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Highly conductive iridium dioxide (IrO2) thin films have been deposited onto in situ oxidized Si(100) substrates by means of a reactive pulsed laser deposition (PLD) process. The polycrystalline IrO2 films were obtained by ablating a metal iridium target under an optimal oxygen background pressure of 200 mtorr and at different substrate deposition temperatures (Td ) ranging from 350 to 550 °C. Conventional and high-resolution transmission electron microscopy (HRTEM) techniques were used to investigate the micro- and nanostructural changes of the PLD IrO2 films as a function of their deposition temperatures. The microstructure and the morphology of the PLD IrO2 films was found to change drastically from an irregular and loosely packed columnar structure at Td = 300 °C to a uniform and densely packed columnar structure for higher Td (≥350 °C). For IrO2 films deposited in the 350 ≤ Td ≤ 550 °C range, HRTEM have revealed the presence of highly textured arrangements of almost spherical IrO2 nanograins (of 3–5 nm diameter, regardless of Td) in the columns (of which diameter was found to increase from 85 ± 15 to 180 ± 20 nm as Td increases from 350 to 550 °C). Lattice resolution and dark-field imaging have pointed out the presence of large IrO2 crystallites made of many similarly oriented nanograins (i.e., under the same Bragg diffraction conditions). Moreover, a high continuity of the lattice planes across the entire crystallite was clearly observed. This latter aspect together with the highly textured nanostructure of the IrO2 films correlate well with their high conductivity (42 ± 6 μω cm for Td ≥ 400), which was found to be comparable with that of bulk single-crystal IrO2.

Chloroaluminum phthalocyanine (C1A1Pc) films have been sublimed on conducting SnO2 substrates and have been structurally modified by a 12 h immersion in aqueous solutions at pH 3 containing various salts. Only two types of structural modifications resulting from anion uptake into the C1A1Pc film have been observed for the entire range of salts used. They have been labeled transformations I and H according to the changes in the Q band absorbance of the modified Pc. The as-sublimed C1A1Pc is characterized by a Q band with a maximum absorbance at about 735 nm. Modifications of the I-type display a Q band characterized by the growth of a peak at 835 + 8 nm, while the Q band after H-type transformations shows two maxima at 638 _+ 11 and 805 -+ 6 nm. The photoelectrochemical activity of C1A1Pc films have been measured with I~/I-before and after transformations. Much variation has been observed from one salt to another. Under white light illumination (35 mW cm-2), as-sublimed films are characterized by short-circuit photocurrents of 0.25 to 0.30 mA cm -2, while after modifications, Jsc ranges from 0.10 to 1.0 mAcm -2. For I-type transformations, the highest Jsc values (0.80 to 0.85 mA cm -2) have been obtained with KI. Part of I-uptaken into the film is oxidized by HO2 or H202 generated inside the organic layer by reaction of Pc+O~ and H § A charge transfer between Pc and iodine, as well as the structural reorganization of the crystallites resulting from the uptake of anions in the film, are thought to be responsible for the photoactivity improvement. For H-type transformations, the highest J~c values (0.8 to 1.0 mA cm -2) have been obtained with KC1, KBr, or KC103. For these salts, the structural reorganization of the crystallites goes along with a drastic change in the film morphology as observed by SEM. The long axis of the C1A1Pc crystallites, perpendicular to the substrate for the as-sublimed film, changes its orientation by 90 ~ to become parallel to the substrate after transformation. The kinetics of this process is very fast, with more than 50% completion of modification after 1 min in contact with the solution. This change in orientation is not observed when an H-type transformation is induced on C1A1Pc films by solutions of salts leading to low photoactivities. From the comparison between absorption and action spectra, it seems that H-type modifications result in two molecular arrangements with only one (the red-shifted one) being photoelectrochemically active, in contradiction with I-type modification where the action spectrum follows the absorption spectrum. TEM shows that the modified films remain crystalline and display the same structure after transformation with all salts except when KI~ is used. Besides amorphous regions in variable proportions, from one salt to another, the common structure for H and I-type films differs from the triclinic slipped stacked strucoture of as-sublimed CIA1Pc. TEM diffractions fit a monoclinic lattice with a = 7.9-8.7 A, b = 9.6-11.0 A, c = 12.5-12.8 A, and ~ = 95 ~ but a t...