[en] The synthesis of diacetylenes was carried out and their solid state polymerization by actinic and photochemical radiation has been studied

[en] The nonlinear optical properties of a polydiacetylene, poly[1,4-(bis-3-quinolyl)-buta-1,3-diyne] (PDQ), in solution, were studied using the Z-scan technique with pulse trains at 532 nm. The results revealed a predominant slow accumulative process caused by thermal effects, with no indication of an electronic contribution. This calls for caution when analyzing nonlinear optical effects on polymer samples under resonant excitation. PDQ is amenable to Langmuir monolayer formation, and several layers may be transferred in optical-quality, Y-type Langmuir-Blodgett (LB) films if mixed monolayers with cadmium stearate (CdSt) are transferred onto solid substrates. Langmuir films were studied by surface pressure and surface potential isotherms, which indicated strong interaction between the two components. FTIR spectra of the mixed LB films confirmed the transfer of CdSt and PDQ, while UV-Vis spectra indicated a uniform transfer of PDQ during multilayer LB deposition. As in the case of most mixed LB films of polymers and CdSt, X-ray diffraction (XRD) results were close to those of pure CdSt films, pointing to CdSt domains in the mixed LB film. It is also found that the thin LB films are not suitable for use with the Z-scan technique, as the films are damaged when the near-resonant condition is employed

[en] In the present work, the structure of CdS-arachidic acid composite LB film has been analyzed using FTIR and XRD techniques, by monitoring the changes (as a function of H₂S exposure) in films deposited on calcium fluoride substrate

[en] CdS nanocrystallites formed in ordered fatty acid LB multilayers exhibited strong surface states emission ∝550 nm and weak excitonic emission ∝400 nm. Treatment with aqueous CdCl₂ resulted in the suppression of surface states emission and enhancement of the blue excitonic emission. Subsequent annealing in air at 200 C caused an order of magnitude enhancement of excitonic emission. The growth of nanocrystallites during annealing as seen from the red-shift of excitonic absorption and emission is suppressed by the CdCl₂ treatment. The hindered growth of nanocrystallites, the significant enhancement of excitonic emission from CdS, and the suppression of surface states emission are attributed to surface passivation of CdS nanocrystallites by surface oxide formation. (orig.)

[en] CdA and CdA-ZnA mixed multilayers were prepared by LB process and characterized by XPS. CdS and CdZnS alloy nanoparticles were formed by post-deposition sulphidation and heat treated in temperature range of 150-250 deg C. A blue shift is observed in absorption and PL peaks of alloy nanoparticles w.r.t. the corresponding features in CdS, confirming the alloy formation. PL studies showed a strong enhancement of excitonic emission and suppression of defect states luminescence on heat treatment up to 200 deg C. (author)

[en] CdS nanocrystallites were prepared by sulphidation of cadmium arachidate LB multilayers. The composite multilayers were treated with aqueous CdCl₂ and heat treated in the range of 100-250 deg C. PL studies show that annealing of CdCl₂ treated multilayers results in strong enhancement of excitonic emission due to passivation of surface states. Atomic force microscopy studies indicate that up to 200 deg C, the CdA present in the multilayers assists in passivation of surface defects and restricts the growth of CdS nanocrystallites. (author)

[en] Core-shell CdS/ZnS nanoparticles in arachidic acid film were prepared through a novel Langmuir-Blodgett (LB) approach. Post-deposition treatment of the precursor LB multilayers of cadmium arachidate with H₂S gas followed by intercalation of Zn²⁺ ions and further sulfidation result in the formation of CdS/ZnS nanoparticles in the LB film. The formation of these nanoparticles and resulting changes in layered structures were studied by FTIR and X-ray reflection measurements. The optical properties were studied using UV-vis absorption and photoluminescence spectroscopy. A red-shift in the absorption spectrum and enhancement of CdS excitonic emission together with reduction of surface states emission suggest that after the intercalation step, a thin layer of ZnS surrounds the CdS nanoparticles, thus forming a core-shell structure. Subsequent to the second sulfidation, a further red-shift in absorption suggests the formation of a thicker ZnS coating on CdS. Electron diffraction of CdS nanoparticles coated with thicker ZnS showed the diffraction patterns of only ZnS, as expected for core-shell structures

[en] Polyion complexation in mixed Langmuir and Langmuir Blodgett (LB) films of photochromic amphiphilic azobenzene carboxylic acids, 11-[4-(4-hexylphenyl)azo] phenoxyundecanoic acid, 11-(4-phenylazo)phenoxyundecanoic acid, and diamine grafted poly(methylmethaacrylate) polymers has been studied. Monolayer behaviour of the pure components and mixed films was studied through pressure-area isotherms and LB films were characterized by spectroscopic, X-ray diffraction and Atomic force microscopy techniques. Aggregation (H-type), often observed in LB films of pure amphiphilic azo acids, was partly avoided in the mixed LB films as indicated by absorption spectral studies. Photoisomerization of the polyion complexed LB films was also studied. The results altogether demonstrate that amine grafted polymer enter into a polyion complexation with azo acid carboxylate group. LB films could be obtained by transfer of the composite monolayers and these LB films exhibited different levels of aggregation of the azo acids. Reversible photoisomerization was observed in LB films with unaggregated azo acid

[en] ZnO and Zn_1-xCd_xO nanocrystallites were prepared by oxidation of zinc arachidate-arachidic acid and zinc arachidate-cadmium arachidate-arachidic acid LB multilayers, respectively. The metal content of the multilayers was controlled by manipulation of subphase composition and pH. Precursor multilayers were oxidized in the temperature range of 400 deg. C-700 deg. C. The formation of ZnO and Zn_1-xCd_xO was confirmed by UV-Visible spectroscopy. Uniformly distributed, isolated and nearly mono-dispersed nanocrystallites of ZnO (11 ± 3 nm) and Zn_1-xCd_xO (18 ± 6 nm) were obtained

[en] Graphene oxide (GO) sheets prepared by chemical exfoliation were spread at the air–water interface and transferred to silicon substrates by Langmuir–Blodgett technique as closely spaced monolayers of 20–40 μm size. Hydrazine exposure followed by annealing in vacuum and argon ambient results in the formation of reduced graphene oxide (RGO) monolayers, without significantly affecting the overall morphology of the sheets. The monolayer character of both GO and RGO sheets was ascertained by atomic force microscopy. X-ray photoelectron spectroscopy supported by Fourier transform infrared spectroscopy revealed that the reduction process results in a significant decrease in oxygen functionalities, accompanied by a substantial decrease in the ratio of non-graphitic to graphitic (sp² bonded) carbon in the monolayers from 1.2 to 0.35. Raman spectra of GO and RGO monolayers have shown that during the reduction process, the G-band shifts by 8–12 cm⁻¹ and the ratio of the intensities of D-band to G-band, I(D)/I(G) decreases from 1.3 ± 0.3 to 0.8 ± 0.2, which is in tune with the smaller non-graphitic carbon content of RGO monolayers. The significant decrease in I(D)/I(G) has been explained by assuming that substantial order is present in precursor GO monolayers as well as RGO monolayers obtained by solid state reduction. - Highlights: ► Graphene oxide (GO) monolayers were deoxygenated to form reduced GO (RGO). ► GO monolayers are 20–40 μm in size, which does not change during reduction. ► Reduction process does not affect the morphological stability of monolayers. ► RGO monolayers show substantial decrease in non-graphitic carbon content. ► Raman studies indicate presence of order in both GO and RGO monolayers.