The formation of fog on CR39 surfaces has been studied. Water droplets form fog coalesce with time, especially during the first 20 s at the beginning of the formation of fog. Consequently, their mean diameter increases. Formation of fog being related to the wettability of the surfaces, the latter has been increased by the implantation of Ar ions into CR39 surfaces under an oxygen partial pressure. A very wetting CR39 surface with advancing (ACA) and receding (RCA) contact angles below 5° has been obtained with an implantation dose of 1.28 × 1017 Ar+ cm−2. In this condition, no formation of fog was observed. Characterization using x-ray photoelectron spectroscopy has shown that the molecular structure of CR39 is strongly modified by Ar+ implantation, which would be responsible for the increase in wettability. Unfortunately, both ACA and RCA increase with time, which is called ageing, and the formation of fog is again observed. The diameter and concentration of water droplets forming fog have been plotted against the contact angle. These plots show that no formation of fog occurs for ACA < ∼40°. Usually, the ACA reaches 40° after an ageing time of ∼200 h. A He pre-implantation with a dose of 5 × 1015 He+ cm−2 and an energy of 2 keV, sufficient to push the ions deeper than the Ar depth profile, delays the ageing effect in such a way that ACA ≅ 40° is reached after ∼2000 h and no formation of fog is observed during these first ∼2000 h.
Thin films of chloroaluminum, chlorogallium, and chloroindium phthalocyanines (ClAlPc, ClGaPc, and ClInPc) have been sublimed on SnO 2 substrates maintained during sublimation at temperatures ranging from -130 to 190°C. Using this procedure, it is possible to obtain molecular semiconductor layers with a structure varying from amorphous to polycrystalline. These layers were immersed in KI 3 /KI or KCl solutions at pH ) 3.0. This treatment was found to improve drastically the photoelectrochemical activity of ClAlPc thin films. Shortcircuit photocurrents J sc ) 0.75 ( 0.25 mA/cm 2 were obtained, using polychromatic illumination (35 mW/ cm 2 ), after immersion of ClAlPc into KCl solutions while lower J sc values (0.3 ( 0.1 mA/cm 2 ) were obtained for KI 3 /KI solutions. No change in the photoactivity was observed either for ClGaPc or for ClInPc when they were immersed in the same solutions. Both molecular semiconductors provided lower short-circuit photocurrents (J sc e 0.15 ( 0.03 mA/cm 2 for ClGaPc; J sc e 0.20 ( 0.02 mA/cm 2 for ClInPc). The characterization of the chloro-trivalent metal phthalocyanine films indicates that the hydrolysis of the metalCl bond is essential for the occurrence of the physicochemical transformation leading to improved photoactivity. The Al-Cl bond of ClAlPc hydrolyzes, but this reaction does not occur for ClGaPc or for ClInPc. In contact with KI 3 /KI or KCl solutions at pH ) 3.0, bulk hydrolysis occurs for ClAlPc, only if both H 3 O + and an anion could diffuse from the solution into the material. The large I 3 -anion is prevented from doing so for polycrystalline ClAlPc films obtained by sublimation on SnO 2 substrates maintained at 180°C. However, it can diffuse easily in more disorganized films obtained at lower substrate temperatures. Powders of the chlorotrivalent metal phthalocyanines as well as bromoaluminum phthalocyanine (BrAlPc) were used to quantify anion incorporation in these materials. After complete hydrolysis of BrAlPc (powder) and ClAlPc (films) there are ca. 50-85% of the anions, generated in situ by the hydrolysis reaction or diffusing from the solution as a consequence of the hydrolysis reaction, that remain in the Pc material. Thus, ca. 50-85% of the protons released by the hydrolysis either protonate the macrocycles or react with Pc + O 2 -already present in the film. In both cases, anions are necessary to neutralize the excess of positive charges. H 2 O is also found in the modified films. The presence of protonated Pcs, of anions, and of H 2 O into what is now HOAlPc (after ClAlPc hydrolysis) modifies the structure of the material as well as its photoactivity.
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...
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