Oxide film superlattices

The annealed alloy (111) oxide films yielded distinctive LEED patterns summarized in Fig. 24. Integral index beams, Type 1 in Fig. 24, were not seen when the oxide film was present, demonstrating that the film was continuous and was thicker than a few atomic layers. Thicknesses of about 2 A were typical. Beams were produced by the oxide film, indicative of a hexagonal superlattice mesh having a lattice constant of about 4.9 A and rotated 30° with respect to the mesh of the clean alloy surface (Type 4 of Fig. 24). These are the correct dimensions for the (001) plane of Cr203 in which the oxygen-oxygen vectors are parallel to the interatomic vectors of the alloy. Beams of Type 2 were also present, which were indicative of a square mesh these... 

In this section, we present TRTS as a suitable tool to be employed for the study of exciton dissociation in excitonic solar cells. TRTS has been employed to study the timescale of charge separation in QD- and dye-senstized meso-porous oxide films. Finally, TRTS studies on carrier transport in QD superlattices (also known as QD solids) are briefly discussed and connected to PV concepts. 

Special film structures were grown, by means of low-temperature molecular beam epitaxy. It consisted of a superlattice which was made up of B spikes which were separated from each other by lOOnm of Si. After dry oxidation, the width of each spike was directly proportional to the interstitial concentration at that depth. Xhe superlattice as a whole thus furnished a depth profile of the time-averaged interstitial concentration. Xhe abrupt dopant concentration transitions which were achievable in low-temperature molecular beam epitaxial films permitted this type of investigation to be carried out at between 750 and 900C. A value of 1.4 x lO cm /s was found at 800C. Overall, the results coidd be described by ... 

In contrast, much more studies have been devoted to the ditfusion of small molecules in the multilayers, because of its importance in applications like permeation membranes or biosensing. Both IR spectroscopy [316] and fluorescence measurements [317] have shown the diffusion of protons in the multilayers, and thus an influence of the pH of the outer solution even far inside the films. The influence of water on the thickness of the multilayers is also well-documented [111,318]. Diffusion of radiolabeled salt ions has also been measured [125,312], Voltamperometry showed that PAH/PAA films had little effect on the diffusion of Fe(CN)g , but that PAH/PSS films could hinder its transport [116], 6-CF [96], acridine orange [81], daunomycin [251], 2 -3 cyclic adenosine monophosphate [252], bisulfite [313], and different diazonium salts [147,313] have been shown to permeate deeply in multilayers built by ESA. Immunoglobulin G (IgG) could permeate or not in a superlattice made of anti-IgG layers and PAH/PSS spacer layers, depending on the thickness of the spacer layer. The diffusion constants of rhodamine and of 2,2,6,6,-tetramethyl-4-piperidinol-l-oxide (TEMPOL) in PAH/PSS multilayers have been quantified [113,114],... 

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