, covered on one side with PPy in contact with the electrolyte solution. The IR beam is totally reflected at the interface between the reflection element and the PPy layer. The penetration depth of the IR beam into the optical thinner medium (polymer and electrolyte) at each total reflection is in the order of some m. Spectral information on this small region is available without disturbances by the bulk electrolyte. Since the counter electrode and the reference electrode can be mounted in an advantageous arrangement, no electrochemical hmitations, connected with a thin electrolyte layei occur using this method. Due to the limited stability of Ge in aqueous electrochemical systems, the water content of the electrolyte solution has to be very low. 

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