X-ray measurements reflectivity

Figure 2.81 (a) Schematic of the system for in situ X-ray reflectivity measurements. Syn = synchrotron source M = monochromator S = slit /0, /R = incident and reflected X-rays beams, respectively 9 = angle of incidence W = teflon windows WE = working electrode RE = reference electrode CF = counter electrode D = scintillation detector, (h) Cyclic voltammogram of Cu-on-Si electrode in borate buffer solution (pH 8.4), scan rate = lOmVs-1. From Melendres... 

Wasserman [186] has described the use of both low-angle X-ray reflectivity and ellipsometry for the determination of thickness of Cio-Cig SAMs prepared on surface silanol groups of silicon plates. Ellipsometry is based on the reflection of polarized light from a sample and depends on the sample s thickness and refractive index. X-ray reflectivity measures the intensity of X-rays reflected from a surface (or interference pattern) that is characteristic of the distance between interfaces. The thickness of the SAMs was consistent with fully extended alkyl chains with all-trans conformations and excellent agreement was observed between the two methods. 

To examine monolayers on liquid surfaces in situ, multiple interactions by mounting mirrors above and below the surface have been used. X-ray reflectivity measurements have been used to study the counterion overlayers at the interface between electrolyte solutions and monolayers of carboxylic acids terminated alkanethiols self-assemblies on Au (Birdi, 1999). 

In fact a liquid surface in the absence of external perturbations such as mechanical vibrations is perhaps the most smooth (disordered) surface that can be achieved by the action of gravity. Clearly, LB films could not be grown in the absence of gravity, e.g., in a Space Shuttle. In the case of water, the flat water/air interface has a roughness of 0.3 nm, a value determined by X-ray reflectivity measurements (Braslau et al, 1985). A further advantage of water is its relatively high surface tension yo. when compared to other liquids, which amounts to 72.8 mN m for pure water at RT. This value originates in the formation of a network of weak... 

Figure 4.1-14 A typical cell used for X-ray reflectivity measurements.

Figure 2.81 (a) Schematic of the system for in situ X-ray reflectivity measurements. Syn -... 

Measurements were performed upon noble and transition metal thin films, deposited by magnetron sputtering onto Si substrates. Since the /3) tensor was expected to depend upon the detailed structure of the sample, X-ray reflectivity measurements were performed to determine the thickness,... 

The direct measurement of the various important parameters of foam films (thickness, capillary pressure, contact angles, etc.) makes it possible to derive information about the thermodynamic and kinetic properties of films (disjoining pressure isotherms, potential of the diffuse electric layer, molecular characteristics of foam bilayer, such as binding energy of molecules, linear tension, etc.). Along with it certain techniques employed to reveal foam film structure, being of particular importance for black foam films, are also considered here. These are FT-IR Spectroscopy, Fluorescence Recovery after Photobleaching (FRAP), X-ray reflectivity, measurement of the lateral electrical conductivity, measurement of foam film permeability, etc. 

Additional data about the structure of black films are obtained by X-ray diffraction method. The first steps [336,338] have been performed with vertical foam films in a frame in a horizontal scanning diffractometer. Black films from decyltrimethyl ammonium decyl sulphate and NaBr solutions have been studied. The film thickness was calculated using a model of the mean electron density projection on the film normal. However, there was no indication whether the films were CBF or NBF. Platikanov et al. [339,340] used a new device for investigation of a horizontal black films from aqueous NaDoS solution (see Section 2.2.6). They found essentially different X-ray diffraction traces for the three types of black films CBF, NBF and stratified black films. This indicates their different structure. Precise X-ray reflectivity measurements with CBF and NBF films from NaDoS and NaCl aqueous solutions [341-343] provided more details about their structure. The data obtained for the thicknesses of the respective layers which detail the film structure are given below... 

Vaknin, D., Kjaer, K., Als-Nielsen, J. and Losche, M. (1991). Structural properties of phosphatidylcholine in a monolayer at the air/water interface. Neutron reflection study and re-examination of x-ray reflection measurements. Biophys. J. 59 1325-1332. 

The results on the NiAl(llO) faee are not yet published, and hence only preliminary results are available [143]. A 6 A-thick oxide was formed, as the result of a 30 min.-long annealing at 950°C under 2T0 Pa of O2. This thickness was determined by X-ray reflectivity measurements. Two different incommensurate struetures were observed, one of which had been previously observed by SPA-LEED. The other, whieh had much stronger reflections, had never been reported previously, and was indeed invisible on the LEED patterns. This new stmcture is still under analysis. 

X-RAY REFLECTIVITY X-ray reflectivity measurements can provide important information about mineral-water interfaces in situ by accurately determining die position of an adsorbed monolayer relative to the substrate surface. By measuring x-ray reflectivity of calcite, with and without lead, Sturchio et al. (1997) established that the lead ions were located in the surface atomic layer. X-ray reflectivity measurements found rubidium to be specifically adsorbed to the rutile surface at the tetradentate site (Zhang et al., 2004). These authors were able to include this information in the CD-MUSIC model to obtain an accurate description of rubidium adsorption. 

Figure 9.2 Scattering geometries with the corresponding initial and final wave vector and kj. (a) Setup for specular X-ray reflectivity measurements which reveal the sample stracture (roughness, lattice spacing) along the surface normal.

X-ray diffraction studies of monolayers provide information about the structure within the plane of the interface, and x-ray reflection measurements give information about the structure in the perpendicular direction. The scattering from monolayers is weak, so even with the high-intensity beams obtainable with synchrotron sources, measurements are confined to high-density monolayer phases. 

Millet F, Nedyalkov M, Renard B, Perrin P, Lafuma F, Benattar JJ. Adsorption of hydrophobically modified poly(acrylic acid) sodium salt at the air/water interface by combined surface tension and x-ray reflectivity measurements. Langmuir 1999 15 2112-2119. 

Recently, Toney et al. [140] published the results of X-ray reflectivity measurements on dilute aqueous sodium fluoride solutions near positively and negatively charged silver electrodes with (111) surface geometry. The analysis shows an oscillatory density profile with three or four density maxima near the interface, qualitatively similar to the results in Fig. 7. They also found a very large shift of the distance of the first... 

We report results of nano-scale surface replication by thin polymer layers. The surfaces of deeply polished Si plates were used as etalon surfaces for the replication. AFM investigations showed that polymer layers replicate the surface of etalon samples fairly well. The X-ray reflectivity measurements showed that the half-width and peak values of the spectral dependences for X-ray mirrors grown on combined glass-polymer substrates practically coincided with those for mirrors on Si etalon substrates. 

Chiarello RP, Wogelius RA, Sturchio NC (1993) In situ synchrotron X-ray reflectivity measurements at the calcite-water interface. Geochim Cosmochim Acta 57 4103-4110 Chisholm-Brause CJ, Brown GE Jr, Parks GA (1989a) EXAFS investigation of aqueous Co(II) adsorbed on oxide surfaces in situ. Physica 158 646-648... 

Dissolution processes. We used X-ray reflectivity measurements to probe the changes in orthoclase surface structure and termination in real time during dissolution. Measurements of the dissolution process were performed in situ in flowing solutions of 0.1 M HC1 and 0.1 M NaOH, having pH values (at 25 °C) of 1.1 and 12.9, respectively (Teng et al. 2001). 

Figure 20. Top experimental X-ray reflectivity measurements obtained with an LBK polymer film which consists of 46P240 monolayers (a) before any irradiation and (b) after several cycles of UV (360nm) and blue-light (450nm) irradiations. In this case, the polymer film was prepared with the prepressure (see the text for more details) it is worth noting that the intensity of the Bragg peak was not affected by this treatment. Bottom schematic drawing of the hairy rod polyglutamate doublelayer structure.

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