Ellipsometry second harmonic

A number of special optical techniques such as the study of second harmonic generation by irradiation of non-centrosymmetric systems by high intensity laser light will be discussed in relation to particular materials and problems. However, one optical technique having a general applicability, namely ellipsometry, must be discussed here. It is one of the best techniques available to determine the thickness of a thin organic film. Such determinations are important as they allow one to have an independent check on the number of layers deposited, given that the thickness of one layer has been determined by X-ray diffraction. 

FIGURE 1.3. Diagram of the second harmonic ellipsometry apparatus used to investigate air/liquid and liquid/liquid interfaces. 

Among the ex situ methods that can be employed in surface analysis, low-energy electron diffraction (LEED) and x-ray photoelectron spectroscopy (XPS) can give the crystal structure and the nature of the surface ad-layers after the electrochemical and adsorption experiments as explained in this chapter [31,32]. Among the in situ non-electrochemical techniques, the radiotracer method [33] gives information about the adsorbed quantities however, infrared spectroscopy in FTIR mode [34] allows the identity of the bonding of the adsorbed molecules, and finally ellipsometry [35] makes possible the study of extremely thin films. Recently, some optical methods such as reflectance, x-ray diffraction, and second harmonic generation (SHG) [36] have been added to this list. 

Brewster angle ellipsometry (BAE) and surface optical second harmonic generation (SHG, see Chap. 5) were used to study the growth of 8CB films, evaporated in air onto glass (BK7) substrates, covered with a 15 nm thick film of poly(vinyl cinnamate) (PVCN) [48]. As the thickness of 8CB on PVCN layers was far below the optical wavelengths, the Drude formula for the ellipsometric coefficient at the Brewster angle, ps, (4.3), was used. The ellipticity coefficient of the 8CB adsorbate was calculated as... 

This chapter does not cover probe-beam deflection used for spectroscopy [22], reflection spectroscopy [23, 24], surface plasmon resonance [23], second harmonic generation [25, 26], ellipsometry (Muller in Refs. [10, 27]), internal reflection ]28], photoacoustic and photothermal spectroscopy ]29] (neither of which has enjoyed widespread application in electrochemistry), or waveguides [30-32]. 

The kinetics from the solution phase have been carried out by Bain etal. using ellipsometry [47]. Later, many research groups have studied the kinetics of SAM formation (more quantitatively) using various spectroscopic techniques [48,75], such as second-harmonic generation (SHG) [76,... 

Figure 9 Characterization of the equilibrium properties of the adsorption layer by ellipsometry and Surface second harmonic generation, SHG. The SHG-signal I (P = 45, d = 90) (circles) is proportional to the surface coverage and increases monotonously with the bulk concentration. The ellipsometric quantity dA = A - Ao (triangles) shows an extremum at an intermediate concentration far below the cmc. The inset clearly shows the nonmonotonic dependency of dA on the adsorbed amount, (redrawn from (20 )...

In this paper we will demonstrate how we can use ellipsometry and optical second harmonic generation (SH) to study the structure of a monolayer of pentadecanoic acid (PDA) [CH3(CH2)i3 COOH] near its LE-LC transition at a water-air interface. By simultaneously measuring the surface pressure versus surface molecular area we can show that this LE-LC transition is accompanied by a reorientation of the molecules and that the two phases are separated by an inhomogeneous coexistence phase. 

In a recent study, the influence of indifferent electrolytes on the adsorption behaviour of cationic soluble surfactant solutions has been investigated by surface tension measurements, ellipsometry and surface second harmonic generation (SHG). ° Each technique addresses different structural aspects and the combined data provide a detailed picture of the interfacial architecture. The analysis gives an indirect proof of the existence of a phase transition between the free and condensed state of the counterions caused by a small increase of surface charge close to the critical micelle concentration (cmc). 

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